TSVWG J. Babiarz Internet-Draft K. Chan Expires: January 5, 2005 Nortel Networks F. Baker Cisco Systems July 7, 2004 Configuration Guidelines for DiffServ Service Classes draft-baker-diffserv-basic-classes-03 Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 5, 2005. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This paper summarizes the recommended correlation between service classes and their usage, with references to their corresponding recommended Differentiated Service Code Points (DSCP), traffic conditioners, Per-Hop Behaviors (PHB) and Active Queue Management (AQM) mechanism. There is no intrinsic requirement that particular DSCPs, traffic conditioner PHBs and AQM be used for a certain service class, but as a policy it is useful that they be applied consistently across the network. Babiarz, et al. Expires January 5, 2005 [Page 1] Internet-Draft Document July 2004 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 Expected use in the Network . . . . . . . . . . . . . . . 4 1.2 Service Class Definition . . . . . . . . . . . . . . . . . 5 1.3 Key Differentiated Services Concepts . . . . . . . . . . . 5 1.3.1 Queuing . . . . . . . . . . . . . . . . . . . . . . . 5 1.3.1.1 Priority Queuing . . . . . . . . . . . . . . . . . 5 1.3.1.2 Rate Queuing . . . . . . . . . . . . . . . . . . . 6 1.3.2 Active Queue Management . . . . . . . . . . . . . . . 6 1.3.3 Traffic Conditioning . . . . . . . . . . . . . . . . . 7 1.3.4 Differentiated Services Code Point (DSCP) . . . . . . 8 1.3.5 Per-Hop Behavior (PHB) . . . . . . . . . . . . . . . . 8 1.4 Key Service Concepts . . . . . . . . . . . . . . . . . . . 8 1.4.1 Default Forwarding (DF) . . . . . . . . . . . . . . . 8 1.4.2 Assured Forwarding (AF) . . . . . . . . . . . . . . . 9 1.4.3 Expedited Forwarding (EF) . . . . . . . . . . . . . . 9 1.4.4 Class Selector (CS) . . . . . . . . . . . . . . . . . 9 1.4.5 Admission Control . . . . . . . . . . . . . . . . . . 10 2. Service Differentiation . . . . . . . . . . . . . . . . . . . 11 2.1 Service Classes . . . . . . . . . . . . . . . . . . . . . 11 2.2 Deployment Scenarios . . . . . . . . . . . . . . . . . . . 16 3. Network Control Traffic . . . . . . . . . . . . . . . . . . . 19 3.1 Administrative Service Class . . . . . . . . . . . . . . . 19 3.2 Network Control Service Class . . . . . . . . . . . . . . 21 3.3 OAM Service Class . . . . . . . . . . . . . . . . . . . . 22 4. User Traffic . . . . . . . . . . . . . . . . . . . . . . . . . 24 4.1 Telephony Service Class . . . . . . . . . . . . . . . . . 24 4.2 Signaling Service Class . . . . . . . . . . . . . . . . . 26 4.3 Multimedia Conferencing Service Class . . . . . . . . . . 27 4.4 Real-time Interactive Service Class . . . . . . . . . . . 30 4.5 Multimedia Streaming Service Class . . . . . . . . . . . . 32 4.6 Broadcast Video Service Class . . . . . . . . . . . . . . 34 4.7 Low Latency Data Service Class . . . . . . . . . . . . . . 35 4.8 High Throughput Data Service Class . . . . . . . . . . . . 37 4.9 Standard Service Class . . . . . . . . . . . . . . . . . . 39 4.10 Low Priority Data . . . . . . . . . . . . . . . . . . . . 40 5. Mapping Applications to Service Classes . . . . . . . . . . . 41 6. Security Considerations . . . . . . . . . . . . . . . . . . . 42 7. Summary of Changes from Previous Draft . . . . . . . . . . . . 43 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 43 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 44 9.1 Normative References . . . . . . . . . . . . . . . . . . . . 44 9.2 Informative References . . . . . . . . . . . . . . . . . . . 45 Babiarz, et al. Expires January 5, 2005 [Page 2] Internet-Draft Document July 2004 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 46 Intellectual Property and Copyright Statements . . . . . . . . 47 Babiarz, et al. Expires January 5, 2005 [Page 3] Internet-Draft Document July 2004 1. Introduction This paper summarizes the recommended correlation between service classes and their usage, with references to their corresponding recommended Differentiated Service Code Points (DSCP), traffic conditioners, Per-Hop Behaviors (PHB) and Active Queue Management (AQM) mechanisms. There is no intrinsic requirement that particular DSCPs, traffic conditioner PHBs and AQM be used for a certain service class, but as a policy it is useful that they be applied consistently across the network. Service classes are defined based on the different traffic characteristics and required performance of the applications/ services. This approach allows us to map current and future applications/services of similar traffic characteristics and performance requirements into the same service class. Since the applications'/services' characteristics and required performance are end to end, the service class notion needs to be preserved end to end. With this approach, a limited set of service classes is required. For completeness, we have defined thirteen different service classes, three for network operation/administration and ten for user/subscriber applications/services. However, we expect that network administrators will implement a subset of these classes relevant to their customers and their service offerings. Network Administrators may also find it of value to add locally defined service classes, although these will not necessarily enjoy end to end properties of the same type. Section 1, provides an introduction and overview of technologies that are used for service differentiation in IP networks. Section 2, is an overview of how service classes are constructed to provide service differentiation with examples of deployment scenarios. Section 3, provides configuration guidelines of service classes that are used for stable operation and administration of the network. Section 4, provides configuration guidelines of service classes that are used for differentiation of user/subscriber traffic. Section 5, provides additional guidance on mapping different applications/protocol to service classes. Section 6, address security considerations. 1.1 Expected use in the Network In the Internet today, corporate LANs and ISP WANs are generally not heavily utilized - they are commonly 10% utilized at most. For this reason, congestion, loss, and variation in delay within corporate LANs and ISP backbones is virtually unknown. This clashes with user perceptions, for three very good reasons. o The industry moves through cycles of bandwidth boom and bandwidth bust, depending on prevailing market conditions and the periodic Babiarz, et al. Expires January 5, 2005 [Page 4] Internet-Draft Document July 2004 deployment of new bandwidth-hungry applications. o In access networks, the state is often different. This may be because throughput rates are artificially limited, or are over subscribe, or because of access network design trade-offs. o Other characteristics, such as database design on web servers (that may create contention points, e.g. in filestore), and configuration of firewalls and routers, often look externally like a bandwidth limitation. The intent of this document is to provide a consistent marking, conditioning and packet treatment strategy so that it can be configured and put into service on any link which itself is congested. 1.2 Service Class Definition A "service class" represents a set of traffic that requires specific delay, loss and jitter characteristics from the network for which a consistent and defined per-hop behavior (PHB) [RFC2475] applies. Conceptually, a service class pertains to applications with similar characteristics and performance requirements, such as a "High Throughput Data" service class for applications like the web and electronic mail, or a "Telephony" service class for real-time traffic such as voice and other telephony services. Such service class may be defined locally in a Differentiated Services domain, or across multiple DS domains, including possibly extending end to end. 1.3 Key Differentiated Services Concepts The reader must be familiar with the principles of the Differentiated Services Architecture [RFC2475]. However, we recapitulate key concepts here to save searching. 1.3.1 Queuing A queue is a data structure that holds packets that are awaiting transmission. The packets may be delayed while in the queue, possibly due to lack of bandwidth, or because it is low in priority. There are a number of ways to implement a queue, a simple model of a queuing system, however, is a set of data structures for packet data, which we will call queues and a mechanism for selecting the next packet from among them, which we call a scheduler. 1.3.1.1 Priority Queuing A priority queuing system is a combination of a set of queues and a scheduler that empties them in priority sequence. When asked for a packet, the scheduler inspects the highest priority queue, and if Babiarz, et al. Expires January 5, 2005 [Page 5] Internet-Draft Document July 2004 there is data present returns a packet from that queue. Failing that, it inspects the next highest priority queue, and so on. A freeway onramp with a stoplight for one lane, but which allows vehicles in the high occupancy vehicle lane to pass, is an example of a priority queuing system; the high occupancy vehicle lane represents the "queue" having priority. In a priority queuing system, a packet in the highest priority queue will experience a readily calculated delay - it is proportional to the amount of data remaining to be serialized when the packet arrived plus the volume of the data already queued ahead of it in the same queue. The technical reason for using a priority queue relates exactly to this fact: it limits delay and variations in delay, and should be used for traffic which has that requirement. A priority queue or queuing system needs to avoid starvation of lower priority queues. This may be achieved through a variety of means such as admission control, rate control, or network engineering. 1.3.1.2 Rate Queuing Similarly, a rate-based queuing system is a combination of a set of queues and a scheduler that empties each at a specified rate. An example of a rate based queuing system is a road intersection with a stoplight - the stoplight acts as a scheduler, giving each lane a certain opportunity to pass traffic through the intersection. In a rate-based queuing system, such as WFQ or WRR, the delay that a packet in any given queue will experience is dependant on the parameters and occupancy of its queue and the parameters and occupancy of the queues it is competing with. A queue whose traffic arrival rate is much less than the rate at which it lets traffic depart will tend to be empty and packets in it will experience nominal delays. A queue whose traffic arrival rate approximates or exceeds its departure rate will tend to be not empty, and packets in it will experience greater delay. Such a scheduler can impose a minimum rate, a maximum rate, or both, on any queue it touches. 1.3.2 Active Queue Management "Active queue management" or AQM is a generic name for any of a variety of procedures that use packet dropping or marking to manage the depth of a queue. The canonical example of such a procedure is Random Early Detection, in that a queue is assigned a minimum and maximum threshold, and the queuing algorithm maintains a moving average of the queue depth. While the mean queue depth exceeds the maximum threshold, all arriving traffic is dropped. While the mean queue depth exceeds the minimum threshold but not the maximum Babiarz, et al. Expires January 5, 2005 [Page 6] Internet-Draft Document July 2004 threshold, a randomly selected subset of arriving traffic is marked or dropped. This marking or dropping of traffic is intended to communicate with the sending system, causing its congestion avoidance algorithms to kick in. As a result of this behavior, it is reasonable to expect that TCP's cyclic behavior is desynchronized, and the mean queue depth (and therefore delay) should normally approximate the minimum threshold. A variation of the algorithm is applied in Assured Forwarding PHB [RFC2597], in that the behavior aggregate consists of traffic with multiple DSCP marks, which are intermingled in a common queue. Different minima and maxima are configured for the several DSCPs separately, such that traffic that exceeds a stated rate at ingress is more likely to be dropped or marked than traffic that is within its contracted rate. 1.3.3 Traffic Conditioning Additionally, at the first router in a network that a packet crosses, arriving traffic may be measured, and dropped or marked according to a policy, or perhaps shaped on network ingress as in A Rate Adaptive Shaper for Differentiated Services [RFC2963]. This may be used to bias feedback loops, such as is done in Assured Forwarding PHB [RFC2597], or to limit the amount of traffic in a system, as is done in Expedited Forwarding PHB [RFC3246]. Such measurement procedures are collectively referred to as "traffic conditioners". Traffic conditioners are normally built using token bucket meters, for example with a committed rate and a burst size, as in Section 1.5.3 of DiffServModel [RFC3290]. With multiple rate and burst size measurements added to the basic single rate single burst size token bucket meter to achieve multiple levels of conformance used by Assured Forwarding PHB [RFC2597]. Multiple rates and burst sizes can be realized using multiple levels of token buckets or more complex token buckets, these are implementation details. Some traffic conditioners that may be used in deployment of differentiated services are: o For Class Selector (CS) PHBs, a single token bucket meter to provide a rate plus burst size control o For Expedited Forwarding (EF) PHB, a single token bucket meter to provide a rate plus burst size control o For Assured Forwarding (AF) PHBs, usually two token buckets meters configured to provide behavior as outlined in Two Rate Three Color Marker (trTCM) [RFC2698] or the Single Rate Three Color Marker (srTCM) [RFC2697]. The two rate three color marker is used to enforce two rates whereas, the single rate three color marker is used to enforce a committed rate with two burst lengths. Babiarz, et al. Expires January 5, 2005 [Page 7] Internet-Draft Document July 2004 1.3.4 Differentiated Services Code Point (DSCP) The DSCP is a number in the range 0..63, that is placed into an IP packet to mark it according to the class of traffic it belongs in. Half of these values are earmarked for standardized services, and the other half of them are available for local definition. 