HTTP/1.1 200 OK Date: Tue, 09 Apr 2002 07:37:41 GMT Server: Apache/1.3.20 (Unix) Last-Modified: Wed, 26 Mar 1997 18:41:00 GMT ETag: "305081-55e6-33396dbc" Accept-Ranges: bytes Content-Length: 21990 Connection: close Content-Type: text/plain Real Time Flow Measurement Working Group S.W. Handelman Internet-draft IBM Hawthorne, NY USA N. Brownlee U of Auckland, NZ Greg Ruth GTE Laboratories, Inc Waltham, MA USA March 25, 1997 expires September 25, 1997 Real Time Flow Measurement Working Group - New Attributes for Traffic Flow Measurement draft-ietf-rtfm-new-traffic-flow-01.txt 1. 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). This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Handelman, Brownlee, Ruth [Page 1] Internet-Draft March 25, 1997 2.1 Introduction The Real-time Traffic Flow Measurement (RTFM) working group has developed a system for measuring and reporting information about traffic flows in the Internet. This document explores the definition of extensions to the flow measurements as currently defined in [1] and [5]. The new attributes described in this document will be useful for monitoring network performance and expand the scope of RTFM beyond traffic measurement. Performance attributes typically deal with throughput, packet loss, and delays. We will explore the methods in which RTFM can extract values from flows which measure these attributes. We will also look at capturing information on jitter and congestion control. The RTFM Working Group has defined the concept of a standardized meter which records flows from a traffic stream according to Rule Sets which are active in the meter[1]. Implementations of this meter have been done by Nevil Brownlee in the University of Auckland, NZ, and Stephen Stibler and Sig Handelman at IBM in Hawthorne, NY, USA. The RTFM WG has also discussed the Meter Reader Program whose job is to fetch the completed group of flows active in the Meter. 2.1.1 RTFM's Definition of Flows The RTFM Meter architecture views a flow as a set of packets between two end-points (as defined by their source and destination attribute values), and as BI-DIRECTIONAL (i.e. the meter effectively monitors two sub-flows, one in each direction). Reasons why RTFM flows are bi-directional: - We are interested in understanding the behavior of sessions between end-points. - We want to perform as much data reduction as possible, so as to reduce the amount of data to be retrieved from a remote meter. - The endpoint attribute values (the "Address" and "Type" ones) are the same for both directions; storing them in bi-directional flows reduces the meter's memory demands. 2.2 RTFM's Current Definition of Flows and their Attributes Flows, as described in the "Architecture" I-D have the following properties: a. They occur between two endpoints, specified as sets of attribute Handelman, Brownlee, Ruth [Page 2] Internet-Draft March 25, 1997 values in the meter's current rule set. A flow is completely identified by its set of endpoint attribute values. b. Each flow may also have values for "computed" attributes (Class and Kind). These are directly derived from the endpoint attribute values. c. A new flow comes into being when the a packet is seen which is not classified by the Rule Set into an existing flow. The meter records the time when this new flow is created. d. Attribute values in (a), (b) and (c) are set when the meter sees the first packet for the flow, and are never changed. e. Each flow has a "LastTime" attribute, which indicates the time the meter last saw a packet for the flow. f. Each flow has two packet and byte counters, one for each flow direction (Forward and Backward). These are updated as packets are observed by the meter. g. ALL the attributes have (more or less) the same meaning for a variety of protocols; IPX, AppleTalk, DECnet and CLNS as well as TCP/IP. Current flow attributes as described above, fit very well into the SNMP data model. They are either static, or are continuously updated counters. They are NEVER reset. In this document they will be referred to as "old-style" attributes. It is easy to add further "old-style" attributes, since they don't require any new features in the architecture. For example: - Count of the number of "lost" packets (determined by watching sequence number fields for packets in each direction; only available for protocols which have sequence numbers). - In the future, RTFM could coordinate directly with the Flow number from the IPv6 header. At the June, 1996 meeting of the RTFM WG, in Montreal, Canada, a proposal was put forth to extend the work of the group to produce an Internet Draft "New Attributes for Traffic Flow Measurement". That proposal has brought forth this