1、CCITT RECMN*Im32 (REV* revised Helsinki, 1993) 1 Introduction The general functional architecture model for the ISDN is described in Recommendation 1.324. The concepts and associated definitions adopted in Recommendation 1.324 also apply to the B-ISDN, i.e. reference configurations, functional group
2、, reference points. The objective of this Recommendation is to provide a basic functional architecture of the B-ISDN to complement Recommendation 1.324. The model is not intended to require or exclude any specific implementation of the B-ISDN but to provide a guide for the specification of B-ISDN ca
3、pabilities. Recommendation 1.310 describes the functions of an ISDN. These functions are by their nature static (i.e. he- independent). The relative distribution and allocation of these functions is the subject of the architecture of the ISDN and is described in this Recommendation. The dynamic aspe
4、cts of these functions are modelled in Recommen- dation 1.3 10 as executive processes. Therefore, the key components in this architecture model are: the functions which are contained in the B-ISDN, where they are located and the relative topology for their distribution in the B-ISDN. 2 General archi
5、tecture of the B-ISDN In B-ISDN implementations some of the B-ISDN functions will be implemented within the same network elements, whereas other specific B-ISDN functions will be dedicated to specialized network elements. Various different B-ISDN implementations are likely to be realized depending o
6、n national conditions. A basic component of the B-ISDN is a network for asynchronous transfer mode (ATM) switching of both constant bit rate (CBR) and variable bit rate WBR) end-to-end connections. These connections will support 64 kbits based ISDN services. : 3 Architectural aspects of the B-ISDN T
7、he basic architectural model defined in Recommendation 1.324 is complemented as shown in Figure 1. This shows the main information transfer and signalling capabilities of the B-ISDN. i The architecture of the B-ISDN includes low Layer capabilities and high Layer capabilities. These capabilities supp
8、ort services within the B-ISDN and within other networks by means of interworking B-ISDN with those other networks. 3.1 Low Layer capabilities From the functional capabilities of the B-ISDN, as shown in Figure 1, the information transfer capabilities require further description. Broadband informatio
9、n transfer is provided by ATM at the B-ISDN user-network interface (UNi) and at switching entities inside the network. ATM is a specific packet oriented transfer mode using an asynchronous time division multiplexing technique. The multiplexed information flow is organized in fixed size blocks, calle
10、d cells. A cell consists of an information field and a header: the primary role of the header is to identify cells belonging to the same virtual channel connection. Cells are assigned on demand, depending on the source activity and the available resources. Cell sequence integrity on a virtual channe
11、l connection is preserved by the ATM layer. Recommendation 1.327 (03/93) 1 1 i i i I .“.“I“. i i i i Highlayer capabilities i Lowlayer capabilities User-buser (user-bnetwork) signalling LFC Lod function capabilities TE Tenninalee(uipment FIGURE lD.327 Basic architecture model of the B-ISDN ATM is a
12、connection oriented technique. A connection within the ATM layer consists of one or more links, each of which is assigned an identifier. These identifiers remain unchanged for the duration of the connection. It should be noted that signalling information for a given connection is conveyed using a se
13、parate identifier. Although ATM is a connection oriented technique, it does offer a flexible transfer capability common to all services, including connectionless services. Examples of mechanisms supporting connectionless data services are illustrated in Annex A. The switching and transmission capabi
14、lities, as described in Recommendation 1.324, are also applicable in B-ISDN. The support of 64 kbitls based ISDN services by a network based on ATM needs further study. 3.2 High layer capabilities Normally, the high layer functional capabilities are involved only in the terminal equipment. However,
15、for the support of some services, provision of high layer functions could be made via special nodes in the B-ISDN belonging to the public network or to centres operated by other organizations and accessed via B-ISDN user-network or network-node interfaces (NNls). 4 Location of functions in the B-ISD
16、N 4.1 Overall In considering a B-ISDN call (i.e. an instance of a telecommunication service) two major functional areas are involved i) ii) the public B-ISDN. the customer equipment (TE and optional customer network), 2 Recommendation 1.327 (03D3) CCITT RECMN*I.7Z? (REV*L) 73 m YBb257L 0580579 637 m
17、 TE In the case where the customer network is a B-ISPBX based network providing the same B-ISDN connection type as the public B-ISDN, then the overall B-ISDN connection ends at the SB reference point as shown in Figure 2. NOTES I, 1 8-ISPBW 1 TE 1 pnvateB-ISDN T Public B-ISDN B-ISPBW private B-ISDN
