PPSP Y.Zhang Internet Draft China Mobile Intended status: Standard Track N.Zong HuaweiTech G. Camarillo Ericsson . J.Seng Plive R.Yang Yale University Expires: November 2009 May 27, 2009 Problem Statement of P2P Streaming Protocol (PPSP) draft-zhang-ppsp-problem-statement-03.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on November 27, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. Zhang Expires November 27, 2009 [Page 1] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract We propose to develop an open peer-to-peer (P2P) streaming protocol named PPSP. This document describes the problems related to PPSP and outlines considerations that have to be taken in account when arriving at equitable solutions. Zhang Expires November 27, 2009 [Page 2] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 Table of Contents 1. Introduction..................................................4 1.1. Research or Engineering..................................4 1.2. Objective and outline....................................5 2. Definitions...................................................6 3. Problem Statement Scope.......................................6 3.1. Proprietary protocols and an open PPSP...................7 3.2. Integrating cache and CDN into P2P streaming.............7 3.3. Integrating existing protocols into P2P streaming........7 3.4. Mobility and wireless issue..............................8 3.4.1. End to end communication is harder..................8 3.4.2. Limited Bandwidth resource..........................9 3.4.3. Other difference...................................10 4. Design Issues................................................11 4.1. Architecture Choice.....................................11 4.2. Integration with existing protocols.....................11 4.2.1. Integration with RELOAD............................11 4.2.2. Integration with ALTO..............................13 4.2.3. Encapsulating RTSP.................................13 4.2.4. Edge Device such as Cache Integration..............13 5. Scope of Work................................................15 6. Security Considerations......................................17 7. Acknowledgments..............................................17 8. References...................................................17 Zhang Expires November 27, 2009 [Page 3] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 1. Introduction Streaming traffic is among the fastest growing traffic on the Internet. In a recent white paper, Cisco predicts that by 2012, 90% of all Internet traffic will be video [Cisco]. There are two basic architectures for delivering streaming traffic on the global Internet: the client-server paradigm and the peer to peer (P2P) paradigm [P2PStreamingSurvey]. A particular advantage of the P2P paradigm over the client-server paradigm is its scalability. As an example, PPLive [PPLive], one of the largest P2P streaming vendors, is able to distribute large-scale, live streaming programs such as the CCTV Spring Festival Gala to more than 2 million users with only a handful of servers. CNN[CNN] reported that P2P streaming by Octoshape played a major role in its distribution of the historical inauguration address of President Obama. It is well demonstrated in practice that P2P streaming can deliver videos encoded at a rate of about 400 Kbps, in the presence of rapid user joins/leaves, with positive user experiences. With the preceding technical advantages, P2P streaming is seeing rapid deployment. Large P2P streaming applications such as PPLive [PPLive], PPstream [PPstream] and UUSee [UUSee] each has a user base exceeding 100 millions. P2P streaming traffic is becoming a major type of Internet traffic in some Internet networks. For example, according to the statistics of a major Chinese ISP, the traffic generated by P2P streaming applications exceeded 50% of the total backbone traffic during peak time in 2008. There were reports that major video distributors such as Youtube [youtube] and tudou [tudou] are conducting trials of using P2P streaming as a component of their delivery infrastructures. Given the increasing integration of P2P streaming into the global content delivery infrastructure, the lacking of an open, standard P2P streaming protocol becomes a major missing component in the Internet protocol stack. Multiple, similar but proprietary P2P streaming protocols result in repetitious development efforts and lock-in effects. More importantly, it leads to substantial difficulties when integrating P2P streaming as an integral component of a global content delivery infrastructure. For example, proprietary P2P streaming protocols do not integrate well with existing cache and other edge infrastructures. 