LTE: Modify EPS Bearer Context Request

·        The purpose of the EPS bearer context modification procedure is to modify an EPS bearer context with a specific QoS and TFT.

·        This procedure is initiated by the network, but it may also be initiated as part of the UE requested bearer resource allocation/modification procedure.

·        The network may also initiate the EPS bearer context modification procedure to update the APN-AMBR of the UE, for instance after an inter-system handover

·        The MME initiates the EPS bearer context modification procedure by sending a MODIFY EPS BEARER CONTEXT REQUEST message to the UE and starts the timer T3486

·        The MME shall include an EPS bearer identity that identifies the EPS bearer context to be modified in the MODIFY EPS BEARER CONTEXT REQUEST message

·        If this procedure was initiated by a UE requested bearer resource allocation/modification procedure, then the MODIFY EPS BEARER CONTEXT REQUEST shall contain the PTI value received by the MME in the corresponding request message.

·        The IEs in this message include, EPS bearer identity, PTI, New EPS QoS, TFT, New QoS, Negotiated LLC SAPI, Radio priority, Packet flow ID, APN-AMBR, and Protocol configuration options etc…

·        After receiving the MODIFY EPS BEARER CONTEXT REQUEST message, the UE shall stop timer T3396 if it is running for the APN associated with the PDN connection, check the received TFT before taking it into use and then send a MODIFY EPS BEARER CONTEXT ACCEPT message to the MME

Reference 3GPP TS 24.301

Example:  Modify EPS Bearer Context Request message

LTE: Bearer Resource Modification Reject

·        If the network cannot accept the bearer resource modification requested by the UE, then the MME shall send a BEARER RESOURCE MODIFICATION REJECT message to the UE.

·        The BEARER RESOURCE MODIFICATION REJECT message shall contain the Procedure Transaction Identity (PTI) which should match the PTI value received in the BEARER RESOURCE MODIFICATION REQUEST.

·        Also, this message shall contain an ESM cause value which indicates the reason for rejecting the UE requested bearer resource modification.

·        If the bearer resource modification requested is for an established LIPA PDN connection, then the network shall reply with a BEARER RESOURCE MODIFICATION REJECT message with ESM cause #60 "bearer handling not supported".

·        If the ESM cause value is #26 "insufficient resources", the network may include a value for timer T3396 value IE in this message. In such a case, the UE should take different actions depending on the timer value as specified in section 6.5.4.4 in 3GPP TS 24.301.

·        After receiving the BEARER RESOURCE MODIFICATION REJECT message, the UE shall stop the timer T3481 and release the traffic flow aggregate description associated to the PTI value.

·        If the ESM cause included in the reject message is #43 "invalid EPS bearer identity", the UE locally deactivates the EPS bearer context(s) without peer-to-peer ESM signalling.

Reference 3GPP TS 24.301

Example:  BEARER RESOURCE MODIFICATION REJECT message

LTE: Bearer Resource Modification Request

·        The purpose of the UE requested bearer resource modification procedure is for a UE to request a modification or release of bearer resources for a traffic flow aggregate or modification of a traffic flow aggregate by replacing or adding packet filters.

·        When requesting a modification of bearer resources for a traffic flow aggregate or a modification of a traffic flow aggregate, the UE can modify the existing GBR.

·        If the network accepts this procedure, it invokes a dedicated EPS bearer context activation, an EPS bearer context modification, or an EPS bearer context deactivation procedure.

·        If there is a PDN connection for emergency bearer services established, the UE shall not request a modification of bearer resources for this PDN connection.

·        In order to request the modification of bearer resources for one traffic flow aggregate, the UE shall send a BEARER RESOURCE MODIFICATION REQUEST message to the MME

·        The UE shall include the EPS bearer identity of the EPS bearer associated with the traffic flow aggregate in the EPS bearer identity for packet filter IE.

·        To request a change of the GBR without changing the packet filter(s), the UE shall set the TFT operation code in the Traffic flow aggregate IE to "no TFT operation" and include the packet filter identifier(s) to which the change of the GBR applies in the Packet filter identifier parameter in the parameters list.

·        The UE shall indicate the new GBR requested for the EPS bearer context in the Required traffic flow QoS IE.

·        To request a modification of a traffic flow aggregate, the UE shall set the TFT operation code in the Traffic flow aggregate IE to "Replace packet filters in existing TFT" or "Add packet filters to existing TFT".

·        If the TFT operation code is set to "Add packet filters to existing TFT", the UE shall include the existing packet filter identifier(s) to which the newly added packet filter(s) is linked in the parameters list.

·        To request a release of bearer resources, the UE shall set the TFT operation code in the Traffic flow aggregate IE to "Delete packet filters from existing TFT".

·     If the UE includes the Required Traffic Flow QoS IE, the UE shall set the QCI to the current QCI value of the EPS bearer context.

