XRT86VL32IB datasheet(92/154 Pages) EXAR

92 / 154 page

XRT86VL3X

T1/E1/J1 FRAMER/LIU COMBO - ARCHITECTURE DESCRIPTION

REV. 1.2.3

8.3

Brief Discussion of Robbed-bit Signaling in DS1 Framing Format

Signaling is required when dealing with voice and dial-up data services in DS1 applications. Traditionally,

signaling is provided on a dial-up telephone line, across the talk-path. Bit robbing, or stealing the least

significant bit (8th bit) in each of the twenty-four voice channels in the signaling frames allows enough bits to

signal between the transmitting and receiving end. That is where the name Robbed-bit signaling comes from.

These ends can be CPE to central office (CO) for switched services, or CPE to CPE for PBX-to-PBX

connections.

Signaling is used to tell the receiver where the call or route is destined. The signal is sent through switches

along the route to a distant end. Common types of signals are:

• On hook

• Off hook

• Dial tone

• Dialed digits

• Ringing cycle

• Busy tone

Robbed-bit Signaling is supported in three DS1 framing formats.

• Super-Frame (SF)

• SLC®96

• Extended Super-Frame (ESF)

In Super-Frame or SLC®96 framing mode, frame number 6 and frame number 12 are signaling frames. In

channelized DS1 applications, these frames are used to contain the signaling information. In frame number 6

and 12, the least significant bit of all twenty-four timeslots is 'robbed' to carry call state information. The bit in

frame 6 is called the A bit and the bit in frame 12 is called the B bit. The combination of A and B defines the

state of the call for the particular timeslot that these two bits are located in.

FIGURE 92. WAVEFORMS FOR CONNECTING THE RECEIVE MULTIPLEXED HIGH-SPEED INPUT INTERFACE AT HMVIP

AND

H.100 16.384MBIT/S MODE

RxSerClk (16.384MHz)

RxSerClk (INV)

RxSer

2 52

0 10 20 20

0 50 60 60

3 73 83 83

2 F2 F3 F3

56 cycles

3 53 63 63 73 73 83 83

2 A2

0 0 0 0

0 A0 B0 B0

3C3D3D3

1 1 1 1

56 cycles

3 A3 B3 B3 C3C3D3D3

RxSig

Start of Frame

y : X is the bit number and y is the channel number

RxSync(input)

H.100, negative sync

RxSync(input)

H.100, positive sync

RxSync(input)

HMVIP, negative sync

RxSync(input)

HMVIP, positive sync

XRT86VL32IB Datasheet(PDF) 92 Page - Exar Corporation

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