Technical Seminar Presentation - 2004
Transcript of Technical Seminar Presentation - 2004
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Manas Ranjan Panda
Technical Seminar Presentation - 2004
IP MULTICASTING
Presented by
Manas Ranjan Panda
Roll # CS200117174
Under the Guidance of
Mr. Debananda Kanhar
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Technical Seminar Presentation - 2004
INTRODUCTION
The TCP/IP family includes four types of distribution of apacket 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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INTRODUCTION CONTD
Anycast:To one host of a group of hostsTo access a resource that is served by several
computers
The packet is seen by one of the receiving hosts
Multicast:To a group of host
The packet is seen by all hosts in the group
The packet is only duplicated when needed
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PICTORIAL REPRESENTATION
A A
B C D B C D
UNICAST MULTICAST
A
B C D
BROADCAST
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A
B
C
D
E
X
Y
Z
Flow of data in multiple unicasting
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Technical Seminar Presentation - 2004
A
B
C
D
E
X
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Flow of data in multicasting
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IP MULTICAST ADDRESSES
IP multicasting uses class D addressesThe first four bits are 1110
The remaining 28 bits specify a multicast group
Multicast addresses:
range is from 224.0.0.0 to 239.255.255.255
lowest address 224.0.0.0 reserved
up to 224.0.0.255 for routing /group
maintenance
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Technical Seminar Presentation - 2004
IP MULTICAST ADDRESSES CONTD
A multicast address
can only be used as a destination address
cannot appear in the source address field or in a
source route.
4 28 bits
class D
Total 2^28-256=268 million addresses
1110 Multicast Group ID
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MULTICAST SCOPE
Members have scope
Members in a single network: scope is the
network
Members in a single organization: scope is
the organization
A host must have to 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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To participate in a multicast that spans multiple networks,
the host must inform local multicast routers
Local routers pass membership information to other
routers IGMP is used to communicate group membership
information
It uses IP datagrams to carry messages
It is a standard for TCP/IP and is required on allmachines that receive IP multicast
IGMP is considered an integral part of IP, not separate
INTERNET GROUP MANAGEMENT
PROTOCOL(IGMP)
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IGMP has two phases
Phase 1: A host joins a multicast group
It sends an IGMP message declaring its membership
Local multicast routers receive the message andpropagate group membership information
Phase 2: Local multicast routers poll hosts to see whothe remaining members are
As long as at least one host responds, the routerkeeps the group active
If none respond, the router stops advertising
INTERNET GROUP MANAGEMENT
PROTOCOL(IGMP)
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IGMPv1
Stands for Internet Group Management Protocol
Manages multicast group membership
Runs between hosts and their immediate
neighboring router
Only two kinds of packets: query and report
Packet format
4 4 4 16 bits
vers ion type unus ed checks um
class D multicast group address
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IGMPv2
Adds an explicit Leave message
Routers can more easily determine when a
group has no interested listeners on a LAN
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Multicast Trees
Paths define a forwarding tree, or a delivery tree The tree contains no cycles Each multicast router corresponds to a node in the tree A network connecting the routers is an edge in the tree The source of a datagram is the root The last router on the path is a leaf
A forwarding tree defines a set of paths through multicastrouters from a source to all members of a multicast group
(size of tables is a concern)
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The Essence of Multicast Routing
A Multicast Router must have knowledge of group
membership
Group membership information must be propagated
across the internet Because membership can change rapidly, information
at a given router is imperfect and routing may lag
changes
Design tradeoff: routing overhead and inefficient datatransmission
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Reverse Path Multicasting
Underlying assumptions
It is more important for a datagram to reach eachmember of the group than it is to eliminateunnecessary transmission
Multicast routers contain a routing table with correctinformation
Needless transmission is eliminated when possible
RPM uses a two-step process
Copies of datagrams are broadcast to the internet Multicast routers inform each other of paths that dont
lead to group members
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Membership information is propagated bottom-up
It starts with hosts that join or leave the group
Hosts communicate with their local router using IGMP
When a router learns that no group member lie beyond a
given network interface, it stops forwarding and notifies therouter on the path back to the root
When a router learns that there are no members along a path,that path ispruned
The system is data-driven
A router does not send group information until datagramsarrive for this group (data arrives and we know where tosend messages)
Reverse Path Multicasting
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RPF
Stands for reverse path forwarding Simple algorithm developed to avoid duplicate packets on
multi-access links
RPF algorithm takes advantage of the IP routing table to
compute a multicast tree for each source.