1.1. Research or Engineering As [P2PStreamSurvey] identifies, there exist multiple proprietary P2P streaming systems including PPLive, PPstream, UUsee, Pando, abacast, Zhang Expires November 27, 2009 [Page 4] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 and Coolstreaming. A natural question to ask is whether the development of P2P streaming is mature and ready for standardization. We admit that P2P streaming will continue to improve and evolve. However, our investigation shows that existing P2P streaming systems are largely converging, sharing similar architecture and signaling protocols [draft-zhang-ppsp-protocol-comparison-measurement-00]. The competition of P2P streaming vendors become increasingly on contents. 1.2. Objective and outline Our objective is to develop a standard P2P streaming protocol that can operate in both fixed and mobile Internet. The protocol will serve as an enabling technology, building on the development experiences of existing P2P streaming protocols. It will integrate with IETF efforts on distributed resource location, traffic localization, and streaming control mechanisms. It allows effective integration with edge infrastructures such as cache and mobile edge equipment. This document provides a problem statement for designing PPSP. The rest of the document is organized as follows. In Section 2, we introduce terminologies. In Section 3, we identify the current problems in providing a scalable and economical streaming system.In Section 4, we describe the main issues to consider when designing PPSP. In Section 5, we outline the main scope of work. Zhang Expires November 27, 2009 [Page 5] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 2. Definitions The following terms have special meaning in the definition of thePeer to Peer Streaming Protocol (PPSP) problem. Tracker: A dedicated server who is in charge of maintaining peer list and replying peer request for peer selection. Peer: A peer refers to a participant in a P2P streaming system who acts both as "client" and "server". Chunk: A chunk is a basic unit of partitioned streaming, which is used for the purpose of storage and advertising to neighbors what parts of a movie a peer holds [Sigcomm:P2P streaming]. Bitmap: Bitmap is a table indicating which chunks a peer has. Peering networks: Two directly connected Internet Service Providers. Apart from infrastructure and operational costs, peering traffic is usually free, within the contract of a peering a greement [draft- marocco-alto-problem-statement-03]. 3. Problem Statement Scope We perceive a number of problems related to scalable and economical streaming on the Internet. The major issues are the following: 1) The difficulty of an open PPSP due to the existence of many proprietary and non-interoperable protocols in current p2p streaming applications; 2) The difficulty of integrating current edge equipments such as cache and content distribution network (CDN) nodes into P2P streaming; 3) The difficulty of integrating related protocols into P2P streaming, like RELOAD,ALTO,RTSP, which is beyond current P2P streaming usage; 4) The lack of a standard solution for scalable and economical streaming signaling interaction suitable both for fixed internet and mobile Internet; a related problem is that the difficulty of deploying p2p streaming in mobile Internet; The subsections below discuss these problems in more detail. Zhang Expires November 27, 2009 [Page 6] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 3.1. Proprietary protocols and an open PPSP Currently there exist some P2P streaming systems like PPLive, PPstream, UUsee, Pando[Pando] and Coolstreaming[Coolstreaming].Although using similar system architecture as well as signaling interaction processes[draft-zhang- ppsp-protocol-comparison-measurement-00], due to their proprietary protocols, it's hard to develop an open PPSP protocol without checking all the typical P2P streaming systems, identifying the key issues and considering all the requirements. 