Network Connectivity - Bridging two channels in dahdi using DACS
Table of Contents
What is DACS?
(AKA DCS and DXC)
DACS - Digital Access and Cross-connect System
DCS - Digital Cross-connect System
DXC - Digital Cross-connect.
What does DACS do?
DACS is a driver-lever circuit switch, as opposed to a packet switch. It is used to switch channels on T1/E1 connections. The traffic from one channel or set of channels will all be switched to another channel or set of channels.
DACSRBS is DACS with Robbed Bit Signaling, which is popular in the US. Contact your Telco to determine if you should use RBS.
How should DACS be configured?
DACS bypasses Asterisk entirely. You should not configure DACS'd channels in chan_dahdi.conf, as Asterisk can not use them. Configuring DACS'd channels will result in unexpected behavior. DACS does not do any signaling, and should be transparent to end users. DACS is a channel-switch, not a packet switch, and doesn't care what's on the T1/E1 channel, it just redirects onto another channel.
DACS is configured in /etc/dahdi/sytem.conf. Here is the information from the sample /dahdi/system.conf file:
# dacs::
# The DAHDI driver cross connects the channels starting at
# the channel number listed at the end, after a colon
# dacsrbs::
# The DAHDI driver cross connects the channels starting at
# the channel number listed at the end, after a colon and
# also performs the DACSing of RBS bits
# The channel list is a comma-separated list of channels or ranges, for
# example:
#
# 1,3,5 (channels one, three, and five)
# 16-23, 29 (channels 16 through 23, as well as channel 29)
Configuration example of a one to one mapping(cross-connect) for two T1 spans:
span=1,0,0,esf,b8zs
span=2,0,0,esf,b8zs
dacs=1-24:25
Result of this configuration:
Span 1 Span 2
Dahdi channel 1 25
Dahdi channel 2 26
Dahdi channel 3 27
...
Dahdi channel 24 48