T1 Voice Signaling Bits

Introduction

Signaling bits are used to indicate the progress of a voice call on a T1 circuit (Off-hook, On-hook, Ringing, Disconnect, etc...) This note will explain the states of the signaling bits.


FXS LOOP-START MODE

(Receiving a call into FXS 2W interface)
System Status
RXA
RXB
TXA
TXB
Comments

1

Idle 0 1 0 1 Loop open; No ringing

2

Ringing 0 0/1 0 1 Ringing cadence follows RXB

3

FXS senses off-hook 0 1 1 1 Ringing tripped, phone is off-hook

4

Connection complet 0 1 1 1 Talking

5A

FXS senses on-hook 0 1 0 1 Disconnection, phone is on-hook

5B

Far end disconnect 1 1 1 1 Far end phone hangs up. 500 ms battery removal while receiving 11.

6B

Idle 0 1 0 1 Disconnection, phone is on-hook, Idle

FXS LOOP-START MODE

(Originating a call from a FXS 2W interface)

System Status
RXA
RXB
TXA
TXB
Comments

1

Idle

0 1 0 1

Loop open; No ringing

2

FXS goes off-hook

0 1 1 1

Off-hook, drawing dialtone

3

Dial address digits

0 1 0/1 1

Dial-pulsing or passing DTMF

4

Addressing complete

0 1 0 1

Dialing done, answered and talking

5A

FXS senses on-hook

0 1 0 1

Disconnection, phone is on-hook (loop open)

5B

Far end disconnect

1 1 1 1

Far end phone hangs up. 500ms battery removal while receiving 11.

6B

Idle

0 1 0 1

Disconnection, phone is on-hook, Idle


FXO LOOP START MODE

(Receiving call into FXO 2W interfac)

System Status
RXA
RXB
TXA
TXB
Comments

1

Idle

0 1 0 1

Loop open; No ringing

2

Ringing

0 1 0 0/1

TXB follows ringing cadence

3

FXO goes off-hook

1 1 0 0

Ringing tripped, FXO is off-hook

4

Connection complete

1 1 0 1

Talking

5A

Far end disconnect

0 1 0 1

Far end phone hangs up.

6A

FXO goes on-hook

0 1 0 1

Disconnection, phone on-hook, idle

5B

FXO goes on-hook

1 1 1 1

Send "far end disconnect" signal

6B

On-hook

0 1 0 1

Idle

FXO LOOP START MODE

(Originating call out of 2W interface)

System Status
RXA
RXB
TXA
TXB
Comments

1

Idle

0 1 0 1

Loop open; No ringing

2

FXO goes off-hook

1 1 0 1

Off-hook, drawing dialtone

3

Dial address digits

1/0 1 0 1

Dial-pulsing or passing DTMF

4

Addressing complete

1 1 0 1

Dialing done, answered and talking, connected

5A

Far end disconnect

0 1 0 1

Far end phone hangs up.

6A

FXO goes on-hook

0 1 0 1

Disconnection, phone on-hook, idle

5B

FXO goes on-hook

1 1 1 1

Send "far end disconnect" signal

6B

On-hook

0 1 0 1

Idle

FXS TANDEM LOOP START MODE

(Receiving a call into FXS 2W interface, wink start and loop-reverse battery enabled)

System Status
RXA
RXB
TXA
TXB
Battery
Comments

1

Idle

0 0 0 0 Normal

On-hook

2

Incoming call

1 1 0 0 Reversed

On-hook, Battery Polarity Reversed

3

Wink back to network

1 1 1 1 Reversed

Wink to Network (250 ms)

4

Wink done

1 1 0 0 R

Wink is finished

5

Ringing FXS port

1 1 0 0 R

Ringing 2S on 4S off, rings when 0

6

Off hook (near end) Connection established

1 1 1 1 R

Ringing stops, talk path is open

7

On-hook

1 1 0 0 R

Near end hangs up

8A

Disconnect (far end)

0 0 0 0 R

Far end hangs up

9A

Disconnect (far end)

0 0 0 0 Off

Battery off (600 ms)

10A

Idle

0 0 0 0 Normal

Battery normal polarity

7B

Disconnect (far end)

0 0 1 1 R

Far end hangs up

8B

Disconnect (far end)

0 0 0 0 Off

Battery off (600 ms) signaling disconnect to analog equipment

9B

Near end hangs up

0 0 0 0 N

Battery normal polarity

10B

Idle

0 0 0 0 N

On-hook

FXS TANDEM LOOP START MODE

(Originating a call from FXS 2W interface, wink start and loop-reverse battery enabled)

