pbx signaling
DESCRIPTION
pbxTRANSCRIPT
PBX Voice SignalingPBX Voice Signaling
Nathalie Crucet+ 33 2 23 28 40 39
Agenda
This presentation include the different aspects linked to Voice signaling Main characteristics of interfaces with associated signaling Level of services that can be offered to each signaling What does it mean in terms of level of services offered in
VoIP architecture Gateway capabilities in terms of voice interface/voice
signaling
The PBX can be connected to the PSTN and to another PBX with different interfaces using different signaling
There are 2 types of interface: Digital interfaces
E1 interface : 30 B channels + 1 D-channel T1 interface : 23B channels + 1 D channel BRI interface : 2B channel + 1D channel
Analog interfaces E&M interfaces FXS/FX0 interface (not detailed in this presentation)
The normalized signaling available are the following ISDN : T1, E1 or BRI QSIG : E1 or BRI CAS (wink start, immediate start, delay start) : E&M or E1 CAS
There are also proprietary protocols available on E1/T1 interfaces
PBX signaling
Ear and Mouth (E&M) : Separate Signaling Path Two wires and four wires refer to the voice wires The Switch listens on the ear (e-lead) The Switch signals on the mouth (m-lead)
E&M voice interface
T and T1
R and R1EM
TR
EM
PBXPBXCO
Switch
2 Wire E and M 4 Wire E and M
SignalingInterfaceExchange
SignalingInterfaceExchange
The E&M signaling allows Supervision of the seizure of the line : it means that the PBX
is able to detect the seizure of the line as well as the disconnect signal
Transport of the called number in-band (using DTMF tones) : it means the PBX is able when he receives a call on E&M interface to route the call by using the information of the called number
In VoIP architecture, you have to know all the parameters in the PBX to configure the same way the gateway Timers parameters Wiring 4 wire/2wires Type of signaling : wink, immediate or delay
Due to the poor signaling, this type of connection is quite difficult to debug
E&M Signaling
E&M signaling states
E-Lead/SGM-Lead/SBConditionE and M Type
Off-Hook
Type I
Type III
Type V
Open
Battery
GroundOn-Hook
Type II
Type IV
Off-Hook
Off-Hook
On-Hook
On-Hook
Ground Ground
Ground
Ground
Battery
Open Open
Open
Open
Loop Current
On-Hook
Off-Hook
Ground
Ground
Open
Ground
Open
Ground
OpenOn-Hook
Off-Hook
E&M voice interface The PBX can send the digits in two way on E&M interface
Transparent mode : The PBX sends the digits on the line that have been dialed by the user transparently (it leads to variable digit duration and interdigit). It will lead to duplication digit issue.
Tandem mode : The PBX waits for complete dialing from the user and then sends the digits on the line (Digit duration and interdigit are fixed). No issue with this mode
Different signaling can be used with E&M interface Wink start : The terminating switch sends a wink start (momentary off-hook) signal
to the originating switch, indicating that the terminating switch is ready to receive digits
Immediate start : The originating switch sends digits immediately after seizure (off-hook) without waiting for a start-dial signal from the terminating switch
Delay start : The terminating switch sends a delay-dial signal (an off-hook signal followed by an on-hook signal) to the originating switch indicating that the terminating switch is ready to receive digits
E&M Immediate signaling
Immediate start : I am always ready to receive the digits
DTMF digits
Sending switch goes off-hook
On-Hook
Off-Hook
Sending switch Receiving switch
M E
Dialout-delay
Receiving switch goes off-hook after connection is established
On-Hook
Off-Hook
Sending switch waits a minimum of 210ms (dialout-delay timer) before sending addressing
Receving switch Sending switch
M E
E&MWink signaling
Wink start : I am ready to receive the digits now
Sending switch goes off-hook and waits the wink signal during a period of time (wait-wink timer)
On-Hook
Off-HookSending switch Receiving switchWait-wink
M E
Receiving switch goes momentarily off-hook for 140 to 200ms (wink duration timer)
On-Hook
Wink durationWink-waitincoming seizure
detection
Receiving switch Sending switch
M E
DTMF digits
Receiving switch goes off-hook after connection is established
On-Hook
Off-Hook
EM
E&MDelay signaling
On-HookOff-Hook
Sending switch goes off-hook and waits for 200ms and check if the far-end is off-hook. If the far end is off hook he waits until he goes on-hook before sending digits
Sending switch Receiving switch
Delay start : Wait I am not ready to receive digits
Receiving switch goes momentarily off-hook for 140 to 200ms (wink duration timer)
On-Hook
Delay durationDelay startincoming seizure
detection
Receiving switch Sending switch
M E
DTMF digits
Receiving switch goes off-hook after connection is established
On-Hook
Off-Hook
EM
Digital signaling - Better
Distorted Analog
Communications
Clear Digital
Communications
300–3400 Hz 4kHz2 x 4 kHz = 8 KHz
8 KHz x 8 bits = 64 kbps
T1 signaling format
Ext
ende
d Su
per
Fram
e
Time Slot #XTime Slot #X1 7 8
1
6
12
18
24
A
B
C
D
Time Slot #24Time Slot #241 7 8
1
6
12
18
24Usa
ble f
or IS
DN or P
BX Sign
aling
Channel Associated Signaling (CAS)
or Robbed Bit SignalingCommon Channel Signaling
E1 signaling format
01 2 8
1
2
3
4
56
10
15
7
8
9
1112
13
14
Sem
i-Mul
tifra
me
(SM
F) 1
Sem
i-Mul
tifra
me
(SM
F) 2
3 4 5 6 70 0 0 X X X X0
A B C D1
