1、ITU-T RECMNaX.35 93 m 4862571 059g374 Tb2 m INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU DATA NETWORKS AND OPEN SYSTEM COMMUNICATIONS PUBLIC DATA NETWORKS x.35 (1 1/93) INTERFACE BETWEEN A PSPDN AND A PRIVATE PSDN WHICH IS BASED ON X.25 PROCEDURES AND E
2、NHANCEMENTS TO DEFINE A GATEWAY FUNCTION THAT IS PROVIDED IN THE PSPDN ITU-T Recommendation X.35 (Previously ?CCITT Recommendation?) FOREWORD The -T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studyi
3、ng technical, operating and tariff questions and issuing Recommen- dations on them with a view to standardizing telecommunications on a worldwide basis The World Telecommunication Standardization Conference (WTSC), which meets every four years, etablishes the topics for study by the ITU-T Study Grou
4、ps which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the IT-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). -T Recommendation X.35 was prepared by ITU-T Study Group 7 (1993-1996) and was app
5、roved under the WTSC Resolution No. 1 procedure on the 16th of November 1993. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O rmT 1994 All rights reserved. No part of this pu
6、blication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. O 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 ITU-T RECMN*X.35 93 m 4862571 0574376 835 m CONTENTS Introduction Scope References
7、 Definitions Abbreviations . Conformance Topologies Addressing . Routing . An interworking function model General considerations . Procedures for restart . Procedures for call Set-up and clearing Procedures for data and interrupt transfer Procedures for flow control Procedures for reset Optional use
8、r facilities . Annex A . Publicfivate Network Interworking using Call Control Mapping Recommendation X.35 (11/93) Page 1 1 1 1 2 2 3 6 7 11 11 12 12 14 14 14 15 30 1 ITU-T RECMN*X.35 93 = 4862591 0594377 771 SUMMARY This Recommendation defines the interface and the procedures applicable for the purp
9、ose of providing a gateway function in a PSPDN to a private PSDN. This Recommendation has been developed in direct response to a market demand for the PSPDN to provide a mechanism for interconnection between a private and public network on a peer-to- peer basis that does not rely on the provisioning
10、 of X.75 STEs in both the private PSDN and the PSPDN. This Recommendation will permit private networks to create Virtual Private Networks (VPNs) across the PSPDNs resources and participate in other features of a PSPDN not available in the private network such as ICUGs. ii Recommendation X.35 (1 1/93
11、) ITU-T RECMN*X.35 93 = 4862593 0594378 bO8 Recommendation X.35 INTERFACE BETWEEN A PSPDN AND A PRIVATE PSDN WHICH IS BASED ON X.25 PROCEDURES AND ENHANCEMENTS TO DEFINE A GATEWAY FUNCTION THAT IS PROVIDED IN THE PSPDN (Geneva, 1993) O Introduction This Recommendation defines the general procedure a
12、nd interface applicable to interworking between a PSPDN and a Private PSDN based upon modified X.25 procedures to define a gateway function that is provided in the PSPDN. Modification of the procedures defined in X.25 are required for successful completion of calls between a PSPDN and a Private PSDN
13、 on a peer-to-peer basis. For clarity and to facilitate interworking between the PSPDN and the Private PSDN, the requirements and examples of actions in the private network have been included. 1 Scope The scope of this Recommendation is to define the interface and the procedures applicable for the p
14、urpose of providing a gateway function in a PSPDN to a Private PSDN. This Recommendation is only applicable to the interface in the PSPDN that is providing the gateway (i.e. interworking) function to a Private PSDN. 2 References - Recommendation X.25 Interface between DTE and DCE terminals operating
15、 in the packet mode and connected to public data networks by a dedicated circuit. - Recommendation X.75 Packet Switched Signalling System between public networks providing data transmission services. - Recommendation X. 1 10 International routing principles and routing plan for PSPDNs. - Recommendat
16、ion X. 121 International numbering plan for public data networks. - Recommendation X.300 General principles for interworking between public networks, and between public networks and other networks for the provision of data transmission services. - Recommendation X.327 General arrangements for interw
17、orking between Packet Switched Public Data Networks (PSPDNs) and private data networks for the provision of data transmission services. - ISO/IEC 8208:1993, Information technology - Data communications - X.25 packet layer prorocol for data terminal equipment. 3 Definitions The terms used for all net
18、works and services must be consistent and compatible. Fascicle 1.3 contains the terms and definitions applicable to this Recommendation. Recommendation X.35 (1U93) 1 ITU-T RECMNoX-35 93 m 4862593 0594379 544 m 4 Ab brevia tions CUG DCE DTE IWF IWU NUI PSDN PSPDN PSPvtDN ROA TOMI Closed User Group Da
