multicast communication

Network Architecture and Design 1

Multicast Communication The Basics of Group Communication

Types of communication Quality of Service

Integrated Services (IntServ) Resource Reservation Protocol (RSVP) ST2

MBone

ReferenceR. Wittman and M. Zitterbart, Multicast Communication, Protocols and Applications, ISBN 1-55860-645-9, 2001.


Unicast Communication (1:1)

One packet for each receiver


Multicast Communication (1:n)

One packet to many receivers Routers replicate the packet Like mailing lists

One email to many receivers


Unicast Vs. Multicast Unicast

With 3 receivers, sender must replicate the stream 3 times. Consider good quality audio/video streams are about

1.5Mb/s (a T1). Each additional receiver requires another 1.5Mb/s of

capacity on the sender network. Multiple duplicate streams over expensive WAN links.

Multicast Source transmits one stream of data for 3 receivers. Replication happens inside routers and switches. WAN links only need one copy of the data, not 3 copies.


How Multicast works?

Nodes consist groups Each group is identified by a single IP address

Class-D addresses Groups may be of any size and members of

groups may be located anywhere in the Internet.

Members of groups can join and leave (IGMP). Senders need not be members.


Class–D Addresses

Class-D IP address In “dotted decimal” notation:

224.0.0.0 — 239.255.255.255 Nodes that support class-D addresses

consist the Multicast Backbone (MBone)

1 1 1 0 group ID


Other Types of Communication

Concast Communication (m:1). Multipeer/multipoint (m:n). Broadcast. Anycast.


Anycast

Distance between client and server is usually large High response time Bandwidth binding in many links Inflexible in topology changes

Need for many service points


What is Anycast Routing?

A means of selecting and communicating with anyone of a set of distributed servers or service access points within a network

The router delivers the datagram to the nearest member of the group.

Appropriate for server-based applications


Unicast Routing Example

Database Server

FTP Server

Database Request

FTP Request


Anycast Routing Example

Database Server groupFTP Server group

Resolver

Database Request

FTP Request


Anycast Routing - Resolver

Close to client Maintains

Anycast group membership Selects web server according to:

Best response time Best server processing time


Multicast Communication

The Basics of Group Communication Types of communication

Quality of Service Integrated Services (IntServ) Resource Reservation Protocol (RSVP) ST2

MBone


IntServ

Change Internet service to provide QoS IntServ is not a protocol but a

framework. Usage of RSVP or ST2. Supports three classes of services

Best Effort Controlled Load Services Guaranteed Services


IntServ

An analogy: Travel by airplane Unreserved seat = Best Effort Reserved Seat = Controlled Load Charter your own flight = Guaranteed

Service


IntServ Best Effort

Bandwidth is not reserved Per-packet delay is not guaranteed

Controlled Load Bandwidth is reserved Per-packet delay is not guaranteed Performs like a lightly loaded Best Effort network

Guaranteed Service Bandwidth is reserved Per-packet delay is guaranteed Performs like having your own network


IntServ

Traffic Flow Multimedia IP traffic is correlated. Each packet from a sender to a receiver is

part of a flow. IntServ provides QoS for a Flow, not

individual packets. Flow specification generally same as TCP

connection (IP Address/Port). Need for reservation setup mechanism.


RSVP

What is RSVP? RSVP: Resource Reservation Protocol Application reserve resources in order to specify

desired QoS to net. Multicast friendly, receiver-oriented.

Why run RSVP? Allows precise allocation of network resources. Guarantees on quality of service. Heterogeneous bandwidth support for multicast.


RSVP Operation

Sender advertises PATH messages to receiver PATH = TSpec + AdSpec

TSpec: Specify the traffic characteristics AdSpec:

Contain information about the path’s resources Updated in every RSVP capable router Help receivers calculate the resources needed to

obtain desired QoS


RSVP Operation (cont) Receiver reserves resources using RESV

messages RESV = Rspec + filterspec + policy data

Rspec: Specify the bandwidth needed Filterspec: How reservations are distributed to data

streams and users. Travel upstream in reverse direction of Path

message Routers receive the RESV messages and make

the reservation (if available resources are more than Rspec resources)


RSVP Example

R4

R5

R3R2

R1

Host A24.1.70.210

Host B128.32.32.69

PATH

2

2. The Host A RSVP daemon generates a PATH message that is sent to the next hop RSVP router, R1, in the direction of the session address, 128.32.32.69.

PATH

PATHPATH

3

3. The PATH message follows the next hop path through R5 and R4 until it gets to Host B. Each router on the path creates soft session state with the reservation parameters.

1. An application on Host A creates a session, 128.32.32.69/4078, by communicating with the RSVP daemon on Host A.

1


RSVP Example

R4

R5

R3R2

R1

Host A24.1.70.210

Host B128.32.32.69

PATHPATH

PATH

PATH

5

4. An application on Host B communicates with the local RSVP daemon and asks for a reservation in session 128.32.32.69/4078. The daemon checks for and finds existing session state.

46

6. Reservation has been made and data flow begins with the guaranteed QoS.

5. The Host B RSVP daemon generates a RESV message that is sent to the next hop RSVP router, R4, in the direction of the source address, 24.1.70.210.

RESV

RESV

RESV

RESV


Internet Stream Protocol Version 2

(ST2)

The communication process takes place in three separate steps: Establishment of an ST2 stream Transfer of user data Termination of an ST2 stream.

Different protocols are applied ST2 SCMP (Stream Control Message Protocol)


RSVP Vs. ST2ST2 RSVP

Functionality Signaling protocol and data transfer.

Signaling.

Connection Types Connection-oriented, multicast, multipeer.

Short-lived connections, multicast.

Reservations Sender or Receiver oriented

Receiver-oriented

Modifications QoS and receiver group through explicit messages

QoS and receiver group through periodic messages

Error Handling Complex control and correction

Periodic message exchange

Heterogeneity No Yes


The MBone

An “interconnected” set of multicast-capable routers, providing the IP multicast service in the Internet

Can be thought of as a virtual network, overlaid on the Internet


Mbone - Example

Multicast Router

Simple Router

Source Node

Tunnel

Destination Node


MBone Tunnels A method for sending multicast packets

through multicast-ignorant routers IP multicast packet is encapsulated in a

unicast packet addressed to far end of tunnel

A tunnel acts like a virtual point-to-point link Each end of tunnel is manually configured

with unicast address of the other end

IP header,dest = unicast

IP header,dest = multicast

transport headerand data…


End of Third Lecture

multicast communication

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