1.3.5 Per-Hop Behavior (PHB) In the end, the mechanisms described above are combined to form a specified set of characteristics for handling different kinds of traffic, depending on the needs of the application. This document seeks to identify useful traffic aggregates and specify what PHB should be applied to them. 1.4 Key Service Concepts While Differentiated Services is a general architecture that may be used to implement a variety of services, three fundamental forwarding behaviors have been defined and characterized for general use. These are basic default forwarding behavior for elastic traffic, the Assured Forwarding behavior, and the Expedited Forwarding behavior for real-time (inelastic) traffic. The terms "elastic" and "real-time" are defined in [RFC1633] Section 3.1, as a way of understanding broad brush application requirements. This document should be reviewed to obtain a broad understanding of the issues in quality of service, just as [RFC2475] should be reviewed to understand the data plane architecture used in today's Internet. 1.4.1 Default Forwarding (DF) The basic forwarding behavior applied to any class of traffic are those described in [RFC2475] and [RFC2309]. Best Effort service may be summarized as "I will accept your packets", with no further guarantees. Packets in transit may be lost, reordered, duplicated, or delayed at random. Generally, networks are engineered to limit this behavior, but changing traffic loads can push any network into such a state. Application traffic in the internet which uses default forwarding is expected to be "elastic" in nature. By this, we mean that the sender of traffic will adjust its transmission rate in response to changes in available rate, loss, or delay. For the basic best effort service, a single DSCP value is provided to identify the traffic, a queue to store it, and active queue Babiarz, et al. Expires January 5, 2005 [Page 8] Internet-Draft Document July 2004 management to protect the network from it and to limit delays. 1.4.2 Assured Forwarding (AF) The Assured Forwarding PHB [RFC2597] behavior is explicitly modeled on Frame Relay's DE flag or ATM's CLP capability, and is intended for networks that offer average-rate SLAs (as FR and ATM networks do). This is an enhanced best effort service; traffic is expected to be "elastic" in nature. The receiver will detect loss or variation in delay in the network and provide feedback such that the sender adjusts its transmission rate to approximate available capacity. For such behaviors, multiple DSCP values are provided (two or three, perhaps more using local values) to identify the traffic, a common queue to store the aggregate and active queue management to protect the network from it and to limit delays. Traffic is metered as it enters the network, and traffic is variously marked depending on the arrival rate of the aggregate. The premise is that it is normal for users to occasionally use more capacity than their contract stipulates, perhaps up to some bound. However, if traffic must be lost or marked to manage the queue, this excess traffic will be marked or lost first. 1.4.3 Expedited Forwarding (EF) Expedited Forwarding PHB [RFC3246] behavior was originally proposed as a way to implement a virtual wire, and can be used in such a manner. It is an enhanced best effort service: traffic remains subject to loss due to line errors and reordering during routing changes. However, using queuing techniques, the probability of delay or variation in delay is minimized. For this reason, it is generally used to carry voice and for transport of data information that requires "wire like" behavior through the IP network. Voice is an inelastic "real-time" application that sends packets at the rate the codec produces them, regardless of availability of capacity. As such, this service has the potential to disrupt or congest a network if not controlled. It also has the potential for abuse. To protect the network, at minimum one must police traffic at various points to ensure that the design of a queue is not over-run, and then the traffic must be given a low delay queue (often using priority, although it is asserted that a rate-based queue can do this) to ensure that variation in delay is not an issue, to meet application needs. 1.4.4 Class Selector (CS) Class Selector provides support for historical codepoint definitions Babiarz, et al. Expires January 5, 2005 [Page 9] Internet-Draft Document July 2004 and PHB requirement. The Class Selector DS field provides a limited backward compatibility with legacy (pre DiffServ) practice, as described in [RFC2474] Section 4. Backward compatibility is addressed in two ways. First, there are per-hop behaviors that are already in widespread use (e.g. those satisfying the IPv4 Precedence queuing requirements specified in [RFC1812], and we wish to permit their continued use in DS-compliant networks. In addition, there are some codepoints that correspond to historical use of the IP Precedence field and we reserve these codepoints to map to PHBs that meet the general requirements specified in [RFC2474] Section 4.2.2.2. No attempt is made to maintain backward compatibility with the "DTR" or TOS bits of the IPv4 TOS octet, as defined in [RFC0791]and [RFC1349]. A DS-compliant network can be deployed with a set of one or more Class Selector compliant PHB groups. As well, network administrator may configure the network nodes to map codepoints to PHBs irrespective of bits 3-5 of the DSCP field to yield a network that is compatible with historical IP Precedence use. Thus, for example, codepoint '011000' would map to the same PHB as codepoint '011010'. 1.4.5 Admission Control Admission control including refusal when policy thresholds are crossed, can assure high quality communication by ensuring the availability of bandwidth to carry a load. Inelastic real-time flows like VoIP (telephony) or video conferencing services can benefit from use of admission control mechanism, as generally the telephony service is configured with over subscription, meaning that some user(s) may not be able to make a call during peak periods. For VoIP (telephony) service, a common approach is to use signaling protocols such as SIP, H.323, H.248, MEGACO, RSVP, etc. to negotiate admittance and use of network transport capabilities. When a user has been authorized to send voice traffic, this admission procedure has verified that data rates will be within the capacity of the network that it will use. Since RTP voice does not react to loss or delay in any substantive way, the network must police at ingress to ensure that the voice traffic stays within its negotiated bounds. Having thus assured a predictable input rate, the network may use a priority queue to ensure nominal delay and variation in delay. Another approach that may be used in small and bandwidth constrained networks for limited number of flows is RSVP [RFC2205][RFC2996]. However, there is concern with the scalability of this solution in large networks where aggregation of reservations[RFC3175] is considered to be required. Babiarz, et al. Expires January 5, 2005 [Page 10] Internet-Draft Document July 2004 2. Service Differentiation There are practical limits on the level of service differentiation that should be offered in the IP networks. We believe we have defined a practical approach in delivering service differentiation by defining different service classes that networks may choose to support to provide the appropriate level of behaviors and performance needed by current and future applications and services. The defined structure for providing services allows several applications having similar traffic characteristics and performance requirements to be grouped into the same service class. This approach provides a lot of flexibility in providing the appropriate level of service differentiation for current and new yet unknown applications without introducing significant changes to routers or network configurations when a new traffic type is added to the network. 2.1 Service Classes Traffic flowing in a network can be classified in many different ways. We have chosen to divide it into two groupings, network control and user/subscriber traffic. To provide service differentiation, different service classes are defined in each grouping. The network control traffic group can further be divided into three service classes: Administrative for flows that are critical for stable operation of the network, requiring lower delay or higher probability of being serviced, Network Control for normal network control flows and OAM for network configuration and management functions. The user/subscriber traffic group is broken down into ten service classes to provide service differentiation for all the different types of applications/services, (see Section 4 for detailed definition of each service class) in summary: o Telephony service class is best suited for applications that require very low delay variation and are of constant rate, such as IP telephony (VoIP) and circuit emulation over IP applications. o Signaling service class is best suited for client-server (traditional telephony) and peer-to-peer signaling and control functions using protocols such as SIP, H.323, H.248, MGCP, etc. o Multimedia Conferencing service class is best suited for applications that require very low delay, variable rate and have the ability to change encoding rate (elastic), such as H.323/V2 video conferencing service. o Real-time Interactive service class is intended for interactive variable rate inelastic applications that require low jitter, loss and very low delay, such as interactive gaming applications that use RTP/UDP streams for game control commands, video conferencing applications that do not have the ability to change encoding rates or mark packets with different importance indications, etc. Babiarz, et al. Expires January 5, 2005 [Page 11] Internet-Draft Document July 2004 o Multimedia Streaming service class is best suited for variable rate elastic streaming media applications where a human is waiting for output and where the application has the capability to react to packet loss by reducing its transmission rate, such as streaming video and audio, web cast, etc. o Broadcast Video service class is best suited for inelastic streaming media applications that may be of constant or variable rate, requiring low jitter and very low packet loss, such as broadcast TV and live events, video surveillance and security. o Low Latency Data service class is best suited for data processing applications where a human is waiting for output, such as web-based ordering, EPR application, etc. o High Throughput Data service class is best suited for store and forward applications such as FTP, billing record transfer, etc. o Standard service class is for traffic that has not been identified as requiring differentiated treatment and is normally referred as best effort. o Low Priority Data service class is intended for packet flows where bandwidth assurance is not required. We provide guidelines for network administrator in configuring their network for the level of service differentiation that is appropriate in their network to meet their QoS needs. It is expected that network operators will configure and provide in their networks a subset of the defined service classes. Our intent is to provide guidelines for configuration of Differentiated Services for a wide variety