Hi Joseph,
I've performed the experiments in our network lab using 1841 routers running 15.1(4)M2 Advanced IP Services, interconnected via Fa0/1 interfaces. The topology:
Generator ---> (Fa0/0) 1841 (Fa0/1) ---> (Fa0/1) 1841 (Fa0/0) ---> Receiver
The shaping was configured on the leftmost 1841 as follows:
policy-map fa0/1-out
class class-default
no fair-queue
shape average 100000 8000 8000
!
interface FastEthernet0/1
service-policy output fa0/1-out
The generator created a flow of IP/UDP packets of total size of 1000 bytes, 150 packets per second, totalling a rate of 1.2 Mbps.
I used Wireshark to capture the flow and graph it out. Following is the screenshot of the graph flow:
Up to the roughly 180th second, the configuration of the shaping was as indicated, i.e. shape average 100k 8000 8000. The graph shows the throughput to oscillate around the configured CIR of 100 Kbps. At around the 180th second, I have modified the command to
shape peak 100000 8000 8000
As it can be seen, the total throughput jumped twofold and now oscillates around the value of 200 Kbps which appears to align with my original explanation and derivation of CIR' = configured CIR * (1+Be/Bc) = configured CIR * 2, as in my case, the Be=Bc.
Furthermore, around the 230th second, I modified the configuration again to:
shape peak 100000 8000 4000
The rate dropped to 150 Kbps which also aligns to the CIR' = configured CIR * (1+4000/8000) = configured CIR * 1.5
This experiment used the generator to create a substantially higher load than the configured CIR. Another experiment was performed under the same sequence of settings on the router, however, the stream consisted of 100 byte packets, 300 packets per second, totalling the rate of 240 Kbps.
In short, the results were absolutely identical, see the following graph:
Till the 95th second, the shape average 100k 8000 8000 command was used. Between the 95th and 130th second, the shape peak 100k 8000 8000 was used. After the 130th second, the shape peak 100k 8000 4000 was used.
If these experiments do not align with what you requested, Joseph, please feel welcome to give me your description of the experiment so that I can replicate it in our lab.
My personal feeling is that the shape peak is good for those customers who have negotiated both the CIR and EIR with their service provider (Bc, Be and Tc), and want to always shape up to CIR+EIR, i.e. they want to always go to the PIR, accepting the risk that the packets over the CIR may get dropped or marked for future dropping. Naturally, they specify the CIR in their shape peak command but the shaping in this case is backed up by the idea that they can always send Bc+Be bytes.
I would love to hear your opinion on all of this.
Best regards,
Peter
