Alex Balashov wrote:
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I'm pretty sure they meant two logical networks.  At least, I hope they did.
Unfortunately, I was indeed referring to two physical networks. Cabling, switches, everything, all the way back to the TDM connection to the PSTN.
David Gibbons wrote:

Two separate networks? Did I miss something? I feel like I'm taking crazy 
pills! Two separate physical networks means twice the hassle, twice the 
maintenance, twice the cost, twice the headache. Not to mention the fact that 
the whole idea of VOIP is to simplify IT and focus on converging data and voice 
networks.

This is what VLANs and QOS do best. I dare say it's what they were designed 
foe. I can't think of any reason that I would ever recommend two ports per desk 
to support telephony -- ever. It's ludicrous to think that two ports will be 
better than one if we're setting up our VLANs and QOS properly. A phone takes 
very, very little bandwidth away from the desktop and a decent one will support 
tagging its frames for the alternate voice VLAN.

I agree, especially about QoS design intent. But I posted my question as a sanity check, and there seems to be no shortage of opinions. Now mine:

I can think of two valid reasons to physically segregate the networks:

1) Insurance. I.e., to eliminate the possibility that otherwise properly configured QoS mechanisms become broken, either by accident, incompetence, or badly-designed or rogue software or hardware - or are otherwise handled carelessly as Jerry Jones suggested. But this is not a compelling argument to me in any but the most critical scenarios such as public-safety applications, etc.

2) Customer preference. If you need the business, then the customer is always right. You might not have adequate credibility with the customer or influence over the design decision, and if a customer in such a situation gets it in their heads that voice and data can't coexist on wires, then it can't.

There is a variety of opinions, but no general consensus about where QoS failures typically occur, when they occur.

I'm wondering if anyone has anyone has ever experienced QoS issues caused by contemporary Polycom phones like IP330s that had workstations hanging off their builtin switches? If you did, were you able to identify the cause, and was it due to any inherent failure of the phone, such as not marking packets or prioritizing dispatch correctly?



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