of applications, services and network configurations. Additionally, network administrators may choose to define and deploy in their network other service classes. Figure 1 provides a behavior view for traffic serviced by each service class. The traffic characteristics column defines the characteristics and profile of flows serviced and the tolerance to loss, delay and jitter columns define the treatment the flows will receive. End-to-end quantitative performance requirements may be obtained from ITU-T Recommendation Y.1541 and Y.1540. There is also new work currently underway in ITU-T that applies to the service classes defined in this document. ------------------------------------------------------------------- |Service Class | | Tolerance to | | Name | Traffic Characteristics | Loss |Delay |Jitter| |===============+==============================+======+======+======| | Administrative| Small packet size, one packet| Very | Very | Yes | | | at a time | Low | Low | | |---------------+------------------------------+------+------+------| | Network |Variable size packets, mostly | | | | | Control |inelastic short messages, but | Low | Low | Yes | | | traffic can also burst (BGP) | | | | Babiarz, et al. Expires January 5, 2005 [Page 12] Internet-Draft Document July 2004 |---------------+------------------------------+------+------+------| | | Fixed size small packets, | Very | Very | Very | | Telephony | constant emission rate, | Low | Low | Low | | | inelastic and low rate flows | | | | |---------------+------------------------------+------+------+------| | Signaling | Variable size packets, some | Low | Low | Yes | | | what bursty short lived flows| | | | |---------------+------------------------------+------+------+------| | Multimedia | Variable size packets, | Low | Very | | | Conferencing | constant transmit interval, | - | Low | Low | | | reacts to loss |Medium| | | |---------------+------------------------------+------+------+------| | Real-time | RTP/UDP streams, inelastic, | Low | Very | Low | | Interactive | mostly variable rate | | Low | | |---------------+------------------------------+------+------+------| | Multimedia |Variable size packets, elastic|Low - |Medium| Yes | | Streaming | with variable rates |Medium| | | |---------------+------------------------------+------+------+------| | Broadcast | Constant and variable rate, | Very |Medium| Low | | Video | inelastic, non bursty flows | Low | | | |---------------+------------------------------+------+------+------| | Low Latency | Variable rate, bursty short | Low |Low - | Yes | | Data | lived elastic flows | |Medium| | |---------------+------------------------------+------+------+------| | OAM |Variable size packets, elastic| Low |Medium| Yes | | | & inelastic short lived flows| | | | |---------------+------------------------------+------+------+------| |High Throughput| Variable rate, bursty long | Low |Medium| Yes | | Data | lived elastic flows | |- High| | |---------------+------------------------------+------+------+------| | Standard | A bit of everything | Not Specified | |---------------+------------------------------+------+------+------| | Low Priority | Non real-time and elastic | High | High | Yes | | Data | | | | | ------------------------------------------------------------------- Figure 1: Service Class Characteristics Note: A "Yes" in the jitter-tolerant column implies that data is buffered in the endpoint, and a moderate level of network-induced variation in delay will not affect the application. Applications that use TCP as a transport are generally good examples. Routing protocols and peer-to-peer signaling also fall in this class; while loss can create problems in setting up calls, a moderate level of jitter merely makes call placement a little less predictable in duration. Service classes indicate the required traffic forwarding treatment in Babiarz, et al. Expires January 5, 2005 [Page 13] Internet-Draft Document July 2004 order to meet user, application or network expectations. Section 3 in this document defines the service classes that MAY be used for forwarding network control traffic and Section 4 defines the service classes that MAY be used for forwarding user traffic with examples of intended application types mapped into each service class. Note that the application types are only examples and are not meant to be all-inclusive or prescriptive. Also it should be noted that the service class naming or ordering does not imply any priority ordering. They are simply reference names that are used in this document with associated QoS behaviors that are optimized for the particular application types they support. Network administrators MAY choose to assign different service class names, to the service classes that they will support. Figure 2 defines the RECOMMENDED relationship between service classes and DS codepoint(s) assignment with application examples. It is RECOMMENDED that this relationship be preserved end to end. ------------------------------------------------------------------ | Service | DSCP | DSCP | Application | | Class name | name | value | Examples | |===============+=========+=============+==========================| |Administrative | CS7 | 111000 | Heartbeats | |---------------+---------+-------------+--------------------------| |Network Control| CS6 | 110000 | Network routing | |---------------+---------+-------------+--------------------------| | Telephony | EF | 101110 | IP Telephony bearer | |---------------+---------+-------------+--------------------------| | Signaling | CS5 | 101000 | IP Telephony signaling | |---------------+---------+-------------+--------------------------| | Multimedia |AF41,AF42|100010,100100| H.323/V2 video | | Conferencing | AF43 | 100110 | conferencing (elastic) | |---------------+---------+-------------+--------------------------| | Real-time | CS4 | 100000 | Video conferencing and | | Interactive | | | Interactive gaming | |---------------+---------+-------------+--------------------------| | Multimedia |AF31,AF32|011010,011100| Streaming video and | | Streaming | AF33 | 011110 | audio on demand | |---------------+---------+-------------+--------------------------| |Broadcast Video| CS3 | 011000 |Broadcast TV & live events| |---------------+---------+-------------+--------------------------| | Low Latency |AF21,AF22|010010,010100|Client/server transactions| | Data | AF23 | 010110 | Web-based ordering | |---------------+---------+-------------+--------------------------| | OAM | CS2 | 010000 | Non-critical OAM&P | |---------------+---------+-------------+--------------------------| |High Throughput|AF11,AF12|001010,001100| Store and forward | | Data | AF13 | 001110 | applications | |---------------+---------+-------------+--------------------------| Babiarz, et al. Expires January 5, 2005 [Page 14] Internet-Draft Document July 2004 | Standard | DF,(CS0)| 000000 | Undifferentiated | | | | | applications | |---------------+---------+-------------+--------------------------| | Low Priority | CS1 | 001000 | Any flow that has no BW | | Data | | | assurance | ------------------------------------------------------------------ Figure 2: DSCP to Service Class Mapping Note for Figure 2: o Default Forwarding (DF) and Class Selector 0 (CS0) provide equivalent behavior and use the same DS codepoint '000000'. It is expected that network administrators will choose the service classes that they will support based on their need, starting off with three or four service classes for user traffic and add others as the need arises. Figure 3 provides a summary of DiffServ QoS mechanisms that SHOULD be used for the defined service classes that are further detailed in Section 3 and Section 4 of this document. Based on what applications/services that need to be differentiated, network administrators can choose the service class(es) that need to be supported in their network. ------------------------------------------------------------------ | Service | DSCP | Conditioning at | PHB | Queuing| AQM| | Class | | DS Edge | Used | | | |===============+======+===================+=========+========+====| |Administrative | CS7 | See Section 3.1 | RFC2474 |Priority| No | |---------------+------+-------------------+---------+--------+----| |Network Control| CS6 | See Section 3.2 | RFC2474 | Rate |Yes | |---------------+------+-------------------+---------+--------+----| | Telephony | EF |Police using sr+bs | RFC3246 |Priority| No | |---------------+------+-------------------+---------+--------+----| | Signaling | CS5 |Police using sr+bs | RFC2474 | Rate | No | |---------------+------+-------------------+---------+--------+----| | Multimedia | AF41 | Using two rate | | | Yes| | Conferencing | AF42 |three color marker | RFC2597 | Rate | per| | | AF43 | | | |DSCP| |---------------+------+-------------------+---------+--------+----| | Real-time | CS4 |Police using sr+bs | RFC2474 | Rate | No | | Interactive | | | | | | |---------------+------+-------------------+---------|--------+----| | Multimedia | AF31 | Using two rate | | | Yes| | Streaming | AF32 |three color marker | RFC2597 | Rate | per| | | AF33 | | | |DSCP| |---------------+------+-------------------+---------+--------+----| |Broadcast Video| CS3 |Police using sr+bs | RFC2474 | Rate | No | Babiarz, et al. Expires January 5, 2005 [Page 15] Internet-Draft Document July 2004 |---------------+------+-------------------+---------+--------+----| | Low | AF21 | Using single rate | | | Yes| | Latency | AF22 |three color marker | RFC2597 | Rate | per| | Data | AF23 | | | |DSCP| |---------------+------+-------------------+---------+--------+----| | OAM | CS2 |Police using sr+bs | RFC2474 | Rate | Yes| |---------------+------+-------------------+---------+--------+----| | High | AF11 | Using two rate | | | Yes| | Throughput | AF12 |three color marker | RFC2597 | Rate | per| | Data | AF13 | | | |DSCP| |---------------+------+-------------------+---------+--------+----| | Standard | DF | Not applicable | RFC2474 | Rate | Yes| |---------------+------+-------------------+---------+--------+----| | Low Priority | CS1 | Not applicable | RFC3662 | Rate | Yes| | Data | | | | | | ------------------------------------------------------------------ Figure 3: Summary of QoS Mechanisms used for each Service Class Notes for Figure 3: o Conditioning at DS edge, means that traffic conditioning is performed at the edge of the DiffServ network where untrusted user devices are connected or between two DiffServ networks. o "sr+bs" represents a policing mechanism that provides single rate with burst size control. o The Administrative service class MAY be implemented using Rate queuing method as long as sufficient amount of bandwidth is guaranteed and latency of scheduler is sufficiently low to meet the requirement. o The PHB for Real-time Interactive service class SHOULD be configured to provide high bandwidth assurance. It MAY be configured as a second EF PHB that uses relaxed performance parameters and a rate scheduler. o The PHB for Broadcast Video service class SHOULD be configured to provide high bandwidth assurance. It MAY be configured as a third EF PHB that uses relaxed performance parameters and a rate scheduler. o In network segments that use IP precedence marking, only High Throughput Data or Low Priority Data service class can be supported. The DSCP value(s) in the unsupported service class MUST be changed to 000xxx on ingress and MUST be changed back to original value(s) on egress of the network segment that uses precedence marking. 