Paradyne BitStorm 2400, User Manual

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1. BitStorm 2400 Overview
2400-A2-GB20-10 December 2002
1-9
Protocols
Extensive protocols and support exist for the distribution of multicast traffic across
the Internet and private GigE links. These protocols include Multicast Open
Shortest Path First (MOSPF), Distance Vector Multicast Routing Protocol
(DVMRP), and Protocol Independent Multicast (PIM, PIM SM, PIM DM).
It is assumed that one these routing protocols will be used to deliver the IP
multicast streams to the BitStorm 2400 IP DSLAM for delivery to subscribers. The
BitStorm 2400 will not directly participate in the routing protocols. In most
circumstances, the BitStorm 2400 will communicate with a router or Layer 3 switch
that performs these routing functions.
IP multicast packets are forwarded to the last router hop and are then delivered on
the router interface as specially formatted layer two broadcasts. Multicast support
is required in the BitStorm 2400 system to efficiently handle the forwarding of
multicast packets at Layer 2.
In the absence of multicast support, all multicast packets delivered to the
BitStorm 2400 IP DSLAM would be flooded to all ports (EtherLoop and Ethernet)
on the system. The result of this flooding is that all users would receive the traffic
for all of the multicasts that any user of the BitStorm 2400 had requested. This
would quickly overwhelm the bandwidth and resources of the system and end
stations.
Multicast support in the BitStorm 2400 system is based on the IETF Internet
Group Management Protocol (IGMP) standards Version 1 and Version 2.
Multiple versions of IGMP exist:
!
IGMP v1 – RFC 1112
!
IGMP v2 – RFC 2236
!
IGMP v3 – Draft
See
IGMP Protocols
on page 1-11 for more information on IGMP operations.
Multicast Support
Support for efficient IP multicasting is critical for streaming applications such as
digital video delivery. Simply replicating packets and sending them serially to users
will not scale. Multicast routing capability is currently available in most routers.
Multicast support for the BitStorm 2400 system will ensure that IP multicasts are
efficiently forwarded at Layer 2 to subscribers and blocked from non-subscribers.
The BitStorm 2400 system operates as an IP Multicast-aware Layer 2 Switch
(Layer 2+).
IP Multicast support involves:
!
Multicast Group Membership Management
!
Multicast Traffic Forwarding (Layer 2)