1、STD-ITU-T RECMN 1.555-ENGL 1777 B 4Bb257L Ob45158 2T3 D INTERNATIONAL TELECOMMUN KATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU . I. SERIES I: INTEGRATED SERVICES DIGITAL NETWORK Internetwork interfaces 1.555 (09/97) Frame Relaying Bearer Service interworking , ITU-T Recommendati
2、on I 555 (Previously CCIlT Recommendation) STD-ITU-T RECMN I-555-ENGL 1997 W 48b259L Ob115357 13T ITU-T I-SERIES RECOMMENDATIONS INTEGRATED SERVICES DIGITAL NETWORK GENERAL STRUCTURE Terminology Description of ISDNs General modelling methods I. 1 00-1.199 I. 1 10-1.1 19 I. 120-1.129 I. 130-1.139 Tel
3、ecommunication network and service attributes I. 140-1.149 General description of asynchronous transfer mode Scope General aspects of services in ISDN Common aspects of services in the ISDN . Bearer services supported by an ISDN Teleservices supported by an ISDN Supplementary services in ISDN SERVIC
4、E CAPABILITIES OVERALL NETWORK ASPECTS AND FUNCTIONS Network functional principles Reference models Numbering, addressing and routing Connection types Performance objectives Protocol layer requirements General network requirements and functions ISDN USER-NETWORK INTERFACES Application of I-series Re
5、commendations to ISDN user-network interfaces Layer 1 Recommendations Layer 2 Recommendations Layer 3 Recommendations I. 150-1.199 1.200-1.299 1.200-1.209 1.2 10-1.2 1 9 1.220-1.229 1.230-1.239 1.240-1.249 1.250-1.299 1.300-1.399 1.310-1.319 I. 320-1.329 1.330-1.339 1.340-1.349 1.350-1.359 1.360-1.3
6、69 1.370-1.399 1.40-1.499 1.420-1.429 I.43-1.439 1.440-1.449 1.450-1.459 A field of Rec. Q.922 I field of Rec. Q.922 + FCS field of Rec. Q.922 T1309860-97/d03 (1) Q.922 frame 0 Encapsulated part Figure 3aA.555 - Encapsulation of LAPB address, control and I-fields in 4.922 core 87654321 A field of LA
7、PB C field of LAPE (1 or 2 octets) II,/,I, FCS t IIIIIIII (1) X.25 (LAPE) frame FCS field of LAPE 1 87654321 - A field of Rec. 0922 I field of Rec. Q.922 FCS field of Rec. (2.922 (1) Q.922 frame T1309870-97/d04 0 Encapsulated part Figure 3bA.555 - Encapsulation of LAPB control and I-fields in Q.922
8、core 6 Recommendation 1.555 (09/97) STD-ITU-T RECMN 1-555-ENGL 1777 48b257L Ob45167 087 a c LI I- 3 PSPDN (Rec. X.25) X.25 PLP - X.25 PLP X.25 PLP a- X.25 PLP .-. LAPB control or Q.922 control Q.922 core core x.25 pp .- _- L4PB control or Q.922 control .-1-11_.-_I_- LAPB - LAPB I- LAPB .-II. .-.- I-
9、 Q.922 I- Q.922 core - Physical - Physical - Physical Physical - Physical - Physical a, C 3 - ; Figure 4/1.555 - Interyorking between FRBS PVC and PSPDN (X.25) virtual capermanent virtual circuit by port access X.25 PLP -I X.25 PLP? - X.25 PLP .-a X.25 PLP x.25 pLp - - - -I LAPB control L4PB control
10、 or or Q,922 control 1-1-1_n Q.922 control LAPB/Q.921 LAPB/Q.921 - (SAPI = 16) and . - data link layer. Details on interworking/interconnecting LANs and FRBS are given in Appendix I. 7 Interworking between FRBS and Circuit Switched Service by port access This clause describes how ISDN circuit mode c
11、onnections can be used to provide access to a remote frame handler. Both switched and permanent connections may be supported by both the circuit and frame mode networks. Circuit Switched access to a remote FRBS is supported by first establishing a circuit connection to the remote frame handler. Alte
12、rnatively, a permanent circuit mode connection may be used. 7.1 FRBS Switched Virtual Circuit (SVC) case The SVC is established using FRBS call procedures in-band (see Recommendation Q.933) between the NT2 or TE and the remote frame handler (Figure 9a). I 7.2 FRBS Permanent Virtual Circuit (PVC) cas
13、e Since the PVC has already been established in the frame mode network, the terminal may transmit frames using the DLCI value pre-allocated for access to the remote frame handler (Figure 9b). NOTE -The mapping between the B- and H-channels and the FRBS SVCs and PVCs may be 1 to 1, 1 to N, N to 1 or
14、N to N. In the 1 to 1 and 1 to N cases, 1 or more FRBS PVCs are carried in the B- or H-channel. In the N to 1 and N to N cases, a number of B-channels are aggregated to create a single higher rate channel which cames one or more FRBS SVCs or PVCs. A protocol for B-channel aggregation is described in
15、 Recommendation H.244. 8 Interworking between FRBS and B-ISDN In this clause interworking is described between FRBS and the Connection Oriented Variable Bit Rate Services provided by Class C services of B-ISDN. 10 Recommendation 1.555 (09/97) STD-ITU-T RECMN 1-555-ENGL 1997 m 4862593 Ob45173 5T ISDN
16、 Frame mode T1313070-9B/dl O NOTE -Examples of signalling used to set up this connection are SS No. 7 and DSS 1. Figure 9an.555 - Interworking between FRBS Switched VC and ISDN Circuit Switched Service . ISDN Frame mode NT2 or TE 6- or H-channel NOTE - Examples of signalling used to set up this conn
17、ection are SS No. 7 and DSS 1. Figure 9bD.555 - Interworking between FRBS Permanent VC and ISDN Circuit Switched Service 8.1 General description The purpose of FR to B-ISDN interworking is to allow one or both of: a) transportation of FR traffic over a B-ISDN network; and b) customers on either type
