1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 ) TELECOMMUNICATION (03/93)STANDARDIZATION SECTOROF ITU).4%2!4%$G0G03%26)#%3G0G0$)4!,.%47/2+G0G0 )3$.G9)3$.G0G053%2G13.%47/2+G0G0).4%2 revised at Helsinki, 1993)1 General1.1 This Recommendation provides the reference configurations for ISDN user-network i
2、nterfaces.1.2 From the users perspective, an ISDN is completely described by the attributes that can be observed at anISDN user-network interface, including physical, electromagnetic, protocol, service, capability, maintenance, operationand performance characteristics. The key to defining, and even
3、recognizing, an ISDN is the specification of thesecharacteristics.1.3 An objective of ISDN is that a small set of compatible user-network interfaces can economically support awide range of user applications, equipment and configurations. The number of different user-network interfaces isminimized to
4、 maximize user flexibility through terminal compatibility (from one application to another, one location toanother, and one service to another) and to reduce costs through economies in production of equipment and operation ofboth ISDN and user equipment. However, different interfaces are required fo
5、r applications with widely differentinformation rates, complexity, or other characteristics, as well as for applications in the evolutionary stages. In this way,simple applications need not to be burdened with the cost of accommodating features employed by complexapplications.1.4 Another objective i
6、s to have the same interfaces used even though there are different configurations(e.g. single terminal versus multiple terminal connections, connections to a PABX versus direct connections into thenetwork, etc.) or different national regulations.2 Definitions2.1 reference configurations are: Concept
7、ual configurations useful in identifying various possible physical useraccess arrangements to an ISDN. Two concepts are used in defining reference configurations: reference points andfunctional groupings. Layout and application examples of reference configurations are given in 3.2.2 functional group
8、s are: Sets of functions which may be needed in ISDN user access arrangements. In aparticular access arrangement, specific functions in a functional group may or may not be present. Note that specificfunctions in a functional group may be performed in one or more pieces of equipment.2.3 reference po
9、ints are: The conceptual points dividing functional groups. In a specific access arrangement, areference point may correspond to a physical interface between pieces of equipment, or there may not be any physicalinterface corresponding to the reference point. Physical interfaces that do not correspon
10、d to a reference point(e.g. transmission line interfaces) will not be the subject of ISDN user-network interface Recommendations.3 Reference configuration3.1 The reference configurations for ISDN user-network interfaces define reference points and types of functionsthat can be provided between refer
11、ence points. Figure 1 shows the reference configurations, while Figures 2, 3 and 4show examples of applications of such configurations.2 Recommendation I.411 (03/93)3.2 The ISDN user-network interface Recommendations in the I-Series apply to physical interfaces at referencepoints S and T, using the
12、recommended interface structures according to Recommendation I.412. At reference point R,physical interfaces in accordance with other Recommendations (e.g. the X-Series interface Recommendations) may beused.NOTES1 Physical interfaces not included in CCITT Recommendations may appear at reference poin
13、t R.2 There is no reference point assigned to the transmission line, since an ISDN user-network interface is not envisaged atthis location.3.3 Figure 1a) defines the reference configuration with the functional groups NT1, NT2 and TE1. Figure 1b)illustrates that TE1 may be replaced by the combination
14、 of TE2 and TA.T1301540-93/D01Reference pointFunctional groupingFIGURE 1/I.411Reference configurations for the ISDN user-network interfacesRSTSTE1NT2 NT1TE2 TAAG9BG9TransmissionlineFIGURE 1/I.411.D01 = 8.5 cm3.4 Lists of functions for each functional group are given below. Each particular function i
15、s not necessarilyrestricted to a single functional group. For example, “interface termination” functions are included in the function lists ofNT1, NT2 and TE. The function lists for NT2, TE and TA are not exhaustive. For a particular access arrangement,specific functions in a functional group are ei
16、ther present or absent.The functional groups are described in relation to the ISDN protocol reference model in Recommendation I.320.3.4.1 Network termination 1 (NT1)This functional group includes functions broadly equivalent to layer 1 (physical) of the OSI reference model. Thesefunctions are associ
