Subject: is Ack always transmitted by TCP ?

From: Taji Rachid <[email-masked]>
Date: Wed, 19 Jan 2000 17:34:48 +0100

Hi All;

What is the policy for reliability of ACK requests ?

By reading the RFC SIP ( chapter 10.6 ), I have understood that the only way
to ensure this reliability is to send the Ack request by TCP connection. Is
it mandotary to send Ack request by TCP even if  UDP is used for sending the
prior INVITE? 

Can you clarify this point ?

Thanks

Rachid

---

From: "Gary Cote" <[email-masked]>
Date: Wed, 19 Jan 2000 11:23:11 -0600

The ACK request certainly may be sent using UDP.
Reliable delivery is assured through a couple conventions.

1. The user agent server continues to retransmit the final
   INVITE response until it receives an ACK request.

2. The user agent client sends the ACK request each time it
   receives a final INVITE response.

Based on those two characteristics, if you actually map out
the message flow, you'll see that the ACK is reliably delivered.
If the ACK is lost in transmission, the user agent server will
retransmit the final INVITE response, which in turn causes the
the user agent client to re-send the ACK request.

 - Gary

--
Gary Cote
AWARD Solutions, Inc.
Richardson, TX

> -----Original Message-----
> From: [email-masked]
> [mailto:[email-masked]]On Behalf Of 
> Taji Rachid
> Sent: Wednesday, January 19, 2000 10:35 AM
> To: [email-masked]
> Subject: is Ack always transmitted by TCP ?
> 
> 
> Hi All;
>