3.Multicast2pp

8/4/2019 3.Multicast2pp

1/51

1

Multicast

Outline

Introduction

Network layer Multicast

Transport layer Multicast

Perspectives


2/51

2

Outline

Introduction Definition

Notion of group

Problem

Network layer Multicast

Transport layer Multicast Perspectives

What Is Multicast?

Efficient communication means 1-to-N

multicast vs. unicast and broadcast

unicast: a single source to a single destination

multicast: a single source to a subset of destinations

broadcast: a single source to all destinations

unicast(1-to-1)

multicast(1-to-N)

broadcast(1-to-all)


3/51

3

What Is Multicast?

Communication 1 to N

Bandwidth-saving technology which reducestraffic by delivering a unique information flowto several receivers simultaneously

Multicast examples The networks material layer supports multicast

efficiently Example: Ethernet allows a packet to be received by

many hosts

Several protocols and different service models Examples: IETF multicast IP, ATM Multipoint

Unicast

R

sender Problem

Sending the same data

towards severalreceivers in unicast is

not efficient

Example

Popular Web sitesbecome serious

bottlenecks


4/51

4

Multicast

R

sender Efficient distribution 1to many

Applications For Multicast

Reliability

Response time

100%

200 ms 2 s 20 s

Real-timeinteractive

Multimediadistribution

distributionof documents

conference Dlay -order

of 100 ms tolerance of

a certainloss rate

Continuousflows, real-time,not interactive,unidirectional

Softwaredistribution

100% reliability Few temporal

constraints


5/51

5

Why Multicast? (1/3)

distribution using TCP/IP

Results Several copies of the same packet

several buffers

several connections

R3

R4R2

R1

S

D1

D2

D3

D4

D5


distribution using multicast

Results A single copy of each packet

A single buffer

A single multicast connection

R3

R4R2

R1

S

D1

D2D3

D4

D5


6/51

6


Uses bandwidth efficiently

Prevents network congestion

minimises servers load

Provides information to more userssimultaneously

Reaches many people at the same time

etc.

Introduction To IP Multicast

Efficient 1-to-several distribution

Data Distribution with a tree

Packets cross networks links only once

Adressing independent of localization

One IP address per multicast group

Receiver-oriented service model

Applications can subscribe and quit multicast groups

Senders dont know who listens

Similar to the television model

Different from telephone or ATM networks


7/51

7

IP Multicast

Service All senders send towards the same group

simultaneously

Receivers subscribe to any group

Routers find receivers

Unreliable delivery

Reserved IP addresses 224.0.0.0 to 239.255.255.255 reserved for

multicast

Static addresse for usual services (e.g. sessionadvertisement protocol)

Notion of Multicast Group

How can we identify a Mcast packets receivers?

unicast: one IP destination address

Here, all destination addresses???

abstraction: multicast group

Links together a set of senders and receivers Exists independently of senders and receivers

senders receiversMulticast

group

Each receiver receivespacket sfrom eachsender


8/51

8

IP Multicast Addresses (1/2)

multicast group: class D address0

10

110

1110

rseau

station

adresse multicast

A

B

C

D

rseau

rseau

station

station

11100000 00000000 00000000 00000000

11101111 11111111 11111111 11111111

...de 224.0.0.0

239.255.255.255.

.

.

224.0.0.0 : unused

224.0.0.1 : represents the set of the considered subnetworksstations

There is no address for the set of all machines on the Internet

IP Multicast Addresses (2/2)

Group addressingS

D

S

DD

D

D

Receivers subscribe to thegroup address 224.1.2.3

@ IP source 224.1.2.3 donnes Mcaster

adresse de

destination

en-tte IP

Address indirection

Each host has its own IP @, independent of the group @

Problems distinction Discover the set of usual Mcast groups Express the wish to receive a groups packets Discover the set of a groups receivers Deliver data to each member of the group


9/51

9

Multicast Problems

Questions... When and how does a group begin and end?

When and how is the group address chosen?

How do new stations join a group?

Are there any conditions to belong to a group?

How do routers interoperate to deliver packets?

Choices... A receiver should be able to join or leave a group during a

transmission

A receiver should be able to join or leave a group without signaling itexplicitly to senders

Statements... Receiver hosts are often connected to local networks...

