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- FOREWORD
- The CCITT (the International Telegraph and Telephone Consultative
- Committee) is a permanent organ of the International Telecommunication Union
- (ITU). CCITT is responsible for studying technical, operating and tariff
- questions and issuing Recommendations on them with a view to standardizing
- telecommunications on a worldwide basis.
- The Plenary Assembly of CCITT which meets every four years, establishes
- the topics for study and approves Recommendations prepared by its Study Groups.
- The approval of Recommendations by the members of CCITT between Plenary
- Assemblies is covered by the procedure laid down in CCITT Resolution No. 2
- (Melbourne, 1988).
- Recommendation X.612 was prepared by Study Group VII and was approved
- under the Resolution No. 2 procedure on the 18 June 1990.
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- ___________________
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- CCITT NOTE
- In this Recommendation, the expression "Administration" is used for
- shortness to indicate both a telecommunication Administration and a recognized
- private operating agency.
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- F ITU 1990
- All rights reserved. No part of this publication 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.
- PAGE BLANCHE
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- Recommendation X.612
- PROVISION OF THE OSI CONNECTION-MODE NETWORK SERVICE
- BY PACKET MODE TERMINAL EQUIPMENT CONNECTED TO AN
- INTEGRATED SERVICES DIGITAL NETWORK (ISDN)
- FOR CCITT APPLICATIONS1)
- 1 General
- 1.1 Introduction, scope and field of application
- This Recommendation specifies the method of providing t e OSI Connection-
- mode Network Service (CONS) by packet mode terminal equipment connected to an
- Integrated Services Digital Network (ISDN) in accordance with the procedures
- described in Recommendation X.31. This is done by specifying the mapping of the
- CONS primitives and parameters to and from the elements of the protocols used by
- two types of packet mode terminal equipment:
- a) an X.25 DTE (TE2) connected to an R reference point and accessing an
- ISDN; and
- b) a packet mode ISDN terminal (TE1) operating the packet layer protocol
- (PLP) of Recommendation X.25 and connected to an ISDN at either the S
- or T reference point.
- Note 1 - The definitions of TE1, TE2 and TA equipment and R, S and T
- reference points are given in Recommendation I.411.
- Note 2 - This Recommendation applies to a TE1 or TE2/TA (i.e. an OSI end
- system) regardless of whether it is a physically separate system or embedded in
- other equipment such as a PBX.
- This Recommendation addresses the provision of the CONS using virtual
- circuits as described in Recommendation X.25. It does not address the use of X.25
- permanent virtual circuits (PVCs). The extension of this Recommendation to
- include the use of X.25 PVCs is for further study.
- Note 3 - This Recommendation uses numbers to identify layers, rather than
- their names. This is done to align the terminology of this document with the
- terminology of the related ISDN Recommendations, and does not imply any change in
- the functionality of the layers from that defined in the reference model of open
- systems interconnection for CCITT applications.
- 1.2 References
- The following Recommendations contain provisions which, through reference
- in this text, constitute provisions of this Recommendation:
- Recommendation I.231 - Circuit-mode bearer service categories;
- Recommendation I.232 - Packet-mode bearer service categories;
- Recommendation I.430 - Basic user-network interface layer 1 specification;
- Recommendation I.431 - Primary rate user-network interface layer 1
- specification;
- Recommendation Q.921 - ISDN user-network interface data link layer
- specification;
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- 1) Recommendation X.612 and ISO 9574 (Information processing - Telecommunications
- interchange between systems - Provision of the OSI connection-mode network service by
- packet mode terminal equipment connected to an integrated service digital network) were
- developed in close collaboration and are technically aligned.
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- Recommendation X.612 PAGE3
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- Recommendation Q.931 - ISDN user-network interface layer 3 specification;
- Recommendation V.25 bis - Automatic calling and/or answering equipment
- on the general switched telephone network (GSTN)
- using the 100-series interchange circuits;
- Recommendation X.21 - Interface between data terminal equipment (DTE) and
- data circuit-terminating equipment (DCE) for
- synchronous operation on public data networks;
- Recommendation X.21 bis - Use on public data networks of data terminal
- equipment (DTE) which is designed for interfacing to
- synchronous V-Series modems;
- Recommendation X.25 - Interface between data terminal equipment (DTE) and
- data circuit-terminating equipment (DCE) for
- terminals operating in the packet mode and connected
- to public data networks by dedicated circuit.
