HTTP/1.1 200 OK Date: Mon, 08 Apr 2002 22:55:36 GMT Server: Apache/1.3.20 (Unix) Last-Modified: Thu, 19 Sep 1996 05:44:28 GMT ETag: "2e6d3d-b4c5-3240ddbc" Accept-Ranges: bytes Content-Length: 46277 Connection: close Content-Type: text/plain INTERNET-DRAFT Marty Borden, Bay Networks, Mark W. Garrett, Bellcore. June, 1996. Interoperation of Controlled-Load and Guaranteed-Service with ATM Status of this Memo This document is an Internet-Draft. 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.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Abstract Service mappings are one aspect of providing interoperability between the IP Integrated Services and ATM networks. These encompass the means of dealing with the different paradigms of each network type to provide effective end-to-end Quality of Service. This draft is an initial exploration of how to provide the QoS of an IP integrated service with ATM subnetworks. It focuses on how to best match ATM service with the IP integrated services. The work here is preliminary and is presented as a baseline for discussion. 1.0 Introduction We are interested in the problem of providing IP Integrated Services with an ATM subnetwork: This is a complex problem with many facets. In this draft, we focus on and specify the parameters and signalling Borden, Garrett Expires December, 1996 [Page 1] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 elements needed for service interoperation between internet Integrated Services protocols and ATM Traffic Management capabilities. The mappings provided of service types, parameters and features between the two technologies can be used to provide effective end-to-end Quality of Service (QoS) for IP traffic that traverses ATM networks. This document is only a part of the total solution to providing the interworking of IP integrated services with an ATM subnetwork. We do not consider the important issues of when ATM VCs should be created or destroyed, how they should be used or coordinated, or of how routing-- QoS sensitive or not-- interacts with the use of VCs, especially in the problem area of multicast (or point-to-multipoint) flows. Instead we concentrate on the mapping of service attributes between IP integrated services and ATM capabilities. The goal of this draft is to provide sufficient information and guidance that it is possible to use the ideas herein to formulate the general solution. At times, we present in-depth discussions of interoperation issues beyond what may be appropriate for a final specification. We assume, for the moment, that this is useful for developing consensus, and that a concise specification document will be derived later. The network architecture we consider is summarized in Figure 1, below. Here, IP-attached hosts use RSVP to establish resource reservation in routers along the internet path for the data flow. How this path is chosen is outside of the scope of this document (although the service mappings we discuss may play a part), but we assume that an ATM network lies in the path, consisting of one or many ATM switches; it uses connections to provide both resources and QoS within the ATM cloud. These connections are set up, added to (in the case of multipoint trees), torn down, and controlled by the edge devices, which are devices capable of IP routing and ATM user-to- network (UNI) interfaces. Consider these edge devices as fully functional in both the IP int-serv/RSVP areas and the ATM UNI areas, as well as translating between them. Borden, Garrett Expires December, 1996 [Page 2] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 ATM Cloud ------------------ H ---\ ( ) /------- H H ---- R -- R -- E --( ATM SW -- ATM SW ) -- E -- R -- R -- H H ---/ | ( ) \ | ------------------ \------- H H ----------R Figure 1: Network Architecture with hosts (H), Routers (R) and Edge Devices (E). Whether edge devices are considered part of the IP internet or part of the ATM cloud, or both, is not an issue in the current problem space, since they must provide capabilities of both environments. The edge devices have normal RSVP capability to process RSVP messages, reserve resources, and maintain soft state (in the control path), and to classify and schedule packets (in the data path). They also have the normal ATM capabilities to signal (and refuse) connections, and to police and schedule cells. In addition, a reservation setup (RESV message) must trigger the edge device to translate the RSVP service requirements from RSVP semantics and syntax to the ATM VC (UNI) semantics, and vice-versa. The difficulty of this must not be minimized. Point-to-multipoint connections within the ATM cloud are used to support general IP multicast flows. Different ATM mechanisms may be available to