Introduction

Network layer Multicast multicast on LANs

IGMP protocol

Service model

Multicast routing algorithms

Multicast routing protocols

Transport layer Multicast

Perspectives

Outline


10/51

10

Multicast on a LAN (1/3)

What currently exists (Ethernet example)

Ethernet relies on a broadcast medium

each station has a network card with a specific

hardware @

There is a broacast address (FF.FF.FF.FF.FF.FF)

What can we do to reach only a subset of

stations? ex: H1 wants to send a Mcast packet to H2 and

H4 who are on the same network as H1

Two possibilities...

Multicast on a LAN (2/3) network multicast using link broadcast

network multicast using link multicast

Ethernet

IPH1

Ethernet

IPH2

Ethernet

IPH3

Ethernet

IPH4

...

Ethernet

IPH1

Ethernet

IPH2

Ethernet

IPH3

Ethernet

IPH4

...

@ de H1 FF.FF.FF.FF.FF.FF IP multicast Packet

@ de H1 @ MAC multicast IP multicast Packet

@src @dst


11/51

11

Multicast on a LAN (3/3)

Translation of IP multicast addresses into Ethernet @

Ethernet multicast addresses format

de 01:00:5e:00:00:00

01:00:5e:7f:ff:ff.

.

.

0000 0001 0000 0000 0101 1110 0111 1111 1111 1111 1111 1111

0000 0001 0000 0000 0101 1110 0000 0000 0000 0000 0000 0000

Translation mechanism

0000 0001 0000 0000 0101 1110 0

1110 xxxx x

23 derniers bits

We know how to Mcast an IP packet on a broadcast LAN!

IP Multicast Architecture Components

hosts

routers

Service model

Host-router Protocol

(IGMP)

multicastrouting protocols (several)


12/51

12

Protocol Involved in Hosts

IP Service Interface

Link-Layer Service Interface

Upper-Layer Protocol Modules

IP Module

Link-Layer Modules(e.g., Ethernet)

IP to link-layer addressmapping (e.g., ARP)

ICMP IGMP

What Is IGMP? How can a router determine if its LAN has receivers for

a given Mcast group?

Internet Group Management Protocol

Allows a host to indicate its local router if he wants to join agroup

Used in broadcast LANs

...

HR

R

R

H

HH

H

H.

.

.

.

.

.

Multicast routinglong distance

IGMP

IGMPIGMPIGMP


13/51

13

IGMP Version 1 (1/1) RFC 1112 (Aug.89)

query/report messages exchange

R

S1

HH

Long distancemulticast routing

S2

H

H

HH

H

query(quelquun intress par un groupe?)

report (225.5.5.5) report (224.9.9.9)

@ IP source 224.9.9.9 donnes

en-tte IP

@ destination

IGMP Version 1 (2/2) Risk of congestion

Answers spreading based on timers

R

H H

request sent

timer armed

answer sent answer reception,timer disarmed

query

report

timer armed

H

Traffic reduction on the LAN if no member

Possible delay (qq s.) before receiving data


14/51

14

IGMP Version 2 (1/2)

RFC 2236 (Nov.97)

A receiver explicitly informs its router when itleaves a group

3 types of messages

Message typemembership_query

gnralspcifique

membership_report

leave_group

Sent by

routerrouter

hosthost

goal

Ask groups to which hosts have subscribedAsk if a given group has members on a LAN

indicate that a host wants to join (or has joined) a groupIndicate that a host leaves a given group

Answers spreading with 0 timer MaxRespTime

IGMP Example (1)

Network 1

Host 1 starts sending packets No IGMP packet sent

Packets stay on network 1

router sends a IGMP Membership Queryperiodically

Network 2Router

1

2 4

3

dinh ky


15/51

15

IGMP Example (2)

Network 1

Host 3joins the conference

He sends a IGMP Membership Report message

router starts to forward packets on the network 2

Host 3 leaves the conference

He sends a IGMP Leave Group message

Sent only if he was the last host to send a IGMPMembership Report message

Network 2Router

1

2 4

33

Membership Report

33

Leave Group

IGMP Version 2 (2/2)

R

S1

HH

routage multicastgrande distance

S2

H

H

HH

H

query

(quelquun intress par un groupe?)

leave_group (225.5.5.5) report (224.9.9.9)


