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101 299
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6.1.3 Services expected from layer 1
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In the context of Frame Relay, the physical link is referred to as the bearer channel. The Frame Relay protocol shall be run across permanently reserved bearer channels on the Gb interface, see GSM 08.14 [4].
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6.1.4 Options selected from FRF 1.1
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6.1.4.1 Support of DL-CONTROL sub-layer
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No end-to-end DL-CONTROL sub-layer shall be implemented on the Gb interface.
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6.1.4.2 Frame length
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The default maximum information field size of 1600 octets shall be supported on the Gb interface. Maximum information field sizes greater than 1600 octets may be agreed to between Frame Relay network operators and users at subscription time.
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6.1.4.3 Congestion control procedures
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Congestion control is defined in FRF 1.1 [6] and consists of congestion avoidance and congestion recovery mechanisms. Congestion control on the Gb interface consists of congestion avoidance based on the DE bit and on explicit notifications via the FECN and BECN bits within the address field of the Frame Relay frame. Congestion avoidance based on the CLLM message (see ITU-T Q.922 [9] clause A.7 or T1.618 [17] for PCS1900 and FRF 1.1 [6] clause 2.2.5) is not required at the BSS and SGSN sides. No congestion control mechanism based on implicit congestion detection (see ITU-T Q.922 [9] clause A.6.1) or T1.618 [17] for PCS1900 is required at the BSS and SGSN sides.
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6.1.4.3.1 DE bit usage
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The BSS and the SGSN shall always set the DE bit to 0 (zero).
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6.1.4.3.2 FECN and BECN bit usage
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Setting of the FECN and BECN bits: The FECN and BECN bits shall be set to 0 by the BSS and the SGSN. Reaction upon receipt of FECN or BECN marked frames: The reaction of the BSS and the SGSN upon reception of FECN or BECN marked frames is implementation dependent. ETSI ETSI TS 101 299 V7.1.0 (1999-07) 18 (GSM 08.16 version 7.1.0 Release 1998) It is recommended to implement ITU-T Q.922 [9] appendix I.2 or T1.618 [17] for PCS1900 procedures or similar procedures, so that the NS entity can reduce or increase the transmission rate, depending on the FECN or BECN bits received. The NS entity shall be able to report the congestion situation to the upper layer. The criteria to be met for congestion being reported to the upper layer are implementation dependent. The upper layer is expected to reduce or increase its transmission rate as appropriate. It shall be up to the upper layer to perform further appropriate actions e.g. flow control with its peer entity, see ITU-T I.370 [12] or T1.606 [15] for PCS1900.
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6.1.4.4 Signalling procedures
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ITU-T Revised Q.933 [11] annex A or T1.617 [16] for PCS1900 procedures shall be implemented at the BSS and the SGSN sides as recommended in FRF 1.1 [6] clause 2.3. On the Gb interface, these procedures shall be initiated by the user side of the UNI, reverse procedures shall not be used. Only periodic polling shall be used, asynchronous status message needs not to be supported. Switched virtual connection procedures , see FRF 1.1 [6] clause 2.3.2, shall not be implemented.
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6.1.4.5 C/R bit usage
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The C/R bit shall not be used and shall be set to 0 by the sending entity. It shall not be checked by the receiving entity.
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6.1.5 Abnormal conditions
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Upon detection of the unavailability of a PVC by the Frame Relay entity or when a PVC becomes available again, the Network Service Control entity shall be informed. Unavailability cases are described in Recommendations ITU-T Q.922 [9] or T1.618 [17] for PCS1900 and ITU-T Q.933 [11] annex A or T1.617 [16] for PCS1900.
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7 Network Service Control protocol
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7.1 Procedures for the transmission of NS SDUs
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NS SDUs are transmitted in unacknowledged mode across the Gb interface by means of an NS-UNITDATA PDU. The NS-UNITDATA PDU is used in both BSS-to-SGSN and SGSN-to-BSS directions.
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7.1.1 Abnormal Conditions
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If the BSS receives an NS-UNITDATA PDU including a BVCI not associated to the NS-VC where the PDU was received, the BSS shall return an NS-STATUS PDU on that NS-VC, cause "BVC unknown on that NSE". Depending on the implementation, the BSS may then ignore the BVCI and treat the rest of the NS-UNITDATA PDU.
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7.2 Blocking / unblocking procedures
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When a BSS (or SGSN) wishes to block an NS-VC between a BSS and SGSN, the following shall be performed: - The transmitting side at the BSS (or SGSN) shall mark the NS-VC as blocked and shall inform the load sharing function. This results in the redistribution of NS-UNIDATA PDUs to other unblocked NS-VCs of the same group, as described in the "Load sharing function" clause. The NS user entity shall also be informed of the new transfer capability by means of an NS-STATUS-Indication primitive for each affected BVC. A BSS (or SGSN) then sends an NS-BLOCK PDU to the peer entity and starts timer Tns-block. ETSI ETSI TS 101 299 V7.1.0 (1999-07) 19 (GSM 08.16 version 7.1.0 Release 1998) - The NS-BLOCK PDU contains the NS-VCI and a Cause element indicating the reason for blocking (typical cause values: Transit network failure, O&M intervention, Equipment failure). The NS-BLOCK PDU may be sent in any alive (blocked or unblocked) NS-VC pertaining to the same group as the NS-VC to be blocked, unless otherwise required for particular cases which may be further described in the rest of this Technical Specification. - At the sending side of the NS-BLOCK PDU, if no failure has occurred in the receive direction (e.g. O&M intervention), the originator of the NS-BLOCK PDU shall continue to accept NS-UNITDATA PDUs received on the NS-VC being blocked, until an NS-BLOCK-ACK PDU is received for this NS-VC. The originator of the NS- BLOCK PDU shall stop to accept NS-UNITDATA PDUs, if the number of retries of the blocking procedures is exceeded. - Upon Receipt of an NS-BLOCK PDU at an SGSN (or BSS) the NS-VC shall be marked as blocked. The SGSN (or BSS) shall immediately inform the load sharing function. The NS user entity shall also be informed of the new transfer capability by means of an NS-STATUS-Indication primitive for each affected BVC. The SGSN (or BSS) then sends in any alive (blocked or unblocked) NS-VC of the relevant group an NS-BLOCK-ACK PDU, for the blocked NS-VC, to the BSS (or SGSN). - On receipt of an NS-BLOCK-ACK PDU or NS-BLOCK PDU, the originator of the NS-BLOCK PDU stops timer Tns-block. The NS-VC shall remain blocked until an NS-UNBLOCK PDU is received indicating that the NS-VC's state has been changed. When a BSS (or SGSN) wishes to unblock an NS-VC between a BSS and SGSN, the following shall be performed: - The BSS (or SGSN) sends an NS-UNBLOCK PDU to the peer entity and starts timer Tns-block. The NS- UNBLOCK PDU shall be sent on the NS-VC to be unblocked (the NS-VC must be alive, see check procedure in clauses "Test of an NS-VC"). The BSS or SGSN may discard any NS-UNITDATA PDU received on the concerned NS-VC until the reception of the NS-UNBLOCK-ACK PDU. - If an NS-UNBLOCK PDU is received by an SGSN (or BSS) for an NS-VC and the SGSN (or BSS) is able to unblock the NS-VC, the SGSN (or BSS) shall return an NS-UNBLOCK-ACK PDU on the NS-VC where the NS-UNBLOCK PDU was received, then the NS-VC shall be marked as unblocked. The load sharing function shall be informed. The NS user entity shall also be informed of the new transfer capability by means of an NS- STATUS-Indication primitive for each affected BVC. - A BSS (or SGSN) shall stop timer Tns-block on receipt of an NS-UNBLOCK-ACK or NS-UNBLOCK PDU, shall mark the NS-VC as unblocked and shall inform the load sharing function in order to allow transmission of NS-UNITDATA PDUs on this NS-VC. The NS user entity shall also be informed of the new transfer capability by means of an NS-STATUS-Indication primitive for each affected BVC. An NS-UNBLOCK PDU received while a BSS (or SGSN) is waiting for an NS-UNBLOCK-ACK PDU shall be acknowledged with an NS- UNBLOCK-ACK PDU. - If an NS-UNBLOCK PDU is received by an SGSN (or BSS) and the SGSN (or BSS) is not able to unblock the NS-VC, the NS-VC shall remain blocked and the NS-VC blocking procedure shall be initiated by returning an NS-BLOCK PDU to the BSS (or SGSN). This NS-BLOCK PDU shall be sent on the NS-VC where the NS- UNBLOCK PDU was received. - If a BSS (or SGSN) receives an NS-BLOCK PDU while waiting for an NS-UNBLOCK-ACK PDU, it shall stop timer Tns-block and the NS-VC shall remain blocked. An NS-BLOCK-ACK PDU shall be returned. An indication shall be issued towards the O&M system, announcing that the unblocking of the NS-VC was not possible at the peer entity. Further actions of the O&M system are out of the scope of this Technical Specification.