support this; it may be that the root of the point-to- multipoint tree controls the tree, which requires coordination between the edge devices, or the leaf initiated join (LIJ) may be appropriate. Thus, VCs are managed according to a combination of standards and local rules, which may be implementation specific; this management may decide to multiplex the requested flow onto an existing VC or may decide that a new VC is warranted. Figure 2 shows the functions of an edge device, summarizing the work not part of IP or ATM abstractly as an InterWorking Function (IWF), and segregating the control and data planes. (Note: for expositional convenience, policy control and other control functions are included as part of the admission control in the diagram.) Borden, Garrett Expires December, 1996 [Page 3] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 IP ATM ____________________ | IWF | | | admission <--> | service mapping | <--> ATM control | VC management | signalling & | address resolution | admission |....................| control | | classification/ | ATM Adaption Layer | cell policing & <--> | Segmentation and | <--> scheduling/ scheduling | Reassembly | shaping | Buffering | ____________________ Figure 2: Edge Device Functions showing the IWF In the logical view of Figure 2, some functions, such as scheduling, are shown separately, since these functions are required of both the IP and ATM sides. However it may be possible in an integrated implementation to combine such functions. It is not possible to completely separate the service mapping and VC management functions. Several examples of why this is so come to mind. (i) Multiple integrated-services flows may be aggregated to use one point-to-multipoint VC; in this case we assume the IP flows are of the same service type and their parameters have been merged. (ii) The VC management function may choose to allocate extra resources in anticipation of further reservations or based on a empiric of changing TSpecs; in this case we assume that the additional resources continue to be specified in the form of an appropriate TSpec. (iii) There must exist a path for best effort flows and for sending the TSpecs; how this interacts with the establishment of VCs for QoS traffic may alter the characteristics required of the VC. Therefore, in discussing the service-mapping problem, we will assume that the VC management function of the IWF presents to the service mapping the need for a VC to support a certain integrated-service type with a given TSpec. The VC required may be a new one or the addition/deletion of a leaf to an existing multipoint tree. We examine the service requirements of a VC supporting this service and TSpec. Borden, Garrett Expires December, 1996 [Page 4] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 Having outlined the scope, we now outline the remainder of this document. The first part of this work, section 2.0, examines each ATM signalling semantic or feature, and discusses it with respect to each of the three IP integrated services -- Guaranteed Service (GS), Controlled Load (CL) and Best Effort (BE) (which is, by default, a service). Each of the ATM specifications, UNI 3.0, UNI 3.1 and 4.0 are considered here. In this regard, we are able to clearly recommend one or more choices for each parameter/feature to match each service; sometimes the choice is obvious, other times there is room for implementation experience or policy guidelines before making any decisions. The following sections (3.0 - 5.0) are specific to each IP integrated service. They provide a summary of the work of section 2.0 with the result of a recommended approach for ATM signalling. 1.1 Related documents Earlier ATM Forum documents were called UNI 3.0 and UNI 3.1. The 3.1 release was used to correct errors and fix alignment with the ITU. Unfortunately UNI 3.0 and 3.1 are incompatible. However this is in terms of actual codepoints, not semantics. Therefore, descriptions of parameter values can generally be used for both. After 3.1, the ATM Forum decided to release documents separately for each technical subcommittee. The Traffic Management and Signalling 4.0 documents are available publically at ftp.atmforum.com/pub. We refer to the combination of traffic management and signalling as TM/UNI 4.0, although specific references may be made to the TM 4.0 specification or the UNI SIG 4.0 specification. Within the IETF area, related material includes: RSVP functional specification, Guaranteed Service specification, Controlled Load service specification, Int-serv data encoding specification, RFC 1577, RFC1755, RFC 1821, draft-crawley-rsvp-over-atm, draft-birman-ipatm-rsvpatm, draft-onvural-srinivasan-rsvp-atm. 1.2 Abbreviations CBR Constant Bit Rate