Question to Class of Service

[uwe.dreier]

I have had lot of discussions on the below question .. maybe somebody can guide me to a 120% watertight answer

If we have say 30Mbps IP bandwidth and the customer requests 8Mbps Rt-Vo (EF). I understand that is there is no Rt-Vo traffic this 8Mbps is still available for other traffic (Date Classes D1, D2, D3). However if I have some (1Mbs for example) voice traffic, will the remaining 7Mbps we available for other traffic or will suddenly only 22Mbps be available for traffic in other CoSs?

[sivai2tech]

EF will have 8Mbps reserved and the reset available BW(22Mbps) is for other queues.

If there is no rate-limit configured for the EF queue & it is not full, then leftover BW from EF + 22Mpbs will be available for other queues.

Thank You,

Siva

[Joseph W. Doherty]

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Posting

Answer depends on how the 8 Mbps has been "reserved".  Usually, it's a soft reservation which means unused bandwidth is available for other purposes.  This would include the reserved class not using any or all of its bandwidth.

For example, a typical CBWFQ policy might look like:

policy-map softReserve

class 8MbpsLLQ4EF

priority 8000000

class class-default

bandwidth 22000000

But an unusual policy might be like this:

policy-map hardReserve

class 8MbpsLLQ4EF

priority 8000000

class class-default

bandwidth 22000000

shape average 22000

If you're wondering why the 2nd policy might be used, could be a ISP policy where you've "contracted" for 8 Mbps of EF bandwidth and 22 Mbps of non-EF bandwidth rather than contracting for 30 Mbps of bandwidth, of which 8 Mbps gets priority treatment.