2.2 Deployment Scenarios It is expected that network administrators will choose the service classes that they will support based on their need, starting off with Babiarz, et al. Expires January 5, 2005 [Page 16] Internet-Draft Document July 2004 three or four service classes for user traffic and adding others as the need arises. In this section we provide three examples of a subset of service classes that could be deployed with the first example being detailed. Example 1: A network administrator determined that they need to provide different performance levels (quality of service) in their network for the services that they will be offering to their customers. They need to enable their network to provide: o Reliable VoIP (telephony) service, equivalent to PSTN o A low delay assured bandwidth data service o As well, support current Internet services For this example, the network administrator's needs are addressed with the deployment of the following service classes: o Administrative service class for heartbeats between routers to insure timely detection and path restoration under link or node failure o Network Control service class for routing and control traffic that is needed for reliable operation of the provider's network o Standard service class for all traffic that will receive normal (undifferentiated) forwarding treatment through their network for support of current Internet services o Telephony service class for VoIP (telephony) bearer traffic o Signaling service class for Telephony signaling to control the service o Low Latency Data service class for the low delay assured bandwidth differentiated data service o OAM service class for operation and management of the network Figure 4, provides a popular industry view of the service differentiation supported in core network. Babiarz, et al. Expires January 5, 2005 [Page 17] Internet-Draft Document July 2004 ------------------------------------------------------------------- | Service | DSCP | Conditioning at | PHB | | | | Class | | DS Edge | Used | Queuing| AQM| |===============+=======+===================+=========+========+====| | Administrative| CS7 | See Section 3.2 | RFC2474 |Priority| No | |---------------+-------+-------------------+---------+--------+----| |Network Control| CS6 | See Section 3.2 | RFC2474 | Rate | Yes| |---------------+-------+-------------------+---------+--------+----| | Telephony | EF |Police using sr+bs | RFC3246 |Priority| No | |---------------+-------+-------------------+---------+--------+----| | Signaling | CS5 |Police using sr+bs | RFC2474 | Rate | No | |---------------+-------+-------------------+---------+--------+----| | Low | AF21 | Using single rate | | |Yes | | Latency | AF22 |three color marker | RFC2597 | Rate |Per | | Data | AF23 | | | |DSCP| |---------------+-------+-------------------+---------+--------+----| | OAM | CS2 |Police using sr+bs | RFC2474 | Rate | Yes| |---------------+-------+-------------------+---------+--------+----| | Standard |DF(CS0)| Not applicable | RFC2474 | Rate | Yes| | | +other| | | | | ------------------------------------------------------------------- Figure 4: Popular Core Network Configuration Notes for Figure 4: o The Administrative service class MAY be implemented using Rate queuing method as long as sufficient amount of bandwidth is guaranteed and latency of scheduler is sufficiently low to meet the requirement. o "sr+bs" represents a policing mechanism that provides single rate with burst size control. o Any packet that is marked with DSCP value that is not represented by the supported service classes, MUST be forwarded using the Standard service class. Example 2: A network administrator determines that they need to support three service classes for control and administration of their network plus five levels of service differentiation for user traffic using the following service classes: o Administrative o Network Control o OAM o Standard o Telephony o Signaling Babiarz, et al. Expires January 5, 2005 [Page 18] Internet-Draft Document July 2004 o Low Latency Data o Real-time Interactive Example 3: An enterprise network administrator determines that they need to provide eight levels of service differentiation for user traffic plus two for running of their network. They would configure their network to support the following service classes: o Network Control o OAM o Telephony o Multimedia Conferencing o Multimedia Streaming o Low Latency Data o Signaling o High Throughput Data o Standard o Low Priority Data 3. Network Control Traffic Network control traffic is defined as packet flows that are essential for stable operation of the administered network as well for information that may be exchanged between neighboring networks across a peering point where SLAs are in place. Network control traffic is different from user application control (signaling) that may be generated by some applications or services. Network control traffic is mostly between routers and network nodes that are used for operating, administering, controlling or managing the network segments. Network Control Traffic may be split into three service classes, i.e. Administrative, Network Control and OAM. 3.1 Administrative Service Class The Administrative service class is intended for control traffic that is within a single administrative network domain. If such traffic does not get through, the administered network domain may not function properly. Example of such type of traffic is heartbeats between core network switches/routers. Such heartbeats are used to determine if the next hop is reachable. If no heartbeat is received within a specified time interval, then the sending router assumes that the particular link or next hop node is unreachable on a particular interface and subsequently reroutes the traffic to a backup interface that can reach the next hop node. This reroute is typically done in a time interval much shorter than the time it would take for the routing protocol to determine that the next hop node is unreachable. Babiarz, et al. Expires January 5, 2005 [Page 19] Internet-Draft Document July 2004 The Administrative service class, if supported MUST be configured using the DiffServ Class Selector (CS) PHB defined in [RFC2474] and MUST be configured with sufficient forwarding resources so that all packets are forwarded quickly. The Administrative service class SHOULD be configured to use a Priority Queuing system such as defined in Section 1.3.1.1 of this document. In network configuration where inter node packets forwarding delays for CS7 marked heartbeats is not stringent, Rate Queuing system such as defined in Section 1.3.1.2 MAY be used, as long as sufficient bandwidth is guaranteed for network heartbeats. Examples of protocols and application that SHOULD use the Administrative service class: o Protocol(s) that are transmitted between nodes within the administered network for detecting link and nodal failures i.e., IP-layer keep-alive The following protocols and application MUST NOT use the Administrative service class: o User Traffic o Inter-network domain (across peering points) control traffic Traffic characteristics of packet flows in the Administrative service class: o Mostly messages sent between routers and network servers o Typically small packet sizes, one packet at a time o Packets requiring immediate forwarding o User traffic is not allowed to use this service class RECOMMENDED DSCP marking is CS7 (Class Selector 7) RECOMMENDED Network Edge Conditioning: o Drop or remark CS7 marked packets at ingress to DiffServ network domain o Packets from users are not permitted access to the Administrative service class o Depending on policy within the administered network, CS7 marked packets MAY be dropped or remarked to CS6 at egress of DiffServ network or across peering points Note: CS7 marked packets SHOULD NOT be sent across peering points. Exchange of control information across peering points SHOULD be done using CS6 marked packets, using Network Control service class. The fundamental service offered to the Administrative service class is enhanced best effort service with guaranteed bandwidth. Since this service class is used to forward inelastic flows, the service SHOULD be engineered so the Active Queue Management (AQM) [RFC2309] is not applied to CS7 marked packets. Babiarz, et al. Expires January 5, 2005 [Page 20] Internet-Draft Document July 2004 3.2 Network Control Service Class The Network Control service class is used for transmitting packets between network devices (routers, servers, etc.) that require control information to be exchanged between different administrative domains (across a peering point) and for non-critical network control information exchange within one administrative domain. Traffic transmitted in this service class is very important as it keeps the network operational and needs to be forwarded in a timely manner. The Network Control service class MUST be configured using the DiffServ Class Selector (CS) PHB defined in [RFC2474]. This service class MUST be configured so that the traffic receives a minimum bandwidth guarantee, to ensure that the packets always receive timely service. The configured forwarding resources for Network Control service class SHOULD be such that the probability of packet drop under peak load is very low in this service class. The Network Control service class SHOULD be configured to use a Rate Queuing system such as defined in Section 1.3.1.2 of this document. Examples of protocols and application that SHOULD use the Network Control service class: o Routing packet flows: OSPF, BGP, ISIS, RIP o Signaling flows between high capacity telephony call servers or soft switches. Such high capacity devices may control thousands of telephony (VoIP) calls o Network services, DNS, DHCP, BootP, high priority OAM (SNMP) like alarms, etc. o Control information exchange within and between different administrative domains across a peering point where SLAs are in place o LSP setup using CR-LDP and RSVP-TE o In 3GPP wireless solutions, UMTS Signaling/control information between wireless nodes The following protocols and applications MUST NOT use the Network Control service class: o User traffic Traffic characteristics of packet flows in the Network Control service class: o Mostly messages sent between routers and network servers o Ranging from 50 to 1,500 byte packet sizes, normally one packet at a time but traffic can also burst (BGP) o User traffic is not allowed to use this service class RECOMMENDED DSCP marking is CS6 (Class Selector 6) Babiarz, et al. Expires January 5, 2005 [Page 21] Internet-Draft Document July 2004 RECOMMENDED Network Edge Conditioning: o At peering points (between two DiffServ networks) where SLAs are in place, CS6 marked packets MUST be policed, e.g. using a single rate with burst size (sr+bs) token bucket policer to keep the CS6 marked packet flows to within the traffic rate specified in the SLA. o CS6 marked packet flows from untrusted sources (for example, end user devices) MUST be dropped or remarked at ingress to DiffServ network. o Packets from users/subscribers are not permitted access to the Network Control service classes. The fundamental service offered to the Network Control service class is enhanced best effort service with high bandwidth assurance. Since this service class is used to forward both elastic and inelastic flows, the service SHOULD be engineered so the Active Queue Management (AQM) [RFC2309] is applied to CS6 marked packets. Some network administrators MAY choose to configure their network so that both Administrative (CS7) and Network Control (CS6) packet flows are forward out of the same queue. If that is the case, it is RECOMMENDED that networks nodes use a Rate Queuing system and the queue is configured to provide high bandwidth assurance for the sum of CS7 and CS6 marked packets. Further, AQM SHOULD only be applied to CS6 mark packets. AQM MUST NOT be applied to CS7 marked packets. If RED [RFC2309] is used as an AQM algorithm, the min-threshold specifies a target queue depth, and the max-threshold specifies the queue depth above which all traffic is dropped or ECN marked. Thus, in this service class, the following inequality should hold in queue configurations: o min-threshold CS6 < max-threshold CS6 o max-threshold CS6 <= memory assigned to the queue Note: Many other AQM algorithms exist and are used; they should be configured to achieve a similar result. 3.3 OAM Service Class The Operation and Management (OAM) service class is RECOMMENDED for non-critical OAM&P (Operation and Management and Provisioning) using protocols such as SNMP, TFTP, FTP, Telnet, COPS, etc. Applications using this service class require a low packet loss but are relatively not sensitive to delay. This service class is configured to provide good packet delivery for intermittent flows. The OAM service class MUST use the Class Selector (CS) PHB defined in [RFC2474]. This service class SHOULD be configured to provide a minimum bandwidth assurance for CS2 marked packets to ensure that Babiarz, et al. Expires January 5, 2005 [Page 22] Internet-Draft Document July 2004 they get forwarded. The OAM service class SHOULD be configured to use a Rate Queuing system such as defined in Section 1.3.1.2 of this document. The following applications SHOULD use the OAM service class: o For provisioning and configuration of network elements o For performance monitoring of network elements o For any non-critical OAM&P (Operation and Management and Provisioning) function Traffic characteristics: o Variable size packets (50 to 1500 bytes in size) o Intermittent traffic flows o Traffic may burst at times o Both elastic and inelastic short lived flows o Traffic not sensitive to delays RECOMMENDED DSCP marking: o All flows in this service class are marked with CS2 (Class Selector 2) Applications or IP end points SHOULD pre-mark their packets with CS2 DSCP value. If the end point is not capable of setting the DSCP value, then the router topologically closest to the end point MUST perform Multifield (MF) Classification as defined in [RFC2475]. RECOMMENDED Conditioning Performed at DiffServ Network Edge: o Packet flow marking (DSCP setting) from untrusted sources (end user devices) SHOULD be verified at ingress to DiffServ network using Multifield (MF) Classification methods defined in [RFC2475]. o Packet flows from untrusted sources (end user devices) MUST be policed at ingress to DiffServ network, e.g. using single rate with burst size token bucket policer to ensure that the traffic stays within its negotiated or engineered bounds. o Packet flows from trusted sources (routers inside administered network) MAY not require policing. o Normally OAM&P CS2 marked packet flows are not allowed to flow across peering points, if that is the case, than CS2 marked packet SHOULD be policed (dropped) at both egress and ingress peering interfaces. The fundamental service offered to "OAM" traffic is enhanced best effort service with controlled rate. The service SHOULD be engineered so that CS2 marked packet flows have sufficient bandwidth in the network to provide high assurance of delivery. Since this service class is used to forward both elastic and inelastic flows, the service SHOULD be engineered so that Active Queue Management [RFC2309] is applied to CS2 marked packets. Babiarz, et al. Expires January 5, 2005 [Page 23] Internet-Draft Document July 2004 If RED [RFC2309] is used as an AQM algorithm, the min-threshold specifies a target queue depth for each DSCP, and the max-threshold specifies the queue depth above which all traffic with such a DSCP is dropped or ECN marked. Thus, in this service class, the following inequality should hold in queue configurations: o min-threshold CS2 < max-threshold CS2 o max-threshold CS2 <= memory assigned to the queue Note: Many other AQM algorithms exist and are used; they should be configured to achieve a similar result. 