- Note - This Recommendation is referred to solely in respect of its packet
- layer protocol description. However, this Recommendation fully specifies
- the behaviour of the DCE while specifying only a minimum set of
- requirements for the DTE. Additional guidance for the design of DTEs is
- available in International Standard ISO/IEC 8208. The development of a
- Recommendation describing X.25 DTE procedures for CCITT applications is
- for further study.
- Recommendation X.31 - Support of packet mode terminal equipment by an
- ISDN;
- Recommendation X.32 - Interface between data terminal equipment (DTE) and
- data circuit terminating equipment (DCE) for terminals
- operating in the packet mode and accessing a packet
- switched public data network through a public switched
- telephone network or an integrated services digital
- network or a circuit switched public data network;
- Recommendation X.223 - Use of X.25 to provide t e OSI connection-
- mode network service for CCITT applications (See also
- ISO 8878);
- 1.3 Definitions
- 1.3.1 Recommendation X.200 definitions
- Network connection
- Network layer
- Network service
- 1.3.2 Recommendation X.210 definitions
- Network service provider
- Network service user
- 1.3.3 Recommendation X.213 definitions
- N-CONNECT request
- N-DISCONNECT indication
- 1.3.4 Recommendation X.25 definitions
- DATA packet
- Data terminal equipment
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- PAGE2 Recommendation X.612
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- INCOMING CALL packet
- Throughput class
- User data field
- 1.3.5 Recommendation X.31 definitions
- Conditional notification class of service
- ISDN Virtual Circuit Bearer Service
- No notification class of service
- Packet handling function
- PSPDN service
- Unconditional class of service
- Semi-permanent access (see Note)
- Demand access
- Note - Some ISDN Recommendations use the term "Permanent" to describe this
- feature.
- 1.3.6 Recommendation I.112 definitions
- Terminal equipment
- Reference point
- 1.3.7 Recommendation I.411 definitions
- R reference point
- S reference point
- T reference point
- Terminal adaptor
- 1.3.8 Recommendation I.412 definitions
- B-channel
- D-channel
- 1.3.9 Recommendation X.121 definitions
- Prefix
- Escape
- 1.4 Abbreviations
- 1.4.1 Reference model abbreviations
- NS Network service
- OSI Open systems interconnection
- 1.4.2 Network service abbreviations
- CONS Connection-mode network service
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- Recommendation X.612 PAGE3
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- QOS Quality of Service
- 1.4.3 X.25 abbreviations
- DCE Data circuit-terminating equipment
- DTE Data terminal equipment
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- LAP Link access procedure
- PLP Packet layer protocol
- PSDN Packet switched data network
- RPOA Recognized private operating agency
- 1.4.4 ISDN abbreviations
- AU Access unit
- ISDN Integrated services digital network
- PH Packet handling function
- SAPI Service access point identifier
- TA Terminal adaptor
- TE Terminal equipment
- HLC Higher layer compatibility
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- 1.5 Overview
- 1.5.1 ISDN environment
- The support of the packet mode terminal equipment within the scope of this
- Recommendation by an ISDN is described in Recommendation X.31. Throughout this
- Recommendation references to Recommendation Q.931 procedures indicate their use
- as described in Recommendation X.31. Two cases for ISDN support of packet mode
- terminal equipment are defined in Recommendation X.31; one, the case where the
- support is via the ISDN Virtual Circuit Service (see Figure 1a), and the other
- where the support is via access to PSDN services (see Figure 1b) respectively
- referred to as "Case B" and "Case A".
- In Case A, an ISDN transparent circuit connection, either semi-permanent
- (i.e. non-switched) or demand
- (i.e. switched) is used. The corresponding ISDN bearer service is a 64 kbit/s
- service as described in Recommendation I.231. The sub-network functions available
- to the user are those f the PSPDN described in Recommendation X.25 (semi-
- permanent-access) and Recommendation X.32 (demand access), as well as in other X
- Series Recommendations (e.g. X.2, X.121).
- In Case B, the ISDN Virtual Circuit Bearer Service is used, as described
- in Recommendation I.232. The sub-network functions available are those described
- in the I.200-Series Recommendations.
- In Case A, only B-channels may be used to access the PSDN, while in
- Case B, both B- and D-channels may be used to access the ISDN packet handling
- function.