18、T : 1 In the case where the customer network is null then the B-ISDN connection type can be considered to end at the coincident SB, TB reference point. 2 3 Other configurations are possible where the cali is asymmetrical, or terminates in or involves HLFs. The terms “B-ISPBX/pnvate B-ISDN and “publi
19、c B-ISDN do not presuppose a particular regulatory situation in any country and are used purely for technical reasons. A general connection element model in B-XSDN is thus described using five functional blocks: a switching block for VPI, the SVPI; a control block for VPI, the CWI; a switching block
20、 for VCI, the SVCI, a control block for VCI, the CVCI, and an interconnection link (see Figure 4). The link block incorporates all the functions implementing the physical layer. Different links may be identified, e.g. access links and transit links. 1 - Customer network - Public network - Customer n
21、etwork - Overall B-ISDN connecticri TI81 8620-92ldO2 FIGURE 2n.w Overall B-ISDN reference configuration for a mixed B-ISPBXlpubiic B-ISDN scenario 4.2 Partitioning of the overall E-ISDN connection The partitioning of functions within the B-ISDN connection type is done by using connection elements, b
22、asic connection components and reference points as defined in Recommendation 1.324. 4.2.1 Connection elements The first level of partitioning of the overall B-ISDN connection type is the connection element (CE). The partitioning is based on the identification of reference points between connection e
23、lements. Figure 3 identifies five CES for a mixed privatdpublic B-ISDN overall connection type: the private access CE, the private transit CE, the public access CE, the public national transit CE and the public international transit CE. 4.2.2 Functional groups in the B-ISDN connection elements In B-
24、XSDN, the virtual path connection is introduced for routing groups of virtual channels in the network. Therefore two levels of connection handling will exist in the B-ISDN. These levels must be represented by two different switching blocks in the connection elements, one switching according to the v
25、irtual path identifier (VPI) and another switching according to the virtual channel identifier (VCI). Each of these switching blocks is under the control of its respective control block. Recommendation 1.327 (03/93) 3 Customer network _-_-_- - - - Private access CE I B-ISPBW : Private B-ISDN , - - -
26、 - - Public Public Public Private Public national international national Public Private Private transit access transit transit transit access transit access CE . CE CE CE CE CE CE CE LA L1 - y- - y- - - -T y- Customer network _-_ : B-ISPBW I , Privatea-ISDN I IRP CRF Connection related functions Int
27、ernal reference points (between connection elements) FIGURE 3A327 Connection elements within an overall B-ISDN connection In a particular reference configuration for connection types, the connection elements can be realized using a subset of the five functional blocks, for example to represent a con
28、nection in the network where only VPI handling is implemented. 4.2.3 B-ISDN connection element generic description The generic B-ISDN connection element is shown in Figure 5. It represents the logical interrelationship between the functional blocks supporting the B-ISDN connections and the means to
29、control the connections. The B-ISDN connection is supported by the links and the switching blocks Svp and SVCI. The connections are controlled by the controi blocks Cvp and CVCI. These control blocks logicaiiy interface to the user-network signalling system on the user side of an access connection e
30、lement and with the internodai signalling network. For the control of semi-pemanent connections, the control blocks also interface to the network management function. These management interface definitions will be the subject of further studies. Link representation VCI-handling representation FIGURE
31、 4L.327 Functional groups in a B-ISDN connection element 4 Recommendation 1.327 (03/93) VPI-hmding representation T181281081K4 I I I I l I l I I l I Switching I User-netvmrk or intemodal I I I I I CVCI SVCI I I Note2 I signalling function II II I I Network I I I I I I SVPI - ! c VPI management I fun
32、ction I I I I Link I n II I *I 1 Connection element NOTES 1 (e.g. Svp and SV could be combined into a single ATM switching entity). 2 study. Figure 5 represents a generic connection element. The functional blocks may be combined into a single entity How the control block for VPI handling relates to
33、signalling and network management functions is for further FIGURE 5A.327 A generic B-ISDN connection element (see Note 1) 4.3 Functionai architecture models for the B-ISDN Appendix I gives examples of functional architecture models using the principles established in Recommen- dation 1.324. These pr