3.2. Integrating cache and CDN into P2P streaming To make P2P streaming stable and traffic local enough, cache and other edge infrastructure is a very promising means [draft-marocco- alto-problem-statement-03]. However there are a few obstacles in deploying P2P caches [HTPT]: firstly, P2P caching systems are likely to be very complicated. Unlike web traffic standardized in using HTTP transport through few dedicated ports like 80, there is no a standard P2P protocol and every P2P protocol uses its own port. Therefore, P2P caching systems are forced to take an ad hoc approach by enumerating and handling every P2P protocol. Another drawback of this ad hoc approach is the requirement of regular update of the P2P cache engines to handle newly emerged popular P2P protocols. Secondly, extra, possibly huge, investment is required for the equipment and facility purchase and also the administrative cost. If we can utilize the existing cache and other edge equipments like CDN nodes, the cost can be heavily reduced. Meanwhile because it's widely used, the performance of P2P streaming can increase much. Therefore how to utilize the edge infrastructure is a big issue. Current web cache or other widely deployed edge equipments like CDN doesn't support P2P streaming yet[HTPT]. 3.3. Integrating existing protocols into P2P streaming There are several protocols related to p2p streaming having been or being defined in IETF, including RELAOD,ALTO,RTSP,etc.., where P2PSIP,ALTO and MMusic are most related WGs. Unfortunately there is no one protocol above considered by current P2P streaming applications. Zhang Expires November 27, 2009 [Page 7] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 We claim that PPSP is not a stand-alone protocol. It could and should integrate with the existing related protocols to the largest extent. We analyze several protocols PPSP may relate to in detail in section4. 3.4. Mobility and wireless issue Mobility and wireless becomes a very important feather to support in future internet [GENI],[FIND]. Some operators have also started research projects on mobile and wireless Internet. For example, China Mobile came out with its DSN (distributed services network) strategy last year to build its mobile Internet [draft-zhang-ppsp-dsn- introduction-00]. Along with the introduction of mobile and wireless characteristics into Internet, mobile streaming will become more and more popular[MobileTV].In Korea the mobilTV subscriber is 17 million accounting one third of the mobile subscriber. In Italy there are 1 million mobileTV users. In the period of Beijing Olympic games, there are more than 1 million usage of China mobile's mobileTV. Most of current mobileTV are developed in client/server model. It's a natural idea to increase its scalability and decrease the cost by deploying P2P mobile streaming. However there are a lot of differences in mobile/wireless Internet compared with fixed Internet environment. This makes it hard to copy current P2P streaming protocol in fixed Internet environment. 3.4.1. End to end communication is harder Unlike fixed Internet, it's difficult to realize end-to-end communication in mobile Internet. Mobile terminals cannot connect with each other directly. The connection must be set up by mobile/wireless access nodes. Therefore mobile terminals are hard to become peers without the cooperation of mobile/wireless access equipments. It's obviously a heavy burden for the mobile/wireless access points. Zhang Expires November 27, 2009 [Page 8] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 +------------------------------------------------------------+ | | | +-------+ | | | Cache | | | +-------+ | | ^ | | | | | Peerlist V | | +---------------+ +----+ +-----------+ | | | Tracker |<---->|PEER|<---->| AP |Bottleneck| | +---------------+ +----+ +-----------+ | | ^ ^ ^ ^ | | | | | Low | | | | | |Bandwidth| | | V V V V | | +---+ End-end +---+ +------+ +------+ | | |PC |<------> |PC | |Mobile|<--->|Mobile| | | | | works | | |Phone | X |Phone | | | +---+ Well +---+ +------+ +------+ | | | | | | | +------------------------------------------------------------+ Figure 1 Mobile Internet communication 3.4.2. Limited Bandwidth resource Even if end-to-end communication is ensured, there are still problems for P2P mobile streaming.As shown in Figure1, the following bandwidth is limited and the transmission cost is relatively high: a) between mobile terminals and mobile access nodes; b) between mobile access nodes; c) between mobile network to fixed network. It raises some requirements for PPSP: 1) The overhead of PPSP cannot be much. Because PPSP is a signaling protocol, the overhead refers to the ratio of signaling traffic with respect to overall streaming traffic. Different solutions have different overhead. [Computer Networks-Traffic]analyzes four P2P streaming overhead, namely PPLive,PPStream,SOPCast and TVAnts.There is a tradeoff consideration in PPSP. We know that frequent exchange in bitmap may cause a big overhead but it also Zhang Expires November 27, 2009 [Page 9] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 enables a small peer cache to keep the smooth