[cisco-voip] QoS on Multilink T1's

[Nick Matthews]

That looks normal.  You can try reducing the tx-ring-limit on the
physical interfaces.  We usually set it to 2 or 3.

-nick

On Fri, Mar 23, 2012 at 1:00 PM, Joseph Mays <mays at win.net> wrote:
> We have the following service policy on a router that priorities VOIP
> traffic according to the ef tag.
>
> class-map match-all dscp-ef
>   match ip dscp ef
> !
> !
> policy-map queue-on-dscp
>  description Prioritizes voice traffic first, signalling next.
>   class dscp-ef
>    priority percent 75
>   class class-default
>    fair-queue
>    random-detect dscp-based
>
> The router primarily contains traffic for T1's routed to several
> destinations.
>
> I can demonstrate that for individual T1's the service policy does as it
> should. Throw normal pings at the remote end, things are low latency and no
> packet loss. Ping flood the remote end with 1500 byte packets and latency
> for normal pings and packet loss go sky high. While still pingflooding,
> pings tagged with DSCP ef still have low latency and no packet loss. This is
> all the way it should be.
>
> However, it generally doesn't work for the multilink client on the box. In
> this case, while ping flooding, packets with and without the EF tag set all
> suffer the same high latency and packet loss during ping flood. Not
> surprisingly, this one client is also having VOIP call quality problems. All
> the clients are using the same service policy. I have been assuming that
> it's something about the fact that this client has two multilink T1's bonded
> together with multilink PPP and other clients just have a single T1.
>
> Is there somethings special that has to done for QoS over multilink PPP? Or
> is there possibly some other thing affecting this one client? There are no
> specific access lists relating to their connection, nor to the ones that
> work. Really, the only thing overt that sets them different from the others
> is that they have bonded T1's, as shown below.
>
> interface Multilink117870
>  description Bonded Pair to Edge Outreach
>  bandwidth 3072
>  ip address 216.24.2.145 255.255.255.252
>  no cdp enable
>  ppp authorization PermT1
>  ppp multilink
>  ppp multilink group 117870
>  service-policy output queue-on-dscp
>
> interface Serial6/0/1:0
>  description Edge Outreach (K1.HCFU.511024..SC)
>  bandwidth 1536
>  no ip address
>  no ip redirects
>  no ip proxy-arp
>  encapsulation ppp
>  ppp authorization PermT1
>  ppp multilink
>  ppp multilink group 117870
> !
> interface Serial6/0/2:0
>  description Edge Outreach (K1.HCFU.511025..SC)
>  bandwidth 1536
>  no ip address
>  no ip redirects
>  no ip proxy-arp
>  encapsulation ppp
>  ppp authorization PermT1
>  ppp multilink
>  ppp multilink group 117870
>
> Here is an example of a plain single T1 client config, in which case the QoS
> service policy works exactly as it should.
>
> interface Serial6/0/3:0
>  description Leonard Brush (K1.HCFU.511093..SC)
>  bandwidth 1536
>  ip address 216.24.0.53 255.255.255.252
>  no ip redirects
>  no ip proxy-arp
>  encapsulation ppp
>  ppp authorization PermT1
>  service-policy output queue-on-dscp
>
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