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7.2.1 Abnormal Conditions
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If an NS-BLOCK-ACK PDU is not received for an NS-BLOCK PDU within Tns-block seconds, then the NS-BLOCK PDU procedure shall be repeated a maximum of NS-BLOCK-RETRIES attempts. After NS-BLOCK-RETRIES unsuccessful retry attempts the procedure is stopped and the O&M system is informed that the blocking procedure has failed. Further actions of the O&M system are out of the scope of this Technical Specification. The NS-VC shall be marked as blocked at the originating side of the blocking procedure. ETSI ETSI TS 101 299 V7.1.0 (1999-07) 20 (GSM 08.16 version 7.1.0 Release 1998) If an NS-UNBLOCK-ACK PDU is not received for an NS-UNBLOCK PDU within Tns-block seconds, the NS- UNBLOCK PDU procedure shall be repeated a maximum of NS-UNBLOCK-RETRIES attempts. After NS- UNBLOCK-RETRIES unsuccessful retry attempts the procedure is stopped and the O&M system is informed that the unblocking procedure has failed. Further actions of the O&M system are out of the scope of this Technical Specification. The NS-VC shall be marked as blocked at the originating side of the unblocking procedure. If an NS-UNITDATA PDU is received on an NS-VC that is marked at a BSS or an SGSN as blocked and no NS-VC unblocking procedure is pending, then an NS-STATUS PDU (Cause value: NS-VC blocked) shall be returned to the peer entity. If an NS-BLOCK PDU is received by a BSS or an SGSN for a blocked NS-VC, an NS-BLOCK-ACK PDU shall be returned. If an NS-UNBLOCK PDU is received by a BSS or an SGSN for an unblocked NS-VC, an NS-UNBLOCK-ACK PDU shall be returned. If an unexpected NS-BLOCK-ACK PDU is received by a BSS or an SGSN and it is related to an NS-VC that is locally blocked, the NS-BLOCK-ACK PDU is discarded. If the NS-BLOCK-ACK PDU is related to an NS-VC that is not locally blocked, then an NS-VC unblocking procedure is initiated. If an unexpected NS-UNBLOCK-ACK PDU is received by a BSS or an SGSN and it is related to an NS-VC that is not locally blocked, the received NS-UNBLOCK-ACK PDU is discarded. If the NS-UNBLOCK-ACK PDU is related to an NS-VC that is locally blocked, then an NS-VC blocking procedure is initiated. If the NS-VCI received in an NS-BLOCK or NS-BLOCK-ACK PDU is unknown, then the error shall be reported to the originator of the PDU by means of an NS-STATUS PDU including the unknown NS-VCI, with the Cause value set to "NS-VC unknown", the O&M system shall be informed, then the NS-BLOCK or NS-BLOCK-ACK PDU shall be ignored. Further actions of the O&M system are out of the scope of this Technical Specification.
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7.3 Reset procedure
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The reset procedure shall be used when a new NS-VC is set-up between a BSS and an SGSN, after processor re-start, after failure recovery or any local event restoring an existing NS-VC in the dead state or when its state is undetermined between remote NS entities. Upon completion of the reset procedure, the successfully reset NS-VC is marked as blocked and alive at both sides of the Gb interface. When a BSS (or SGSN) wishes to reset an NS-VC, the following shall be performed: - The NS entity at the BSS (or SGSN) informs the NS user entity of the new transfer capability by means of an NS- STATUS-Indication primitive for each affected BVC. The BSS (or SGSN) then sends an NS-RESET PDU to its peer entity indicating the NS-VCI and the NSEI. The NS-RESET PDU is sent on the NS-VC being reset. The NS-RESET PDU includes a Cause information element. - The sending entity of the NS-RESET PDU then marks the NS-VC as blocked and dead and starts timer Tns-reset. - Receipt of an NS-RESET PDU at an SGSN (or BSS) shall be acknowledged with an NS-RESET-ACK PDU including the NS-VCI and the NSEI, provided that the receiving side is able to reset the NS-VC (i.e. no local condition prevents the receiving side from resetting the NS-VC). The NS-RESET-ACK PDU shall be sent on the NS-VC being reset. - The entity receiving the NS-RESET PDU then marks the acknowledged NS-VC as blocked and alive and informs the NS user entity of the new transfer capability by means of an NS-STATUS-Indication primitive for each affected BVC. The test procedure is then initiated on this NS-VC. - When the sending entity of an NS-RESET PDU receives the NS-RESET-ACK PDU, it stops timer Tns-reset, marks the NS-VC as blocked and alive and initiates the test procedure on this NS-VC. The originator of the NS- RESET PDU is then responsible for unblocking this NS-VC. In case of collision between reset procedures initiated at both sides of the Gb interface, the following shall apply: - When an NS entity awaiting an NS-RESET-ACK PDU in response to an NS-RESET PDU receives an NS- RESET PDU, it shall acknowledge it as described above, and in addition, it shall treat it as an NS-RESET-ACK PDU. ETSI ETSI TS 101 299 V7.1.0 (1999-07) 21 (GSM 08.16 version 7.1.0 Release 1998) When an NS entity is awaiting an NS-RESET-ACK PDU, any PDU other than NS-RESET or NS-RESET-ACK received on one of the NS-VCs being reset shall be ignored. The reset procedure overrides any other pending procedure on the affected NS-VC i.e. other pending procedures are stopped, other running timers are stopped.
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7.3.1 Abnormal conditions
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If the sending entity of an NS-RESET PDU receives no NS-RESET-ACK PDU before timer Tns-reset expires the corresponding NS-VCs shall remain blocked and dead and the entire reset procedure shall be repeated. If the reset procedure remains unsuccessful for a period of time established by the operator, the O&M system shall be informed, and the reset procedure shall be stopped. Further actions of the O&M system are out of the scope of this Technical Specification. If the NS-VCI received in an NS-RESET PDU is different from the NS-VCI locally associated to this NS-VC, the O&M system shall be informed, an NS-RESET-ACK PDU shall be returned including the NS-VCI locally associated to this NS-VC, then the NS-RESET PDU shall be ignored as if not received. If the NSEI received in an NS-RESET PDU is different from the NSEI locally associated to this NS-VC, the O&M system shall be informed, an NS-RESET-ACK PDU shall be returned including the NSEI locally associated to this NS- VC, then the NS-RESET PDU shall be ignored as if not received. If the NS-VCI received in an NS-RESET-ACK PDU is different from the NS-VCI locally associated to this NS-VC or if the NSEI received in an NS-RESET-ACK PDU is different from the NSEI locally associated to this NS-VC, the O&M system shall be informed, then the reset procedure shall be stopped. Further actions of the O&M system are out of the scope of this Technical Specification. If an NS-RESET-ACK PDU is received when not expected, it shall be ignored.
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7.4 Test procedure
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The test procedure shall be used when a BSS (or SGSN) wishes to check that end-to-end communication with its peer entity exists on an NS-VC. Both sides of the Gb interface may initiate this procedure independently from each other. This procedure shall be initiated upon successful completion of the reset procedure (as specified in subclause "Reset procedure") and shall then be periodically repeated. Upon successful completion of an NS-VC reset procedure, a BSS (or SGSN) shall start timer Tns-test, then: - Upon Tns-test expiry, a BSS (or SGSN) sends an NS-ALIVE PDU on the NS-VC to be checked, starts timer Tns-alive and waits for an NS-ALIVE-ACK PDU on this NS-VC. - Upon receipt of an NS-ALIVE PDU on an alive NS-VC, an SGSN (or BSS) shall return an NS-ALIVE-ACK PDU on the NS-VC where the NS-ALIVE PDU was received. - Upon receipt of the NS-ALIVE-ACK PDU in response to an NS-ALIVE PDU, the originator of the NS-ALIVE PDU, shall stop timer Tns-alive and shall start again timer Tns-test. The procedure is repeated each time Tns-test expires.
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7.4.1 Abnormal conditions
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If an NS-ALIVE-ACK PDU is received when not expected, it shall be ignored. If no NS-ALIVE-ACK PDU is received before Tns-alive expires, the test procedure shall be repeated a maximum of NS-ALIVE-RETRIES attempts. After NS-ALIVE-RETRIES unsuccessful retry attempts, the procedure is stopped, the NS-VC is marked as dead and blocked, the O&M system and the load sharing function are informed, and an NS- STATUS-Indication is sent to the NS user entity. A blocking procedure is initiated using an alive NS-VC, if any. Further actions of the O&M system are out of the scope of this Technical Specification. ETSI ETSI TS 101 299 V7.1.0 (1999-07) 22 (GSM 08.16 version 7.1.0 Release 1998)
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7.5 Procedure for error reporting
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The reporting of protocol errors to the remote entity is done by means of the NS-STATUS PDU, as further described in the rest of this Technical Specification. Upon receipt of an NS-STATUS PDU, the O&M system is informed. Further actions of the O&M system are out of the scope of this Technical Specification.
