Định tuyến Multicast groups

Giới thiệu về multicast groups .các giao thức chạy trong định tuyến multicast

Multicast networking

Multicast

Broadcast

Class MulticastSocket

Using multicast

A peer-to-peer multicast chat system

A client/server multicast chat system Wrapping up

Conclusion

Multicast networking

Multicast and broadcast are datagram network protocols.

Broadcast packets can not get across a router, while multicast packets can.

Multicast, thus, requires a router to be multicast

aware: both the hosts and routers must support

IGMP

Multicast networking

Internet Group Management Protocol (IGMP)

(packets) need to inform their

immediately-neighboring routers that they are interested in

receiving multicast messages sent to certain

multicast groups

one or more multicast groups and receive the

multicast packets sent to those groups

this information with their local routers is called Internet Group Management Protocol (IGMP)

A packet is sent to a multicast group All the interested recipients in the group will receive the packet

As with UDP, multicast is packet-based and does not guarantee reliability

Successful delivery may be different for different recipients in packet lost,

duplication, and order

Multicast groups

A multicast group is simply an IP

address that falls into IP class D

(224.0.0.0~239.255.255.255)

Recipients express an interest in

receiving packets addressed to a particular multicast group

The underlying network protocols announcing this interest to relevant routers on the network

Multicast groups

To multicast is to simply insert a packet into the network with the appropriate

target address

A sender need not even be a member

of the group

The packet will also be picked up by

routers that will forward it as appropriate

to adjacent networks that are interested

The significant complexity of multicast is how routers will know what adjacent

networks are interested

Multicast groups

The MBone

The largest deployment of multicast on the Internet is perhaps the Mbone.

A multicast packet is

transported as usual

within a island, but is

also picked up by

router hosts that

transmit the data

through TCP tunnels

to other router hosts

on other islands.

TTL-Time To Live

Multicast packets use a TTL field to limit how far a packet will propagated

The definition of the TTL field depends

on the routing protocol

There are other reliable multicast

protocols such as MTP, RAMP, RMP, RMTP, RTP, TMTP, or XTP

Similar at a local level to multicast:

every broadcast-based network has a

broadcast address

Clients must

choose a UDP

port number

on which to

operate

Multicast vs broadcast

Multicast is preferable.

Multicast is often supported correctly, but

broadcast results in a permission error.

Multicast and broadcast result in almost the same traffic.

From java, only a single client can listen to

broadcast to a particular port on a single

machine, while many clients can engage in

the same multicast conversation from a single machine.

Class MulticastSocket

The MulticastSocket class extents the

DatagramSocket class by adding support for IP multicast.

The additional methods are:

 A send() method that allows the TTL of a multicast

packet to be specified.

Java does not support querying the destination

address of a received packet, so it is up to every

application to manually determine whether or

Applets are restricted to receiving multicast packets from a single host, from which they came from

They are usually

not allowed to

transmit multicast

packets

IGMP must be

used

Using multicast

Using multicast is similar to using UDP except that a TTL can be specified

when a packet is sent through a

MulticastSocket

Using multicast

Receiving a multicast packet involves

one more step

The receiver must join a multicast group before waiting for packets to arrive

An

code frag

ment

A peer-to-peer multicast

chat system Multicast and broadcast allow the

development of true peer-to-peer applications

- there is no central server.

This example

shows how

clients in a

multicast-based

chat system

communicate

A client/server multicast

chat system

This implementation combines unicast

and multicast to overcome the Java

applet security limitation

Each client unicasts its message to a

central server, which then multicast it

back to all the client

This requires that the server must reside

at the Web server’s location to comply with Java applet security limitation

A client/server multicast

chat system

This system consists of two classes –

MixedcastChat and MixedcastServer

A client/server multicast

chat system

To deployed as a web-based chat system, the server must run on the same machine as the web server.

Client can only connect if they are

multicast-connected to the server.