play of the program. On one hand, the overhead should be minimum to reduce the traffic and increase the efficiency so the bitmap exchange frequency should be small. On the other hand, a mobile terminal has usually small cache size so the bitmap exchange frequency should be large. How to solve the conflict and balance between the cache size and bitmap exchange frequency is a problem PPSP may face with. 2) Cross-domain traffic must be reduced. For most mobile Internet domains, their network scale is rather smaller compared with the Tier1 and Tier2 peering networks. Currently peering networks are free from the cross-traffic. However the low-tier ISPs have to pay for dual-directional traffic fee even it's a traffic initiated from higher tier ISPs. It makes mobile Internet provider worse in case P2P streaming applications generate great traffic with a low-cross-domain bandwidth. 3.4.3. Other difference Mobility, low battery and capability of mobile terminals make us considering more factors in peer selection to ensure smooth streaming. A new protocol might therefore allow more information to report for trackers to do peer selection. Zhang Expires November 27, 2009 [Page 10] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 4. Design Issues This section introduces key issues when designing PPSP. 4.1. Architecture Choice There are multiple proposed p2p streaming solutions. Some are used in practice and while others are popular in theory. The basic idea of P2P streaming is to partition streaming into chunks and peers are used in relaying chunk transmission. The solutions can be categorized by tree-based and mesh-based [Survey]. The former is "pushing" chunks to the audience and the latter is enabling the audience to "pulls" the desired chunks from the peers who has. In the tree-based p2p streaming, tree construction and maintenance can be done in either a centralized or a distributed fashion [Survey]. In the mesh-based p2p streaming, no specific topology maintenance is needed. The task is how to locate and retrieve real-time data from multiple sources with different chunks for a streaming. In order to realize this, each peer has to actively locate cache and exchange chunks from other peers by the guidance of the tracker. The biggest challenge in tree-based p2p streaming is two-fold: First, the depth of the tree affects the maximum delay the system has; Second, tree-based streaming still cannot recovery fast enough to handle frequent peer churn. Therefore they are hardly used in practice. On the contrary mesh-based p2p streaming is widely used to overcome these drawbacks for real deployment, like pplive, ppstream, coolstreaming, etc,.. 4.2. Integration with existing protocols PPSP will not be a stand-alone protocol. A major advantage of a standard protocol is that we can explicit consider its interactions with other protocols, and design for an integrated system. In particular, we identify that PPSP will interact with the following protocols: RELAOD, ALTO, and RTSP, where P2PSIP, ALTO and MMusic are the most related WGs. 4.2.1. Integration with RELOAD RELOAD defined by P2PSIP deals with resource location in end to end commutation. The iterative and recursive routing process in RELOAD is shown in Fig4, which is different from PPSP. That is, the data stored in RELOAD is user profile data and the requester knows exactly what the data is (e.g., the location of Alice@chinamobile.com). While in Zhang Expires November 27, 2009 [Page 11] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 PPSP, there are many peers storing different data pieces of ''CNN Live''. The only thing a peer must know is the metadata of the movie. A gossip protocol to communicate with other peers is needed to get the real data quickly. +------------------------------------------------+ | +---------------+ | | | Peer | | | +---------------+ | | ^ | ^ | | | 1,2 | |1' 3,4| |3' | | | | | | | | V V V V | | +-------------+ 2' +------------+ | | | Peer |----->| Peer | | | +-------------+ +------------+ | | | +------------------------------------------------+ Figure 2 P2PSIP process The biggest difference between P2PSIP and PPSP lies in their different Search efficiency requirements. PPSP requires retrieving real-time/para real-time data and therefore a tree/mesh topology is built. DHT based topology supported in RELAOD may not be suitable for peer organization. Although P2PSIP doesn't fit for streaming peer organization, it can be deployed in PPSP environment to some extent. First, the topology organization of DHT defined in RELOAD can be used to organize multiple trackers. Due to the large population, some