- 1.5.2 CONS in this ISDN environment
- Recommendation X.223 specifies the method for providing the OSI-CONS
- through the use of the Recommendation X.25 PLP. When operating in an ISDN
- environment, a few requirements additional to those contained in
- Recommendation X.223 are necessary.
- The requirements for providing CONS by terminal equipment connected to an
- ISDN at the S or T reference points are specified in Section 2.
- The requirements for providing CONS in X.25 DTEs presenting an X.21, X.21
- bis, or V.25 bis interface at the R reference point and connected to an ISDN
- through a TA are specified in Section 3.
- This Recommendation uses the X.25 PLP to convey all elements of all three
- phases of the OSI-CONS.
- Fig. 1 = 14cm
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- 2 Provision of the CONS in systems attached at the S/T reference point
- 2.1 Procedures for TE1s and TE2/TAs to provide CONS
- This S 2 covers the three cases that exist, taking into account the
- various types of underlying connections that can be available to the packet mode
- TE1 or TE2/TA (see Table 1). The protocol layers applicable to these cases are
- given in Figures 2 and 3 as referenced in Table 1.
- The mapping of the elements of the CONS to the protocol and procedures of
- Recommendation X.25 shall be as required by Recommendation X.223. The remaining
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- subsections of Section 2 specify the provisions required in addition to these
- mappings, by systems attached to an interface at the S/T reference point.
- include 612-t1-e.docTABLE 1
- Cases covered by S 2
- Underlying connection Figure Subsection
- perceived
- by the terminal equipment
- D-channel 2 2.2
- B-channel : semi-permanent 3 2.3.1
- B-channel : demand 3 2.3.2
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- 2.2 Additional procedures for a TE1 or TE2/TA to provide the CONS when using
- the ISDN D-channel
- This section is only applicable in Case B access. TE1s and TE2/TAs
- supporting packet operation on the ISDN D-channel present a stack of protocols at
- the S or T reference point in accordance with the Recommendations indicated in
- Figure 2. At the physical layer I.430 shall be used if the ISDN access is a basic
- interface and I.431 shall be used if the ISDN access is a primary rate interface.
- At the data link layer, Q.921 shall be used to provide the LAPD procedures. At
- the network layer, X.25 shall be used to provide the packet layer protocol and
- Q.931 may be used to provide the "call-offering procedure" which, when present,
- takes place before the conveyance of X.25 incoming call packets. The Q.931
- procedures enable terminal identification (basic access) and a determination of
- which channel
- (D or B) a specific incoming call packet is to be conveyed on. The following
- limitations shall apply:
- 1) the maximum user data field length of X.25 data packets shall not
- exceed 256 octets;
- 2) the Recommendation X.25 throughput class used shall not exceed 16
- kbit/s on a basic interface.
- The subscription and negotiated facilities in the X.25 call establishment
- packets shall be used, as necessary, to indicate values consistent with these
- restrictions.
- 2.2.1 Outgoing calls
- Recommendation X.25 procedures shall be operated over the ISDN layer 2
- procedures using SAPI=16 as defined in Recommendation X.31. No additional
- procedures are required.
- Note - The address fields of the Recommendation X.25 packe s contain sub-
- network addresses that are valid for the ISDN (e.g. Recommendation E.164 for
- public ISDNs, where a valid Recommendation E.164 format address could be Escape
- Code + Recommendation X.121 number; a network dependant prefix may also be
- required).
- 2.2.2 Incoming calls
- The procedures applying to incoming calls vary according to whether the
- ISDN call offering procedures are used.
- Note - The address fields of the Recommendation X.25 packe s contain sub-
- network addresses that are valid for the ISDN.
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- Fig. 2 = 10cm
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- 2.2.2.1 Without call offering procedures
- These procedures are used by the sub-network if:
- a) the interface to which the TE1 or TE2/TA is connected has subscribed to
- the "conditional notification class of service", and the network does
- not use the call offering procedures for this incoming call; or
- b) the interface on which the TE1 or TE2/TA is connected has subscribed to
- the "no notification class of service".
- Recommendation X.25 procedures shall be operated over the ISDN layer 2
- procedures using SAPI=16 as described in Recommendation X.31. No additional
- procedures are required.
