1、INTERNATIONAL TELECOMMUNICATION UNION)45 4 8 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU).4%27/2+). “%47%. .%47/2+3-/“),% $!4! 42!.3-)33)/. 3934%-3).4%27/2+). “%47%. 0!#+%437)4#(%$ 05“,)# $!4! .%47/2+3 !.$05“,)# -!2)4)-% -/“),% 3!4%,)4% $!4!42!.3-)33)/. 3934%-3)45 4 Recommendation 8 (Extract from
2、the “LUE “OOK)NOTES1 ITU-T Recommendation X.352 was published in Fascicle VIII.6 of the Blue Book. This file is an extract fromthe Blue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, thecontents of the file are identical to the Blue Book v
3、ersion and copyright conditions remain unchanged (see below).2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both atelecommunication administration and a recognized operating agency. ITU 1988, 1993All rights reserved. No part of this publication may be r
4、eproduced or utilized in any form or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle VIII.6 - Rec. X.352 1Recommendation X.352INTERWORKING BETWEEN PACKET SWITCHED PUBLIC DATA NETWORKSAND PUBLIC MARITIME MOBILE SATELLITE
5、DATA TRANSMISSION SYSTEMS(Malaga-Torremolinos, 1984; amended at Melbourne, 1988)The CCITT,considering(a) that the Maritime Satellite is now being operated by the International Maritime Satellite Organization(INMARSAT);(b) that interworking between the Maritime Satellite Service and public data netwo
6、rks is required;(c) that Recommendation X.350 specifies general interworking requirements for data transmission in PublicMobile Satellite Systems and Recommendation X.353 outlines the routing principles for interconnecting Public MobileSatellite Systems with public data networks;(d) that Recommendat
7、ion X.25 specifies the interface between data terminals and data circuit-terminatingequipment for terminals operating in the packet mode on public data networks, and that Recommendation X.75 specifiesdetailed procedures applicable to call control between public networks providing data transmission s
8、ervices;(e) that the physical link between a mobile earth station and a data switching exchange (DSE) will only existon a temporary basis, i.e. so long as a virtual call exists between the ship and the DSE;(f) that Recommendation X.141 provides guidance with respect to general principles for the det
9、ection andcorrection of errors in public data networks,unanimously recommendsthat the following interworking principles and interface conditions should apply for operations at the networklayer in the packet mode between a mobile DTE and a public data network.1 DefinitionsFor definitions of terms use
10、d in relation with data transmission in public mobile satellite systems, seeRecommendation X.350.For the purpose of this Recommendation the mobile satellite data switching exchange (MSDSE) is defined asthe functional interface between the public mobile satellite data transmission system and a packet
11、 switched public datanetwork.The MSDSE provides the following functions:- interworking between the signalling systems used in the public mobile satellite data transmission systemand the PSPDN;- routing and call control for calls to and from mobile earth stations;- charging.The composition of the pub
12、lic maritime mobile satellite data transmission system for interconnection withpacket switched PDN is shown in Figure 1/X.352.The Packet Switched Data Access Unit (PSDAU) provides a means of interconnecting a mobile DTE with theterrestrial packet switched public data network, through a mobile earth
13、station and coast earth station equipped withpacket switched data facility.2 Fascicle VIII.6 - Rec. X.352Fascicle VIII.6 - Rec. X.352 32 Interface conditionsThe following interfaces need to be specified for interworking and call control purposes:- the interface between the mobile DTE and the PSDAU (
14、mobile local circuit);- the interface between the PSDAU and the mobile earth station (mobile local circuit);- the interface between the mobile earth station and the coast earth station including the interface to thenetwork coordination station (mobile satellite circuit);- the interface between the c
15、oast earth station and the MSDSE (mobile terrestrial circuit);- the interface between the MSDSE and a packet switched PDN.The interfaces are shown for layers 1, 2 and 3 in Figure 2/X.352.2.1 Interface between the mobile DTE and the Packet Switched Data Access Unit (PSDAU)2.1.1 Layer 1 (physical laye
16、r) between the mobile DTE and the PSDAU may be realised by the use of the interfacesdefined in:- Recommendation X.21;- Recommendation X.21 bis;- Recommendation V.24 and V.25.The Recommendation X.21 interface should be included in new PSDAU designs. The Recommendation X.21bis interface (or the Recomm
17、endation V.24 interface) may be used for existing designs.The basic requirements of the layer 1 interface are:i) For calls originating in the mobile DTE the interface should provide for the following functions:- it should enable the DTE to provide the mobile earth station with the address of the coa
