1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 8 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU05“,)#G0G0$!4!G0G0.%47/2+3.%47/2+G0G0!30%#43(90/4(%4)#!,G0G02% amended at Malaga-Torremolinos, 1984)The CCITT,bearing in mind(a) the international user classes of service indicated in Recommendation X.1;(b) t
2、he overall user-to-user performance objectives;(c) the need to standardize the procedures for use over public synchronous data networks;(d) in the case of packet switching, the need to standardize several procedural levels,unanimously recommendsthe use of the five hypothetical reference connections
3、contained in this Recommendation.1 The five hypothetical reference connections set down in the present Recommendation (see Figure 1/X.92) areintended for assessing the overall customer-to-customer performance objectives, for determining some datacharacteristics requirements of the various items in t
4、he connections and for setting limits to the impairments these itemsmay introduce.These hypothetical reference connections should be used for circuit-switched services, packet-switched servicesand leased line services in public synchronous data networks.Other hypothetical reference connections may b
5、e set up in the future after experience of the design ofsynchronous public data networks has been gained.2 The hypothetical reference connections of Figure 1/X.92 are intended for the user data signalling rates asrecommended in Recommendation X.1.Between points Y and Z, transmission takes place over
6、 64 kbit/s digital paths. Such paths may include digitalsections using modems over analogue facilities.It should be assumed that the signalling for the circuit-switched data call control follows the same route as thedata connection.2 Fascicle VIII.3 - Rec. X.92Fascicle VIII.3 - Rec. X.92 33 The logi
7、cal links to be considered in the case of packet switching are indicated in Figure 1/X.92 by the dottedlines.To allow for the incorporation of packet assembly/disassembly facilities, the variants to logical Link D ofFigure 1/X.92, which are shown in Figure 2/X.92, are recognized.4 It would be permis
8、sible to include a satellite in the transmission path of the national or local link. To allow forthis, the variants of logical Links A and D of Figure 1/X.92, which are shown in Figures 3/X.92 and 4/X.92 respectively,are recognized.In any connection, the maximum number of links via satellite should not exceed three (see Note).Note - The maximum number of links via satellite allowable in a connection requires further study, in the lightof signalling time-outs and quality of service considerations.4 Fascicle VIII.3 - Rec. X.92
