[tcmtf] New version (v9) of the TCM-TF Charter draft
"Jose Saldana" <jsaldana@unizar.es> Wed, 27 November 2013 14:41 UTC
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From: Jose Saldana <jsaldana@unizar.es>
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Date: Wed, 27 Nov 2013 15:41:39 +0100
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Cc: 'Martin Stiemerling' <mls.ietf@googlemail.com>, 'Spencer Dawkins' <spencerdawkins.ietf@gmail.com>
Subject: [tcmtf] New version (v9) of the TCM-TF Charter draft
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TCM-TF charter draft v9 Description of Working Group 1. RFC4170 (TCRTP) defines a method for grouping packets when a number of RTP VoIP flows share a common path, considering three different layers: header compression by means of ECRTP; multiplexing by means of PPPMux; tunneling by means of L2TPv3. VoIP using RTP is a clear example of a real-time service using small packets with high overhead, where efficiency can be substantially improved in certain scenarios. As said in RFC4170, "TCRTP solves the VoIP bandwidth discrepancy, especially for large, voice-trunking applications." 2. In addition to VoIP, in the last years we are witnessing the raise of new real-time services that use the Internet for the delivery of interactive multimedia applications e.g. videoconferencing, telemedicine, video vigilance, online gaming, etc. Due to the need of interactivity, many of these services use small packets (some tens of bytes), since they have to send frequent updates between the extremes of the communication. In addition, some other services also send small packets, but they are not delay-sensitive (e.g., instant messaging, m2m packets sending collected data in sensor networks using wireless links). For both the delay-sensitive and delay-insensitive applications, their small data payloads incur significant overhead, and it becomes even higher when IPv6 is used, since the basic IPv6 header is twice the size of the IPv4 one. 3. In the moments or places where network capacity gets scarce, allocating more bandwidth is a possible solution, but it implies a recurring cost. However, the inclusion of a pair of boxes able to optimize the traffic (reducing bandwidth and packets per second) when/where required is a one-time investment. Thus, in scenarios including a bottleneck with a single Layer-3 hop, header compression algorithms (e.g. ROHC) can be used for reducing the overhead of each flow, at the cost of additional processing. However, if header compression is to be deployed in a network path including several Layer-3 hops, tunneling can be used in order to allow the header-compressed packets to travel end-to-end, thus avoiding the need to compress and decompress at each intermediate node. In these cases, compressed packets belonging to different flows can be multiplexed together, in order to share the tunnel overhead. In this case, a small multiplexing delay will be necessary as a counterpart, in order to join a number of packets to be sent together. This delay has to be maintained under a threshold in order to grant the delay requirements. 4. However, in the last years, emerging real-time services which use bare UDP instead of UDP/RTP have become popular. In addition, a significant effort has been devoted to the deployment of new header compression methods with improved robustness (ROHC). So there is a need of widening the scope of RFC4170 in order to consider these new header compression methods, and also UDP in addition to UDP/RTP. The same structure of three layers will be considered: * Header compression: Taking into account that real-time applications use different headers (RTP/UDP, UDP), different protocols can be used: no compression, ECRTP, IPHC and ROHC. * Multiplexing: If a number of flows share a path between an origin and a destination, a TCM-optimizer (called TCM-ingress optimizer) can build a bigger multiplexed packet in which a number of payloads share a common header. Another TCM-optimizer (called TCM-egress optimizer) is then necessary at the end of the common path, so as to rebuild the packets as they were originally sent. PPPMux will be the main option. Other ones are not discarded. * Tunneling will be used to send the multiplexed packets end-to-end. The options in this layer are L2TP, GRE and MPLS. 5. Furthermore, new scenarios where bandwidth savings are desirable, in addition to those considered in RFC4170, have been identified. This is a classification: * Multidomain, in the sense the TCMT-TF tunnel goes all the way from one network edge to another, and therefore can cross several domains. Note that this is not from border to border (which could be covered with specialized links) but from edge to edge (e.g. managing all traffic from individual users arriving at a Game Provider, regardless users' location). * Single Domain, so TCM-TF is only activated inside an ISP, from the edge to border inside the network operator. The geographical scope and