HP 2800 series and QoS over WAN links

[newman00]

We have a customer that wants to run IP telephony and QoS. They have three locations linked by T-1's, but all in the same class C subnet. They are all on the same domain so there is a problem with too much traffic on these links. We have HP 2800 switches managing the bridged connections between locations. We are having ongoing phone difficulties and need to re-engineer a solution. The question is - what should we be proposing? This solution was kind of thrust upon us by the IP phone vendor. Or is what we have workable with proper QoS setup?

[André Beck]

Hi,

the *actual* problematic points in this setup are the devices that have the bandwidth slope, I assume these are Ethernet-T1-Bridges? The optimum solution would of course be to separate IP networks and start to route the WAN, but it's not impossible to have QoS even through a bridged WAN. It requires the bridges to do the QoS, though, or devices that are in front of the bridges and pre-shape to the T1 rates, applying QoS on the artificial queues constructed this way. If you never overfeed the bridges, their queuing behavior will not interfere any longer. This is actually a well-known workable setup, here in DE essentially all deployed customer DSL is PPPoE and there is often a dedicated "DSL Modem" that's actually a bridge between Ethernet and AAL5-SNAP on top of the DSL PHY. The bridge is typically unmanaged and has an arbitrary internal queue, but VoIP setups through such devices work better than expected just by pre-shaping.

I can't help you with doing that using ProCurve switches, though, and I don't have a clue with ProCurve routers. If I had to solve this, I'd do it by first making the WAN routed and then bringing in Cisco routers for the WAN and QoS work. The triple T1 sounds like a marvelous target for Multilink PPP with LFI (Link Fragmentation and Interleave), and MQC will allow any needed QoS protection for the voice traffic (taking away from the unprivileged data traffic, of course). I've done such stuff with triple E1 and Cisco CCM phones on either sides, worked like a charm even though their was a fair at one end, with countless people banging the Internet quite hard for traffic.

And IMO getting away from the bridged WAN is the only sane design choice in the long run anyway, for data too. If the IP phone vendor loathes it, they should not call their phones IP-phones - IP implies routing.

HTH,
Andre.

[Pieter 't Hart]

you may consider configuring a router at each location with one interface in the T1-subnet and another to a dedicated local subnet/vlan for VOIP.

each router communicates through the T1-network to the other voip-subnets.
But now you are able to differentiate this traffic from the other network traffic and configure QoS on the T1-links, based on source or destination network.
And locally based on vlan/subnet.

Pieter

[André Beck]

Pieter,

> you may consider configuring a router at
> each location with one interface in the
> T1-subnet and another to a dedicated local
> subnet/vlan for VOIP.

Not only the VoIP network(s). The data network(s) have to be hauled through this router as well, it has to sit in front of the T1 links *exclusively* for any QoS to be achieved.

If there's desire to stay with the Ethernet-T1-bridges (yes I know, they are already there and paid for), the router has to do the pre-shaping to eliminate the adverse effects of the queues in those bridges. If these are actually three independent bridges (or media converter style devices) bundled by a link aggregate, things get even worse because there is no known max bandwidth to pre-shape to (due to the well know property of Ethernet link aggregates to load-balance statistically only).

Given all these issues, I'd strongly recommend to eliminate the Ethernet-T1-conversion hardware entirely and use T1 serial interfaces in the routers. With MP and LFI, you win big time and achieve perfect QoS.

HTH,
Andre.