asterisk users - Mar 2006 - Managed Switches QoS to deal with network bottleneck

Good Day Everybody,

 

I am in the process of planning a phone system for a small business (15
extensions - 4 PSTN lines [to be connected by ATAs]). The plan is to install an
IP Phone everywhere there is an existing computer workstation - using the same
LAN for phones and computers.

 

The layout involves workstations connected to two switches (the unmanaged
'dumb' type) and the switches linked to each other by a buried cable. 
This link between the switches is a bottleneck - large file transfers through
the link are common enough that a disruption to VoIP traffic is pretty much
guaranteed.

 

I'm convinced that a QoS-based approach is the way to ensure file transfers
do not interrupt VoIP traffic.   (not to mention the fact that I don't want
to have to dig a ditch in the ground to run another cable parallel to the
existing link).

 

What are your opinions and experiences with:  3COM 4500,  Linksys SRW224G4?  
(The 3COM is already pushing the budget limit. I'm sure you get what you pay
for with Linksys but - that being said - would it work? Decently well?)

 

Any thoughts on cheaper approaches such as: D-Link DI-102 (Little Packet
Priortizer with 2 RJ45 ports),  or lower-end routers with QoS abilities like a
WRT54GS?  (I'm guessing these are more likely to cause a lot more packet
loss than using managed switches)

 

We are planning on using either Polycom 501, or SNOM 320/360s.  Does the switch
built into the phone handle QoS for the attached computer?

 

 

 

 

Thank you for your input.





Dana Harding
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On Thursday 02 March 2006 11:46, Dana Harding wrote:
> Good Day Everybody,
Hi.
> I'm convinced that a QoS-based approach is the way to
> ensure file transfers do not interrupt VoIP traffic.  
> (not to mention the fact that I don't want to have to
> dig a ditch in the ground to run another cable parallel
> to the existing link).
I've always said (I work for an ISP), apart from your 
customer and upstream links, what other links does a 
network expect to saturate? My basis for this thought is 
that local, core, internal bandwidth is cheap to install, 
maintain and upgrade.

Let's say your switches are "switching" Layer 2 frames 
like they should, are you already reaching 75% of the 
switch's switching capacity? Of course, the amount of 
bandwidth you can push through a single switch will 
depend on the vendor and model - but let's say you have a 
decent switch that can dos ome 80Mbps before it falls 
over, have you started hitting this already?

Let's look at your cabling - Cat-5 is generally good 
enough to run 100Mbps (sometimes 1000Mbps). Then again, 
you could run use fibre to interconnect the switches over 
a 1Gbps port trunk.

Either way, buying a switch that will do 10/100/1000Mbps 
per port including uplink ports, and support fibre uplink 
connectivity, is much better than trying to run QoS on a 
LAN. QoS has its own complications, but is really 
unnecessary on a well (read: over) engineered LAN; I 
think.

Just get yourself small 2950T Cisco switches (they have 2x 
1Gbps uplink ports), or a 3750 Cisco switch that has 
Gig-E support on all switch ports. Both are relatively 
inexpensive for the amount of bandwidth you'll achieve.

Cheers,

Mark.
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