19、ta Circuit Terminating Equipment Data Terminal Equipment Interworking Function Interworking Unit Network User Identification Packet Switched Data Network Packet Switched Public Data Network Packet Switched Private Data Network Recognized Operating Agency Type of AddressNumbering Plan Identifier. 5 C
20、onformance Conformance to this Recommendation can be stated in one of two ways. The first is the case where the PSPDN is providing the DTE like interface to the private PSDN. In this case, to conform to this Recommendation it is necessary that the PSPDN provide a full set of capabilities as describe
21、d herein including an addressing alternative, routing functionality, an IWU and/or IWF, a complete set of procedures for restart, reset, setup, clearing, interrupt, facility handling, and flow control. The second is the case where the PSPDN is providing a DCE interface to the private PSDN. In this c
22、ase, to conform the PSPDN will provide the following as described by section: Clause 6 At least one of the topologies in Figure 5; Clause 7 At least item a) with b) and c) being optional; Subclause 7.1 Either 7.1.1 or 7.1.2; Subclause 7.2 Optional; Subclause 7.3 Optional; Clause 10 Optional; Clause
23、li Optional; Subclause 12.1 Optional; Subclause 12.2 This subclause must be supported, however the clearing procedure corresponding to the PSPDN IWF operating as DTE are optional; Clause 13 Optional; Clause 14 Clause 15 This clause must be supported; This clause must be supported, however the reset
24、procedure corresponding to the PSPDN IWF operating as a DTE are optional Clause 16 Optional. 2 Retommendation X.35 (lv93) ITU-T RECflN*X-35 93 4862593 0594380 266 X.25 i i X25 PSPVtDN XE 6 Topologies i X25 DTE PSPDN (IWO I. Four cases are addressed by this Recommendation (see Figures 1 to 4). The ca
25、ses differ on what network administers the WF (PSPDN or PSPvtDN) and the WF location (i.e. embedded in or detached from the administering network). Furthermore, six PSPDNPSPvtDN interworking topologies are addressed in this Recommendation. The existence of six topologies is due to the following: a)
26、PSPDNPSPvtDN interworking may be single-link (one link connecting the PSPDN and the PSPvtDN) or multiple-link (more than one link connecting the PSDN and the PSPvtDN) interworking. In a multiple- link interworking, the links PSPDN end-points may be geographically distant; the same applies to the PSP
27、vtDN end points. b) A PSPvtDN may interwork with one PSPDN or concurrently with multiple PSPDNs. c) A PSPDN may interwork with PSPvtDN or concurrently with multiple PSPvtDNs. For all topologies, the only interfaces considered are those using X.25 virtual calls (VCs) and permanent virtual circuits (P
28、VCs) that are established (or preprovisioned) between a PSPDN and a PSPvtDN. All addressing and routing alternatives may not be suitable for all interworking cases or topologies. When appropriate, a note will be included to point out these incompatibilities. X25 I i x.25 - - DTE DTE : T07145M)-93/do
29、5 Interface O Interface 2 Interface 3 FIGURE VX.35 PSPDN/PSPvtDN interworking - Case 1: embedded IWF in the PSPvtDN FIGURE 2Bc.35 PSPDNlPSPvtDN interworking - Case 2: embedded IWF in the PSPDN Recommendation X.35 (1 1/93) 3 ITU-T RECMN*X-35 73 4862571 0574381 IT2 x25 i DTE i x25 DTEI IWU IDTE - DTE
30、FIGURE 3K.35 PSPDN/PSPVtDN interworking - Case 3: physically detached IW administered by the PSPvtDN PSPltDN ii interiace 0 i PSPDN . Interiace 1 interfce 3 FIGURE 4K.35 PSPDNPSPVtDN interworking - Case 4: physically deached W administered by the PSPDN 6.1 TopologyA This is the simplest topology. Th
31、e PSPvtDN is connected to a single PSPDN via one X.25 link. Figure 5 a) illustrates topology A. 6.2 TopologyB The PSPvtDN is connected to a single PSPDN via multiple X.25 links. Figure 5 b) illustrates topology B. 6.3 Topology C The PSPvtDN is connected to multiple PSPDNs via one X.25 link to each P
32、SPDN. Figure 5 c) illustrates topology C. 6.4 TopologyD The PSFWDN is connected to multiple PSPDNs via multiple X.25 links to each PSPDN. Figure 5 d) illustrates topology D. 6.5 TopologyE The PSPDN is connected to multiple PSPvtDNs via one X.25 link to each PSPvtDN. Figure 5 e) illustrates topology
33、E. 6.6 TopologyF The PSPDN is connected to multiple PSPvtDNs via multiple X.25 links to each PSPvtDN. Figure 5 f) illustrates toplogy F. 4 Recommendation X.35 (11/93) ITU-T RECMN*X*35 73 4862573 0574382 039 X.25 4 m PSPDN PSWDN PSPDN TO71 4540-9YdG9 NOTE - PSPvtDNs shall not act as transit networks
34、between two PSPDNs. FIGURE YX.35 PSPDNmSPvtDN intenvorking topologies Recommendation X.35 (11/93) 5 ITU-T RECMN+X.35 93 = 4862591 0594383 T75 7 Addressing There are three PSPVtDN DTE addressing alternatives: a) b) The PSPDN shares its address space with the PSPvtDN DTEs. Each PSPvtDN DTE address is
