Specifications

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Cisco MWR 2941 Mobile Wireless Edge Router Software Configuration Guide, Release 12.2(33)MRB
OL-21227-02
Chapter 1 Cisco MWR 2941 Router Overview
Features
ASM requires group address allocation within the network. At any given time, an ASM group should
only be used by a single application. When two applications use the same ASM group simultaneously,
receiver hosts of both applications will receive traffic from both application sources. This may result in
unexpected excess traffic in the network. This situation may cause congestion of network links and
malfunction of the application receiver hosts.
Note Release 12.2(33)MRB does not support Any Source Multicast.
Source Specific Multicast
Source Specific Multicast (SSM) is a datagram delivery model that best supports one-to-many
applications, also known as broadcast applications. SSM is a core network technology for the Cisco
implementation of IP multicast targeted for audio and video broadcast application environments and is
described in RFC 3569. Source specific multicast consists of
• Protocol Independent Multicast source-specific mode (PIM-SSM)
• Internet Group Management Protocol Version 3 (IGMPv3)
For the SSM delivery mode, an IP multicast receiver host must use IGMP Version 3 (IGMPv3) to
subscribe to channel (S,G). By subscribing to this channel, the receiver host is indicating that it wants
to receive IP multicast traffic sent by source host S to group G. The network will deliver IP multicast
packets from source host S to group G to all hosts in the network that have subscribed to the channel
(S, G).
SSM does not require group address allocation within the network, only within each source host.
Different applications running on the same source host must use different SSM groups. Different
applications running on different source hosts can arbitrarily reuse SSM group addresses without
causing any excess traffic on the network.
Protocol Independent Multicast
The Protocol Independent Multicast (PIM) protocol maintains the current IP multicast service mode of
receiver-initiated membership. PIM is not dependent on a specific unicast routing protocol; it is IP
routing protocol independent and can leverage whichever unicast routing protocols are used to populate
the unicast routing table, including Open Shortest Path First (OSPF), Border Gateway Protocol (BGP),
and static routes. PIM uses unicast routing information to perform the multicast forwarding function.
Although PIM is called a multicast routing protocol, it actually uses the unicast routing table to perform
the reverse path forwarding (RPF) check function instead of building up a completely independent
multicast routing table. Unlike other routing protocols, PIM does not send and receive routing updates
between routers.
PIM is defined in RFC 2362, Protocol-Independent Multicast-Sparse Mode (PIM-SM): Protocol
Specification.