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1 1 (12) DESCRIPTION OF NETWORK INTERFACES ; Digital interface for connection of digital PBXs to PSTN ; Signalling characteristics (System P7) ; Traffic direction PSTN PBX Contents page 1 Introduction Terminology and abbreviations References Signalling characteristics General Interface Set up and disconnection of calls Signalling for external call forwarding Signalling state table Signalling state diagram Information tones Ringing tone Warning tone Conference call Warning tone Operator intervening Telia AB (publ) Skanova, Network Solutions

2 2 (12) 1 INTRODUCTION This document has been produced by Telia in order to meet the interface publication responsibility as set forth in Article 4.2 of the R&TTE directive [1]. The document describes the signalling at a digital PSTN interface intended for connection of a digital PBX using the Swedish national P7 system for signalling on an exchange line configured for traffic PSTN PBX. The information in this document is intended to assist the designers of PBXs capable of using the services provided at the interface. The characteristics of the network is defined at the Network Termination Point (NTP) which is the physical point at the boundary of the telephone network intended to accept the connection of the PBX terminal equipment. 2 TERMINOLOGY AND ABBREVIATIONS CAS E1 LE NTP PBX PSTN TE Channel Associated Signalling 2048 kbit/s interface Local Exchange (in PSTN) Network Termination Point Private Branch exchange Switched Telephone Network Terminal Equipment

3 3 (12) 3 REFERENCES [1] Directive 1999/5/EC of the European Parliament and of the Council of 9 March 1999 on radio equipment and telecommunications terminal equipment and the mutual recognition of their conformity. [2] Telia document 21/1551-LZBA ; Description of network interfaces ; Digital interface for connection of digital PBXs to PSTN ; Signalling characteristics (System P7) ; Traffic direction PBX PSTN. [3] Telia document 24/1551-LZBA ; Description of network interfaces ; Digital interface for connection of digital PBXs to PSTN ; Transmission characteristics. 4 SIGNALLING CHARACTERISTICS 4.1 General P7 is the Swedish national channel-associated signalling (CAS) system for oneway or both-way traffic configurations at a digital NTP. P7 is used for signalling between PSTN digital local exchanges (LEs) and digital PBXs via digital exchange lines. The characteristics of the PSTN at the NTP during the different call processes and the expected performance of the PBX are described in the following subclauses in the signalling state table in clause 5 in the signalling state diagram in clause 6. Performance by the PBX that is indicated as expected, is regarded as necessary for the correct interworking between PBX and PSTN. Performance by the PBX that is indicated as recommended, is not strictly necessary from the interworking point of view but is nevertheless highly recommended. This description is applicable for lines having a one-way configuration carrying traffic from PSTN to the PBX. The line may have a both-way configuration, in which case it is expected, when idle, to enter the state defined in this description. Description of the interface having a one-way configuration carrying traffic in the reverse direction, from the PBX to PSTN, is found in Telia document 21/1551- LZBA [2].

4 4 (12) 4.2 Interface The frame and multi-frame structure and associated functions at the 2048 kbit/s interface E1 is defined in Telia document 24/1551-LZBA [3]. a f b f NTP E1 Traffic direction PBX a b b b There are four signalling bits a, b, c and d contained in time slot 16 in each transmission direction of each circuit concerned. index f (e.g. a f ) denotes the forward direction (PSTN PBX) index b (e.g. a b ) denotes the backward direction (PBX PSTN). Each signalling bit can be set to the value of 0 (binary ZERO), or 1 (binary ONE). The network expects the PBX to set the values of a b and b b as described in the following clauses. The network expects the PBX to make the following permanent setting of bit values : c b =0 and d b =1. The signalling process also includes certain information tones (see clause 7).

5 5 (12) 4.3 Set up and disconnection of calls The set up and disconnection of calls is described in this subclause. Numbers given within circles refer to state numbers as used in the signalling state table in clause 5 and the signalling state diagram in clause 6. Recognition time The PBX is recommended not to recognize switchover to a signalling state with a duration of < 10 ms. The PBX is recommended to recognize switchover to a signalling state with a duration of > 15 ms. 1 Idle state The PSTN indicates idle state by setting bit values a f =1 and b f =0. The PBX is expected to indicate idle state by setting bit values a b =1 and b b =0. It is expected that a PBX in idle state is able to receive a seizure from the PSTN. 2 Seizure The PSTN indicates seizure by setting bit values a f =0 and b f =1. In the PBX, the received seizure signal should preferably result in an alert signal (e.g. ringing signal) to the PBX operator s equipment. At the same time, the PBX is expected to send Ringing tone (subclause 7.1) in the outgoing voice frequency channel. The PBX is expected to send the alerting signal and ringing tone until answer (state no.3) or state no.16 or no.17 take place. 3 Answer When the PBX operator answers the call, the PBX is expected to send an answer signal by setting bit values a b =0 and b b =0. 4 Through-connection The PSTN will send a through-connection signal ms after having received the answer signal from the PBX (state no.3) by setting bit values a f =0 and b f =0. 5 Conversation state The PSTN indicates conversation state by retaining bit values a f =0 and b f =0. The PBX is expected to indicate conversation state by retaining bit values a b =0 and b b =0. When the PBX operator makes the switchover to an extension, the PBX is expected to send Ringing tone (subclause 7.1) in the outgoing voice frequency channel until the extension anwers the call.

