From: Peter Whittle (peter@xxxxxxxxxxxxxxxxxxxxxxxxxxx)
Date: Tue Nov 27 2001 - 20:03:31 GMT-3
Jon,
I think that your problems are quite common on this group in that the
focus, quite rightly, is on CPE equipment, whereas CIR is primarily a
function of the frame relay cloud, the service provider's switching
network.
CIR on directly connected routers that use encapsulation type frame
relay has no effect what so ever! Indeed until recently Cisco routers
configured as frame relay switches lacked support for traffic contract
policing. (This has now been remedied in some flavours of 12.2 IOS.)
The traffic contract CIR, EIR & Tc are functions of the ingress port to
the frame relay network. If the traffic contract is enforced then the
rate of traffic inbound to the frame relay network will be monitored and
frames that exceed the CIR defined for each circuit (dlci whether from a
PVC or an SVC) will be marked by having the DE bit set in their frame
header. This monitoring and setting of the DE bit is normally only
carried out on ingress to the frame cloud.
These DE marked frames will normally be carried through the frame relay
network and delivered to their destinations. However, if any of the
nodes (switches or ports on switches) in the frame relay network are
congested then these DE marked frames may be selectively discarded by
the network.
There are 2 circumstances in which the CPE needs to know what the CIR on
a particular circuit are:
1) When implementing traffic shaping to try to ensure that the
flow of traffic out of the router meets the parameters of the traffic
contract and hence to minimise the potential loss of frames.
2) When setting up the circuit by making an SVC call. In this
case the CIR desired needs to be communicated to the network as part of
the call setup process.
-----
So in answer to your question 'does setting frame-relay CIR have any
effect' it depends. If you are using SVCs - Yes!
If you are using FRTS - Yes!
If you are running IOS 12.2 and you are configured
as a frame relay switch and traffic policing is enabled - Yes!
Otherwise no.
I hope that this helps
Peter
In message <008c01c17783$84d42000$0201010a@tde.tdb.dk>, Jon B
<cciestudy@bennedsgaard.dk> writes
>Hello Group
>
>I have a problem with understanding the 'frame-relay cir' command and how it
>relates to PVCs. On the list there are lots of examples using this command
>in a map-class to enforce Frame-Relay Traffic Shaping. In the command
>reference (IOS 12.1) I find this:
>
>"Usage Guidelines
>Use this command to specify a CIR for an SVC. The specified CIR value is
>sent through the SETUP message to the switch, which then attempts to
>provision network resources to support this value."
>
>To me this sounds like a specific command for SVCs. Does the command have
>any effect on PVCs? Any thoughts?
>
>Thanks,
>Jon B
-- Peter Whittle
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