Cell Relay Archive

[Jon Gauthier <jgauthier@mitre.org>]

With most current-generation DSL Intelligent Access Devices (IADs)
today, the ATM adaptation does indeed occur in the IAD. AAL-5 for IP
data, AAL-2 (or AAL-1) for voice.

Previously, in the earlier stages of carrier ATM transport deployment,
the adaptation was done at the ATM edge switch so as to allow legacy
devices (telephone PBXs, IP routers) to migrate without putting the onus
on the customer to upgrade their equipment. Plus, the carriers were able
to continue charging high leased-line prices as they upgraded their
TDM/DACS networks to ATM...

There are frame relay-based IADs deployed out there in the real world,
but most are outdated. With the adoption of an ATM AAL-2 loop
emulation-based VoDSL recommendation by the DSL Forum, FR-based
solutions are being phased out.

One thing your diagram doesn't show is what the ATM switch connects to.
In the case of a pure IP data network, the switch could do AAL-5
adaptation back to IP frames for handoff to a non-ATM router via a DS-3
or similar link, but current implementations put that function in the
router, so your switch becomes a pure cell switch with no adaptation.

Perhaps your ATM information source is not familiar with the VoDSL
recommendation?


Kostas Kapetanakis wrote:
> 
> Hi!
> 
> I have one question about AAL. Assume we have the bellow diagram on an ATM
> only network.
>  Where is the AAL performed? On which device?
> 
> End user        NTE        MDF        DSLAM        ATM switch
>   ----               --            ----             ----                  --
> ----
>   |    |               |  |            |    |            |     |
> |      |
>   |    |  -------- |  |--------|    |--------|     |------------- |
> |-------->to network
>   |    |               |  |            |    |            |     |
> |      |
>   ----               --            ----             ----                  --
> ----
> 
> <----------------------- UNI 4.0 ------------------->      <----PNNI
> 1.0 --------->
> 
> For me it makes sense that it is performed at the end user so that we have
> ATM cells
> all over the route form the one end user to the other. However I have been
> told that
> for practical reasons the AAL functionality is performed on the ATM switch.
> Is this
> true? If it is so then what kind of connection we have between the end user
> and the
> switch. Do we still have ATM cells?Isn't it necessary to use AAL before we
> transmit
> ATM cells?
> 
> Thanks in advance!
> Regards,
> Kostas.