- 2.2.2.2 With call offering procedures
- These additional procedures are used if:
- a) the interface to which the TE1 or TE2/TA is connected has subscribed to
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- the "unconditional notification class of service"; or
- b) the interface to which the TE1 or TE2/TA is connected has subscribed to
- the "conditional notification class of service" and the network uses
- the call offering procedures for this incoming call.
- Recommendation X.25 protocol procedures shall be used over the ISDN layer
- 2 procedures using SAPI=16. In addition, the ISDN call offering procedures are
- also operated over the ISDN layer 2 procedures, using either SAPI=0 or SAPI=16.
- Systems conforming to this Recommendation that operate these ISDN call offering
- procedures, shall implement these procedures using SAPI=0 and may also implement
- these procedures using SAPI=16 (see Notes 1 and 2). The ISDN call offering
- procedures (see Notes 3 and 4) determine which TE1 or TE2/TA is to receive the
- call and are not visible to the NS user. The Recommendation X.25 procedures are
- then operated after the ISDN call offering procedures have been completed.
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- Note 1 - Recommendation X.31 states (Note 4 of S 6.2.2.3.1): networks
- providing packet mode call offering shall provide Q.931 signalling procedures for
- packet mode calls on SAPI=0. For an interim period, some networks, by
- subscription agreement, may offer SAPI=16 broadcast call offering procedures for
- providing Q.931 signalling. This option will use all Q.931 procedures for packet
- mode calls with the following restriction: a l calls will be offered as "D-
- channel exclusive" and will not provide channel negotiation procedures. Terminals
- implementing SAPI=16 procedures shall also implement SAPI=0 procedures for
- portability.
- Note 2 - In order to maximize terminal portability during the interim
- period identified in Note 1, systems should implement the call offering
- procedures on both SAPI=0 and SAPI=16.
- Note 3 - These procedures may u e Recommendation Q.931 addressing, sub-
- addressing and compatibility checking information elements, to determine which
- TE1 or TE2/TA is to receive the call. In order to avoid unnecessary connection
- failures, it is suggested that incoming calls are accepted on the basis of
- compatibility information unless this information identifies functionality that
- is not within the capability of the terminal. It is also suggested that incoming
- calls are accepted in the case where compatibility information is not present.
- Incoming calls can be rejected for other reasons. Care must be taken when
- connecting terminals operating according to this specification to a passive bus
- with other terminals that may accept incoming calls without compatibility
- information.
- Note 4 - These procedures may require D-channel selection, or may offer
- the terminal a choice of D- or
- B-channels. No distinction is made between these ways of selecting the D-channel.
- Section 2.3 covers the case where a B-channel is selected.
- 2.3 Additional procedures for a TE1 or TE2/TA to provide the CONS when using
- the ISDN B-channel
- TE1s and TE2/TAs supporting packet operation on the ISDN B-channel present
- stacks of protocols at the S or T reference point in accordance with the
- Recommendations indicated in Figure 3. One stack, which may be null, is used to
- support signalling on SAPI=0 for circuit switched access to the packet handling
- function, and the other is used to support packet switched signalling and
- information transfer. At the physical layer, I.430 shall be used if the ISDN
- access is a basic interface, and I.431 shall be used if the ISDN access is a
- primary rate interface. At the data link layer, Q.921 shall be used ov r the D-
- channel (signalling) and X.25 LAPB shall be used over the B-channel
- (information). At the network layer, Q.931 shall be used over the D-channel to
- convey circuit switched signalling and for the ISDN call offering procedure.
- Also, at the network layer, the X.25 PLP shall be used over the B-channel for the
- packet layer protocol (see note).
- The following sub-sections specify the additional provisions required in
- cases of an underlying semi-permanent connection and an underlying demand access
- connection between the TE1 or TE2/TA and the packet handling function.
- Note - In Case B, the address fields of the Recommendation X.25 packets
- contain sub-network addresses that are valid for the ISDN. In Case A, the address
- fields of the Recommendation X.25 packets contain sub-network addresses that are
- valid for the PSPDN.
- Fig. 3 = 12cm
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- 2.3.1 Semi-permanent B-channel connection
- Both the basic interface and the primary rate interface provide for the
- semi-permanent connection of a
- B-channel between the S or T reference point and the packet handling function.
- 2.3.1.1 Virtual call originated by the TE1 or TE2/TA
- No additional procedures are required.
