IP multicast Advisor: Prof. Wanjiun Liao Instructor: De-Nian Yang e-mail: [email protected].
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Transcript of IP multicast Advisor: Prof. Wanjiun Liao Instructor: De-Nian Yang e-mail: [email protected].
Multicast
• Why multicast?
• MBONE– Internet’s Multicast Backbone
– More than 2800 subnets in over 25 country by 1996 March
– A semi-permanent IP multicast testbed
– Use IP tunneling to send data– Multicast routing protocol: DVMRP, MOSPF, PIM
– How to join MBONE?
Related protocols• Group management protocol:
– IGMP(Internet Group Management Protocol)
• Multicast routing protocol:– Source-based tree
• Multicast tree per (S,G)
• DVMRP, MOSPF, PIM-DM
– Shared tree• Multicast tree per (*,G)
• CBT, PIM-SM
Ethernet
Host A Host B
RouterQuery Query
IGMP• The multicast router use IGMP to obtain the
group-membership information of the LAN.
Report Report
Periodically
Source-based tree
Source B
A
. Source A and B use the same multicast address to send data.. Intermediate routers use (S,G) to forward data.. Intermediate routers create forward entry while receiving data.
DVMRP
• Distance vector multicast routing protocol• Rely on distance vector based unicast routing prot
ocol(RIP)• For each (S,G), grow a shortest-path tree rooted on
the source• Use distance vector routing algorithm to support r
everse path multicasting(RPM)
DVMRP(cont’d)Receiver
Sender
SPT branch
Prune message
data
. Data and Prune messages will be sent periodically.
DVMRP(cont’d)Receiver
Sender
SPT branch
Graft message
. Receiver sends a graft message toward the to join the group quickly.
MOSPF
• Multicast open shortest path first routing protocol• Rely on link state based unicast routing protocol
(OSPF)• For each (S,G), grow a shortest-path tree rooted on
the sources• Use Dijkstra’s algorithm and group-membership L
SAs to compute shortest path tree
Shared tree
Source B
A
Sender
Receiver
Core
. Intermediate routers use (*,G) to forward data.. Receivers join the multicast tree before receiving data.
CBT
• Core based trees multicast routing protocol• For each group, grow a shortest-path tree rooted o
n the core.• To join a group, the DR sends a Join_Request tow
ard the core of the group.• Join_Ack is returned by an on-tree router or the co
re.
CBT(cont’d)
• To leave a group, the DR sends a Quit_Notification to its parent router.
• An on-tree router sends Echo_Requests and Echo_Replys to maintain the multicast tree.
• If the sender doesn’t want to join the group, it encapsulates data packets and unicasts them to the core.
Comparison of source-based tree and shared tree
• Source-based tree mechanisms scales worse than shared tree counterparts– Table size:
• Source-based tree: group * source
• Shared tree: group
– Large overhead• DVMRP: periodically sending prune message if group density
is low
• MOSPF: periodically flooding link states
Comparison of source-based tree and shared tree
• Shared tree mechanisms also have drawbacks– Core might be point of failure
– Larger delay than source-based tree counterparts
– Traffic concentration
• PIM uses hybrid architecture to gain advantages of source-based tree and shared tree.
PIM-SM
Data from S2
Data from S1
While the data rates of S1 and S2 areboth low, data travel through RP to the receiver.
PIM-SM
Data from S2
Data from S1
While the data rate of S2 is above somethreshold, DR of the receiver decides to switch the traffic from shared tree to source-based tree.
PIM-SM
Data from S2
Data from S1
While receiving data from S2 directly, theintermediate router sends a prune message to RP.
Prune message
More about multicast• Why shortest path tree? Is it reasonable?• Multicast with QoS
– QoS routing
– Multi-path reservation
– IP multicast in MPLS and differentiated service network
– QoS extension to legacy multicast routing protocols
• Multicast with mobility• Reliable multicast• Secure Internet multicast