A B C D2
A B C D3
A B C D4
A B C D8
A B C D5
A B C D9
A B C D12
A B C D7
A B C D6
A B C D10
A B C D11
A B C D13
A B C D14
A B C D14
A B C D17
A B C D18
A B C D19
A B C D20
A B C D24
A B C D21
A B C D25
A B C D28
A B C D23
A B C D22
A B C D26
A B C D27
A B C D29
A B C D30
A B C D31
1 2 8
1
2
3
4
56
10
15
7
8
9
1112
13
14
3 4 5 6 70
Usabl
e for
ISDN or
PBX Si
gnali
ng
Channel Associated Signaling Common Channel Signaling
Time Slot #16Time Slot #16 Time Slot #16Time Slot #161 2 8
2
4
5
10
15
7
8
9
1112
14
6 70
1 2
1
2
3
4
56
10
15
7
8
9
1112
13
14
0
Channel Associated Signaling Common Channel Signaling
Digital interfaces
The signaling that can be used on digital interface (PRI or BRI) are
ISDN signaling : a user to network signaling QSIG signaling : PBX to PBX signaling E1/T1 CAS (Channel Associated signaling) : PBX to PBX
signaling with poor signaling (same level as E&M)
The ISDN signaling have been defined in order to allow the connection of PBX to the PSTN
The purpose of QSIG signaling is to extend facilities normally available between extension on a single PBX to all extensions on PBX’s that are connected together in a private network
Signaling that can be used on E1 CAS interface are Wink start, immediate start and delay start.
Digital interfaces ISDN signaling
ISDN signaling is a User to Network signaling that allows Convey information from a PBX to another Network can send information to the PBX Users on the PBX can activate services on the network
Description of some ISDN services with the example below A calls B, as B is unavailable, C Answers the call
PBXPBX
A = calling number
PSTN
Called number = B
C = connected number
Digital interfaces ISDN signaling The PBX can send the digits to the network in two ways
Enbloc sending : the complete called number is in the Setup message send by the PBX
Overlap sending : The PBX sends the setup message and then the called number is send in Information message (digit by digit)
Description of main ISDN services : Convey of number identification : called number, calling number (CLIP)
connected number (COLP) Convey of User to User information Network provides charging information to the PBX : Advice of charge
during the call and at the end of the call The PBX can activate some services provided by the Network
Call forwarding unconditional Secret of number identification : Calling restriction (CLIR), Connected restriction
(COLR)
ISDN Call completion
CallingParty Network
Setup
Setup Acknowledge
Information
Call ProceedingSetup
Call Proceeding
Alerting
Alerting Connect
ConnectConnect Acknowledge
Connect Acknowledge
CalledParty
Digital interfaces QSIG signaling QSIG signaling allows to have a good level of services in a
PBX networking. QSIG basic call offers the following services
Number identification : called number, calling number (CLIP) connected number (COLP)
Name identification : called name, calling name (CNIP) connected name (CNOP)
QSIG Generic Functionnal offers the following services that can be activate in the PBX networking Call forwarding (unconditional, on busy and no reply) Call transfer Call completion Do not disturb ...
Digital interfaces - QSIG signaling
On the router it is not possible to distinguish QSIG Basic call from QSIG Generic Functionnal.
It leads to some restrictions in case of PBX interconnexion through Gateway if one PBX support QSIG GF and the other one no, it will
not work because the PBX that support only QSIG basic call will receive some services (which it is not able to decode) from the other PBX (Services are conveyed transparently through the gateway)
If both PBXs support QSIG GF but not with the same level of services, it will lead to some issues also.
Voice signaling recommended E&M interface
Low cost solutionAvailable on all PBXs world wildOnly basic call without servicesDifficult to debugNo backup solution
E1 CAS interfaceOnly basic call without servicesDifficult to debugNo backup solution
Voice signaling recommended ISDN signaling (E1, T1 or BRI)
Provide basic call with some services (like calling party)Easy to debugGood for backup solutionGood solution for heterogeneous PBXsNo networking services
QSIG signaling (E1, T1 or BRI)A good level of services for PBX networkGood solution for homogeneous PBXsGood for backup solutionMore complicated to debug than ISDNInternetworking issues in PBX heterogeneous
Proprietary signaling When a customer asks for PBXs interconnexion using
proprietary protocol (ABC for Alcatel, MOVACS for Matra, DCS for Lucent …) on E1 interfaces, the gateway offers the TCCS (Transparent Common Channel Signaling) mode
The gateway do not decode D channel so it is like a tunnel mode for D-channel between the local and distant gateway.
This mode is bandwidth consuming : 84 kbit/s for D-channel transport (even if there is no call on the link)
The voice channels can be compressed (using G729 codec for example)
Not a standard solution (high score)
Overflow and backup
IP Network
PABX B
R1 R2
PBXPABX APBX
PSTN network
Release (failure cause)
Problem in the network
The recommended solution of overflow is described below In case of problem on the distant link or in the IP network, the
overflow strategy consists of sending a release message with a configured cause to the PBX that is able to reroute the call to the PSTN on reception of this cause.
It works only with ISDN or QSIG signaling
Thank you !!!