[h323plus] H323 error codes

Paul E. Jones paulej at packetizer.com
Fri Sep 19 14:13:42 EDT 2008


> > What do you mean by this?
> Can error message comes in between the call signaling ?

There really are no H.225.0 Call Signaling error "messages", though there
are error codes in Release Complete.  Those may or may not indicate an
"error" -- they could indicate normal call termination.  There are several
places where error responses messages might be used in RAS (communication
with the Gatekeeper)

> > > I am able to find these kind of codes specifically in SIP with
> > > the
> > > response messages with their numbers(Ex:400,500,..),similarly the
> > > case with
> > > the MGCP protocol.But,I am very much confused with the H.323.

In SIP, the 5xx messages means the server could not process your request.
This might be due to the fact that the server failed or that the message was
garbage.  H.323 devices would generally just send a Release Complete with an
appropriate Q.850 Cause Code.  4xx is similar, but indicates a different
nature to the problem -- again, there are equivalent Q.850 cause codes.  3xx
is different -- that is a redirection.  H.323 devices will do that, too, but
the procedure is different.  Send a SETUP to a device and it might return a
FACILITY message with the "Reason" field set to "callForwarded".  That's the
same as a 3xx.  The calling H.323 device sends a Release Complete and then
places a new call to the new destination.  2xx means things were processed
normally.  We do not need an error code for normal operations.  SIP does
that because it was a hack of HTTP, which is a client/server
request/response system.  H.323 is not a request/response system, so it
works differently.

> > Look at Q.850
> >
> > > 2)What could be the case with the  H.245 protocol.
> >
> > No, as I said before, this is not in H.245. There is just endSession
> and it
> > has no Q.931 information in it.

H.245 does have error messages, such as "functionNotUnderstood".  Otherwise,
there aren't any and there really is no need.  H.245 does have rejection
messages (like OpenLogicalChannelReject) that includes a reason for why the
OLC is rejected.

I hope that helps.

Paul Jones

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