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7.5.1 Abnormal conditions
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If an error is detected in a received NS-STATUS PDU, then the error shall not be reported to the remote NS entity.
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8 General protocol error handling
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This clause is not applicable to the Sub-Network Service protocol. The following "General case" subclause applies unless otherwise stated in the "Special cases" subclause.
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8.1 General case
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This clause specifies procedures for the handling of unknown, unforeseen, and erroneous protocol data by the receiving entity. These procedures are called "error handling procedures", but in addition to providing recovery mechanisms for error situations they define a compatibility mechanism for future extensions of the protocol. Most error handling procedures are mandatory for a BSS and SGSN. Detailed error handling procedures are implementation dependent and may vary from PLMN to PLMN. However, when extensions of this protocol are developed, networks shall be assumed to have the error handling that is indicated in this clause as mandatory ("shall") and that is indicated as strongly recommended ("should"). In this clause the following terminology is used: - Syntactical error: an IE is defined to be syntactically incorrect in a PDU if it contains at least one value defined as "reserved" or "reserved for future use", or if its value part violates coding rules specified in the relevant protocol specification, e.g. a too short IE (the length indicator shall be used to determine the boundary of the IE). However, it is not a syntactical error that an IE specifies in its length indicator a greater length than defined in the relevant protocol specification; and - Semantic error: a PDU is defined to have semantically incorrect contents if it contains information which, possibly dependent on the state of the receiver, is in contradiction to the resources of the receiver and/or to the procedural part of the relevant protocol specification. To allow for the introduction of new functions the following rules shall be used to determine the actions of a receiving entity when it receives a PDU, part or all of which it is unable to understand. As the recipient is unable to tell the difference between a new, previously unspecified coding and an erroneous coding, the recipient also uses the same rules for error handling. The robustness of a recipient in handling erroneous PDUs does not relax the requirement that the transmitter shall obey this Technical Specification. However, it is intended that functionality can be gradually added to an entity, and no obstacle to intermediate phase equipment is intended.
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8.1.1 Presence requirements of Information Elements
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There are three different presence requirements (M, C, or O) for an IE within a given PDU: - M ("Mandatory") means that the IE shall be included by the sending side, and that the receiver diagnoses a "missing essential IE" error when detecting that the IE is not present. - C ("Conditional") means: ETSI ETSI TS 101 299 V7.1.0 (1999-07) 23 (GSM 08.16 version 7.1.0 Release 1998) - that inclusion of the IE by the sender depends on conditions specified in the relevant protocol specification; - that there are conditions for the receiver to expect that the IE is present and/or conditions for the receiver to expect that the IE is not present; these conditions depend only on the PDU itself, and not on the state in which the PDU was received; they are known as static conditions; - that the receiver detecting that the IE is not present when sufficient static conditions are fulfilled for its presence, shall diagnose a "missing essential IE" error; - that the receiver detecting that the IE is present when sufficient static conditions are fulfilled for its non-presence, shall treat the IE as an optional one, see below. - O ("Optional") means that the receiver shall never diagnose a "missing essential IE" error or shall never diagnose an error because it detects that the IE is present or that the IE is not present. There may however be conditions depending on the states, resources, etc. of the receiver to diagnose other errors. In addition, the following definitions apply: - Essential Elements: These are the conditional (C) elements when the condition for their reception is fulfilled, plus the mandatory (M) elements. Any exception to this rule is explicitly stated in the relevant protocol specification. - Non-Essential Elements: Non-essential elements are all the information elements that are not defined as essential.
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8.1.2 Erroneous events
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The following events shall be regarded as errors by the recipient and shall be treated as specified below. Certain types of error shall be reported to the sending side, in that case the erroneous PDU and the error cause shall be returned to the sending side by means of the appropriate error reporting PDU. The following rules shall be applied in order of precedence: 1) a PDU whose type is non-existent or unrecognisable: the error shall not be reported, the PDU shall be ignored; 2) a PDU not consistent with the recipient's state: the error shall be reported with cause "PDU not compatible with the protocol state", the PDU shall be ignored; 3) a PDU sent in the wrong direction: the error shall be reported with cause "Protocol error - unspecified", the PDU shall be ignored; 4) a missing essential information element: the error shall be reported with cause "Missing essential IE", the PDU shall be ignored; 5) syntactical error in an essential IE: the error shall be reported with cause "Invalid essential IE", the PDU shall be ignored.
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8.1.3 Non-erroneous events
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The following events shall not be regarded as errors by the recipient: 1) spare bits with an unexpected value in any information element; 2) the use of additional octets in any information element with a length indicator, that is: when the indicated length is greater than defined in the relevant protocol specification (the length indicatorl shall be used to determine the boundary of the IE); 3) a missing non-essential information element; 4) an unknown information element identifier; 5) any unexpected information element; and 6) a syntactical error in any non-essential information element. ETSI ETSI TS 101 299 V7.1.0 (1999-07) 24 (GSM 08.16 version 7.1.0 Release 1998) When the recipient detects one or more of these events the receiving entity shall ignore the information that it is unable to understand and treat the PDU on the basis of the information that remains. Additionally, when more information elements of a particular type are received than are expected, the last one(s) shall be ignored. If, because information was ignored, the rest of the PDU can no longer be handled then the receiving entity shall report the error to the sending side by means of the appropriate error reporting PDU including the incorrect PDU received and the cause "semantically incorrect PDU".
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8.1.4 Other events
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The following events should be treated on a case by case basis and the outcome may depend upon the capabilities of the recipient. 1) The recipient may accept PDUs that contain information elements that do not appear to be in the correct sequence. Elements that occur more than once in a PDU shall be assumed to have been transmitted in the correct order. Recipients that do not accept out of sequence information elements shall regard the PDU as containing unexpected and/or missing information elements and follow the procedures defined in the rest of this "General case" clause. 2) When any IE with semantically incorrect contents is received, the receiving entity shall react according to the relevant protocol specification. If however no such reactions are specified, the receiving entity shall ignore that IE and treat the rest of the PDU. If, because this IE was ignored, the rest of the PDU can no longer be handled then the receiving entity shall report the error to the sending side by means of the appropriate error reporting PDU including the incorrect PDU received and the cause "semantically incorrect PDU".
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8.2 Special cases
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In case of conflict between this subclause and the above "General case" subclause, this subclause takes precedence. In case of conflict between this subclause and the specific "Abnormal conditions" subclauses in chapter "Network Service Control protocol", the "Abnormal conditions" subclauses take precedence over this "Special cases" subclause.
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8.2.1 Deviations from the "General case" subclause
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The Cause information element (see subclauses "General PDU definitions and contents" and "General information elements coding") shall be considered as a non-essential information element even when mandatory in a PDU.
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8.2.2 Error reporting
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The NS-STATUS PDU shall be used to report error to the remote NS entity, see subclause "Procedure for error reporting". The NS-STATUS PDU shall never be used to report an error detected in a received NS-STATUS PDU.
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9 General PDU definitions and contents
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This clause is not applicable to the Sub-Network Service protocol.
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9.1 General structure of a PDU
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This subclause defines the general structure of the PDUs on the Gb interface. The general PDU structure is composed of: a) a PDU type information element; and b) other information elements, as required. ETSI ETSI TS 101 299 V7.1.0 (1999-07) 25 (GSM 08.16 version 7.1.0 Release 1998) The PDU type IE occupies the first octet position in the PDU. This general structure and the numbering convention used on the Gb interface are illustrated in figure 7/GSM 08.16. The bits are grouped into octets. The bits of an octet are shown horizontally and are numbered from 1 to 8. Multiple octets are shown vertically and are numbered from 1 to n. The octets shall be transmitted by increasing order of octet number. Within each octet, the bits shall be transmitted by increasing order of bit number i.e. bit 1 of octet 1 shall be transmitted first, bit 8 of octet n shall be transmitted last. 8 7 6 5 4 3 2 1 octet 1 PDU type octets 2, 3, ...n other information elements Figure 7/GSM 08.16: General PDU structure and numbering convention Each PDU definition includes a table listing the information elements (IEs) known in the PDU and the order of their appearance in the PDU. Unless specified otherwise in the PDU descriptions, a particular information element shall not be present more than once in a given PDU. All information elements that may be repeated are explicitly indicated. For each information element the table indicates: a) The name of the information element (which may give an idea of the semantics of the element). b) Possibly a reference to another GSM Technical Specification where the information element is described. c) The presence requirement indication (M, C, or O) for the IE as defined in clause "General protocol error handling". d) The format (T, L, V) of the information element. See further description of the type (T), length (L) and V (value) fields in subclause "General structure of the information elements". e) The length of the information element (or permissible range of lengths), in octets, in the PDU, where "?" means that the maximum length of the IE is only constrained by the lower layer protocol. This indication is non- normative. The indicated length includes all the T, L, V fields present in the IE. f) Subclauses specifying, where appropriate, conditions for IEs with presence requirement C or O in the relevant PDU which together with other conditions specified in GSM 08.16 define when the information elements shall be included or not, what non-presence of such IEs means, and - for IEs with presence requirement C - the static conditions for presence and/or non-presence of the IEs, see clause "General protocol error handling".
