ÿWPCL ûÿ2BJ|xÐ ` ÐÐÌÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿH øÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÌÐÐ °°°è ÐÑ Âx„|ü@Ž ÑÐ Å@8Ø'@8Ø'Å ÐSECTION 2 © EXCHANGE INTERFACES, FUNCTIONS AND CONNECTIONS Áà1ÁÓÓÃÃContents of Recommendation Q.511Äă Áà,ÁEXCHANGE INTERFACES TOWARDS OTHER EXCHANGESƒ 1.ÁHÁGeneral ÁHÁ 2.Á   ÁScope of Recommendation Ð € Ð3.ÁHÁCharacteristics of digital interfaces towards other exchanges 4.ÁHÁCharacteristics of analogue interfaces towards other exchanges ÁàðEÁ*ƒ ÁàðEÁƒ ÁàðDÁ*     *ƒ ÃÃRecommendation Q.511ÄÄ Áàð0ÁEXCHANGE INTERFACES TOWARDS OTHER EXCHANGESƒ 1.ÁHÁÃÃGeneralÄÄ Ð 8 ÐÁHÁThis Recommendation applies to digital local, combined, transit and international exchanges for telephony in Integrated Digital Networks (IDN) and mixed (analogue/digital) networks, and also to local, combined, transit and international exchanges in an Integrated Services Digital Network (ISDN). ÁHÁThe field of application of this Recommendation is more fully defined in Recommendation Q.500. 2.ÁHÁÃÃScope of RecommendationÄÄ Ð Ð ÐÁHÁThis Recommendation is not intended to define any systems or equipment in or connected to, a digital exchange via these interfaces. Therefore only the characteristics of the interfaces are described. ÁHÁThe exchange interfaces described in this Recommendation are used to connect these exchanges to transmission facilities towards other exchanges. ÁHÁAll interfaces that have been studied in detail are described, and illustrated in Figure 1/Q.511 but it is not intended to specify every interface. Other interfaces are for further study (e.g. those for broadband facilities). 3.ÁHÁÃÃCharacteristics of digital interfaces towards other exchangesÄÄ 3.1ÁHÁÃÃInterface AÄÄ 3.1.1ÁHÁÃÃGeneralÄÄ ÁHÁInterface A is a digital interface to allow interconnection at the first level of a digital transmission hierarchy towards other exchanges. 3.1.2ÁHÁÃÃElectrical characteristicsÄÄ ÁHÁThe electrical characteristics of interface A are described in Recommendation G.703. ÁHÁThe frame structure at interface A should be identical to that of the first order multiplexes described in Recommendations G.704 and G.705. ÁHÁTiming in the transmitting direction will be derived within the digital exchange. 3.1.3ÁHÁÃÃChannel types, channel allocation and signallingÄÄ: ÁHÁ©Âà  Ânumber of channel timeslots per frame: 32/24, numbered 0©31/1©24;ÆÆ ÁHÁ©Âà  Âadditional channel timeslots may be utilized for common channel signalling when more signalling capacity is required between exchanges. For 2048 kbit/s systems, they should be selected from the channel 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 selected from channel timeslots allocated for voice channels.ÆÆ ÁHÁFor 2048 kbit/s systems: ÁHÁ©Âà  Âchannel timeslot 16 is primarily intended for signalling but should be switchable. On systems between exchanges (not involving PCM primary muldex) when channel 16 is not assigned to carry signalling it may be allocated to speech or other services;ÆÆ ÁHÁ©Âà  Âchannel timeslot 0 is used for frame alignment, alarm indication, network synchronization and other purposes;ÆÆ ÁHÁ©Âà  Âalthough no specific application is at present foreseen for switching timeslot 0, it is recommended that the possibility of read and write access to this timeslot should be retained as a safeguard for future requirements. Such access would allow processing of some or all of the information contained in this timeslot, in particular those bits reserved for national and international use. The need to switch channel timeslot 0 as a normal channel, without special access, requires further study. In any case the incoming frame alignment signal will not be passed through the exchange to an outgoing system.