trackers may cooperatively serve a channel/file. Considering the great amount of channels, there are many trackers in practice. Because the search time of which channel/file the tracker stores accounts small percentage in the whole searching procedure, DHT can be used to query for peer list in case of thousand of channels or million of files which are hard to use one tracker. Second, there is a detailed solution for Firewall/NAT transversal in in RELOAD. PPSP faces with the same problem, although not as serious as RELAOD because there are lots of peer candidates with public addresses. But we can definitely reuse RELAOD in case of NAT/Firewall transversal which may occur in mobile environment. Zhang Expires November 27, 2009 [Page 12] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 4.2.2. Integration with ALTO ALTO is to define a protocol realizing local traffic mostly for P2P applications. The goal of an ALTO solution would be to help peers to find the best sources and the best destinations for media flows they receive and relay. In [draft-marocco-alto-problem-statement-03], the authors mentioned p2p live streaming that can benefit from ALTO service. As we have seen in Section 1, P2P streaming traffic account much on the Internet backbone. PPSP has to consider operator-friendly ways to reduce the cross-backbone traffic in order to control the transmission cost. ALTO is a good candidate to do so. ALTO provides a 3rd party to provide peer locality information based on the premise that the 3rd party has the knowledge of the network topology. In addition there may have extra traffic localization means, e.g., in [draft-zhang-alto-traceroute-00], peers can cluster the nearby peers by simple and lightweight measurements. We can use this mechanism in peer selection to further reduce the traffic. 4.2.3. Encapsulating RTSP At a first sight, the function of PPSP protocol is similar to traditional client/server streaming control protocols, RTSP. But in fact RTSP don't involve the problems PPSP has. In RTSP, the focus is to control the streaming, like PLAY, PAUSE; however PPSP focuses on signaling peers for real-time resource discovery, merge and synchronization instead of how to realize streaming control. On the other hand, considering the prevalence of RTSP, it can also be reused in clients without installing PPSP-compatible software to use P2P streaming service. The basic idea in that is to set up a proxy node (e.g., using a cache) which can act as a RTSP server who is actually a peer of PPSP. 4.2.4. Edge Device such as Cache Integration As stated in Section 3, if the widely deployed web cache and CDN nodes can be reused in p2p streaming, the video quality, local traffic and some security problems may be better solved.[HTPT] proposes a solution similar to what we propose in section 4.5 to encapsulate and transport them using the HTTP protocol so that they Zhang Expires November 27, 2009 [Page 13] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 are cacheable. Zhang Expires November 27, 2009 [Page 14] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 5. Scope of Work We propose to develop an open peer to peer streaming protocol, namely PPSP. The basic task of PPSP is to define a protocol of locating and transmitting real-time data efficiently from multiple sources with different pieces in peer to peer environment. PPSP focuses on how to negotiate with un-preassigned peers for needed chunks. Therefore, PPSP is mainly a signaling protocol and the protocol stack of PPSP is shown in Figure 3. +-----------------------------+ | PPSP Application | |-----------------------------| | PPSP Signaling Protocol | |-----------------------------| | Transport Layer | +-----------------------------+ Figure 3 PPSP Position in Protocol Stack In order to locate real-time data efficiently from multiple sources with different pieces, we have to solve the following problems: 1) To standardize the architecture for locating the data efficiently. Tracker-based structure is widely used in current p2p streaming practice. However some tracker-less structures like DHT peer management solutions are also proposed. We need to decide which one is better for p2p streaming; 2) To standardize the signaling interaction process. In this part we actually want to standardize client registration process (analogous to TCP 3-way handshake procedure), client information exchange process (analogous to SIP session setup process) and client report process. The current tracker-based means is a two-step searching, i.e., peer reporting to tracker coarse information about it has. Once the tracker is asked, it informs