Borden, Garrett Expires December, 1996 [Page 5] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 VBR Variable Bit Rate rtVBR Real-time VBR nrtVBR Non-real-time VBR UBR Unspecified Bit Rate ABR Available Bit Rate BCOB Broadband Connectioned Oriented Bearer BCOB-{A,C,X} Bearer Class A, C, or X PCR Peak Cell Rate SCR Sustained Cell Rate MBS Maximum Burst Size CDV Cell Delay Variation CTD Cell Transfer Delay CDVT Cell Delay Variation Tolerance BT Burst Tolerance MCR Minimum Cell Rate CLP Cell Loss Priority (bit) CLR Cell Loss Ratio CL Controlled Load GS Guaranteed Service BE Best Effort 2.0 ATM Protocol Features In this section, we discuss each of the items that must be specified in the setup of an ATM VC. For each of these we discuss which specified items and values may be most appropriate for each of the integrated services. The ATM Call Setup is sent by the edge device to the ATM network to establish end-to-end [ATM] service. This setup contains the following information. Service Category/Broadband Bearer Capability AAL Parameters Broadband Low Layer Information Calling and Called Party Addressing Information Traffic Descriptors QoS Parameters Additional Parameters of TM/UNI 4.0 We will discuss each of these, except addressing information, as they relate to the translation of GS and CL to ATM services. We also Borden, Garrett Expires December, 1996 [Page 6] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 discuss the tagging and conformance definitions for IP and ATM, since the policing method is implicit in the call setup. 2.1 Service Category and Bearer Capability The highest level of abstraction distinguishing features of ATM VCs is in the service category or bearer capability. Service categories were introduced in TM/UNI 4.0; previously the bearer capability was used to discriminate at this level. In each version of the ATM specifications, these indicate the general properties required of a VC: whether there is a real-time delay constraint, whether the traffic is constant or variable rate, the applicable traffic and QoS description parameters and (implicitly) the complexity of some supporting switch mechanisms. For UNI 3.0 and UNI 3.1, there are only two distinct options for bearer capabilities (in our context): BCOB-A: constant rate, timing required, unicast/multipoint; BCOB-C: variable rate, timing not required, unicast/multipoint. There is a third capability, BCOB-X, but in the case of AAL5 (which we require -- see below) it can be used interchangeably and consistently with the above two capabilities. In TM/UNI 4.0 the service categories are: Constant Bit Rate (CBR) Real-time Variable Bit Rate (rtVBR) Non-real-time Variable Bit Rate (nrtVBR) Unspecified Bit Rate (UBR) Available Bit Rate (ABR) The first two of these are real-time services, so that rtVBR is new to TM/UNI 4.0. The ABR service is also new to TM/UNI 4.0. UBR exists in all specifications, except perhaps in name, through the ``best effort'' indication flag or, in UNI 3.x, the QoS Class 0. The encoding used in 4.0 is consistent with the earlier versions. For example, the Service Category is indicated solely by the combination of the Bearer Capabilty and the Best Effort indication flag. In principle, it is possible to support any forseeable integrated service through the use of BCOB-A/CBR. This is because the CBR Borden, Garrett Expires December, 1996 [Page 7] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 service is equivalent to having a ``pipe'' with specified bandwidth/timing. However, it may be desirable to make better use of the ATM network's resources by using other, less demanding, services when available. (See RFC 1821 for a discussion of this.) Guaranteed Service There are two possible mappings for GS: CBR (BCOB-A) rtVBR GS requires real-time support, that is, timing is required. Thus in UNI 3.x, the bearer class BCOB-A (or an equivalent BCOB-X formulation) must be used. In TM/UNI 4.0 either of CBR or rtVBR is appropriate, the latter allowing the network to possibly take advantage of the statistical multiplexing gain of variable rate flows and to use tagging (see section 2.2). Neither the BCOB-C bearer class, nor nrtVBR, UBR, ABR are matches for the GS service. These provide no delay estimates and one cannot expect low, predictable, or consistent delays. Specification of BCOB-A or CBR requires specification of a PCR. The PCR should be specified as the the token bucket rate parameter, with appropriate conversion from bytes to cells (and overhead), of the GS TSpec. For both of these, the network provides a nominal clearing rate of PCR with toleration (bucket size) CDVT, specified in a network specific manner (see below). Specification of rtVBR requires the specification of two rates, SCR and