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9.2 Network Service Control PDUs
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The Network Service Control PDUs are also referred to as NS PDUs in the rest of this Technical Specification.
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9.2.1 NS-ALIVE
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This PDU is used to test an NS-VC. PDU type: NS-ALIVE Direction: BSS to SGSN, SGSN to BSS Table 1/GSM 08.16: NS-ALIVE PDU contents Information element Reference Presence Format Length PDU type M V 1 ETSI ETSI TS 101 299 V7.1.0 (1999-07) 26 (GSM 08.16 version 7.1.0 Release 1998)
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9.2.2 NS-ALIVE-ACK
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This PDU acknowledges a received NS-ALIVE PDU and is sent on the NS-VC where the NS-ALIVE PDU was received. PDU type: NS-ALIVE-ACK Direction: SGSN to BSS, BSS to SGSN Table 2/GSM 08.16: NS-ALIVE-ACK PDU contents Information element Reference Presence Format Length PDU type M V 1
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9.2.3 NS-BLOCK
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This PDU indicates that an NS-VC shall be blocked at the recipient entity. PDU type: NS-BLOCK Direction: BSS to SGSN, SGSN to BSS Table 3/GSM 08.16: NS-BLOCK PDU contents Information element Reference Presence Format Length PDU type M V 1 Cause M TLV 3 NS-VCI M TLV 4
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9.2.4 NS-BLOCK-ACK
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This PDU acknowledges that an NS-VC has been blocked for use. PDU type: NS-BLOCK-ACK Direction: SGSN to BSS, BSS to SGSN Table 4/GSM 08.16: NS-BLOCK-ACK PDU contents Information element Reference Presence Format Length PDU type M V 1 NS-VCI M TLV 4
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9.2.5 NS-RESET
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This PDU indicates that the NS peer entity is trying to reset one NS-VCs. PDU type: NS-RESET Direction: BSS to SGSN, SGSN to BSS ETSI ETSI TS 101 299 V7.1.0 (1999-07) 27 (GSM 08.16 version 7.1.0 Release 1998) Table 5/GSM 08.16: NS-RESET PDU contents Information element Reference Presence Format Length PDU type M V 1 Cause M TLV 3 NS-VCI M TLV 4 NSEI M TLV 4 Typical cause values are: O&M intervention, Equipment failure.
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9.2.6 NS-RESET-ACK
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This PDU acknowledges the reset of the indicated NS-VCs. PDU type: NS-RESET-ACK Direction: BSS to SGSN, SGSN to BSS Table 6/GSM 08.16: NS-RESET-ACK PDU contents Information element Reference Presence Format Length PDU type M V 1 NS-VCI M TLV 4 NSEI M TLV 4
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9.2.7 NS-STATUS
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This PDU is used to report error conditions. PDU type: NS-STATUS Direction: SGSN to BSS, BSS to SGSN Table 7/GSM 08.16: NS-STATUS PDU contents Information element Reference Presence Format Length PDU type M V 1 Cause M TLV 3 NS-VCI C TLV 4 NS PDU C TLV 3-? BVCI C TLV 4
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9.2.7.1 Static conditions for NS-VCI
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The "NS-VCI" IE shall be included when the "Cause" IE is set to one of the following values: a) "NS-VC blocked", b) "NS-VC unknown", and shall not be included otherwise.
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9.2.7.2 Static conditions for NS PDU
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The "NS PDU" IE shall be included if the NS-STATUS message is sent in response to a received NS PDU within which an error was detected i.e. when the "Cause" IE is set to one of the following values: ETSI ETSI TS 101 299 V7.1.0 (1999-07) 28 (GSM 08.16 version 7.1.0 Release 1998) a) - "Semantically incorrect PDU", b) - "PDU not compatible with the protocol state", c) - "Protocol error - unspecified", d) - "Invalid essential IE", e) - "Missing essential IE", and shall not be included otherwise. This is the whole PDU received with error. This PDU may be truncated if it exceeds the information carrying capacity of the NS.
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9.2.7.3 Static conditions for BVCI
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The "BVCI" IE shall be included when the "Cause" IE is set to one of the following values: a) " BVCI unknown on that NSE", and shall not be included otherwise.
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9.2.8 NS-UNBLOCK
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This PDU indicates that an NS-VC shall be unblocked at the recipient entity. PDU type: NS-UNBLOCK Direction: BSS to SGSN, SGSN to BSS Table 8/GSM 08.16: NS-UNBLOCK PDU contents Information element Reference Presence Format Length PDU type M V 1
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9.2.9 NS-UNBLOCK-ACK
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This PDU acknowledges that an NS-VC has been unblocked. PDU type: NS-UNBLOCK-ACK Direction: SGSN to BSS, BSS to SGSN Table 9/GSM 08.16: NS-UNBLOCK-ACK PDU contents Information element Reference Presence Format Length PDU type M V 1
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9.2.10 NS-UNITDATA
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This PDU transfers one NS SDU between the BSS and SGSN. PDU type: NS-UNITDATA Direction: BSS to SGSN, SGSN to BSS ETSI ETSI TS 101 299 V7.1.0 (1999-07) 29 (GSM 08.16 version 7.1.0 Release 1998) Table 10/GSM 08.16: NS-UNITDATA PDU contents Information element Reference Presence Format Length PDU type M V 1 spare octet M V 1 BVCI M V 2 NS SDU M V 1-? The length of the "NS SDU" information element shall be derived by the Network Service Control entity from the length of the complete NS-UNITDATA PDU provided by the Sub-Network Service entity to the Network Service Control entity.
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10 General information elements coding
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This clause is not applicable to the Sub-Network Service protocol.
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10.1 General structure of the information elements
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The general information element structure is composed of (see Figure 8/GSM 08.16): a) an Information Element Identifier (also referred to as the T field), b) a length indicator (also referred to as the L field), c) the information element value (also referred to as the V field). Information elements have the TLV or the V format, as specified in the relevant protocol specification. The format of any given information element may depend on the context e.g. on the message type. 8 7 6 5 4 3 2 1 octet 1 Information Element Identifier (IEI) octets 2, 2a length indicator octet 3 information element value ... octet ... n Figure 8/GSM 08.16: Information element structure, TLV format 8 7 6 5 4 3 2 1 octet 1 information element value ... octet ... n Figure 9/GSM 08.16: Information element structure, V format When a field extends over more than one octet, the order of bit values progressively decreases as the octet number increases. The least significant bit of the field is represented by the lowest numbered bit of the highest numbered octet of the field. ETSI ETSI TS 101 299 V7.1.0 (1999-07) 30 (GSM 08.16 version 7.1.0 Release 1998)
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10.1.1 Information Element Identifier
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The first octet of an information element having the TLV format contains the IEI of the information element. If this octet does not correspond to an IEI known in the PDU, the receiver shall assume that the next octet is the first octet of the length indicator field and shall interpret it as described in the "Length indicator" clause. This rule allows the receiver to skip unknown information elements and to analyse any following information elements.
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10.1.2 Length indicator
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The length indicator shall be included in all information elements having the TLV format. Information elements may be variable in length. The length indicator is one or two octet long, the second octet may be absent. This field consists of the field extension bit, 0/1 ext, and the length of the value field which follows, expressed in octets. The field extension bit enables extension of the length indicator to two octets. Bit 8 of the first octet is reserved for the field extension bit. If the field extension bit is set to 0 (zero), then the second octet of the length indicator is present. If the field extension bit is set to 1 (one), then the first octet is the final octet of the length indicator. The length of the value field of the IE occupies the rest of the bits in the length indicator. 8 7 6 5 4 3 2 1 octet 2 0/1 ext length octet 2a length Figure 10/GSM 08.16: Length indicator structure The BSS or SGSN shall not consider the presence of octet 2a in a received IE as an error when the IE is short enough for the length to be coded in octet 2 only.
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10.2 Information element description
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The descriptions of the information elements are organized in alphabetical order of the IE name. Each IE is described in one subclause. A figure of the subclause defines the structure of the IE indicating: - the position of the IEI, when present; - the fields the IE value part is composed of; - the position of the length indicator, when present; - possibly octet numbers of the octets that compose the IE. Finally, the subclause may contain figures defining the structure and value range of the fields that compose the IE value part. Where the description of information elements in this Technical Specification contains bits defined to be "spare bits", these bits shall set to zero by the sending side, and their value shall be ignored by the receiving side. The term "default" may be used, implying that the value defined shall be used in the absence of any assignment, or that this value allows negotiation of alternative values in between the two peer entities.