4. User Traffic User traffic is defined as packet flows between different users or subscribers. It is the traffic that is sent to or from end-terminals and that support very wide variety of applications and services. User traffic can be differentiated in many different ways, therefore we investigated several different approaches to classify user traffic. We looked at differentiating user traffic as real-time versus non real-time, elastic versus inelastic, sensitive versus insensitive to loss as well traffic categorization as interactive, responsive, timely and non-critical as defined in ITU-T Recommendation G.1010. At the end, we added up using all of the above for service differentiation, mapping of applications that have the matching traffic characteristics that fit the traffic profile and performance requirements of the defined service classes. Network administrators can categorize their applications based on the type of behavior that they require and MAY choose to support all or subset of the defined service classes. Figure 2 provides some common applications and the forwarding service class that best supports them based on their performance requirements. 4.1 Telephony Service Class The Telephony service class is RECOMMENDED for applications that require real-time, very low delay, very low jitter and very low packet loss for relatively constant-rate traffic sources (inelastic traffic sources). This service class MUST be used for IP telephony service. The fundamental service offered to traffic in the Telephony service class is minimum jitter, delay and packet loss service up to a specified upper bound. Operation is in some respect similar to an ATM CBR service, which has guaranteed bandwidth and which, if it stays within the negotiated rate, experiences nominal delay and no loss. The EF PHB has a similar guarantee. Typical configurations negotiate the setup of telephone calls over IP Babiarz, et al. Expires January 5, 2005 [Page 24] Internet-Draft Document July 2004 using protocols such as H.248, MEGACO, H.323 or SIP. When a user has been authorized to send telephony traffic, the call admission procedure should have verified that the newly admitted flow will be within the capacity of the Telephony service class forwarding capability in the network. For VoIP (telephony) service, call admission control is usually performed by a telephony call server/ gatekeeper using signaling (SIP, H.323, H.248, MEGACO, etc.) on access points to the network. The bandwidth in the core network and the number of simultaneous VoIP sessions that can be supported needs to be engineered and controlled so that there is no congestion for this service. Since RTP telephony flows do not react to loss or substantial delay in any substantive way, the Telephony service class SHOULD forward packet as soon as possible. The Telephony service class MUST use Expedited Forwarding (EF) PHB as defined in [RFC3246] and SHOULD be configured to receive guaranteed forwarding resources so that all packets are forwarded quickly. The Telephony service class SHOULD be configured to use a Priority Queuing system such as defined in Section 1.3.1.1 of this document. The following application SHOULD use the Telephony service class: o VoIP (G.711, G.729 and other codecs) o Voice-band data over IP (modem, fax) o T.38 fax over IP o Circuit emulation over IP, virtual wire, etc. o In wireless 3GPP applications, traffic that is mapped into the UMTS Conversational Traffic Class Traffic characteristics: o Mostly fixed size packets for VoIP (60, 70, 120 or 200 bytes in size) o Packets emitted at constant time intervals o Admission control of new flows is provided by telephony call server, media gateway, gatekeeper, edge router, end terminal or access node that provides flow admission control function. Applications or IP end points SHOULD pre-mark their packets with EF DSCP value. If the end point is not capable of setting the DSCP value, then the router topologically closest to the end point MUST perform Multifield (MF) Classification as defined in [RFC2475]. RECOMMENDED DSCP marking is EF for the following applications: o VoIP (G.711, G.729 and other codecs) o Voice-band data over IP (modem and fax) o T.38 fax over IP o Circuit emulation over IP, virtual wire, etc. o Conversational UMTS Traffic Class Babiarz, et al. Expires January 5, 2005 [Page 25] Internet-Draft Document July 2004 RECOMMENDED Network Edge Conditioning: o Packet flow marking (DSCP setting) from untrusted sources (end user devices) SHOULD be verified at ingress to DiffServ network using Multifield (MF) Classification methods defined in [RFC2475]. o Packet flows from untrusted sources (end user devices) MUST be policed at ingress to DiffServ network, e.g. using single rate with burst size token bucket policer to ensure that the telephony traffic stays within its negotiated bounds. o Packet flows from trusted sources (media gateways inside administered network) MAY not require policing. o Policing of Telephony packet flows across peering points where SLA is in place is OPTIONAL as telephony traffic will be controlled by admission control mechanism between peering points. The fundamental service offered to "Telephony" traffic is enhanced best effort service with controlled rate, very low delay and very low loss. The service MUST be engineered so that EF marked packet flows have sufficient bandwidth in the network to provide guaranteed delivery. Normally traffic in this service class does not respond dynamically to packet loss. As such, Active Queue Management [RFC2309] MUST NOT be applied to EF marked packet flows. 4.2 Signaling Service Class The Signaling service class is RECOMMENDED for delay sensitive client-server (traditional telephony) and peer-to-peer application signaling. Telephony signaling includes signaling between IP phone and soft-switch, soft-client and soft-switch, media gateway and soft-switch as well as peer-to-peer using various protocols. Applications using this service class requiring a relatively fast response as there are typically several message of different size sent for control of the session. This service class is configured to provide good response for short lived, intermittent flows that require real-time packet forwarding. To minimize the possibility of speech-clipping and/or ring-clipping at start of call when interfacing to the PSTN (TDM Central Office equipment), the Signaling service class SHOULD be configured so that the probability of packet drop or significant queuing delay under peak load is very low in IP network segments that provide this interface. See Section 5 for explanation of mapping different signaling methods to service classes. The Signaling service class MUST use the Class Selector (CS) PHB defined in [RFC2474]. This service class SHOULD be configured to provide a minimum bandwidth assurance for CS5 marked packets to ensure that they get forwarded. The Signaling service class SHOULD be configured to use a Rate Queuing system such as defined in Section 1.3.1.2 of this document. Babiarz, et al. Expires January 5, 2005 [Page 26] Internet-Draft Document July 2004 The following applications SHOULD use the Signaling service class: o Peer-to-peer IP telephony signaling (e.g., using SIP, H.323) o Peer-to-peer signaling for multimedia applications (e.g., using SIP, H.323) o Peer-to-peer real-time control function o Client-server IP telephony signaling using H.248, MEGACO, MGCP, IP encapsulated ISDN or other proprietary protocols Traffic characteristics: o Variable size packets (50 to 1500 bytes in size) o Intermittent traffic flows o Traffic may burst at times o Delay sensitive control messages sent between two end-points RECOMMENDED DSCP marking: o All flows in this service class are marked with CS5 (Class Selector 5) Applications or IP end points SHOULD pre-mark their packets with CS5 DSCP value. If the end point is not capable of setting the DSCP value, then the router topologically closest to the end point MUST perform Multifield (MF) Classification as defined in [RFC2475]. RECOMMENDED Conditioning Performed at DiffServ Network Edge: o Packet flow marking (DSCP setting) from untrusted sources (end user devices) SHOULD be verified at ingress to DiffServ network using Multifield (MF) Classification methods defined in [RFC2475]. o Packet flows from untrusted sources (end user devices) MUST be policed at ingress to DiffServ network, e.g. using single rate with burst size token bucket policer to ensure that the traffic stays within its negotiated or engineered bounds. o Packet flows from trusted sources (application servers inside administered network) MAY not require policing. o Policing of packet flows across peering points SHOULD be performed to the Service Level Agreement (SLA). The fundamental service offered to "Signaling" traffic is enhanced best effort service with controlled rate and delay. The service SHOULD be engineered so that CS5 marked packet flows have sufficient bandwidth in the network to provide high assurance of delivery and low delay. Normally traffic in this service class does not respond dynamically to packet loss. As such, Active Queue Management [RFC2309] MUST NOT be applied to CS5 marked packet flows. 4.3 Multimedia Conferencing Service Class The Multimedia Conferencing service class is RECOMMENDED for applications that require real-time and very low delay for variable Babiarz, et al. Expires January 5, 2005 [Page 27] Internet-Draft Document July 2004 rate elastic traffic sources. Video conferencing is such an application. The traffic sources (applications) in this traffic class have the capability to reduce their transmission rate based on feedback received from the receiving end. Detection of packet loss by the receiver is sent using the applications control stream to the transmitter as an indication of possible congestion; the transmitter then selects a lower transmission rate based on pre-configured encoding rates (or transmission rates). Note, today many H.323/V2 video conferencing solutions implement fixed step bandwidth change (usually reducing the rate), traffic resembling step-wise CBR. In the future, it is expected that these services will generate continuously variable rate traffic with packet marking indicating flow importance. Typical video conferencing configurations negotiate the setup of multimedia session using protocols such as H.323 or SIP. When a user/end-point has been authorized to start a multimedia session the admission procedure should have verified that the newly admitted data rate will be within the engineered capacity of the Multimedia Conferencing service class. The bandwidth in the core network and the number of simultaneous video conferencing sessions that can be supported SHOULD be engineered to control traffic load for this service. The Multimedia Conferencing service class MUST use the Assured Forwarding (AF) PHB defined in [RFC2597]. This service class SHOULD be configured to provide a bandwidth assurance for AF41, AF42, and AF43 marked packets to ensure that they get forwarded. The Multimedia Conferencing service class SHOULD be configured to use a Rate Queuing system such as defined in Section 1.3.1.2 of this document. The following application SHOULD use the Multimedia Conferencing service class: o H.323/V2 Video conferencing (interactive video) o Video conferencing applications with rate control or traffic content importance marking o Application