peer of the coarse information; the grain information is achieved by peers exchanging bitmap each other. Some other means, e.g., peer reporting to tracker grain information directly and tracker informs peer of the exact information or DHT based searching, should be evaluated. In each proposal we also need to define the message format in the interactions. Zhang Expires November 27, 2009 [Page 15] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 3) To discuss how to incorporate node information such as online time, link status, node capability, battery information and some application requirements parameters into the protocol to expand the peer selection. In this part, we actually want to standardize PPSP message headers (analogous to IP header definition) and PPSP metadata format (analogous to SIP header definition). Zhang Expires November 27, 2009 [Page 16] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 6. Security Considerations PPSP has a similar assumption in peer privacy as P2PSIP, i.e., all participants in the system are issued unique identities and credentials through some mechanism not in the scope of this working group, such as a centralized server. Hence the WG will not attempt a solution to these issues for P2P streaming networks in general. However PPSP has some unique privacy issue different from P2PSIP: 1) The content published by peers may not be checked by centralized certificating server because of the high amount. Therefore P2P streaming network faces with more serious malicious content distribution danger than P2PSIP. 2) Content Pollution is a phenomenon P2PSIP may not meet with. But these is a common problem faced by P2P streaming and file sharing. It's recorded that there are about 50% of the content is polluted in file sharing applications. Although it's not as serious as file sharing content pollution, it's still a big issue P2P streaming applications face with. 3) Because there is a tracker server who is critical to the P2P streaming systems. It has more probability to launch attacks to the tracker. PPSP may include some security mechanisms to prevent malicious nodes to pollute or launch attacks to the tracker. Security issues in PPSP need to be further investigated. 7. Acknowledgments We have to acknowledge many people. For the record: D.Bryan from SIPeerior; E.Marocco from TI;V.Gurbani from AT&T;R.Even from Huawei;H.Zhang from NEC Labs,USA;C.Schmidt and L.Xiao from NSN;C.Williams from ZTE;V.Pasual from Tekelec; X.Zhang from PPlive; H.Deng from China Mobile;and J. Lei from Univ. of Goettingen. 8. References [Cisco] Approaching the Zettabyte Era by Cisco. [PPLive] www.pplive.com [PPStream] www.ppstream.com [UUSee] www.uusee.com Zhang Expires November 27, 2009 [Page 17] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 [youtube] www.youtube.com [tudou] www.tudou.com [CNN] www.cnn.com [Octoshape] www.octoshape.com [ATT]http://mobile.sooyuu.com/Article/content/200905/217315094629281_ 1.shtml [Sigcomm:P2P streaming]Challenges, Design and Analysis of a Large- scale P2P-VoD System,Yan Huang et al, Sigcomm08. [draft-marocco-alto-problem-statement-03], Application-Layer Traffic Optimization (ALTO) Problem Statement, E. Marocco et al, draft- marocco-alto-problem-statement-03 [Pando]www.pando.com [CoolStreaming] CoolStreaming/DONet: A Data-Driven Overlay Network for Efficient Live Media Streaming, Xinyan Zhang et al, [HPTP] HPTP: Relieving the Tension between ISPs and P2P, Guobin Shen et al, [draft-zhang-ppsp-protocol-comparison-measurement- 00]www.ietf.org/internet-drafts/draft-zhang-ppsp-protocol-comparison- measurement-00.txt [GENI] www.geni.net [FIND]www.nets-find.net [draft-zhang-ppsp-dsn-introduction-00]www.ietf.org/internet- draft/draft-zhang-ppsp-dsn-introduction-00.txt [MobileTV] MobileTV,Turning in or switching off, Arthur D. Little [Computer Networks:Traffic] Traffic analysis of peer-to-peer IPTV communities, Thomas Silverston et al, Computer Networks, 53 (2009) 470-484 [Survey]A survey on peer-to-peer video streaming systems Yong Liu et al, Peer-to-Peer Netw Appl (2008) 1:18-28,Springer. Zhang Expires November 27, 2009 [Page 18] Internet-Draft Problem Statement of P2P Streaming Protocol May 2009 [draft-zhang-alto-traceroute-00] www.ietf.org/internet-draft/draft- zhang-alto-traceroute-00.txt Author's Addresses Yunfei Zhang China Mobile Communication Corporation zhangyunfei@chinamobile.com Ning Zong Huawei Technologies Co., Ltd. zongning@huawei.com Gonzalo Camarillo Ericsson Gonzalo.Camarillo@ericsson.com James Seng PPLive james.seng@pplive.com Richard Yang Yale University yry@cs.yale.edu Zhang Expires November 27, 2009 [Page 19]