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10.3 Network Service Control information element description
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The IEI values defined for the Network Service Control protocol are indicated in table 11/GSM 08.16: ETSI ETSI TS 101 299 V7.1.0 (1999-07) 31 (GSM 08.16 version 7.1.0 Release 1998) Table 11/GSM 08.16: IEI coding IEI coding Information element name 8 7 6 5 4 3 2 1 0 0 0 0 0 0 0 0 Cause 0 0 0 0 0 0 0 1 NS-VCI 0 0 0 0 0 0 1 0 NS PDU 0 0 0 0 0 0 1 1 BVCI 0 0 0 0 0 1 0 0 NSEI other values reserved for future use
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101 299
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10.3.1 BVCI
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This IE is used for multiplexing BVCs on NS-VCs. 8 7 6 5 4 3 2 1 octet 1 IEI octets 2, 2a length indicator octet 3 most significant octet of BVCI octet 4 least significant octet of BVCI Figure 11/GSM 08.16: BVCI information element
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101 299
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10.3.2 Cause
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This IE may be used to indicate to the peer NS entity the reason which triggered a procedure, or the reason of an abnormal condition. 8 7 6 5 4 3 2 1 octet 1 IEI octets 2, 2a length indicator octet 3 cause value Figure 12/GSM 08.16: Cause information element The cause values are indicated in Table 12/GSM 08.16: Table 12/GSM 08.16: Cause values Cause value coding Cause name 8 7 6 5 4 3 2 1 0 0 0 0 0 0 0 0 Transit network failure 0 0 0 0 0 0 0 1 O&M intervention 0 0 0 0 0 0 1 0 Equipment failure 0 0 0 0 0 0 1 1 NS-VC blocked 0 0 0 0 0 1 0 0 NS-VC unknown 0 0 0 0 0 1 0 1 BVCI unknown on that NSE 0 0 0 0 1 0 0 0 Semantically incorrect PDU 0 0 0 0 1 0 1 0 PDU not compatible with the protocol state 0 0 0 0 1 0 1 1 Protocol error - unspecified 0 0 0 0 1 1 0 0 Invalid essential IE 0 0 0 0 1 1 0 1 Missing essential IE other values reserved for future use ETSI ETSI TS 101 299 V7.1.0 (1999-07) 32 (GSM 08.16 version 7.1.0 Release 1998)
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10.3.3 NS PDU
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This IE is included in the NS-STATUS PDU sent in answer to an erroneous NS PDU. This IE contains the erroneous PDU received. The erroneous PDU may be truncated in order to fit in the maximum size of the NS-STATUS PDU. 8 7 6 5 4 3 2 1 octet 1 IEI octets 2, 2a length indicator octet 3 NS PDU ... octet n Figure 13/GSM 08.16: NS PDU information element
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10.3.4 NS SDU
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This IE contains one and only one NS SDU transmitted across the Gb interface. This IE has the V format. 8 7 6 5 4 3 2 1 octet 1 NS SDU ... octet n Figure 14/GSM 08.16: NS SDU information element In this "NS SDU" information element, bit i of octet j is equal to bit i of octet j of the NS SDU, as defined in the NS user protocol specification.
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10.3.5 NS-VCI
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This IE unambiguously identifies one NS-VC amongst all the NS-VCs used between one SGSN and the connected BSSs. 8 7 6 5 4 3 2 1 octet 1 IEI octets 2, 2a length indicator octet 3 most significant octet of NS-VCI octet 4 least significant octet of NS-VCI Figure 15/GSM 08.16: NS-VCI information element
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10.3.6 NSEI
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This IE unambiguously identifies one NSE 8 7 6 5 4 3 2 1 octet 1 IEI octets 2, 2a length indicator octet 3 most significant octet of NSEI octet 4 least significant octet of NSEI Figure 16/GSM 08.16: NSEI information element
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10.3.7 PDU type
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The PDU type has the V format. ETSI ETSI TS 101 299 V7.1.0 (1999-07) 33 (GSM 08.16 version 7.1.0 Release 1998) Table 13/GSM 08.16: PDU type coding PDU type coding PDU name 8 7 6 5 4 3 2 1 0 0 0 0 0 0 0 0 NS-UNITDATA 0 0 0 0 0 0 1 0 NS-RESET 0 0 0 0 0 0 1 1 NS-RESET-ACK 0 0 0 0 0 1 0 0 NS-BLOCK 0 0 0 0 0 1 0 1 NS-BLOCK-ACK 0 0 0 0 0 1 1 0 NS-UNBLOCK 0 0 0 0 0 1 1 1 NS-UNBLOCK-ACK 0 0 0 0 1 0 0 0 NS-STATUS 0 0 0 0 1 0 1 0 NS-ALIVE 0 0 0 0 1 0 1 1 NS-ALIVE-ACK other values reserved for future use
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10.3.8 Spare octet
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This IE is included in a PDU e.g. when it is needed to align another IE on a 32 bit boundary. This IE has the V format. All bits are spare. 8 7 6 5 4 3 2 1 octet 1 spare Figure 17/GSM 08.16: NS-VCI information element
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11 List of system variables
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Table 14/ GSM 08.16: System timers timer name timer value notes relation to other timers Tns-block 1s to 120s Guards the blocking and unblocking procedures none Tns-reset 1s to 120s Guards the reset procedure none Tns-test 1s to 60s Periodicity of the NS-VC test procedure none Tns-alive 3s Guards the NS-VC test procedure none Table 15/ GSM 08.16: System counters counter name value notes NS-BLOCK-RETRIES 3 recommended value NS-UNBLOCK-RETRIES 3 recommended value NS-ALIVE-RETRIES 10 recommended value ETSI ETSI TS 101 299 V7.1.0 (1999-07) 34 (GSM 08.16 version 7.1.0 Release 1998) Annex A (informative): Recommended usage of BVCI and NSEI This annex recommends a way to use BVCIs and NSEIs, avoiding huge and unflexible configuration data at the SGSN. This annex uses concepts defined in GSM 08.18 [5]. The key points are: - A BVCI needs not to be unique within an SGSN, a BVCI is unique within an NS Entity. BVCI together with NSEI uniquely identify a BVC within an SGSN (the global identifier within an SGSN is BVCI+NSEI). - BVCIs corresponding to PTP functional entities need not to be statically configured at the SGSN side: no fixed, permanent relationship is required in the SGSN between PTP BVCIs and NS-VCs. With the NSEI, the SGSN needs not to be updated when a new cell (BVCI) is added to a BSS (NSEI). The pre- configuration of a cell in the SGSN and the constraint in the number of BVCs in an SGSN are not needed: - The SGSN keeps detailed MM information about an MS while the MS is in the READY state, i.e. the SGSN knows the BVCI and NSEI which can be used to contact the MS for downlink transmission. The BVCI and NSEI are passed from NS to BSSGP and from BSSGP to the upper layers as a primitive parameter in every uplink packet received by the SGSN. Subsequent downlink LLC frames to this MS shall be transmitted by the SGSN over the BVC identified by this BVCI+NSEI. - An SGSN in STANDBY state will page an MS before sending downlink traffic. The MS will respond with an LLC packet that will put the MM context in READY state and will deliver the BVCI and NSEI to the user of BSSGP. For paging purposes, the SGSN only needs to know the correspondence between each Routeing Area and one or more NSEI(s) where to send the corresponding paging messages. Paging messages for a mobile in STANDBY state shall always be sent over BVCI=0 of an NSEI and for a mobile in READY state the circuit page is sent over the PTP BVC identified by the BVCI+NSEI. There may be NSEI(s) where BVCI=0 is not used. ETSI ETSI TS 101 299 V7.1.0 (1999-07) 35 (GSM 08.16 version 7.1.0 Release 1998) Annex B (informative): Change control history Document history <Version> <Date> <Milestone> proposed 0.0.0 01/08/1997 Document creation. First draft. proposed 0.1.0 11/09/1997 Updated after drafting session, Berlin, and SMG2/3 WPA meeting, Kista, August 1997: - Editorial improvements. - Removal of text redundant with FRF 1.1. - Introduction of "Addressing" clause. - Introduction of load sharing function. - Introduction of blocking / unblocking procedure. - Introduction of NS protocol. 1.0.0 2/10/1997 Agreed by SMG2 to submit to SMG#23 for information. Updated after drafting session, Berlin, September 1997: - Editorial improvements. - Terminology improved. - Abbreviation list updated. - "Addressing" clause made more abstract. - Introduction of BVC. - Creation of informative annex "Illustration of the addressing scheme on the Gb interface". - Introduction of the reset procedure. - Clarification to the load sharing function. - Re-ordering of clauses describing PDUs and IEs in order to respect the alphabetical order. 1.1.0 10/11/1997 Updated after drafting sessions, Swindon, October 1997 & Paris, November 1997: - Editorial improvements and corrections. - Miscellaneous clarifications. - Definitions improved. - Re-definition of the BVC. - Service primitives updated. - Description of Frame Relay support improved. - Blocking / unblocking procedures improved. - Re-definition of the reset procedure. - Introduction of the test procedure. - Protocol error handling re-written and made common to 08.16 and 08.18. 1.2.0 18/11/1997 Updated after SMG2/3 WPA meeting, Sophia Antipolis, November 1997: - Editorial corrections and improvements, clarifications, removal of useless text. - Editorial improvements to clauses 9 and 10 concerning all issues common to 08.16 and 08.18. - Improvements to protocol error handling: "reserved for future use" and "reserved" are the same. - Removal of the T and L fields from the BVCI and NS SDU IEs, and clarification to the mapping of NS SDUs onto the "NS SDU" IE. proposed 2.0.0 26/11/1997 Presented to SMG2#24 for agreement. 5.0.0 12/1/1998 Approved at SMG#24 preliminary 6.0.0 17/3/1998 Inclusion of CRs approved at SMG#25: - CRs A001, A002, A003r1, A004, A005, A006r1, A008r1 6.1.0 23/6/98 Inclusion of CRs approved at SMG#26: A007r3, A011, A012 6.2.0 12/2/99 Inclusion of CRs approved at SMG#28: A014, A015 ETSI ETSI TS 101 299 V7.1.0 (1999-07) 36 (GSM 08.16 version 7.1.0 Release 1998) 7.0.0 12/2/99 Inclusion of CR approved at SMG#28: A013 7.1.0 15/7/99 Inclusion of CR approved at SMG#29: CR A019 Removal of Annex A and B CR A020 Clarification of Annex C ETSI ETSI TS 101 299 V7.1.0 (1999-07) 37 (GSM 08.16 version 7.1.0 Release 1998) History Document history V7.1.0 July 1999 Publication ISBN 2-7437-3331-4 Dépôt légal : Juillet 1999
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1 Scope
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The present document specifies the physical layer on the Base Station System (BSS) to Serving GPRS Support Node (SGSN) interface (Gb interface) and references layer 1 standards to be used on this interface. The protocol stack on the Gb interface is defined in the stage 2 GSM 03.60 [3].
