Transcript PPT

IP-Multicast
An Introduction
How to solve the “many to many”
communication problem?
Peter Parnes
LTU-CDT/Marratech AB
Telia Research AB - 980827
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Overview
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Peter Parnes, CDT
Multicasting
MBone
Applications
Conferencing Tools - MBone and mStar
Protocols
MBone and the Internet
Usage
Research issues and further development
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Many to Many
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How to implement “many-to-many”
traffic?
1. Central server: Have a central server that
duplicates packets to all other members.
2. (Fully) connected mesh: Let every member
have a connection to all/some other
members.
3. Multicasting: Let the network duplicate the
packet when needed.
1 and 2 wastes bandwidth!!!!
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IP Addressing
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The TCP/IP family includes four types of
distribution of a packet 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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IP Addressing
 Anycast: To one host of a group of hosts
 To access a resource that is served by several
computers
 IP6
 The packet is “seen” by one off the receiving
hosts
 Multicast: To a group of hosts
 The packet is seen by all hosts in the group
 The packet is only duplicated when needed
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Multicast vs. Unicast
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Multicasting
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Multicast traffic uses a special range of
IP-addresses:
 224.0.0.0 - 239.255.255.255
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A host much 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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MBone?
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The MBone is both a network-technology
and a suite of tools.
 The network part is today deployed as a
virtual network on the Internet. Sites need to
have special MBone-feeds. The setup is
handled manually (but only once for each
site)
 The tools consists today primarily of
conferencing tools but more is coming...
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Applications
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The MBone is today used for:
 “Broadcasting”: conferences, meetings,
seminars, concerts and radio-stations are
multicasted daily.
 Conferencing: The MBone is used for
traditional video-conferencing (but MUCH
cheaper!!)
 News: Distribution of Usenet-News
 M-FTP: Multi-user File Transfer
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Applications Tomorrow
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Applications tomorrow include:
 Software-distribution: Forget the very
costly procedure of new software CDs for
each new release and bug-fix! Just supply
the latest version in a known multicastgroup.
 Mirroring: Instead of letting each client
fetch all new files from a server, send out the
changed files using multicast!
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Applications Tomorrow
 Real News: All news is transmitted on the
net. Indexed and ready. (Reuters have this
since 1996!)
 TV: Why not watch your favourite TVchannel over the network?
 File-Caches: If all file-requests are issued
using multicasting it’s much easier to cache
them locally!
 And much much much.......
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Conferencing tools
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The MBone tools today consists of:
 SDR: The session directory, “the channelguide”
 WB: A distributed white-board (postscript
and text)
 VIC: A video-tool
 VAT/RAT: Two audio-tools
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mStar!
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MBone bild extern!
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Extern bild!
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The mStar Family
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A family of tools for scalable distributed
electronic teamwork.
It supports a number of different
conferencing media:
 audio/video
 shared whiteboard, chatting, voting
 Web based electronic presentations
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multicast Audio: mAudio
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Video - VIC
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multicast Web: mWeb
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multicast WhiteBoard: mWB
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multicast Vote: mVote
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multicast Chat: mChat
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multicast Media On Demand: mMOD
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As all traffic is network and multicast
based, it is very easy to record it.
mMOD is another member of mStar that
support recording and later playback.
Web based control
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multicast Tunnel: mTunnel
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Some links do not support multicast
 ISDN, analog modem
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mTunnel allows for easy tunnelling of
multicast traffic over non-multicast links.
It also allows for traffic transformation:
 recoding, mixing, switching, scaling
 This allows users to join into high bandwidth
sessions even if they do not have the needed
bandwidth.
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mStar Design Issues
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Scalable: The environment should scale to a
very large number of users - IP-Multicast is the
solution!
Robust: The environment should survive
network failures and not be dependent on any
central services
Accessible: Users should be able to participate
from their desktop
Network based: No need for any special ISDN
connections, just the standard local network and
the Internet.
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Protocols
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MANY different protocols involved with
Multicasting - UDP, RTP, SRM, MTP-2,
MTCP
UDP: User Datagram Protocol
 Unreliable == Packets can be lost
 The applications has to take care of
reliability
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RTP
RTP - Real-Time Transfer Protocol
 Developed by the IETF (RFC1889/90)
and later copied into ITU/H.225.
 End-to-End transport functionality for
real-time data
 Designed for multicasting
 Completely network layer independent
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Reliable Multicasting
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No standard today (IETF/ITU are not
working on this problem although several
other groups are)
Multicast Transport Protocol 2 - MTP2
 NACK based
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Fanout TCP - MTCP
 Star-topology with a TCP connection to each
receiver
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Reliable Multicasting
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Scalable Reliable Multicasting - SRM
 NACK based - every member participates in
repairs and not only the original sender of a
packet
 Used in the MBone WB
 I have designed a RTP-extension to include
SRM.
 This is today implemented and used in the
mStar WhiteBoard.
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More Protocols
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Session Description Protocol - SDP
Session Announcement Protocol - SAP
Real-time Streaming Protocol - RTSP
Session Initiation Protocol - SIP
Receiver-based Layered Multicast - RLM
Plus many more….
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MBone and the Internet
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To simplify the development process of
the MBone-network, it was first deployed
as a virtual network using IP-tunnels
but is now changed into a standard IPservice == all routers need to know about
multicasting
Multicasting is both an Internet and an
Intranet technology
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Usage Scenarios of mStar
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Electronic Meetings
 Meeting using your desktop computer
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Distance Education
 Distribution of lectures over the Internet
where participants can ask questions and be
active
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Electronic Corridor
 Daily work where users run the tools 24
hours a day
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Usage Examples
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Education Direct
 Distribution of lectures to the county of
Norrbotten
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Ericsson Erisoft
 Electronic meetings and teamwork between their
offices and Ericsson in Stockholm and other
countries
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Daily work at CDT
 mStar is used for electronic meetings, the
electronic corridor, multicast of seminars and
courses
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Future Research Issues
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Multicast address allocation - MALLOC
Layered encodings for both audio and
video
Better bandwidth control (TCP-friendly)
New audio and video encodings that
perform better in lossy environments.
H.323/T.120 integration/interoperability
Better security
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Further Development of mStar
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Marratech AB
Collaboration projects with TRAB
 Roxy
 MediaSite
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Education Direct
CDT Distributed Software Lab - NUTEK
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Native Multicast in Sweden
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SUNET: The whole network
Telia: Almost working in the county
network. Nothing in the rest of the
production network
Tele-2: Nothing yet
GlobalOne: Full native multicast support
in their backbone network
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Summary
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IP multicast provides a scalable solution
for “many-to-many” communication.
A number of tools are being deployed on
the Internet today to utilize the power of
IP multicast.
mStar being turned into a product.
Native multicast is slowly being deployed
around the world.
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Questions?
[email protected]
http://www.cdt.luth.se/~peppar/
http://www.cdt.luth.se/mStar/
http://www.marratech.com/
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Multicasting and FireWalls
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Political question NOT technical
There is nothing special about
multicasting in comparison to other IPtraffic. There are four solutions to the
FireWall problem:
1 Open the wall for all multicast-traffic.
Simple and a router can control which
networks within a company should have
MBone access.
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Multicasting and FireWalls
2 Set up a tunnel through the wall
3 Rent a dedicated line that isn’t connected to
the rest of the companies network and is
only used for Multicasting
4 Stay behind the rest and don’t use
multicasting at all! :-)
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