- 2.3.1.2 Virtual call originated toward the TE1 or TE2/TA
- The procedures applying to incoming calls vary according to whether the
- ISDN call offering procedures are used. The use of call offering procedures
- cannot result in the selection of a semi-permanent B-channel in Case A access.
- Therefore, no additional procedures are required for Case A.
- 2.3.1.2.1 Without call offering procedures
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- No additional procedures are required if:
- a) the interface to which the TE1 or TE2/TA is connected has subscribed to
- the "conditional notification class of service" and the network does
- not use call offering procedures for this incoming call; or
- b) the interface to which the TE1 or TE2/TA is connected has subscribed to
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- 2.3.1.2.2 With call offering procedures
- These additional procedures are used if:
- a) the interface to which the TE1 or TE2/TA is connected has subscribed to
- the "unconditional notification class of service"; or
- b) the interface to which the TE1 or TE2/TA is connected has subscribed to
- the "conditional notification class of service" and the network uses
- the call offering procedures for this incoming call.
- The ISDN call offering procedures (see Note) determine which B-channel is
- to be used. These procedures are not visible to the NS user. Following successful
- channel selection, Recommendation X.25 layers 2 and 3 procedures shall apply.
- Note - These procedures may offer the terminal a choice of B-channels with
- or without the choice of the
- D-channel. No distinction is made here between these ways f selecting a semi-
- permanent B-channel. Paragraph 2.3.2 covers the case whe e a demand access B-
- channel is selected. Paragraph 2.2 covers the case where a D-channel is selected.
- 2.3.2 Demand access B-channel connection
- Both the basic interface and the primary rate interface provide for demand
- access connection of a B-channel between the S or T reference point and the
- packet handling function.
- These additional procedures shall be used if a B-channel is not already
- established between the TE1 or TE2/TA and the packet handling function, or if an
- additional B-channel is needed to support the additional traffic, or if
- notification of an incoming call is required.
- 2.3.2.1 Demand access B-channel connection originated by the TE1 or TE2/TA
- The receipt by layer 3 of an N-CONNECT request primitive shall first cause
- the ISDN D-channel signalling procedure for demand access to be used to establish
- a B-channel (see Note). Following successful establishment of this B-channel
- connection, including its entering the data transfer phase at layer 1, the
- procedures specified in Recommendation X.25 shall apply for layers 2 and 3.
- Failure to establish the B-channel connection is indicated to the NS user by
- means of an N-DISCONNECT indication primitive with the originator parameter
- indicating "NS provider" and the reason parameter given in Table 2.
- Note - For Case A, a circuit-switched bearer service is requested, and the
- Recommendation Q.931 called party number information element contains the ISDN
- party number information element contains the ISDN address of the PSDN access
- unit. For Case B, a packet-switched bearer service is requested, and the
- Recommendation Q.931 called party number information element is not used.
- include 612-t2-e.docTABLE 2
- Mapping of Q.931 caises tp CONS reasons
- Ite Q.931 Cause NS Reason (see Note)
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- 1 1:Unassigned or unallocated Connection rejection - NSAP
- number unreachable -permanent
- 2 3:No route to destination Connection rejection - NSAP
- unreachable -permanent
- 3 6:Channel unacceptable Connection rejection - reason
- unspecified - transient
- 4 17:User busy Connection rejection - reason
- unspecified - transient
- 5 18:No user responding Connection rejection - reason
- unspecified - permanent
- 6 22:Number changed Connection rejection - reason
- unspecified - permanent
- 7 27:Destination out of service Connection rejection - reason
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- unspecified - permanent
- 8 28:Invalid number Connection rejection - reason
- format (incomplete number) unspecified - permanent
- 9 34:No circuit/channel available Connection rejection - NSAP
- unreachable - transient
- 10 38:Network out of order Connection rejection - reason
- unspecified - permanent
- 11 41:Temporary failure Connection rejection - reason
- unspecified - transient
- 12 42:Switching equipment congestion Connection rejection - reason
- unspecified - transient
- 13 44:Requested circuit or channel Connection rejection - reason
- not available unspecified - transient
- 14 47:Resources unavailable - Connection rejection - reason
- unspecified unspecified - transient
- 15 57:Bearer capability not Connection rejection - reason
- authorised unspecified - permanent
- 16 58:Bearer capability not presently Connection rejection - reason
- available unspecified - permanent
- 17 63:Service or option not available Connection rejection - reason
