Cisco Systems SPA9000 manual Bandwidth Requirements and Call Capacity, Bandwidth Budgeting

Configuring Phone Lines and Calling Routing Behavior	4
Configuring Line Interfaces on the SPA9000

Bandwidth Requirements and Call Capacity

The available connection bandwidth determines the maximum number of simultaneous calls that the system can support with the appropriate audio quality. Before installing and configuring the Cisco SPA components, use this information to determine the maximum number of simultaneous VoIP connections that the system can support. For asymmetric connections, such as ADSL, the maximum number of calls is determined by the upstream bandwidth. In general it is a good practice to use no more than 75% of the total available bandwidth for calls. This provides space for data traffic and helps ensure good voice quality.

The following table provides the approximate bandwidth budget for different codecs.

Table 1 Bandwidth Budgeting

Codec

Approximate bandwidth budget (kbps)

Each side of	2 calls	4 calls
conversation

6 calls

8 calls

G.711	110	220	440	660	880
G.726-40	87	174	348	522	696
G.726-32	79	158	316	474	632
G.726-24	71	142	284	426	568
G.726-16	63	126	252	378	504
G.729	55	110	220	330	440

SPA9000 Voice System Administration Guide 64