6 6 (12) 6 Clear back When the called party has terminated the call during state no.5, the PBX is expected to send a clear back signal by setting bit values a b =1 and b b =0 during at least 200 ms. 7 Clear forward after clear back When the calling party has terminated the call after state no.6, the PSTN indicates clear forward by setting bit values a f =1 and b f =0. After state no.6 followed by no.7, the call is disconnected in the PSTN and the PBX is expected to return to idle state (no.20) within 250 ms. A new seizure from the PSTN may take place after 1 s. 8 Forced release after clear back If a clear back signal (state no.6) has been received from the PBX but no clear forward (state no.7) is received from the calling party, the PSTN will send a forced release signal 90 s after the clear back signal was received. This forced release signal consists of bit values a f =1 and b f =0. After state no.6 followed by no.8, the call is disconnected in the PSTN and the PBX is expected to return to idle state (no.20) within 250 ms. A new seizure from the PSTN may take place after 1 s. 9 Clear forward When the calling party has terminated the call during state no.5, the PSTN indicates clear forward by retaining bit values a f =0 and b f =0. 10 Clear back after clear forward When the called party has terminated the call after state no.9, the PBX is expected to send a clear back signal by setting bit values a b =1 and b b =0 during at least 200 ms. The PSTN will respond to the clear back signal by setting bit values a f =1 and b f =0 at an instant at least 150 ms after the start of this signal. After state no.9 followed by no.10, the call is disconnected in the PSTN and the PBX is expected to return to idle state (no.20) within 250 ms. A new seizure from the PSTN may take place after 1s. 11 New calling party off-hook after clear forward After clear forward (state no.9), and if clear back (state no.10) has not taken place, it is possible for the calling party to continue the call by making a new off-hook within 2-3 s (i.e. before the forced release (state no.12) takes place).

7 7 (12) 12 Forced release after clear forward If the PSTN has sent a clear forward signal (state no.9) but no clear back (state no.10) is received from the called party within 2-3 s, the PSTN will send a forced release signal by setting bit values a f =1 and b f =0. The PBX is expected to respond to this forced release by setting bit values a b =1 and b b =0 within 250 ms but not before 150 ms. After state no.9 followed by no.12, the call is disconnected in the PSTN and the PBX is expected to return to idle state (no.20) within 250 ms. A new seizure from the PSTN may take place after 1s. 13 Repeated public operator call request After sending a clear back signal (state no.6) and provided that a clear forward from the PSTN (state no.7) has not yet taken place, the PBX is expected to be able to detect a repeated call request by a public operator. The call request should preferably result in an alert signal (e.g. ringing signal) to the PBX operator s equipment. The PSTN will indicate the repeated call request by setting bit values a f =0 and b f =1. 14 Clear forward If the public operator discards the call request in state no.13 before answer, this is indicated by the PSTN by setting bit values a f =1 and b f =0. The PBX is expected to return to idle state (no.20) within 250 ms. A new seizure from the PSTN may take place after 1s. 15 Register recall To send a register recall in conversation state (state no.5), the PBX is expected to set bit values a b =1 and b b =0 during 90 ± 40 ms. 16 Clear forward before answer If the calling party terminates the call attempt before answer from the PBX (state no.3), the PSTN indicates clear forward by setting bit values a f =1 and b f =0. After state no.16, the PBX is expected to return to idle state (no.20) within 250 ms. A new seizure from the PSTN may take place after 1s.

