Frame-Relay traffic-shaping : delay kicks in too early ?

[MMostert]

Hi,

Have a query about Frame-Relay traffic-shaping; When should the traffic-shaping start delaying traffic (i.e. moving traffic to traffic shaping queue) ?

Reason I am asking is it seems like my Cisco 7206VXR starts delaying traffic much too early (i.e. before CIR threshold is reached) on a Frame-Relay interface having traffic-shaping enabled.

Traffic-shaping config:

frame-relay traffic-rate 736000 768000

frame-relay adaptive-shaping becn

frame-relay mincir 384000

Show frame-relay PVC output:

note:

+ no incoming BECNs

+ about 21000 packets being "delayed"

sh frame-relay pvc 729

PVC Statistics for interface Hssi4/0 (Frame Relay DTE)

[...]

input pkts 84738 output pkts 121884 in bytes 18747345

out bytes 81715139 dropped pkts 206 in pkts dropped 0

out pkts dropped 206 out bytes dropped 103505

late-dropped out pkts 206 late-dropped out bytes 103505

in FECN pkts 0 in BECN pkts 0 out FECN pkts 0

out BECN pkts 0 in DE pkts 252 out DE pkts 0

out bcast pkts 220 out bcast bytes 20799

Shaping adapts to BECN

pvc create time 17w2d, last time pvc status changed 2d05h

cir 736000 bc 736000 be 32000 byte limit 9750 interval 63

mincir 384000 byte increment 5796 Adaptive Shaping BECN

pkts 121889 bytes 81699787 pkts delayed 21743 bytes delayed 18635169

shaping inactive

traffic shaping drops 0

Queueing strategy: fifo

Output queue 0/40, 206 drop, 21743 dequeued

[vcjones]

Traffic shaping should kick in as soon as the traffic during the averaging interval used for CIR (63 milliseconds in your case) exceeds the allowed burst rate. So even small spikes, such as a half dozen full size packets arriving at once, can trigger traffic shaping.

Keep in mind that the loading reported by the interface is a weighted five minute average (unless you have configured a non-default value), so these short bursts will not show up on your monitors. But you could see them on a protocol analyzer connected to the LAN where they enter the router.

Good luck and good hunting!

Vincent C Jones

http://www.networkingunlimited.com