Cell Relay Archive

["Rajgopalan Sampath" <rajagopalan.sampath@wipro.com>]

Hi,
I still have some confusion.
Spec says that the DATA passed to the AAL1 is constant and the time difference
between two consecutive Requests is also constant.

For example, in a Circuit Emulation Service ( N x 64kbps )  it has to pass '1'
byte of data from each channel to the AAL1 once in every 125/N micro seconds.
According to the spec, Circuit emulation used SDT. So, always a Structure
information will be passed to AAL1.
My question is:
1. Does the AAL1 user request the AAL1 once in every 125/N micro seconds with 1
byte of data? In that case do AAL1 need to do any buffering until it gets 47
octets from the user?
2. My assumption is, the pointer ( P-format ) is always send in the PDU with Seq
Count '0'? Is this right? If the pointer is sent in the first PDU of a cycle (
i.e. the PDU with Sequence count 0 ), what'll be sent in the remaining PDUs of
the same cycle ( i.e in the PDUs with Seq Count 2, 4, 6 )? Can we send a Non-P
format cells in place of P-format cells? i.e. the whole PDU ( 47 bytes)
will  be filled only with user information irrespective of the sequence number?
Is there any hard and fast rule like the Non-P format cells should be sent only
with Seq Count 1, 3, 5 and 7?

If I'm wrong, what the mechanism, in which the AAL1 user sends data to the AAL1.

Also, in a Voiceband signal service, only one 64kbps voice channel is used, in
which the data doesn't use any structure information. In this case, how the DATA
is passed to the AAL1?
The data always sent in Non-P format in a cycle, except the 7th PDU with Seq
Count '6'. In which the pointer always takes the value "127" ( the default )
value.

Can I assume that, at transmit side, the AAL1 user guarantees CBR? So, partial
filling of PDUs will not be needed at CS layer to compensate the "cell assembly
delay".

Plse tell, whether my understanding is correct.

Thanks in advance.

-Rajagopalan.

XuHonggang wrote:

> Hi,
> Pointer field is 7 bits, so max offset which it can idicate is 127 Octets
> which < 3 ATM cells p and > 2 ATM cells, so standard maker decided to use 96
> as max number wich align with 2 ATM cells.
> You put a pointer in no.0 cell, it can cover all possible offset in no.0 and
> no.1, so second pointer only need to appear in no.2, the same thing happen
> to no.4 and no.6 cell.
> Yes, a octet means 8 bits, means one sample of a voice channel. How many
> octets
> in your structure means how many voice channels in your structure.
> wish it help
> XuHonggang
> SwitchingSystemDepartment
> CET Techologies of Singapore Technologies
> 24 AngMoKio Str. 65
> Singapore 569061
> -----Original Message-----
> From: Nuzhath Shereen <shereen@chequemail.com>
> To: sasos@nortelnetworks.com <sasos@nortelnetworks.com>
> Cc: rajagopalan.sampath@wipro.com <rajagopalan.sampath@wipro.com>;
> cell-relay@cell.onecall.net <cell-relay@cell.onecall.net>
> Date: Thursday, July 27, 2000 5:26 PM
> Subject: Re: CR: Structured Data Transfer in AAL Type 1 !
>
> >
> >
> >Hello Saso,
> >
> >Can you explain more about this SDT format. The ITU-T I.363.1  says that
> the pointer format may be used only if the sequence count value is 0,2,4 or
> 6. This is because the 1,3,5 and 7 values are reserved for SRTS.
> >
> > I didn't understand the rest of the explanation in the standard. What is
> this 93-octet payload it refers to. By octet, Is it referring to one 64kps
> channel (I had read that somewhere) or is the digital 8 bits.
> >
> >Please give links or references , if you have any
> >
> >Regards,
> >Shereen@chequemail.com
> >
> >On Wed, 26 July 2000, "Saso Stojanovski" wrote:
> >
> >>
> >>
> >> 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.
> >
> >
> >Chequemail.com - a free web based e-mail service that also pays!!!
> >http://www.chequemail.com
> >
> >

--
Rajagopalan Sampath,
Wipro Technologies,
Bangalore.
Ph: 5722293/96. Extn: 5134.