8 8 (12) 17 Forced release before answer If no answer (state no.3) has been received from the PBX and no clear forward (state no.16) has taken place, the PSTN will release the call 180 ms after the seizure. This forced release signal consists of bit values a f =1 and b f =0. After state no.17, the PBX is expected to return to idle state (no.20) within 250 ms. A new seizure from the PSTN may take place after 1s. 18 Blocking The PBX may block the line for new incoming calls by setting bit values a b =1 and b b =1. 19 Unblocking The PBX may unblock the blocked line (state no.18) by setting bit values a b =1 and b b =0. After state no.19, the PBX is expected to return to idle state (no.20) within 250 ms. 20 Return to idle state After state no.7, 8, 10, 12, 14, 16, 17 and 19, the PBX is expected to return to idle state within 250 ms and be able to receive a seizure (state no.2) from the PSTN. 4.4 Signalling for external call forwarding A PBX may connect a call on an incoming exchange line to an outgoing exchange line (external call forwarding). The signalling performance is described in the Telia document 21/1551-LZBA [2].

9 9 (12) 5 SIGNALLING STATE TABLE No Signal or state signals from PSTN signals expected from PBX a f b f NTP E1 1 Idle t a f b f a b b b t Traffic direction a b b b PBX 2 Seizure Answer Throughconnection 5 Conversation state 02 6 Clear back Legend bit value=1 bit value=0 7 Clear forward Forced release after No.6 9 Clear forward Clear back New calling party off-hook after No Forced release after No Continues on next page Timing t01 t02 = ms t53 tnn* > 200 ms (minimum duration of signal) t54 t73 < 250 ms t04 t00 > 1 s t03 t06 = 90 s t56 t73 < 250 ms t06 t00 > 1 s t58 tnn* > 200 ms (minimum duration of signal) t08 t09 > 150 ms t59 t73 < 250 ms t09 t00 > 1s t07 t11 = 2-3 s t61 t62 = ms t62 t73 < 250 ms t12 t00 > 1s *) time interval where tnn is not indicated in the table

10 10 (12) No Signal or state signals from PSTN signals expected from PBX a f b f NTP E1 13 Repeated public operator call request after No.6 t 13 a f b f a b b b t Traffic direction a b b b PBX 14 Clear forward Legend 15 Register recall 66 signal after No.5 67 bit value=1 bit value= Clear forward after No.2 Forced release after No.2 Blocking from 18 PBX 19 Unblocking from PBX 20 Return to idle state Timing t64 t73 < 250 ms t14 t00 > 1s t66 t67 = 90 ± 40 ms t68 t73 < 250 ms t18 t00 > 1s t00 t19 = 180 s t69 t73 < 250 ms t19 t00 > 1s t72 t73 < 250 ms

11 11 (12) 6 SIGNALLING STATE DIAGRAM Return to idle state 20 Unblocking 19 Blocking 18 1 Idle Clear forward 16 2 Seizure 17 Forced release 3 Answer 4 Through-connection 11 Clear back New calling party off-hook 9 10 Clear forward 12 Forced release Conversation state Clear back Clear forward 8 R- signal 15 Repeated public operator call request 13 Forced release 14 Clear forward

12 12 (12) 7 INFORMATION TONES In this clause, the audible information tones are described that the PBX is expected to send over the voice frequency channel to the PSTN to inform about the state of the telephone call. Each information tone is a sound composed of one or several frequencies. The cadence is the pattern of sound/silence in a tone which gives it a characteristic rhythm. E.g. for a tone with a cadence of 1,0 s on and 5,0 s off, the cadence is denoted as 1,0 5,0 s. The level of the tones is defined in terms of dbm0. Cadences and levels are given as recommendations and are the same as those used in the PSTN to which the PBX is connected. 7.1 Ringing tone The PBX is expected to send Ringing tone, when a seizure signal is received from the PSTN (state no.2), to indicate that an alerting signal is being applied to the PBX operator s equipment. The PBX is also expected to send Ringing tone, after through-connection (state no.4), to indicate that an alerting signal is being applied to the called extension. Cadence: 1,0 5,0 s ±10 % Duration: As long as the call has not been answered, however a maximum of 180 s Frequency: 425 Hz ± 15 Hz (sinusoidal) Level: -10 dbm0 7.2 Warning tone Conference call The PBX is expected to send Warning tone Conference call, during a conference call, to indicate that more than two parties are involved in the call. Cadence: 0,33 15 s Duration: As long as the conference call is in progress Frequency: 1400 Hz ± 50 Hz (sinusoidal) Level: -20 dbm0 7.3 Warning tone Operator intervening The PBX is expected to send Warning tone Operator intervening, during a call, to indicate that the privacy of the conversation can no longer be assured because of intervention of an operator. Cadence: 0,1 1,5 s ± 10 % Duration: As long as the intervening is in progress Frequency: 1400 Hz ± 21 Hz (sinusoidal) Level: -20 dbm0