|
group address |
source |
Destination(s) |
|
(SG) |
IP_address (N2) |
IP_address (N1) |
Figure 4.14 Example of rBNM in SReM
4.5 Delivery of Packets
4.5.1 SReM header and packet delivery
Data packets delivery happens by using unicast packet delivery from the source to the next
BNR. These packets travel between BNRs until they reach the LMRs, from there they are
forwarded using the standard multicast. The data packet format used in SReM is similar to
the packet format used for unicast data packet with some differences. At SReM data packet,
the IP destination address is always the next BNR hop. Also the pair of (S,G) that distinguish
each multicast session is added to the header. Figure 4.15 shows the data packet format with
SReM header.
To multicast a data packets, a SReM header is added to each packet by BNRs (including the
source itself). Each BNR encodes the address of one next BNR in data packet, which leads to
a fixed size of packets towards the next BNR.
IP Header SReM Header Payload
I
Group Address Destination Address
(S,G) (Next BNR)
Figure 4.15 SReM Header format in Data Packet
At the start of multicasting, the source will send a copy of data packet with respective SReM
headers to all BNRs in its MFT. Upon receiving this packet, each BNR needs to properly
process the SReM header and performs the following steps for processing the data packet:
- Checks its MFT and replicates the packet so that there is only one copy of the packet
for each of its next BNRs.
- Modifies the SReM header in each data packet copy by changing the destination IP
address to the IP address of the next BNR.
- Sends the modified copies of the data packets to their destinations unicastly.
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