[j-nsp] A conceptual advice on QoS is needed

[Victor Sudakov]

Adam Vitkovsky wrote:
> >
> > We have Juniper switches interconnected by a transport network (NEC
> > equipment mostly). The nodes of the transport network are Ethernet
> > switches in their own right, they have 4 or 8 interface queues and can do
> > priority queueing and/or WRR queueing based on 802.1p codepoints in
> > received frames.
> >
> > Now if you had to implement QoS policies, where would you do the actual
> > prioritization:
> >
> > 1. Classify the frames on the Juniper switches, but do the actual
> > queueing/prioritization in the transport network.
> >
> > 2. Configure one FIFO queue on the transport network nodes and do both
> > classification and prioritization on the switches.
> >
> > It may be important to know that most switches are connected to the
> > transport network by Gigabit interfaces, but the real throughtput of the
> > transport network itself is about 150 Mbit/s.
> >
> > But there is another branch of the transport network where all interfaces on
> > the nodes are 100BaseT, so the switches are connected at
> > 100 Mbit/s.
> >
> > Thanks in advance for any opinions.
> >
> Victor,
> 
> If your network carries traffic of higher priority that is interleaved with traffic of lower priority then the below questions are relevant:
> 
> 1) Can it happen on Juniper switches that BW on input > BW on output
> (e.g. traffic incoming on multiple ports will be transmitted out one
> port)?

Very unlikely.

> 
> 2) Can it happen on NEC transport switches that BW on input > BW on output?

Most likely.


> If yes then you need QOS (classification and scheduling)

The question is, where I need QoS: before the traffic enters the
transport switches or inside them.

-- 
Victor Sudakov,  VAS4-RIPE, VAS47-RIPN
sip:sudakov at sibptus.tomsk.ru