18、 of network to communicate with one another. The need to transport FR traffic over a B-ISDN network arises when network operators use a core B-ISDN infrastructure to provide multiple services, such as Frame Relay. There is also a need for FR and B-ISDN terminals to be able to communicate directly. T
19、his Recommendation covers various aspects of FR to B-ISDN interworking. Two interworking types between B-ISDN and FR networks are defined; service interworking and Network Interworking. Service interworking applies when a FRBS TE interacts with an ATM TE; the FRBS TE does not perform any ATM functio
20、ns and the ATM TE does not perform any FR functions. All interworking is performed by an Interworking Function (IW). In contrast, with network intenvorking, the ATM TE performs specific functions in the FR-SSCS within the AAL layer. Recommendation 1.555 (09197) 11 STD-ITU-T RECMN 1-555-ENGL 1797 9 4
21、8b259L Rbq5L74 44b In addition the Post access from B-ISDN (ATM-TE) to FRBS TE is based on a two-step approach. In the first step, a B-ISDN VCC is established between B-ISDN TE to IWF using Q.2931 call control procedures. Only the second step needs to be repeated to set up additional FR connections.
22、 The IWF is acting only as a relay for FR signalling and data flows. The release of the B-ISDN VCC is done after the last FR connections are released. The generic interworking requirements are given below, and three interworking scenarios are outlined. For the PVC interworking case, each interworkin
23、g scenario is specified in detail covering the protocol mapping, management mapping, and OAM mapping between FR and ATM. The SVC interworking case is also covered by this Recommendation. NOTE - Either UNI or NNI protocols can be used at the interfaces of IWF. However, the various cases described in
24、this subclause use UNI signalling only. 8.2 Generic interworking requireme.nts Figure 10 is a representation of the generic FRBS to B-ISDN interworking arrangements defined in this Recommen- dation. This figure shows only interworking cases where UNI protocols are used on both sides of the IWF/AU. T
25、here are additional cases where NNI protocols are used on both sides of the IWF. The interworking arrangements are between FRBS and B-ISDN Class C, message mode, non-assured operation. Interworking between FRBS and B-ISDN Class C services is performed either by call control mapping (SVCs) or by prov
26、isioning (PVCs). The call control mapping procedures can be carried either by tunneling the FR signalling protocol through the ATM network (network interworking scenario) or by translation between the FR and ATM signalling protocols at the IWF (service interworking scenario). Directly provisioned (P
27、VC) interworking configurations are handled by the M-plane (Management Plane). Interworking configurations which are established on demand using SVCs must include the call control mappings in the C-plane (Control Plane). Once a connection through the interworking function has been established, eithe
28、r by the M-plane or by the C-plane, the user data is then subject to the interworking rules of the U-plane (User Plane). The need for interworking between FF3S and B-ISDN Class C, message mode, assured operation is for further study. -II C-plane U-plane NOTE 1 - 4.2933 is only used for network inter
29、working and in the case of service interworking 1.365.1 is not used but Q.293 1 is used. NOTE 2 - Both Q.933 Case A and Case B access methods on the Frame Relay side are supported. NOTE 3 - Either UNI or NNI protocols may be used at the interfaces of IWF. NNI protocol X.76 is applicable at the inter
30、face between the ISDN and 1F. Figure 10A.555 - Interworking between FRBS and B-ISDN 12 Recommendation 1.555 (09/97) STD*ITU-T RECMN 1-555-ENGL 1997 48b2591 Ob45175 382 W A set of generic requirements for interworking between Frame Relaying and B-ISDN services are: - mapping of the Frame Relaying los
31、s priority and congestion control indications; - negotiation procedures for Frame Relaying frame size; - message mode unassured operation without flow control; - immediate transfer of user data once the connection has been established without AAL parameter negotiation procedures. 8.2.1 Interworking
32、in the M-plane Permanent Virtual Circuit (PVC) interworking connections are established by creating separate permanent FR and B-ISDN connections on either side of the interworking function via M-plane communications. The M-plane is responsible for establishing the FR PVC and B-ISDN PVC connections a
33、nd assigning appropriate traffic parameters to them. . ,. The traffic parameters used to describe a Frame Relay connection are CIR, B, Be and T. The corresponding traffic parameters used to describe the B-ISDN Class C service depend on the specific ATC chosen. The mapping between Frame Relay and B-I
