In SReM, the formats of RqM and RpM messages are similar to the format of IGMP
messages with some changes as follows:-
• The Max Resp. Time field in IGMP message is changed to a one bit flag field used by
SReM registration messages, called S flag.
• An address field is added to the payload of the message. This field carries the receiver
or the existing BNR address.
RqM and RpM are encapsulated in IP datagram, where the source is one of the LMRs and the
destination is always the multicast source. Figure 4.2 shows the format for RqM and RpM
messages.
|
0 7 15 31 | |||
|
Type |
S |
reserved |
Checksum |
|
Source-specific class D address | |||
|
Receiver’s address / an existing BNR’s address | |||
Figure 4.2 RqM / RpM message format
Where
- Type: This field for RqM or RpM message type :
> 11: specifies a member joining packet (RqM). This packet sent by the LMR.
> 00: specifies a membership confirmation packet (RpM). This is sent by the
source or BNR.
> 01: specifies a member leaving the multicast group (RqM). This packet is sent
by the LMR.
> 10: specifies the update of branching nodes (RqM). This is sent by the BNRs.
- S bit: This one bit field is set to 1 when the packet type is (11). For other types of it
is unset to 0. This field is sent with (11) packet with value 1 to indicate that any BNR
or IMR in the route can process this message. As soon as this packet processed by
one of BNRs or IMRs it is unset to the value of 0 which means that no more
processing is required from any of BNRs or IMRs.
- Reserved bits: for any future use.
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