PCR. This models bursty traffic with specified peak and average rates. With rtVBR, it is appropriate to map the PCR to the line rate of incoming traffic and the SCR to the GS TSpec bucket rate. The ATM bucket sizes are CDVT, in a network specific manner, and CDVT+BT, respectively for the PCR and SCR parameters (see below). Controlled Load There are three possible mappings for CL: CBR (BCOB-A) ABR nrtVBR (BCOB-C) Note that under UNI 3.x, only the first and third choices are Borden, Garrett Expires December, 1996 [Page 8] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 applicable. The first, with a CBR/BCOB-A connection, provides a higher level of QoS than is necessary, but it may be convenient to simply allocate a fixed-rate ``pipe'', which should be ubiquitously supported in ATM networks. However unless this is the only choice available, this appears to be wasteful of network resources. The ABR category with a positive MCR aligns with the CL idea of ``best effort with floor.'' The ATM network agrees to forward cells with a rate of at least MCR, which should be directly converted from the token bucket rate of the TSpec. The bucket size parameter measures the amount of buffer required at the IWF. The nrtVBR/BCOB-C category can also be used. It does introduce some unaligned complexity in the conformance definition (see section 2.2) by the use of two leaky buckets. The CL rate parameter would correspond to the SCR, while the PCR should be set to the line rate, as for Guaranteed Service. The remaining service categories are inappropriate for CL. The rtVBR category adds complexity without providing useful features: there is no need for tightly constrained delays, and the double-rate traffic description is not needed. The UBR category does not provide enough capability for Controlled Load. The point of CL is to allow an allocation of resources, which is facilitated by the token bucket traffic descriptor, and is unavailable in UBR. Best Effort Any of the service categories has the capability to carry Best Effort service, but the natural service category is UBR (or, in UNI 3.x, BCOB-C or BCOB-X, with the best effort indicator flag). A CBR or rtVBR clearly could be used, and since the service is not real-time, a nrtVBR connection could also be used. In these cases the rate parameter used reflects a bandwidth allocation in support of the edge device's best effort connectivity to the far edge router. It would be normal for many flows to be aggregated on this connection; indeed, since Best Effort is the default IP behavior, the individual flows are not necessarily identified or accounted for. An ABR connection could similarly be used to support Best Effort traffic. This is the purpose for which ABR was specifically designed. It is conceivable that a separate ABR connection would be made for different IP flows, although the normal case would probably have all IP Best Effort traffic with a common exit router sharing a single ABR connection. Borden, Garrett Expires December, 1996 [Page 9] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 2.2 Cell Loss Priority Bit, Tagging and Conformance Definitions An ATM header carries the Cell Loss Priority (CLP) bit. Cells with bit CLP=1 are said to have been tagged and have lower priority. This tagging may have been done by the source or an upstream switch. Options involving the use of tagging are decided at call setup time. A Conformance Definition is a rule that determines whether a cell is conforming to the traffic descriptor of the VC. The conformance definition is given in terms of a Generic Cell Rate Algorithm (GCRA), which may be implemented using a leaky bucket algorithm, for CBR and VBR services. (UBR and ABR have network specific conformance definitions.) The network may tag cells which are non-conforming, rather than dropping them only if the VC is set up to request tagging and the network supports the tagging option. When congestion occurs, a switch must attempt to discard tagged cells in preference to the discarding of CLP=0 cells. However, the mechanism for doing this is completely implementation specific. Tagged cells are treated with a behavior which is Best Effort in the sense that they are transported when bandwidth is available, queued when buffers are available, and dropped when the resources are overcommitted. Since GS and CL services require excess traffic to be treated as Best Effort, the tagging option should always be chosen (if supported) in the VC setup as a means of ``downgrading'' nonconformant cells. However, we wish to point out that the term ``best effort'' seems to be used with two distinguishable meanings in the int-serv specs. The first interpretation is that of a service class that, in some typical scheduler