Subject: Clarification on the MGCP retransmission logic

From: Arun Kumar S <[email-masked]>
Date: Wed, 23 Aug 2000 20:03:52 +0530

Hi,

        I would like some clarifications on the re-transmission logic that is
mentioned
        in the MGCP RFC2705.
        I feel that the diagram and the text contradict and hence the need for the
clarification.

SCENARIO 1
-------------------
        When the GW started up it resolved the Call Agent's(CA) address and got a
single IP
        address (interface). Now a command was sent and the CA does not send an
ack.
        What is the expected behaviour of the GW with regard to the re-transmission
logic??
        The expected behaviour in the GW is,
        - The GW should retransmit the command Max1 times and query DNS on the
retry count
          reaching Max1 times, or
        - The GW should retransmit the command Max2 times and then query the DNS to
look for
          any new IP addresses.

SCENARIO 2
--------------------
        When the GW started up it resolved the CA's domain name into multiple IP
addresses (say 3).
        Now a command is sent to the CA and it does not respond with an ACK. The GW
re-transmits
        the command. The gateway should retransmit the command to the first IP
address in the list of
        IP addresses Max1 times. Once Max1 is reached,
        - The next IP (2nd) address in the original list is then tried after
re-setting the retry-count to zero
          for Max1 times again. Then the last (3rd) address is again tried for Max2
times before
          performing a DNS re-lookup. Then retransmissions are carried out in a
similar fashion with the
          new set of addresses.
        - A DNS query is performed on trying for Max1 times with the first address.
Then with the first
          address in the new set of IP addresses if re-transmission is performed, a
re-lookup will again
          need to be done after re-transmitting for Max1 times and so retry count
reaching Max2 times
          will never occur.

        Which of the two approaches above is correct?? OR is there any other way in
which the
        retransmission logic should work?? In other words referring to the diagram
on page 97 in
        RFC 2705 how do we interpret "(if N=Max1 or N=Max2 check DNS)"??
        What are the conditions under which we should query DNS (Single and
multiple IP interface)??

Regards,
Arun.S
___________________________________________________
Arun Kumar S
ishoni Networks (India) Pvt Ltd (http://www.ishoni.com)
...Broadband for everyone
email: [email-masked]
Phone: +91-80-2292125 (Work)
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