@ destination

en-tte IP

Message format

type MaxRespTime Checksum

Multicast Group Address

Reduction of Leaves latency


16/51

16

IGMP Version 3A receiver can select the sources he wants to hear

(or not)

R

S1

HH

routage multicastgrande distance

S2

H

H

HH

H

query(quelquun intress par un groupe?)

report

(224.9.9.9,

source=S2)


@ destination

en-tte IP

report

(225.5.5.5,

sourceS3)

S3

Internet Group Management Protocol (IGMP)

Protocol to manage the membership to a group

IP hosts report their Mcast groups membership to theirneighbor routers

Messages in IGMPv2 (RFC 2236)

Membership Query (from routers)

Membership Report (from hosts)

Leave Group (from hosts)

Advertise-listen protocol with suppression

Hosts answer only if no other host answered

Soft State protocol


17/51

17


hosts

routers

Service Model

Host-router protocol(IGMP)

Multicast routing protocols(several)

Multicast Service Model

Based on S. Deerings work

Transmission features IP multicast: transmission of an IP packet to a group of hosts

identified by a single destination address

best efforttransmission

Group features Dynamic membership

No restriction on localization and members #

One host may be member of several groups simultaneously

A host does not need to be member of a group to be a source

Permanent/temporary group

The Joinoperation is receiver-driven


18/51

18

Senders do not control who joins the group

No control on who sends to the group

Packets coming from different sources may be interlaced

2 different groups may choose the same @

Role of local Mcast routers co-resident or separated from traditional routers

A local router who receives a Mcast packet from one of itshosts, with a TTL>1, forwards it to all subnetworksconnecting receiver memberstant le paquet en local


RFC 1112 specifies necessary host extensions tosupport

3 conformity levels 0: host does not support Mcast 1: host can send packets to a group 2: host supports multicast for sending and receiving

Host IP implementation model

module IP

module LAN(Ethernet)

traduction d@(ARP)

interface de service

LAN

ICMP

interface de service IP

IGMP

modules de protocoles de niveau sup.


tron lan vao nhau


19/51

19

Extensions for Mcast sending IP service interface

use SendIP

dest@ = group@

The upper level must be able to specify a TTL

IP Module if IP-dest is on the same local network

or if IP-dest is a group @

then send packet locally to IP-dest

else send packet locally to GatewayTo (IP-dest)

LAN service interface LAN Module

Mcast IP@ / Mcast MAC@ translation mechanism


Extensions for Mcast reception

IP service interface use ReceiveIP

add JoinHostGroup (group-address, interface)

add LeaveHostGroup (group-address, interface)

IP module

Maintain list of groups of which the host is member for each interface(updates with Join and Leave)

integration of IGMP and subscription to 224.0.0.1

LAN service interface add JoinLocalGroup (group-address)

add LeaveLocalGroup (group-address)

LAN module Filtering mechanisms by the card (recommended)



20/51

20

IP Multicast Service Model

(RFC-1112)

Each group is identified by a unique IPaddress

Groups can be of any size

Group members may be anywhere on theInternet

Group members may join or leave a groupas they wish

Sources dont need to be members

Service Model

Group membership not explicitly known

Analogy:

Each multicast address is like a radio frequencywhich anyone may send to and that anyone may

listen to


21/51

21


hosts

routers

Service Model

Host-router protocol(IGMP)

Multicast routing protocols(several)

Multicast Routing

The multicast service model makes thelocalization of receivers difficult

Anonymity

Join/leave dynamically

Current options (not very efficient)

Flood the network with packets

Tell routers all possible groups and receivers so

that they may create routes (trees)


22/51

22

First Routing Techniques

Flooding and pruning Start with flooding all the network with traffic

Prune branches with no receiver

"unwanted"state where there is no receiver

Link state multicast protocols

Routers advertise groups for which they havereceivers in the whole network

Trees computation on demand

unwanted"state where there is no source

Rendez-Vous Options

Broadcast first packets from each source towards the

whole network: non members prune

Examples: DVMRP, PIM-DM

Broadcast group membership advertisements from

each receiver to the whole network Example: MOSPF

Specify a meeting place" where sources send the

first packets and where receivers subscribe; thisrequires a mapping between the multicast group

address and the rendez-vous point

Examples: CBT, PIM-SM


23/51

23

Shared (group) vs Source-based Trees

Source-based trees

Different shortest path tree for each source

Shared (group) trees

Unique tree shared by all members

Data pass through the same tree whatever the

source is

Multicast Trees Taxonomy

Multicast routing can build different types ofdistribution trees

Separate tree whose root is each data source

(DVMRP, MOSPF, PIM-DM, PIM-SM) Shared tree whose root is the groups core /

rendez-vous point (CBT, PIM-SM)


