Cell Relay Archive

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

hi rajagopalan,

when using AAL-1 for circuit emulation, you either care to specify to the
receiver where the TDM frame boundary is or you don't.

in the former case you would use SDT, and in the latter case you would
rely on the sync mechanism which is built in the TDM frame itself.

for instance, if you emulate a whole E-1 circuit, then you could use UDT,
since the first timeslot (out of 32) in the E-1 frame contains a sync
pattern.

on the other hand, if you are to emulate a fractional E-1 circuit (say
only k 64 kbit/s channels), then you must use SDT in order to tell the
receiver where exactly in the ATM payload the TDM frame (whose length is
only k octets) starts. that is exactly what the pointer points at.

cheers,
    v
--saso




rajagopalan.sampath@wipro.com wrote:

> Hi,
>
> Can somebody help me in implementing AAL type 1  ( ITU-T I.363.1 )?
>
> What's SDT ( Structured Data Transfer ) and why it's used?
> How SDT is performed at transmitting and receiving end? It's basically
> about when to select P-format and when to select Non-P format PDUs?
> What does the pointer value represent in the P-format PDUs?
>
> Thanks.
>
> Regds,
> Rajagopalan Sampath.