Multicast Introduction Group management Routing Real-time - - PowerPoint PPT Presentation

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Multicast Introduction Group management Routing Real-time - - PowerPoint PPT Presentation

Jul 10, 2023 275 likes •797 views

Multicast Introduction Group management Routing Real-time transfer and control protocols Resource reservation Session management MBone Petri Vuorimaa 1 Introduction There are three ways to transport data in

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Petri Vuorimaa 1

Multicast

  • Introduction
  • Group management
  • Routing
  • Real-time transfer and control protocols
  • Resource reservation
  • Session management
  • MBone
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Petri Vuorimaa 2

Introduction

  • There are three ways to transport data in computer

networks:

+ Unicast + Broadcast + Multicast

  • Broadcast and multicast require special group

addresses

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Petri Vuorimaa 3

Unicast

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Petri Vuorimaa 4

Broadcast

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Petri Vuorimaa 5

Multicast

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Petri Vuorimaa 6

Protocols

  • Group management
  • Routing
  • Real-time transfer and control protocols
  • Resource reservation
  • Session management
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Petri Vuorimaa 7

Group Management

  • 1. Group addresses
  • 2. Mechanism to join the groups
  • 3. Routing protocols
  • 4. Generation and control of the data
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Petri Vuorimaa 8

Group Addresses

  • IPv4: class D

+ addresses 224.0.0.0 - 239.255.255.255 + addresses 244.0.0.0 - 244.255.255.255 are reserved for routing etc.

  • IPv6:

+ flags: fourth bit tells whether the route is permanent + scope: tells how wide the group is

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Petri Vuorimaa 9

IPv4 vs. IPv6

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Petri Vuorimaa 10

Joining to The Groups

  • Two alternatives:

+ A) The computer tells the router it wants to join a group + B) The router announces the groups and asks the hosts to join

  • The latter case uses the Internet Group

Management Protocol (IGMP) protocol

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Petri Vuorimaa 12

Routing

  • The router looks the next target from a routing

table

  • The routers exchange and update the information

in the routing tables

  • Two basic methods:

+ Distance Vector + Link Status

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Petri Vuorimaa 13

Routing table

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Petri Vuorimaa 14

Distance Vector

  • Router tell its distance to other routers to its

neighbors

  • Easy to compute
  • Does not work well, if there a often

disconnections between routers

  • Does not scale well
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Petri Vuorimaa 15

Operation

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Petri Vuorimaa 16

Link Status

  • The routers exchange information about

connections instead of distances to other routers

  • The receiving router updates the information

about the available routers

  • The routes are calculated using the Dijkstra’s

shortest path algorithm

  • This method scales better
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Petri Vuorimaa 17

Multicast Routing

  • Multicast routing is also based on routing tables
  • In addition, the routers build a multicast tree
  • The dynamic changes of the multicast tree is the

problem

+ Old members leave and new join the Multicast tree

  • The biggest problem is scaling
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Petri Vuorimaa 18

Pruning

  • The multicast trees can grow very big, so they

have to be pruned constantly

  • Branches, which do not have hosts, are removed

from the multicast tree

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Petri Vuorimaa 20

Flooding

  • Flooding is the easiest way to build the multicast

trees

  • Multicast packets are flooded to all output ports of

the router

  • A router forwards those packets which it has not

seen previously

  • Unnecessary branches can be pruned later on
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Petri Vuorimaa 21

Pruning

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Petri Vuorimaa 22

Multicast Routing Protocols

  • Distance-Vector Multicast Routing Protocol

(DVMRP)

  • Multicast Extension to Open Shortest Path First

(MOSPF)

  • Protocol Independent Multicast (PIM)
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Petri Vuorimaa 23

DVMRP

  • Distance Vector Multicast Routing Protocol

(DVMRP) is based on RPM algorithm

  • Original Mbone routing protocol
  • Easy to implement
  • Does not scale well
  • Works well only with distance vector routing

protocols

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Petri Vuorimaa 24

MOSPF

  • Multicast Extension to Open Shortest Path First

(MOSPF) is based on link state method

  • Multicast packets are flooded only to nearby area
  • The tree is build as usual
  • Then the tree is pruned to a multicast tree
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Petri Vuorimaa 25

Properties of the MOSPF

  • Reacts fast
  • Computation of the trees is heavy
  • Works only with link state protocols
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Petri Vuorimaa 26

PIM

  • Protocol Independent Multicast (PIM) is

independent of the actual routing protocol

  • Two versions:

+ Dense Mode (PIM-DM) + Sparse Mode (PIM-SM)

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Petri Vuorimaa 27

Real-time transfer protocols

  • Protocol family

+ Real-Time Transport Protocol (RTP) + Real-Time Control Protocol (RTCP) + Real-Time Streaming Protocol (RTSP)

  • Suitable for general continuous media transport -

not just multimedia

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Petri Vuorimaa 28

Relationships of the protocols

RTSP RTP/ RTCP Reliable Multicast RSVP UDP TCP IP

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Petri Vuorimaa 29

RTP

  • Real-Time Transport Protocol (RTP)