server to application server non bursty data transfer requiring very low delay o IP VPN service that specifies two rates and mean network delay that is slightly longer then network propagation delay. o Interactive, time critical and mission critical applications. o In wireless 3GPP applications, traffic that is mapped into the UMTS Interactive Traffic Class with Traffic Handling Priority 1 (THP=1). Traffic characteristics: Babiarz, et al. Expires January 5, 2005 [Page 28] Internet-Draft Document July 2004 o Variable size packets (50 to 1500 bytes in size) o Higher the rate, higher is the density of large packets o Variable packet emission time o Variable rate o Source is capable of reducing its transmission rate based on detection of packet loss at the receiver RECOMMENDED DSCP marking: o Video conferencing packets are marked with AF4x o VPN service may be marked with AF4x, depending on the service characteristics o Server to server data transfer with AF4x, depending on the service characteristics o UMTS Interactive THP=1 packets are marked with AF4x Applications or IP end points SHOULD pre-mark their packets with DSCP values as shown below. If the end point is not capable of setting the DSCP value, then the router topologically closest to the end point MUST perform Multifield (MF) Classification as defined in [RFC2475] and mark all packets as AF41. Note: In this case, the two rate three color marker will be configured to operate in Color-Aware mode. RECOMMENDED DSCP marking: o AF41 = up to specified rate "A" o AF42 = in excess of specified rate "A" but below specified rate "B" o AF43 = in excess of specified rate "B" o Where "A" < "B" Note: One might expect "A" to approximate the sum of the mean rates and "B" to approximate the sum of the peak rates. RECOMMENDED DSCP marking when performed by H.323/V2 video conferencing equipment: o AF41 = H.323 video conferencing audio stream RTP/UDP o AF41 = H.323 video conferencing video control RTCP/TCP o AF41 = H.323 video conferencing video stream up to specified rate "A" o AF42 = H.323 video conferencing video stream in excess of specified rate "A" but below specified rate "B" o AF43 = H.323 video conferencing video stream in excess of specified rate "B" o Where "A" < "B" RECOMMENDED Conditioning Performed at DiffServ Network Edge: o The two rate three color marker SHOULD be configured to provide the behavior as defined in trTCM [RFC2698]. Babiarz, et al. Expires January 5, 2005 [Page 29] Internet-Draft Document July 2004 o If packets are marked by a trusted sources or previous trusted DiffServ domain, then the two rate three color marker SHOULD be configured to operate in Color-Aware mode. o If the packet marking is not trusted, then the two rate three color marker MUST be configured to operate in Color-Blind mode. The fundamental service offered to "Multimedia Conferencing" traffic is enhanced best effort service with controlled rate and delay. For video conferencing service, typically a 1% packet loss detected at the receiver triggers an encoding rate change, dropping to next lower provisioned video encoding rate. As such, Active Queue Management [RFC2309] SHOULD be used primarily to switch video encoding rate under congestion, changing from high rate to lower rate i.e. 1472 kbps to 768 kbps. The probability of loss of AF41 traffic MUST NOT exceed the probability of loss of AF42 traffic, which in turn MUST NOT exceed the probability of loss of AF43 traffic. If RED [RFC2309] is used as an AQM algorithm, the min-threshold specifies a target queue depth for each DSCP, and the max-threshold specifies the queue depth above which all traffic with such a DSCP is dropped or ECN marked. Thus, in this service class, the following inequality should hold in queue configurations: o min-threshold AF43 < max-threshold AF43 o max-threshold AF43 <= min-threshold AF42 o min-threshold AF42 < max-threshold AF42 o max-threshold AF42 <= min-threshold AF41 o min-threshold AF41 < max-threshold AF41 o max-threshold AF41 <= memory assigned to the queue Note: This configuration tends to drop AF43 traffic before AF42 and AF42 before AF41. Many other AQM algorithms exist and are used; they should be configured to achieve a similar result. 4.4 Real-time Interactive Service Class The Real-time Interactive service class is RECOMMENDED for applications that require low loss, jitter and very low delay for variable rate inelastic traffic sources. Interactive gaming and video conferencing applications that do not have the ability to change encoding rates or mark packets with different importance indications are such applications. The traffic sources in this traffic class does not have the ability to reduce their transmission rate based on feedback received from the receiving end. Typically, applications in this service class are configured to negotiate the setup of RTP/UDP control session. When a user/ end-point has been authorized to start a new session the admission procedure should have verified that the newly admitted data rates will be within the engineered capacity of the Real-time Interactive Babiarz, et al. Expires January 5, 2005 [Page 30] Internet-Draft Document July 2004 service class. The bandwidth in the core network and the number of simultaneous Real-time Interactive sessions that can be supported SHOULD to be engineered to control traffic load for this service. The Real-time Interactive service class MUST use the Class Selector (CS) PHB defined in [RFC2474]. This service class SHOULD be configured to provide a high assurance for bandwidth for CS4 marked packets to ensure that they get forwarded. The Real-time Interactive service class SHOULD be configured to use a Rate Queuing system such as defined in Section 1.3.1.2 of this document. Note, this service class MAY be configured as a second EF PHB that uses relaxed performance parameter, a rate scheduler and CS4 DSCP value. The following application SHOULD use the Real-time Interactive service class: o Interactive gaming and control o Video conferencing applications with out rate control or traffic content importance marking o IP VPN service that specifies single rate and mean network delay that is slightly longer then network propagation delay o Inelastic, interactive, time critical and mission critical applications requiring very low delay Traffic characteristics: o Variable size packets (50 to 1500 bytes in size) o Variable rate non bursty o Application is sensitive to delay variation between flows and sessions o Packets lost if any are usually ignored by application RECOMMENDED DSCP marking: o All flows in this service class are marked with CS4 (Class Selector 4) Applications or IP end points SHOULD pre-mark their packets with CS4 DSCP value. If the end point is not capable of setting the DSCP value, then the router topologically closest to the end point MUST perform Multifield (MF) Classification as defined in [RFC2475]. RECOMMENDED Conditioning Performed at DiffServ Network Edge: o Packet flow marking (DSCP setting) from untrusted sources (end user devices) SHOULD be verified at ingress to DiffServ network using Multifield (MF) Classification methods defined in [RFC2475]. o Packet flows from untrusted sources (end user devices) MUST be policed at ingress to DiffServ network, e.g. using single rate with burst size token bucket policer to ensure that the traffic stays within its negotiated or engineered bounds. Babiarz, et al. Expires January 5, 2005 [Page 31] Internet-Draft Document July 2004 o Packet flows from trusted sources (application servers inside administered network) MAY not require policing. o Policing of packet flows across peering points SHOULD be performed to the Service Level Agreement (SLA). The fundamental service offered to "Real-time Interactive" traffic is enhanced best effort service with controlled rate and delay. The service SHOULD be engineered so that CS4 marked packet flows have sufficient bandwidth in the network to provide high assurance of delivery. Normally traffic in this service class does not respond dynamically to packet loss. As such, Active Queue Management [RFC2309] SHOULD NOT be applied to CS4 marked packet flows. 4.5 Multimedia Streaming Service Class The Multimedia Streaming service class is RECOMMENDED for applications that require near-real-time packet forwarding of variable rate elastic traffic sources that are not as delay sensitive as applications using the Multimedia Conferencing service class. Such applications include streaming audio and video, some video (movies) on demand applications and Web casts. In general, the Multimedia Streaming service class assumes that the traffic is buffered at the source/destination and therefore, is less sensitive to delay and jitter. The Multimedia Streaming service class MUST use the Assured Forwarding (AF) PHB defined in [RFC2597]. This service class SHOULD be configured to provide a minimum bandwidth assurance for AF31, AF32 and AF33 marked packets to ensure that they get forwarded. The Multimedia Streaming service class SHOULD be configured to use Rate Queuing system such as defined in Section 1.3.1.2 of this document. The following applications SHOULD use the Multimedia Streaming service class: o Buffered streaming audio (unicast) o Buffered streaming video (unicast) o Web casts o IP VPN service that specifies two rates and is less sensitive to delay and jitter o In wireless 3GPP applications, traffic that is mapped into the UMTS Streaming Traffic Class Traffic characteristics: o Variable size packets (50 to 4196 bytes in size) o Higher the rate, higher density of large packets o Variable rate o Elastic flows Babiarz, et al. Expires January 5, 2005 [Page 32] Internet-Draft Document July 2004 o Some bursting at start of flow from some applications Applications or IP end points SHOULD pre-mark their packets with DSCP values as shown below. If the end point is not capable of setting the DSCP value, then the router topologically closest to the end point MUST perform Multifield (MF) Classification as defined in [RFC2475] and mark all packets as AF31. Note: In this case, the two rate three color marker will be configured to operate in Color-Aware mode. RECOMMENDED DSCP marking: o AF31 = up to specified rate "A" o AF32 = in excess of specified rate "A" but below specified rate "B" o AF33 = in excess of specified rate "B" o Where "A" < "B" Note: One might expect "A" to approximate the sum of the mean rates and "B" to approximate the sum of the peak rates. RECOMMENDED Conditioning Performed at DiffServ Network Edge: o The two rate three color marker SHOULD be configured to provide the behavior as defined in trTCM [RFC2698]. o If packets are marked by a trusted sources or previous trusted DiffServ domain, then the two rate three color marker SHOULD be configured to operate in Color-Aware mode. o If the packet marking is not trusted, then the two rate three color marker MUST be configured to operate in Color-Blind mode. The fundamental service offered to "Multimedia Streaming" traffic is enhanced best effort service with controlled rate and delay. The service SHOULD be engineered so that AF31 marked packet flows have sufficient bandwidth in the network to provide high assurance of delivery. Since the AF3x traffic is elastic and responds dynamically to packet loss, Active Queue Management [RFC2309] SHOULD be used primarily to reduce forwarding rate to the minimum assured rate at congestion points. The probability of loss of AF31 traffic MUST NOT exceed the probability of loss of AF32 traffic, which in turn MUST NOT exceed the probability of loss of AF33. If RED [RFC2309] is used as an AQM algorithm, the min-threshold specifies a target queue depth for each DSCP, and the max-threshold specifies the queue depth above which all traffic with such a DSCP is dropped or ECN marked. Thus, in this service class, the following inequality should hold in queue configurations: o min-threshold AF33 < max-threshold AF33 o max-threshold AF33 <= min-threshold AF32 o min-threshold AF32 < max-threshold AF32 Babiarz, et al. Expires January 5, 2005 [Page 33] Internet-Draft Document July 2004 o max-threshold AF32 <= min-threshold AF31 o min-threshold AF31 < max-threshold AF31 o max-threshold AF31 <= memory assigned to the queue Note: This configuration tends to drop AF33 traffic before AF32 and AF32 before AF31. Many other AQM algorithms exist and are used; they should be configured to achieve a similar result. 