Cell Relay Archive

[rajeev@trillium.com (Rajeev Gupta)]

> On 12 Feb 1998 06:43:20 GMT, "Leonid Shousterman"
> <leonids@breezecom.co.il> wrote:
>
> >Greetings All,
> >
> >Sometimes I hear the term Wireless ATM. Can anyone explain
> >me what is meant by it? Why should ATM be affected by
> >nature of the physical carrier?

Wireless ATM implies extending the ATM connection over wireless media
to a mobile terminal. The physical characteristics of the wireless
media are very different from that of wireline media, with respect
to loss and throughput. Moreover, the wireless media is shared.

Thus, at the air interface, a number of issues need to be dealt with,
such as:

- RF modulation, encoding, ciphering
- media access control, scheduling transmissions
- forward error correction, ARQ mechanisms

The above functions are often referred to as the Wireless Access Layer 
(WAL) and comprise PHY, MAC and DLC functions. WAL will typically reside
below the ATM layer in the protocol stack and thus should be largely
transparent to the applications using ATM. However, WAL needs to be
specified with the needs of ATM in mind. This work is being done in
the ETSI BRAN project.

In addition to the wireless aspects, WATM also has to deal with mobility
management in the network (this is sometimes referred to as mobile
ATM, MATM). There are two major aspects of mobility management:

- location management: when a call is to be placed to a mobile terminal,
  its current location must be determined by the network.

- handover: when a mobile terminal moves while maintaining connections, 
  the connections need to be rerouted in the network in order to
  maintain connectivity.

These functions require support in the network in the form of storage
functions (e.g. location registers) and control functions (e.g. signalling
for handover). This work is being done in the WATM group of the
ATM Forum. Most likely the work will result in specifying enhancements
to existing protocols (e.g. UNI, PNNI, BICI) to support mobility.

Still other aspects of ATM that are affected relate to traffic management,
security, network management, etc. This will also be considered by
the WATM group (eventually).

______________________________________________________________________
Rajeev Gupta                            Trillium Digital Systems, Inc.
mailto:rajeev@trillium.com                     http://www.trillium.com