Subject: [Sigtran] Regarding INAP parameter Tags

From: prabath weerasinghe <[email-masked]>
Date: Wed, 24 May 2017 11:13:27 +0530

Hi All,

This is regarding INAP PDU encoding and decoding. I'm working on an INAP
protocol implementation and was referring  ASN.1 specification. Here
follows an excerpt from the spec for InitialDP.

InitialDPArg ::= SEQUENCE {
 *serviceKey [0] *ServiceKey,
 *calledPartyNumber [2] *CalledPartyNumber OPTIONAL,
 callingPartyNumber [3] CallingPartyNumber OPTIONAL,
 callingPartysCategory [5] CallingPartysCategory OPTIONAL,
 cGEncountered [7] CGEncountered OPTIONAL,
 iPSSPCapabilities [8] IPSSPCapabilities OPTIONAL,

As per the specification, serviceKey has the tag value of 0 and
calledPartyNumber has a tag value of 2 an so on. When I checked a sample
INAP pcap
INAP-Sample-PCAP
<https://www.cloudshark.org/captures/028324459536?filter=inap> , it was
showing the tag values for serviceKey and calledPartyNumber as 80 and 82 in
Hex.
Could anyone please explain the reason for the difference ?  Is there any
special way of encoding the tag value ?

Thanks and Regards,
-- 
Prabath Weerasinghe

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