shape peak vs shape average

Answered Question
Dec 29th, 2007

If we have an access interface with:

Cir 384K

Access 512K

To use all of bandwidth (if available) I need to configure a shape peak but shape peak is 256 or 512 ?

I'm asking because if I configure 512, the output of "show policy map int X" show's 1024000/512000 and I'm confuse about this 1024000.

Attachment: 
Correct Answer by aravindhs about 9 years 1 month ago

That was helpful. Just gave you a deserved vote/rating too.

Cheers

Arav

Correct Answer by Edison Ortiz about 9 years 1 month ago

shape peak 512000 will default to a guarantee CIR of 512kbps and burstable to 1024000kbps (double the value).

Here are other samples I did (double the value)

Target/Average Byte Sustain Excess Interval Increment

Rate Limit bits/int bits/int (ms) (bytes)

600000/300000 1950 7800 7800 26 1950

Target/Average Byte Sustain Excess Interval Increment

Rate Limit bits/int bits/int (ms) (bytes)

800000/400000 2500 10000 10000 25 2500

_______________________

If your target is 300kbps with burst up to 512kbps, you need to enter

shape peak 300000 3000 2120

Service-policy output: test

Class-map: class-default (match-any)

183 packets, 2463 bytes

5 minute offered rate 0 bps, drop rate 0 bps

Match: any

Traffic Shaping

Target/Average Byte Sustain Excess Interval Increment

Rate Limit bits/int bits/int (ms) (bytes)

512000/300000 640 3000 2120 10 640

Adapt Queue Packets Bytes Packets Bytes Shaping

Active Depth Delayed Delayed Active

- 0 4 136 0 0 no

__________________

The formula is as follow, you take the guarantee bandwidth (300kbps) and multiply by the interval for the first 2 values on the shape peak command. I use 10ms as my interval, you can choose a different value.

300000 * .010 = 3000

for the excess burst

512000 - 300000 = 212000

212000 * .010 = 2120

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 4.9 (6 ratings)
Loading.
Edison Ortiz Sat, 12/29/2007 - 15:33

Usage Guidelines

Traffic shaping limits the rate of transmission of data. In addition to using a specifically configured transmission rate, you can use Generic Traffic Shaping (GTS) to specify a derived transmission rate based on the level of congestion.

You can specify two types of traffic shaping; average rate shaping and peak rate shaping. Average rate shaping limits the transmission rate to the CIR. Using the CIR ensures that the average amount of traffic being sent conforms to the rate expected by the network.

Peak rate shaping configures the router to send more traffic than the CIR.

To determine the peak rate, the router uses the following formula:

peak rate = CIR(1 + Be / Bc)

where:

•Be is the Excess Burst size.

•Bc is the Committed Burst size.

Peak rate shaping allows the router to burst higher than average rate shaping.

However, using peak rate shaping, the traffic sent above the CIR (the delta) could be dropped if the network becomes congested.

If your network has additional bandwidth available (over the provisioned CIR) and the application or class can tolerate occasional packet loss, that extra bandwidth can be exploited through the use of peak rate shaping. However, there may be occasional packet drops when network congestion occurs. If the traffic being sent to the network must strictly conform to the configured network provisioned CIR, then you should use average traffic shaping.

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cr/hqos_r/qos_s1h.htm#wp1085303

a.azambuja Tue, 01/01/2008 - 15:09

The following example uses peak rate shaping to ensure a bandwidth of 300 kbps but allow throughput up to 512 kbps if enough bandwidth is available on the interface: (cisco document reference)

bandwidth 300

shape peak 512000

When I configure this, the output of show policy map int X/X shows:

Traffic Shaping

Target/Average

Rate

1024000/512000

Why is displayed 1024000 and not only 512000 ?

I read a lot of some other forums and documents but I'm still confuse...

Correct Answer
Edison Ortiz Tue, 01/01/2008 - 16:13

shape peak 512000 will default to a guarantee CIR of 512kbps and burstable to 1024000kbps (double the value).

Here are other samples I did (double the value)

Target/Average Byte Sustain Excess Interval Increment

Rate Limit bits/int bits/int (ms) (bytes)

600000/300000 1950 7800 7800 26 1950

Target/Average Byte Sustain Excess Interval Increment

Rate Limit bits/int bits/int (ms) (bytes)

800000/400000 2500 10000 10000 25 2500

_______________________

If your target is 300kbps with burst up to 512kbps, you need to enter

shape peak 300000 3000 2120

Service-policy output: test

Class-map: class-default (match-any)

183 packets, 2463 bytes

5 minute offered rate 0 bps, drop rate 0 bps

Match: any

Traffic Shaping

Target/Average Byte Sustain Excess Interval Increment

Rate Limit bits/int bits/int (ms) (bytes)

512000/300000 640 3000 2120 10 640

Adapt Queue Packets Bytes Packets Bytes Shaping

Active Depth Delayed Delayed Active

- 0 4 136 0 0 no

__________________

The formula is as follow, you take the guarantee bandwidth (300kbps) and multiply by the interval for the first 2 values on the shape peak command. I use 10ms as my interval, you can choose a different value.

300000 * .010 = 3000

for the excess burst

512000 - 300000 = 212000

212000 * .010 = 2120

Correct Answer
aravindhs Wed, 01/02/2008 - 03:52

That was helpful. Just gave you a deserved vote/rating too.

Cheers

Arav

a.azambuja Wed, 01/02/2008 - 08:12

Ok man !!! You are the best !!! Now I see how to use this command.

Tks !!!

Actions

This Discussion