Line Coding - HP ProCurve 7000dl Series Basic Management And Configuration Manual

By default, the speed for channels is 64 kbps, and this setting will be used for
all E1-carrier lines and most T1-carrier lines. The speed 56 setting is used
only if your public carrier is using a 56 Kbps setting for the connection. In this
case, your public carrier will tell you to set the speed for each channel to 56
kbps. For all other environments, you should simply accept the default setting
of 64 kbps.

Line Coding

In addition to configuring the number of channels for the E1 or T1 connection,
you must configure the interface to use the same line coding that your public
carrier is using. Line coding defines how digital signals are configured for
transport through a physical transmission medium. Line coding schemes use
electrical signals to represent the logical 0 and 1 bits in a data stream.
E1- and T1-carrier lines have slightly different options for line coding.
E1 Line Coding. E1-carrier lines use the following line coding schemes:
Alternate mark inversion (AMI)
High-density bipolar of order 3 (HDB3)
AMI uses alternating positive and negative voltage (referred to as alternating
polarity or bipolarity) to represent logical ones, and zero voltage to represent
logical zeros. Because AMI uses zero voltage for logical zeros, it can cause
synchronization loss between peers at each end of a WAN connection if a data
stream contains a long string of logical zeros.
Although HDB3 is based on AMI, HDB3 prevents synchronization loss by
limiting the number of consecutive zero signals in a data stream to three. HDB3
replaces four logical zeros with three signals at zero voltage and a violation
bit with the same polarity as the last AMI logical one detected.
Because HDB3 is the most common line coding scheme used in E1 lines, it is
the default setting for all E1 interfaces on the ProCurve Secure Router.
To configure line coding on an E1 interface, enter the following command from
the E1 interface configuration mode context:
Syntax: coding [ami | hdb3]
For example, to configure the line coding as AMI, enter:
ProCurve(config-e1 1/1)# coding ami
Configuring E1 and T1 Interfaces
ProCurve Secure Router Modules
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