Chapter IX: Telephone Exchange (PDF)

CHAPTER IX TELEPHONE EXCHANGE 9.1 RAILWAY EXCHANGES 9.1.1 Telephone Exchanges being used on IR are of Automatic, Electronic, Digital, Stored Programme Controlled (SPC) type with conventional digital technology [(...

CHAPTER IX TELEPHONE EXCHANGE 9.1 RAILWAY EXCHANGES 9.1.1 Telephone Exchanges being used on IR are of Automatic, Electronic, Digital, Stored Programme Controlled (SPC) type with conventional digital technology [(Pulse Code Modulation (PCM), Time Division Multiplexing (TDM)] or with IP technology. All new exchanges shall be with IP technology. 9.1.2 For IP telephony Session Initiation Protocol (SIP) shall be used. The exchange software shall work on any common off-the-shelf server. 9.1.3 Normally, open source software for VoIP shall be used for ease in integration and cost optimization. 9.1.4 IP exchanges with “open standards” only shall be used in the Railway Telecommunication Network for the sake of interoperability. These exchanges shall support third party phones. Licenses if any required for this purpose shall be provisioned. The system shall also support Video telephony. 9.1.5 IP telephony shall be integrated with existing LAN infrastructure. For this purpose, Railnet switches may be configured to carry voice traffic on a separate voice VLAN. This voice VLAN frames shall have priority over the general data frames. The SRTP/RTP/SIP data packets shall be provided priority using QoS in the whole network. 9.1.6 Intercom facilities shall be provided either through independent exclusive exchange of suitable capacity or may be built through such features of main exchanges using common telephony infrastructure. Railways should endeavour to optimise their requirements of multiple Intercom systems. 9.1.7 FXS gateways shall be used for interfacing FAX, analog telephones and other analog telephony equipment if any. FXS gateways can be used in a centralized or a distributed architecture. 9.1.8 IP phones used in the network shall be PoE enabled and shall draw power from the PoE switches and ensuring UPS backup for the PoE switches. Local adaptors for the phones may be avoided. IP phone should have two Gigabit Ethernet ports one port for connecting the IP phone with LAN on PoE, and other port to connect PC through IP phone to avoid separate LAN wiring in room from distribution switch. 9.1.9 SIP Trunk/ PRI gateway shall be used to connect to NGN or PSTN. In cases where availability of PRI from PSTN is a challenge, FXO can be used. 9.1.10 Telephones used in the VoIP exchanges shall also be open standard. Thus, these phones shall work with third party exchanges/ SIP servers as well. It Indian Railways Telecom Manual - 2021 Page 92  must also be possible to use third party SIP clients loaded on mobile phones using Wi-Fi. 9.1.11 Separate trunk Exchanges are normally not required as trunk exchange function is handled by NGN (Next Generation Network) network. NGN uses MPLS network of RCIL to provide a distributed trunk exchange with which all zonal and divisional exchanges are connected using E1 links and all trunk calls are routed through this network. A back up for trunk connectivity at Zonal and divisional level may be done using direct E1/ SIP/ PRI connectivity. 9.1.12 Provision for remote maintenance of the exchange from a remotely located operation & maintenance center shall be available in the system. Remote maintenance devices / Interface should be built within the system. All access should be through a secure method like SSH, HTTPS etc. 9.1.13 The system shall be capable of use as a local, tandem, transit exchange or combination of these. 9.1.14 The system shall also support Video telephony. Hence, IP video phones can also be used for telephony. 9.1.15 Subscriber Telephone Set a. The subscriber telephone set can be analog or IP including softphones and video phones. The IP telephone shall support SIP b. Analog phones shall preferably be provided with CLI facility. 9.1.16 All the divisional exchange and the headquarter exchange shall be connected with NGN using either PRI or SIP Trunk. Subdivisional exchanges may also be connected with NGN if feasible. As far as possible, the railway exchanges shall be connected through different routes to multiple media gateways of NGN to ensure better reliability. 9.1.17 Other sub divisional exchanges shall be connected to the divisional exchange using PRI or SIP Trunk in mesh/ring configuration if feasible. Wherever feasible, Division IP exchange may be used for whole division. 