Peer-to-Peer Networks (3) - IPTV

Hongli Luo

CEIT, IPFW

Internet Video Broadcasting

References:

“Opportunities and Challenges of Peer-to-Peer Internet Video Broadcast” by Liu et al.

“Insights into PPLive: A Measurement Study of a Large-Scale P2P IPTV System” by Hei et al.

Background

Large-scale video broadcast over Internet

Real-time video streaming

Applications:• Internet TV

• Broadcast of sports events

• Online games

• Distance education

Need to support large numbers of viewers• AOL Live 8 broadcast peaked at 175,000 (July 2005)

• CBS NCAA broadcast peaked at 268,000 (March 2006)

Very high data rate• TV quality video encoded with MPEG-4 would require 1.5 Tbps

aggregate capacity for 100 million viewers

• NFL Superbowl 2007 had 93 million viewers in the U.S. (Nielsen Media Research)

Possible Solutions

Broadcasting is possible in air, cable networks, or

local area networks

Possible solutions for broadcasting over Internet

Single server - unicast

IP multicast

Multicast overlay networks

Content delivery networks (CDNs)

Application end points (pure P2P)

Single Server

Application-layer solution

Single media server unicasts to all clients

Needs very high capacity to serve large number of clients

CPU

Main memory

Bandwidth

Impractical for millions of simultaneous viewers

IP Multicast

Network-layer solution

Routers responsible for multicasting

Efficient bandwidth usage

Requires per-group state in routers

High complexity

Scalability concern

Violates end-to-end design principle

IP Multicast

Unicast via Multicast

S

C

C

C

Server

Clients

S

C

C

C

Server

Clients

Unicast Multicast

Multicast group

IP Multicast

End-to-end design principle: a functionality should be

Pushed to higher layers if possible, unless

Implementing it at the lower layer can achieve significant performance befits that outweigh the cost of additional complexity

Slow deployment

IP multicast is often disabled in routers

Difficult to support higher layer functionality

Error control, flow control, and congestion control

Needs changes at the infrastructure level

IP Multicast

“Smart Network”

Berkeley

Gatech Stanford

Per-group Router State

Source:

Purdue

Source: Sanjay Rao’s lecture from Purdue

Multicast Overlay Network

Consists of user hosts and possibly dedicated servers scattered through the Internet

Hosts, servers and logical links between them form an overlay network, which multicasts traffic from the source to users

Originally in IP multimcast, router responsible for forwarding packets, application run on the end systems.

New applications can now make their own forwarding decisions.

A logical network implemented on top of a physical network.

Consists of application-layer links

Application-layer link is logical link consisting of one or more links in underlying network

Each node in the overlay processes and forwards packets in an application-specific way

Used by both CDNs and pure P2P systems