12_draft-wang-p2pi-localization-00.txt

P2PI Workshop                                                   Y. Wang 
                                                                 S. Tan 
                                                               R. Grove 
Internet Draft                                                Microsoft 
Intended status: Informational                              May 9, 2008 
Expires: November 2008 
                                    
 
                                      
     Traffic Localization with Multi-Layer, Tracker-Based Peer-to-Peer 
                     Content Distribution Architecture 
                    draft-wang-p2pi-localization-00.txt 


Copyright Notice 

   Copyright (C) The IETF Trust (2008). 

Abstract 

   The goal of this document is to provide a high level overview of the 
   challenges to the infrastructure created by peer-to-peer 
   applications coupled with the emergence of media-centric content. To 
   illustrate the need for solution areas IETF could address, this 
   document sketches out a straw man peer-to-peer content delivery 
   framework based on a multi-layer tracker scheme to localize peer 
   traffic. The mechanisms and protocols required to achieve traffic 
   localization and to reduce impact on the infrastructure are 
   summarized at the end. 

1. Introduction 

   Peer-to-peer (P2P) applications and the emergence of media-centric 
   content present a host of challenges to the current Internet 
   infrastructure. The delivery model for P2P systems differs from 
   traditional distributed systems in the follow manner: 

   1. Symmetric delivery (peer distribution) vs. asymmetric download 
     (client/server) 
   2. Multiple, concurrent, dynamic connections vs. single, static 
     connection per content unit 
   3. Routing at multiple layers vs. traditional end-to-end connection 
     at the Network layer 

   These new characteristics coupled with the growing size for rich-
   media content stretch current network service provider 
   infrastructure to the limit in handling the traffic. Capacity 
   provisioning is falling behind demand. Recent, anecdotal report [1] 
 
 
 
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   shows the 80/20 phenomenon in that a small portion of high volume 
   users is consuming the majority of the bandwidth. Most of the 
   regular user experience degrades as a result of the capacity 
   exhaustion, and also because of the lack of an isolation mechanism 
   for per-user or per-application traffic. 

   There are several approaches to mitigate the problems, such as 
   increasing the infrastructure bandwidth provisioning, reducing the 
   traffic though codec optimization, selectively dropping traffic with 
   layered encoding, or signaling and admission control to achieve 
   fairness. For an infrastructure-centric approach, this document 
   explores traffic localization to lessen the impact. The next section 
   presents an example framework for P2P content delivery with traffic 
   localization to illustrate some mechanisms and protocols required to 
   achieve the desired results. 

2. Straw Man P2P Content Delivery Architecture with Multi-Layer 
   Trackers and Traffic Localization 

   The framework described in this section is not a formal proposal for 
   a solution, but rather a generic, albeit simplified example to 
   demonstrate the need for several mechanisms to achieve traffic 
   localization. It is built on a multi-layer, tracker-based P2P 
   content delivery scheme [2], although the localization principle is 
   applicable to other P2P streaming content types. 

   In a normal tracker-based P2P system, a client searches an index to 
   locate a tracker for the desired content. The tracker typically 
   contains the content information, including seeds and active peers 
   to retrieve various parts of the content. The retrieval can happen 
   concurrently with multiple peer nodes and seeds based on a 
   predefined scheduling algorithm. 

   The multi-layered tracker scheme introduces additional trackers 
   (local trackers) for the same content located in participating 
   provider networks, each with seeds and peers for the content located 
   within its network scope respectively. The key is how the initial 
   query to the global tracker results in the right local tracker based 
   on the network location of the client. There are two elements to 
   this approach: 

   1. The network locality algorithm to determine the "nearest" tracker, 
     and also for selecting the seeds and peers within the local 
     tracker 
   2. The mechanisms to redirect the query from the global tracker to 
     the selected local tracker 

 
 
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   Tracker redirection can be accomplished with the following options: 

   1. Explicit delegation where each local tracker registers with the 
     global tracker in advance, and the client will try to locate the 
     nearest tracker for its provider network 
   2. Implicit redirection where the infrastructure intercepts and 
     redirects the original query to its local trackers 
   3. Proxy-based approach where the service network provides a proxy 
     for P2P services 

   Among the redirection options listed, the preference is to adopt an 
   explicit standard mechanism that is not in-path for both reliability 
   and performance consideration. 