- unspecified - permanent
- 18 65:Bearer service not implemented
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- Connection rejection - reason
- unspecified - permanent
- 19 66:Channel type not implemented Connection rejection - reason
- unspecified - permanent
- 20 79:Service or option not Connection rejection - reason
- implemented - unspecified unspecified - permanent
- 21 81:Invalid call reference value Connection rejection - reason
- unspecified - permanent
- 22 82:Identified channel does not Connection rejection - reason
- exist unspecified - permanent
- 23 88:Incompatible destination Connection rejection - reason
- unspecified - permanent
- 24 95:Invalid message Connection rejection - reason
- unspecified - permanent
- 25 96:Mandatory information element Connection rejection - reason
- is missing unspecified - permanent
- 26 97:Message type non-existent or Connection rejection - reason
- not implemented unspecified - permanent
- 27 98:Message not compatible with Connection rejection - reason
- call state or message type non- unspecified - permanent
- existent or not implemented
- 28 99:Information element non- Connection rejection - reason
- existent or not implemented unspecified - permanent
- 29 100:Invalid information element
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- contents Connection rejection - reason
- unspecified - permanent
- 30 101:Message not compatible with Connection rejection - reason
- call state unspecified - permanent
- 31 111:Protocol error - unspecified Connection rejection - reason
- unspecified - permanent
- 32 127:Interworking - unspecified Connection rejection - reason
- unspecified - permanent
- Note - The Diagnostic field of the Q.931 Cause information element may contain an
- indication of the permanence or transience of the condition. The NS Reason passed
- to the NS User may be modified to reansfer this additional information.
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- 2.3.2.2 Demand access B-channel connection originated toward the TE1 or TE2/TA
- The procedures applying to incoming calls vary according to whether the
- ISDN call offering procedures are used.
- 2.3.2.2.1 Without call offering procedures
- No additional procedures are required if:
- a) the interface to which the TE1 or TE2/TA is connected has subscribed to
- the "conditional notification class of service" and the network does
- not use call offering procedures for this incoming call; or
- b) the interface to which the TE1 or TE2/TA is connected has subscribed to
- the "no notification class of service".
- 2.3.2.2.2 With call offering procedures
- These additional procedures are be used if:
- a) the interface to which the TE1 or TE2/TA is connected has subscribed to
- the "unconditional notification class of service"; or
- b) the interface to which the TE1 or TE2/TA is connected has subscribed to
- the "conditional notification class of service" and the network uses
- the call offering procedures for this incoming call.
- The ISDN call offering procedures (see Notes 1 and 2) determine which TE1
- or TE2/TA is to receive the call (basic access) and which B-channel is to be
- used. These procedures are not visible to the NS user. Following successful
- establishment of this B-channel connection, including entering the data transfer
- phase at layer 1, Recommendation X.25 layers 2 and 3 procedures shall apply.
- Note 1 - These procedures may use Recommendation Q.931 addressing,
- sub-addressing and compatibility checking information elements, to determine
- which TE1 or TE2/TA is to receive the call. In order to avoid unnecessary
- connection failures, it is suggested that incoming calls are accepted on the
- basis of compatibility information unless this information identifies
- functionality that is not within the capability of the terminal. It is also
- suggested that incoming calls are accepted in the case where compatibility
- information is not present. Incoming calls can be rejected for other reasons.
- Care must be taken when connecting terminals operating according to this
- specification to a passive bus with other terminals that may accept incoming
- calls without compatibility information.
- Note 2 - These procedures may require a particular B-channel, or may offer
- the terminal a choice of
- B-channels with or without the choice of the D-channel. No distinction is made
- here between these ways of selecting a demand access B-channel. Paragraph 2.3.1
- covers the case where a semi-permanent B-channel is selected. Paragraph 2.2
- covers the case where a D-channel is selected.
- 2.3.2.3 Disconnection of the B-channel
- If one or more OSI network connections are established or are in the
- process of being established on an established B-channel and that B-channel is
- disconnected, this disconnection shall be indicated to the NS user by means of an
- N-DISCONNECT indication primitive with the originator parameter indicating "NS
- provider" and the reason parameter as given in the Table 2, for each OSI network
- connection established or in the process of being established.
