Specifications

2-19
Cisco AS5x00 Case Study for Basic IP Modem Services
11/24/1999
Section 2 Commissioning the Cisco AS5300 Hardware
Enabling the T1 Controllers
!
controller T1 3
framing esf
linecode b8zs
pri-group timeslots 1-24
!
Table 2-4 describes some of the T1-controller concepts that are applied in the previous example.
Table 2-4 T1 Controller Concepts and Descriptions
Concept Description
Framing type Defines the control bits and data bits. Cisco supports super frame (SF) and extended
super frame (ESF) for T1s.
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ESF—Extended super frame. Required for 64 kb operation on DS0s.
ESF requires 2k-framing bits for synchronization. The remaining 6k is used for
error detection, CRC, and data link monitoring. ESF is recommended for PRI
configurations.

SF—Super frame. SF (D4) is used in channel bank robbed bit signalling (RBS)
configurations. SF uses the framing bit to identify the channel and voice-related
signaling within the frame. SF is not recommended for PRI configurations.
Line code type An encoding method used to allow synchronous data to be transmitted in a
compatible format for T1 transmission. Common line codes are RZ (return to zero),
NRZ (non-return to zero), B8ZS, AMI, and HDB3 (high density bipolar order 3).

AMI—Alternate mark inversion. Signal transitions are referenced by a binary 1
(mark). AMI is used on older T1 circuits. It is not reliable.

B8ZS—Most popular line-code scheme used in North America. To maintain
clock synchronization, B8ZS replaces string 8 binary 0s with variations. B8ZS
is more reliable than AMI, and it should be used with PRI configurations.
Clock source Refers to both timing and synchronization of the T1 carrier. Timing is encoded within
the transmitted data signal, and it ensures synchronization throughout the network.
By default, the access server uses the line clock from the switch that is coming in on
controller 0. Controller 0 is the primary clock source. Controllers 1 and higher are
secondary clock sources. If a primary clock fails, a secondary clock steps in.
Timeslot
assignment
Timeslots are assigned to channels. For T1 PRI scenarios, all 24 T1 timeslots are
assigned as ISDN PRI channels. After the timeslots are assigned by the
pri-group
command, D-channel serial interfaces are automatically created in the configuration
file (for example S0:23, S1:23, and so on).