HP 200 Series Services And Applications page 294

Linking Up with Frame Relay
Local Management Interface
to the network. The network will respond with a full status reply, which
indicates that DLCI 100 is available (active and new bits set). Both routers
are now able to communicate.
When R3 comes on line and sends its full status poll to the network, the
network will respond with a full status reply indicating that DLCIs 131 and
132 are available. R1 and R2 will learn about the availability of PVCs to R3
after they send their next full status poll to the network. This continues until
each router knows about the PVCs to each of the other routers.
If one of the routers fails or is powered off, the remaining routers are
informed that its DLCI to the affected router is "inactive" (active bit cleared).
Multicast
An optional feature of the FRF's LMI is the ability to send a frame to all user
devices that belong to a multicast group. In essence, a router transmits a
single frame to the network (on a special multicast DLCI), and that frame is
delivered to all members of the multicast group. This is a useful feature for
the transmission of routing updates and other types of broadcast messages.
The FRF's LMI reserved four DLCIs for this use. The multicast feature is not
available in ANSI T1.617 Annex D.
Without multicast support, by contrast, whenever a broadcast message such
as a routing update must be sent, it is transmitted on each DLCI. In figure 2,
for example, when R1 broadcasts a routing update (RIP, OSPF, etc.), it is
sent three times—once on each DLCI to each of the other routers.
As a practical matter, the multicast feature is of limited value. Since there
are only four DLCIs reserved for multicast, it is impractical to offer this
feature on public networks. Multicast support probably offers the greatest
utility on private Frame Relay networks.
StrataCom, one of the leading suppliers of Frame Relay switches to public
networks, has recently withdrawn its support for multicast capability on its
Frame Relay switches. It is therefore doubtful that this feature in its current
form will find much use on today's Frame Relay networks.
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