17、ated with the proper physical and electromagnetic termination of the network. NT1 functions are: line transmission termination; layer 1 line maintenance functions and performance monitoring; timing; power transfer; layer 1 multiplexing; interface termination, including multidrop termination employin
18、g layer 1 contention resolution.Recommendation I.411 (03/93) 33.4.2 Network termination 2 (NT2)This functional group includes functions broadly equivalent to layer 1 and higher layers of the Recommendation X.200reference model. PABXs, local area networks, and terminal controllers are examples of equ
19、ipment or combinations ofequipment that provide NT2 functions. NT2 functions include: layers 2 and 3 protocol handling; layers 2 and 3 multiplexing; switching; concentration; maintenance functions; and interface termination and other layer 1 functions.For example, a simple PABX can provide NT2 funct
20、ions at layers 1, 2 and 3. A simple terminal controller can provideNT2 functions at only layers 1 and 2. A simple time division multiplexer can provide NT2 functions at only layer 1. In aspecific access arrangement, the NT2 functional group may consist of only physical connections.3.4.3 Terminal equ
21、ipment (TE)This functional group includes functions broadly belonging to layer 1 and higher layers of the Recommendation X.200reference model. Digital telephones, data terminal equipment, and integrated work stations are examples of equipment orcombinations of equipment that provide the functions. T
22、he TE functions are: protocol handling; maintenance functions; interface functions; connection functions to other equipment.3.4.3.1 Terminal equipment type 1 (TE1)This functional group includes functions belonging to the functional group TE, and with an interface that complies withthe ISDN user-netw
23、ork interface Recommendations.3.4.3.2 Terminal equipment type 2 (TE2)This functional group includes functions belonging to the functional group TE but with an interface that complies withinterface Recommendations other than the ISDN interface Recommendation (e.g. the X-Series interfaceRecommendation
24、s) or interfaces not included in CCITT Recommendations.3.4.4 Terminal adaptor (TA)This functional group includes functions broadly belonging to layer 1 and higher layers of the Recommendation X.200reference model that allow a TE2 terminal to be served by an ISDN user-network interface. Adaptors betw
25、een physicalinterfaces at reference points R and S or R and T are examples of equipment or combinations of equipment that provideTA functions.4 Physical realizations of reference configurations4.1 Figure 2 gives examples of configurations illustrating combinations of physical interfaces at reference
26、points R, S and T; Figures 2a) and 2b) show separate interfaces at S and T; Figures 2c) and 2d) show an interface at Sbut not T; Figures 2e) and 2f) show an interface at T but not S; Figures 2g) and 2h) show an interface at S and T wherethey coincide. Additionally, Figures 2b), 2d), 2f) and 2h) show
27、 an interface at reference point R.4 Recommendation I.411 (03/93)TE2 TA NT2 NT1TE1 NT2 NT1TE2 TATE1TE2 NT1NT1TE2 TA NT1TE1 NT1NT2 + NT1NT2 + NT1TE + NT2TA + NT2T1301550-93/D02AG9BG9CG9DG9EG9FG9GG9HG9Configurations where ISDN physical interfaces occur at reference points S and Tat S at Tat R at S at
28、Tat Sat Rat Tat Rat Sat Tat S and Tcoincidenten RPhysical interface at the designated reference pointEquipment implementing functional groupsConfigurations where ISDN physical interfaces occur at reference point S onlyConfigurations where ISDN physical interfaces occur at reference point T onlyat S
29、and TcoincidentConfigurations where a single ISDN physical interface occurs at a location where bothreference points S and T coincideFIGURE 2/I.411Examples of physical configurationsFIGURE 2/I.411.D02 = 20cm4.2 Figures 3 and 4 show examples of physical implementations. The examples given in Figure 3
30、 show physicalrealizations of functional groups TE, NT1 and NT2, based on physical interfaces occurring at reference points R, Sand T. The examples given in Figure 4 show applications of the reference configurations to physical configurationswhen multiple physical interfaces occur at a reference poi
31、nt.The examples given in Figure 4 are not intended to be either exhaustive or mandatory. Square blocks in Figures 3 and 4represent equipment implementing functional groupings.NOTE TE1 or TE2 + TA may be used interchangeably in Figure 4.Recommendation I.411 (03/93) 5T1301560-93/D03AG9BG9CG9DG9ISDNter
32、minalequipment(s)e.g.multi-dropdistributionPABX, LAN,or terminalcontroller(NT2)Networktermination(NT1)TransmissionlineNetwork termination and e.g.multi-drop distribution PABX,LAN, or terminal controller(NT2 + NT1)at Sat Tat SAn implementation see Figure 2a) where ISDN physical interfaces occur at re
