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Do we really need stiches for IP Phones?

Unanswered Question

Hi, there is one think that I always wondered:


does anyone know of any study that talks about having call manager and ip phones work in an environment without catalyst switches.


Sorry for a newbie question, but why exactly CAN'T we use a normal ethernet hub instead? IS QoS affected that much?


In the normal user environment using 100MBps, do we really need to purchase the switch or can we really get by without it? Fopr a 50 seat office, would it be possible to get by with 100MBps LAN and just have one router to connect to outside?


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gordon.hawkins Fri, 01/17/2003 - 08:44
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How many users are we talking about here? The linchpin to voice quality in IP Telephony is QoS or Quality of Service. Without QoS, you'll get laggy and lost voice packets because the SKINNY streams are TCP and by definition TCP is best effort, not best delievery. Voice is very *time sensitive* and you must tag it and have the voice traffic prioritized over all other traffic.


Last time i checked, hubs don't have QoS. I would highly recommend getting some catalyst power switches.. and using those. How are you getting power to the phones if it's not through the switch?

If you have 50 phones that are used an average amount of time, don't put them on hubs. There will be too many collisions and voice will likely suffer for it due to retransmits. Also, you will get global synchronization unless the hub performs WRED. That will cause retransmits for voice. Am I missing anything?


If by "normal ethernet hub" you really mean a "switched hub" from any vendor, you can get by, but do not expect to be able to transmit your voice data over a WAN, because you need to be able to mark voice data and send it ahead of less important data. If you cannot mark, you cannot queue or otherwise manipulate your traffic on the LAN and on the the LAN egress.


Also, unless you have an inline powered patch panel, you need to get 50 power supplies for the phones if you do not use Cisco's inline powered switches. That isn't totally cheap.


Finally, if you are spending the money on a Call Manager and maybe Unity or some other voicemail solution, why not use the complete solution? In the future when you want to add video to your network or some other interactive realtime media, you will have problems. It will cause more loss in time troubleshooting bad phone calls than it is worth.



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