implementations, would correspond to a separate queue. Placing excess traffic in best effort in this sense would be giving it lower delay priority. The other sense is more generic, meaning that the network would make a best effort to transport the traffic. A reasonable expectation is that a network with no contending traffic would transport the packet, while a very congested network would drop the packet. A packet that could be tagged with lower loss priority would not be as likely to be transported out of order with respect to the conforming portion of the flow. Such a mechanism would agree with the latter definition of best effort, but not the former. In TM/UNI 4.0 tagging does not apply to the CBR or ABR services. However, there are three subcategories of VBR service (for both rtVBR and nrtVBR) to consider. In VBR, only the conformance definition VBR.3 supports tagging and applies the GCRA with PCR to the aggregate CLP=0+1 cells, and another GCRA with SCR to the CLP=0 cells. Thus Borden, Garrett Expires December, 1996 [Page 10] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 this conformance definition should always be used. For UBR service, conformance definition UBR.2 supports the use of tagging, but a CLP=1 cell does not imply non-conformance; it is a hint of network congestion. Once an ATM connection is established, the use of the conformance definition and resulting policing action is mandatory. Since the conformance algorithm operates on cells, when mapping rates and bucket sizes from IP services to corresponding ATM parameters, a correction needs to made (at call setup time) for the ATM segmentation overhead. Unfortunately this overhead, as a ratio, depends on packet length, with the overhead largest for small packets. Thus the appropriate correction could be based on minimum packet size, expected packet size, or otherwise in a network specific manner, determined at the edge device IWF. 2.3 ATM Adaptation Layer The AAL type 5 encoding must be used, as in RFC 1483 and RFC 1755. AAL5 requires specification of the maximum SDU size in both the forward and reverse directions. Both GS and CL specify a maximum packet size as part of the TSpec and this value should be used as the maximum SDU in each direction for unicast connections, but only in one direction for point-to-multipoint connections, which are unidirectional. When more than one flow is to use the same VC, the TSpecs can be merged to yield the largest packet sizes. In no case can this exceed 65535 (or, of course, the MTU of the link). 2.4 Broadband Low Layer Information The B-LLI Information Element is transferred transparently by the ATM network between the edge devices and is used to specify the encapsulation method. Multiple B-LLI IEs may be sent as part of negotiation. The default encapsulation LLC/SNAP must be supported as in RFC 1577 and RFC 1755. Additional encapsulations are discussed in RFC 1755 and we refer to the discussion there. 2.5 Traffic Descriptor The ATM traffic descriptor always contains specification of a peak cell rate (PCR) (in each direction). For variable rate services it also contains specification of a sustainable cell rate (SCR) and Borden, Garrett Expires December, 1996 [Page 11] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 maximum burst size (MBS). The Best Effort indicators and Tagging indicators are also part of the traffic descriptors in the signalling sense. In UNI SIG 4.0 there is an additional parameter, the Frame Discard indicator in the traffic descriptor. The latter is used to indicate the request that if a cell is to be dropped, then all subsequent cells of a frame be dropped up to the End of Message (EOM) cell (AAL 5); see section 2.7. In ATM UNI SIG 4.0 there are also the notions of Alternative Traffic Descriptors and Minimal Traffic Descriptors. Alternative Traffic Descriptors enumerate other acceptable choices for traffic descriptors and do not seem to be relevant here. Minimal Traffic Descriptors are used in ``negotiation,'' a term which when interpreted colloquially will lead to confusion. Very roughly it works like this, e.g., for PCR. A minimal PCR and a requested PCR are signalled, the requested PCR being the usual item signalled, and the minimal PCR being the absolute minimum that the source edge device will accept. When sensing the existence of both minimal and requested parameters, intermediate switches along the path may reduce the requested PCR to a comfortable level. If at any point the requested PCR falls below the minimal PCR then the call is cleared. This is a very rough sketch, but we do see potential to make use of Minimal Traffic Descriptors in future versions of this draft in order to present an acceptable range for parameters and have higher