[alcatel-nsp] Smoothness of egress shaped scheduler-policy with multi-service-site.

Pawel_Sikora at netia.pl Pawel_Sikora at netia.pl
Mon Mar 28 12:42:02 EDT 2011

I was forced to use ill-behaving transmission devices (EoSDH) that have 
netto speed STM-1 and GE ports, but have only single 16kB packet buffer 
available at the bottleneck.
The traffic I must pass through it is rather bursty*  and comes from the 
GE port of 7750.
It is sourced from dozen of SAP-s (several different services with 
aggregated classes).
*(mainly Internet access)

I can shape it together to the given average max rate (i.e.150Mbps), using 
multiservice-site scheduler-policy with parent port scheduler, but observe 
still some bursts of traffic leaves from the SR port that 16kB buffer 
cannot accomodate (mtu used on every service is no more than 1564B).
The symptoms are both reported as buffer overflows on EoSDH port (sdh 
side) and visible as lost packets in ordinary ping.
Unfortunately the lost packets are observed even at average utilization of 
70-80 Mbps, far below the physical link capacity.

Constant, non-bursty flows generated form traffic tester show proper 
shaping and smooth operation of EoSDH box,
 but after introducing some burstiness on traffice source (that enters SR) 
I observe drops on the the EoSDH small buffer.

Is there any parameter or guideline how to tune the scheduler behaviour , 
to achieve better smoothness on egress port traffic?

In contrast, I've connected the Cisco 3750 with ordinary egress port 
bandwith limit feature (still using four different traffic classes within 
shaped speed),
and there are no drops on EoSDH box, up to the link capacity on the same 
traffic type.


(SR-7 with 8.0.6 and IOM2)
Otrzymana przez Panią/Pana wiadomość oraz załączone do niej pliki stanowią 
prawnie chronioną tajemnicę przedsiębiorstwa i są przeznaczone tylko dla 
adresatów. Jeżeli nie są Państwo zamierzonym odbiorcą, proszę poinformować 
o tym fakcie nadawcę oraz usunąć wiadomość ze swojego systemu. Nie powinni 
Państwo także wykorzystywać, ujawniać ani przekazywać otrzymanych 
informacji, jak również sporządzać jakichkolwiek ich kopii.
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