Subject: [Megaco] question on Message Identifier (MID) of H.248 messages

From: "Oikonomou, Ioannis" <[email-masked]>
Date: Fri, 13 Jan 2006 10:46:23 +0200

Hello,

I have a question concerning the Message Identifier (MID) of H.248
messages:

*       In the H.248 standard it says that:

The Message Identifier (MID) of a message is set to a provisioned name
(e.g. domain address/domain name/device name) of the entity transmitting
the message. Domain name is a suggested default. An H.248.1 entity
(MG/MGC) must consistently use the same MID in all messages it
originates for the duration of control association with the peer
(MGC/MG).

*       In paragraph 3.1.1 (MGC accepting registration) of
draft-ietf-megaco-callflows document (Madhubabu, et al.), the following
flow is presented:

Step 1:
MG to MGC:
   MEGACO/1 [209.110.59.34]: 20000
   Transaction = 1234 {
       Context = - {
           ServiceChange = ROOT {Services {
               Method=Restart,
               ServiceChangeAddress=15000, Profile=ResGW/1,
                      12345677T87654320}
           }
       }
   }

Step 2: 
MGC to MG:
   MEGACO/1 [216.33.33.61]:2944
   Reply = 1234 {
      Context = - {ServiceChange = ROOT {
        Services {ServiceChangeAddress=25000, Profile=ResGW/1 , 
                         12345678T87654321} } }
   }

Step 3:
MGC to MG:
   MEGACO/1 [216.33.33.61]:25000
   Transaction = 9999 {
       Context = - {
           Modify = * {
                  Events = 1234 {al/of}
           }
       }
   }

Step 4:
MG to MGC:
   MEGACO/1 [209.110.59.34]:15000
   Reply = 9999 {
      Context = - {Modify = A1}
      Context = - {Modify = A2}
      Context = - {Modify = A3}
   }

Because of port redirection by both sides (MG requests at Step 1 further
communication to port 15000, MGC requests at Step 2 further
communication to port 25000), the MID of H.248 messages is changed:

For MG: In Step 1 it uses "[209.110.59.34]:20000", while from Step 4 and
on, "[209.110.59.34]:15000" is used.

For MGC: In Step 2 it uses "[216.33.33.61]:2944", while from Step 3 and
on, "[216.33.33.61]:25000" is used.

*       Questions:

My opinion is that the above procedure is correct; since port
redirection is used, it makes sense that the MID is changed once during
the registration procedure.

What is your opinion?

Thank you in advance,

Ioannis Oikonomou

Siemens AE

Athens, Greece

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