liklihood of call admission. Minimal Traffic Descriptors are not explored further in this version of the draft. The Traffic Management viewpoint, which we examine next, is more concerned with the value of the PCR, SCR and MBS parameters after call setup. PCR and CDVT are used in the CBR and VBR conformance definitions as parameters for a leaky bucket. However CDVT is not signalled and is determined by the network operator as a measure of the ``clumping'' done by the network. This makes it difficult to map any leaky bucket description of a TSpec to the PCR-CDVT leaky bucket. Additional buffering will be needed at the IWF to account for the depth of the bucket. The SCR and MBS are used with the VBR services. They are used in an implementation specific manner to allocate resources. The Burst Tolerance (BT) is derived from MBS (see TM 4.0) to be used in a second SCR-BT leaky bucket. Since both parameters are available to be signalled, this leaky bucket has the potential to be used in the same way as the integrated services bucket. Note that the segmentation overhead and minimum policed unit need to be taken into account when translating the bucket parameters. Borden, Garrett Expires December, 1996 [Page 12] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 For Guaranteed Service there is a bucket rate, r and a service rate, R. The bucket rate describes the traffic, and can be used for policing, while the service rate (which cannot be smaller) is the allocated service rate. When mapping Guaranteed Service onto a rtVBR VC, the mapping is straightforward. The bucket rate maps to the SCR and the peak rate maps to PCR. The bucket depth parameter maps to MBS. The minimum policed unit may need to be taken into account when translating the leaky bucket parameters. Note that due to cell segmentation, the ATM traffic parameters will increase due to the additional headers. The minimum packet size can be used to identify the worst case situation. For GS over CBR, the bucket rate can be mapped to the PCR parameter. As noted above, the edge device may need to ensure that adequate buffering exists at the ATM network ingress to accommodate the TSpec bucket depth. If the available buffering is not sufficient, then a VC may have to be set up using the IP peak rate parameter mapping to PCR. It is probably inadvisable to try to set the PCR to a value between the bucket rate and the peak rate, since such a value would depend on assumptions about the statistical properties of the source. Controlled Load service has a single bucket rate and corresponding depth parameter. The minimum policed unit and maximum packet size play the same roles in mapping parameters as for Guaranteed Service. When using nrtVBR, the bucket rate and depth map to SCR and MBS, while the PCR parameter can be set to the line rate as a worst case value. For ABR VCs, the bucket rate would be used to set the minimum cell rate (MCR) parameter. The bucket depth parameter does not map directly to a signalled ATM parameter, but the edge device should check that the buffering at the ATM ingress is sufficient to account for the size of bursts allowed by that parameter. Finally for CBR, the bucket rate sets the PCR, and again, the available buffering in the edge device must be adequate to accommodate possible bursts. For Best Effort service, there is no traffic description. The UBR service category allows negotiation of PCR, simply to identify to the source the smallest physical bottleneck along the path. 2.6 QoS Classes and Parameters In TM/UNI 4.0 the three QoS parameters may be individually signalled. These parameters are the Cell Loss Ratio (CLR), Cell Transfer Delay (CTD), and Cell Delay Variation (CDV). In UNI 3.x the setup message includes only the QoS Class, which is essentially an index to a network specific table of values for these three parameters. A network provider may choose to associate other parameters, such as Borden, Garrett Expires December, 1996 [Page 13] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 Severely Errored Cell Block Ratio, but these are less well understood and accepted compared to the basic loss, delay and jitter parameters mentioned here. The ITU may include a standard set of parameter values for a number (probably four) of QoS classes. In that case, the network provider could define further network-specific QoS classes in addition. The problem of agreement between network providers as to the definition of QoS classes is completely unaddressed to date. We will adopt a convention expressed in UNI 3.x, that assumes that QoS class 1 is appropriate for low-delay, low-loss CBR connections, and QoS class 3 is appropriate for variable rate connections with loss and delay roughly appropriate for non- real-time