1、CEPT T/GSI*04-01 E 2326434 000563b 8 TGs04-01 Page E 1 Recommendation T/GSI 04-01 (Nice 1985, revised by correspondance, June 1987) INTERFACE STRUCTURES AND ACCESS CAPABILITIES Recommendation proposed by the Special Group Integration (GSI) Text of the Recommendation adopted by the “Telecommunication
2、s Commission: “The European Conference of Posts and Telecommunications Administrations, considering - the common CEPT approach to the ISDN and general CEPT assumptions and policies for the evolution towards ISDN, - the I. Series Recommendations of the CCITT, as well as other CCITT Recommendations on
3、 ISDN, to which - the need for CEPT Administrations to have more precise answers to their specific European requirements, i.e. - the need for CEPT Administrations to have as a base a comprehensive set of Recommendations, in order to CEPT Administrations have contributed most significantly, to select
4、 and further define material from CCITT Recommendations, promote and strengthen European harmonisation, O recommends to the member Administrations of the CEPT that they evolve their telecommunication networks towards ISDN according to the specifications given in the attached text.” CCITT Recommendat
5、ions 1.410,1.411 and 1.412 deal with the general aspects of the user to network interfaces, the reference configurations, the channel structure and access capabilities. Recommendations 1.410 and 1.41 1 also apply to Europe without further addition or alteration. Recommendation 1.412 applies to Europ
6、e provided that all references to 1,536 and 1,544 kbit/s be deleted, the following reviewed text is the European version of that Recommendation. Edition of October 31. 1987 CEPT T/GSI*04-01 E = 2326434 0005b37 T = T/GSI 04-01 E Page 2 1. 2. 2.1. 2.2. 2.3. 2.4. 3. 3.1. 3.1.1. 3.1.2. 3.1.3. 3.1.4. GEN
7、ERAL This Recommendation defines limited sets of both channel types and interface structures for ISDN user-network physical interfaces. DEFINITIONS A channel represents a specified portion of the information-carrying capacity of an interface. Channels are classified by channel types, which have comm
8、on characteristics. Channel types are specified in paragraph 3. The channels are combined into interface structures, specified in paragraph 4. An interface structure defines the maximum digital information-carrying capacity across a physical interface. In an actual access arrangement some of the cha
9、nnels available across an ISDN user-network physical interface, as defined by the applicable interface structure, may not be supported by the network. Some ISDN services will not require the full capacity of a B channel; in those cases in which users require only such services, the access capability
10、 might be further reduced. The capability provided by those channels that are actually available for communication purposes is referred to as the access capability provided through the in terface. CHANNEL TYPES AND THEIR USE B channel A B channel is a 64 kbit/s channel accompanied by timing. Note: t
11、he method for providing this timing is a subject of the individual interface Recommendations. A B channel is intended to carry a wide variety of user information streams. A distinguishing characteristic is that a B channel does not carry signalling information for circuit switching by the ISDN. Sign
12、alling information used for circuit switching by the ISDN is carried over other types of channels, e.g. a D channel. User information streams may be carried on a B channel on a dedicated, alternate (within one call or as separate calls), or simultaneous basis, consistent with the B-channel bit rate.
