[Asterisk-Users] What business IP phone to use

[Cory Andrews]

Has anyone tried the Linksys SRW224P? 24 Port managed switch, 10/100, 2 Gig 
Uplink Ports, PoE:
  a.. Delivers reliable power over 10/100 Ethernet ports using IEEE 802.3af 
standard
  b.. Secure management via SSH/SSL and secure user control via 802.1x & MAC 
filtering
  c.. IGMP snooping, L2/L3 COS, queuing & scheduling makes solution ideal 
for Voice/Video
  d.. Intelligent traffic management with Rate Limiting, Policing ACLs, and 
Storm control
All that for around $450....we have not put one of these through any heavy 
duty production stress tests, but I was amazed at the features on this thing 
for the price.

Cory J Andrews
++++++++++++
VOIPSupply.com
454 Sonwil Drive
Buffalo, NY 14225
++++++++++++++
voice - 716.630.1555 X22
email - Cory at VOIPSupply.com
AIM - B2CORY
----- Original Message ----- 
From: "mustardman29" <mustardman29 at hotmail.com>
To: "'Asterisk Users Mailing List - Non-Commercial Discussion'" 
<asterisk-users at lists.digium.com>
Sent: Friday, February 24, 2006 8:01 PM
Subject: RE: [Asterisk-Users] What business IP phone to use


> 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.
>>
>>
>>
>>
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