24/51

24

Shared Tree Example

RP

Source-Based Tree Examples


25/51

25

Shared Trees v.s. Source-Based Trees

Source-based trees

Shortest path trees low delay, better load

balancing

More states in routers (1 state/source)

Efficient for multicast in high-density spaces

Shared trees

Higher delay, traffic concentration 1 state/group in routers

Efficient for multicast in low-density spaces

Protocols Taxonomy

DVMRP source-based trees

MOSPF source-based trees

PIM shared and source-based trees


26/51

26

Multicast Routing Algorithms

Goal: compute a tree of links connecting allrouters belonging to the group

3 families

Shortest Path Tree algorithms

Minimum Cost Tree algorithms

Constrained Tree algorithms

SPT Algorithms (1/2)

Goal: compute a tree With S = source

Which covers all receivers Di of the group

So that the distance between S and Diis minimum

Basic algorithms Bellmann-Ford: distance vectors

Dijkstra: link state

1 tree / source


27/51

27

SPT Algotrithms (2/2)

S

R1

R3

R5

R6

R9

R11

R2

R8

D1

D2

D3 R4

D4 R7

R10 D6

D7

D5

S

R1

R3

R5

R6

R9

R11

R2

R8

D1

D2

D3 R4

D4 R7

R10 D6

D7

D5

Topology example Tree obtained with avector distance algorithm

MCT Algorithms (1/2)

Goal: minimize the trees total cost

2 families

Minimum Spanning Tree algorithms

constraint: the tree must contain no node which is not amember of the group

Ex: Prims algorithm

les algorithmes Minimum Steiner Tree

la contrainte est leve

problme NP-complet

ils supposent de connatre toutes les liaisons du rseau

ils sont monolithiques

ils nexploitent pas les informations dj disponibles deroutage unicast


28/51

28

MCT Algorithms (2/2)SR1

R3

R5

R6

R9

R11

R2

R8

D1

D2

D3 R4

D4 R7

R10 D6

D7

D5

Tree obtained with adistance vector algorithm

S

R1

R3

R5

R6

R9

R11

R2D1

D2

D3

D4

R10 D6

D7

D5

Steiners tree

rq: dist(S, D6) = 5 rq: dist(S, D6) = 7

CT Algorithms

Goal: minimize simultaneously dist(S, Di) etand trees total cost

Principle Associate 2 metrics to each link (distance/delay

and cost)

Look for the minimum cost tree such that

dist(S, Di)


29/51

29

What Do We Call IP Multicast ?

Mechanism used in the Internet to build anefficientand loop-freemulticast routingalgorithm

IGMP + Mcast routing protocol

RPF (1/2)

Reverse Path Forwarding (Source-based Routing)

One of the first used techniques

Goal: build a tree with root S which minimizes dist(S, Di)

Principle: use flooding with

If a packet is received by the interface used par router to reach Sthen the packet is forwarded to the other interfaceselse the packet is discarded

Simple mechanism Used information is the same as unicast routing

Ri doesnt need to know spanning trees

No particular mechanism to stop flooding


30/51


31/51

31

Truncated Broadcasting (1/2)

Goal: reduce traffic on LANs leaves

Idea: use membership information providedby IGMP to determine whether a packetshould be Mcasted on a leaf LAN or not

Kind of leaves pruning

No traffic reduction in the center of the network

Truncated Broadcasting (2/2)

F

R2

H4

H5

F

H2

H3R3

H6

H7R4

H8

R5

H12

H13R9H14

H15R8

R6H9

R7H10

H11

R12

H16

H17

H18

R13

H19

F

H20 H21

R11

H22

F

H23 H24

R10

H25 H26

H1 R1F F

F

F

FF

F

F FF

F

FF

FF

F

F

F


32/51


33/51


34/51

34

DVMRP (5/6)Tree after

graftD

R2

H4

H5

D

H2

H3R3

H6

H7R4

H8R5

H12

H13R9H14

H15R8

R6H9

R7

H10

H11

R12

H16

H17

H18

R13

H19

D

H20 H21

R11

H22

D

H23 H24

R10

H25 H26

H1 R1D

D

D

DD

D

DD

DVMRP (6/6)

