Cell Relay Archive

["Albert Manfredi" <albert.e.manfredi@boeing.com>]

""Steven Lau"" <gunnerstkd@lycos.com> wrote in message
GIECFPEDDGFAEAAA@mailcity.com">news:GIECFPEDDGFAEAAA@mailcity.com...
> hello.. I've read most of the RFCs concerning using IP over an ATM
network.. but they doesn't provide much details.. Here are some
questions i would like to ask..
>
> I want to modify the classical IP over ATM (CLIP) model a bit.. so
I would have all routers connected to one ATM switch. I don't want
to utilize NHRP. Is this configuration possible?.. this is because
if for a very large network, I presume that it would minimize the
number of hops to get to the farthest network.

NHRP is not mandatory for CLIP. As you say, it is used to provide
shorter paths through ATM networks, by bypassing IP routers. If you
don't use NHRP, the ATM network becomes nothing more than a way to
interconnect the IP routers, and could also be used as a LAN
replacement for the IP subnets.

So you could set up multiple IP subnets from multiple IP routers.
The routers can be interconnected via ATM PVCs, SPVCs, or SVCs.
Going the SVC route is nice in that ATM assets are not used unless
they are required. RFC 2225 supports either SVCs or PVCs. If a
packet arrives at Router A and must be transferred across the ATM
network to a Router B, as determined by IP routing, and if Router A
has no link to Router B at the time, then Router A will set up an
ATM SVC to Router B. That ATM SVC will remain set for a configurable
amount of time after the last IP packet has been sent. Then the SVC
is torn down.

Or you can use LANE as well, as far as that goes. In this case, it
would operate much like CLIP with SVCs.

> If i transfer pure ATM cells and also IP encapsulated in ATM cells
via the CLIP network, is it possible??

The IP routers would probably discard anything that they don't
understand. So it's possible to use the ATM backbone network for
native ATM, but you'd have to teach the IP routers what to do with
non-IP packets they might see, if you expect the IP routers to
forward these non-IP packets through.

> How would a destination recognizes/identifies all the cells
intended for it as IP packets are encapsulated into ATM AAL5 PDUs
and then segmented into 53bytes cells?? and how to it recognizes the
arrangement of the cells during reassembly stages??

Whatever you build will have to take care of this. There are many
ways. CLIP assumes IP is being carried. It addresses nothing else.
If you want to mix protocols, read RFC 2684 or LANE. These provide
Link Layer encapsulation, so that the packets carried across the ATM
networks can all be identified. CLIP instead layers IP directly over
ATM AAL5.

> and ATM MUX is for a single source or for many sources MUX into
one??.. if the latter is the case, then how would the destination
recognize which ATM cells (IP encapsulation) intended for it and the
arrangement for the reassembly??

Same answer as above.

Bert
albert.e.manfredi@boeing.com