9.1.18 NGN network shall carry STD traffic. Every HQ exchange and divisional exchange shall have a railway STD code allotted by the Railway Board. All the exchanges in the division shall have the same STD code. Number planning for the sub-divisional exchanges may be done by the Railways. All exchanges shall be available on the IR STD network. 9.1.19 SIP/ PRI/ E1 connectivity shall be provided to link between the sub-divisional exchange and the divisional exchange. SIP/ PRI/ E1 connectivity may also be provided between the Zonal HQ exchange and the divisional exchange. 9.1.20 Railways may define a closed numbering scheme whereby each of their divisions are available through a uniform 5 digit number across the zonal Railway telephone network. However, it must be ensured that the divisional Indian Railways Telecom Manual - 2021 Page 93  exchanges are connected to NGN and are accessible to other zones through the STD code allotted to the division. 9.1.21 Wherever possible interconnection to PSTN exchange shall be provided through Direct Inward Dialing (DID) and Direct Outward Dialing (DOD) facility. SIP/PRI/E1 connectivity may be provided between the Railway exchange and the PSTN exchange. The traffic for such trunk lines shall be taken as 0.8 Erlang/Trunk line and calculation of trunk lines shall be done accordingly. 9.1.22 All India Intercom i. An All India Intercom (IP phone ) may be provided to SAG and above officers in HQ and JAG and above officers in divisions. ii. This can be integrated with the Railway exchange. iii. No Boss-secretary configuration shall be done in this intercom. 9.1.23 IP exchange server should be provided on a common off-the-shelf hardware so as to work on generic hardware platform. It should support both IP and analog telephones. The IP exchange software shall be installed on this hardware. Telephone Exchange equipment room should be air-conditioned. 9.1.24 IP exchange servers with redundant power supply shall always be provided in 1+1, active-passive or active-active configuration i.e. if one Server fails the second server should be able to take the complete load of the calls automatically (without any manual intervention) without dropping any existing calls. It shall be possible to keep redundant/standby server in the same location (of primary Server) or may be kept at a geographically different location in order to protect against common catastrophe damage. 9.1.25 The IP Exchange should log important events that may help in analysis of failures. 9.1.26 The end-to-end security may be planned if so required using secure protocols like SRTP, SIPS etc. However, it is preferred to secure the network instead. 9.2 PARAMETERS OF EXISTING TDM EXCHANGE 9.2.1 The exchange has ports to connect subscribers with - DTMF phones - Key telephones - Hot line - Long distance - Trunk through all media of communication (Copper Cable, Radio link, OF link) - Attendant consoles 9.2.2 2 Mbps/higher speed trunk ports have been provided in the exchange for high speed connectivity between exchanges. 9.2.3 The capacity of the exchange is defined with the following details :- Indian Railways Telecom Manual - 2021 Page 94  - Wired Capacity - Equipped Capacity with  No. of subscriber ports.  No. of long distance subscriber ports, trunk ports with various type of signaling.  2 MB or higher speed trunk ports.  Ports for attendant console. 9.2.4 The Architecture of the Exchange is with the following protection arrangement. a) Up to 128 ports CPU and control cards -1 + 0 Configuration Memory -1 + 0 Configurations Power supply unit -1 + 1 hot Standby (S/B) b) Exchange with capacity higher than 128 ports CPU & control card -1+1 hot Standby configuration & hot swappable Memory -1+1 hot Standby configuration & hot swappable Power supply card -1+1 hot Standby configuration & hot swappable 9.2.5 The TDM exchange is non-blocking type and all the port cards have equal access to any free available time slot and have equal access to TDM bus. 9.2.6 The Signalling used: i) User line signalling * Decadic dc loop/disconnect signalling * DTMF signalling * D-Channel protocol (ISDN) ii) Inter Exchange * 4W E&M Signalling * 4W digital (64 kbps) * DC - loop/disconnect signalling * R2 MFC (Indian version) * CCITT Signalling system No.7 (Common Channel Signalling) * Q-Sig for feature transparency 9.3 SYSTEM REQUIREMENTS 9.3.1 The railway telephone number is a 5 digit long number. Every HQ and divisional exchange is allotted an STD code by the Railway Board. The STD code is 3 digit long including the preceding zero (‘0’). Thus, the full railway number is 8 digit long including STD code. 9.3.2 In HQ, GM intercom shall be provided on a separate telephone set. Similarly, in the division, the DRM intercom shall be provided on a separate telephone Indian Railways Telecom Manual - 2021 Page 95  set. Departmental intercoms, if provided, shall be integrated with the 5-digit Railway telephone itself. These Intercoms shall be of 2 or 3 digit number. 