System Status
RXA
RXB
TXA
TXB
Battery
Comments

1

Idle

0 0 0 0 Normal

on-hook

2

Off-hook

0 0 1 1 N

loop closed

3

Off-hook, start wink

1 1 1 1 Reversed

wink back from network (140-290ms)

4

Off-hook finish wink

0 0 1 1 N

dial-tone

5

Dial pulsing

0 0 1 1 N

send address info DTMF or dial pulse

6

Off hook addressing done

0 0 1 1 N

far end ringback

7

Off-hook, far end answer, Connection established

1 1 1 1 R

far end answers, talk path is open

8A

On-hook

1 1 0 0 R

near end hangs up

9A

Disconnect (far end)

0 0 0 0 R

far end hangs up

10A

Disconnect (far end)

0 0 0 0 Off

Battery off (600 ms)

11A

Idle

0 0 0 0 N

On-hook

8B

Disconnect (far end)

0 0 1 1 N

Far end hangs up

9B

Disconnect (far end)

0 0 0 0 Off

Battery off (600 ms) signaling disconnect to analog equipment

10B

Near end hangs up

0 0 0 0 N


11B

Idle

0 0 0 0 N

On-hook

FXS GROUND-START MODE

(Receiving a call into FXS 2W interface)

System Status
RXA
RXB
TXA
TXB
Tip Ground
Ring Ground
Comments

1

Idle

1 1 0 1 Ungrounded U

On-hook

2

Tip gnd asserted

0 1 0 1 Grounded U

Line seized

3

Tip gnd & ringing

0 0 0 1 G U

RXB follows ringing cadence

4

Tip gnd & not ringing

0 1 0 1 G U

Line seized, no ringing

5

Off hook (loop closed)

0 1 1 1 G G

Loop closed, connection established

6A

Far end (FXO) disconnect

1 1 1 1 U G

Call disconnecting

7A

Idle

1 1 0 1 U U

Loop open returned to far end

6B

Near end (FXS) disconnect

0 1 0 1 G U

Loop open from far end

7B

Idle

1 1 0 1 U U

Idle

FXS GROUND-START MODE

(Originating a call from FXS 2W interface)

System Status
RXA
RXB
TXA
TXB
Tip Ground
Ring Ground
Comments

1

Idle

1 1 0 1 Unground U

Idle condition

2

Ring gnd detected

1 1 0 0 U G

 

3

Tip gnd returned

0 1 0 0 Ground G

Tip-gnd returned in response to ring-gnd

4

Loop closed

0 1 1 1 G G

Send loop closure out NI(T1)

5

Dial pulsing

0 1 0/1 1 G G

Passing address digits or DTMF

6

Connection established

0 1 1 1 G G

 

7A

Far end disconnect

1 1 1 1 G G

No Tip-gnd, call disconnecting

8A

Idle

1 1 0 1 U U

 

8B

Near end disconnect

0 1 0 1 G U

No ring-gnd & loop open

7B

Idle

1 1 0 1 U U

No tip-gnd returned from far end

FXS TANDEM GROUND START MODE

(Receiving a call into FXS 2W interface, wink start and loop-reverse battery enabled)

System Status
RXA
RXB
TXA
TXB
Comments

1

Idle

0 X 0 0

Tip open at FXS output

2

Tip ground

1 X 0 0

Incoming call

3

Wink back to network

1 X 1 1

Wink back for 250ms

4

Wink done

1 X 0 0

 

5

Ringing FXS port

1 X 0 0

Ringing 2s on 4s off

6

Ring ground or ring tip

1 X 1 1

Off-hook, loop closed

Connection established

1 X 1 1

 

7A

On-hook (near end)

1 X 0 0

Near end hangs up

8A

Disconnect (far end)

0 X 0 0

Tip not grounded

9A

Idle

0 X 0 0

Idle, tip open at 2W interface

7B

Disconnect (far end)

0 X 1 1

Far end hangs up

8B

Idle

0 X 0 0

Tip open at 2W interface

FXS TANDEM GROUND START MODE

(Originating a call from FXS 2W interface, wink start)

System Status
RXA
RXB
TXA
TXB
Comments

1

Idle

0 X 0 0

Tip open at 2W output

2

Ring ground, GS seized

0 X 1 1

2W seized

3

Start wink

1 X 1 1

Tip grounded, Wink back from network (140-290 ms)

4

Finish wink

0 X 1 1

Loop closed/off-hook, dial tone

5

Dial pulsing

0 X 0/1 0/1

Send address info DTMF or dial pulse

6

Off hook (near end)

0 X 1 1

Addressing finished, far end ringing

7

Off hook (far end)

1 X 1 1

Far end answers

Connection established

       

 

8A

On-hook (near end)

