technical seminar presentation - 2004

8/14/2019 Technical Seminar Presentation - 2004

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Technical Seminar Presentation - 2004

IP MULTICASTING

Presented by

Manas Ranjan Panda

Roll # CS200117174

Under the Guidance of

Mr. Debananda Kanhar


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INTRODUCTION

The TCP/IP family includes four types of distribution of apacket from a single host:

Unicast :To one host Normal IP- traffic The packet is seen only by the receiving host

Broadcast : To all hosts on a network When trying to find another host The packet is seen by all hosts on the local network


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INTRODUCTION CONTD

Anycast:To one host of a group of hostsTo access a resource that is served by several

computers

The packet is seen by one of the receiving hosts

Multicast:To a group of host

The packet is seen by all hosts in the group

The packet is only duplicated when needed


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PICTORIAL REPRESENTATION

A A

B C D B C D

UNICAST MULTICAST

A

B C D

BROADCAST


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A

B

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D

E

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Z

Flow of data in multiple unicasting


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A

B

C

D

E

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Flow of data in multicasting


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IP MULTICAST ADDRESSES

IP multicasting uses class D addressesThe first four bits are 1110

The remaining 28 bits specify a multicast group

Multicast addresses:

range is from 224.0.0.0 to 239.255.255.255

lowest address 224.0.0.0 reserved

up to 224.0.0.255 for routing /group

maintenance


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IP MULTICAST ADDRESSES CONTD

A multicast address

can only be used as a destination address

cannot appear in the source address field or in a

source route.

4 28 bits

class D

Total 2^28-256=268 million addresses

1110 Multicast Group ID


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MULTICAST SCOPE

Members have scope

Members in a single network: scope is the

network

Members in a single organization: scope is

the organization

A host must have to join a specific group to receive

the traffic in that group but can send to a group

without joining.

Membership is controlled by the IGMP protocol.


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To participate in a multicast that spans multiple networks,

the host must inform local multicast routers

Local routers pass membership information to other

routers IGMP is used to communicate group membership

information

It uses IP datagrams to carry messages

It is a standard for TCP/IP and is required on allmachines that receive IP multicast

IGMP is considered an integral part of IP, not separate

INTERNET GROUP MANAGEMENT

PROTOCOL(IGMP)


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IGMP has two phases

Phase 1: A host joins a multicast group

It sends an IGMP message declaring its membership

Local multicast routers receive the message andpropagate group membership information

Phase 2: Local multicast routers poll hosts to see whothe remaining members are

As long as at least one host responds, the routerkeeps the group active

If none respond, the router stops advertising

INTERNET GROUP MANAGEMENT

PROTOCOL(IGMP)


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IGMPv1

Stands for Internet Group Management Protocol

Manages multicast group membership

Runs between hosts and their immediate

neighboring router

Only two kinds of packets: query and report

Packet format

4 4 4 16 bits

vers ion type unus ed checks um

class D multicast group address


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IGMPv2

Adds an explicit Leave message

Routers can more easily determine when a

group has no interested listeners on a LAN


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Multicast Trees

Paths define a forwarding tree, or a delivery tree The tree contains no cycles Each multicast router corresponds to a node in the tree A network connecting the routers is an edge in the tree The source of a datagram is the root The last router on the path is a leaf

A forwarding tree defines a set of paths through multicastrouters from a source to all members of a multicast group

(size of tables is a concern)


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The Essence of Multicast Routing

A Multicast Router must have knowledge of group

membership

Group membership information must be propagated

across the internet Because membership can change rapidly, information

at a given router is imperfect and routing may lag

changes

Design tradeoff: routing overhead and inefficient datatransmission


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Reverse Path Multicasting

Underlying assumptions

It is more important for a datagram to reach eachmember of the group than it is to eliminateunnecessary transmission

Multicast routers contain a routing table with correctinformation

Needless transmission is eliminated when possible

RPM uses a two-step process

Copies of datagrams are broadcast to the internet Multicast routers inform each other of paths that dont

lead to group members


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Membership information is propagated bottom-up

