[Asterisk-Users] What business IP phone to use

[mustardman29]

Interesting,

So are there any sort of specifications to look for?  What your talking
about does not sound like a managed vs unmanaged issue.  More like cheap
crap vs half decent.  I would never want any switch to drop packets VoIP or
not.  Does not sound like QoS could help resolve that or jitter if the
conflicting packets both have SIP priority.

Managed switches used to imply higher quality but I think we are starting to
see cheap and crappy managed switches coming onto the market.  I would still
choose a $500 unmanaged switch over a $100 managed switch.  If the switch is
doing it's job you should never have to view what is going on in there
anyways.

> -----Original Message-----
> From: Rich Adamson [mailto:radamson at routers.com] 
> Sent: Friday, February 24, 2006 9:43 AM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: RE: [Asterisk-Users] What business IP phone to use
> 
> 
> > Aha, micro seconds in networking terms is normally written 
> usecs or us 
> > (actually it's the greek letter mu as in ulaw) rather than ms which 
> > are milliseconds seconds - what had me puzzled was that it 
> was stated 
> > that this could harm the voice path!
> > 
> > > The difference can also cause unnecessary delays and 
> therefor echo 
> > > in the path. For example, procurve switches typically have 13ms 
> > > switching time, the high-end netgears about 21ms. As soon as you 
> > > stack a couple of switches you are talking 26ms vs 42ms 
> extra delay in the path!
> > 
> > There is then only 8 usecs between the two switches, how on earth 
> > would this make any difference to the voice path at all? 
> Let alone induce any echo...
> > 
> > Obviously the originally poster didn't understand the 
> difference. And 
> > based on this, he's probably advising people not to use Netgear 
> > switches for voice, oh dear.
> 
> I'll jump in here to make a couple of comments relative to 
> ethernet switches.
> Not all switches are created equal!!!
> 
> If you take the cover off a switch, write down the part 
> numbers for the chips used, and read the doc on those chips, 
> you'll see major differences.
> (We've actually tested several switches over the past several 
> years in real customer's networks as well.)
> 
> Many entry level switches on the market have only minimal 
> buffering for inbound and outbound packets. Its not uncommon 
> for output buffers to be limited to one or two packets, and 
> as a user, you can't chnage it.
> 
> Port congestion frequently shows up when two (or more) 
> devices connected to a switch (assume 100 mbs for now) try to 
> communicate via a single upstream port (assume 100 mbs for 
> now). The instantanous offered traffic is essentially 200 
> mbs, and the switch is expected to send that traffic out via 
> a 100 mbs port. For those devices with minimal buffering, 
> packets will be dropped. For newer switches with deeper 
> buffers, "some" packets will be held up in the chip's 
> internal queue waiting to get on the outbound port's wire. 
> The delay in the buffer will become jitter, and depending 
> upon exactly how many ports are contending for the outboud 
> port, the jitter _can_ become noticable. (That _is_ one of 
> the reasons why some switch vendors support QoS.)
> 
> One can talk about "wire speed throughput", etc, and it 
> doesn't mean squat. Those are all marketing and sales words, 
> not engineering specs.
> 
> There are plenty of very well known switch vendors that 
> purchase switches from other manufacturers and put their 
> names on the front covers. Some of those have characteristics 
> as noted above, while others manage the buffering and queuing 
> much better then what their marketing/sales words imply.
> 
> Its fairly common to see engineers in large corporate 
> networks using workgroup switches to consolidate traffic from 
> multiple wiring closets, and not pay any attention whatsoever 
> to "dropped packets" in the switches.
> That's about the time when senior mgmt intervens and asks an 
> external company to assess their network performance to 
> resolve the internal fingerpointing. Our company has 
> completed many of these.
> 
> The _only_ way to know for sure what a switch is doing (eg, 
> dropping pkts) is to ensure the switches have some form of 
> network management. Even the simple Dell 2708 (eight port gig 
> switch for $100) has "some" level of mgmt in it. Certainly 
> not the best, but at least you can identify some issues.
> 
> With the pricing drops that we've all seen over the last 
> couple of years, its fairly easy to find managed switches at 
> very reasonable cost. I'd _never_ using unmanaged switches in 
> any environment where critical application data flows across 
> the net, and I'd suggest voip traffic represents "critical" 
> traffic in all production networks.
> 
> 
> 
>