ÆÆ 3.1.4ÁHÁÃÃFunctional characteristicsÄÄ ÁHÁThe use of the Cyclic Redundancy Check (CRC) procedures described in Recommendation G.704 is recommended for interfaces which carry ISDN traffic and optional for other applications. The frame alignment, CRC multiframe alignment and CRC monitoring functions are in accordance with Recommendation G.706. 3.2ÁHÁÃÃInterface BÄÄ 3.2.1ÁHÁÃÃGeneralÄÄ ÁHÁInterface B is a digital interface to allow interconnection at the second level of a digital transmission hierarchy towards other exchanges. 3.2.2ÁHÁÃÃElectrical characteristicsÄÄ ÁHÁThe electrical characteristics of interface B are described in Recommendation G.703. ÁHÁThe frame structure at interface B should be identical to that of the second order multiplexes described in Recommendations G.704 and G.705. Ô w.ÔŒÁHÁTiming in the transmitting direction will be derived within the digital exchange. 3.2.3ÁHÁÃÃChannel types, channel allocation and signallingÄÄ: ÁHÁ©Á  Ánumber of channels: 132/98 numbered 0©131/1©98. ÁHÁFor 8448 kbit/s systems: ÁHÁ©Âà  Âwhere signalling capacity is required between exchanges, timeslots 67, 68, 69 and 70 can be utilized for signalling in this order of descending priority. Those channels not used for signalling can be used for speech or other purposes. If a channel timeslot is reserved for service purposes within the switch, it shall be channel timeslot 1; ÆÆ ÁHÁ©Âà  Âit is left for mutual agreement whether or not channel timeslot 1 will carry traffic;ÆÆ ÁHÁ©Âà  Â128 of the channel timeslots may carry traffic through the exchange.ÆÆ ÁHÁFor 6312 kbit/s systems: ÁHÁ©Âà  Âthe multiplex structure contains 5 bits and 98 channel timeslots, numbered 1©98, each of 64 kbit/s, of which 96 may carry traffic through the exchange;ÆÆ ÁHÁ©Âà  Âfive bits per frame are assigned for a frame alignment signal and for other signals. Timeslots 97 and 98 are assigned to signalling between exchanges;ÆÆ 3.2.4ÁHÁÃÃFunctional characteristicsÄÄ ÁHÁThe use of the Cyclic Redundancy Check (CRC) procedures described in Recommendation G.704, is recommended for interfaces which carry ISDN traffic and optional for other applications. The frame alignment, CRC multiframe alignment and CRC monitoring functions are in accordance with Recommendation G.706. 4.ÁHÁÃÃCharacteristics of analogue interfaces towards other exchangesÄÄ 4.1ÁHÁÃÃInterface CÄÄ 4.1.1ÁHÁÃÃGeneralÄÄ ÁHÁInterface C is a 2©wire or a 4©wire analogue interface, used where direct interconnection analogue facilities is required. This implies that a PCM codec, associated with this interface, is incorporated in the digital exchange. The equipment on the exchange side of interface C may include a muldex within the exchange termination functions. Differences in circuit configurations with respect to transmission parameters are likely to result in the need to specify a number of different C interfaces, depending on the application environment. This is likely to reduce the flexibility in interconnection possibilities. These C interfaces are specified in Recommendation Q.551. The transmission characteristics of 2©wire interface C2 are described in Recommendation Q.552 and of 4©wire interface C1 in Recommendation Q.553. 4.1.2ÁHÁÃÃChannel types, channel allocation and signallingÄÄ ÁHÁThe signalling characteristics of interface C vary considerably from country to country, and therefore it is not intended that this interface should be the subject of CCITT Recommendations beyond those aspects covered in Recommendations Q.552 and Q.553.