- It is a local matter as to under what conditions a TE1 or TE2/TA would
- initiate a disconnection of the
- B-channel(s), using Q.931 procedures as specified in X.31.
- 3 Provision of the CONS in systems attached at the R reference point
- 3.1 Procedures for TE2s to provide the CONS at the R reference point
- This Section 3 covers the three cases that exist at the R reference point,
- taking into account the various types of underlying connections that can be
- available to the TE2 (see Table 3). The protocol layers applicable to these cases
- are given in Figure 4.
- The mapping of information elements of the CONS to the protocol and
- procedures of X.25 PLP shall be as required by Recommendation X.223 for a
- conforming implementation. The remaining subsections of Section 3 specify the
- provisions required in addition to these mappings, by systems attached to an
- interface at the R reference point.
- include 612-t3-e.docTABLE 3
- Cases covered in S 3
- Underlying connection Subsecti
- perceived on
- by the terminal equipment
- Leased circuit 3.2.1
- Direct call 3.2.2
- Circuit switched 3.2.3
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- 3.2 Additional procedures for a TE2 to provide the CONS at the R reference
- point
- TE2s implement all three protocol layers of Recommendation X.25 (see
- Figure 4). At the physical layer (and for signalling for a circuit switched
- connection), either X.21 or X.21 bis or V-Series interfaces may be used. At the
- data link layer, X.25 LAPB shall be used. At the network layer, the X.25 PLP
- shall be used.
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- The following subsections define the additional procedures required for
- each of the three types of underlying connections that can be perceived by the
- TE2 at the R reference point: leased circuit connection, direct call connection
- and circuit switched connection.
- It is not visible to the TE2 whether Case A or Case B access is being
- used, except perhaps for Quality of Service (QOS) restrictions if the D-channel
- is used. These QOS restrictions are caused by restrictions in packet sizes and
- throughput class (see S 2.2).
- 3.2.1 Leased circuit connection
- The X.21, X.21 bis and V-Series Recommendation interfaces provide for a
- leased circuit connection at the R reference point. This leased circuit
- connection perceived by the TE2 may, by means of functions in the TA, use either
- the ISDN D-channel, semi-permanent B-channel or demand access B-channel to access
- the ISDN packet handling function or the PSDN access unit. This is not visible to
- the TE2, except perhaps for a few Quality of Service items.
- No additional procedures are required.
- 3.2.2 Direct call connection
- X.21, X.21 bis and V.25 bis interfaces provide for direct call connection
- at the R reference point. This direct call connection perceived by the TE2 may,
- by means of functions in the TA, use either the ISDN D-channel, semi-permanent B
- channel or demand access B-channel to access the ISDN packet handling function or
- the PSDN access unit. This is not visible to the TE2, except perhaps for a few
- Quality of Service items.
- The additional provisions contained in the subsections below apply.
- 3.2.2.1 Direct call circuit switched connection originated by a TE2 at the R
- reference point
- If the circuit switched connection at the R reference point is not already
- established, the receipt by layer 3 of an N-CONNECT request primitive shall first
- cause the X.21, X.21 bis or V.25 bis procedures for direct call to be used to
- establish the connection. Following the successful establishment of this
- connection and the X.21, X.21 bis or V.25 bis procedures for entering the data
- transfer phase at layer 1, the procedures specified in Recommendation X.25 for
- layers 2 and 3 shall apply.
- Failure to establish the circuit switched connection is indicated to the
- NS user by means of an
- N-DISCONNECT indication primitive with the originator parameter indicating "NS
- provider"and the reason parameter as given in Table 4.
- 3.2.2.2 Circuit switched connection originated toward the TE2
- The Recommendation X.21 procedures need to be in the layer 1 ready state,
- the Recommendation X.21 bis procedures must have circuit 107 OFF, and the
- Recommendation V.25 bis procedures must have circuit 108/2 ON, in order to enable
- a connection to be established towards the TE2. Once this connection is
- established and the X.21 or X.21 bis procedures have entered the data transfer
- state at layer 1, the procedures specified in Recommendation X.25 shall apply at
- layers 2 and 3.