34、SDN traffic descriptors is carried out by the M-plane, and can be implemented in numerous ways, depending on how conservatively the loss ratios in both networks should match. One possible mapping of the traffic descriptors is covered in the FFUATM element mappings clause, in the subclause on bandwid
35、th mapping (8.4.1.3). 8.2.2 Interworking in the C-plane The establishment and release of SVC interworking connections in the involved networks is carried out by the C-plane interworking. The general protocol stacks for C-plane network interworking between FRBS and B-ISDN is described in Annex C. Onl
36、y the 1 to 1 mapping of FR to B-ISDN VCCs is supported. The N to 1 mapping is for further study. Since both the F3BS and the B-ISDN call control are handled in a separate call control plane, it is assumed similar call control functions are used, which can be appropriately mapped. Call Control mappin
37、g is provided in a way that U-plane connections am established and released in both interworking networks, interconnected by the IWF. C-plane procedures must provide for the negotiation of U-plane parameters (e.g. throughput, maximum frame size). The traffic parameters used to describe a Frame Relay
38、 connection are CIR, B, Be and T. The corresponding traffic parameters used to describe the B-ISDN Class C service depend on the specific ATC chosen. The mapping between Frame Relay and B-ISDN traffic descriptors is carried out by the C-plane, and can be implemented in numerous ways, depending on ho
39、w conservatively the loss ratios in both networks should match. One possible mapping of the traffic descriptors is covered in the WATM element mappings section, in the subclause on bandwidth mapping (8.4.1.3). Details of specific cases of C-plane interworking are discussed in 8.3. 8.2.3 Interworking
40、 in the U-plane Interworking in the U-plane consists of interworking the FRBS and B-ISDN Class C services, message mode, unassured operation. In particular, B-ISDN Class C, message mode, unassured operation provides basic similar functions (see Table i) as the Frame Relaying core service, and as suc
41、h supports the FFU3S. Recommendation 1.555 (09197) 13 Recommendation 1.363.5s AAL type 5 (SAR and CPCS), in conjunction with either the FR-SSCS (1.365.1) or the Null SSCS, provides the required B-ISDN support for the FRBS. AAL type 5 (SAR and CPCS) is common to all FRBS and B-ISDN interworking scena
42、rios. Subclause 8.3 provides more details on the protocol reference architecture for different interworking scenarios. The B-ISDN ATC used to support interworking with B-ISDN will depend on the traffic parameter mapping chosen (see 8.4.1.3) and is left to the network operators implementation. 8.3 In
43、terworking scenarios These interworking scenarios apply to both PVCs and SVCs. 8.3.1 Network interworking . 8.3.1.1 Network interworking - U-plane (Scenario 1) Figure 11 represents the case, where B-ISDN is interposed between Frame Relaying networks to provide a high speed interconnection capability
44、. In this case, the Frame Relaying networks are users of B-ISDN. The CPE and FR network are unaware of the underlying ATM backbone, due to the isolation provided by the interworking function at each interface to the ATM network. The FR-SSCS, as shown in Figure 11, supports the Frame Relaying core fu
45、nctions of Recommendation 1.233.1. Table 1 illustrates the division of core functions among FR-SSCS, CPCS, SAR sublayer and ATM layer. The ATM layer should be in accordance with Recommendation 1.361 and the .4AL composed of the SAR and CPCS sublayers is specified in Recommendation 1.363.5. AAL type
46、5 (SAR and CPCS) shall be used for Frame Relaying and B-ISDN interworking. The FR-SSCS should be in accordance with Recommendation 1.365.1. The FR-SSCS-PDU has exactly the same structure as the 4.922 core frame without the fiags, zero bit insertion and FCS, as specified in Recommendation 1.365.1. Th
47、ere are two methods of multiplexing FRBS connections over B-ISDN, N to 1 mapping and 1 to 1 mapping. N to 1 mapping case % A number of Frame Relaying logical connections are multiplexed into a single ATM virtual channel connection. Multiplexing is accomplished at the FR-SSCS sublayer using DLCIs. Th
48、is is illustrated in Figure 12. 1 to 1 mapping case Each Frame Relaying logical connection is mapped to a single ATM virtual channel connection and multiplexing is accomplished at the ATM layer using VPWCIs. This is illustrated in Figure 13. In both multiplexing schemes, the FRBS connections are ide
49、ntified by the 4.922 core DLCI. The FR-SSCS links are identified by VPWCI in the 1 to 1 case. The FR-SSCS may provide for the multiplexing into the VCC, of the single user data stream and PVC status monitoring information in accordance with Annex A. The status monitoring stream shall use DLCI = O and the user data stream may use any DLCI not = O. DLCI = O shall not carry any call control signalling in this case. Call control signalling can be carried on DLCI = O only for
