[Winpcap-users] Probloem with h.323 protocol in reading headers
jithinpg007 at gmail.com
Sat Mar 20 03:59:31 PDT 2010
Hi, i am using WinPcap with MSVC for monitoring VoIP calls using H.323 over
a LAN. I've studied about the protocol and found that it uses h.225 messages
for call signaling purposes. I am able to get the h.225 session descriptions
with winpcap but not in plaintext. the packets were encrypted and i found
out that session descriptions in h.323 are ASN.1 encoded using PER method.
since i am not familiar with ASN.1 and PER encodings and also there is no
available examples on internet about this, i'm very much confused on how to
extract the actual messages from this encoded raw binary format. The web had
some examples on DER and BER encodings, but PER is mentioned rarely and in
some places it is described in a way which can only be digested by an
expert. Since i am a novice, i need a sample code in C or C++ for converting
these PER encoded bytes into readable ASN.1 format. I can then compile the
ASN.1 messages back to C data structures.
Thanks & Regards.
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