QOS between 3750 and 2921 Voice Gateway

[Tomas Mazur]

Can anyone advise if I should add QOS to interfaces between 3750 and 2921 VG?

* 3750 - core

* 2921 - PSTN gateway 

Current settings are:

3750	2921
interface GigabitEthernet1/0/15 description <<UK-PSTN-01 Gi0/0>> switchport access vlan 50 switchport mode access flowcontrol receive on spanning-tree portfast trunk	interface GigabitEthernet0/0 description $ETH-LAN$$ETH-SW-LAUNCH$$INTF-INFO-GE 0/0$ ip address 172.21.100.5 255.255.255.0 duplex auto speed auto

Also QOS Maps

3750	2921
Dscp-cos map: d1 : d2 0 1 2 3 4 5 6 7 8 9 --------------------------------------- 0 : 00 00 00 00 00 00 00 00 01 01 1 : 01 01 01 01 01 01 02 02 02 02 2 : 02 02 02 02 03 03 03 03 03 03 3 : 03 03 04 04 04 04 04 04 04 04 4 : 05 05 05 05 05 05 05 05 06 06 5 : 06 06 06 06 06 06 07 07 07 07 6 : 07 07 07 07 Cos-dscp map: cos: 0 1 2 3 4 5 6 7 -------------------------------- dscp: 0 8 16 26 32 46 48 56	Dscp-cos map: dscp: 0 8 10 16 18 24 26 32 34 40 46 48 56 ----------------------------------------------- cos: 0 1 1 2 2 3 3 4 4 5 5 6 7 Cos-dscp map: cos: 0 1 2 3 4 5 6 7 -------------------------------- dscp: 0 8 16 26 32 46 48 56

[Joseph W. Doherty]

If there's nothing but VoIP traffic on that link, there's almost no benefit to having QoS.  However, as the 3750 is an all ports or no ports QoS, if QoS is globally enabled, you may want to customize its port settings to the 2921.

On the 2921, you can do per port QoS, but again, if the only traffic on the port to the 3750 is VoIP, very, very little benefit and using QoS (assuming you don't need to remark traffic or some such).

[Tomas Mazur]

Thanks Joseph

It is only VOIP and router management traffic. QOS is already enabled on the 3750. Can you recommend any particular settings to apply to the 3750 port connecting to 2921?

Tom

[Joseph W. Doherty]

You could use a different queue-set to optimize buffer resources for the queue(s) being used between the 3750 and 2921.  Also, if your management traffic comprises "stuff" like SNMP stats and an IGP.  You should prioritize VoIP and the IGP over SNMP.  How VoIP and IGP should be prioritized relative to each other, can be a little more difficult to determine.  I.e. if either, if using PQ can starve the other, perhhaps PQ shouldn't even be used for either.

[Georg Pauwen · Accepted solution]

Hello Tom,

in addition to all the other suggestions, this link provides examples for various CoS maps on different platforms and traffic types:

http://www.dslreports.com/faq/13324

[Georg Pauwen]

Hello,

are you asking if you should configure QoS on the link between the 3750 and the 2921 (or is it a 2960) ? Do you already have 'mls qos' configured globally, and e.g. auto qos ?