network depth of TCM-TF activation could be on demand, according to traffic conditions. * "Private Solutions". TCM-TF is used to connect private networks geographically apart (e.g. corporation headquarters and subsidiaries), without the ISP being aware (or having to manage) those flows. As an example, an end-to-end tunnel between appliances located in two different offices of the same company. In some cases the tunnel is already included for security reasons. Another example can be a shared wireless Internet in a place with low Internet penetration. This can happen in a community network (typically deployed in rural areas or in developing countries), in which a number of people in the same geographical place share their connections in a cooperative way, and a number of wireless hops are required in order to reach a router connected to the Internet; * Mixed Scenarios, any combination of the previous scenarios. 6. As a result, the next objectives can be achieved: * Significant bandwidth reductions (as an example, bandwidth savings of 55% can be obtained for VoIP if IPv4 is used, and 65% using IPv6. For certain online games, 33% of the bandwidth can be saved for IPv4, and 55% when using IPv6). * A reduction of the amount of packets per second managed by the network. A reduction factor of 10 or 20 can easily be achieved. This can be translated into smaller processing delays and energy savings in intermediate routers. 7. So the main objective of this group is to specify the protocol stack for Tunneling, Compressing and Multiplexing Traffic Flows (TCM-TF). Since standard protocols are being used at each layer, the signaling methods of those protocols will be used. Thus, interactions with the Working Groups and Areas in which these protocols are developed can be expected. However, the development of new compressing, multiplexing or tunneling protocols is not an objective of this Working Group. In addition, since the current RFC 4170 would be considered as one of the options, this RFC could be obsoleted. 8. A first document (TCM-TF - reference model) will define the different options which can be used at each layer. It will include a detailed specification of the scenarios of interest. Specific problems caused by the interaction between layers will have to be issued, and suitable extensions may have to be added to the involved protocols. The impact on other protocols will also be studied. 9. If a pair of ingress/egress optimizers want to establish a TCM-TF session, they have first to use a mechanism to negotiate which concrete option would they use in each layer: header compression, multiplexing and tunneling. This will depend on the protocols that each extreme implements at each level, and in the scenario. So another document (TCM-TF - negotiation protocol) will include: * a mechanism to setup/release a TCM-TF session between an ingress and an egress-optimizer, also including: * a negotiation mechanism to decide the options to use at each layer (header compression, multiplexing and tunneling) between an ingress and an egress-optimizer. 10. As a counterpart of the bandwidth saving, TCM-TF may add some delay and jitter. This is not a problem for the services which are not sensitive to delay. However, regarding delay-sensitive services, the Working Group will also develop a document (TCM-TF - recommendations) with useful recommendations in order to decide which packet flows can or can not be multiplexed and how. The document will present a list of available traffic classification methods which can be used for identification of the service or application to which a particular flow belongs, as well as recommendations of the maximum delay and jitter to be added depending of the identified service or application. The eventual impact of multiplexing on protocol dynamics (e.g. the loss of a multiplexed packet, MTU-related issues) will also have to be addressed. 11. The working group may identify additional deliverables that are necessary/useful, e.g., a mechanism for a TCM-ingress optimizer to discover an egress optimizer, and vice versa. The working group would re-charter to add them before working on them. 12. Interactions with other Working Groups can be expected, since TCM-TF uses already defined protocols for compression, multiplexing and tunneling (ROHC, PPPMux, MPLS, GRE, L2TP). ----------------------------------- Goals and Milestones Specification of TCM-TF reference model and the scenarios of interest. Specification of TCM-TF negotiation protocol. Specification of TCM-TF recommendations of using existing traffic classification methods, maximum delay and jitter to add, depending on the service. --------------------------------- Current version of Document (TCM-TF - reference model): https://datatracker.ietf.org/doc/draft-saldana-tsvwg-tcmtf/ Current version of Document (TCM-TF - recommendations): http://datatracker.ietf.org/doc/draft-suznjevic-tsvwg-mtd-tcmtf/
- [tcmtf] New version (v9) of the TCM-TF Charter dr… Jose Saldana