1、 TIA STANDARD QoS Signaling for IP QoS Support TIA-1039 May 2006 TELECOMMUNICATIONS INDUSTRY ASSOCIATION Representing the telecommunications industry in association with the Electronic Industries Alliance Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for
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24、 LIMITATIONS. Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2 CONTENTS 1 Overview . 4 1.1 Scope . 4 1.2 Objectives 4 1.3 Document Organization. 5 1.4 Abbreviations. 5 1.5 Defi
25、nitions 6 1.6.1 Normative References 7 1.6.2 Informative References. 7 2 System Architecture.8 2.1 Satellite and Radio Links. 8 2.2 Network Architecture Satellite Networks 10 2.3 QoS Service Goals 12 2.4 QoS Signaling Model for Available Rate 14 2.5 QoS Signaling Model for Maximum Rate. 15 2.6 QoS S
26、ignaling Model for Guaranteed Rate . 15 3 Limitations in current Qos Techniques 16 3.1 Introduction . 16 3.2 Diffserv Limitations. 16 3.3 IntServ Limitations 16 3.4 TCP Limitations 17 3.5 QoS Feature Summary. 17 3.5.1 Maximum Rate 18 3.5.2 AR Rate Feedback . 18 3.5.3 Preemption Priority. 19 3.5.4 Ch
27、arging Direction . 19 3.6 Router Operation . 19 4 Procedures for Signaling QoS . 20 4.1 Authentication . 20 4.2 Standard IP Case20 4.3 QoS Signaling Operation. 21 4.3.1 QoS Structure 21 4.3.2 Request Procedure . 22 4.3.3 Response Procedure (at Destination). 22 4.3.4 Response Receipt (Back at Source)
28、. 23 4.3.5 Renegotiate Every 128 Packets . 23 4.3.6 Sender Rules 23 4.3.7 Router Rate Negotiation 24 4.3.8 DiffServ Marking 24 4.3.9 Router Discovery of Missed Start Packet. 24 4.3.10 Mobility in IPv4. 25 Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for
29、 ResaleNo reproduction or networking permitted without license from IHS-,-,-3 4.3.11 Non-Compliant Routers any packet loss at high rates over long distances creates a major slow down of the flow. Even at normal cross-country distances, maximum TCP throughput is limited to megabits/second rather than
30、 gigabits/second. TCPs use over satellites is so deficient that for IPv4 intermediate TCP “spoofing” devices are generally used at either end of any satellite link. However, this will not work when the data is encrypted as in IPv6, in IPv4 with IPSEC or in either with HAIPE encryptors inserted. Howe
31、ver since the hop-by-hop option field in IPv6 should not be encrypted, it provides a solution to passing QoS information to the routers. The second problem with using packet loss as a rate control mechanism is that the typical method of dealing with congestion is to discard random packets, even if t
32、he flow in question is not yet up to the speed of other flows. This is usually done using Random Early Detection (RED) or Weighted Random Early Detection (WRED). This procedure slows down the TCP rate so that it does not get up to the maximum network speed as fast as possible. This problem has been
33、magnified as the network speeds have increased such that an average 120 K byte web page transfer over a 10 Mbps access line can take many seconds rather than the fraction of a second actually required. The TCP situation is improved 6 by marking packets for congestion, using Explicit Congestion Notif
34、ication (ECN) before discarding becomes necessary. ECN avoids discarding the packet, but the search for the rate the network can support is still a binary search that leads to significant loss of throughput that does not improve the slow-start problem. Marking packets in this way, also presumes that
35、 the network has sufficient storage to signal congestion well before the problem becomes critical. This obviously leads to either additional network delays due to long queue traversals, or to lower network utilization (already a problem). When the concept of marking packets is coupled with the feedb
36、ack of the maximum rate the network could support, it is feasible for the TCP source to avoid slow-start and achieve extremely high-speed throughput. Instead of marking or discarding packets when congestion occurs, the network can inform all TCP sources as soon as possible of the rate that they can
37、operate at safely. As conditions change, additional feedback is required. This concept was simulated and tested extensively 5 with (ABR) in ATM systems. It was found to dramatically decrease the time to transfer a web page and significantly decrease the buffering required in the network. The QoS Sig
38、naling protocol specified in this document brings this concept to the IP world. 3.5 QoS Feature Summary Weve established that there are four main areas that need to be supported, in order to improve the services available over IP: 1. Maximum rate accommodation for streaming media flows. 2. TCP rate
39、feedback to eliminate the low throughput encountered due to any significant delay in the flow path. Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-18 3. Preemption to support e
40、mergency services. 4. Identifying the direction of charging to permit 800 type services and more flexible peering. 3.5.1 Maximum Rate The QoS parameters in 7 8 9 10 11 are somewhat similar, but not necessarily compatible, with those used in IntServ (RFC 1633, 2212, 2215, 2998, 2474) and ATM. The cal
41、l setup speed (calls per second) will also need to be much faster than the two latter schemes. Thus, the need for hardware support and a forward path setup have become necessary. The QoS features important to setting up an interactive voice, video, or streaming media flow, not supported in Diffserv,
42、 include the maximum rate requested, the burst tolerance required, the delay priority, and the multi-level preemption priority (PP). With the ability to specify these parameters, IP can be used to deliver the same high quality voice and video as the TDM network but at much lower cost and with much h
43、igher line utilization particularly for variable bandwidth streams. These services are moving to IP due to consolidation and cost and it is important to provide the best quality and efficiency possible. As this occurs, preemption priority must be included so that emergency situations can be supporte
44、d. 3.5.2 AR Rate Feedback The concept of Available Rate is the basis of the Internets current stability. Today, TCP is the primary protocol in use, and it accepts whatever Available Rate the network can support. This concept is needed to allow data traffic, to adjust to, and be limited by, the netwo
45、rks capacity. However the current feedback method, leads to very poor results at high speed. This is especially true in the presence of noise errors or long delay paths. Except for a few lost packets, the current discard based binary feedback is similar to concepts in 6 on Explicit Congestion Notifi
46、cation (ECN). The proposed Rate Feedback procedure introduced in this memo, determines the maximum Available Rate the network can accommodate, by the collection of said information (AR) across the forward path and its return to the source. This has proven to be as much as 100 times better than simpl
47、e binary congestion feedback methods like ECN or the discarding used today. A complete analysis is given in 1. Currently when encountering long delays or radio noise, TCP sessions cannot support large throughputs, have major delays in face of packet loss, and are treated very unfairly versus competi
48、ng TCP connections with only short fiber connections. This will be dramatically improved when the network can feed back the maximum rate it could support to the source using this protocol. When the rate feedback is received by the sender, it can adjust its TCP rate to the network-supported rate. If
49、the network capacity changes, the network will send a new rate. Thus the user can continue to send at the agreed rate in the face of packet loss and just retransmit the lost packets without slowing down. This allows users to operate over extremely noisy links with only a linear loss of throughput. Without this capability, if TCP performance cannot be improved, users will convert to
