- Checksum: This field contains 16-bit checksum.
- Source-Specific class D Address: this field contains a source-specific multicast
group address.
- Receiver’s address / an existing BNR’s address: This field specifies an address of
a multicast member. For the first three types of packets this field contains the
receiver address joining or leaving the multicast group. For the fourth type of packets
this field contains the address of the existing BNR.
In SReM the (“10”) message type is important in maintaining and updating the multicast tree.
With this type (i.e. “10”), the field of receiver’s address in the message (RqM) should be the
address of new branching node (not like other three types), which is stored in the existing
BNR’s MFT. This message is triggered if a RqM message with the type=(“10”) (i.e. a
leaving message) is arrived at an existing BNR which has only one forwarding branch in its
MFT, sent by this existing BNR (no longer being BNR now), and will be sent to and
terminated at its upstream BNR.
In the rest of the chapter the previous messages will be specified as RqMs(Type) and
RpMs(Type), where (s) is the state bit and can be either 0 or 1, and (Type) describes the
message type discussed before. For example, RqM1(11) is a non interrupt (s =1) request
message sent by one LMR towards the source on behalf of a new receiver join.
The third type of messages is the branching node messages, which consists of two branching
node messages, enquiry Branching node Message (eBNM) and replying Branching Node
Message (rBNM). The eBNM format shown in Figure 4.3 is as follows:
([src= the IP_branching node address; group address = (S,G); dest = IP_new LMR router, IP_next branching
node; previous branching node]).
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