[asterisk-users] Cisco Router QOS and IAX2

[Bruce Reeves]

Thank you so much. After fighting with a large/extensive QOS policy from
Cisco's SDM tool, I used your sample and tweaked it for my needs and
everything started working fine.

Bruce

On 8/23/06, Rich Adamson <radamson at routers.com> wrote:
>
> Bruce Reeves wrote:
> > I'm needing some pointers from anyone who has been able to get Cisco
> > routers to recognize the iax protocol and perform QOS on it. Or if there
> > is a better way to get my iax traffic prioritized by the router.
> >
>
> You can either match on udp/4569, or, match on TOS header bits. I like
> using the TOS header bits personally as lots of other protocols (eg,
> dns) will eventually match on udp/4569.
>
> For the TOS bits & v1.2.10, use tos=lowdelay in iax.conf and on the
> cisco use an access list to match on the tos bits. Something like:
> access-list 103 permit ip any any dscp cs3
> access-list 103 permit ip any any dscp ef
> access-list 103 permit ip any any tos min-delay  <= same as tos=lowdelay
> access-list 103 permit ip any any tos 12
>
> For the TOS bits & svn truck, the tos= settings have changed in
> asterisk. Look in the supplied documentation (eg, readme's, sample
> configs) for exactly what is allowed in terms of DiffServ (new term for
> TOS basically). You'll find examples that support the above access list
> item "dscp cs3" and "dscp ef".
>
> If you're not all that experienced on cisco qos, then the following is
> an example of a working config that you should be able to translate into
> your router config one way or another.
>
> class-map match-all voice-rtp
>    match access-group 103
> class-map match-all www-traffic
>    match access-group 105
> !
> policy-map voice-policy
>    class voice-rtp
>      priority percent 40
>    class www-traffic
>     bandwidth percent 30
>    class class-default
>     fair-queue
> !
> interface Dialer0
>   bandwidth 555
>   <snip, my specific interface config statements>
>   service-policy output voice-policy
> !
> access-list 103 permit ip any any dscp cs3
> access-list 103 permit ip any any dscp ef
> access-list 103 permit ip any any tos min-delay
> access-list 103 permit ip any any tos 12
> access-list 105 permit tcp any eq www any
>
> The above config provides low-latency "priority" to voice-rtp, then
> provides an additional qos piece to ensure www-traffic is given
> bandwidth before all of the "class-default" traffic. In other words,
> voice-rtp traffic will always get 40% of the bandwidth (eg, 40% of
> bandwidth=555 above) "if" voice traffic is present. If voice traffic
> isn't present, that bandwidth can be used by other qos sections or by
> the default class. Same with www-traffic "after" the router deals with
> voice-rtp traffic. The default class always gets what bandwidth is left
> over (or all bandwidth if there is no voice-rtp or www-traffic).
>
> To troubleshoot the above, do a "show access-list 103" from the CLI (on
> the router) and watch for matching packets in each access list line.
> Once you've structured the access list to truly match asterisk traffic,
> then do a "show policy-map interface dialer0" to display how the overall
> qos structure is functioning.
>
> Note that cisco didn't get real serious about IOS qos until v12.2 of
> their IOS code. In v12.2 (and later versions of IOS) there has been a
> significant amount of work to bring all of their products into industry
> standard implementations / conformance / expectations. If you want to
> get real serious with cisco's qos stuff, purchase the book "End-to-end
> QoS Network Design" and read the 700+ pages devoted to the subject. It
> is an excellent book with lots of examples, etc. The book (and actual
> practice) suggests IOS v12.3 has more QoS funtionality then v12.2, and
> v12.4 has more then v12.3. (The authors of the book back that statement
> up 100% as well, and they are cisco employees.)
>
> In the above config, the "bandwidth=555" statement is very important. It
> should represent the "actual" outgoing bandwidth for whatever interface
> you are using and not the theoretical max that someone said you should
> get.
>
> Also note that for relatively slow speed interfaces (eg, most dsl's),
> the outgoing bandwidth is rather slow. If you calculate how much time is
> consumed sending a non-voice 1500-byte packet, the time is likely to be
> more then the 20 millisecond interval for sip/iax traffic. If that is
> your case, then you may need to forcibly reduce the MTU size of packets
> originating from other non-voice workstations/servers. The later cisco
> IOS versions have a parameter to do that if you can't do it via the
> workstation/server configuration parameters. If memory serves correctly,
> that parameter appeared around v12.4 of their IOS.
>
> One last item... all of the above deals only with "outgoing" traffic.
> You would need to talk to your ISP about QoS for your incoming traffic,
> and most of the local ISP's don't have a clue. Increasingly, some of the
> larger backbone isp's are beginning to understand QoS and some have
> actually implemented something. However, those isp's are heading towards
> providing QoS as a value-add chargeable service (as in MPLS, etc).
>
> R.
>
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-- 
Bruce
Nortex Networks
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