Subject: [Megaco] Binary Encoding (Universal or Automatic Tag)

From: "Deepak Pokharna" <[email-masked]>
Date: Thu, 1 Sep 2005 08:08:34 -0700

Hi 

    I am having one query regarding ASN encoding of a megaco message.
According to draft it is said that automatic tagging should be used i.e
that

No where universal tag should be used then how we  should  start
encoding of a SEQUENCE let say MegacoMessage .

A0   14   A1 12   80   01.......    Let say we select A0 has tag of
SEQUENCE type of element.

30   14   30  12   80   01........     Here 30 is universal Tag for
SEQUENCE type of element.

     Out of above which one is correct encoded message.. Also to encode
a message should we use universal tag any where in message and what
should be starting value for a automatic tag in sequence . I am
attaching the draft section for your reference

      MEDIA-GATEWAY-CONTROL {itu-t(0) recommendation(0) h(8) h248(248) 

      modules(0) media-gateway-control(0) version2(2)} 

      DEFINITIONS AUTOMATIC TAGS ::= 

      BEGIN 

      MegacoMessage ::= SEQUENCE 

      { 

         authHeader     AuthenticationHeader OPTIONAL, 

         mess           Message 

      } 

      AuthenticationHeader ::= SEQUENCE 

      { 

         secParmIndex   SecurityParmIndex, 

         seqNum         SequenceNum, 

         ad             AuthData 

      } 

      SecurityParmIndex ::= OCTET STRING(SIZE(4)) 

      SequenceNum       ::= OCTET STRING(SIZE(4)) 

      AuthData          ::= OCTET STRING (SIZE (12..32)) 

      Message ::= SEQUENCE 

      { 

         version           INTEGER(0..99), 

         -- The version of the protocol defined here is equal to 2. 

         mId               MId,  -- Name/address of message originator 

         messageBody CHOICE 

         { 

            messageError      ErrorDescriptor, 

            transactions      SEQUENCE OF Transaction 

         },

Thanks in advance for your reply

Regards

Deepak

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