voice calls over best effort qos

[santoshdpawar]

Hi Guys,

Do we get good voice quality for VOIP calls over best effort qos ? I do not have any dial peer or voice related configuration but only a best effort QOS.

Is there any specific config required for this ?

Best regards,

Santosh

[Chris Deren · Accepted solution]

Sure, as long as there is no congestion on the network. remember QoS comes into play only when the link(s) are congested. If there is congestion and you do not have QoS in place we will surely experience poor quality.

As to configuration it comes down to what kind of WAN links you have, the WAN router type, switch types, i.e. blades, supervisor, etc. Designing QoS is all about understanding the equipment's capabilities and ensuring end to end QoS.

HTH,

Chris

[santoshdpawar]

Hi Chris,

I am receiving voice traffic with DSCP EF on router 1. Telco has provided only default class ( best effort) on the link.

             dscp  EF                 Fa0/1                                                        Fa0/1               EF

[ voip ]-----------Fa0/0--------(R1) ---------------- MPLS with Best effort----------------------(R2)-----FA0/0 ------[voip]

As far as what I know telco ( MPLS provider) has only default class but I am getting my EF packets from R1 to R2 and vice versa. The only problem is I am getting packet drops if I ping from R1 to R2 with dscp EF (TOS set) which I guess is normal as telco may try to drop EF UDP rate.

Though it is best effort I have configured QOS on wan Fa0/1 with priority class and other classes. I still feel something is missing. Do I need RSVP, ACL with UDP ports etc etc

Best regards,

Santosh

[Chris Deren]

Correct, typically provider will drop all EF traffic that exceeds what you are guaranteed (paying for), so this is expected. You have to options here:

1. Order EF class based on the percentage you anticipate needing for your Voice class - this is what most customers that are serious about voice quality do.

2. Re-mark everything down to BE and send across WAN, this will put you in carrier's destiny as no QoS will be guaranteed.

I strongly urge you to consider option 1, if you are worrying about the amount of voice traffic being sent you can use Call Admission Control to control it (i.e RSVP, Locations based). 

Keep in mind that Cisco's best practice is to allocate 33% of link to voice class, but it really depends on link speeds and call requirements.

HTH,

Chris

[santoshdpawar]

Hi Chris, Cisco techies,

I am getting my af markings end to end and if I remark my EF packets from LAN to AF11 and use priority on the two routers ?

EF packets are being dropped if I try ping with above 300 byte size but if I remark to AF11 its not dropping. I hope it should change the way packets are being prioritized ?

Regards,

Santosh

[Chris Deren]

This is expected as I explained above as providers drop only EF class traffic.  AF11 might be better than BE but it is certainly not prioritized as EF in the MPLS cloud. So, if carrier experiences congestion your AF11 traffic will be dropped before other customer's EF traffic which they pay premium for.

HTH,

Chris