Problems common to distance vectorprotocols

Peridodical flooding process for each source

Memorization of prune (Source, Group)

records


35/51

35

MOSPF

RFC 1584 (March 94)

Multicast Open Shortest Path First

Principle

Operates in an AS which uses OSPF for unicastrouting

extends OSPF by adding membership informationto link state information broadcast by OSPF

problem: scalability(network size)

Memorization of one record per group and pernetwork link

One tree/source

Multicast OSPF (MOSPF)

OSPF extension (Open Shortest-Path First,intra-domain link state unicast routingprotocol)

Each router indicates groups for which it hasdirectly connected members


36/51

36

MOSPF

Link state advertisements are completed bythe addresses of multicast groups to whichlocal members have subscribed

The link state routing algorithm isaugmented to compute the shortest path

distribution tree between any source andany set of destinations

S1

R1

R2

X

Y

Z

Link state: each router floods with link state advertisement

Multicast: membership information added to link state info

Each router computes the multicast tree for each active source and

creates an entry with the list of exit interfaces


37/51

37

S1

R1

R2

X

Y

Z has the networks map, including members below X and Y

Z computes the shortest path tree from S1 to X and YZ creates a multicast entry with an exit interface

W, Q and R each create a multicast entry

Z

W

Q

R

R1

R2

X

Y

Z

W

Q

R

S1

The link state advertisement with the new topology can require

a new computation of the tree and of the tables entries


38/51

38

R1

R2

X

Y

Z

W

Q

R

S1

T

R3

The link state advertisement (T) with a new membership advertisement

(R3) may require the incremental computation and the additionof an interface to the list of exit interfaces (Z)

Impact on the Route Computation

Source-based multicast trees cannot all bepre-computed

On demand computation when the first packetfrom a source S to a group G arrives

Packet forwarding on exit interfaces whichcorrespond to the local portion of the tree


39/51

39

CBT (1/3)

RFC 2189 et 2201 (Sept.97)

Core Based Tree (Group-shared Tree)

Goal: avoid DVMRP and MOSPF drawbacks

Scalable: one single tree for the group

Efficiency (avoid floodings): explicit Join and Leave

messages

Principle: build a bidirectional shared tree, with a

unique core

CBT (2/3)

Trees construction

A local router which has a new member for a group sends ajoin-request message to the core in unicast

The core or the first router on the path which alreadybelongs to the tree answers with a join-ack

Each router which saw the join-request markes the if onwhich it received it

Trees maintenance Each router periodically sends echo-request to its

upstream router

The upstream router answers with echo-reply

If a downstream router does not receive any answer after Ntrials, it prunes its subtree by sending a flush-tree

message


40/51

40

CBT (3/3) R1 sends a join (G) to the core R2 marks the R2-R1 if to forward

packets in the future

R3 marks the R3-R2 if

the core marks the core-R3 if

when R4 joins G, its joinstops at R2

R2 marks the R2-R4 if

to send a packet to G, S sends it inunicast to the core which forwards it

R1

S

R2 R3

R4

cur

Advantages No flooding (vs. DVMRP)

A host may join/leave a group without delay (vs. DVMRP)

One record/group with exit interfaces (vs. DVMRP)

No explicit tree computation (vs. MOSPF)

Drawbacks Problems of reliability, robustness and congestion for the core

The tree is not optimal for all sources

PIM (1/3)

RFC 2362 (June 98)

Protocol Independent Multicast

Idea: explicit distinction between 2 distributionscenarios

Dense mode

Members are geographically concentrate in a zone

Idea: RPF with flood-and-prune, similar DVMRP

seems reasonable


41/51

41

PIM (2/3)

Sparse mode

Members are geographically scattered

Goal: a router shouldnt have to work, unless it joins a tree

Principle: center-basedapproach, similar to CBT

Excepted: No acknowledgement in response to join

the join is sent periodically to refresh the tree

The RDV point informs an active source that it should stopsending when there is router left in the tree