data applications. Since no IP layer counterparts to these ATM QoS parameters exist in any of the IP services, they must be set by policy of the edge device. The QoS classes can be chosen relatively easily. QoS class 1 should be used with Guaranteed Service and QoS class 3 should be used with Controlled Load Service. Best Effort Service always gets QoS class 0, which is unspecified QoS by definition. There are two issues which amount to the same thing: First, the choice of individually signalled parameter values (under TM/UNI 4.0) for GS and CL is the edge device policy. The second issue is choosing parameter values for the two QoS classes, which is the ATM network policy. If the same network operator controls both, then these problems are identical; if not, an agreement to make the values identical would be extremely desirable. Note that we have mapped QoS class 1 and 3 onto Guaranteed and Controlled Load service respectively. This is regardless of what service category is used. So when running CL over a CBR pipe, it would not be inappropriate to use QoS class 3. This leaves the delay unspecified (or much looser than with QoS 1). These comments should be taken as preliminary, as these issues are far from clear, and industry consensus should be sought. 2.7 Additional Parameters -- Frame Discard Mode In TM/UNI 4.0 ATM allows the user to choose a mode where a dropped cell causes all cells up to the last remaining in the AAL5 PDU to be also dropped. This improves efficiency and the behavior of end-to- end protocols such as TCP, since the remaining cells of a damaged PDU are useless to the receiver. For IP over ATM, Frame Discard should always be used in both directions, if available, for all services. Borden, Garrett Expires December, 1996 [Page 14] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 3.0 Guaranteed Service over ATM This section describes how to create ATM VCs appropriately matched for Guaranteed Service. The key points differentiating among ATM choices are that real-time timing is required, that the data flow may have a variable rate, and that demotion of nonconforming traffic to best effort is desired. For this reason, we prefer a rtVBR service in which tagging is supported. The encodings assume a point-to-multipoint connection. For a unicast connection, the backward parameters would be equal to the forward parameters. Encoding GS as a real-time variable bit rate service AAL Type 5 Forward CPCS-SDU Size parameter M of TSpec Backward CPCS-SDU Size 0 Mode 1 (Message mode) Note 1 SSCS Type 0 (Null SSCS) Traffic Descriptor Forward PCR CLP=0+1 From TSpec peak rate Backward PCR CLP=0+1 0 Forward SCR CLP=0 From TSpec token bucket rate Backward SCR CLP=0 0 Forward MBS (CLP=0) From TSpec bucket size param Backward MBS (CLP=0) 0 BE indicator NOT included Forward Frame Discard bit 1 Note 2 Backward Frame Discard bit 1 Note 2 Tagging Forward bit 1 (Tagging requested) Note 2 Tagging Backward bit 0 (No Tagging) Note 2 Broadband Bearer Capability Bearer Class 16 (BCOB-X) Note 3 ATM Transfer Capability 9 Note 2 Traffic Type 010 (Variable Bit Rate) Timing Requirements 01 (Timing Required) Susceptible to Clipping 00 (Not susceptible) User Plane Configuration 01 (For pt-to-mpt) Broadband Low Layer Information Layer 2 protocol 12 (ISO 8802/2) Layer 3 protocol 204 (ISO/IEC TR 9577) Borden, Garrett Expires December, 1996 [Page 15] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 QoS Class QoS Class Forward 1 Note 4 QoS Class Backward 1 Note 4 QoS Parameters Transit Delay 100ms Notes 2,5 Forward CLR (CLP=0) 1.0e-6 Notes 2,5 Backward CLR (CLP=0) 1.0e-6 Notes 2,5 Forward CDV 30ms Notes 2,5 Backward CDV 30ms Notes 2,5 Note 1: Only included for UNI 3.0. Note 2: Only included in TM/UNI 4.0. Note 3: Value 1 (BCOB-A) can also be used. Note 4: Optional in TM/UNI 4.0. Note 5: Values chosen to initiate discussion. It is also possible to support GS using a CBR ``pipe.'' The advantage of this is that CBR is probably supported; the disadvantage is that data flows may not fill the pipe (utilization loss) and there is no tagging option available. Encoding GS as a constant bit rate service AAL Type 5 Forward CPCS-SDU Size parameter M of TSpec Backward CPCS-SDU Size parameter M of TSpec Mode 1 (Message mode) Note 1 SSCS Type 0 (Null SSCS) Traffic Descriptor Forward PCR 0+1 From TSpec token bucket rate Backward PCR 0+1 0 BE indicator NOT included Forward Frame Discard bit 1 Note 2 Backward Frame Discard bit 1 Note 2 Tagging Forward bit 0 (No Tagging) Note 2 Tagging Backward bit 0 (No Tagging) Note 2 Broadband Bearer Capability Bearer Class 16 (BCOB-X) Note 3 ATM Transfer Capability 7 Note 2 Traffic Type 001 (Constant Bit Rate) Timing Requirements 01 (Timing Required) Susceptible to Clipping 00 (Not susceptible) Borden, Garrett Expires December, 1996 [Page 16] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 User Plane Configuration 01 (For pt-to-mpt) Broadband Low Layer Information Layer 2 protocol 12 (ISO 8802/2) Layer 3 protocol 204 (ISO/IEC TR 9577) QoS Class QoS Class Forward 1 Note 4 QoS Class Backward 1 Note 4 QoS Parameters Transit Delay 100ms Notes 2,5 Forward CLR (CLP=0) 1.0e-6 Notes 2,5 Backward CLR (CLP=0) 1.0e-6 Notes 2,5 Forward CDV 30ms Notes 2,5 Backward CDV 30ms Notes 2,5 Note 1: Only included for UNI 3.0. Note 2: Only included in TM/UNI 4.0. Note 3: Value 1 (BCOB-A) can also be used. Note 4: Optional in TM/UNI 4.0. Note 5: Values chosen to initiate discussion. 