document. The goal of this work is to produce a simple set of abstractions, which can be easily implemented and at the same time enhance the value of RTFM meters. This document also defines a method for organizing the flow abstractions to preserve the existing RTFM flow table. Handelman, Brownlee, Ruth [Page 3] Internet-Draft March 25, 1997 At the December, 1996 meeting of the RTFM WG and at a joint meeting of the RTFM and IPPM working groups the concepts of this document were discussed. The suggestions given at these discussions are included in this document. An addition to the main architecture document of RTFM is the use of High Watermarks, to set up Alerts when the value of a flow record variable exceeds a watermark, e.g. the total byte count exceeds a preset amount, such as no user should send more than 2,000,000 packets. This is a generalization of the concept defined in RTFM to send Traps when a Meter finds an exception condition in its own processing (The Architecture Document refers to running out of buffer space). 2.3 RTFM Flows, Integrated Services, IPPM and Research in Flows The concept of flows has been studied in various different contexts. For the purpose of extending RTFM, a starting point is the work of the Integrated Services WG. We will measure quantities that are often set by Integrated Services and configuration programs. We will look at the work of the Benchmarking - Internet Provider Performance Metrics Working Group, and also look at the work of Claffy, Braun and Polyzos. We will demonstrate how RTFM can compute throughput, packet loss, and delays from flows. An example of the use of capacity and performance information is found in "The Use of RSVP with IETF Integrated Services". [2]. RSVP's use of Integrated Services revolves around Token Bucket Rate, Token Bucket Size, Peak Data Rate, Minimum Policed Unit, Maximum Packet Size, and the Slack term. These are set by TSpec, ADspec and FLowspec (Integrated Services Keywords), and are used in configuration and operation of Integrated Services. RTFM could monitor explicitly Peak Data Rate, Minimum Policed Unit, Maximum Packet Size, and the Slack term. RTFM could infer details of the Token Bucket. We will develop measures to work with these service metrics. RTFM will work with several traffic measurements identified by IPPM [3]. There are three broad areas in which RTFM is useful for IPPM. 1) RTFM could act as a passive device that can gather traffic and performance statistics at appropriate places in TCP/IP networks (servers or client locations). 2) RTFM could give detailed analyses of IPPM test flows that pass through the Network segment that RTFM is monitoring. Handelman, Brownlee, Ruth [Page 4] Internet-Draft March 25, 1997 3) RTFM could be used to identify most used paths in a network mesh, such that detailed IPPM work could be applied to the most used paths. 3. Flow Abstractions Performance attributes include throughput, packet loss, delays, jitter, and congestion analysis. RTFM will calculate these attributes in the form of extensions to the RTFM flow attributes according to three general classes: o 'packet traces' - collections of individual packets in a flow or a segment of a flow o 'aggregates' - statistics derived from the flow taken as a whole (e.g. mean rate, max packet size). o 'series'- sequences of attributes that depend on more than one packet (e.g. inter-arrival times) The following sections suggest implementations for each of these classes of extensions. As an introduction to flow abstractions one fact must be emphasized. Several of the measurements enumerated below can be implemented by a Meter Reader that is tied to the meter with instantaneous response, and very high bandwidth. If the Meter Reader and Meter can be arranged in such a way, RTFM could collect Packet Traces with time stamps, and provide them to the Meter Reader for processing by the Meter Reader. A more useful alternative is to have the meter calculate some flow statistics locally. This allows a looser coupling between the meter and Meter Reader. RTFM will create an 'extended attribute' depending upon settings in the Rules table of RTFM. By default, RTFM will not create any extensions without explicit instructions in the Rule table. RTFM's traditional flows can be analyzed at two levels. The first is to analyze the Network traffic in terms of time, e.g. traffic load of a particular flow, to be called Network Flows. These flows can be looked at as an extension of the "old-style" flow attributes. The second, is to derive a value from the flow, e.g. analyzing packet sequence numbers and ACKS and estimating delay. This second type will be called Derived Attributes. 