CR-Mode

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No we will discuss about Reliable Transfer on Multi-access Links with Conditional Receive Flag. This bit indicates that receivers should only accept the packet if they are in Conditionally Received mode. A router enters Conditionally Received mode when it receives and processes a HELLO packet with a SEQUENCE TLV and find its own Router information

By default Conditional Receive will not be set

1. Router R8 is sending a multicast update packet out to this multi access segment with Seq-15 and Ack-0	.
.	2-R10 will send Ack with Seq-0 & Ack-15 And assume that Ack is lost in the network
.	3-R11 will send Ack with Seq-0 & Ack-15
Received by R8---------------------------------------- Received by R8---------------------------------------	4- R12 will send Ack with Seq-0 & Ack-15
Now after the retransmission timer expire Router R8 will send update to R10 , but before that timer expire if router R8 gets new changes and has to send new update to this Multi-access segment but that update must not send to R10 because it has not received last Ack and is in Queue, so it will first send a new Hello packet over this Multi-access segment that contains Router R10 address in Squence_Type_TLV with next update Sequence number.	.

5- Router R8 will send Hello with Seq-0, Ack-0 & SEQ_TLV (R10 ) & next-update Seq 16	.
.	6-Router 10 Receive the hello & will find its entry so it will not set CR-mode for this Seq
.	7-Router 11 Receive the hello and did not find its entry and will set CR-Mode
.	8- Router 12 Receive the hello and did not find its entry and will set CR-Mode

9-Rotuer R8 will send Multicast update over this Multi-access segment with Seq-16, Ack-0 & CR-Flag=1	.
.	10-Router R10 will ignore this update because this update contains CR-Flag and Router R10 is not in CR mode
.	11-Router R11 will get the update and sends Ack Seq-0, Ack-16
.	12-Router R12 will get the update and sends Ack Seq-0, Ack-16

Here we can see the information

        *R8 is sending hello with Sequence TLV
        *R8 is sending update with CR-Flag to Multi-Access Segment
        *R10 is ignoring update and is not sending any ACK.
        *R11 is sending ACK
        *R12 is sending ACK

Now after this process Router R8 will try to do a retransmission for last packet With Seq 15	.
13-Router R8 will send unicast update to Router R10 with Seq-15, Ack-0	.
.	14-Router R10 Receives it and send Ack with Seq-0, Ack-15
15- Router R8 will send unicast update to Router R11 with Seq-16, Ack-0	.
.	16- Router R10 Receives it and send Ack with Seq-0, Ack-16

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