9.3.3 No Boss-secretary configuration shall be done in the GM/DRM/departmental intercom. 9.3.4 Boss-secretary configuration can be of two types. One is that the secretary's phone rings and if it is unanswered, the call gets transferred to the boss. In the other method, the call to the boss is not made through unless screened by the secretary. 9.3.5 Audio conferencing features shall be available in divisional/zonal IP exchanges. In case Railways use a video conferencing solution, then the video conferencing system shall have a SIP interface to integrate with Railway exchange so that railway exchange subscribers can join the video conference meeting using only audio if required. The Video conferencing solution can be part of the IP exchange or can be a separate system. 9.4 Exchange General Components and Cabling 9.4.1 The various components of the exchange system shall be a) Exchange hardware b) Exchange software c) FXS/FXO/PRI gateway d) Man Machine Interaction Terminal PC with Printer e) Test and measuring instruments f) Power supply Arrangement consisting of Batteries, Charger, Changeover panel and stand-by system. g) Intermediate Distribution Frame h) Main Distribution Frame i) Protection arrangement j) Attendant consoles k) Cable (underground and switch board) l) Subscriber telephone sets - Analog, digital and VoIP based m) Maintenance tools n) Documentation o) Lightning protection and Earthing arrangement 9.4.2 The man machine language must be in English and user friendly. A VDU, keyboard and a printer along with a PC must be available for interaction with the Exchange. 9.4.3 IP exchanges shall be worked on 230V AC/-48V DC. In case of provision of 230V AC, 2 sets of UPS along with 2 sets of batteries of adequate capacity shall be provided at each location. In case of provision -48V DC, 2 sets of Telecom chargers along with 2 sets of batteries shall be provided to ensure minimum 12 hours of back up at each location. The charger shall be of SMPS (Switch Mode Power Supply) type. Indian Railways Telecom Manual - 2021 Page 96 9.4.4 The IDF (Intermediate Distribution Frame) shall have disconnecting type connectors with facility for isolating exchange indoor and outdoor side. The cable terminals shall be installed on a rack. Protection arrangement shall be available on the IDF. The IDF frame shall be connected to proper earth for effective use of protection devices. No testing for the line side shall be done from IDF. All testing for the line side shall be done from the MDF. The IDF may be accommodated in the exchange equipment room. 9.4.5 All outdoor cable shall be terminated on a rack forming the Main Distribution Frame (MDF). This shall provide connectivity between outdoor cable and indoor switch board cable. The Main Distribution Frame shall be installed in a separate room but not in the exchange room. An earth is connected across the frame for its entire length and preferably this shall be a copper strip clamped to the frame. 9.4.6 Cables: The outdoor cables shall be jelly filled underground type. The indoor cables shall be twisted pair switch board cables. The outdoor cable shall have outdoor Termination Box/Location Box with terminals for proper termination of the cable. The indoor cable shall be terminated on CT boxes of appropriate size. The cables, cable Terminals in CT Boxes shall be planned with 30% spare capacity. All outdoor cable sheath shall be earthed while entering the exchange at MDF. 9.4.7 Lightning and surge protection and Earthing arrangement This shall in general be provided as per chapter on “Protection of Telecom Equipments against Lightning”. The telecom earthing arrangement shall consist of - Two earth wires connecting Earth Electrodes to Earth Distribution Frame - Earth wires from each equipment to Earth Distribution Frame (Exchange rack, IDF, MDF, Charger, Battery, Cables) 9.4.8 Civil Infrastructure: The exchange room shall be dustproof, with false ceiling, mosaic/tile flooring, windows with double doors, underground duct or overhead trough for running of indoor cables. Separate Operator Console room, Power supply room, Battery room, DG set room and MDF room shall be provided. Floor should be strictly level and high enough to avoid flooding. 