Subject: [SIP] What does that 'maddr' mean?

From: 이희석 <[email-masked]>
Date: Sat, 14 Apr 2001 11:28:54 +0900

This is draft-ietf-sip-call-flows-04.txt.

3.1.5 Successful SIP to SIP through SIP Firewall Proxy

   User A          FW Proxy         Proxy 1          User B
     |                |                |                |
     |   INVITE F1    |                |                |
     |--------------->|   INVITE F2    |                |
     |    (100) F3    |--------------->|   INVITE F4    |
     |<---------------|    (100) F5    |--------------->|
     |                |<---------------|    (100) F6    |
     |                |                |<---------------|
     |                |                |      180 F7    |
     |                |     180 F8     |<---------------|
     |     180 F9     |<---------------|                |
     |<---------------|                |      200 F10   |
     |                |    200 F11     |<---------------|
     |     200 F12    |<---------------|                |
     |<---------------|                |                |
     |     ACK F13    |                |                |
     |--------------->|     ACK F14    |                |
     |                |--------------->|     ACK F15    |
     |                |                |--------------->|
     |    RTP Media   |        Both Way RTP Media       |
     |<==============>|<===============================>|
     |     BYE F16    |                |                |
     |--------------->|     BYE F17    |                |
     |                |--------------->|     BYE F18    |
     |                |                |--------------->|
     |                |                |     200 F19    |
     |                |     200 F20    |<---------------|
     |     200 F21    |<---------------|                |
     |<---------------|                |                |
     |                |                |                |

User A sends INVITE , ACK , BYE message to FW Proxy.
INVITE, ACK message have a maddr parameter in their Request-URI, 
but BYE message doesn't have maddr parameter.
is this why?

First of all,
I don't understand why the maddr parameter is needed in this flow.
and i want to know that general meaning of maddr parameter.

Best Regard.
Have a nice day!!!