How does QoS/VoIP work with SmartPorts Wizard on ESW switches?

[davebainum]

Hi all,

Okay, so here's a question as I continue to try to learn the innards of these Cisco ESW switches.  Hopefully this isn't too horrible of a "stupid newbie" question - however I just haven't had time to read the full 600-800 page ESW Switch manual yet ;-), and mainly I've used a lot of Netgear switches over the past few years...

So - how does Cisco handle QoS, particularly for VoIP phone systems, when you use the SmartPorts wizard?  E.g. if you set a port profile of Switch, Router, or Server - will it automatically give VoIP/RTP traffic priority over other type of traffic?  I assume that it does so if you use the "PC and Phone" profile - but I wasn't as sure if you use a Switch, Router, or Server profile.

Along those lines - which SmartPorts profile is recommended for an IP PBX?  Server?

TIA,

-- Dave Bainum (dbainum@ritetech.net),  PMP*
[PMP=PMI Certified Project Management Professional]
<Interested in great RP & other IT deals?? See tinyurl.com/plf8wz>
RiteTech LLC / www.ritetech.net / +1 (703) 561-0607
Creators of the www.RPConnect.net suite of applications

[David Harper]

The main difference from a QoS perspective between the different port types is what policing is applied to the various traffic streams, and whether we trust the QoS settings from the device.  In the case of an IP PBX, I'd suggest using Router, as that profile assumes a trusted device and there is no policing.  That means you won't overrun any limits if the IP PBX is terminating multiple voice streams like you would get if it has a conference bridge or similar media-terminating functionality.  I'd suggest Router over Switch as with Router, the spanning tree configuration should have portfast enabled so if the interface bounces for any reason, you won't have a 30-45 second outage while spanning tree reconverges.

Cheers,

Dave.

[davebainum]

Thanks so much for the response - greatly appreciated.

Okay, so to follow-up and just confirm that I'm understanding your guidance correctly, here's what I'm trying to set up over here with the ESW switches w/TB:

1. I have two sites linked together via site-to-site VPN (same ISP, same firewall on both ends).  The ESW 8 port switch is the "core switch" at each location, meaning directly connected into the firewall (which is in turn connected to high-speed cable modem), and the rest of the network fans out from there.  Site #1 is the primary location, which is where the IP PBX is located.  The IP PBX is directly connected to the ESW switch

>> Question - so from your message, you're suggesting that I apply I "Router" SmartPorts profile to the IP PBX port on that ESW switch, correct?

2. There are more devices on each network, of course, than the 8 ports.  So I have had to daisy-chain some non-Cisco switches to expand those ports out.

>> Question - so should I use "switch" or "router" smart profile for those ports that are connected to non-Cisco switches?  Keep in mind that there are some IP phones (as well as phones with PC's connected behind them using the phone's PC port) on some of those daisy-chained switches.

3. General question.  When the "IP plus phone" profile is used, I noticed that it automatically seems to set a voice VLAN (100) and I'm guessing does some other things under the scenes as well.  Is the ESW switch then automatically bumping up the priority of the RTP streams passing on those ports?  How does it then handle bumping up their priority on the port(s) connected to the IP PBX, or in turn, on the ports connected to the Internet interface (firewall)?  Would those ports also need to be assigned "IP plus phone" profile as well, or would the Router profile be sufficient as well?

4. And lastly - part of what's been going on (and what I'm trying to resolve) have been some voice quality issues that have recently erupted.  e.g. Jitter, latency, one way audio, etc..  This just started about 7-10 days ago.  It is probably not anything related to the LAN (I'm not sure, however) since things have been fine for months.  However as you know, it's notoriously tedious to track down the root causes of these issues.  I've done traces with the ISP and the ITSP - next steps (after confirming it's not issues on their end) would be to set up a monitor port with Wireshark and try to investigate where exactly these packets keep getting dropped or munged up.

Thanks so much for your assistance,

-- Dave Bainum (dbainum@ritetech.net),  PMP*
[PMP=PMI Certified Project Management Professional]
tinyurl.com/plf8wz>
RiteTech LLC / www.ritetech.net / +1 (703) 561-0607
Creators of the www.RPConnect.net suite of  applications

[David Harper]

So to try and tackle your quesions in order:

1. Yes, the 'Router' smartports setting should give you the best set of configuration settings for an IP PBX.

2. For connections to other switches, you should pretty much always use the 'Switch' setting.  Though if the other switch is an unmanaged device and does not support VLANs or 802.1Q trunking, then using 'Other' would be a better choice.  But you may need to manually tweak some settings in that case - in particular, the policing of voice traffic if there are voice devices on that switch.

3. If you set the port to Desktop+Phone or Router or Switch, the ESW won't remap DSCP/CoS settings so much as trust the setting applied by the attached device.  Desktop+Phone is slightly different in that the port will trust the settings only up to a point.  If the volume of traffic exceeds a certain threshold, then packet QoS settings will be remarked.

4. Voice quality issues can be tricky.  The first step is to try an isolate the problem to the LAN or the WAN.  Have you tried checking calls made purely within the LAN envirnment - direct extension to extension calls in other words?  If those calls are working reliably than that almost defnitely points towards the WAN or the router.  At the moment though, it sounds a bit like you're digging around in the dark.

Cheers,

Dave.