Changing mode is possible: from shared tree to source-based tree

RDV points periodically send downstream to indicate theiractivity

PIM (3/3)

Changing mode allows to unload the core

In case of failure, hosts which have changed mode keepreceiving

PIM doesnt tell how a router determines a groups rendez-vous point

PIM doesnt tell how to determine whether a group issparse or dense

R1 knows that its SP to S passes through its R1-R4 if or, R1 receives Mcast packets on its R1-R2 if

R1 sends a join to R4

R1 then sends a prune to the core

the core stops Mcast forwarding on core-R2

and R2-R1D

S

R1 R2

R3

cur

R4

Path with CBT

Pathwith PIM


42/51

42

Mbone (1/3)

Problem To bring Mcast to play on the Internet, all routers must have Mcast

functions and local routers must support IGMP

Most Internet routers dont support Mcast !!!

Idea Build Mcast-capable subnetworks on the edges of the Internet

Interconnect them through tunnels, tunnels ends are stations withmrouted and an OSs support for Mcast

Multicast Backbone of the Internet

Virtual overlay network, transient solution First tunnel in 88 between BBN and Stanford

Thousands of subnetworks today

Used to broadcast IETF sessions or IEEE/ACM conferences

Mbone (2/3)

Principle: tunneling Encapsulation of Mcast packets transmitted on the Mbone in

traditional IP packets

The receiving end of the tunnel detects that it has a IP packetencapsulated in a IP packet (protocol=4)

after decapsulation, it forwards the Mcast packet

Either locally on its subnetwork, if it has members Or to the next Mcast router, after re-encapsulation

M1 M2

R1 R2

tunnel

Real path

encapsulation decapsulation

@ M1

unicast

@ M2

unicast

@ M1

unicast224.5.5.5 data

Original Mcast packetUnicast IP header


43/51

43

Mbone (3/3)

Traffic Conferences typically generate 100-300 kbits/s (limited to

500 kbit/s)

No policy mechanism but user deontology

Applications Session directories (sd, sdr)

audio conferences (vat , nevot , rat)

Video conferences (nv , ivs , vic , nevit)

whiteboard (wb)

Text editor (nte)

Interactive distributed games (MiMaze)

Outline

Introduction

Network Layer Multicast

Transport Layer Multicast Reliability

SRM

RMTP

Perspectives


44/51

44

Reliablity Can we extend the approach used in unicast (ACK)?

Each destination must send an ACK for each (group of) message(s)

a msg is retransmitted until reception of an acknowledgement fromeach destination

Network congestion

Source implosion

Idea: use NAK The control goes from source to receivers

The source transmits without caring about ACK

Receivers detect losses thanks to sequence Ns holes

Man protocols have been proposed

Atomicity: either 0 or all recievers have received the message

Termination: the result of a transmission is known in a finitetime

SRM, RMTP, RAMP, RMP, etc.

SRM (1/2)

Scalable Reliable Multicast Offers a reliable transmission, no sequence, scalable (because

receiver-based+ local retransmission)

2 components

One component independent from the application: offers mechanisms to

ask for and recuperate missing data segments

One component dependent on the application: responsible forsequencing and segments naming so that they may be identifieduniquely by the whole group

Idea: a missing segment is not necessarilyretransmitted by the source When a loss is detected, the retransmission request is multicasted

The closest receiver from the requestor multicasts the retransmission


45/51

45

SRM (2/2)

S1/D1

S2/D2

S3/D3

D4D5

D7D6

new msgsretransm. Req.retransmissions

Goal: minimize traffic One single member asks for the

retransmission

One single member retransmits themissing segment

Principle Requests sending: slotting+ damping

Request Timer

Retransmissions sending

Repair Timer

Difficulty Timers dimensioning

RTT estimation for each pair (Di,Dj)

hyp : D5, D6 and D7have a missing msg

RMTP Reliable Multicast Transport Protocol

Offers a reliable point-to-multipoint transmission with maintanedsequence

Ideas notion of hierarchy

Reduce source implosion

Reduce response time

notion of local retransmission

principle Receivers are clustered in

local regions

There is one DR (DesignatedReceiver) per region, incharge of status msgaggregation

