Cell Relay Archive

[Calin Poenaru <calin@univermed-cdgm.ro>]

On Tue, 19 May 1998 paull@euristix.ie wrote:

> I am currently working on a SS7 over ATM project. I am told that
> Q.2140 and Q.SAAL both aid in mimicking the role played by MTP2.
> 
> I am currently trying to figure out "How Q.SAAL measures the
> health of a link".
> 
> As an example, take MTP2. In MTP2, the health of a link is calculated
> with the SUERM parameter, using the leaking bucket algorithm. This
> means that for every PDU in error the count is increased and for every
> block of 256 good PDUs, the count is decreased by one. If this count
> is greater  than a threshold value then link changeover occurs in
> MTP3.
> 
> In ATM, there is no SUERM parameter. 
> 
> I was wondering whether anybody out there, knows how
> 
> 1) Bad links are detected in ATM.
> 

I am sorry if I am out of topic (no flame, please!), but my impression is
that is the right time to mention the OAM cells. Please correct me if I am
wrong: 
    - OAM F1, F2, F3 are dedicated to detection and indication of 
unavailability state and transport defect information towards the affected end
points. Also they are dedicated to performance monitoring and reporting or for 
localization of failed equipment at physical layer.
    - OAM F4, F5 are used to do the same things at VP/VC level on ATM
layer.

So, if I understand well, at physical layer (F1&F3 cells, as long as F2 is not
 used) you can detect the loss of signal, the loss of frame, an unacceptable 
error performance etc. At ATM layer (F4&F5 cells) you can  report defect 
indications on forward or backward direction, you can estimate performance 
etc.

May be somebody want to comment this. 

All the best!

Calin Poenaru

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