33、ference points S and Tat R at Te.g.PABX, LAN,or terminalcontroller(NT2 + TA)Networktermination(NT1)at S and TcoincidentPhysical interface at the designated reference pointEquipment implementing functional groupsFIGURE 3/I.411Examples of implementation of NT1 and NT2 functionsTransmissionlineTransmis
34、sionlineISDNterminalequipment(s)An implementation see Figure 2c) where an ISDN physical interface occurs at reference points S but not TNon-ISDNterminalequipment(s)An implementation see Figure 2f) where an ISDN physical interface occurs at reference point T but not SISDNterminalequipment(s)Networkte
35、rmination(NT1)TransmissionlineAn implementation see Figure 2g) where a single ISDN physical interface occurs at a location where bothreference points S and T coincide(NT + TA)FIGURE 3/I.411.D03 = PAGE PLEINE6 Recommendation I.411 (03/93)4.2.1 Figures 4a) and 4b) show applications of the reference co
36、nfigurations in the cases where NT2 functions consistof only physical connections. Figure 4a) describes the direct physical connection of multiple TEs (TE1s or TE2s + TAs)to NT1 using a multidrop arrangement (i.e. a bus). Figure 4b) illustrates the separate connection of a number of TEs toNT1.In the
37、se cases, all of the characteristics of the physical interfaces applied at reference points S and T must be identical.4.2.2 Figure 4c) shows the provision of multiple connections between NT2 and TEs. NT2 may include various typesof distribution arrangements, such as star, bus or ring configuration i
38、ncluded within the equipment. Figure 4d) shows acase where a bus distribution is used between TEs and the NT2 equipment.4.2.3 Figures 4e) and 4f) show arrangements where multiple connections are used between NT2 and NT1equipment. In particular, Figure 4e) illustrates the case of multiple NT1 equipme
39、nt, while Figure 4f) refers to the casewhere NT1 provides layer 1 upward multiplexing of the multiple connections.4.2.4 Figure 4g) illustrates the case where NT1 and NT2 functions are merged in the same equipment; thecorresponding merging of NT1 and NT2 functions for other configurations in Figure 4
40、 may also occur.4.2.5 Figure 4h) illustrates the case where TA and NT2 functions are merged in the same equipment; thecorresponding merging of TA and NT2 functions for other configurations in Figure 4 may also occur.T1301570-93/D04AG9BG9CG9DG9TE2 TANT2 NT1EG9FG9GG9HG9TE2 TANT2 NT1at R at S at Tat R
41、at S at TPhysical interface at the designated reference pointReference points locationEquipment implementing functional groupsFIGURE 4/I.411Examples of physical configurations employing multiple connectionsTE1 or TE2and TATE1 or TE2and TAFIGURE 4/I.411.D04 = 15.5 cmRecommendation I.411 (03/93) 74.2.
42、6 In addition to the examples of physical implementation shown in Figures 3 and 4, a possible combination ofNT1, NT2 and TA into one physical entity could be considered, in which both reference points S and T exist but are notrealized as physical interfaces. Such an implementation is to be considere
43、d an interim means of providing connection toan ISDN and might be used to complement the recommended means of connecting terminals via physical interfaces atreference points S and T in the early stages of ISDN implementation. This should not be considered as a referenceconfiguration because it poses
44、 significant problems in relation to the models of ISDN presently being studied.4.2.7 These physical implementations are limited in their arrangements and combinations by the electrical and othercharacteristics of the interface specifications and equipment.4.3 The reference-configurations given in F
45、igure 1 apply for the specification of the interface structures and accessarrangements given in Recommendation I.412.4.4 Clarification of the reference point and interface point conceptsA reference point, when physically realized by an interface, requires the specification of at least two interface
46、points (seeFigure 5).T NT NIAIBT1301580-93/D05FIGURE 5/I.411FIGURE 5/I.411 D05 =5.5cm4.4.1 interface pointOne of at least two physical locations associated with an interface. The interface points mark the end of the transmissionmedium which supports the interface and may be the location of connector
47、s (if used).The reach of any interface may be extended by the use of a transmission system, providing that the transmission systemis transparent with regard to the functions transported by the interface. In such a case, two further interface points wouldbe required (see Figure 6).TIAIBBT1301590-93/D06NIAAIBMedium MediumTransmissionfunctionFIGURE 6/I.411NOTE The insertion of a transmission system to a specific interface may be limited by performance related requirements.FIGURE 6/I.411 D06 = 5 cm
