Cisco VPN 3000 User's Guide download pdf (Page 91)

Configuration | Interfaces | WAN Card in Slot N | Port A B as T1 or E1

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VPN 3000 Concentrator Series User Guide

WAN Parameters tab

This tab lets you configure T1/E1 parameters: line coding, line framing, line buildout, clock source, data

inversion, loopback mode, and timeslots.

Line Coding

A T1/E1 line uses a bipolar format for generating signals, with alternating plus and minus pulses. The

line codes maintain synchronization on the line. To set the correct line code, consult your T1/E1 carrier.

Click the drop-down menu button and select the line coding type:

B8ZS = Bipolar with 8-Zero Substitution. B8ZS is a bipolar line code that maintains an AC signal. If

a long string of zeros occurs on a line, the signal approaches DC and loses synchronization. To

synchronize the line, B8ZS replaces a string of 8 consecutive zeros with an 8-bit B8ZS code

(actually called a bipolar violation) when transmitting a message. On the receiving end, the B8ZS

code is removed. This is the default selection for T1, and it is not available for E1.

HDB3 = High Density Bipolar 3-Zero. HDB3 is a bipolar line code that also maintains an AC signal

and line synchronization. It substitutes one of four bit patterns for every string of four consecutive

zeros. The bit patterns depend on the polarity and number of the preceding ones. CCITT

Recommendation G.703 governs HDB3 coding. This is the default selection for E1, and it is not

available for T1.

AMI = Alternative Mark Inversion. AMI is a bipolar line code that transmits binary zero as zero volts

and binary one as either positive or negative depending on the previous pulse (each pulse

transmitted is opposite the one before it). If you choose this type, you must also enable

Data Inversion

below.

Line Framing

This parameter sets the format of data frames. The framing format of the T1/E1 line must match that of

your T1/E1 carrier, otherwise you receive line framing errors. Click the drop-down menu button and

select the frame format that the T1/E1 carrier specifies for the line.

T1 selections:

ESF = Extended Super Frame. Each ESF comprises 24 frames of 192 bits each, plus a 193rd bit for

timing, etc. This option provides enhanced signaling, error checking, and synchronization and

allows testing on the line when the line is in use. This is the default selection for T1.

SF/D4 = Super Frame or D4. Each SF comprises 12 frames of 192 bits each, plus a 193rd bit for

timing, error checking, etc.

E1 selections:

E1/CRC4 = E1 16-Frame Multiframe with CRC-4 error detection. The frame structure is as below,

plus timeslot 0 of each frame in the multiframe carries 4-bit CRC signatures for error detection.

This is the default selection for E1.

E1 = E1 16-Frame Multiframe. The frame structure (a multiframe) consists of 16 frames. Each frame

is 256 bits, or 32 8-bit timeslots.

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Cisco VPN 3000 User's Guide Page 91