18、st earth stationthrough which the call is to be established, and the access-request code of the packet switched dataservice.Note 1 - The address of the call DTE is provided as part of the level 3 procedure.Note 2 - The PSDAU should provide an indication of call progressa) visually, for use by an ope
19、rator; and/orb) as call progress signals to the DTE when the attempt to establish the mobile satellite circuit fails. Thecall progress signals to be used are given in 6.1. Such call progress signals to the DTE may not bepossible always, e.g. when the DTE interfaces the PSDAU in accordance with Recom
20、mendationV.24.ii) For calls originating in a PDN the interface should allow for automatic connection of the mobile DTE tothe circuit.Interchange circuits shall be provided in order to meet these requirements. The required interchange circuits aredefined in the Recommendations applicable to the inter
21、face used. The control of these interchange circuits shall be suchas to ensure proper establishment and clearing of the mobile satellite circuit. It should also be observed that since mobilesatellite circuit is established on a call by call basis, it must be ensured that the mobile DTE acquires sync
22、hronism to theelement timing of the PDN before the full procedure on layer 2 is established. Until synchronism is obtained the DTEshould send contiguous 1s.See also Recommendation X.32.2.1.2 Layer 2 should be in accordance with 2 of Recommendation X.25. The extended control field (module 128)may be
23、used if required.Note - For reasons given in Recommendation X.141 it may be advantageous to use the selective reject (SREJ)command.The mobile DTE should start sending the flag sequence as soon as synchronism with the MSDSE has beenestablished.4 Fascicle VIII.6 - Rec. X.3522.1.3 Layer 3 should be in
24、accordance with 3 through 7 of Recommendation X.25.Default values for network layer parameters such as number of virtual connections, use of extended packetsequence numbering, window size, packet size and throughput may be defined by the service provider.Composition of the address field of the call
25、request packet is given in 4 of this Recommendation.2.2 Interface between the PSDAU and the mobile earth stationThis interface is to be defined under the responsibility of the service provider.2.3 Interface between the mobile earth station (mobile satellite circuit)The set-up and clearing procedures
26、 for the maritime satellite circuit are to be defined by the service provider inaccordance with the interworking procedures defined in 2.1 and 2.4.The mobile earth station and the coast earth station must be transparent for layers 2 and 3 ofRecommendation X.25.Note - Forward error correction may be
27、employed on the mobile satellite circuit in order to improve the bit errorperformance. See Recommendation X.141.2.4 Interface between the coast earth station and the MSDSE (mobile terrestrial circuit)The mobile terrestrial circuit must be transparent for layers 2 and 3 of Recommendation X.25.Interwo
28、rking between the coast earth station and the international circuit interconnecting the MSDSE witha PDN should take place as follows:i) For mobile originated calls the coast earth station should provide the MSDE with the INMARSAT mobilenumber (see Recommendation E.215/F.125) of the calling mobile ea
29、rth station for insertion in the callingDTE address field of the call request packet. This information will be provided to the coast earth station aspart of the signalling procedure for setting up the mobile satellite circuit and will be available before layer3 has been established between the mobil
30、e DTE and the MSDSE.Note - If it is impractical to implement this procedure, the INMARSAT mobile number could be obtainedfrom the calling DTE address in the call request packet.The coast earth station must also give an indication to the MSDSE that the set-up of the mobile satellitecircuit has been c
31、ompleted so that layers 2 and 3 of the protocol can be established.ii) For incoming calls from a PDN the MSDSE must transfer the INMARSAT mobile number contained inthe call request packet to the coast earth station in order to set up the mobile satellite circuit. When themobile satellite circuit has
32、 been set up, the coast earth station must provide the MSDSE with a signalindicating that setting up of layers 2 and 3 may commence.In the event of unsuccessful call set-up of the mobile satellite circuit, the coast earth station must indicateto the MSDSE the reason for call set-up failure so that t
33、he MSDSE may return the appropriate callprogress signal (and diagnostic code) in the clear request packet. The call progress signals to be used aregiven in 6.2.iii) The MSDSE should start sending the flag sequence as soon as the coast earth station has indicated that themobile satellite circuit has
34、been established and through-connected by the coast earth station.If the flag sequence has not been received from the mobile DTE within a given time-out periodof 6 seconds, the MSDSE should initiate clearing of the satellite circuit.In order to ensure full call control by the MSDSE also for mobile o
