Paul,
Since we agree that CRVs should be unique between two endpoints, what is the ideal behavior in the following case?
Let us say there are two endpoints running on the same machine..which means that they have the same source IP address. Since the two endpoints are independent entities, they will generate CRVs independently. Now let us say both the endpoints make a call to another endpoint/GK with the same CRV. So at the receiver's side, we see two incoming calls with exactly the same CRV and exactly same "source" IP address. Is this a valid configuration? How is a receiver supposed to handle these incoming calls, particularly is there is no "callId"?
Thanks -Archana
-----Original Message----- From: Paul E. Jones [mailto:paulej@PACKETIZER.COM] Sent: Tuesday, January 16, 2001 12:40 PM To: ITU-SG16@mailbag.cps.intel.com Subject: Re: H.225- CRV
Chris,
Considering that V1 only allowed a single call over a single TCP connection, what would have been the point of a CRV in the Setup message? If they could all be the same, it makes them worthless. (Of course, I've found CRVs in packet-switched systems mostly worthless, but not entirely.)
From H.323: ``One CRV is used to associate the call signalling messages. This CRV shall be used in all call signalling messages between two entities (endpoint to Gatekeeper, endpoint-to-endpoint, etc.) related to the same call.''
Note the text that says "between two entities". If the intent was that these values were only unique "per connection", it would say so. The CRVs are unique between two entities.
From H.225.0: ``Note that the CRV is only unique on a particular part of a call, e.g. between two terminals, or between a terminal and a gatekeeper. If a given terminal has two calls in the same conference, each shall have the same conference ID but different CRVs.''
The latter sentence is more important: when communicating between two entities, it states clearly that there must be different CRVs. Again, with V1 those two calls would have been using different TCP connections, yet the text clearly says the CRVs must be different.
Now, I may be wrong-- this is just my interpretation of the text. I'd like to hear other comments.
Paul
----- Original Message ----- From: "Chris Wayman Purvis" cwp@isdn-comms.co.uk To: "Paul E. Jones" paulej@packetizer.com Cc: ITU-SG16@mailbag.cps.intel.com Sent: Tuesday, January 16, 2001 5:16 AM Subject: Re: H.225- CRV
Paul,
I disagree. CRV is surely unique per connection. One may be well advised to keep it more unique than that, because in gatekeepered environments you're liable to end up with
problems if you're not
careful because of your note 1 - but if I receive Q.931 messages on
separate
TCP connections giving the same CRV I shouldn't expect them
to refer to the
same call. I argue that this is rooted in the principal of
TransportAddress
throughout the H.323 standards including the SAPI (IP port
number) as well as
actual address.
Regards, Chris
"Paul E. Jones" wrote:
Archana,
(a) is closer to the way things actually work.
Essentially, you can use whatever values you wish so long
as you never place
two calls to the same endpoint using the same CRV value.
So, whether two
calls to an endpoint use the same TCP connection or different
connections,
the CRV must be unique.
You should also consider the possibility that an endpoint
may have two call
signaling addresses. How would you know if this were the
case? The safest
thing to do is never have two calls with the same CRV at
the same time.
However, if you know that the destination endpoints are unique, you
could
re-use the CRV value.. at least when a Gatekeeper is not
being used.
There are also so other properties of CRVs:
- The CRV sent in an ARQ to place a call shall be the
same as the
CRV in the resulting Setup message
- The CRV sent in an ARQ to accept a call should *not* be taken from the incoming Setup message-- it should be
locally generated so
that it is a unique between the endpoint and the GKPaul
----- Original Message ----- From: "Nehru, Archana" archie@trillium.com To: "'Paul E. Jones'" paulej@PACKETIZER.COM Cc: ITU-SG16@mailbag.cps.intel.com Sent: Monday, January 15, 2001 10:28 PM Subject: H.225- CRV
hi all,
I have a question about H.323 -CRV values. Q.931 specs
says that a CRV
value
should be unique per D-channel layer 2 logical link.
In H.225 context, does the above mean that:
a) CRV values should be unique across all outgoing H.225
calls that have
the
same "destination" IP address ?
b) CRV value only needs to be unique across all H.225 connections
using
the
same TCP connection? In other words, if an endpoint A makes two
simultaneous
calls to endpoint B, then the same CRV can be used on
both the calls, as
long as they use different TCP connections?
I would appreciate any help on this.
Regards Archana
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