Internet Engineering Task Force Integrated Services WG INTERNET-DRAFT Scott Shenker draft-ietf-intserv-charac-00.txt XEROX PARC 14 November 1995 Expires: ?/?/96 Specification of General Characterization Parameters 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 document is a product of the Integrated Services working group of the Internet Engineering Task Force. Comments are solicited and should be addressed to the working group's mailing list at int- serv@isi.edu and/or the author(s). Abstract This memo defines general characterization parameters for network elements supporting enhanced qualities of service. General characterization parameters are those that are not specific to a particular quality of service. Shenker Expires ?/?/95 [Page 1] INTERNET-DRAFT draft-ietf-intserv-charac-01.txt ?, 1995 Introduction This memo defines general, or service-independent, characterization parameters for network elements. General characterization parameters are those that are not specific to a particular quality of service. A discussion of how these parameters fit into an integrated services architecture can be found in [1]. Please refer to that document for definitions and additional information about the specification of qualities of service within the IP protocol family. The specifications of the various qualities of service ([2-4]) describe the associated characterization parameters that must be exported. However, there are some quantities of interest that are not specific to a particular quality of service. These "general" characterizations are described in this document. Characterization parameters associated with a particular service are attached to a service_name. The service-name associated with general characterizations is 0. We describe these general characterization parameters below. Number of IS Hops IS stands for "integrated services aware". An integrated services aware network element is one that conforms to the various requirements described in this document and the documents [1-4] (it need not offer those services, but if it does it supports and characterizes the services in conformance with the relevant specification). The composition rule is to increment the counter by one. This quantity, when composed end-to-end, informs the endpoint of the number of Integrated-Services aware network elements traversed along the path from sender to receiver. The parameter_name for this field is 1. The characterization parameter may be represented as a single 16-bit unsigned integer in network byte order. Number of IP Hops The local parameter is the number of IP hops between the last (i.e., upstream) IS network element and this one. Observe that since the network element may not be aware of its neighbor on the the upstream path, *the local parameter must be provided to the network element by the setup protocol* (possibly by tracking the TTL value). Shenker Expires ?/?/95 [Page 2] INTERNET-DRAFT draft-ietf-intserv-charac-01.txt ?, 1995 The composition rule is additive. This quantity, when composed end- to-end, informs the endpoint of the number of IP network elements ("hops") traversed along the path from sender to receiver. The parameter_name for local parameter is 2. The parameter_name for the composed quantity is 3. These characterization parameters may be represented as 16-bit unsigned integers in network byte order. Comparison of the end-to-end composition of the two previous characterization values will yield the number of non-IS network elements along the path. Bandwidth The local parameter is the bandwidth of the network element. For links, this value would be the bandwidth of the link. The composition rule is to take the minimum of the network element's value and the previously composed value. This quantity, when composed end-to-end, informs the endpoint of the minimal bandwidth link along the path from sender to receiver. The parameter_name for the bandwidth of the network element's link is 4. The parameter_name for the composed minimal bandwidth along the path is 5. These values are measured in bytes per second, and can range from 1 byte per second to as large as 40 terabytes per second (or about what is believed to be the maximum theoretical bandwidth of a single strand of fiber). Clearly, particularly for large bandwidths, only the first few digits are significant and so the use of floating point representations, accurate to at least 0.1% is encouraged. These characterizations of bandwidth can be represented by floating point numbers in single-precision IEEE floating point format. NOTE: If the number of IS hops is less than the number of IP hops, end systems should treat this value as a hint rather than a reliable value. Latency The local parameter is the latency of the link associated with the network element, where the latency is defined to be the minimal possible packet delay along the path taken by the flow. This delay may result from "speed-of-light" propagation delay, or from packet processing limitations, or both. The composition rule is additive. This quantity, when composed end-to-end, informs the endpoint of the minimal packet delay along the path from sender to receiver. The parameter_name for the latency of the network element's link is 6. The parameter_name for the cumulative latency along the path is 7. Shenker Expires ?/?/95 [Page 3] INTERNET-DRAFT draft-ietf-intserv-charac-01.txt ?, 1995 The delays are measured in units of one microsecond. An individual element can advertise a delay value between 1 and 2**28 (somewhat over two minutes) and the total delay added across all elements can range as high as (2**32)-1. Should the sum of the different elements delay exceed (2**32)-1, the end-to-end advertised delay should be (2**32)-1. Note that while the granularity of measurement is microseconds, a conforming element is free to measure delays more loosely. The minimum requirement is that the element estimate its delay accurately to the nearest 100 microsecond granularity. Elements that can measure more accurately are, of course, encouraged to do so. NOTE: If the number of IS hops is less than the number of IP hops, end systems should treat this value as a hint rather than a promised value. NOTE: Measuring in milliseconds is not acceptable, because if the minimum delay value is a millisecond, a path with several hops will lead to a composed delay of at least several milliseconds, which is likely to be misleading. The characterization parameters may be represented as 32-bit unsigned integers in network byte order. NOTE: There are some subnet technologies where determining this minimal delay is difficult. For instance, the speed-of-light delays on an ethernet bridged via satellite with another ethernet vary by several orders of magnitude. The exported values should be conservative estimates of the delays. Any additional delays (that is, delays larger than this minimal amount) must be considered part of the variable delays which are described by characterizations specific to the individual services. For example, in predictive service the maximal delay experienced going from one network element to the next should be the delay bound plus the latency. MTU The local characterization parameter is the MTU, where the MTU of a network element is defined to be the maximum transmission unit the network element can accommodate without fragmentation. The composition rule is to take the minimum of the network element's MTU and the previously composed value. This quantity, when composed end- to-end, informs the endpoint of the maximum transmission unit that can traverse the path from sender to receiver without fragmentation. Shenker Expires ?/?/95 [Page 4] INTERNET-DRAFT draft-ietf-intserv-charac-01.txt ?, 1995 The parameter_name for the MTU of the network element's link is 8. The parameter_name for the composed MTU along the path is 9. NOTE: If the number of IS hops is less than the number of IP hops, end systems should treat this value as a hint rather than a promised value. Service Availability The INT SERV working group is still developing proposals for handling heterogeneity. When that work is complete, a set of requirement parameters will be defined. Security Considerations Security considerations are not discussed in this memo. References [1] S. Shenker and J. Wroclawski. "Network Element Service Specification Template", Internet Draft, June 1995, [2] S. Shenker, C. Partridge, and J. Wroclawski. "Specification of Controlled Delay Quality of Service", Internet Draft, ?? 1995, [3] S. Shenker and C. Partridge. Specification of Guaranteed Quality of Service", Internet Draft, ?? 1995, [4] S. Shenker, C. Partridge, B. Davie, and L. Breslau. "Specification of Predictive Quality of Service", Internet Draft, ?? 1995, Author's Address: Scott Shenker Xerox PARC 3333 Coyote Hill Road Palo Alto, CA 94304-1314 shenker@parc.xerox.com Shenker Expires ?/?/95 [Page 5] INTERNET-DRAFT draft-ietf-intserv-charac-01.txt ?, 1995 415-812-4840 415-812-4471 (FAX) Shenker Expires ?/?/95 [Page 6]