Telecom operators deploying content delivery networks for OTT, IPTV, Gaming and other services need to take into account the content traffic flowing over a P2P overlay network on their networks.
Existing P2P applications, while selecting peers do not take into account
network topology. As a result, from the selected close peer-list, few peers
appear within the same ISP networks and few across multiple ISP networks.
To address this issue, several potential solutions have been suggested to
localize P2P traffic i.e. having peers take into account network topology when
selecting their close peers. This paper focuses on e-Cohorting, which means to
have a cohort of peers and to localize P2P content traffic in Hybrid-CDN
architecture. Here the word cohort means grouping of peers that have similar
Video and P2P content is increasing Internet bandwidth
demands. Recent data  indicates global internet bandwidth is growing at
approximately 40 percent to 60 percent per year. Cisco projects 49 percent
annual growth from 2007 to 2012 in overall Internet traffic, with 31% annual
growth for P2P. Cisco estimated that 60 percent to 70 percent of P2P traffic is
actually video . P2P traffic traverses multiple ISP networks and core
networks, even though the same content could be retrieved from a much closer
location. An article  showed that 99.5 percent of current P2P traffic (using – eDonkey – in France) traversed national or
international networks. Major ISPs including AT&T, Comcast, and Verizon
Communications participated in the field trials coordinated by Pando Networks
and Yale University during fall 2008 as an activity of the P4P Working Group
(P4PWG), a multi-industry initiative sponsored by the Distributed Computing
Industry Association (DCIA). The results ,  demonstrated improved
performance for all categories of users and for all participating ISPs, using
cable, digital-subscriber-line (DSL), and fiber-to-the-home (FTTH). The
percentage of data delivered within each ISP increased from 14 percent for
normal P2P delivery to as much as 89 percent for P4P delivery. In addition, a
majority (up to 60 percent) of the internal data delivered using P4P was
delivered within the same metro area. Another aspect is the upload concern. The
ISP’s network is asymmetrically designed, where the bandwidth for download is
more compared to upload. Due to rapid growth in user generated contents, there
is a paradigm shift towards content sharing and distribution. The momentary
bandwidth requirement for upload could be better satisfied by P2P technology.
This allows ISP to re-use the existing infrastructure without installing
additional hardware components.
Localization of P2P traffic provides information about
peers, which enables them to choose neighbors, not randomly but close to
themselves in the underlying network topology. Researchers have investigated
and proposed several approaches to reduce P2P traffic by sharing underlying
network information with P2P applications. The objective is that P2P client
should use underlying network information to choose their close peers more
efficiently. This reduces core network congestion and significantly increases
download speed for P2P applications. In following paragraphs, we survey few
existing approaches for P2P traffic optimization where network layer
information is shared with P2P applications to improve P2P neighbor selection.
Path Selection Service: A decentralized approach of
conveying network layer information to P2P clients is proposed in . The
paper  focuses on the Ono project where the peer selection is based on path
selection service. It reuses information provided by content delivery networks
for close peer selection using existing infrastructure of CDN to minimize
download latency. CDN redirection method is used to direct the clients to CDN
replica servers. The whole idea is based on the concept that if two client are
sent to same CDN replica server they are likely to be located close to each
other on the network topology. Here close is in the respect of the CDN’s point
of view and not necessarily the ISPs. As per Figure-1, Ono-enabled Peer
periodically looks up a list of CDN names to determine redirection behavior and
encodes this information as ratio maps. The request routing system in the CDN
triggers distance measurements (RTT) between the replica server and the peer’s
local DNS server. The peer is redirected to the best replica server and updates
its redirection ratio map. Ono-enabled peers exchange ratio maps at connection
handshake. The close peer selection is based on the cosine similarity of the
ratio map between two peers.
Operator provided topological information: The P4P Working Group’s (P4PWG) research project has developed a framework that
allows ISPs to convey network information to P2P applications. The framework of P4P project is interface centric. It mandates the network operator to host an iTracker. This iTracker serves as the portal to be used by P2P applications within the network provider’s network to acquire network layer information through the exposed REST interfaces. For tracker-less P2P system, this iTracker
directly communicates with P2P client and for tracker-based P2P system, iTracker communicates with P2P client through Application Tracker (AppTracker).
By configuring the iTracker, network provider logically groups its network and computes the pDistance between the peers. pDistance is a metric representing network information or preference between PIDs (Partition-ID – provider defined logical group of networks) This pDistance is computed based on routing policies, topology information, inter-ISP cost agreements, etc. Thus P4P allows ISP to secure its network from the disruption by abstracting the detailed network information. At the time of close peer selection, P2P client queries iTracker to retrieve the pDistance between the selected peers. Based on the pDistance, P2P client reduces the selected peer-list that serves the content with reduced network cost and improved download speed. For the selection of good reduced peer list, P4P client could select intra-PID peers, then intra-ISP peers and then inter-ISP peers. Here, the objective is to have an ISP preference for better close peer selection not necessary close but rather efficient route selection to minimize traffic cost.
Benefits of localizing P2P traffic
1. To manage peak demand: Localizing P2P traffic in
Hybrid CDN architecture enables network provider to manage peak bandwidth
demand which lasts for a short duration. For any hosted sport event e.g.
Olympics, network provider could effectively distribute the content with the
existing infrastructure and P2P technology. Hence for such kind of rare events
the network provider does not have to add additional hardware components into
their existing infrastructure.
Enables P2P client to choose close peers within the ISP networks thereby
retrieving the content from the local or close by network avoiding multiple
intra-ISP traffic cost. This significantly reduces the load on the core network
and network congestion in the ISP networks.
3. Better performance of P2P application:
By serving the content from the local or intra-ISP network, the P2P clients gets better download speed in the localized network.
4. To efficiently manage the network:
For P4P, an ISP has to logically group their networks while configuring iTracker. This enables ISP to provide limited network information and abstracts the network details to prevent any further disruption, thereby managing network efficiently.
5. Regional Ad-insertion:
By localizing P2P traffic, network provider could generate additional revenue by localized advertisement insertion along with efficient distribution of regional content.
Telcos and ISPs can offer peer enabled services as a part of their CDN offerings. This will benefit Telco/ISPs both in terms of rapidly scaling a content service as well as reduce abuse of other ISP/Telco peering arrangements by content providers. Moreover, identification, management and optimization of P2P traffic as a part of CDN strategy would also provide many monetization opportunities including localized ad-insertions, monetization of upload bandwidth in access networks. Hence, it is recommended to include localized P2P as part of hybrid CDN strategy.
Pradip Pathak, tech lead, CSU IP Network Solutions
Shruti Kapre, senior technical associate, CSU IP Network Solutions at Tech Mahindra