Weight Chart for IP Telephony Devices
Weight per Instance per Total Device
Device Type Instance Device Weight
IP phone 1 1 1
Analog gateway ports 3 Variable 3 per DS0
T1 gateway 3 24 72 per T1
E1 gateway 3 30 90 per E1
Conference resource 3 Variable 3 per instance
(hardware)
Conference resource 3 48 144*
(software)
Transcoding resource 3 Variable 3 per instance
Software MTP 3 48 144*
CTI port (TAPI or JTAPI) 20 1 20
Messaging (voice mail) 3 Variable 3 per instance
Cisco SoftPhone 20 1 20
Inter-cluster trunk 3 Variable 3
*If installed on the same server as Cisco CallManager, the maximum number
of sessions is 48.
For example, an infrastructure containing 1,250 IP phones, 2 T1 gateways, a
software conference resource, and two Cisco SoftPhones, would constitute the
following formula: (1,250 x 1) + (2 x 72) + (144 x 1) + (20 x 2) = 1,540 total
device weight (device units).Table 4.4 details the maximum number of device
units that may be serviced by specific server platforms. Currently, you cannot
have more than 2,500 IP phones registered with a single Cisco CallManager,
even if the maximum device units allow it.