+ sequences numbers of the packets + time stamps + identification of different payloads

  • Operates usually on top of UDP
  • Does not guarantee successful transport -> no QoS

properties

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Petri Vuorimaa 30

Application RTCP RTP Media UDP IP AAL5 ATM ST-II IPX Ethernet Signaling Conference control

RTP and other protocols

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Petri Vuorimaa 31

RTCP

  • Real-Time Control Protocol (RTCP) controls RTP

connections

  • Functions:
  • 1. Transfers information about the RTP connection (e.g.,

QoS)

  • 2. Transfers information about source of the RTP

connection

  • 3. Limits the amount of control information (5 %)
  • 4. Transfers information about the session
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Petri Vuorimaa 32

RTSP

  • Real-Time Streaming Protocol (RTSP) builds and

manages the real-time transport connections

  • Works well with RTP and RTCP protocols
  • Has similar functions to the HTTP protocol
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Petri Vuorimaa 33

RTSP - Operation

HTTP GET SETUP PLAY RTP audio PAUSE TEARDOWN RTP video Web Server Multimedia Server Web browser Media Player Workstation

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Petri Vuorimaa 34

Resource reservation

  • Real-time transfer protocols do not alone

quarantine QoS of real-time traffic

  • Required resources have to be reserved separately

from all routes of the route

  • For this purpose, there are special protocols
  • Best known protocol is Resource ReSerVation

Protocol (RSVP)

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Petri Vuorimaa 35

RSVP

  • RSVP is based on announcements made by the

receivers

  • The sender sends first a “Path” message
  • If necessary, the routers can send “PathErr”

message

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Petri Vuorimaa 36

RSVP (cont.)

  • Routers record the connections

+ Soft state + each connection has a cleanup and restart counter

  • The receiver sends the “Resv” message

+ at the same time, the QoS requirements are defined

  • The “Resv” messages go through the routers

+ the routers check the resources and make final reservations

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Petri Vuorimaa 37

RSVP messages

Sender Receiver 1 Receiver 2 Receiver 3 “Path” message “Resv” messages

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Petri Vuorimaa 38

Soft state

  • Each connection has to be recorded
  • The information is outdated after certain time

period

  • That is why the state is called soft
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Petri Vuorimaa 39

QoS requests

  • The receivers use “Resv” messages to ask for

certain QoS parameters

  • Each router checks whether there is enough

resources

  • If there is, then the connection is recorded (soft

state)

  • If necessary, the requests can be combined

(multicast)

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Petri Vuorimaa 40

RSVP combination

“Resv” message (31 Mbps) “Resv” message (15 Mbps) Connection point Combined “Resv” message (31 Mbps)

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Petri Vuorimaa 41

RSVP status

  • Not in wide use
  • Problems

+ scaling of the method (control, connections, reestablishment of the connections) + good algorithm for checking resources does not exist + billing and bookkeeping difficult

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Petri Vuorimaa 42

Session management

  • The available multicast sessions have to be

advertised some how

  • Thus directory services are needed
  • Three protocols exist for this purpose: SDP, SAP,

and SIP

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Petri Vuorimaa 43

SDP

  • Session Description Protocol (SDP) distributes

information about the available sessions and the attributes

  • SDP is actually a format to announce the

information

  • Three parameter classes:

+ Session description + Time description + Media description

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Petri Vuorimaa 44

SAP

  • Session Announcement Protocol (SAP) distributes

the session descriptions to different directories

  • Announcements are send as multicast

transmissions

  • Email lists and www-pages are used more often,

though

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Petri Vuorimaa 45

SIP

  • Session Initiation Protocol (SIP) can be used,

when certain participant have to be invited to the multicast session

  • The participants can be persons or “robots”
  • Robots are video-on-demand servers, video

cameras, etc.

  • SIP can use directory services when searching

persons

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Petri Vuorimaa 46

Robots

Directory Multimedia session Person Person Chairman Invited person Media server Announces SIP RTSP

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Petri Vuorimaa 47

Person search

  • 1. Call henning@

cs.columbia.edu

  • 2. henning
  • 3. hgs@play
  • 4. Call

hgs@play

  • 5. 200 OK
  • 6. 200 OK

hgs@play cz@cs.tu-berlin-de

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Petri Vuorimaa 48

MBone

  • Originally developed in research project

+ University of Southern California’s Information Sciences Institute + Massachusetts Institute of Technology + Xerox Palo Alto Research Center + Lawrence Berkeley National Laboratory

  • DARPA Research Test bed, DARTNET -90

+ Unix workstation, T1 connections

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Petri Vuorimaa 49

MBone - development

91 92 93 94 95 96 DARTNet multicast vt vat IETF audiocast ivs nevat wb nv vic nte rat sdr 32 subnetworks MBone grows 3000 subnetworks

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Petri Vuorimaa 50

Mbone archives

  • Merit Networks

+ www.merit.edu/~mbone/index/titles.html

  • Henning Schulzrinne

+ www.cs.columbia.edu/~hgs/rtp/

  • Mbone FAQ

+ www.cs.columbia.edu/~hgs/internet/mbone-faq.html