Encoding of H.248 in H.323

Paul Long plong at IPDIALOG.COM
Thu May 10 10:52:46 EDT 2001


The way I understand it, the redundant ABNF/BER encoding scheme was a
compromise between the text and binary people. I don't know about H.323
Annex L, but in H.248, MGCs must support both encodings, but MGs only have
to support one. As it happens, very few MGs support BER. I believe it's too
late now to specify PER instead of or in addition to BER.

I agree with your observation concerning BER, though. I asked the same
question awhile back among the Megaco crowd. The answer I got was simply,
"Some people wanted a binary encoding, and the H.323 folks said to use BER
because PER is too hard." That's it. I thought the H.323 folks had long
since recovered from the mind-numbing complexity of ASN.1 PER ;-), and that
this was now a non-issue with them. Moreover, it was mentioned long ago on
the ASN.1 reflector (by Bancroft Scott, I believe) that BER was really a bad
choice nowadays and that if one was considering BER, one should always use
DER instead. Go figure.

Paul Long
ipDialog, Inc.

-----Original Message-----
From: Mailing list for parties associated with ITU-T Study Group 16
[mailto:ITU-SG16 at mailbag.cps.INTEL.COM]On Behalf Of Frank Derks
Sent: Thursday, May 10, 2001 8:08 AM
To: ITU-SG16 at mailbag.cps.INTEL.COM
Subject: Encoding of H.248 in H.323

H.248 specifies both a binary (using the BER) and a text format
for the encoding of its messages. states that either
of these formats can be used for H.323 Annex L.

Are there reasons, other than the fact that the BER and text are
specified in H.248, to dissallow encoding using the PER? It would
seem that having to use two different encoding schemes (PER+BER or
PER+text) makes things unnecessarily complex.



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