1、-1- Rep. ITU-R M.2009 REPORT ITU-R M.2009 DIRECT-DIAL TELEPHONE SYSTEMS FOR THE MARITIME MOBILE SERVICE (1995) General Although the DSC system may be used to establish fully automatic systems in the directions ship-to-shore, shore-to-ship and ship-to-ship, there may be a need to establish systems wh
2、ich do not provide all the facilities specified for the DSC system. Several administrations are operating MF, HF and VHF maritime mobile systems with automatic facilities for dialling-through to the public switched telephone network (PSTN). The major characteristics of some systems are given in Anne
3、xes 1 and 2. ANNEX 1 System 1 1 Introduction 1.1 The system uses data signalling to set up and clear down calls over the radio path on the same working channels as used for the telephone connection. (VHF according to Appendix 18 of the Radio Regulations, MF/HF according to Article 60 of the Radio Re
4、gulations.) 1.2 After a working channel has been manually selected, the system provides an automatic direct-dial ship-to- PSTN service and offers a limited shore-to-ship paging service which informs the ship that a PSTN user has requested a connection. 1.3 The interface between the radio path and th
5、e PSTN is normally a maritime coast station equipped with a suitable processor controlled interface which provides the necessary functions described in this Annex and which complies with the necessary interconnection requirements to the PSTN. 1.4 The system allows existing manual services and direct
6、-dial services to use the same working channel. 1.5 The ship terminal may be a single and separate unit which connects directly into the microphone input of the ships existing MF, HF or VHF transceiver. 1.6 Identification that a working channel is free, is performed either by manual listening or aut
7、omatically if the ship equipment is tuned to a particular working channel. 1.7 Up to 99 five-digit passwords or personal identification numbers (PIN) can be associated with each ship terminal to enable separate billing records to be produced for different users using the same terminal. 1.8 To preven
8、t connections being set up over a radio path which is too poor to support a telephone conversation, the coast station may measure the signal-to-noise ratio of the initial data call and reject the conversation request if the signal-to-noise ratio is below a predetermined level. 1.9 To provide securit
9、y against unwanted interception of calls, an optional scrambling facility may be included. -2- Rep. ITU-R M.2009 HEADER 2 Technical characteristics MESSAGE FIELD END OF MESSAGE Data transmission parameters - modulation : FSK - mode of operation - data link protocol - data rate - start bit :1 - data
10、bits - parity : even - stop bit :1 : full duplex : asynchronous CCITT V.21 : 300 bids : 8 bits - coast station modulation frequency: - ship station modulation frequency : mark (1) 980Hz space (O) 1180Hz mark (1) 1650Hz space (O) 1850Hz - frequency tolerance: 11 Hz 2.2 Structure of data messages tran
11、smitted in a compressed form - see Q 2.4 below): Data messages have the following format and contain ASCII characters (although those in the message field are 2.2.1 Header This consists of the ASCII STX (decimal 02) character. 2.2.2 Message field This consists of the following three parts: - a nine-
12、digit “ship number“ (preferably the Maritime Mobile Service Identity - MMSI) which identifies the ship terminal from which the message is transmitted or to which the message is addressed; - a one-digit “message type“; - a variable length data field which, for some messages, has a length of zero. 2.2
13、.3 End of message This consists of a two-character parity check followed by a carriage return character (see Q 2.5 below). 2.3 Content of message field below. Apart from the ship number part of the message field, the contents of the various message fields are described -3- Rep. ITU-R M.2009 Value of
14、 the type field 1 2 3 4 5 8 2.3.1 Ship-to-shore messages The following message types may be sent in the ship-to-shore direction (see also Fig. 1): Meaning No. of data digits call request 5+9+16 call continuity/scrambler on O call continuity/scrambler off O call termination O special service call req
15、uest 2 reply to shore-to-ship call O A detailed description of the purpose and content of the above messages is given below: 2.3.1.1 Ship message type 1 (call request) This message is sent by the ship to request a telephone connection. The data field contains the password/PIN number (five digits), c
16、oast station identification (nine digits - see 3.2.1.1) and telephone number (16 digits padded by blanks where the telephone number is less than 16 digits). The coast station will respond with an acknowledgement message (coast station message type 1). Note that if the call request telephone number i
17、s 22 the coast station sends back details of queued shore-to-ship calls (coast station message type 7). 2.3.1.2 Ship message type 2 (call continuity/scrambler on) This message is sent by the ship to activate the scrambler facility and also, during scrambled calls, every 128 s to indicate that the ca