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2 References
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The following documents contain provisions which, through reference in this text, constitute provisions of the present document. • References are either specific (identified by date of publication, edition number, version number, etc.) or non-specific. • For a specific reference, subsequent revisions do not apply. • For a non-specific reference, the latest version applies. • A non-specific reference to an ETS shall also be taken to refer to later versions published as an EN with the same number. • For this Release 1998 document, references to GSM documents are for Release 1998 versions (version 7.x.y). [1] GSM 01.04 (ETR 350): “Digital cellular telecommunications system (Phase 2+); Abbreviations and acronyms”. [2] GSM 02.60: “Digital cellular telecommunications system (Phase 2+); General Packet Radio Service (GPRS); Service description; Stage 1”. [3] GSM 03.60: “Digital cellular telecommunications system (Phase 2+); Stage 2 Service Description of the General Packet Radio Service (GPRS)”. [4] GSM 08.04: “ Digital cellular telecommunications system (Phase 2); Base Station System - Mobile-services Switching Centre (BSS - MSC) interface Layer 1 specification”. [5] FRF 1.1 (January 19, 1996): “The Frame Relay Forum User-to-Network Implementation Agreement (UNI)”. [6] CCITT Recommendation G.704 (Blue Book): “Synchronous frame structures used at 1544, 6312, 2048, 8488 and 44 736 kbit/s hierarchical levels”. [7] ANSI T1.403 (1995): “Carrier to Customer Installation DS1 Metallic Interface”. [8] Bellcore TR-NWT-001203 Issue 2, December 1992: “Generic Requirements for the Switched DS1/Switched Franctional Capability from an ISDN Interface”.
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3 Definitions, symbols and abbreviations
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3.1 Definitions
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Refer to GSM 02.60 [2].
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3.2 Symbols
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Refer to GSM 03.60 [3]. ETSI ETSI TS 101 298 V7.0.1 (1999-08) 6 (GSM 08.14 version 7.0.1 Release 1998)
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3.3 Abbreviations
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For the purposes of the present document, the following abbreviations apply. Additional applicable abbreviations can be found in GSM 01.04 [1] and GSM 03.60 [3]. DCE Data Circuit-terminating Equipment DTE Data Terminal Equipment E1 A four wire symmetrical digital transmission path carrying PCM signal at 2048 kbit/s. FRF Frame Relay Forum T1 A four wire symetrical digital transmission path carrying PCM signal at 1544 kbit/s.
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4 Layer 1 specification
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Since Frame Relay shall be used on the Gb interface for phase 1 of GPRS, see TS GSM 03.60 [3], this version of this Technical Specification refers to “The Frame Relay Forum User-to-Network Implementation Agreement (UNI)” [5] which recommends physical layer interfaces to be used in conjunction with Frame Relay.
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4.1 Physical configuration of the Gb interface
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The detailed physical configuration of the Gb interface is subject to negociation between operators and equipment providers and is out of the scope of this Technical Specification. For example, point-to-point physical lines or an intermediate Frame Relay network may be used. In the latter case, the two ends of the Gb interface may use different types of physical interfaces.
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4.2 Physical layer interface
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Each of the physical layer of the Gb interface shall conform to one of the following FRF 1.1 [5] clauses. This does not mean that each BSS and SGSN equipment has to support all of these physical interfaces, it means that the supported physical interfaces shall be compliant with the corresponding clause of FRF 1.1 [5]. a) clause 2.1.1: ANSI T1.403. b) clause 2.1.2: V.35, physical circuit and DTE/DCE interface clauses. c) clause 2.1.3: G.703. d) clause 2.1.4: G.704. e) clause 2.1.5: X.21. f) clause 2.1.6: ANSI-530-A-1992. g) clause 2.1.7: HSSI. The Gb interface may be multiplexed with the A interface on the same E1 (2048 kbit/s), or T1 (1544 Kbit/s) digital path. In case of E1 interface, CCITT Recommendation G.704 [6] shall be applied according to FRF 1.1 [5] and GSM 08.04 [4] as appropriate, and in case of T1 interface ANSI Recommendation T1.403 [7] shall be applied according to FRF 1.1 [5] and GSM 08.04 [4] as appropriate. In the case where multiple 64 kbit/s channels are used on an E1 (2048 kbit/s), digital path on the Gb interface, it is recommended to aggregate them into one nx64 kbit/s channel, see CCITT Recommendation G.704 [6], clause 5 and included sub-clauses. In case where multiple 64kbit/s channels are used on a T1 (1544 kbit/s) digital path on the Gb interface, it is recommended to aggregate them into nx64kbit/s (where 2<=n<=24) channel, see Bellcore TR-NWT- 1203 [8]. This approach optimises the use of the available bandwidth by taking advantage of the statistical multiplexing at the upper layer. However, this approach requires that no slipping occurs between individual 64 kbit/s channels e.g. when passing through intermediate equipment between BSS and SGSN.
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4.3 Error rate
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The error rate experienced at the physical layer between the BSS and the SGSN shall be compatible with the operation of the upper layers. ETSI ETSI TS 101 298 V7.0.1 (1999-08) 7 (GSM 08.14 version 7.0.1 Release 1998)
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4.4 Provision of physical channels
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The physical channels on the Gb interface shall be permanently reserved by means of administrative procedures. ETSI ETSI TS 101 298 V7.0.1 (1999-08) 8 (GSM 08.14 version 7.0.1 Release 1998) Annex A (informative): Document change history SPEC SMG# CR PHA SE VERS NEW_VE RS SUBJECT 08.14 s24 new R97 2.0.0 6.0.0 Gb interface Layer 1 08.14 s28 new R98 6.0.0 7.0.0 ANSI references ETSI ETSI TS 101 298 V7.0.1 (1999-08) 9 (GSM 08.14 version 7.0.1 Release 1998) History Document history V7.0.1 August 1999 Publication ISBN 2-7437-3422-1 Dépôt légal : Août 1999
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1 Scope
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The present document provides the description of the Subnetwork Dependent Convergence Protocol (SNDCP) for the General Packet Radio Service (GPRS). The user of the services provided by SNDCP is a packet data protocol (PDP) at the mobile Station (MS) or the Relay at the Serving GPRS Support Node (SGSN). Additionally, a control entity, e.g., AT command interpreter, may be an SNDCP user. SNDCP uses the services provided by the Logical Link Control (LLC) layer [4] and the Session Management (SM) sub-layer [2]. The main functions of SNDCP are: - Multiplexing of several PDPs. - Compression / decompression of user data. - Compression / decompression of protocol control information. - Segmentation of a network protocol data unit (N-PDU) into Logical Link Control Protocol Data Units (LL-PDUs) and re-assembly of LL-PDUs into an N-PDU. GSM 04.65 is applicable to GPRS MS and SGSN.