4.6 Broadcast Video Service Class The Broadcast Video service class is RECOMMENDED for applications that require near-real-time packet forwarding with very low packet loss of constant and variable rate inelastic traffic sources that are not as delay sensitive as applications using the Real-time Interactive service class. Such applications include broadcast TV, streaming of live audio and video events, some video on demand applications and video surveillance. In general, the Broadcast Video service class assumes that the destination end point has a dejitter buffer, for video application usually a 2 - 8 video frames buffer (66 to several hundred of milliseconds) therefore, is less sensitive to delay and jitter. The Broadcast Video service class MUST use the Class Selector (CS) PHB defined in [RFC2474]. This service class SHOULD be configured to provide high assurance for bandwidth for CS3 marked packets to ensure that they get forwarded. The Broadcast Video service class SHOULD be configured to use Rate Queuing system such as defined in Section 1.3.1.2 of this document. Note, this service class MAY be configured as a third EF PHB that uses relaxed performance parameter, a rate scheduler and CS3 DSCP value. The following applications SHOULD use the Broadcast Video service class: o Video surveillance and security (unicast) o TV broadcast including HDTV (multicast) o Video on demand (unicast) with control (virtual DVD) o Streaming of live audio events (both unicast and multicast) o Streaming of live video events (both unicast and multicast) Traffic characteristics: o Variable size packets (50 to 4196 bytes in size) o Higher the rate, higher density of large packets o Mixture of variable and constant rate flows o Fixed packet emission time intervals o Inelastic flows RECOMMENDED DSCP marking: o All flows in this service class are marked with CS3 (Class Selector 3) Babiarz, et al. Expires January 5, 2005 [Page 34] Internet-Draft Document July 2004 o In some cases, like for security and video surveillance applications, it may be desirable to use a different DSCP marking. If so, than locally user definable (EXP/LU) codepoint(s) in the range '011xxx' MAY be used to provide unique traffic identification. The locally user definable (EXP/LU) codepoint(s) MAY be associated with the PHB that is used for CS3 traffic. Further, depending on the network scenario, additional network edge conditioning policy MAY be need for the EXP/LU codepoint(s) used. Applications or IP end points SHOULD pre-mark their packets with CS3 DSCP value. If the end point is not capable of setting the DSCP value, then the router topologically closest to the end point MUST perform Multifield (MF) Classification as defined in [RFC2475]. RECOMMENDED Conditioning Performed at DiffServ Network Edge: o Packet flow marking (DSCP setting) from untrusted sources (end user devices) SHOULD be verified at ingress to DiffServ network using Multifield (MF) Classification methods defined in [RFC2475]. o Packet flows from untrusted sources (end user devices) MUST be policed at ingress to DiffServ network, e.g. using single rate with burst size token bucket policer to ensure that the traffic stays within its negotiated or engineered bounds. o Packet flows from trusted sources (application servers inside administered network) MAY not require policing. o Policing of packet flows across peering points SHOULD be performed to the Service Level Agreement (SLA). The fundamental service offered to "Broadcast Video" traffic is enhanced best effort service with controlled rate and delay. The service SHOULD be engineered so that CS3 marked packet flows have sufficient bandwidth in the network to provide high assurance of delivery. Normally traffic in this service class does not respond dynamically to packet loss. As such, Active Queue Management [RFC2309] MUST NOT be applied to CS3 marked packet flows. 4.7 Low Latency Data Service Class The Low Latency Data service class is RECOMMENDED for elastic and responsive typically client/server based applications. Applications forwarded by this service class are those requiring a relatively fast responses and typically have asymmetrical bandwidth need, i.e. the client typically sends a short message to the server and the server responds with a much larger data flow back to the client. The most common example of this is when a user clicks a hyperlink (~few dozen bytes) on a web page resulting in a new web page to be loaded (Kbytes of data). This service class is configured to provide good response for TCP [RFC1633] short lived flows that require real-time packet Babiarz, et al. Expires January 5, 2005 [Page 35] Internet-Draft Document July 2004 forwarding of variable rate traffic sources. The Low Latency Data service class MUST use the Assured Forwarding (AF) PHB defined in [RFC2597]. This service class SHOULD be configured to provide a minimum bandwidth assurance for AF21, AF22 and AF23 marked packets to ensure that they get forwarded. The Low Latency Data service class SHOULD be configured to use a Rate Queuing system such as defined in Section 1.3.1.2 of this document. The following applications SHOULD use the Low Latency Data service class: o Client/server applications o SNA terminal to host transactions (SNA over IP using DLSw) o Web based transactions (E-commerce) o Credit card transactions o Financial wire transfers o ERP applications (e.g., SAP/BaaN) o VPN service that supports CIR (Committed Information Rate) with up to two burst sizes o In wireless 3GPP applications, traffic that is mapped into the UMTS Interactive Traffic Class with Traffic Handling Priority 2 (THP=2) Traffic characteristics: o Variable size packets (50 to 1500 bytes in size) o Variable packet emission rate o With packet bursts of TCP window size o Short traffic bursts o Source capable of reducing its transmission rate based on detection of packet loss at the receiver or through explicit congestion notification Applications or IP end points SHOULD pre-mark their packets with DSCP values as shown below. If the end point is not capable of setting the DSCP value, then the router topologically closest to the end point MUST perform Multifield (MF) Classification as defined in [RFC2475] and mark all packets as AF21. Note: In this case, the single rate three color marker will be configured to operate in Color-Aware mode. RECOMMENDED DSCP marking: o AF21 = flow stream with packet burst size up to "A" bytes o AF22 = flow stream with packet burst size in excess of "A" but below "B" bytes o AF23 = flow stream with packet burst size in excess of "B" bytes o Where "A" < "B" RECOMMENDED Conditioning Performed at DiffServ Network Edge: Babiarz, et al. Expires January 5, 2005 [Page 36] Internet-Draft Document July 2004 o The single rate three color marker SHOULD be configured to provide the behavior as defined in srTCM [RFC2697]. o If packets are marked by a trusted sources or previous trusted DiffServ domain, then the single rate three color marker SHOULD be configured to operate in Color-Aware mode. o If the packet marking is not trusted, then the single rate three color marker MUST be configured to operate in Color-Blind mode. The fundamental service offered to "Low Latency Data" traffic is enhanced best effort service with controlled rate and delay. The service SHOULD be engineered so that AF21 marked packet flows have sufficient bandwidth in the network to provide high assurance of delivery. Since the AF2x traffic is elastic and responds dynamically to packet loss, Active Queue Management [RFC2309] SHOULD be used primarily to control TCP flow rates at congestion points by dropping packet from TCP flows that have large burst size. The probability of loss of AF21 traffic MUST NOT exceed the probability of loss of AF22 traffic, which in turn MUST NOT exceed the probability of loss of AF23. Active queue management MAY also be implemented using Explicit Congestion Notification (ECN) [RFC3168]. If RED [RFC2309] is used as an AQM algorithm, the min-threshold specifies a target queue depth for each DSCP, and the max-threshold specifies the queue depth above which all traffic with such a DSCP is dropped or ECN marked. Thus, in this service class, the following inequality should hold in queue configurations: o min-threshold AF23 < max-threshold AF23 o max-threshold AF23 <= min-threshold AF22 o min-threshold AF22 < max-threshold AF22 o max-threshold AF22 <= min-threshold AF21 o min-threshold AF21 < max-threshold AF21 o max-threshold AF21 <= memory assigned to the queue Note: This configuration tends to drop AF23 traffic before AF22 and AF22 before AF21. Many other AQM algorithms exist and are used; they should be configured to achieve a similar result. 4.8 High Throughput Data Service Class The High Throughput Data service class is RECOMMENDED for elastic applications that require timely packet forwarding of variable rate traffic sources and more specifically is configured to provide good throughput for TCP longer lived flows. TCP [RFC1633] or a transport with a consistent Congestion Avoidance Procedure [RFC2581][RFC2582] normally will drive as high a data rate as it can obtain over a long period of time. The FTP protocol is a common example, although one cannot definitively say that all FTP transfers are moving data in bulk. Babiarz, et al. Expires January 5, 2005 [Page 37] Internet-Draft Document July 2004 The High Throughput Data service class MUST use the Assured Forwarding (AF) PHB defined in [RFC2597]. This service class SHOULD be configured to provide a minimum bandwidth assurance for AF11, AF12 and AF13 marked packets to ensure that they are forwarded in timely manner. The High Throughput Data service class SHOULD be configured to use a Rate Queuing system such as defined in Section 1.3.1.2 of this document. The following applications SHOULD use the High Throughput Data service class: o Store and forward applications o File transfer applications o Email o VPN service that supports two rates (committed information rate and excess or peak information rate) o In wireless 3GPP applications, traffic that is mapped into the UMTS Interactive Traffic Class with Traffic Handling Priority 3 (THP=3) Traffic characteristics: o Variable size packets (50 to 1500 bytes in size) o Variable packet emission rate o Variable rate o With packet bursts of TCP window size o Source capable of reducing its transmission rate based on detection of packet loss at the receiver or through explicit congestion notification Applications or IP end points SHOULD pre-mark their packets with DSCP values as shown below. If the end point is not capable of setting the DSCP value, then the router topologically closest to the end point MUST perform Multifield (MF) Classification as defined in [RFC2475] and mark all packets as AF11. Note: In this case, the two rate three color marker will be configured to operate in Color-Aware mode. RECOMMENDED DSCP marking: o AF11 = up to specified rate "A" o AF12 = in excess of specified rate "A" but below specified rate "B" o AF13 = in excess of specified rate "B" o Where "A" < "B" RECOMMENDED Conditioning Performed at DiffServ Network Edge: o The two rate three color marker SHOULD be configured to provide the behavior as defined in trTCM [RFC2698]. o If packets are marked by a trusted sources or previous trusted DiffServ domain, then the two rate three color marker SHOULD be Babiarz, et al. Expires January 5, 2005 [Page 38] Internet-Draft Document July 2004 configured to operate in Color-Aware mode. o If the packet marking is not trusted, then the two rate three color marker MUST be configured to operate in Color-Blind mode. The fundamental service offered to "High Throughput Data" traffic is enhanced best effort service with a specified minimum rate. The service SHOULD be engineered so that AF11 marked packet flows have sufficient bandwidth in the network to provide assured delivery. It can be assumed that this class will consume any available bandwidth, and packets traversing congested links may experience higher queuing delays and/or packet loss. Since the AF1x traffic is elastic and responds dynamically to packet loss, Active Queue Management [RFC2309] SHOULD be used primarily to control TCP flow rates at congestion points by dropping packet from TCP flows that have higher rates first. The probability of loss of AF11 traffic MUST NOT exceed the probability of loss of AF12 traffic, which in turn MUST NOT exceed the probability of loss of AF13. In such a case, if one network customer is driving significant excess and another seeks to use the link, any losses will be experienced by the high rate user, causing him to reduce his rate. Active queue management MAY also be implemented using Explicit Congestion Notification (ECN) [RFC3168]. If RED [RFC2309] is used as an AQM algorithm, the min-threshold specifies a target queue depth for each DSCP, and the max-threshold specifies the queue depth above which all traffic with such a DSCP is dropped or ECN marked. Thus, in this service class, the following inequality should hold in queue configurations: o min-threshold AF13 < max-threshold AF13 o max-threshold AF13 <= min-threshold AF12 o min-threshold AF12 < max-threshold AF12 o max-threshold AF12 <= min-threshold AF11 o min-threshold AF11 < max-threshold AF11 o max-threshold AF11 <= memory assigned to the queue Note: This configuration tends to drop AF13 traffic before AF12 and AF12 before AF11. Many other AQM algorithms exist and are used; they should be configured to achieve a similar result. 