End to End QoS Questions

[abodden]

Here's an excerpt from the Cisco Press QoS book.  I do recommend the book.

"Example 4-7 shows class-based shaping on a T1 interface to a 768-Kbps CIR with the Bc set to the recommended value for real-time networks Be set to 0."

"shape average 768000 7680 0"

Szigeti, Tim; Hattingh, Christina; Barton, Robert; Briley, Jr., Kenneth (2013-11-21). End-to-End QoS Network Design: 

Why is the Be set to 0 for a T1 carrying voice?  Should all voice carrying links have their Be set to 0?

Thanks

[Vasilii Mikhailovskii]

Hello.

Actually BC and BE defines token bucket capacity and Tc interval. BC responsible for conformed traffic; BE for exceeded.

So, per my understanding, if you want not to exceed link/class capacity (on shape average), you need to keep BE equal to zero.

[abodden]

Thanks for your replies.

It sounds like if the ISP's policing policy is unknown then Be=0 is the safe bet for voice links.

[manish arora]

By Default, The IOS set Bc = Be if not mentioned in the configuration. Setting Be = 0 is not a requirement for Voice or any other traffic, The value of Be depends upon the policing method being used by the ISP, if the ISP is capable of handling the extra bits that are being sent using the secondary Be bucket tokens than you use this 2 Bucket configuration otherwise you stick to Be = 0.

Manish