It starts with hosts that join or leave the group

Hosts communicate with their local router using IGMP

When a router learns that no group member lie beyond a

given network interface, it stops forwarding and notifies therouter on the path back to the root

When a router learns that there are no members along a path,that path ispruned

The system is data-driven

A router does not send group information until datagramsarrive for this group (data arrives and we know where tosend messages)

Reverse Path Multicasting


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RPF

Stands for reverse path forwarding Simple algorithm developed to avoid duplicate packets on

multi-access links

RPF algorithm takes advantage of the IP routing table to

compute a multicast tree for each source.

RPF check

When a multicast packet is received, note its source (S) and

interface (I)

IfI belongs to the shortest path from S, forward to all interfaces

except I

If test in step 2 is false, drop the packet

Packet is nevernever forwarded back out the RPF interface.


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IPv4 multicast routing protocols

DVMRP (Distance Vector Multicast Routing Protocol)

PIM-DM (Protocol Independent Multicast, Dense Mode)

PIM-SM (Protocol Independent Multicast, Sparse Mode) CBT (Core-Based Tree)


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DVMRP

First multicast routing protocol ever deployed in the Internet Each router maintains a multicast routing table by

exchanging distance vector information among routers

Constructs a source tree for each group using reverse

path forwarding

There is a designated forwarder in each subnet

Multiple routers on the same LAN select designated

forwarder by lower metric or lower IP address (discoverwhen exchanging metric info.)

Once tree is created, it is used to forward messages from

source to receivers


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PIM-DM

Similar to DVMRP

Floods multicasts out of all interfaces except the

source interfaceUses RPM

Prune message to eliminate unneeded branches

Protocol-independent

Needs to establish its own router-to-router dialogs


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PIM-SM

Designed to provide efficient communication betweenmembers of sparsely distributed groups

Rendezvous point (RP) are used by senders to

announce their existence and by receivers to learn

about new senders of a group Requires host group members explicitly join a

delivery tree by transmitting Join message

One set of RPs per sparse-mode domain, not per

group. Each group has precisely one RP at any given time.

DR sends Join/Prune messages toward the RP and

maintain the active RP


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CBT

Construct a single tree shared by a Group Protocol independent

Core router equivalent to RP

CBT state bi-directional

Data flows in either direction along the branch Advantage

Less traffic

Better scalability

Disadvantage Bottleneck at CR

Single point failure


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Protocol Independent Multicast (PIM)

PIM consists of two protocols

PIM Dense Mode (PIM-DM) Most networks have hosts that listen to each multicast group

Uses RPF to broadcast datagrams to every group

Strops sending when it receives prune requests Assumes router also uses conventional routing protocols

PIM Sparse Mode (PIM-SM) Members of multicast groups occupy a small subset of possible

networks

Like CBT, requires a point to which joins are sent

Builds a forwarding tree, trees rooted at rendezvous point


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MULTICAST APPLICATIONS

Multicast VideoconferencingMulticast NewsfeedsMulticast Access to On-Demand ServicesNon-media Applications


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[1] Banikazemi,MohammadIP Multicasting: Concepts, Algorithms, andProtocols

http://www.cis.ohio-state.edu/~jain/cis788-97/ip_multicast/index.htm

[2] Juan-Mariano de Goyeneche, Multicast over TCP/IP HOWTO

http://www.tascnets.com/mist/doc/mcpCompare.html.

[3] Williamson, Beau. Developing IP Multicast NetworksIndianapolis: Cisco

Press,2000. Multicast Quick Start Configuration Guide

http://www.cisco.com/warp/customer/105/48.html

[4] Dave Price, Sandy Spence, University of WalesJANET Technical

Guides

http://www.ja.net/documents/

[5] Forouzan Behrouz A. , Data Communications and Networking, 2nd edition,

TATA McGRAW-HILL Edition

REFERENCES


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Thank you !

technical seminar presentation - 2004

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