AT&T Telephone DS1/DMi/ISDN-PRI Instrukcja Użytkownika Pobierz pdf (Strona 36)

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INTRODUCTION

ESF Framing

Initially, this format was called F , pronounced “F sub e,” for framing extended. It is now called

extended superframe (ESF). The ESF framing format was developed after the D4 format. Not all

equipment used with a DS1/DMI-BOS interface supports ESF. Specifically, most D4-channel banks

(unless they are configured as LIU-3ESF or equivalent) and CDMs do not currently support ESF

framing. (See figure 1-5, DS1 Extended Superframe Format.)

FRAME BIT

FRAME

NUMBER

FRAME BIT

DEFINITIONS

CHANNEL 1

CHANNEL 2

DATA LINK F BIT (DL)

CRC-6 F BIT

DATA LINK SIGNAL

FRAME SYNC PATTERN

DATA LINK SIGNAL

CRC-6 F BIT

DATA LINK SIGNAL

FRAME SYNC PATTERN

DATA LINK SIGNAL

8-BITS

7-BITS

8-BITS

7-BITS

8-BITS

7-BITS

8-BITS

7-BITS

A ROBBED BIT (OPTIONAL)

CRC-6 F BIT

DATA LINK SIGNAL

FRAME SYNC PATTERN

DATA LINK SIGNAL

CRC-6 F BIT

DATA LINK SIGNAL

FRAME SYNC PATTERN

DATA LINK SIGNAL

ROBBED BIT (OPTIONAL)

CRC-6 F BIT

DATA LINK SIGNAL

FRAME SYNC PATTERN

DATA LINK SIGNAL

CRC-6 F BIT

DATA LINK SIGNAL

FRAME SYNC PATTERN

ROBBED BIT (OPTIONAL)

Figure 1-5. DS1 Extended Superframe Format

The ESF format consists of a 24-bit framing pattern. Compared to the 12-bit fixed pattern for D4,

only 6 of the 24 bits carry a fixed pattern. The other 18-bits consist of a 6-bit error detection code,

called the cyclic redundancy check (CRC) sum, and a 12-bit facility data link signal. At the transmit

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AT&T Telephone DS1/DMi/ISDN-PRI Instrukcja Użytkownika Strona 36

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