Configuring a T1 CAS Trunk
Configuring a T1 CAS block involves the agreement of ambassador settings as able-bodied as
voice anchorage parameters.
Controller Settings
Before configuring a T1 or E1 trunk, you charge adjudge on a array of ambit for the
T1 or E1 agenda controller. The afterward discussions explain the implications of these
parameter selections.
Framing Formats
The framing architecture constant describes the way $.25 are beggared from specific frames to
be acclimated for signaling purposes. The ambassador charge be configured to use the aforementioned framing
format as the band from the PBX or CO that connects to the articulation anchorage you are configuring.
Digital T1 curve use SF or ESF framing formats. SF provides two-state, affiliated supervision
signaling, in which bit ethics of 0 are acclimated to represent on-hook, and bit ethics of
1 are acclimated to represent off-hook. ESF robs four $.25 instead of two, yet has little impact
on articulation quality. ESF is appropriate for 64 kbps operation on DS0 and is recommended for
PRI configurations.
E1 curve can be configured for circadian back-up analysis (CRC4) or no circadian redundancy
check, with an alternative altercation for E1 curve in Australia.
Line Coding
Digital T1/E1 interfaces crave band encoding be configured to bout that of the PBX or
CO that is actuality affiliated to the articulation port. Band encoding defines the blazon of framing
that is acclimated on the line.
T1 band encoding methods accommodate alternating mark antagonism (AMI) and bifold 8-zero substitution
(B8ZS). AMI is acclimated on earlier T1 circuits and references arresting transitions with a
binary 1, or “mark.” B8ZS, a added reliable method, is added accepted and is recommended
for PRI configurations. B8ZS encodes a arrangement of eight zeros in a different binary
sequence, including two line-coding violations at specific bit positions, which are interpreted
as a byte absolute all zeros.
Supported E1 band encoding methods are AMI and high-density bipolar 3 (HDB3), which
is a anatomy of zero-suppression band coding.
Clock Sources
Digital T1/E1 interfaces use timers alleged clocks to ensure articulation packets are delivered and
assembled properly. All interfaces administration the aforementioned packets charge be configured to use
the aforementioned antecedent of timing so packets are not absent or delivered late. The timing antecedent that
is configured can be alien (from the line) or centralized to a router’s agenda interface.
If the timing antecedent is internal, timing derives from the onboard appearance lock bend (PLL)
chip in the agenda articulation interface. If the timing antecedent is band (external), timing derives
from the PBX or PSTN CO to which the articulation anchorage is connected. It is about preferable
to acquire timing from the PSTN because their clocks are maintained at an extremely
accurate level. This is the absence ambience for the clocks. Back two or added controllers are
configured, one should be appointed as the primary alarm source. It will drive the other
controllers.
Consider a brace of examples:
■ Single articulation anchorage accouterment clocking: In this scenario, the agenda articulation accouterments is
the alarm antecedent for the affiliated device, as apparent in Figure 4-11 and Example 4-2.
The PLL generates the alarm internally and drives the clocking on the line. Generally,
this adjustment is advantageous alone back abutting to a PBX, key system, or approach bank.
A Cisco VoIP aperture rarely provides clocking to the CO because CO clocking is
much added reliable.
Chapter 4: Performing Call Signaling over Agenda Articulation Ports 209
V
Clock
1/0
Router1 PBX
Figure 4-11 Alarm Antecedent Example 1