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2 References
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The following documents contain provisions which, through reference in this text, constitute provisions of the present document. • References are either specific (identified by date of publication, edition number, version number, etc.) or non-specific. • For a specific reference, subsequent revisions do not apply. • For a non-specific reference, the latest version applies. • A non-specific reference to an ETS shall also be taken to refer to later versions published as an EN with the same number. • For this Release 1998 document, references to GSM documents are for Release 1998 versions (version 7.x.y). [1] GSM 01.04: "Digital cellular telecommunications system (Phase 2+); Abbreviations and acronyms". [2] GSM 02.60: "Digital cellular telecommunication system (Phase 2+); General Packet Radio Service (GPRS); Service Description, Stage 1". [3] GSM 03.60: "Digital cellular telecommunication system (Phase 2+); General Packet Radio Service (GPRS); Service Description, Stage 2". [4] GSM 04.07: "Digital cellular telecommunications system (Phase 2+); Mobile radio interface signalling layer 3; General aspects". [5] GSM 04.08: "Digital cellular telecommunications system (Phase 2+), Mobile radio interface layer 3 specification". [6] GSM 04.64: "Digital cellular telecommunications system (Phase 2+); General Packet Radio Service (GPRS); Mobile Station – Serving GPRS Support Node (MS - SGSN) Logical Link Control (LLC) layer specification". [7] GSM 09.60: "Digital cellular telecommunications system (Phase 2+), General Packet Radio Service (GPRS); GPRS Tunnelling Protocol (GTP) across the Gn and Gp Interface". ETSI ETSI TS 101 297 V7.3.0 (2000-03) 8 (GSM 04.65 version 7.3.0 Release 1998) [8] ITU-T, Recommendation V.42 bis: "Data compression procedures for data circuit- terminating equipment (DCE) using error correcting procedures". [9] RFC-1144, V. Jacobson: "Compressing TCP/IP Headers for Low-Speed Serial Links".
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3 Definitions and abbreviations
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3.1 Definitions
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In addition to abbreviations in 01.04 [1] and 02.60 [2] the following abbreviations apply: N201 LLC layer parameter (see GSM 04.64 for clarity). Defines maximum number of octets in the information field of LL-PDU. Separate values are applicable for I (see N201-I), U and UI (see N201-U) LL-PDUs. N201-I LLC layer parameter (see GSM 04.64 for clarity). Defines maximum number of octets available to a SN-DATA PDU for a specific SAPI. N201-U LLC layer parameter (see GSM 04.64 for clarity). Defines maximum number of octets available to a SN-UNITDATA PDU for a specific SAPI. N-PDU number A sequence number assigned to N-PDUs per NSAPI. NSAPI For each SN-PDU the NSAPI is an index to the PDP context of the PDP that is using the services provided by the SNDCP layer. Receive N-PDU number The value of the N-PDU number expected in the next N-PDU received by an NSAPI using acknowledged peer-to-peer LLC operation. Recovery state A state for an NSAPI in which duplicated received N-PDUs shall be detected and discarded. The recovery state only applies to NSAPIs using acknowledged peer-to-peer LLC operation. SAPI SAPI identifies the Service Access Point that the SN-PDU is using at the LLC layer. Segment number A sequence number assigned to SN-UNITDATA PDUs carrying segments of an N-PDU. Send N-PDU number The value to be assigned as the N-PDU number to the next N-PDU received from the SNDCP user by an NSAPI using acknowledged peer-to-peer LLC operation. Send N-PDU number (unacknowledged) The value to be assigned as the N-PDU number to the next N-PDU received from the SNDCP user by an NSAPI using unacknowledged peer-to-peer LLC operation. SNDCP entity The SNDCP entity handles the service functions provided by the SNDCP layer. The SNDCP entity is temporary logical link identity specific. SNDCP management entity The SNDCP management entity handles communication with SM sub-layer and controls the operation of the SNDCP entity. SNDCP user Protocol entity that is using the services provided by the SNDCP layer. PDP entities and control entities, e.g., AT command interpreter, are the SNDCP users at the MS. Relay entity is the SNDCP user at the SGSN. SNDCP XID block The collection of SNDCP XID parameters being negotiated. It is transferred by the LL-XID and LL-ESTABLISH primitives between SNDCP and LLC. Refer to GSM 02.60 [2] for further GPRS definitions. ETSI ETSI TS 101 297 V7.3.0 (2000-03) 9 (GSM 04.65 version 7.3.0 Release 1998)
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3.2 Abbreviations
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In addition to abbreviations in GSM 01.04 [1], GSM 02.60 [2], and GSM 03.60 [3], the following abbreviations apply: DCOMP Identifier of the user data compression algorithm used for the N-PDU F First segment indicator bit GMM GPRS Mobility Management IP Internet Protocol LLC Logical Link Control M More bit used to indicate the last segment of N-PDU N-PDU Network Protocol Data Unit NSAPI Network Layer Service Access Point Identifier P Propose bit PCOMP Identifier of the protocol control information compression algorithm used for the N-PDU PDP Packet Data Protocol e.g., IP or X.25 PDU Protocol Data Unit PTP Point to Point QoS Quality of Service SAPI Service Access Point Identifier SDU Service Data Unit SGSN Serving GPRS Support Node SM Session Management SNDCP Subnetwork Dependent Convergence Protocol SNSM SNDCP-SM TCP Transmission Control Protocol TLLI Temporary Logical Link Identifier X Spare bit
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4 General
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The present document describes the functionality of the GPRS SNDCP. The overall GPRS logical architecture is defined in GSM 03.60 [3]. Location of the SNDCP in GPRS protocol stack can be seen in Figure 1. RLC MAC Relay Network Service GTP Application IP / X.25 SNDCP LLC RLC MAC GSM RF SNDCP LLC BSSGP L1bis GSM RF BSSGP L1bis Relay L2 L1 IP Um Gb MS BSS SGSN Network Service UDP / TCP Figure 1: GPRS protocol stack Network layer protocols are intended to be capable of operating over services derived from a wide variety of subnetworks and data links. GPRS supports several network layer protocols providing protocol transparency for the users of the service. Introduction of new network layer protocols to be transferred over GPRS shall be possible without any changes to GPRS. Therefore, all functions related to transfer of Network layer Protocol Data Units (N-PDUs) shall be carried out in a transparent way by the GPRS network entities. This is one of the requirements for GPRS SNDCP. Another requirement for the SNDCP is to provide functions that help to improve channel efficiency. This requirement is fulfilled by means of compression techniques. ETSI ETSI TS 101 297 V7.3.0 (2000-03) 10 (GSM 04.65 version 7.3.0 Release 1998) The set of protocol entities above SNDCP consists of commonly used network protocols. They all use the same SNDCP entity, which then performs multiplexing of data coming from different sources to be sent using the service provided by the LLC layer (Figure 2). The Network Service Access Point Identifier (NSAPI) is an index to the PDP context (see GSM 03.60 [3]) of the PDP that is using the services provided by SNDCP. One PDP may have several PDP contexts and NSAPIs. However, it is possible that each allocated NSAPI is used by separate PDP. Each active NSAPI shall use the services provided by the Service Access Point Identifier (SAPI) in the LLC layer. Several NSAPIs may be associated with the same SAPI. Since the adaptation of different network layer protocols to SNDCP is implementation dependent, it is not defined in the present document. SNDCP Packet Data Protocol LLC NSAPI N-PDU SAPI SN-PDU Packet Data Protocol Packet Data Protocol . . . Figure 2: Example for multiplexing of different protocols
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5 Service primitives and functions
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5.1 Service primitives
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This subclause explains the service primitives used for communication between the SNDCP layer and other layers. See also GSM 04.07 [4] to get an overall picture of the service primitives. Figure 3 illustrates the service access points through which the primitives are carried out. ETSI ETSI TS 101 297 V7.3.0 (2000-03) 11 (GSM 04.65 version 7.3.0 Release 1998) Session Management entity LL5 LL9 LL3 LL11 5 6 PDP or Relay SNDCP entity LLC layer SNDCP users SNDCP management entity PDP or Relay 15 NSAPI SAPI . . . SNDCP layer SNSM Control Entity Figure 3: Service Access Points provided and used by SNDCP
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5.1.1 SNDCP service primitives
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The primitives provided by the SNDCP layer are listed in Table 1. Table 1: SNDCP layer service primitives Generic Name Type Parameters Request Indication Response Confirm SNDCP User (PDP or the SGSN Relay) ↔ ↔ ↔ ↔SNDCP SN-DATA X - - - N-PDU, NSAPI, N-PDU Number SN-DATA - X - - N-PDU, NSAPI SN-UNITDATA X X - - N-PDU, NSAPI SN-XID X X - - Requested SNDCP XID Parameters SN-XID - - X X Negotiated SNDCP XID Parameters
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5.1.1.1 SN-DATA.request
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Request used by the SNDCP user for acknowledged transmission of N-PDU. The successful transmission of SN-PDU shall be confirmed by the LLC layer. The SN-DATA.request primitive conveys NSAPI to identify the PDP using the service. N-PDU Number, if present, indicates the N-PDU number previously assigned to this N-PDU. NOTE: An N-PDU number may have been assigned to an N-PDU by the old SGSN before an inter-SGSN routeing area update. ETSI ETSI TS 101 297 V7.3.0 (2000-03) 12 (GSM 04.65 version 7.3.0 Release 1998)
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5.1.1.2 SN-DATA.indication
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Indication used by the SNDCP entity to deliver the received N-PDU to the SNDCP user. Successful reception has been acknowledged by the LLC layer.