·        If the bearer resource modification requested is accepted by the network, the MME shall send ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST, MODIFY EPS BEARER CONTEXT REQUEST or DEACTIVATE EPS BEARER CONTEXT REQUEST message with a PTI which matches the value used for the BEARER RESOURCE MODIFICATION REQUEST message.

·        If the bearer resource modification requested cannot be accepted by the network, the MME shall send a BEARER RESOURCE MODIFICATION REJECT message to the UE.

Reference 3GPP TS 24.301

Example:  BEARER RESOURCE MODIFICATION REQUEST message

LTE: Bearer Resource Allocation Reject

·        If the bearer resource allocation request cannot be accepted by the network, then the MME sends a BEARER RESOURCE ALLOCATION REJECT message to the UE.

·        The BEARER RESOURCE ALLOCATION REJECT message shall contain the Procedure Transaction Identity (PTI) which is equal to the PTI value in the BEARER RESOURCE ALLOCATION REQUEST received from the UE

·        This message shall also contain an ESM Cause value indicating the reason for rejecting the UE requested bearer resource allocation.

·        The UE, after receiving the BEARER RESOURCE ALLOCATION REJECT message, shall stop the timer T3480 and release the traffic flow aggregate description associated to the received PTI value

·        If the ESM cause value is #26 "insufficient resources", the network may include a value for timer T3396 value IE in the BEARER RESOURCE ALLOCATION REJECT message. Depending on the timer value, the UE shall take different actions as explained in 6.5.3.4 in 3GPP TS 24.301

Reference 3GPP TS 24.301

Example:  BEARER RESOURCE ALLOCATION REJECT message

LTE: Bearer Resource Allocation Request

·       The purpose of the UE requested bearer resource allocation procedure is (for an UE) to request an allocation of bearer resources for a traffic flow aggregate.

·        The UE requests a specific QoS demand (QCI) and optionally sends a Guaranteed Bit Rate (GBR) requirement for a new traffic flow aggregate.

·        If accepted by the network, this procedure invokes a dedicated EPS bearer context activation procedure or an EPS bearer context modification procedure.

·        If there is a PDN connection for emergency bearer services established, the UE shall not request additional bearer resources for this PDN connection.

·        The UE initiates this procedure by sending a BEARER RESOURCE ALLOCATION REQUEST message to the MME and starts the timer T3480.

·        The UE shall include the IE Linked EPS bearer identity and set it as the EPS bearer identity of the default EPS bearer associated with the requested bearer resource.

·        The UE shall set the TFT operation code in the Traffic flow aggregate IE to "Create new TFT".

·        In the Required traffic flow QoS IE, the UE shall indicate a QCI (QoS Class Identifier) and, if the UE also includes a GBR, the additional GBR required for the traffic flow aggregate.

·        If the bearer resource allocation request is accepted by the network, the MME shall send either an ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST or MODIFY EPS BEARER CONTEXT REQUEST message with a PTI value received in the BEARER RESOURCE ALLOCATION REQUEST message.

·        If the UE doesn’t receive response to the BEARER RESOURCE ALLOCATION REQUEST message before the expiry of the timer T3480, the UE shall resend this message and reset/restart T3480. This retransmission is repeated four times, i.e. on the fifth expiry of T3480, the UE shall abort the procedure, release the PTI allocated for this activation.

·        The Protocol Configuration Options IE is included in the BEARER RESOURCE ALLOCATION REQUEST message if the UE wishes to transmit (protocol) data (e.g. configuration parameters, error codes or messages/events) to the network.

·        The UE shall include the IE Device Properties in this message if the UE is configured for NAS signalling low priority

Reference 3GPP TS 24.301

Example:  BEARER RESOURCE ALLOCATION REQUEST message

LTE: Deactivate EPS Bearer Context Accept

·       The UE after receiving the DEACTIVATE EPS BEARER CONTEXT REQUEST message, shall delete the EPS bearer context identified by the EPS bearer identity.

·       If the EPS bearer identity indicated in the DEACTIVATE EPS BEARER CONTEXT REQUEST is that of the default bearer to a PDN, the UE shall delete all EPS bearer contexts associated to the PDN.

·       After deactivating the identified EPS bearer context (s), the UE shall respond to the MME with the DEACTIVATE EPS BEARER CONTEXT ACCEPT message.

·        If due to the EPS bearer context deactivation, there is only one PDN connection active and that is for emergency bearer services, then the UE shall consider itself attached for emergency bearer services only

·        In the DEACTIVATE EPS BEARER CONTEXT ACCEPT message, the UE shall include Procedure Transaction Identity (PTI) as received in the DEACTIVATE EPS BEARER CONTEXT REQUEST message

·        Other IEs in the DEACTIVATE EPS BEARER CONTEXT ACCEPT message include, EPS bearer identity and Protocol configuration options

Reference 3GPP TS 24.301

Example:  DEACTIVATE EPS BEARER CONTEXT ACCEPT message