13、 The following are examples of user information streams: i) voice encoded at 64 kbit/s according to Recommendation G.711; ii) data information corresponding to circuit or packet-switching user classes of service at bit rates less than or equal to 64 kbit/s, according to Recommendation X.l; iii) wide
14、band voice encoded at 64 kbit/s; *) and iv) voice encoded at bit rates lower than 64 kbit/s alone, or combined with other digital information streams. It is recognized that a B channel may also be used to carry user information streams not covered by CCITT Recommendations. B channels may be used to
15、provide access to a variety of communication modes within the ISDN. Examples of these modes are: i) circuit switching; ii) iii) semi-permanent connections. In case i), the ISDN can provide either a transparent end-to-end 64 kbit/s connection or a connection specifically suited to a particular servic
16、e, such as telephony, in which case a transparent 64 kbit/s connection may not be provided. In case ii), the B channel will carry protocols at layers 2 and 3 according to Recommendation X.25 which have to be handled by the network. The application of D channel protocols for this case is for further
17、study. In case iii), the semi-permanent connection can be provided, for example by using circuit or packet- switching modes. Single information streams at bit rates less than 64 kbit/s should be rate adapted to be carried on the B channel as described in Recommendation 1.460. packet switching, suppo
18、rting packet mode terminals; and *) These applications are currently under consideration by the CCITT. Edition of October 31, 1987 CEPT T/GSI*O4-01 E m 2326434 000563 3 m 3.1.5. 3.2. 3.2.1. 3.2.2. 3.3. 3.3.1. O 3.3.2. 3.4. O 4. 4.1. 4.1.1. 4.1.1.1. 4.1.1.2. 4.1.1.3. TIOSI 04-01 E Page 3 Multiple inf
19、ormation streams from a given user may be multiplexed together in the same B channel, but for circuit switching an entire B channel will be switched to a single user-network interface. This multi- plexing should be in accordance with Recommendation 1.460. Note. Independent routing of subrate channel
20、s circuit switched to different destinations is for further study in the 1985-1988 study period. D channel A D channel may have different bit rates as specified in paragraph 4. A D channel is primarily intended to carry signalling information for circuit switching by the ISDN. A D channel uses a lay
21、ered protocol according to Recommendations T/CS 46-20, T/CS 46-30. In particular the link access procedure is frame oriented. In addition to signalling information for circuit switching a D channel may also be used to carry teleaction information and packet-switched data. In a hybrid access arrangem
22、ent (see paragraph 5.2.) the D channel will also carry none, some or all of the signalling information for the analogue channel. H channels H channels have the following bit rates, accompanied by timing. (Note: The method for providing this timing is a subject of the individual interface Recommendat
23、ion.) HO channel: 384 kbit/s. H1 channels: 1,920 (H12) kbit/s. Higher rate H channels are for further study. An H channel is intended to carry a variety of user information streams. A distinguishing characteristic is that an H channel does not carry signalling information for circuit-switching by th
24、e ISDN. User information streams may be carried on an H channel on a dedicated, alternate (within one call or as separate calls), or simultaneous basis, consistent with the H channel bit rates. The following are examples of user information streams: i) fast facsimile; ii) video: e.g. for teleconfere
25、ncing; iii) high speed data; iv) high quality audio or sound programme material; v) information streams, each at rates lower than the respective H channel bit rate (e.g. voice at 64 kbit/s), which have been rate adapted or multiplexed together; vi) packet-switched information. Other channels For fur
26、ther study. INTERFACE STRUCTURES ISDN user-network physical interfaces at ISDN reference points S and T shall comply with one of the interface structures defined below. B channel interface structures Basic interface structure The basic interface structure is composed of two B channels and one D chan
27、nel, 2 B + D. The bit rate of the D channel in this interface structure is 16 kbit/s. The B channels may be used independently; i.e. in different connections at the same time. With the basic interface structure, two B channels and one D channel are always present at the ISDN user-network physical in
28、terface. One or both B channels, however, may not be supported by the network. See Appendix 1. Note. The basic interface structure may also be used in association with a conventional analogue channel in a hybrid access arrangement; see paragraph 5.2. Edition of October 31, 1987 CEPT T/GSI*04-01 E =
29、2326434 0005619 3 W T/GSI 04-01 E Page 4 4.1.2. 4.1.2.1. 4.1.2.2. 4.1.2.3. 4.1.2.4. 4.2. 4.2.1. 4.2.1.1. 4.2.1.2. 4.2.1.3. 4.2.1.4. 4.2.2. 4.2.2.1. 4.3. 4.4. Primary rate B channel interface structures These structures correspond to the primary rate of 2,048 kbit/s. The primary rate B channel interf
30、ace structures are composed of B channels and one D channel. The bit rate of this D channel is 64 kbit/s. At the 2,048 kbit/s primary rate the interface structure is 30 B + D. With the primary rate B channel interface structures, the designated number of B channels are always present at the ISDN use