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5.1.1.3 SN-UNITDATA.request
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Request used by the SNDCP user for unacknowledged transmission of N-PDU. The SN-UNITDATA.request primitive conveys NSAPI to identify the PDP using the service.
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5.1.1.4 SN-UNITDATA.indication
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Indication used by the SNDCP entity to deliver the received N-PDU to the SNDCP user.
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5.1.1.5 SN-XID.request
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Request used by the SNDCP user at the initiating entity to deliver the list of requested XID parameters to the peer entity.
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5.1.1.6 SN-XID.indication
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Indication used by the SNDCP entity to deliver the list of requested XID parameters to the SNDCP user.
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5.1.1.7 SN-XID.response
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Response used by the SNDCP user to deliver the list of negotiated XID parameters to the peer entity.
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5.1.1.8 SN-XID.confirm
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Confirm used by the SNDCP entity to deliver the list of negotiated XID parameters to the SNDCP user.
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5.1.2 Service primitives used by SNDCP layer
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The SNDCP layer uses the service primitives provided by the SM sublayer and the LLC layer (see Table 2). SM is specified in GSM 04.08 [5] and LLC in GSM 04.64 [6]. ETSI ETSI TS 101 297 V7.3.0 (2000-03) 13 (GSM 04.65 version 7.3.0 Release 1998) Table 2: Service primitives used by the SNDCP entity Generic Name Type Parameters Request Indication Response Confirm SNDCP ↔ ↔ ↔ ↔LLC LL-RESET - X - - TLLI LL-ESTABLISH X - - - TLLI, XID Requested LL-ESTABLISH - X - - TLLI, XID Requested, N201-I, N201-U LL-ESTABLISH - - X - TLLI, XID Negotiated LL-ESTABLISH - - - X TLLI, XID Negotiated, N201-I, N201-U LL-RELEASE X - - - TLLI, Local LL-RELEASE - X - - TLLI, Cause LL-RELEASE - X TLLI LL-XID X - - - TLLI, XID Requested LL-XID - X - - TLLI, XID Requested, N201-I, N201-U LL-XID - - X - TLLI, XID Negotiated LL-XID - - - X TLLI, XID Negotiated, N201-I, N201-U LL-DATA X - - - TLLI, SN-PDU, Reference, QoS Parameters, Radio Priority LL-DATA - X - - TLLI, SN-PDU LL-DATA - - - X TLLI, Reference LL-UNITDATA X - - - TLLI, SN-PDU, QoS Parameters, Radio Priority, Cipher LL-UNITDATA - X - - TLLI, SN-PDU LL-STATUS - X - - TLLI, Cause SNDCP ↔ ↔ ↔ ↔SM SNSM-ACTIVATE X - - TLLI, NSAPI, QoS profile, SAPI, Radio Priority SNSM-ACTIVATE - - X TLLI, NSAPI SNSM-DEACTIVATE - X - - TLLI, NSAPI(s), LLC Release Indicator SNSM-DEACTIVATE - - X - TLLI, NSAPI SNSM-MODIFY - X - - TLLI, NSAPI, QoS Profile, SAPI, Radio Priority, Send N-PDU Number, Receive N-PDU Number SNSM-MODIFY - - X - TLLI, NSAPI SNSM-STATUS X - - - TLLI, SAPI, Cause SNSM-SEQUENCE - X X - TLLI, NSAPI, Receive N-PDU Number SNSM-STOP-ASSIGN - X - - TLLI, NSAPI
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5.1.2.1 LL-RESET.indication
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Indication used by the LLC layer in the SGSN to indicate to the SNDCP layer that the Reset XID parameter has been transmitted, and by the LLC layer in the MS to indicate to the SNDCP layer that the Reset XID parameter has been received. Upon receipt of the LL-RESET.indication, the SNDCP layer shall: - treat all outstanding SNDCP ↔LLC request type primitives as not sent; - reset all SNDCP XID parameters to their default values; - in the MS, for every NSAPI using unacknowledged peer-to-peer LLC operation, set the Send N-PDU number (unacknowledged) to 0; and ETSI ETSI TS 101 297 V7.3.0 (2000-03) 14 (GSM 04.65 version 7.3.0 Release 1998) - for every NSAPI using acknowledged peer-to-peer LLC operation, enter the recovery state and suspend the transmission of SN-PDUs until an SNSM-SEQUENCE.indication primitive is received for the NSAPI. In the SGSN the SNDCP layer shall re-establish acknowledged peer-to-peer operation for the affected SAPIs in the LLC layer.
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5.1.2.2 LL-ESTABLISH.request
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Request used by the SNDCP layer to establish or re-establish acknowledged peer-to-peer operation for a SAPI in the LLC layer. XID Requested is used to deliver the requested SNDCP XID parameters to the LLC layer.
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5.1.2.3 LL-ESTABLISH.indication
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Indication used by the LLC layer to inform the SNDCP layer about establishment or re-establishment of acknowledged peer-to-peer operation for a SAPI in the LLC layer. XID Requested is used to deliver the requested SNDCP XID parameters to the SNDCP layer. In case of a re-establishment, all NSAPIs mapped to the affected SAPI shall enter the recovery state, and all buffered N-PDUs (i.e., the ones whose complete reception has not been acknowledged and the ones that have not been transmitted yet) shall be transmitted starting with the oldest N-PDU when the link is re- established. Also all compression entities using acknowledged peer-to-peer LLC operation on this SAPI are reset.
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5.1.2.4 LL-ESTABLISH.response
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Response used by the SNDCP layer after reception of the LL-ESTABLISH.indication. XID Negotiated is used to deliver the negotiated SNDCP XID parameters to the LLC layer.
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5.1.2.5 LL-ESTABLISH.confirm
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Confirmation used by the LLC layer to inform the SNDCP layer about successful initiation of acknowledged peer-to- peer operation for a SAPI in the LLC layer. XID Negotiated is used to deliver the negotiated SNDCP XID parameters to the SNDCP layer. In case of a re-establishment, all NSAPIs mapped to the affected SAPI shall enter the recovery state, and all buffered N-PDUs (i.e., the ones whose complete reception has not been acknowledged and the ones that have not been transmitted yet) shall be transmitted starting with the oldest N-PDU when the link is re-established. Also all compression entities using acknowledged peer-to-peer LLC operation on this SAPI are reset.
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5.1.2.6 LL-RELEASE.request
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Request used by the SNDCP layer to release acknowledged peer-to-peer operation for a SAPI in the LLC layer. The Local parameter indicates whether the termination shall be local (see 04.64 for details).
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5.1.2.7 LL-RELEASE.indication
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Indication used by the LLC layer to inform the SNDCP layer about termination of acknowledged peer-to-peer operation for a SAPI in the LLC layer. The Cause parameter indicates the cause for the termination. On receipt of LL-RELEASE.indication, compressed N-PDUs queuing to be forwarded to the affected SAPI are deleted from the SNDCP layer. Also all compression entities using acknowledged peer-to-peer LLC operation on this SAPI are reset.
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5.1.2.8 LL-RELEASE.confirm
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Confirmation used by the LLC layer to inform the SNDCP layer about termination of acknowledged peer-to-peer operation for a SAPI in the LLC layer. On receipt of LL-RELEASE.confirm, compressed N-PDUs queuing to be forwarded to the affected SAPI are deleted from the SNDCP layer. Also all compression entities using acknowledged peer-to-peer LLC operation on this SAPI are reset.
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5.1.2.9 LL-XID.request
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Request used by the SNDCP layer to deliver the requested SNDCP XID parameters to the LLC layer. ETSI ETSI TS 101 297 V7.3.0 (2000-03) 15 (GSM 04.65 version 7.3.0 Release 1998)
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5.1.2.10 LL-XID.indication
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Indication used by the LLC layer to deliver the requested SNDCP XID parameters to the SNDCP layer.
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