   Once a tracker is located, the client may still need to determine 
   the "closest" seeds or peers to further localize the traffic. The 
   locality information can either be recorded in the tracker by the 
   network operators (the oracle approach), or can be determined 
   dynamically through network synthetic coordinate protocols similar 
   to Vivaldi [3], but focus on network locality instead of latency. 
   Network operators can further optimize the traffic by providing one 
   or more local caches within their networks as content seeds or 
   regular peers in the local trackers. The cache can be provisioned 
   beforehand with content providers or on demand upon the first 
   request. 

   The same approach for multi-layered trackers and traffic 
   localization also applies to streaming content types. Although in 
   the streaming distribution, a cache or proxy becomes necessary as an 
   aggregation point for a provider network that both aggregates the 
   streaming data from the source (or the global P2P delivery network) 
   and serves all the local participating peers. 

   This simple example highlights the need for network synthetic 
   coordinates, either through operator provisioning or dynamic 
   measurements, and the need for a generic tracker redirection or 
   delegation mechanism. Note though there are two additional aspects 
   not covered in this example: a federation-based authentication 
   and/or authorization scheme if necessary, and cross-layer topology 
   matching to improve traffic efficiency, especially for ad hoc, 
   wireless networks. 

3. Summary - Potential Solution Areas 

   This section summarizes the potential work areas for IETF. It is not 
   the intent of this document to provide details for each target 
   areas, but merely the high level requirements and rationales. 
 
 
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3.1. Network Synthetic Coordinate Protocol 

   This is the key element for localizing the traffic. It is used to 
   select both the nearest local tracker for a client and the nearest 
   seeds and peers within from the tracker to limit the scope of the 
   traffic. Network operators can also utilize this protocol to 
   construct a pseudo network map (i.e., the oracle). A solution should 
   take into account both the relative coordinates between node 
   addresses in question and the condition of the network traffic 
   whenever possible. From an infrastructure perspective, the notion of 
   "scope" and the capability to administratively inject or define 
   scopes in the coordinate systems are also necessary. 

3.2. Multi-Layer Tracker Redirection 

   It is useful to standardize on the redirection mechanism for similar 
   type of multi-layer tracker architecture. The redirection will work 
   in conjunction with the network coordinate measurement to direct a 
   client query to the nearest local tracker. Off-path, explicit 
   mechanisms are preferred for reliability reasons because it will be 
   easier to diagnose, and can avoid introducing new bottlenecks to the 
   packet flow. 

3.3. Cross-Layer Topology Matching 

   Topology matching between the overlay and the underlying Link layer 
   affects the efficiency especially in ad hoc wireless networks. 
   Topology mismatch may cause a single hop between two peer nodes to 
   traverse multiple hops in the Link layer topology unnecessarily, 
   often results in redundant packets over the same physical link.  

3.4. QoS-Related Signaling and Admission Control 

   QoS signaling and admission control are not considered for this 
   solution. The notion of end-to-end path reservation based on QoS 
   policy [4] is not scalable in the Internet scale. Any packet marking 
   scheme [5] suffers from the tragedy of the commons problem. Note 
   though these may work in a closed environment or within a single 
   provider network. 

4. Security Considerations 

   Security considerations are not addressed in this document. 




 
 
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5. Acknowledgments 

   This document has benefited from discussion with Scott Briggs, Nick 
   Holt, Paul Harris, and Tyler Barton. 

References 

   [1]   http://gigaom.com/2008/04/22/shocking-new-facts-about-p2p-and-
         broadband-usage/ 

   [2]   Cohen, B. "The BitTorrent Protocol Specification," BEP-003, 
         http://www.bittorrent.org/beps/bep_0003.html, January 2008. 

   [3]   Dabek, F., Cox, R., Kaashoek, F., and R. Morris, "Vivaldi: A 
         Decentralized Network Coordinate System," SIGCOMM 2004, August 
         2004. 

   [4]   Braden, B., Zhang, L., Berson, S., Herzog, S., and S. Jamin, 
         "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional 
         Specification", RFC 2205, September 1997. 

   [5]   Nichols, K., Blake, S., Baker, F., and D. Black, "Definition 
         of the Differentiated Services Field (DS Field) in the IPv4 
         and IPv6 Headers", RFC 2474, December 1998. 

Authors' Addresses 

   Yu-Shun Wang 
   See-Mong Tan 
   Rich Groves 
    
   Microsoft Corp 
   One Microsoft Way 
   Redmond, WA 98052 
   US 
       
   Phone: +1 425 722 6980 
   Email: yu-shun.wang@microsoft.com 









 
 
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