1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 8 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU05“,)#G0G0$!4!G0G0.%47/2+342!.3-)33)/. G0G03).!,).G0G0!.$G0G037)4#().-%4(/$G0G0/(b) that Recommendation X.50 defines some envelope data formats which can be used in public datanetworks;(c) that the use of a f
2、ull 64 kbit/s data stream for the transmission of a single lower speed synchronous datachannel may be economically attractive in some applications, when a low cost 64 kbit/s channel is available;(d) that for customer access to circuit switched data services in the ISDN, a method for adaption ofsynch
3、ronous user data rates to a 64 kbit/s bearer rate is defined in Recommendation X.30, but that in certainapplications as mentioned under (c) a simpler method is preferred,unanimously declaresthat for networks using a 6 + 2 envelope structure, a single low speed synchronous data channel (i.e. 600,2400
4、 4800, 9600 bit/s) shall be transmitted through a 64 kbit/s data stream by using the following method:The 6 + 2 envelopes related to the low speed channel shall be repeated as many times as required to reach the64 kbit/s speed.The receive end can recover the original data signal by taking out of th
5、e received 64 kbit/s stream an envelopefor every envelope period of the chosen data rate.In the networks which transmit the 8 kHz envelope timing, no alignment circuit is required in the receiver; inthe networks not transmitting the 8 kHz timing, the alignment is obtained by transmitting an alignment pattern in theframing bit position of each envelope. When the framing bit is not used for alignment, it is available to transmithousekeeping information or, when this is not required, it is set to zero. Further study is needed for the case of 8 + 2envelope structure.
