Subject: [Megaco] Service Change Reason - ASN.1 binary encoding

From: "Maruo, Luciano Mikio" <[email-masked]>
Date: Mon, 3 Oct 2005 17:24:20 -0300

For the service change reason parameter it is stated in the Annex A.2 of
H.248.1 that 
 
"This string is first BER-encoded as an IA5String.
 The result of this BER-encoding is then encoded as
 an ASN.1 OCTET STRING type, "double wrapping" the
 value as was done for package elements."
 
For the service change reason "901 Cold Boot" which of the following
encoding is correct?

1) with IA5 String tag from X.690
A4 11 04 0F 16 0D 39 30 31 20 43 6F 6C 64 20 42 6F 6F 74
|  |  |  |  |  |  |--> 901 Cold Boot
|  |  |  |  |  |-----> length
|  |  |  |  |--------> tag for IA5 String (BER)
|  |  |  |-----------> length
|  |  |--------------> tag for octet string (ASN.1)
|  |-----------------> length
|--------------------> automatic tag for Service Change Reason  

2) without IA5 String tag from X.690
A4 0F 04 0D 39 30 31 20 43 6F 6C 64 20 42 6F 6F 74
|  |  |  |  |--> 901 Cold Boot
|  |  |  |-----> length
|  |  |--------> tag for octet string 
|  |-----------> length
|--------------> automatic tag for Service Change Reason 

Thank you very much,
Luciano Mikio Maruo

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