34、inciples are basically those of reference points and functional groups identified in Figure 8. Annex A (This annex forms an integral part of this Recommendation) Recommendation 1.211 identifies the connectionless data service aspects of B-ISDN. The transport of connectionless data units in B-ISDN is
35、 supported using the B-ISDN ATM switched capabilities between specific functional groups (connectionless services functions, CLSF) able to handle the connectionles protocol and to realize the adaptation of the connectionless data units into ATM cells. The CLSF functional groups may be located outsid
36、e B-ISDN, in a private connectionless network or in a specialized service provider, or inside B-ISDN . As a result, two mechanisms (in 2.7A.211 for supporting connectionless data services are envisaged: 1) 2) indirectly via a B-ISDN connection-oriented service (Case A), directly via a B-ISDN connect
37、ionless data service (Case B). Recommendation 1.327 (03/93) 5 The respective functional architecture models for Case A and Case B are representd in Figures A.l and A.2. In case A, no constraints are imposed on the connectionless protocols to be adpted in the CLSF functional groups located outside B-
38、ISDN, but suitable interfaces shall be recommended at he SB or TB and at the M reference points. In addition, Figure A.3 shows an example where Cases A and B coexist. For the provision of the connectionless data service, ATM connections are to be established bem-een the user and the CLSF and between
39、 CLSFs. These connections may be: semi-permanent virtual path connection (VPC); all the VC connections in these VP connections are dedicated to connectionless data service: a switched or semi-permanent virtual channel connections (VCC)l) . - - The CLSF, independently of its location, terminates the
40、B-ISDN connectionless protocol and routes the connectionless data units towards a destination user according to addressing information included in the connectionless data units. The connectionless broadband data service on B-ISDN is described in Recommendation F.812. - y- / , specialized / I B-ISDN
41、customer / / -_- . / / I -CLsF-. , / M -. .- CLSF I I I TI 8171 30-92ld06 i- -_- semi permanent connection Call by call connection _-_-. CLSF Connectionless service function %,TB. M Reference points FIGURE A.1h.327 Indirect provision of eonnectionless data service (Case A) The use of semi-permanent
42、or switched VCC between CLSFs shall be considered for consistency with other CCm Recommendations currently under study. 6 Recommendation 1.327 (03/93) CCITT RECMNtI-327 (REV*1) 93 m Y862591 O580603 998 m -_ , * -B-ISDN - _-_ . /-. . customer -1 _- I CLSF ; / - , CLSF ; *. -w *.; - / customer I / SB
43、or TB -.- - - /I _- L P P y - I CLSF 4 * T181714(lguan CLSF -_- i_- / -_-_- , B-ISDN I SBorTB , customer , - CLSF P, S, T Semi permanent connection Call by call connection Connectionless service function Reference points FIGURE m.327 Direct provision of Connectionless Data Service (Case B) Specializ
44、ed service provider ) _- , Piivate connectioniess , / -. TI 81 71 WWCC -_ * SB orT, , customer , / , B-ISDN -_ Semi permanent connection Call by call connection Connectionless service function Reference points FIGURE A.3D.327 Example of coexistence of Cases A and B Recommendation 1.327 (03/93) 7 CCI
45、TT RECMN*I=327 (REV*L) 93 D 4862593 0580604 824 D ACE AL B-NT1 B-ISPBX CBR CE CLSF CRF DPL PL IRP LE LFC LT “I PLK RU SP SPL TCE TCRF TE VBR VCI VPI 8 Annex B Alphabetical list of abbreviations used in this Recommendation (This annex forms an integral part of this Recommendation) Access connection e
46、lement Access link Network termination 1 for B-ISDN Private branch exchange for B-ISDN Constant bit rate Connection element Connectionless service function Connection related function Primary link for distribution services Primary link for interactive services Internal reference point Local exchange
47、 Lod function capabilities Line termination Network-node interface Pnmary link Remote unit Service provider Service provider link Transit connection element Transit connection related function Terminal equipment Variable bit rate Virtual channel identifier Virtual path identifier Recommendation 1.32
48、7 (03193) CCITT RECMN*1-327 (REV*L) 93 4462593 0580605 760 Appendix I Examples for functional architecture models for B-ISDN (This appendix does not form an integral part of this Recommendation) Functional architecture models aim to identify various possible physical arrangements for the realization
49、 of the network when interconnecting equipment. Depending on the national situations and on the type of access, a number of different functional architecture models exist for accessing the B-ISDN: - a star structure where customers have direct individual links to the local exchange (LE) (see Figure 1.1); - a multistar structure with a remote unit (RU) between the customer and the main exchange. This is a two stage local network, each stage being star structured (see Figure 1.2);