9.4.9 Electrical Supply: Standard 230V AC single phase supply with voltage level display continuously shall be available with power lines suitable for taking the load. Alternate supply shall be provided - either traction supply or DG supply. The power Indian Railways Telecom Manual - 2021 Page 97  supply shall enter the room through MCB and changeover switch (preferably auto change-over) with proper earthing arrangement. 9.4.10 The exchange equipment room shall be air conditioned. 22-25 degree C. shall be maintained inside the room. 50% standby air conditioners shall be provided. Lighting shall be adequate for maintenance. 9.4.11 All equipment shall be provided on racks. Mounting on the walls shall be avoided. The equipment rack shall be minimum 1 meter away from the wall. The racks shall be fixed on the floor with proper arrangement. Underground ducts shall be provided for entry of UG cables. Duct/overhead troughs shall be provided to run the indoor cables. In case of UG cable entry the duct shall be filled with sand and plastered on the top. 9.5 Man Machine Communication 9.5.1 The man machine language (MML) should be in common English, not in Mnemonics or Crypts, easy to learn & use, easy to input commands & interpret outputs. 9.5.2 The MML shall contain commands, output, control actions for operation, maintenance, testing of switching system. The MML structure shall be such that addition of any new function will have no influence on the existing ones, also MML shall provide facilities for editing, cancelling. 9.5.3 Execution of any command shall not result in malfunctioning and / or overloading of the system. The system shall also ensure that operator is not locked out. 9.5.4 The errors in commands or control action shall not stop the system or unduly alter the system configuration. 9.5.5 Command errors detected by the system shall be indicated by the output of error messages 9.6 Supervision 9.6.1 Provision shall be made for continuous testing of the system to allow system quality check & fault indication as and when fault arises. 9.6.2 The following types of supervision shall be provided in the system: a) Continuous supervision of its own power supply system b) Automatic detection of abnormalities in processing 9.6.4 The system shall have the capacity to monitor its own performance and to detect, locate and report faults. 9.6.5 No single hardware failure in the core system shall result in complete system break down. The backup of system software and configuration to be Indian Railways Telecom Manual - 2021 Page 98  maintained in cloud / CD / External Hard disk/Pen drive/any other media so as to restore the system quickly in a new hardware. 9.7 PROTECTIVE DEVICES ON IDF 9.7.1 The basic requirements of the protective device provided on IDF are as under: i) The device shall not operate on speech or signaling currents/voltages. ii) It shall not decrease the efficiency of speech or signaling circuit. iii) The device shall promptly operate in cases of the specified voltages or currents being reached. For this requirement its voltage rating must be only slightly above the exchange fed voltage levels in the subscriber circuits. If the voltage rating of the protective device is very high, it won’t protect until surge or other extraneous voltage level reaches to that high level and in the meantime the damage might have already taken place. iv) The device shall promptly isolate the equipment and prevent further damage in cases of overload due to artificial or natural causes. v) The current/voltage rating of the device shall be such that they do not produce noticeable heat in the components of the main equipment. vii) The device shall be as far as possible self restoring type. viii) The prospective devices shall consist of normal fuse or self restoring type fuse & lightning discharger. The fuse shall be connected in series with each external line. ix) The Integrated Protection Modules shall be provided in case of Krone type connectors. x) The rating of the fuse shall be as per the requirement of exchange equipment. xi) The Protection arrangement shall be installed on IDF or MDF if there is no IDF. xii) The subscriber’s protective device assembly shall consist of a single compact dust proof unit containing fuse and lightning arrester. 