Linksys SPA9000 Administration Guide

Linksys Voice System Administration Guide 51
Configuring Line Interfaces on the SPA9000
Configuring Phone Lines and Calling Routing Behavior
Configuring Call Capacity for a Line Interface
Each line interface has a limited number of simultaneous calls that are allowed, based on the
Call Capacity parameter. When the maximum call capacity is reached, the SPA9000 does not
allocate any more calls to that line interface.
This section includes the following topics:
• ”Bandwidth Requirements and Call Capacity,” on page 51
• ”Setting the Call Capacity Parameter,” on page 52
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 LVS 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.
Table 4-1 provides the approximate bandwidth budget for different codecs.
Table 4-1 Bandwidth Budget
Codec
Approximate bandwidth budget (kbps)
Each side of
conversation 2 calls 4 calls 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

Linksys SPA9000 Specifications

Physical Interfaces

Ethernet ports	2 10/100BaseT RJ-45
Phone ports	2 RJ-11 FXS
Ring voltage	40-55 VRMS
Ring frequency	10 Hz - 40 Hz
Maximum ringer load	3 REN

Power

On-hook voltage	-50 V NOMINAL
Off-hook current	25 mA min
Terminating impedance	Configurable, including 600 ohms