Multicast In Wireless Mobile Environments

Reporter: 江俊毅

Introduction Wireless Network Categories Multicasting for wireless mobile hosts in an

IP network is a challenging task We first introduce the issues involved in

providing multicast in a mobile environment

Discuss details of proposed multicast routing protocols

Wireless Network Categories

Infrastructure Wireless: base station network is connected to the wired Internet.

Ad hoc Wireless:wireless nodes communicate directly with one another.

Wireless LANs

(a) Infrastructure Wireless (b) Ad hoc Wireless

Issues In Mobile Environments Multicast Forwarding Algorithm A source-based protocol like DVMRP ,DVMRP

forwards multicast packets only if it receives them on the correct interface

when mobile host (MH) moves to a new domain , its interface to the multicast router changes , resulting in the packets being dropped

Issues In Mobile Environments Dense or Sparse Model Protocol The dense mode protocols are useful if there are a l

ot of users and bandwidth availabilitiy is not a problem, whereas sparse mode protocols are meant for widely distributed users with limited bandwidth.

Issues In Mobile Environments Qos Provisioning Quality of service (QoS)-based wireless multicastin

g is an open issue In this section we first describe Mobile-IP based mul

ticasting protocols

Proposals for Multicast over MIP Remote Subscription In remote subscription an MH resubscribes to the m

ulticast group each time it moves to a new foreign network.

It is the simplest way of providing multicast through Mobile IP.

Remote Subscription

Out-of-synch problem

Proposals for Multicast over MIP Bidirectional Tunneling In this scheme MHs send and receive multicast pack

ets by way of their home agents (HAs), using unicast Mobile IP tunnels from their HAs.

Bidirectional Tunneling

Tunnel convergence

Multicast support using Mobile IP

Multicast support using Mobile IP (MoM) MoM is based on bidirectional tunneling MoM selected HA among the given set of HA is calle

d designated multicast service provider (DMSP)

MoM

DMSP select

Classify 1.Agent based 2.Count-based 3.Proximity-based 4.Random-based

RBMoM Range-Based Mobile Multicast (RBMoM) RBMoM provides a trade-off between the shortest

delivery path and the frequency of multicast tree reconfiguration

It selects a router called a multicast HA(MHA) Every MH can have only one MHA MHA(Multicast HA) is responsible for tunneling mu

lticast data to foreign networks

Select the new MHA

Proposals for Multicast over MIP Multicast for Mobility Protocols (MMP) MMP uses a sparse mode multicast routing

protocol Core Base Trees (CBT) to handle the movement of mobile nodes within a foreign network.

This scheme uses a shared-tree, to and from a centre point called the core of the network.

MMP relies on Mobile IP Agent Discovery procedure in order for mobile hosts to discover relevant Mobility Agents and obtain a multicast care-of-address.

MMP1.BS transmit periodic beacons with Agent Advertisement messages

2.MN transmits a Registration Request to the base station

3.BS will send a Join request to the Core and create a permanent group

4.MN moves to another cell, it will initiate handoff when it receives a stronger beacon

MobiCast MobiCast is designed for an internetwork environm

ent with small wireless cells, with many cells grouped together and served by domain FAs (DFAs).

MobiCastWHEN MN JOIN GLOUP X

1.MN send IGMP message to DFA

2.DFA instead MN join X

3. Construct multicast group Y and MN join group Y

Y YY 4.X-> DFA-> Y-> all AP

Reliable Wireless Multicast Protocols

Reliable Multicast Data Distribution Protocol (RMDP): Uses Forward Error Correction (FEC) and Automatic R

etransmission reQuest (ARQ) information to provide reliable transfer. Redundant information is inserted into the FEC, often enabling a receiver to reconstruct the original packet.

In the event that such information is not enough, an ARQ is sent to the multicast source which in turn, multicasts the requested packet to all receivers.

Reliable Wireless Multicast Protocols

RM2 RM2 is a reliable multicast protocol that can be use

d for both wired and wireless environments. RM2 is a hierarchical protocol that divides a multica

st tree into subtrees where subcasting within these smaller regions is applied using a tree of retransmission servers (RSs)

RS having a retransmission subcast address shared by its members and which may be dynamically configured using the IETF’s Multicast Address Dynamic Client Allocation Protocol (MADCAP).

The receivers are required to send negative acknowledgments (NACKs), pointing out the packets to be retransmitted.

Reliable Wireless Multicast Protocols

RM2

compare

Conclusion This article is an attempt to give an overview of curr

ent research in wired and wireless multicast field and show that this area is rapidly growing and evolving.

Future directions in wireless multicast need to consider QoS, security, and so on.

Furthermore , a detailed investigation is desirable for both unreliable and reliable environments.

END

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