Status msg

S

DR1

D

DR2

D D

DR3

D D DDR4

D D

Difficulty: Build the logical tree


46/51

46

Outline

Introduction

Network layer multicast

Transport layer multicast

Research perspectives Network layer

Transport layer Application layer

Network Layer Perspectives

Adressing and routing withina group

Multicast routing in a mobile network

Multicast routing with QoS

S

R1

R2 R3

R4

D1

D2

R5D DD

D D D DD

S

R1

R2 R3

R4

D2

R5D D

D D D D1D

multicast on a subtree reachcast


47/51

47

Transport Layer Perspectives

Flow / Congestion control

Reliability (assisted by routers)

Group members auto-configuration

Application Layer Perspectives

Multicast addresses allocation

Shared objects naming


48/51

48

Multicast IP in the Real World

Commercial Motivation

Problem Internet traffic grows by 100% each year

Routers technology improves by 70% each year

Rapid enough routers are very expensive

ISPs must find a way of reducing traffic

Multicast could be used for the Web: distribute data from popular sited to caches on

the Internet

Send Multicast audio/video flows

Software distribution


49/51

49

ISPs Problems

Multicast leads to a high networks utilization

One source can produce a high load on the network

Experimental multicast applications require relatively muchbandwith: audio and video

No flow control in most multicast applications

Multicast breaks the Telco/ISP billing model

Currently, both sender and receiver pay for BW

Multicast allows the source to buy less BW and reach as many

receivers The load on the ISPs network in not proportional to the sources

rate

Multicasts Economics

One packet sent to several receivers

source+ benefits from the load reduction on the network

compared to unicast+ lower cost for network connectivity

Network service provider- One sent packet may cause a higher load than a

unicast packet n

+ reduces the global traffic on the network

Receiver= same number of received packets as in unicast


50/51

50

Multicast Issues Multicast is not mature

protocols and applications not mature

Tools are difficlut to use, debugging is difficult

Routing protocols leave many unsolved questions

Interoperability flooding and pruning / explicit subscribttion

Routing instability

The multicast development focused on academic problems,not on commercial issues

Multicast breaks the telco/ISP billing model

Routing has not considered policies

PIM, DVMRP, CBT do not consider ISP policies issues

BGMP considers them a little bit, but it is currently being developed

Current Multicast Solution For ISPs

Restriction of multicast data sources

Charge source for multicast traffic distribution

Static agreements

Dont transmit multicast traffic Some ISP propose multicast traffic to their users

(e.g. UUNET UUCast)

ISPs start to negociate agreements betweenpeers

chin chan, ky cang


51/51

Bibliography

[RFC 1112] S. Deering, Host Extensionsfor IP Multicasting, August 1989.

[RFC 1075] D. Waitzman, S. Deering, C. Partridge, Distance Vector Multicast Routing Protocol,November 1988.

[RFC 1584] J. Moy, Multicast Extensions to OSPF, March 1994.

[RFC 2189] A. Ballardie, Core Base Trees (CBT Version 2) Multicast Routing: ProtocolSpecification, September 1997.

[RFC 2201] A. Ballardie, Core Base Trees (CBT Version 2) Multicast Architecture, September1997.

[RFC 2236] R. Fenner, Internet Group Management Protocol, Version 2, November 1997.

[RFC 2362] D. Estrin, D. Farinacci, A. Helmy, D. Thaler, S. Deering, M. Handley, V. Jacobson, C.Liu, P. Sharma, L. Wei, Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol

Specification, June 1998.

C. Diot, W. Dabbous, J. Crowcroft, Multipoint Communication: A Survey of Protocols, Functionsand Mechanisms, IEEE JSAC, Vol.15, N3, April 1997.

S. Floyd, V. Jacobson, S. McCanne, C.G. Liu, L. Zhang, A Reliable Multicast Framework for Light-

weight Sessions and Applications Level Framing, Proc. of ACM SIGCOMM95, October 1995. S. Paul, K.K. Sabnani, J.C. Lin, S. Bhattacharyya, Reliable Multicast Transport Protocol (RMTP),

IEEE JSAC, Vol.15, N3, April 1997.

S. Paul, Multicasting on the Internet and its Applications, Kluwer Academic Publishers, 1998.

http://www.mbone.com

3.Multicast2pp

Documents

Transcript of 3.Multicast2pp