35、riginated calls, the MSDSE mayinitialize layer 2 by sending the SABM command as soon as the flag sequence has been detected.iv) If the mobile satellite circuit is interrupted (see 7.2) or abnormally cleared (e.g. priority over-ride), anindication should be given to the MSDSE so that the terrestrial
36、part of the virtual circuit may be clearedwith an appropriate call progress signal.The MSDSE must be capable at any time to receive an indication from the coast earth station that thesatellite circuit has been cleared or interrupted.v) the MSDSE must also be capable of indicating to the coast earth
37、station that the mobile satellite circuit canbe released.Fascicle VIII.6 - Rec. X.352 52.5 Interface between the MSDSE and a packet switched PDNThis interface should correspond to Recommendation X.75.3 Detailed call set-up and clearing proceduresExamples of call set-up and clearing procedures and in
38、terworking between various system elements are givenin Annex A.4 Composition of the call request packet at the mobile DTE4.1 The general format of the call request packet shall be as defined in Recommendation X.25.4.2 The called DTE address shall be composed as follows for calls to subscribers of a
39、PDN:- prefix 0;- the international data number of the called DTE in accordance with Recommendation X.121.4.3 The calling DTE address composed as defined in Recommendation X.350 should always be inserted in the callrequest packet.4.4 For the maritime mobile service, the calling DTE address to be inse
40、rted by the MSDSE in the call request packetshould be composed of the DNIC (111S) associated with the ocean area in which the ship is located and the relevantT digit followed by the INMARSAT mobile number and, if present, the optional digit specifying a specific mobile DTE.4.5 Some MSDSEs may offer
41、access to special terminations using abbreviated addresses. The called DTE addressshall in such cases consist only of the abbreviated address (see Recommendation X.350). All such abbreviated addresseswill have a first digit different from 0 in order to distinguish them from calls to an international
42、 data number. If therequired termination is in a PDN the MSDSE must perform all necessary digit conversion to the international datanumber associated with the required termination before the call can be forwarded into a PDN.5 Clearing of the mobile satellite circuitIf more than one virtual call exis
43、ts, the MSDSE must not initiate clearing of the mobile satellite circuit whendetecting a clearing condition for one of the virtual calls.If only one virtual call exists when a clear packet is received from either of the parties, the MSDSE shall startclearing of the HDLC LAPB link as follows:i) If th
44、e clearing was initiated by the PDN, clearing of the HDLC LAPB link should commence when eitherof the following conditions has been met:-a DTE clear confirmation or a clear request packet has been received from the mobile DTE;- timer T13 (Annex D to Recommendation X.25) has expired.Note 1 - Before c
45、learing of the HDLC link the MSDSE may issue a clear indication packet with diagnosticcode No. 50 (timer expired for clear indication).Note 2 - It is desirable to have a smaller value than 60 seconds on timer T13 for mobile satelliteapplications in order to reduce the traffic load on the satellite c
46、ircuits. The minimum value is for furtherstudy.ii) If the clearing was initiated by the mobile DTE, the MSDSE should forward the clear request packet intoPDN and immediately return a DCE clear confirmation packet to the mobile DTE without awaiting thereturn of any clear confirmation packet from the
47、PDN. As soon as the clear confirmation packet has beensent to the mobile DTE clearing of the HDLC link should commence.6 Fascicle VIII.6 - Rec. X.352Note - In order to allow the DTE to place a new call immediately after clearing of the last existing virtualcall, the clearing of the HDLC link may be
48、delayed by a short time-out period. If the clearing was initiatedfrom the PDN, the timer should be started when the DTE clear confirmation packet is received from themobile DTE. If the clearing was initiated by the mobile DTE, the timer should be started when the DCEclear confirmation packet is sent
49、 to the mobile DTE. If a new call request packet is received from either ofthe parties during this time-out period, the satellite circuit should not be cleared. The time-out should beshort in order to avoid undue holding of the satellite circuit in those cases where no further calling isintended.An indication that the physical link may be cleared should be provided to the coast earth station as soon as theMSDSE has entered the disconnected phase. The actual clearing of the mobile satellite circuit would then be undertakenby the coast earth station.Note - With the above
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