35、assigned from the PSPDN address space or is one-to-one mapped from a PSPDN address (see 7.1). The IWFs address is assigned from the PSPDN address space or an IWF identifier is recognized by the PSPDN. PSPvtDN DTEs are not assigned addresses from a PSPDN address space nor mapped from a PSPDN address
36、(see 7.2). The PSPvtDN DTE addresses are not assigned from a PSPDN address space nor mapped from a PSPDN addressing. No IWF address exists. That is, the PSPvtDN address space is independent (or disjoint) from and PSPDN address space (see 7.3). Taking into account the existing PSPDN and PSPvtDN envir
37、onment, backward compatibility considerations, and the ease of implementation, it is recommended that PSPDNs (i.e. IWFs and IWUs under the administration of the PSPDN) support at a minimum addressing alternative a) (see 7.1). Annex A provides a detailed description of the call flow for different top
38、ologies and addressing alternatives. c) 7.1 Under this alternative, a PSPDN shares its X.121 address space with the PSPvtDN. Each PSPvtDN DTE address is one-to-one mapped from a PSPDN address (see 7.1.1) or is assigned from the PSPDN address space (see 7.1.2). 7.1.1 A block of PSPDN X.121 addresses
39、is reserved for addressing a PSPvtDNs DTEs by DTEs outside the PSPvtDN. Each of these addresses is mapped one-to-one (by the IWF) into an internal PSPvtDN DTE address (i.e. the address by which the DTE is known to other DTEs inside its PSPvtDN). In this case, a PSPvtDN DTE is known by one address to
40、 DTEs inside its PSPvtDN and by a different address) to DTEs outside its PSPvtDN. One-to-one mapping options include both mapping a complete X.121 address into an internal PSPvtDN DTE address, or mapping part of an X.121 address (see 7.1.1) into an internal PSPvtDN DTE address. PSPDN address space s
41、haring for PSPVtDN DTEs One-to-one PSPvtDN DTE address mapping 7.1.2 A block of PSPDN X.121 addresses is reserved for assignment to PSPvtDN DTEs. In this case, a DTE on the PSPvDN is known only by this address (i.e. it is addressed the same way by DTEs on the PSPDN or by other DTEs on its PSPvtDN).
42、Only topologies A, B, E, and F apply to this addressing alternative. However, this does not preclude a PSPvtDN from obtaining addresses from more than one PSPDN. If the X.121 PSPDN Network Termination Numbers (NT”s) address length is less than 10 digits long, the mechanism described in Appendix IV/C
43、CIT Rec. X.25, can be used. That is, additional complementary address digits may be reserved to be assigned to a PSPvtDNs DTEs. Each reserved X.121 PSPDN address assigned to a PSPvtDN DTE is divided into two subfields: the first subfield is the X.121 PSPDN address assigned to the PSPvtDN, the second
44、 subfield (i.e. the complementary address digits) identifies the PSPvtDN DTE. A limitation is that the number of digits in the two subfields must be 10 or less for international use. PSPvtDN addresses from the PSPDN address space 7.2 If this alternative is used, then the IWF is assigned a PSPDN addr
45、ess or an identifier recognizable by the PSPDN. One option is for the IWF PSPDN address to be contained in the called address field of an X.25 call setup/clearing packets. A mechanism to carry the PSPvtDN DTE address must be also be available. One possible mechanism is to carry the PSPvtDN DTE addre
46、ss in the address extension facility. When a PSPDN DTE transmits a CALL REQUEST packet to establish a VC with a PSPvtDN DTE, this packet contains an address that identifies the PSPvtDN (e.g. the IWFs PSPDN address or identifier assignment for the PSPDN/PSPVtDN IWF i) The PSPvtDN DTE may be known by
47、multiple different addresses (one for each PSPDN to which the PSFvtDN is connected). 6 Recommendation X.35 (11/93) ITU-T RECMN*X.35 93 4862593 0594384 901 registered PSPDN address) in the culled address field, and the PSPvtDNs DTE address in the X.25 address extension facility. 7.3 Independent PSPvt
48、DN address space Under this alternative, all PSPvtDN addresses are independent (i.e. disjoint) from the PSPDN addressing space. That is, an independent PSPvtDN address is one which is not assigned from a PSPDN address space nor mapped from a PSPDN address. No IWF address exists. Two methods exist as
49、 described in 7.3.1 and 7.3.2. 7.3.1 Separate DNIC address space from PSPvtDNs An addressing alternative is described in 1988 CCIT Recommendation X.121. 1988 CCITT Recommendation X.121, Annex B, provides an example, for illustrative purposes only, of a PSPvtDN addressing method. The described altemative requires the allocation of a separate DNIC to be used exclusively for PSPvtDN addressing; the DNIC is shared among multiple PSPvtDNs. Each PSPvtDN is assigned one or more Private Network Identification Code(s) (PNIC). When viewed from the public network, the PNIC, which
