From: Senthil Kumar (senthil.kumar@intechnology.co.uk)
Date: Mon Oct 14 2002 - 09:47:12 GMT-3
good explanation.
i thought i'd sequence some bits about qos that i was gathering..
you can either shape a traffic or police a traffic -
the difference is when shapping extra bursts are queued for delivery.
policing drops the excess bursts.
also
shapping/policing and queing are different as such.
the cycle ( when cbqwf/llq is used)
- classify the traffic
- assign an bandwidth for that class using bandwidth/priority command
( both commands are effective during congestion only, but priority command
alone makes sure the max bandwidth allocation doesnot exceed the
rate-speicified) you could also use a police command at the queueing
level.. which ensures the minimum bandwidth allocated even during periods of
non congestion.
- do a traffic shapping / policing at the main interface, which limits the
maximum outgoing traffic ( use map-class on a per pvc basis if frame-relay
is involved )
- the method you choose for classifying the traffic is upto you, choose the
easiest method..also conider dscp.
- avoid overlap in classificaton
- keep your configs simple
- choose the right method.
when voice is used at any point- you could effectively use ip rtp priority
command to set a total bandwidth allocated for the voice session, this
overrides other class markings and policies, by putting the voice packets
straight into the priority queue of llq and the interface queue.
if you want to use integrated services, yes consider using RSVP, allocate
session based bandwidth between two end points.
i use this method.
- classify packets on entry into the network
- prefer modular qos as its easy to implement
- use map class and give a map class labels to each set of traffic
- use policy-map and allocate bandwidth/priority bandwidth to the class map
labels
- apply this policy map to the interface. where these classified packets and
lots of non classified packets will be transported, so this interface itself
needs a service policy for limiting outgoing packets - do traffic shapping
or policying. (allocate buffer when shapping is implemented)
it works.
it took me quite some time to put things togeather, as no one piece of paper
helped me understanding it end2end..now its clear.
hope this helps!
also if you have 3550 in equation. remember that always dscp is used across
the domain for qos.
so classify packets on an entry and allocate a dscp value to it, using one
of the *-to-dscp maps depening on the values you trust or you assign as
default.
then remember that you can traffic shape the packet on entry into the qos
domain using police command. ( excess bits dropped at entry)
on the exit, remembet dscp is mapped to cos, and cos is mapped to the output
queues.
there are 4 egress queues, which are scheduled on intervels set using the
weight. ( so do this)
you can assign two threshold values to each queue and each can have a
limited buffer.
you can map dscp to the threshold..( you can choose one of two threshold
values per dscp value)
if your egress is gig. - you can enabke wred or tail drops.
if your egress is fast ethernet - you cannot do wred, only tail drop is
supported but you can assign a reserve level to the queue. which you set it
before assignig it to the queue using min-reserve command.
-
cheers! senthil
-----Original Message-----
From: \mit Askan (Teknoloji Gvz|mleri) [mailto:umit.askan@probil.com.tr]
Sent: 14 October 2002 12:08
To: 'Mark'
Cc: Ccie (E-mail)
Subject: RE: Test lab QoS question.
if you want to limit rtp for some bwith use rate-limit,
if you want to give a bwith for rtp use ip rtp [priority | reserve ] ...
for limiting each stream to 20kb/s use rsvp;
(config)# ip rsvp bandwith [interface_kbps] [per_flow_kbps]
(config-dialpeer)# req-qos guaranteed-delay ------- for limiting your
rtp stream
hth
umit
-----Original Message-----
From: Mark [mailto:ms6275@yahoo.de]
Sent: Monday, October 14, 2002 13:18
To: ccielab@groupstudy.com
Subject: Test lab QoS question.
I'm supposed to configure an HDLC interface to 400kb/s for rtp which I
think
I have an answer for but I'm supposed to also limit each stream to
20kb/s.
Would this also be possible on a frame-relay link with different
settings
per PVC ?
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