Design an Application Layer Multicast

CHUN-TING, WUTeacher: KAI-WEI, KE

2

Outline

Introduction MANET Examples Performance Matrics Conclusions

3

Overview

Traditional network architectures distinguish between two types of entities› end systems (hosts) and the network

(routers and switches). The key architectural question is: what

new features should be added to the IP layer?› Multicast and QoS

4

What is a multicast

Delivery of information to a group Creating copies only when the links to

the multiple destinations

5

Why multicasting

video-on-demand live media streaming video conferencing multiplayer games

Real time and large data flow

6

IP layer vs. Application layer

In deciding whether to implement multicast services at the IP layer or at end systems, there are two conflicting considerations that we need to reconcile.

7

IP layer vs. Application layer

First, IP Multicast requires routers to maintain per group state› violate the “stateless” architectural

principle, and introduce high complexity and serious scaling.

Second, IP Multicast calls for changes at the infrastructural level› slows down the pace of deployment.

8

Finally, IP Multicast is providing higher level features such as reliability, congestion control, flow control, and security has been shown to be more difficult than in the unicast case.

9

We consider a model in which multicast related features, such as group membership, multicast routing and packet duplication, are implemented at end systems, assuming only unicast IP service.

10

To be resolved

An overlay approach to multicast, however efficient, cannot perform as well as IP Multicast.

It is impossible to completely prevent some redundant traffic on physical links.

Communication between end systems involves increasing latency.

11

(b) naive unicast transmission. (c) the IP Multicast tree constructed by

DVMRP (d) an “intelligent” overlay tree

12

Conceptual comparison

Issues IP multicast Application multicast

efficiency in terms of delay/bandwidth

High Low — Medium

Complexity or Overhead

Low Medium — High

Ease of deployment Low Medium — High

OSI layer works Network layer Application layer

13

ALM properties

GROUP MANAGEMENT› Mesh First vs. Tree First› Source Specific Tree vs. Shared Tree› Refinement

ROUTING MECHANISM› Shortest Path› Minimum Spanning Tree› Clustering Structure

14

Mesh First vs. Tree First

Tree-based› Source node as the root, thus there is only

one single path between every pair of sender and receiver.

› It’s very efficient since the routing information needs to be maintained is very little.

Mesh-based› More than one path between each sender

and receiver pair exists.› More robust but less efficient.

15

Source Specific Tree vs. Shared Tree

Source-tree-based› It construct a multicast tree among all the member nodes

for each source node.(usually this is a shortest path tree)› More efficient.› Too much routing information to maintain.

Shared-tree-based› It constructs only one multicast tree for a multicast group

including several source nodes. (usually this is a minimum spanning tree)

› Every source uses this tree to do multicast. › Less efficient.› It reduces the overhead greatly by maintaining less routing

information.

16

Refinement

Constructed trees might be different› Depending upon the order of joining

requests› Construct the tree in real time and have no

a-priori knowledge of node arrivals

Local optimum to the global optimum and improves the system’s performance

17

Shortest Path

A Shortest Path Tree constructs a minimum cost path from a source node to all its receivers

A source-specific multicast tree or in graph theoretic terms a rooted tree

18

Minimum Spanning Tree

Construct a low cost tree Used by a shared tree

19

Clustering Structure

Construct a hierarchical cluster of nodes with each cluster having a head

Advantages› Reduction in control overhead› Faster joining and leaving› A sub-optimal tree

20

MANET

Form a temporary and dynamic wireless network on a wireless channel without the fixed infrastructure

Self-organizing collection of Mobile Nodes

Low bandwidth, mobility and low power Due to the limited transmission range,

multiple hops may be needed

21

IP network and MANET

router vs. forwarding node traverse internet vs. multi-hops routing fixed vs. topology changes frequently

22

Flooding-based

Proactive (table-driven)› continuously evaluate routes› maintain up-to-date routing information› periodically flood its location to other

nodes› maintains a location table

Reactive (on-demand)› routing creates routing only when desired› in searching of the destination

23

Quorum-based

Explicit› Location update is sent to a defined subset

(update quorum)› Location query is sent to a subset (query

quorum) Implicit

› Location servers are chosen via a hashing function

24

MAODV

Multicast On-demand Distance Vector routing protocol

This protocol uses broadcast to find the route in an on-demand way and constructs a shared routing tree.