18、ll is continuing. This guards against the coast station maintaining a radio channel which the ship had cleared, in the event that the ships call termination message was not received. If three call continuity messages are not received by the coast station it will terminate the call. The coast station
19、 does not send a response message (but will activate its own scrambler). 2.3.1.3 Ship message type 3 (call continuity/scrambler off) This message is sent by the ship to deactivate the scrambler facility and also, during non-scrambled calls, every 128 s to indicate that the call is continuing. The co
20、ast station does not send a response message (but will deactivate its own scrambler if it was previously activated). 2.3.1.4 Ship message type 4 (request call termination) This message is sent by the ship to terminate the call. 2.3.1.5 Ship message type 5 (special service call request) This message
21、is sent by the ship, after a call has been accepted by the coast station, to request a special service (e.g. data or facsimile). The data field contains a two-digit service code (O1 for data, 02 for facsimile or O0 to return to speech). On receipt of this message, the coast station disables the call
22、 continuity function (see Q 2.3.1.2 and 2.3.1.3), switches in any additional subsystems if needed and logs the request for billing purposes. 2.3.1.6 Ship message type 8 (reply to shore-to-ship call) This message is sent by the ship to confirm reception of a shore-to-ship call (coast station message
23、type 7 - see Q 2.3.2.7 below). 2.3.2 Coast station messages The following message types may be sent in the shore-to-ship direction (see also Fig. 2): -4- Rep. ITU-R M.2009 Value of the type field Meaning No. of data digits 1 2 3 4 5 acknowledgement (ack) O engaged O call accepted O call not accepted
24、 2 call termination 24 6 7 8 A detailed description of the purpose and content of the above messages is given below: 2.3.2.1 Coast station message type 1 (ack) This message is sent by the coast station to indicate correct reception of a call request message (ship message type 1) or a call terminatio
25、n (ship message type 4), i.e. parity check correct. channel free O shore-to-ship call see 3 2.3.2.7 telephone line status 2 2.3.2.2 Coast station message type 2 (engaged) This message is sent by the coast station to indicate that the automatic system is unavailable. This message, where possible, is
26、transmitted to all ships (using ship number 000000000). 2.3.2.3 Coast station message type 3 (call accepted) This message is sent by the coast station following its transmission of an ack (coast station message type 1) to indicate that the ships call request is acceptable. 2.3.2.4 Coast station mess
27、age type 4 (call not accepted) This message is sent by the coast station following its transmission of an ack (coast station message type 1) to indicate that the ships call request is not acceptable. The data field contains two digits giving the reason (e.g. O0 = ship number not registered, O1 = pas
28、sword (PIN) error, 02 = stop list, 04 = SYN ratio too low). 2.3.2.5 Coast station message type 5 (call termination) This message is sent by the coast station to indicate the reason for termination and the duration of the call. The data field contains two digits giving the reason for termination (e.g
29、. O0 = ship or PSTN user terminated, O1 = telephone line fault, 02 = call continuity message not received, 03 = manual call terminated by operator, 04 = time out, 05 = ship protocol error, 06 = coast station host computer error) and six characters giving the call duration (hours, minutes and seconds
30、 in the format hmm:ss, e.g. 1 hour, 20 minutes, 30 seconds is coded in ASCII as 120:30). 2.3.2.6 Coast station message type 6 (channel free) This message is sent by the coast station to all ships (using ship number 000000000) when the channel becomes free (e.g. after an existing direct-dial or manua
31、l call has terminated or after the coast station system has been restored to service following maintenance). This enables ships monitoring a channel to determine automatically when it is free. 2.3.2.7 Coast station message type 7 (shore-to-ship call) This message is sent by the coast station to indi
32、cate that the coast station has received a call from a PSTN user for the ship or in reply to a request from the ship (ship message type 1 with telephone number 22 - see Q 2.3.1.1 above). The data field contains a “call digit“ (1) followed by the “call data“ digits coast station identification (nine
33、digits), user code (two digits identifying which of up to 99 users the call is for), personal code (one digit - see Note i), telephone -5- Rep. ITU-R M.2009 number (16 digits), day month hour minutes (eight digits), blank (one digit). In the event that no calls are stored for the ship (in reply to s
