Subject: Re: [PWE3] TDMoIP AAL2 and TSSI structures

From: Javi Muñoz <[email-masked]>
Date: Fri, 16 Dec 2011 19:16:23 +0100

Yaakov,

You wrote me:

> When using TDMoIP in AAL2 mode, sample order is guaranteed
>
> [Javi] ITU-T I.140 defines:
>
> + TSSI structure (time slot sequence integrity): if a sample "bi" is
> send and, later, a second sample "bk" (for any two different channels of
> an aggregate of channels, B1 and B2), "bi" always come first.
>
>
> If we use a TDMoPW TDMoIP AAL2 to emulate the aggregate of that channels
> (B1 and B2), would TSSI structure be guaranteed?

I agreed with you. However, after thinking more slowly, I have some doubts.

TSSI requires that if we have two channels B1 and B2 in CEa (source CE 
source) and CEb (destination CE) then:

* if in CE1: a sample "b1a" is send on channel B1 and, later, a second 
sample "b2a" is send on channel B2

* then, in CE2: sample "b1a" must reach CE2 (on its channel B1) before 
"b2a" (on its channel B2)

The same for other samples "b1b", "b2b" sent later.

          b1a          b1b
     B1 ==|============|==================
CE1       \  b2a       \      b2b
     B2 ====\=|==========\======|=========
             \  \         \      \
              \   \         \      \
               \b1a  \        \b1b  \
     B1 ========|=====\========|=====\====
CE2                    \ b2a         \b2b
     B2 ==================|============|==

In TDMPW AAL2-mode, we migth have a TDMPW packet with the payload:

TDMPW Payload:        [CPS packet of B1][CPS packet of B2]

where:

[CPS packet of B1] = [CPS header, with CID=B1] [CPS payload: samples 
b1a, b1b, b1c, b1d]

[CPS packet of B2] = [CPS header, with CID=B1] [CPS payload: samples 
b2a, b2b, b2c, b2d]

So, I understand that CEs first read all the samples of "CPS packet of 
B1" (so "b1a, b1b, ...") and later, all the samples of "CPS packet of 
B2" (so "b2a, b2b, ..."), which does not coincide with the delivery 
order (b1a, b2a, b1b, b2b, b1c, ...)

Am I wrong?

Regards,

Javi