25

26

MAODV Example

L

Group Join Process

Broadcast - RREQ

Only GM Responds

Multicast ActivationBroadcast Group Hello

Group member

Multicast Tree member

Ordinary node

Potential Group member

Multicast link

Communication link

27

MAODV Example

L

Leaving a Multicast Group

Non leaf NodeMust remain as a Tree

member

Leaf NodeCan remove itself

from MTAgain Leaf Node

Remove himself from MT

Group member

Multicast Tree member

Ordinary node

Potential Group member

Multicast link

Communication link

28

Local Connectivity Management

Node must periodically hear from active neighbors to know they are still within range

Every time hear broadcast, update lifetime

If no broadcast with hello_interval, broadcast Hello packet

Failure to hear from a neighbor for› (1 + allowed_hello_loss ) * hello_lifetime

indicates loss of link

29

Unicast Route Discovery Source broadcasts

› Route Request(RREQ)› <J_flag, R_flag, Bcast_ID,

Src_Addr, Src_Seq#, Dst_Addr, Dst_Seq#, HopCnt>

Node can reply to RREQ if› – It is the destination› – It has a “fresh enough” route to

the destination Nodes create reverse route entry Record Src IP Addr / Broadcast ID

to prevent multiple processing

Source

Destination

RREQ

30

Unicast Route Discovery Source broadcasts

› Route Request(RREQ) Node can reply to RREQ if

› – It is the destination› – It has a “fresh enough”

route to the destination Nodes create reverse

route entry Record Src IP Addr /

Broadcast ID to prevent multiple processing

Source

Destination

RREP

31

Unicast Route Discovery Source broadcasts

› Route Request(RREQ) Node can reply to RREQ if

› – It is the destination› – It has a “fresh enough”

route to the destination Nodes create reverse

route entry Record Src IP Addr /

Broadcast ID to prevent multiple processing

Source

Destination

32

Forward Path Setup

Nodes along path create forward route to dest

Source begins sending data when receives first RREP

Source

Destination

Data

33

Design properties

GROUP MANAGEMENT› Tree First› Shared Tree› No refinement

ROUTING MECHANISM› Minimum Spanning Tree

MANET ROUTING› Reactive› Flat

34

Performance Matrics

Latency› end-to-end delay

Bandwidth› throughput at the receiver

Stress› number of identical copies of a packet

carried by a physical link

35

Performance Matrics Resource Usage

› 57 / 30 / 32 Protocol Overhead

› total bytes of non-data traffic

36

Conclusions Although, MANET multicast is an ALM,

using wired mech. cannot perform well. Actually, there is no a “one-for-all”

scheme that works well with different scenarios.

Highly dynamic environment, nodes move arbitrarily, thus network topology changes frequently and unpredictably

Moreover, bandwidth and battery power are limited.

Make multicast extremely challenging

37

References

Tu, W. & Jia, W., “An End Host Multicast Protocol for Peer-to-Peer Networks,” LCN '05: Proceedings of the The IEEE Conference on Local Computer Networks 30th Anniversary IEEE Computer Society, 2005, pp. 392-399

Hosseini, M., Ahmed, D., Shirmohammadi, S. & Georganas, N., “A Survey of Application-Layer Multicast Protocols,” Communications Surveys & Tutorials, IEEE, 2007, Vol. 9(3), pp. 58-74

Junhai, L., Danxia, Y., Liu, X. & Mingyu, F., “A survey of multicast routing protocols for mobile Ad-Hoc networks,” Communications Surveys Tutorials, IEEE, 2009, Vol. 11(1), pp. 78 -91

Perkins, C. & Royer, E., “Ad-hoc on-demand distance vector routing,” Mobile Computing Systems and Applications, 1999. Proceedings. WMCSA '99. Second IEEE Workshop on, 1999, pp. 90 -100