Hybrid cd ns_leveragingthebestofbothworlds

© Tech Mahindra Limited 2010

Hybrid CDNs Leveraging the Best of Both Worlds

Abstract:

CDNs have evolved to distribute and deliver media content

to millions of users, across geographically disparate

locations. However, the challenges on the networks to

deliver quality content without succumbing to traffic loads

and routing decisions, have only compounded. This paper

investigates the dimension of a Hybrid CDN involving

P2P/P4P schemes to improve the network health, and

touches upon considerations that may be currently going

unnoticed.

Authors:

Chitresh Markanda, Principal Consultant –IP networks

Gururaj Phadnis, Sr. Consultant- IP networks

Raj Sahakari, Sr. Consultant- Customer Premise Technologies

Chirag Shinde, Consultant in Wireless Technologies

1 © Tech Mahindra Limited 2010

Table of Contents

Introduction ............................................................... 2

Distribution using P2P ................................................... 2

Disciplining using P4P .................................................... 3

Architecture of a Hybrid CDN .......................................... 3

Benefits to Telcos ........................................................ 4

Other Considerations .................................................... 5

Conclusion ................................................................. 6

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Introduction

Simple CDNs have so far enjoyed wide-spread acceptance as channels to guarantee media content

delivery over the internet to large numbers of users. However, these CDNs have reached some

limitations as per scale - Akamai’s CEO acknowledges that the load introduced by a million users

watching a typical internet TV multimedia clip streamed at 400 Kbps would result in traffic exceeding

Akamai’s current peak capacity by about 30%. Simple CDNs function by copying media streams to a

large number of servers along a customer facing “edge”. User load is distributed over this edge.

Limitations of this approach stem from the fact that a streamer can handle at most a few hundred users

simultaneously. For handling the typical viewership of popular content one would need hundreds of

thousands of streamers, a requirement that is simply not practical.

This limitation of scale has created the need for other paradigms of media distribution. Prominent

among these approaches is Peer-To-Peer media sharing.

Distribution using P2P

Peer-To-Peer media distribution or media sharing as it is often called, achieves scalability by using

viewer numbers to its own advantage. It leverages viewer equipment itself to distribute and

redistribute media.

A consumer of media receives “pre-designated” fragments from other peers who already have those

fragments. This means consumers no longer load “edge streamers” as in the case of traditional CDNs.

Media distribution load is evenly spread throughout the viewership. This system, in fact, performs

better with an increasing number of users and easily scales to 100s of millions of users.

Though P2P was only created with the ability to “download” media in mind, suitable modifications to

the mechanisms can enable streaming applications to view media on-the-fly. Just like traditional CDNs

need edge streamers, P2P needs to guarantee the existence of a “small” number of “seed” viewers to

begin the process of disseminating content among a larger user community and to guarantee its

availability. P2P does this with the help of designated nodes which are “always on” and connected to

media origin servers with high-speed links. In fact, minus actual viewers, P2P looks just like a simple

CDN and can “piggy-back” on existing Simple CDNs giving rise to the notion of “Hybrid CDNs”.

One side-effect of P2P is that more users can share their own User Generated Content (UGC) leading to

an explosion of content available in P2P communities. P2P was designed with this in mind and

automatically organizes and updates a content search database. The considerable computational power

required to update and search this vast database is derived again through distribution of both, the

database and the search functions, among certain available P2P nodes called DHT (Distributed Hash

Table) nodes. Some DHT nodes are designated by Hybrid CDN creators to guarantee functioning of their

networks, while some are P2P nodes volunteering to serve these functions. P2P networks locate and

query DHT nodes with keywords to find available content and the corresponding peers willing to share

it.

Though P2P presents a very powerful paradigm for media distribution it creates significant challenges

for ISPs. P2P nodes essentially connect with each other in an undisciplined manner. In particular, a P2P

node regards any node from which it can obtain content as a “neighbor”. Such neighbors can lie over

large geographical distances translating to a high amount of traffic between “neighbors” going over

OPEX-intensive long distance ISP backbone links. The problem is further compounded by the popularity

of P2P for publishing User Generated Content. The ISPs typically end up playing for this additional

traffic with no compensatory arrangement with content providers and consumers.


While some ISPs have attempted to block P2P traffic completely, their attempts have been rebuked by

government authorities that tend to encourage openness of communication and user empowerment.

The need to discipline P2P traffic however, can be addressed by extending the role of content locators

within peer communities. Some ISPs have been researching the notion of P4P to deal with this aspect.

Disciplining using P4P

P4P disciplines P2P traffic by making DHT nodes aware of network topology, altering the notion of the

“neighbor” to be cost-sensitive. DHT nodes are made to query ISP provided portals providing network

path costs to be incorporated when advising P2P peers searching for content. This way, P2P nodes

locate and download content fragments from peers to which they can talk over local links.

Content that is not locally available continues to be obtained over long distance links. However, a

population of a few hundred users effectively downloads content once over long distance links and

shares it locally. Without P4P, most of these users would end up repeatedly downloading the same

“remote” content, thus increasing the ISPs long distance bills. P4P has been observed to be very

effective in practice, limiting long distance P2P traffic by over 80%.

P4P was not designed with streaming in mind. Peers attempt to download “rarer” content fragments

with higher priority. This is to mitigate the risk of peers dropping off the network. The result is that

content fragments arrive in no particular order making it harder to watch a multi-media clip on-the-fly.

