ip telephony

[mgupta]

In a campus environment I need to provide 2000 nodes

and equal number of phones. Is it safe to go entirely

for IP phones without a single conventional phone or PABX. How many IP phones a single call manager server can support.

[geremy]

The purpose of the Call Manager is to replace the conventional PBX. I am assuming you mean analog when you say conventional phones, which are supported for limited use through FXS ports on a voice enabled router.

Cisco's recommendation for the number of phones supported by a single Call Manager is not as cut and dry as you might think. In a lot of the documentation that you will read, Cisco throws around the figure 2500. While you might inclined to think this means phones, in actuality it means "Device Units" with each device that registers with a Call Manager carrying a different weight. For instance an IP phone carries a weight of 1. Doing the math, 2500 phones multiplied by 1 device unit per phone equals 2500 device units. Or Cisco's claim that a single Call Manager can handle 2500 phones. Soft phones on the other hand carries a weight of about 25 I think, and a DSP carries a weigh of 3. So any combination of the above must not exceed 2500. Mind you 2500 is not a hard line, but rather Cisco's recommendation. Performance will begin to degrade the more devices you add that exceed the 2500 device unit limit. Hence the use of clustering.

[kechambe]

Here is some addition information on device weights per server:

MCS-7835 -- PIII 733Mhz, 1G Ram

Maximum Device Units: 5000

Maximum IP Phones: 2500

MCS-7830 -- PIII 500Mhz, 1G Ram

Maximum Device Units: 3000

Maximum IP Phones: 1500

MCS-7830 -- PIII 500Mhz, 512M Ram

Maximum Device Units: 1000

Maximum IP Phones: 500

MCS-7822 -- PIII 550Mhz, 512M Ram

Maximum Device Units: 1000

Maximum IP Phones: 500

MCS-7820 -- PIII 500Mhz, 512M Ram

Maximum Device Units: 1000

Maximum IP Phones: 500

Thanks,

Keith

[gbabade]

it is not safe because your system will not be scalable therefore you must have at least one conventional phone,

[mtashiro]

The majority of our implementations has been to replace the PBX. We usually start with one CM and if redundancy is required or additional nodes is required then we add CM's.

While a conventional POTS line is not required we recommend at least one POTS line in case of a catastophic failure to be used for emergency cases. With the prevalence of cell phones, many customers do not install a POTS line.

[pkireev]

Telephony calls are busines critical and as I suppose if you are going to implement IP telephony network with 2k nodes you must think about redundancy and load sharing.

So I guess to deploy redundant design.

Regards

Petr

[sofia]

A single CallManager support upp to 2500 phones

[lferre]

A single call manager (MCS 7835) can support 2500 voice "unit". Devices are using defined number of units on a call manager. For example, an IP phone use 1 unit (which mean you can support 2500 phones) but a soft phone use 20 (along with H323 gateway and other stuff).

So to support 2000 phone, I would think a tandem call manager (primary and secondary for redundancy) would do the job nicely.

You also can add servers in a cluster at a later date, to support additionnal phones / users.