3.1. Packet Traces Handelman, Brownlee, Ruth [Page 5] Internet-Draft March 25, 1997 The simplest way of doing this in the meter would be to have a new attribute called, say, "PacketTrace." This would be a table, with a column for each property of interest. For example, one could have - Arrival time (TimeTicks from SysUptime, or microseconds from FirstTime for the flow). - Direction (Forward or Backward) - Sequence number (for protocols with sequence numbers) - Flags (for TCP at least). To add a row to the table, we only have to have a rule which PushPkts the PacketTrace attribute. To use this, one would write a rule set which selected out a small number of flows of interest, and PushPkted PacketTrace for each of them. A MaxTraceRows default value of 2000 would be enough to allow a Meter Reader to read 1-second ping traces every 10 minutes or so. More realistically, a MaxTraceRows of 500 would be enough for one- minute pings, read once each hour. 3.2. Aggregate Attributes Performance aspects of flows are interesting in the case of a flow between a server and client. RTFM could find the same data in TCP/IP and UDP flows, and can find additional data in TCP flows. The performance data found by this method define the flow capacity used by the individual flow, as experienced in the locale of the RTFM meter. For both TCP/IP and UDP, RTFM's "old-style" flow attributes count the bytes/packets for packets which match the rule set for an individual flow. In addition to these totals, RTFM could calculate Packet size and Bit rate statistics. Bit rate statistics point to the throughput of performance metrics. Packet size - RTFM's packet flows can be examined to determine the maximum packet size found in a flow. This will give the Network Operator an indication of the MTU being used in a flow. It will also give an indication of the sensitivity to loss of a flow, for losing large packets causes more data to be repeated. Bit rate - The data could also be recorded as the maximum and minimum data rate of the flow, found over specific time periods Handelman, Brownlee, Ruth [Page 6] Internet-Draft March 25, 1997 during the lifetime of a flow. Bit rate could be used to define the he throughput of a flow, and if the RTFM flow is defined to be the sum of all traffic in a network, one can find the throughput of the network. Note that aggregate attributes are a simple extension of the their values are never reset. For example, an array of counters could hold a 'total bits observed' distribution. The counters continue to increase, a meter reader will collect their values at regular intervals, and an analysis application will compute and display distributions of the data rate for each interval. In this situation, the interval will be specified by the manager which controls the meter and meter reader. 3.3 Series Attributes The notion of series attributes, is to keep simple statistics that involve more than one packet. Methods to derive simple percentiles, means, and other statistics can be developed for each flow. The notation to construct such an attribute would be a command in the rule set, instructing the meter to compute the attribute. This is similar to the definition above of creating an aggregate attribute. Whereas aggregate attributes (see above) only require the meter to increment counters, series attributes require the meter to compute attribute values. For example, if we want to produce a distribution of '10-second' forward data rates, the meter might compute this for each flow of interest as follows: - maintain an array of counters to hold the flow's 10-second data rate distribution. - every 10 seconds, compute the 10-second octet count, and save a copy of the flow's forward octet counter. To achieve this, the meter will have to keep a list of aggregate flows and the intervals at which they require processing. It will require careful programming to achieve this, but provided the meter is not asked to do this for very large numbers of flows, it should not be too difficult! TCP and UDP Inter-arrival statistics - TCP and UDP. RTFM knows the time that it encounters each individual packet. Statistics can be kept to record the inter-arrival times of the packets, which would give an indication of the jitter found in the Flow. TCP Only - Packet loss - RTFM can calculate packet loss performance metrics. This is an area for further study. TCP packets have byte sequence numbers and SYNS, FINS, and ACK's associated with them. RTFM Handelman, Brownlee, Ruth [Page 7] Internet-Draft March 25, 1997 could track the sequence numbers in the flows, and calculate the packet loss occurring in a flow, and thus we can develop a metric of lost packets and useful traffic. Delay analysis - TCP