This can be addressed without fundamentally modifying P2P mechanisms. Re-prioritization of content

fragments based on sequence, rather than on “rarity” has been successfully employed for streaming

applications.

Architecture of a Hybrid CDN

Figure 1: Telco CDN 2.0 – Hybrid CDN

Figure 1, presents various CDNs which are needed to deliver content effectively. Typically, the Edge

(between Core and Access network) is the “middle mile” or peering point for a CDN. CDNs traditionally

are overlaid beyond the Edge (into the Core) via small number of dedicated content distribution

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servers. Hybrid CDN covers content distribution both on the core and the access networks. Some of the

key objectives of Hybrid CDNs include:

Ability to deliver HD (High Definition) Content over the CDN

Ability to stream live content

Ability to monetize the content at the Edge – via Byte billing or advert insertion

Ability to localize traffic - especially P2P and UGC traffic

For end to end content delivery SLAs – Service management, Rights management, Reliability and Price

are important considerations. Another important consideration is the QoS guarantee across CDN

networks.

P2P traffic management within the access network is important for a Telco in order to ensure

democratic utilization of available network capacities. Localization of P2P would ensure that edge

routing is reduced and hence lower cost of peering. Implementation of P4P makes P2P location aware.

Also, data centre/hosting costs are dramatically reduced by implementation of P2P/P4P based

technologies in the access network.

Edge caching is done for reasons of content caching and monetizing CDN traffic. Cloud technologies

today offer the edge caching capabilities and hence are being increasingly used. Ad-insertion via Ad-

splicing and other content adaptations at the Edge can further help monetize the assets. In case of P2P

traffic, if the edges are being used, Ad-funded schemes can be developed to enable such “add-ons”.

Benefits to Telcos

Some of the advantages of the proposed architecture arise from better management of user generated

traffic. They principally include:

Being able to launch multi-tenant services and being able to guarantee reliable, optimized

service delivery

Help telcos launch HD content over their networks – for video streaming, download, P2P traffic

Effectively enable UGC over telco networks and monetize it

Launch live-streaming services, both events and user generated, over telco networks

Being able to launch Ad-funded revenue models for P2P and user generated traffic

Finally, deliver good user experience via better management and traffic shaping

With this strong infrastructure backup, telcos are in a position to launch a wide range of applications,

such as:

Broadcast and Stagger cast TV

HDTV

EPG and Interactive TV

User Generated Broadcast

Video Conferences

Video on Demand

Application/Web Hosting and Edge caching services


Other Considerations

Network Optimization

The inherent unpredictability of content flow in a P4P network makes the quality of service particularly

difficult to guarantee. There is a need for mechanisms within or complementary to P4P to address QoS

provisioning in peer networks. This provisioning mechanism must be robust enough to handle the large

numbers of peers joining and dropping off the network, while maintaining the desired QoS. Statistical

techniques analogous to those used in high capacity web content delivery setups could be combined

with peer “reservation” mechanisms to achieve guaranteed content flow in peer networks.

Need for Standardization

The ability of a CDN to interact with other CDNs plays an important role, especially when telcos wish to

extend their content services beyond their current subscriber base. Also, telco CDNs could get loaded

and would need the assistance of other CDNs to offload traffic. Thus, the need to standardize CDN

interworking is greatly felt.

However, most of the current day CDNs are proprietary and IP protected, thus causing challenges in

integration. Standards bodies such as the Open IPTV Forum and ETSI have initiated the standardization

process, but have primarily focused on the internal CDN functional entities and the associated

reference points. Interfaces for inter-CDN communication, which typically cater to ingest, redirection,

access requests, network statistics, etc., are required to be defined.

Need for DRM

Illegal content distribution is the prime concern that content providers are attempting to tackle. This

includes both, downloadable as well as streaming content. Introduction of P2P/P4P distribution

schemes exacerbates the issues as it introduces an expensive tradeoff with DRM enforcement.

DRM policies for professionally available content and UGC, especially for P2P/P4P networks, are

required to be defined for controlling the usage and redistribution of the content, thus preventing

copyright breaching. Run-time encryption coupled with efficient key management could help address

DRM needs in a P2P/P4P environment. Also, as content flows across diverse CDNs, aspects related to

DRM interoperability need to be considered.

Strategies for Home Networks

The interconnection of devices in the home to watch multimedia is scaling by the day and is creating a

network that needs efficient management. P2P-based CDNs, in a modified and adapted form, are a

good candidate to fit the bill.

Such CDNs could typically overlay existing home networks – DLNA (Digital Living Network Alliance),

G.hn, HPNA (Home Phone line Networking Alliance), HANA (High-Definition Audio-Video Network

Alliance), MoCA (Multimedia over Coax Alliance), etc. – to host, distribute and deliver

services/applications, integrate with the physical networks, as well as manage the load and usage of

the home networks.

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Conclusion

Telcos need to introduce CDNs in their networks as demand for user generated as well as professionally

available content is becoming more and more profound. Telcos can adopt various strategies including

upgrade of network equipment, service management equipment; create/lease overlay networks for the

core network. For the access network, telcos need to focus on user generated traffic (UGC, semi,

professional content) and optimize both the cost of transmission and storage of these contents. By

using a hybrid CDN approach involving a simple CDN coupled with a P2P/P4P scheme, telcos can

leverage the best of both worlds.

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Hybrid cd ns_leveragingthebestofbothworlds