Cell Relay Archive

["Saso Stojanovski" <sasos@nortelnetworks.com>]

hi,

depends on what you mean by "voice trunking gateways".

my understanding of af-vtoa113 and af-vmoa145 is the following:

  - af-vtoa113 is typically used for PBX-to-PBX or PBX-to-LEX
interconnection;

  - af-vmoa145 is used exclusively in the local loop for interconnecting
POTS and ISDN BRI users to the LEX.


both standards use the same protocol stacks for:

  - voice transport: a set of profiles defining voice encodings into
AAL-2 CPS packets and enabling a rapid switch between different
compression algorithms;
  - transport of DTMF tones via special AAL-2 packets;
  - transport of voiceband data: either transparently by using a
high-rate voice encoding algorithm, or by employing a fax demodulation/
remodulation procedures.


the main difference between the two lies in the signalling protocols:

  - af-vtoa113 typically uses Q.931 signalling; in the so-called
"switched trunking" configuration, every IWF is supposed to terminate
and interpret Q.931 signalling; dynamic AAL-2 channel allocation for a
new narrowband call is performed by a special IE in the Q.931 SETUP
message, carrying the AAL-2 CID to be used.


        E-1           -----           E-1
 +-----+   +-----+   /     \   +-----+   +-----+
 | PBX |---| IWF |---  ATM  ---| IWF |---| PBX |
 +-----+   +-----+   \     /   +-----+   +-----+
                      -----

      Q931.SETUP
       ------->
             Q931.SETUP (+AAL2 CID)
              -------------------->
                                   Q931.SETUP
                                  ---------->

note that the IWFs intercept the narrowband signalling messages and
modify them (by adding the AAL-2 CID info). the same remark applies in
the opposite direction for the Q931.CONNECT message.



  - on the contrary, a typical af-vmoa145 application connecting ISDN
BRI users to a LEX would look like this:


      S/T             -----          V5.2
 CPE-------+-----+   /     \   +-----+   +-----+
 CPE-------| IWF |---  ATM  ---| IWF |---| LEX |
 CPE-------+-----+   \     /   +-----+   +-----+
                      -----

                      Q931.SETUP
    ----------------------------------------->
                                   BCC.ALLOC
                                 <------------
                ELCP.ALLOC (AAL2 CID)
              <--------------------
                ELCP.ALLOC_COMPLETE
              -------------------->
                                  BCC.ALLOC_COMPLETE
                                  ------------>
                                                Q931.SETUP
                                               ------------>

note that in this case the Q.931 signalling traverses the ATM network
transparently and is terminated only at the LEX. in order to provide
dynamic binding between a given narrowband circuit and an AAL-2 channel,
one has to use the BCC protocol (defined for the V5.2 interface),
together with the ELCP protocol (defined specifically for af-vmoa145).

this example covers only the ISDN BRI users. similar figure can be drawn
for POTS users, by replacing Q.931 signalling with the V5 PSTN
signalling protocol (originated at the customer premises IWF and
terminated in the LEX).

cheers,
    v
--saso





John Jacob wrote:

> Hi
>
> To support modem traffic from  voice trunking gateways which of the
> following atm spec applies
> af-vtoa113  or af-vmoa 145
>
> Is at-vtoa113 for VTOA application. and af-vmoa145 for VoDSL
> application?
>
> Thanks in advance.
> jacob