1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 1 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU$)4!,G0G0%8#(!.%3%8#(!.%G0G0).4%2- additional channel timeslots may be utilized for common channel signalling when more signallingcapacity is required between exchanges. For 2048 kbit/s systems, they should b
2、e selected from thechannel timeslots allocated in PCM multiplexes for data purposes according to Recommendation G.735.When no such channel timeslots are allocated or available, additional channel timeslots may be selectedfrom channel timeslots allocated for voice channels.For 2048 kbit/s systems:- c
3、hannel timeslot 16 is primarily intended for signalling but should be switchable. On systems betweenexchanges (not involving PCM primary muldex) when channel 16 is not assigned to carry signalling itmay be allocated to speech or other services;- channel timeslot 0 is used for frame alignment, alarm
4、indication, network synchronization and otherpurposes;- although no specific application is at present foreseen for switching timeslot 0, it is recommended that thepossibility of read and write access to this timeslot should be retained as a safeguard for futurerequirements. Such access would allow
5、processing of some or all of the information contained in thistimeslot, in particular those bits reserved for national and international use. The need to switch channeltimeslot 0 as a normal channel, without special access, requires further study. In any case the incomingframe alignment signal will
6、not be passed through the exchange to an outgoing system.3.1.4 Functional characteristicsThe use of the Cyclic Redundancy Check (CRC) procedures described in Recommendation G.704 isrecommended for interfaces which carry ISDN traffic and optional for other applications. The frame alignment, CRCmultif
7、rame alignment and CRC monitoring functions are in accordance with Recommendation G.706.3.2 Interface B3.2.1 GeneralInterface B is a digital interface to allow interconnection at the second level of a digital transmission hierarchytowards other exchanges.3.2.2 Electrical characteristicsThe electrica
8、l characteristics of interface B are described in Recommendation G.703.The frame structure at interface B should be identical to that of the second order multiplexes described inRecommendations G.704 and G.705.Timing in the transmitting direction will be derived within the digital exchange.3.2.3 Cha
9、nnel types, channel allocation and signalling: number of channels: 132/98 numbered 0-131/1-98.For 8448 kbit/s systems: where signalling capacity is required between exchanges, timeslots 67, 68, 69 and 70 can be utilized forsignalling in this order of descending priority. Those channels not used for
10、signalling can be used forspeech or other purposes. If a channel timeslot is reserved for service purposes within the switch, it shallbe channel timeslot 1; it is left for mutual agreement whether or not channel timeslot 1 will carry traffic; 128 of the channel timeslots may carry traffic through th
11、e exchange.For 6312 kbit/s systems: the multiplex structure contains 5 bits and 98 channel timeslots, numbered 1-98, each of 64 kbit/s, ofwhich 96 may carry traffic through the exchange; five bits per frame are assigned for a frame alignment signal and for other signals. Timeslots 97 and 98are assig
12、ned to signalling between exchanges.4 Fascicle IV.5 - Rec. Q.5113.2.4 Functional characteristicsThe use of the Cyclic Redundancy Check (CRC) procedures described in Recommendation G.704, isrecommended for interfaces which carry ISDN traffic and optional for other applications. The frame alignment, C
13、RCmultiframe alignment and CRC monitoring functions are in accordance with Recommendation G.706.4 Characteristics of analogue interfaces towards other exchanges4.1 Interface C4.1.1 GeneralInterface C is a 2-wire or a 4-wire analogue interface, used where direct interconnection analogue facilities is
14、required. This implies that a PCM codec, associated with this interface, is incorporated in the digital exchange. Theequipment on the exchange side of interface C may include a muldex within the exchange termination functions.Differences in circuit configurations with respect to transmission paramet
15、ers are likely to result in the need to specify anumber of different C interfaces, depending on the application environment. This is likely to reduce the flexibility ininterconnection possibilities. These C interfaces are specified in Recommendation Q.551. The transmissioncharacteristics of 2-wire i
16、nterface C2 are described in Recommendation Q.552 and of 4-wire interface C1 inRecommendation Q.553.4.1.2 Channel types, channel allocation and signallingThe signalling characteristics of interface C vary considerably from country to country, and therefore it is notintended that this interface should be the subject of CCITT Recommendations beyond those aspects covered inRecommendations Q.552 and Q.553.
