Question about a new install

We are planning on installing an Asterisk server in our new office. The problem being is that the electricians only pulled one cat5 to each desk. Here’s a basic description of our setup:
4 POTS lines
5-6 IP phones+fax machine
Digium 1AEX841EF (I’m thinking this card, it looks like the one that will suit our needs)
P4 3.2ghz 2gb ram (dedicated to asterisk)

Right now our router is a linksys 54gl running DD-WRT and has been solid so far. And a couple of cheap switches to connect everything. But that can be upgraded too if need be. I was thinking about getting a 8 port switch to tidy everything up.

Our computers that are hooked into our current network right now don’t use a ton of bandwidth with our software, but there are times when larger files are emailed out during the day. And there are 5-6 computers on the network at one time.

Will we have issues running dual ethernet phones and hooking the PC’s into that? Or should I be trying to run two separate 100base networks down one cat5 to keep it separate? If we really have too, I’ll pull more line and just install it in conduit on the walls instead, but I’d kindof like to avoid that one if possible.

Any suggestions are welcome!

For the voice you need 64Kbps per line. Can you make some QoS/ToS?

Yep, that can be done with the router that I have. Or would it work to just run two separate networks down the one cat5 line? None of the runs are terribly long, around 20-30 feet. I’m just worried about interference slowing everything down.

I have done that, where a single cable had to be split between voice and data, but it’s not ideal. If all you need is data, stay with one network. Are you sure it’s category 5 - if it’s a recent installation it could be cat 6, which should support a gigabit network (but this would require all 4 pairs.) If you are concerned about the physical network, I suggest you invest in a good quality network tester e.g From your description, it seems like you will not be passing any voice traffic through the router to the outside world, in which case qos on the router isn’t going to give you very much.

Have fun

[quote=“pmlco”][quote]From your description, it seems like you will not be passing any voice traffic through the router to the outside world, in which case qos on the router isn’t going to give you very much.

Ian, could you elaborate on the above statement?

Wouldn’t QoS give him the ability to push the very large emails at times without causing his VoIP traffic from lagging? I mean if your on a call and send a large email, your call would become choppy. With QoS his VoIP traffic should take priority and keep his call normal.

Okay wait, rereading what you said, you specifically mention the router. Which is correct, if the VoIP traffic is not going through the router, QoS on the router will not mater.

What he needs is a switch that does QoS, for the reasons stated above.

For what its worth, I’m running around 120 Aastra 6757 phones on our company network. The phones are dual port, didn’t want to come back and run extra wires. We put in NetGear FS728TP switches on each floor. These are POE switches, have QoS 10/100, with 2 - gigabit ports. The mulitple switches connect to the main switch over the gigabit port.

You are correct, but unless he has a really congested network, I doubt that qos on the switches is necessary, particularly if he can have a gigabit network. Your setup looks cool though, and if he is going to buy a switch anyway, might as well get one that can do qos.


Mostly true, until it isn’t. The networking issue with realtime traffic such as voice is regular (20mS interval default for most voice codecs) access to the network; early delivery is ok but late is same as dropped and we become dependent on the codec’s ability to cover. The lower bandwidth codecs are most susceptible to loss, G.729 mean opinion score (MOS) falls off rapidly from 3.8 to low 2 (poor mobile phone quality) in the presence of loss (or delayed)

Most folks think in terms of network bandwidth and network delay as being inversely proportionate, which it mostly is in the absence of any queuing or buffering.

Preferential queuing (aka QoS) only changes default queuing behavior in the presence of outbound queue congestion which would prevent a higher class of traffic from receiving the designated service level; any condition that causes outbound queue to backup, even for short period of time can cause realtime traffic to be delayed while awaiting dequeuing, QoS would move the time sensitive traffic forward in the queue to ensure service delivery.

The net result: there is no penalty to enabling QoS in a network, QoS only changes network behavior in presence of congestion which would negatively impact realtime traffic without QoS. If you think of QoS as ensuring network policy then QoS becomes much more useful even as a security tool: imagine what happens when a NIC goes bad or a machine becomes infected and generates large quantities of traffic. QoS describes the nominal network behavior for all classes of traffic and anything outside the norm is treated appropriately. For example a phone should not generate more than 100kbps of traffic anything outside that should be treated as an exception which QoS will do… did someone unplug the phone and doing something unauthorized?

Will it work without QoS? probably. Is it a good idea to enable QoS to provide all traffic classes the desired service level and protect the network from exceptions? absolutely.

Agreed - budget permitting.

So from what I can gather, two networks on one line might work, but its far from ideal. But with the number of phones + computers that we are running, a shared 100base network should be ok with QoS setup properly. Thankfully that is doable with the router that I have, and a decent switch. I was considering gigabit, but the phones that I was looking at don’t have gigabit anyway.

Well, I sure am learning a lot about networking today. :stuck_out_tongue:

Someone please correct me if I’m wrong, but the QoS on the router really won’t do much on an internal network right? It looks like that would be handled by the switch. So if I do try to go the route of having everything on one network, computers & phones, a good switch with QoS would be necessary right? But would that still work if I’m running the computers off of the phone’s dual ethernet ports?

Correct, the original suggestion for router QoS was probably assuming you’d be using that connection for SIP trunking to ensure voice traffic received higher priority over all other internet traffic… which is a very good idea if you ever intend SIP trunking, a single PC checking email can have an impact on voice quality… and given the asymmetrical nature of most broadband connections the uplink direction is usually impacted first meaning your caller’s voice may sound fine to you but your’s may be broken; be careful assuming because everything sounds good to you that everything is working correctly. I have first-hand experience deploying large telecommuter voice networks where the home user thought everything was peachy but outside callers thought otherwise.

Correct, QoS on the network switch will be most beneficial in this type of deployment. “Necessary” is perhaps too strong but if the budget permits I would consider almost necessary. What will you do if you do not have QoS on a lesser switch and voice quality is impacted? End users, and management, have very low tolerance for poor voice quality.

That depends on the phones you intend to use, the two ports on some phones my just be a layer2 switch with no awareness of QoS, or worse a hub. Some phones are very QoS aware even to the point of remarking PC traffic coming from behind, the phone enforces the QoS admission into the network; Cisco Enterprise phones are good examples of QoS aware phones for the PC port.

Best practice for QoS deployment is to place the policy enforcement/admission as close to the source as possible: if phones and PCs share a common network switch then place QoS on that common switch, if PC uses network port provided by the phone then place QoS on the phone… assuming you can; this may not be a good deployment model if you cannot.

well, thanks everyone for the help! We’re going to just run some more cable in the office so that we can keep the networks separate. That seems like the best solution, albeit not the cleanest looking, for the budget that we’ve got and for my experience level too. But I sure did learn a lot in the last couple of days! :smile: