Study of the Relationship between Peer-to-Peer Systems and IP Multicasting

T. Oh-ishi, K. Sakai, K. Kikuma, and A. KurokawaNTT Network Service Systems Laboratories, NTT Corporation

IEEE Communications Magazine, vol41(1), Jan. 2003

Presented by Ho Tsz Kin28/01/2004

Agenda Introduction Features of P2P Systems IP Multicasting over P2P Systems Routing Protocol Evaluation Conclusion

Introduction Peer-to-peer (P2P) systems

Involve a number of directly connected “peers” exchanging various types of information among themselves

Problems of P2P systems Not specific application Generate a lot of network traffic Require the resources of every peer (e.g.

CPU, memory, and bandwidth)

Introduction IP multicasting

Is mainly for live streaming services Can solve problems of P2P systems

Applying IP multicasting to P2P systems Is it applicable? Is it worth? What is the suitable routing protocol? What happen when part of the network does

not support IP multicasting?

Features of P2P Systems Current P2P systems

Send broadcast packets or a series of identical unicast packets to peers

Two types Hybrid P2P Pure P2P

Two phases

Features of P2P systems Discovery phase

Heavier traffic in Pure P2P system Delivery phase

No differences between Pure and Hybrid P2P systems All peers must have the same messages. When new

messages arrive, they should be passed on to all the other peers

Features of P2P systems P2P systems essentially require a broadcast mechanism

use a series of unicast or broadcast packets Continuous unicast packets

Need substantial CPU power and bandwidth of peers and all of the network resources

Broadcast packets wasting various resources Security problem

IP multicasting Solution for broadcast mechanism in P2P systems

IP multicasting over P2P Systems

Almost all P2P application produce heavy traffic

Reduction of such traffic using IP multicasting seems to be effective

IP multicasting over P2P Systems

Comparison between live streaming and P2P systems

Live Streaming P2P Systems

Contents sender Can only be streaming servers

All peers can be senders

Opportunities to update member list

Updating when content receivers joins/leaves

Updating when content senders and receivers joins/leaves

Types of traffic flow Video streams Few packets per event

Range of propagation

Intra-ISP or inter-ISP Intra-ISP or inter-ISP

Number of content senders

Smaller than the number of content receiver

Same as the number of content receivers

Join/leave of contents sender

Statically Dynamically

Routing Protocol PIM

The protocols compose multicast trees using routing tables made by an arbitrary unicast routing protocol

Protocol Independent Multicast-Sparse Mode (PIM-SM) Peers send IGMP join message

to rendezvous point (RP) The multicast tree is originating

from the RP When a peer sends multicast

content, the packets is encapsulated by the closest edge router, and sent to RP

Routing Protocol PIM-Source Specific Multicast (PIM-SSM)

Source-specific protocol The contents receiver can specify the addresses of

desired sources in the IGMP join message When the closest edge

router receives an IGMP join, it configures the shortest path between the receiver and the sender

Sequence for joining groups PIM-SM

One IGMP join/leave to RP PIM-SSM

Joining• Send IGMP join to all senders• Get all other peers to send it an IGMP join

Leaving• Send IGMP leave to all senders

Comparison of PIM-SM and PIM-SSM

Conclude that PIM-SM is better for P2P systems

PIM-SM PIM-SSM

Load balancing

By distributing RPs By using a unicast routing protocol

Routercomplexity

Slightly more complex procedures

Simpler

Group-joining procedure

simpler More complex

Evaluation Simulation Model

Members exchange information across two ISPs• ISP-A does not support IP multicasting• ISP-B support IP multicasting

Only one router in each ISP All peers belong to a virtual group

Evaluation Simulation #1

Peers of ISP-A use unicast to all other peers Peers of ISP-B use unicast to peers of ISP-A and

multicast to peers of ISP-B Simulation #2

Peers of ISP-A use unicast to peers of ISP-A, and send multicast packets to ISP-B’s RPs

Peers of ISP-B use unicast to peers of ISP-A and multicast to peers of ISP-B

Conclusion Analyze features of P2P systems Suitable routing protocol is discussed IP multicasting is the solution for heavy

traffic generated in P2P systems Future Works

Sequence for joining/leaving groups Effect of RP’s location on traffic characteristics Multicast address allocation and traffic control

methods for the entire network

Discussion Combining Peer-to-Peer and IP

Multicasting The simulation details are not

mentioned, e.g. traffic characteristics, duration, application

Benefits of using IP multicasting over P2P systems