1 X 0 0

Near end hangs up

9A

Disconnect (far end)

0 X 0 0

Tip open at 2W interface

10A

Idle

0 X 0 0

Tip open at 2W interface

8B

Disconnect (far end)

0 X 1 1

Far end hangs up

9B

Idle

0 X 0 0

Tip open at 2W interface

FXO GROUND START MODE

(Receiving a call into FXO 2W interface)

System Status
RXA
RXB
TXA
TXB
Comments

1

Idle

0 1 1 1

Idle condition

2

Tip gnd detected

0 1 0 1

TXA indicates tip gnd, line seized

3

Tip gnd & ringing

0 1 0 0

TXB follows ringing cadence

4

Tip gnd & not ringing

0 1 0 1

Line seizure, no ringing

5

Off hook (lopp closed)

1 1 0 1

Loop closed, connection established

6A

Near end (FXO) disconnect

1 1 1 1

No tip-gnd, call disconnecting

6B

Idle

0 1 1 1

No ring-gnd & loop open returned from far end

7A

Far end (FXS) disconnect

0 1 0 1

No ring-gnd & loop open from far end

7B

Idle

0 1 1 1

No tip-gnd returned from FXO

FXO GROUND START MODE

(Originating call from FXO 2W interface)

System Status
RXA
RXB
TXA
TXB
Comments

1

Idle

0 1 1 1

Idle condition

2

FXO applies ring-gnd

0 0 1 1

Ring-gnd applied in response

3

FXO detects tip-gnd

0 0 0 1

Tip-gnd returned in response

4

FXO off-hook (loop closed)

1 1 0 1

Loop closure

5

Dial pulsing

0/1 1 0 1

Passing address digits or DT

6

Connection established

1 1 0 1

 

7A

Near end (FXO) disconnect

1 1 1 1

No tip-gnd, call disconnecting

8A

Idle

0 1 1 1

 

7B

Far end (FXS) disconnect

0 1 0 1

No ring-gnd & loop open from far end

8B

Idle

0 1 1 1

No tip-gnd returned from FXO

DIAL PULSE TERMINATE (DPT)MODE

(Receiving a call into FXO 2W interface)

System Status
RXA
RXB
TXA
TXB
Comments

1

Idle

0 X 0 0

On-hook, normal battery polarity

2

Off-hook

1 X 0 0

Incoming call

3

Start wink (battery reversal)

1 X 1 1

PBX returns wink to request digits. Battery reversal is detected.

4

End wink (battery normal)

1 X 0 0

End of wink

5

Pulsing digits

1/0 X 0 0

Passing address digits to PBX to complete call

6

Pulsing complete

1 X 0 0

PBX has routed call, ringing station phone

7

Answer, call complete

1 X 1 1

PBX returns answer supervision by reversing battery polarity

8A

Battery normal

1 X 0 0

PBX on-hook first

9A

On-hook, Idle

0 X 0 0

C. O. disconnect, back to idle

8B

On-hook

0 X 1 1

C. O. disconnects first

9B

Battery Normal, Idle

0 X 0 0

PBX on-hook, back to idle

E&M SIGNALING

(Receiving a call into E&M interface, immediate start)

System Status
RXA
RXB
TXA
TXB
Comments

1

Idle

0 0 0 0

 

2

Trunk seized

1 1 0 0

Incoming call

3

Passing digits

0/1 0/1 0 0

Passing DTMF or pulse dialing digits

4

Call

1 1 1 1

Connection complete

5

Far end disconnect

0 0 1 1

Far end hangs up

6

Near end disconnect

0 0 0 0

Idle now

E&M SIGNALING

(Originating a call from E&M interface, immediate start)

System Status
RXA
RXB
TXA
TXB
Comments

1

Idle

0 0 0 0

 

2

Trunk seized

0 0 1 1

Outgoing call

3

Passing digits

0 0 0/1 0/1

Passing DTMF or pulse dialing digits

4

Call

1 1 1 1

Connection complete

5

Far end disconnect

0 0 1 1

Far end hangs up

6

Near end disconnect

0 0 0 0

Idle now

FXS PLAR

System Status
RXA
RXB
TXA
TXB
Comments

1

Idle

1 X 1 1

Idle

2

Off-hook (near end)

1 X 0 0

Ringing far end, 2S on 4S off

3

Off-hook (far end)

0 X 0 0

Connection complete

4A

On-hook (far end)

1 X 0 0

No ringing

5A

On-hook (near end)

0 X 0 0

Idle

4B

On-hook (near end)

0 X 1 1

No ringing

5B

On-hook (far end)

1 X 1 1

Idle


Modified: 07 May 2003.