9.8 MAINTENANCE 9.8.1 PREVENTIVE MAINTENANCE In case of non-availability of continuous automatic logging features for taking measurements in the system, the following measurements are to be taken manually; A) Daily: i) Battery set voltage and UPS/charger output/input voltage. ii) Failure list of the subscribers. iii) Working of Lights, Air conditioners. iv) System status listing. v) Failure history list. vi) Alarm checking viii) Room temperature recording Indian Railways Telecom Manual - 2021 Page 99  B) Fortnightly: i) Individual cell Voltage and load test of the batteries, sulphation of terminals. ii) Testing of all the trunk circuits. C) Monthly: i) Specific gravity in case of non-VRLA batteries ii) The different modes of operation of FCBC, iii) Earthing connections of all equipment with earth electrodes. iv) All cabinets of equipment, Man machine interaction, terminal printer, attendant consoles if available to be cleaned. v) Cable termination MDF and IDF to be cleaned and checked. vi) Cable runs-inter rack, rack to IDF, MDF and Attendant consoles to be checked. vii) BER test of all trunk circuits viii) Checking of lightning and surge protection devices ix) Functional Testing of Attendant console if available x) Wiring and connecting terminals of power supply arrangement xi) Data Back up to be updated. D) Quarterly: i) Testing of All Service features from the Test Telephones. ii) Cleaning of terminations in CT boxes, Location boxes. iii) Complete testing of power supply system E) Six monthly: i) Earth resistance value measurement ii) Line loop resistance and insulation testing F) Yearly: i) Checking of wiring of subscribers premises, CT boxes and location boxes. ii) Testing of spare cards 9.8.2 Inspection: The following are the details to be checked during routine Inspection. a) Subscriber’s office i) CT boxes ii) Wiring iii) Lightning/surge arrester iv) Batteries/power supply arrangement b) Cables i) Type of cable and length ii) Cable route conditions with special attention at culverts, bridges, road crossings, track crossing, building entry points. iii) All registers pertaining to cable laying, testing Indian Railways Telecom Manual - 2021 Page 100  c) Exchange i) MDF/IDF wiring, connectors, terminals, fuses, Protection devices. ii) Earth connections, Earth readings. iii) Power supply arrangement, battery registers, battery terminals, wiring, charger and power panel. iv) Internal cabling, cabinets, visual inspection of wiring. v) Fault register (Electronic/Paper) d) Periodical Inspection i) All exchanges and related installations shall be inspected by ADSTE/DSTE/Sr. DSTE at least once in a year. Maintenance records and fault registers shall be checked for their proper upkeep. ii) Sr. Section Engineer/Telecom should carry out detailed and effective inspection and testing once in a quarter year and Junior Engineer/Tele once in a month. 9.8.3 Testing and Commissioning: i) Cable testing shall be conducted for each subscriber. Insulation, loop resistance for cable is to be tested and recorded. ii) Provision of fuses, IPMs are to be checked for all lines. iii) The earth resistance for each earth electrode is to be measured. The connectivity of earth wires to each equipment is to be checked. iv) Hardware testing shall be conducted as per instructions of manufacturer. v) Software testing shall be done as per guidelines given by supplier. 9.8.4 Documentation : The exchange shall have the following documentation: a) Indoor Equipment - Exchange layout plan - Rack layout plan for each rack with connection details - MDF and IDF termination plan - Installation manual for equipment - Software documentation - Operation and maintenance manual - Wiring diagram for power panel - Manual for chargers/UPS and all other equipment - Troubleshooting flowchart - Pin Configuration chart of LAN cable and Type D connectors and euro connectors and other connectors - LAN/ IP implementation scheme Indian Railways Telecom Manual - 2021 Page 101  b) Outdoor Equipment: - Telephone No. wise subscriber’s details - Subscriber wise Telephone Directory - Cable layout plan - Subscriber premises wiring plan typical. 9.8.5 The tools available in exchange shall consist of - Screw drivers assorted - Nose Plier - Spanner - Normal plier - Crimping tool - Krone Extractor - Cutter - Soldering kit - Wrapping and unwrapping Tool - Torch 9.8.6 The following test and measuring instruments shall be available in exchange for testing and maintenance * Line tester to test line conditions * Megger for testing of insulation of line. * Digital multimeter * BER Tester * Earth Tester * Cable Route Tracer * Cable Fault Locator * Clamp Meter * Throughput Tester * LAN Tester -x-x-x- Indian Railways Telecom Manual - 2021 Page 102