31、r-network physical interface. One or more of the B channels may not be supported by the network. In the case of a user-network access arrangement containing multiple interfaces, it is possible for the D channel in one structure to carry the signalling for B channels in another primary rate structure
32、 without an activated D channel. When a D channel is not activated, the designated time slot may or may not be used to provide an additional B channel, depending on the situation; e.g. 30 B for a 2,048 kbit/s interface. H channel interface structure Primary rate HO channel interface structures The p
33、rimary rate HO channel interface structures are composed of HO channels with or without a D channel, as indicated below. When present in the same interface structure the bit rate of the D channel is 64 kbit/s. Additional HO channel interface structures are for further study. At the 2,048 kbit/s prim
34、ary rate the HO channel interface structure is 5 HO + D. In the case of a user-network access arrangement containing multiple interfaces, it is possible for the D channel in one structure to carry the signalling for HO channels in another primary rate interface without a D channel in use. With the p
35、rimary rate HO channel interface structures, the designated number of HO channels are always present at the user-network physical interface. One or more of the HO channels may not be supported by the network. In the case of a user-network access arrangement containing multiple interfaces, it is poss
36、ible for the D channel of one structure to carry the signalling for HO channels in another primary rate interface structure without an activated D channel. Primary rate HI-channel interface structures 1,920 kbit/s H12-channel Interface Structure The 1,920 kbit/s H12-channel interface structure is co
37、mposed of one 1,920 kbit/s H12-channel and a D channel. The bit rate of the D channel is 64 kbit/s. Signalling for the H12-channel, if required, is carried in this D channel or the D channel of another interface structure within the same user-network access arrangement. Primary Rate Interface Struct
38、ures for Mixtures of B and HO Channels A primary rate interface may have a structure consisting of a single D channel and any mixture of B and HO channels. The bit rate of the D channel is 64 kbit/s. In the case of a user-network access arrangement containing multiple interfaces, a D channel is not
39、activated, its 64 kbit/s capacity may or may not be used for the mixture of B and HO channels, depending on the situation. Other interface structure(s) For further study. Edition of October 31, 1987 CEPT T/GSI*04-01 E = 2326434 0005b20 T T/GSI04-01 E Page 5 5. EXAMPLES OF APPLICATION OF INTERFACES S
40、TRUCTURES 5.1. Access arrangement for PABX, terminal controller, local area network, etc. Figure 1 (T/GSI 04-01) illustrates a typical PABX, or LAN access arrangement. For this particular configuration it is not necessary to apply the same interface structure at both S and T reference points. For ex
41、ample, basic interface structures may be used for interfaces located at reference point S. Either basic or primary rate of other interface structures may be used at interfaces located at reference point T. S T I N T2 I I I Figure 1 (T/GSI 04-01). Example of the reference configurations for ISDN user
42、-network interfaces applied to physical configuration employing multiple connections. 5.2. Hybrid access arrangement Figure 2 (T/GSI 04-01) illustrates a possible configuration for a variety of hybrid access arrangements. A hybrid access arrangement consists of a digital interface structure used in
43、conjunction with an analogue channel. A physical interface is shown at reference points S and T, where the basic interface structure may be used. In addition to the analogue channel, the hybrid access arrangement includes one of the following digital access capabilities. i) D; ii) BfD; or iii) 2 B+D
44、. p-+q-;-l“Tr Transmission I I Physical interface at reference point +)- designated ISDN - - - - Analogue Combined analogue and digital -cc Digital Figure 2 (T/GSI 04-01). Reference configuration for hybrid access arrangements for ISDN user-network interface. Edition of October 31, 1987 CEPT T/GSI*0
45、4-03 E 2326434 0005b21 1 T/GSI 04-01 E Appendix 1, page 6 Appendix 1 (to Recommendation T/GSI 04-01) ACCESS CAPABILITIES As stated in section 2.4., not all of the channels present in an ISDN user-network physical interface are necessarily supported by the network. The resulting capability provided i
46、n an ISDN user-network access arrangement is defined as the access capability. To assist in guiding the implementations of ISDN equipment and services around the world, several preferred access capabilities are identified here. While these preferred arrangements do not preclude the implementation of
47、 other access capabilities, they are intended to assist in the worldwide commonality which is a key objective of ISDN. Preferred basic access capabilities: - 2 B+D - B+D -D Primary rate - B channel access capabilities: -n B+D n 30 for 2,048 kbit/s primary rate, unless signalling is provided in another physical interface (see paragraph 4.1.2.) the n = 31 may be allowed. Other channel structure access capabilities For further study. Edition of October 31, 1987
