1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 ) TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU).4%2!4%$G0G03%26)#%3G0G0$)4!,G0G0.%47/2+G0 )3$.G93%26)#%G0G0#!0!“),)4)%3$%- 3.1 kHz audio;- multiple subrate information streams multiplexed into 64 kbit/s by the user;- transparent access to an X.25 public
2、network I.462 case a).User information is transferred over a B-channel, signalling is provided over a D-channel.TABLE 1/I.230Recommended overall provision of bearer service categoriesCircuit-mode bearer service categories1) 64 kbit/s unrestricted E2) Speech E3) 3.1 kHz audio E4) Alternate speech / 6
3、4 kbit/s unrestricted A5) 2 64 kbit/s unrestricted A6) 384 kbit/s unrestricted A7) 1536 kbit/s unrestricted A8) 1920 kbit/s unrestricted APacket-mode bearer service categories1) Virtual call and permanent virtual circuit E2) Connectionless FS3) User signalling FSFascicle III.7 - Rec. I.230 5I.231.2
4、Circuit-mode 64 kbit/s, 8 kHz structured bearer service category usable for speech informationtransferThis bearer service category is intended to support speech.The digital signal at the S/T reference point shall conform to Recommendation G.711 (A-law or -law). Thenetwork may use processing techniqu
5、es appropriate for speech such as analogue transmission, echo cancellation andlow-bit rate voice encoding. Hence, bit integrity is not assured. This bearer service category is not intended to supportmodem derived voice-band data.All Recommendations for the transfer of speech information in the netwo
6、rk apply to this bearer servicecategory.I.231.3 Circuit-mode 64 kbit/s, 8 kHz structured bearer service category usable for 3.1 kHz audio informationtransferThis bearer service category corresponds to the service which is currently offered in the PSTN. This bearerservice category provides for the tr
7、ansfer of speech and of 3.1 kHz bandwidth audio information such as voice-banddata via modems and facsimile group 1, 2 and 3 information. The digital signal at the S/T reference point shall conformto Recommendation G.711 (A-law or -law).Connections provided for these services should offer the transf
8、er capability for the information indicatedabove. (This means that the network may include speech processing techniques provided they are appropriatelymodified or functionally removed prior to non-speech information transfer.) The control of echo control devices,speech processing devices, etc., is o
9、nly made by use of disabling tones (see Recommendation V.25). Bit integrity is notassured. The network may use analogue transmission.All Recommendations for the transfer of speech information in the network apply to this bearer servicecategory.I.231.4 Circuit-mode, alternate speech/64 kbit/s unrestr
10、icted, 8 kHz structured bearer service categoryThis bearer service category provides the alternate transfer of either speech or 64 kbit/s unrestricted digitalinformation within the same call.The request for this alternate capability and the initial mode desired by the user must be identified at call
11、 set-up time.This bearer service category is provided for the support of multiple capability terminals or single capabilityterminals.For the speech mode of this bearer service, the same applies as for the speech bearer service category. For theunrestricted mode of this bearer service category, the s
12、ame applies as for the unrestricted bearer service category.I.231.5 Circuit-mode 2 64 kbit/s unrestricted, 8 kHz structured bearer service categoryThis bearer service category provides the unrestricted transfer of two 64 kbit/s user information flows overtwo B-channels at the user network interface.
13、I.231.6 Circuit-mode 384 kbit/s unrestricted, 8 kHz structured bearer service categoryThis bearer service category provides the unrestricted transfer of 384 kbit/s user information over a H0channel at the S/T reference point. The transfer of OAM information for reserved and permanent services may be
14、provided over a D-channel in the same or in another interface structure.I.231.7 Circuit-mode 1536 kbit/s unrestricted, 8 kHz structured bearer service categoryThis bearer service category provides the unrestricted transfer of 1536 kbit/s user information over a H11,channel at the S/T reference point
15、. The transfer of OAM information for reserved and permanent services may beprovided via a D-channel in another interface structure.6 Fascicle III.7 - Rec. I.230I.231.8 Circuit-mode 1920 kbit/s unrestricted, 8 kHz structured bearer service categoryThis bearer service category provides the unrestrict
16、ed transfer of 1920 kbit/s user information over a H12channel at the S/T reference point. The transfer of OAM information for reserved and permanent services may beprovided over a D-channel.4.2 Packet mode bearer service categoriesI.232.1 Virtual call and permanent virtual circuit bearer service cat
17、egoryThis bearer service category provides the unrestricted transfer of user information in a packetized manner overa virtual circuit within a B- or D-channel at the S/T reference point. Signalling information for virtual call and/orpossibly OAM information for permanent virtual circuit services are
18、 transferred via a D- or B-channel as described inRecommendation I.462 (X.31).I.232.2 Connectionless packet-hearer service categoryThe definition of services in this bearer service category is for further study.I.232.3 User signalling bearer service categoryThe definition of services in this bearer service category is for further study.
