Frame Relay Traffic Shaping - Part I

Traffic shaping is designed to delay excess traffic whereas policing is designed to drop excess traffic.

A mock lab question stated apply a CIR of 128000 to an interface, ensure the minumum tc value is used and ensure no bursting above this rate is allowed.

The initial solution I applied was as follows…

I) create a frame-relay map class and apply the necessary parameters
map-class frame-relay 204
frame-relay tc 10
frame-relay cir 128000
frame-relay be 0

II) turn on traffic shaping and apply to the interface

Int s2/0
Frame-relay traffic-shaping
Frame-relay interface-dlcI 204
Class 204

To verify my solution I used the show traffic-shape command

Access Target Byte Sustain Excess Interval Increment Adapt VC List Rate Limit bits/int bits/int (ms) (bytes) Active
204 128000 2000 128000 0 125 2000 -

I noticed from the above that despite explicitly setting the tc in the map-class statement it was NOT in use, instead the default 125 ms tc was still in effect!

In fact the correct method to manipulate the tc is by indirectly setting the bc (committed burst). Remembering the formula Bc = CIR * tc…

Now adjusting my solution accordingly I achieved the required result.

#map-class frame-relay 204
#no frame-relay tc 10
#frame-relay bc 1280

Show traffic-shape Interface Se2/0
Access Target Byte Sustain Excess Interval Increment Adapt
VC List Rate Limit bits/int bits/int (ms) (bytes) Active
204 128000 160 1280 0 10 160 -