RPF check
When a multicast packet is received, note its source (S) and
interface (I)
IfI belongs to the shortest path from S, forward to all interfaces
except I
If test in step 2 is false, drop the packet
Packet is nevernever forwarded back out the RPF interface.
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IPv4 multicast routing protocols
DVMRP (Distance Vector Multicast Routing Protocol)
PIM-DM (Protocol Independent Multicast, Dense Mode)
PIM-SM (Protocol Independent Multicast, Sparse Mode) CBT (Core-Based Tree)
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DVMRP
First multicast routing protocol ever deployed in the Internet Each router maintains a multicast routing table by
exchanging distance vector information among routers
Constructs a source tree for each group using reverse
path forwarding
There is a designated forwarder in each subnet
Multiple routers on the same LAN select designated
forwarder by lower metric or lower IP address (discoverwhen exchanging metric info.)
Once tree is created, it is used to forward messages from
source to receivers
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PIM-DM
Similar to DVMRP
Floods multicasts out of all interfaces except the
source interfaceUses RPM
Prune message to eliminate unneeded branches
Protocol-independent
Needs to establish its own router-to-router dialogs
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PIM-SM
Designed to provide efficient communication betweenmembers of sparsely distributed groups
Rendezvous point (RP) are used by senders to
announce their existence and by receivers to learn
about new senders of a group Requires host group members explicitly join a
delivery tree by transmitting Join message
One set of RPs per sparse-mode domain, not per
group. Each group has precisely one RP at any given time.
DR sends Join/Prune messages toward the RP and
maintain the active RP
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CBT
Construct a single tree shared by a Group Protocol independent
Core router equivalent to RP
CBT state bi-directional
Data flows in either direction along the branch Advantage
Less traffic
Better scalability
Disadvantage Bottleneck at CR
Single point failure
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Protocol Independent Multicast (PIM)
PIM consists of two protocols
PIM Dense Mode (PIM-DM) Most networks have hosts that listen to each multicast group
Uses RPF to broadcast datagrams to every group
Strops sending when it receives prune requests Assumes router also uses conventional routing protocols
PIM Sparse Mode (PIM-SM) Members of multicast groups occupy a small subset of possible
networks
Like CBT, requires a point to which joins are sent
Builds a forwarding tree, trees rooted at rendezvous point
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MULTICAST APPLICATIONS
Multicast VideoconferencingMulticast NewsfeedsMulticast Access to On-Demand ServicesNon-media Applications
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[1] Banikazemi,MohammadIP Multicasting: Concepts, Algorithms, andProtocols
http://www.cis.ohio-state.edu/~jain/cis788-97/ip_multicast/index.htm
[2] Juan-Mariano de Goyeneche, Multicast over TCP/IP HOWTO
http://www.tascnets.com/mist/doc/mcpCompare.html.
[3] Williamson, Beau. Developing IP Multicast NetworksIndianapolis: Cisco
Press,2000. Multicast Quick Start Configuration Guide
http://www.cisco.com/warp/customer/105/48.html
[4] Dave Price, Sandy Spence, University of WalesJANET Technical
Guides
http://www.ja.net/documents/
[5] Forouzan Behrouz A. , Data Communications and Networking, 2nd edition,
TATA McGRAW-HILL Edition
REFERENCES
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Thank you !