flows could be examined for the timing between Transmissions and ACKS and thus we can get some measure of delay of performance metrics . This assumes the forward and reverse packets are both visible to the meter. In the case of asymmetric flows, RTFM can be run on multiple paths, and with precise timing create packet traces, which can be compared at later times. Subflow analysis - TCP flows, e.g. a Web server's httpd flows actually contain many individual sub flows. Given, a well known Web Server WW, and a client CC, RTFM would normally pick up an aggregation of all the flows of text, graphics, Java programs, etc. that are sent between WW and CC. By analyzing the Sequence numbers, RTFM could estimate when each subflow occurs, and thus maintain statistics about the subflows on a network. Congestion Analysis - In a TCP/IP flow we have information on the negotiation of Window sizes which are used by TCP/IP to control congestion. Well behaved flows honor these requests and in the vast majority of cases the sender will slow down and thus decrease its rate of injecting packets into the congested network. We will look for cases where flows do not honor these congestion control and are not slowing down. We will also look for flows which have the "precedence" fields turned on and thus are aggressively competing for network resources. 3.4 Action on Exceptions The user of RTFM will have the ability to define Network and Derived flows, as having High Watermarks. The existence of abnormal service conditions, such as non-ending flow, a flow that exceeds a given limit in traffic (e.g. a flow that is exhausting the capacity of the line that carries it) causes an ALERT to be sent to the Meter Reader for forwarding to the Manager. Operations Support may define service situations in many different environments. This is an area for further discussion on Alert and Trap handling. 4. Packet Flow Table The architecture of RTFM has defined the structure of flows, and this draft does not change that structure. The flow table could have ancillary tables called "Packet Flow Tables", which would contain rows of values and or actions as defined under packet traces, aggregate attributes and series attributes. Each Packet Flow table would be marked with the number of its corresponding flow in the RTFM Handelman, Brownlee, Ruth [Page 8] Internet-Draft March 25, 1997 flow table. In order to identify the data in a Packet Flow Table, the value of the Rules Table Extension will be pushed into a string at the head of each row. For example, if a Packet Flow table entry has Bit Rates for a particular flow, the "BitRate" string would be found at the head of the row. A method of bundling the Packet Flow table and the packet data will be developed such that an SNMP manager can retrieve whole flow table entries, and whole Packet Flow Tables, with SNMP v2 Getbulk instructions. This will be accomplished by creating a flow attribute called FlowDataPackage. This will be an encoded sequence of all the objects such that the Getbulk could operate on the whole structure. 4.1 Note on Interchange between Meter and Meter Reader The above information on Getbulk could be superseded in the near future by the work of the RMONMIB Bulk Data Transfer. 5. Extensions to the Rules Table The Rules Table of "old-style" attributes will be extended for the new flow types. A list of actions, and Keywords, such as "BitRate"- for Bit Rate, "MaxPack", for Max Packet size will be developed and used to inform RTFM to collect a set of extended values for a particular flow (or set of flows). 6. Acknowledgments We thank Stephen Stibler of IBM for his comments on this draft. 7. Security Considerations Security considerations are not discussed in this memo. 8. Author's Address: Sig Handelman IBM Research Division Hawthorne, NY Phone: 1-914-784-7626 E-mail: handel@watson.ibm.com Nevil Brownlee The University of Auckland New Zealand Phone: +64 9 373 7599 x8941 E-mail: n.brownlee@auckland.ac.nz Handelman, Brownlee, Ruth [Page 9] Internet-Draft March 25, 1997 Greg Ruth GTE Laboratories Waltham, MA Phone: 1 617 466 2448 E-mail: grr1@gte,com 9. References: [1] Brownlee, N, Mills, C., Ruth, G.: "Traffic Flow Measurement: Architecture", RFC 2063, 1997 [2] Wroclawski, J., : "The Use of RSVP with IETF Integrated Services Internet" Draft, October, 1996 [3] Almes, G. et al: "Framework for IP Provider Metrics" Internet Draft. July 1996 [4] Claffy, K., Braun, H-W, Polyzos, G. "A Parameterizable Methodology for Internet Traffic Flow Profiling," IEEE Journal on Selected Areas in Communications, Vol. 13, No. 8, October 1995. [5] Mills, C., Ruth, G.: "Internet Accounting Background," RFC 1272, 1992 Handelman, Brownlee, Ruth [Page 10]