- include 612-t4-e.docTABLE 4
- Mapping of Recommendation X.21 progress signals to CONS reasons
- Cod X.21 Significance NS Reason
- e
- 20 No connection Connection rejection - NSAP
- unreachable - transient
- 21 Number busy Connection rejection - reason
- unspecified - transient
- 22 Selection signals - procedure error Connection rejection - reason
- unspecified - transient
- 23 Selection signals - transmission Connection rejection - reason
- error unspecified - transient
- 41 Access barred Connection rejection - reason
- unspecified-- permanent
- 42 Changed number Connection rejection - reason
- unspecified - permanent
- 43 Not obtainable Connection rejection - NSAP
- unreachable - permanent
- 44 Out of order Connection rejection - reason
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- unspecified - permanent
- 45 Controlled not ready or DTE Connection rejection - reason
- inactive until ..... unspecified - permanent
- 46 Uncontrolled not ready Connection rejection - reason
- unspecified - permanent
- 47 DCE power off Disconnection - permanent
- 48 Invilid facility request Connection rejection - reason
- unspecified - permanent
- 49 Network fault in local loop Connection rejection - reason
- unspecified - permanent
- 51 Call information service Connection rejection - reason
- unspecified - permanent
- 52 Incompatible user class of service Connection rejection - reason
- unspecified - permanent
- 61 Network congestion Connection rejection - reason
- unspecified - transient
- 71 Long-term network congestion Connection rejection - reason
- unspecified - permanent
- 72 RPOA out of order Connection rejection - reason
- unspecified - permanent
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- 3.2.2.3 Disconnection of the circuit switched procedures
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- If one or more OSI network connections are established or in the process
- of being established on an established circuit switched connection and the
- circuit switched connection is disconnected or fails, then the provisions of
- Recommendations X.25 and X.223 concerning the failure of layer 1 shall apply to
- the mapping to an
- N-DISCONNECT indication primitive for each OSI network connection established or
- in the process of being established.
- It is a local matter as to under what conditions a TE2 would initiate a
- disconnection, via X.21, X.21 bis or V.25 bis procedures, of the circuit switched
- connection.
- 3.2.3 Circuit switched connection
- The X.21, X.21 bis and V.25 bis interfaces provide for a circuit switched
- connection at the R reference point. This circuit switched connection perceived
- by the TE2 may, by means of functions in the TA, use either the ISDN
- D-channel or demand access B-channel to access the packet handling function or
- the PSDN access unit. This is not visible to the TE2 except perhaps for a few
- Quality of Service items.
- The additional provisions given in the subsections below apply.
- 3.2.3.1 Circuit switched connection originated by a TE2 at the R reference
- point
- If the circuit switched connection at the R reference point is not already
- established, the receipt by layer 3 of an N-CONNECT request primitive shall first
- cause the X.21, X.21 bis or V.25 bis procedures for circuit switching to
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- be used to establish the connection. Following the successful establishment of
- this connection, including its entering the data transfer phase at layer 1, the
- procedures specified in Recommendation X.25 for layers 2 and 3 shall be used.
- Failure to establish the circuit switched connection is indicated to the
- NS user by means of an
- N-DISCONNECT indication primitive with the originator parameter indicating "NS
- provider" and the reason parameter as given in Table 4.
- If the circuit switched connection is already established, then there are
- no additional procedures.
- 3.2.3.2 Circuit switched connection originated toward the TE2
- The additional provisions of S 3.2.2.2 apply.
- 3.2.3.3 Disconnection or failure of the circuit switched connection
- The additional provisions of S 3.2.2.3 apply.
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- ANNEX A
-
- (This annex does not form an integral part of this Recommendation.)
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- Bibliography
- Recommendation E.164 - Numbering plan for the ISDN era.
- Recommendation I.112 - Vocabulary of terms for IDSNs.
- Recommendation I.411 - ISDN user-network interface - Reference configurations.
- Recommendation I.412 - ISDN user-network interface - Interface structures and
- access capabilities.
- Recommendation X.2 - International data transmission services and optional user
- facilities in public data networks.
- Recommendation X.121 - International numbering plan for public data networks.
- Recommendation X.200 - Reference model of open systems interconnection for CCITT
- applications (see also
- ISO 7498).
- Recommendation X.210 - Open systems interconnection layer service conventions
- (see also
- ISO TR8509).
- Recommendation X.213 - Network service definition for open systems
- interconnection for CCITT applications (see also ISO 8348 and
- ISO 8348/Add.2).
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