34、hip message type i), the data field contains two digits - “no call“ (O) followed by blank. NOTE 1 - Code that can be used to give additional information to the ship user. The meaning of the values of this personal code are to be decided between the ship user and the PSTN subscriber. 2.3.2.8 Coast st
35、ation message type 8 (telephone line status) This message is sent by the coast station when the coast station has finished dialling the requested PSTN user. The data field contains two digits (02) indicating “end of dialling“. 2.4 Message field compression 2.4.1 In order to reduce the amount of data
36、 transmitted, the message field is compressed as described below. 2.4.2 For numeric characters in the message field and for the colon (:) character, the most significant four bits of each eight-bit character are removed and the value of the resulting four-bit nibble is increased by one to avoid the
37、creation of code 02 (which is the message header character). In the case of a blank (ASCII space character), a unique four-bit code is used. The values of the compressed characters are given in Table 1. TABLE 1 Character compression -6- Rep. ITU-R M.2009 Uncompressed ASCII characters Compressed code
38、d bytes Transmitted bit sequence 2.4.3 Each successive pair of four-bit nibbles is combined to form half the number of eight-bit bytes compared to the uncompressed message field (noting that all message fields have an even number of characters). It should be noted, that considering a group of compre
39、ssed bytes representing the information to be transmitted, the most significant byte of the group is transmitted first but that within each byte the least significant bit is transmitted first. As an example, for a ship message type 4, with a ship number of 123456789, the compressed message field wou
40、ld contain five bytes, as illustrated in Table 2. 12 34 56 78 94 0010001 1 o 1 O00 1 o1 o1 1001 11 10001001 10100101 11000100 10100010 11 1001 10 10010001 10100101 TABLE 2 Example of compressed character transmission O time 2.5 Parity check characters 2.5.1 The two parity check characters followed b
41、y a carriage return character (ASCII decimal 13) are the last characters transmitted. The parity check characters which check the message field for the presence of errors are formed as follows: 2.5.1.1 An eight-bit byte is formed by making each of its eight bits equal to the exclusive-or of the corr
42、esponding bits of all of the compressed message field characters (equivalent to the least significant bit of the modulo-2 sums - i.e. even vertical parity). For example, bit 3 equals the exclusive-or of bit 3 of all of the characters in the compressed message field. 2.5.1.2 The decimal equivalent of
43、 the resulting eight-bit byte can be represented as a four-digit number in the range O000 to 0255. This four-digit number is then compressed to two bytes using the algorithm described in Q 2.4 and Table 1. E.g.: XOR result: 11010010 Decimal value: 0210 Parity check in binary: First byte transmitted:
44、 00010011 O001 O011 O010 0001 “1st bit transmitted -8- Rep. ITU-R M.2009 3 Operational procedures 3.1 Introduction These procedures are based on the use of special messages from the ship station and the coast station, which Appendices 1,2, 3 and 4 indicate the timing of the various calling sequences
45、. are described in Q 2. 3.2 3.2.1 Ship station initiates call 3.2.1.1 follows: Operational procedures in the ship-to-shore direction The user aboard the ship (hereafter referred to as the user) composes the calling sequence on his terminal as - enters his five-digit PIN; - - (the ship number is ente
46、red automatically); Note 1 - The user may insert the nine-digit address of the coast station equipment if required. However, unless the working channels are shared by coast stations in the same area, this nine-digit address is not needed and a default value of nine zeros is automatically included; i
47、nserts the required subscriber number (e.g. telephone number). - 3.2.1.2 The user selects the appropriate VHF, MF or HF working channel and transmits the calling sequence (ship message type 1) after checking as far as possible that there are no calls in progress on that frequency (determined either
48、by manual listening or by ship terminal automatically detecting the coast stations channel-free message). 3.2.1.3 If the ship station does not receive an error-free acknowledgement (coast station message type 1) from the coast station within 20 s, the user should, either repeat the transmission of t
49、he call on the same working channel or initiate a call on another working channel. 3.2.2 Coast station acknowledgement 3.2.2.1 If, on receipt of an error-free message, the coast station can comply immediately with the call request, including measurements that the S/N is acceptable, then it should, within 20 s of receiving it, transmit an acknowledgement (coast station message type 1) and within a further 10 s the call accepted message (coast station message type 3). 3.2.2.2 If the coast station cannot comply, it transmits instead of coast station message type 3, coast station message ty
