MQC question

[anitachoi3]

Hi,

I have two configuration A and B.

The config A is from ONT book and it should be correct setting.

The config B is from me and it may not work.

My questions are that:

1. for config B, what happen if I config it?

2. for config A, why "service-policy" in policy-map? why it below the class-default?

rdgs

! R1 configration A

class-map match-any voip

match ip precedence 5

match protocol rtp

!

policy-map pri-q

class voip

priority 96

policy-map default

class class-default

shape peak 128000

service-policy pri-q

interface serial1/0

service-policy output default

! R2 configration B

class-map match-any voip

match ip precedence 5

match protocol rtp

!

policy-map pri-q

class voip

priority 96

class class-default

shape peak 128000

interface serial1/0

service-policy output pri-q

[Giuseppe Larosa]

Hello Anita,

class-default stays for every packet that doesn't match the configured class-maps.

You don't need to configure class-map class-default it is available to use in the policy-map.

In your case every packet that:

doesn't have IP precedence 5 in the ip header AND it is not an RTP packet will be a match for class-default.

So in this way a priority queue for VoIP traffic is defined that allows one G.711 conversation and its signalling traffic.

All other traffic is shaped to 128 Kbps.

I think config A is wrong because it applies to the interface policy-map default that simply shapes all traffic to 128 Kbps.

Config B is correct for providing LLQ to VoIP and shaping all other traffic.

Hope to help

Giuseppe

[Marwan ALshawi]

hi Giuseppe

i think it ok i mean config A

because class defualt mean everything

and the idea is here for teaching the nested policy map

by the way in config A it if we use a GK the policy not enough for one g711 call as with CAC with GK each call need 128 bandwith while with CCM CAC 80 enough

so the CONFIG A shape the entire trafic to 128 and give voip 96 from that 128

hope this helpful

[Giuseppe Larosa · Accepted solution]

Hello Marwan,

thanks for your helpful correction I had missed the call of child policy inside policy default so I thought wrongly it wasn't a correct nested policy.

With CCM is 80 kbps: 64 kbps for codec G.711 and 16 kbps as headers overhead.

Best Regards

Giuseppe

[Marwan ALshawi]

no worries and thanks for rating :)

[Marwan ALshawi · Accepted solution]

the service policy in policy map here caqlled nested QOS

the first policy whic is defualt shape the traffic (overall traffic ) to 128K

then for this 128k it apply a policy map

then is will give 96k to voice from 128

this helpful when u have subintefrfaces and each subinterface has bandwith diffrent from the original physical bandwitdh like suninterface 1 need 128 and the other 512

with this way u can avieve it

with config B

the voip will take 96k from the link and all other traffic will take max as 128K any traffic go above 128 will be droped even if the bandwidth available

while the voip class will use over 96 if the bandwdth available on the link and the link not conjisted

good luck

if helpful Rate

[anitachoi3]

Hi,

some questions

1. for the config A, if there is 600K b/w leave and no another flow (class) using any b/w. Can voip use more than 96? if yes, can voip use up all idle b/w (e.g. 600K)?

2. for the config B, if there is 600K b/w leave and no another flow (class) using any b/w. Can voip use more than 96? if yes, can voip use up all idle b/w (e.g. 600K)?

3. "this helpful when u have subintefrfaces and each subinterface has bandwith diffrent from the original physical bandwitdh like suninterface 1 need 128 and the other 512", I cannot catch your idea. could you explain more?

4. for the config A, the min b/w is 128K, isn't it?

5. for the config B, the min b/w is 128K + 96K, isn't it?

6. which config is better ? A or B

rdgs

[sajan.mathew · Accepted solution]

Hi,

I am not a Qos expert, but responding with the best of knowledge.

1. --> Yes, but since the class is attached to the default class which is 128k, you will get only an effective 128, not the full.

2. --> Yes, voip class can use all the bandwidth, but please note that at the scenario of congestion, the class will get policed at 96.

3. --> I think what is mentioned is that, if you have different interfaces which needs similar configuration, you can just add the "service-policy" entry into the class rather than re-defining the class in each and every interface. It is also good if you have to change the bandwidth of the voip class as you would only have to redo the "pri-q" class rather than all the individual policies.

4/5. --> No, minimum bandwidth is 96.

6. --> That is tough and it also depends on what you are trying to do. Both configs are slightly different. If you are trying to manage the voip alone, I think B is better.

Hope this helps,

[Joseph W. Doherty · Accepted solution]

"1. for config B, what happen if I config it?"

If there's interface congestion such that packets are software queued, the voip class packets will be sent first if any packets are queued to it, but if their rates exceed 96 those voip class queued packets will be dropped. Also, non-voip class packets will queue in the class-default class. Such queued packets witll be sent when the voip queue is empty.

Regardless of interface congestion, class-default class packets will not be allowed to have an average send rate higher than 128 Kbps. Those that do, will be queued and will be sent such to not exceed an average rate of 128 Kbps.

"2. for config A, why "service-policy" in policy-map? why it below the class-default?"

A shaper alone, when it shapes traffic, as far as I know, uses fair-queue but instead of this default, a subordinate policy determines how the packets queued by the shaper are released. For instance, config A would release voip class packets queued by the shaper before non-voip class packets.

Why is the service policy applied with class-default is because that's where the shaper is applied.