4.0 Controlled Load Service over ATM This section describes how to create ATM VCs appropriately matched for Controlled Load. CL traffic is delay tolerant and variable rate. We see nrtVBR and ABR (for TM/UNI 4.0 only) as possible choices in supporting CL. Controlled Load Support using ABR AAL Type 5 Forward CPCS-SDU Size parameter M of TSpec Backward CPCS-SDU Size parameter M of TSpec SSCS Type 0 (Null SSCS) Traffic Descriptor Forward PCR CLP=0+1 From line rate Backward PCR CLP=0+1 From line rate Forward MCR CLP 0+1 From TSpec token bucket rate Backward MCR CLP 0+1 From TSpec token bucket rate BE indicator NOT included Borden, Garrett Expires December, 1996 [Page 17] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 Forward Frame Discard bit 1 Backward Frame Discard bit 1 Tagging Forward bit 0 (Tagging not requested) Tagging Backward bit 0 (Tagging not requested) Broadband Bearer Capability Bearer Class 16 (BCOB-X) Note 3 ATM Transfer Capability 12 Traffic Type 010 (Variable Bit Rate) Timing Requirements 10 (Timing Not Required) Susceptible to Clipping 00 (Not susceptible) User Plane Configuration 00 (For pt-to-pt) Broadband Low Layer Information Layer 2 protocol 12 (ISO 8802/2) Layer 3 protocol 204 (ISO/IEC TR 9577) QoS Class QoS Class Forward 3 Note 4 QoS Class Backward 3 Note 4 ABR Setup Parameters For Further Study ABR Additional Parameters For Further Study Note 3: Value 3 (BCOB-C) can also be used. Note 4: Optional in TM/UNI 4.0. Controlled Load support using nrtVBR AAL Type 5 Forward CPCS-SDU Size parameter M of TSpec Backward CPCS-SDU Size 0 Mode 1 (Message mode) Note 1 SSCS Type 0 (Null SSCS) Traffic Descriptor Forward PCR CLP=0+1 From line rate Backward PCR CLP=0+1 0 Forward SCR CLP=0 From TSpec token bucket rate Backward SCR CLP=0 0 Forward MBS (CLP=0) From TSpec bucket size param Backward MBS (CLP=0) 0 BE indicator NOT included Borden, Garrett Expires December, 1996 [Page 18] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 Forward Frame Discard bit 1 Note 2 Backward Frame Discard bit 1 Note 2 Tagging Forward bit 1 (Tagging requested) Note 2 Tagging Backward bit 0 (No Tagging) Note 2 Broadband Bearer Capability Bearer Class 16 (BCOB-X) Note 3 ATM Transfer Capability Absent Note 2 Traffic Type 010 (Variable Bit Rate) Timing Requirements 10 (Timing Not Required) Susceptible to Clipping 00 (Not susceptible) User Plane Configuration 01 (For pt-to-mpt) Broadband Low Layer Information Layer 2 protocol 12 (ISO 8802/2) Layer 3 protocol 204 (ISO/IEC TR 9577) QoS Class QoS Class Forward 3 Note 4 QoS Class Backward 3 Note 4 QoS Parameters Forward CLR (CLP=0) 1.0e-6 Notes 2,5 Backward CLR (CLP=0) 1.0e-6 Notes 2,5 Note 1: Only included for UNI 3.0. Note 2: Only included in TM/UNI 4.0. Note 3: Value 3 (BCOB-C) can also be used. Note 4: Optional in TM/UNI 4.0. Note 5: Values chosen to initiate discussion. 5.0 Best Effort Service over ATM This section describes how to create ATM VCs appropriately matched for Best Effort. The BE service does not need a reservation of resources. Best Effort Service using UBR AAL Type 5 Forward CPCS-SDU Size MTU of link Backward CPCS-SDU Size MTU of link Mode 1 (Message mode) Note 1 Borden, Garrett Expires December, 1996 [Page 19] INTERNET DRAFT Interoperation of CL and GS with ATM June, 1996 SSCS Type 0 (Null SSCS) Traffic Descriptor Forward PCR CLP=0+1 From line rate Backward PCR CLP=0+1 0 BE indicator included Forward Frame Discard bit 1 Note 2 Backward Frame Discard bit 1 Note 2 Tagging Forward bit 1 (Tagging requested) Note 2 Tagging Backward bit 0 (no tagging) Note 2 Broadband Bearer Capability Bearer Class 16 (BCOB-X) Traffic Type 010 (Variable Bit Rate) Timing Requirements 10 (Timing not required) Susceptible to Clipping 00 (Not susceptible) User Plane Configuration 01 (For pt-to-mpt) Broadband Low Layer Information Layer 2 protocol 12 (ISO 8802/2) Layer 3 protocol 204 (ISO/IEC TR 9577) QoS Class QoS Class Forward 0 QoS Class Backward 0 Note 1: Only included for UNI 3.0. Note 2: Only included in TM/UNI 4.0. Borden, Garrett Expires December, 1996 [Page 20]