H.225- CRV

Callaghan, Robert Robert.Callaghan at ICN.SIEMENS.COM
Thu Jan 18 10:45:25 EST 2001


The object is to uniquely identify the signaling part of a call.  The
uniqueness consists of two points, the signaling link and the CRV.  The real
question is the definition of the signaling link.  In a direct call routed
model, the endpoints define the link, not the TCP connection.  For the
gatekeeper routed model, it is more complicated.  For a call going
EP->GK->GK->EP there are three links.  The CRV must be unique for each of
the three links.  In that the originating endpoint can determine uniqueness
for the first (EP->GK) link but not for the following links, it may be
necessary for the GKs to change the CRV for a call transiting the GK is
forwarded to the next link.

I agree that this has not been clear for a long time, and was not properly
clarified.  The rules should be more clearly defined.


Robert Callaghan
Siemens Enterprise Networks
5500 Broken Sound Blvd,      Boca Raton, Fl 33487
Tel: +1 561 923-1756            Fax: +1 561 923-1403
Email: Robert.Callaghan at ICN.Siemens.com

 -----Original Message-----
From:   Chris Wayman Purvis [mailto:cwp at ISDN-COMMS.CO.UK]
Sent:   Tuesday, January 16, 2001 5:16 AM
To:     ITU-SG16 at mailbag.cps.intel.com
Subject:        Re: H.225- CRV


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
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
actual address.


"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
> 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
> signaling addresses.  How would you know if this were the case?  The
> 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:
>   1) The CRV sent in an ARQ to place a call shall be the same as the
>      CRV in the resulting Setup message
>   2) 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 GK
> Paul
> ----- Original Message -----
> From: "Nehru, Archana" <archie at trillium.com>
> To: "'Paul E. Jones'" <paulej at PACKETIZER.COM>
> Cc: <ITU-SG16 at 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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Dr Chris Purvis -- Development Manager
ISDN Communications Ltd, The Stable Block, Ronans, Chavey Down Road
Winkfield Row, Berkshire.  RG42 6LY  ENGLAND
Phone: +44 1344 899 007
Fax:   +44 1344 899 001

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