4.9 Standard Service Class The Standard service class is RECOMMENDED for traffic that has not been classified into one of the other supported forwarding service classes in the DiffServ network domain. This service class provides the Internet's "best effort" forwarding behavior. This service class typically has minimum bandwidth guarantee. The Standard service class MUST use the Default Forwarding (DF) PHB defined in [RFC2474] and SHOULD be configured to receive a small percentage of forwarding resources (at least 5%). This service class Babiarz, et al. Expires January 5, 2005 [Page 39] Internet-Draft Document July 2004 SHOULD be configured to use a Rate Queuing system such as defined in Section 1.3.1.2 of this document. The following application SHOULD use the Standard service class: o Any undifferentiated application/packet flow transported through the DiffServ enabled network o In wireless 3GPP applications, traffic that is mapped into the UMTS Background Traffic Class Traffic Characteristics: o Non deterministic, mixture of everything RECOMMENDED DSCP marking is DF (Default Forwarding) '000000' Network Edge Conditioning: There is no requirement that conditioning of packet flows be performed for this service class. The fundamental service offered to the Standard service class is best effort service with active queue management to limit over-all delay. Typical configurations SHOULD use random packet dropping to implement Active Queue Management [RFC2309] or Explicit Congestion Notification [RFC3168], and MAY impose a minimum or maximum rate on the queue. If RED [RFC2309] is used as an AQM algorithm, the min-threshold specifies a target queue depth, and the max-threshold specifies the queue depth above which all traffic is dropped or ECN marked. Thus, in this service class, the following inequality should hold in queue configurations: o min-threshold DF < max-threshold DF o max-threshold DF <= memory assigned to the queue Note: Many other AQM algorithms exist and are used; they should be configured to achieve a similar result. 4.10 Low Priority Data The Low Priority Data service class serves applications that run over TCP [RFC0793] or a transport with consistentcongestion avoidance procedure [RFC2581][RFC2582], and which the user is willing to accept service without guarantees. This service class is specified in [QBSS] and [RFC3662]. The following applications MAY use the Low Priority Data service class: o Any TCP based application/packet flow transported through the DiffServ enabled network that does not require any bandwidth assurances Babiarz, et al. Expires January 5, 2005 [Page 40] Internet-Draft Document July 2004 Traffic Characteristics: o Non real-time and elastic Network Edge Conditioning: There is no requirement that conditioning of packet flows be performed for this service class RECOMMENDED DSCP marking is CS1 (Class Selector 1) The fundamental service offered to the Low Priority Data service class is best effort service with zero bandwidth assurance. By placing it into a separate queue or class, it may be treated in a manner consistent with a specific service level agreement. Typical configurations SHOULD use Explicit Congestion Notification [RFC3168] or random loss to implement Active Queue Management [RFC2309]. If RED [RFC2309] is used as an AQM algorithm, the min-threshold specifies a target queue depth, and the max-threshold specifies the queue depth above which all traffic is dropped or ECN marked. Thus, in this service class, the following inequality should hold in queue configurations: o min-threshold CS1 < max-threshold CS1 o max-threshold CS1 <= memory assigned to the queue Note: Many other AQM algorithms exist and are used; they should be configured to achieve a similar result. 5. Mapping Applications to Service Classes Here we provide some examples for mapping different applications into the defined service classes. Mapping for Signaling: There are many different signaling protocols, ways that signaling is used and performance requirements from applications that are controlled by these protocols. Therefore we have determined that the different signaling protocols be mapped to service classes that best meet the objectives of application they are controlling. The following mapping is recommended: o Peer-to-peer signaling using SIP/H.323 are marked with CS5 DSCP and are forwarded using Signaling service class o Client-server signaling as used in many implementation for IP telephony using H.248, MEGACO, MGCP, IP encapsulated ISDN or proprietary protocols are marked with CS5 DSCP and are forwarded using the Signaling service class Babiarz, et al. Expires January 5, 2005 [Page 41] Internet-Draft Document July 2004 o Signaling between call servers or soft-switches in carrier's network using SIP, SIP-T, IP encapsulated ISUP, are marked with CS6 DSCP and are forwarded using the Network Control service class. o RSVP signaling, depends on the application. If RSVP signaling is "on-path" as used in IntServ or NSIS, than it needs to be forwarded from the same queue (service class) as application data that it is controlling. Mapping for NTP: From tests that were performed, indications are that precise time distribution requires a very low packet delay variation (jitter) transport. Therefore we would suggest the following guidelines for NTP be used: o When NTP is used for providing high accuracy timing within administrator's (carrier's) network or to end users/clients, the Telephony service class should be used and NTP packets be marked with EF DSCP value. o For applications that require "wall clock" timing accuracy, the Standard service class should be used and packets should be marked with DF DSCP. 6. Security Considerations This document discusses policy, and describes a common policy configuration, for the use of a Differentiated Services Code Point by transports and applications. If implemented as described, it should require the network to do nothing that the network has not already allowed. If that is the case, no new security issues should arise from the use of such a policy. It is possible for the policy to be applied incorrectly, or for a wrong policy to be applied in the network for the defined service class. In that case, a policy issue exists that the network must detect, assess, and deal with. This is a known security issue in any network dependent on policy directed behavior. A well known flaw appears when bandwidth is reserved or enabled for a service (for example, voice transport) and another service or an attacking traffic stream uses it. This possibility is inherent in DiffServ technology, which depends on appropriate packet markings. When bandwidth reservation or a priority queuing system is used in a vulnerable network, the use of authentication and flow admission is recommended. To the author's knowledge, there is no known technical way to respond to an unauthenticated data stream using service that it is not intended to use, and such is the nature of the Internet. Babiarz, et al. Expires January 5, 2005 [Page 42] Internet-Draft Document July 2004 The use of a service class by a user is not an issue when the SLA between the user and the network permits him to use it, or to use it up to a stated rate. In such cases, simple policing is used in the Differentiated Services Architecture. Some service classes, such as Network Control, are not permitted to be used by users at all; such traffic should be dropped or remarked by ingress filters. Where service classes are available under the SLA only to an authenticated user rather than to the entire population of users, AAA services such as described in [I-D.iab-auth-mech] are required. 7. Summary of Changes from Previous Draft NOTE TO RFC EDITOR: Please remove this section during the publication process. Made corrections to typos and grammar throughout document. Incorporated comments received from Mike Pierce. Moved some subsections in section 1 for better flow in document. Added document overview to section 1. Section 2, 3, and 4 were significantly reworked to incorporate changes that coauthors discussed at Seoul meeting. Mainly using a single PHB or PHB group per service class. Incorporated changes to the service classes that support video conferencing and video streaming applications that we received from video encoding subject area experts . Incorporated requested change from mailing list to separate telephony singling from the Telephony service class. Removed telephony signaling from the Telephony server class and generated a service class just for application signaling. Also added an OAM service class for operations and management and provisioning. As well, made changes to section 2 to reflect the above changes. 8. Acknowledgements The authors acknowledge a great many inputs, most notably from Bruce Davie, Dave Oran, Ralph Santitoro, Gary Kenward, Francois Audet, Brian E Carpenter, Morgan Littlewood, Robert Milne, John Shuler, Nalin Mistry, Al Morton, Mike Pierce, Ed Koehler Jr., Tim Rahrer and Fil Dickinson. Kimberly King, Joe Zebarth and Alistair Munroe each did a thorough proof-reading, and the document is better for their contributions. Babiarz, et al. Expires January 5, 2005 [Page 43] Internet-Draft Document July 2004 9. References 9.1 Normative References [I-D.iab-auth-mech] Rescorla, E., "A Survey of Authentication Mechanisms", draft-iab-auth-mech-03 (work in progress), March 2004. [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981. [RFC1349] Almquist, P., "Type of Service in the Internet Protocol Suite", RFC 1349, July 1992. [RFC1812] Baker, F., "Requirements for IP Version 4 Routers", RFC 1812, June 1995. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2309] Braden, B., Clark, D., Crowcroft, J., Davie, B., Deering, S., Estrin, D., Floyd, S., Jacobson, V., Minshall, G., Partridge, C., Peterson, L., Ramakrishnan, K., Shenker, S., Wroclawski, J. and L. Zhang, "Recommendations on Queue Management and Congestion Avoidance in the Internet", RFC 2309, April 1998. [RFC2474] Nichols, K., Blake, S., Baker, F. and D. Black, "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers", RFC 2474, December 1998. [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z. and W. Weiss, "An Architecture for Differentiated Services", RFC 2475, December 1998. [RFC2597] Heinanen, J., Baker, F., Weiss, W. and J. Wroclawski, "Assured Forwarding PHB Group", RFC 2597, June 1999. [RFC3246] Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec, J., Courtney, W., Davari, S., Firoiu, V. and D. Stiliadis, "An Expedited Forwarding PHB (Per-Hop Behavior)", RFC 3246, March 2002. [RFC3662] Bless, R., Nichols, K. and K. Wehrle, "A Lower Effort Babiarz, et al. Expires January 5, 2005 [Page 44] Internet-Draft Document July 2004 Per-Domain Behavior (PDB) for Differentiated Services", RFC 3662, December 2003. 9.2 Informative References [QBSS] "QBone Scavenger Service (QBSS) Definition", Internet2 Technical Report Proposed Service Definition, March 2001. [RFC1633] Braden, B., Clark, D. and S. Shenker, "Integrated Services in the Internet Architecture: an Overview", RFC 1633, June 1994. [RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S. and S. Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification", RFC 2205, September 1997. [RFC2581] Allman, M., Paxson, V. and W. Stevens, "TCP Congestion Control", RFC 2581, April 1999. [RFC2582] Floyd, S. and T. Henderson, "The NewReno Modification to TCP's Fast Recovery Algorithm", RFC 2582, April 1999. [RFC2697] Heinanen, J. and R. Guerin, "A Single Rate Three Color Marker", RFC 2697, September 1999. [RFC2698] Heinanen, J. and R. Guerin, "A Two Rate Three Color Marker", RFC 2698, September 1999. [RFC2963] Bonaventure, O. and S. De Cnodder, "A Rate Adaptive Shaper for Differentiated Services", RFC 2963, October 2000. [RFC2996] Bernet, Y., "Format of the RSVP DCLASS Object", RFC 2996, November 2000. [RFC3168] Ramakrishnan, K., Floyd, S. and D. Black, "The Addition of Explicit Congestion Notification (ECN) to IP", RFC 3168, September 2001. [RFC3175] Baker, F., Iturralde, C., Le Faucheur, F. and B. Davie, "Aggregation of RSVP for IPv4 and IPv6 Reservations", RFC 3175, September 2001. [RFC3290] Bernet, Y., Blake, S., Grossman, D. and A. Smith, "An Informal Management Model for Diffserv Routers", RFC 3290, May 2002. Babiarz, et al. Expires January 5, 2005 [Page 45] Internet-Draft Document July 2004 Authors' Addresses Jozef Babiarz Nortel Networks 3500 Carling Avenue Ottawa, Ont. K2H 8E9 Canada Phone: +1-613-763-6098 Fax: +1-613-765-7462 EMail: babiarz@nortelnetworks.com Kwok Ho Chan Nortel Networks 600 Technology Park Drive Billerica, MA 01821 US Phone: +1-978-288-8175 Fax: +1-978-288-4690 EMail: khchan@nortelnetworks.com Fred Baker Cisco Systems 1121 Via Del Rey Santa Barbara, CA 93117 US Phone: +1-408-526-4257 Fax: +1-413-473-2403 EMail: fred@cisco.com Babiarz, et al. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Babiarz, et al. Expires January 5, 2005 [Page 47]