LTE: Deactivate EPS Bearer Context Request

·        The purpose of the EPS bearer context deactivation procedure is to deactivate an EPS bearer context or disconnect from a PDN by deactivating all EPS bearer contexts to that PDN.

·        This procedure is initiated by the network, and it may be triggered by the UE by means of the Bearer Resource Modification or PDN Disconnect procedure.

·        If a NAS signalling connection exists when the MME initiates this procedure, then the MME shall initiate the EPS bearer context deactivation procedure by sending a DEACTIVATE EPS BEARER CONTEXT REQUEST message to the UE and start the timer T3495.

·        If there no NAS signalling connection exists when the MME initiates this procedure, then the ESM entity in the MME shall locally deactivate the EPS bearer context towards the UE without any peer-to-peer ESM signalling between the MME and the UE.

·        The DEACTIVATE EPS BEARER CONTEXT REQUEST message contains an ESM cause typically indicating one of the following:

#8:  operator determined barring

#36: regular deactivation

#38: network failure

#39: reactivation requested or

#112: APN restriction value incompatible with active EPS bearer context

·        If the deactivation is triggered by a UE initiated bearer resource modification or PDN disconnect procedure, the DEACTIVATE EPS BEARER CONTEXT REQUEST message shall contain the PTI value received from the UE in the corresponding message.

·        When the MME wants to deactivate all EPS bearer contexts to a PDN and thus disconnect the UE from the PDN, the MME shall include the EPS Bearer Identity of the default bearer associated to the PDN in the DEACTIVATE EPS BEARER CONTEXT REQUEST message.

·        If the MME doesn’t receive a response for DEACTIVATE EPS BEARER CONTEXT REQUEST before the expiry of the timer T3495, the MME shall resend this message and shall reset and restart T3495. This retransmission is repeated four times, i.e. on the fifth expiry of T3495, the MME shall abort the procedure and deactivate the EPS bearer context locally without any peer-to-peer ESM signalling between the MME and the UE.

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

Reference 3GPP TS 24.301

Example:  DEACTIVATE EPS BEARER CONTEXT REQUEST message

LTE: PDN Disconnect Request

·        The purpose of the PDN Disconnect procedure is for a UE to request the network to disconnect from one PDN.

·        The UE can initiate this procedure to disconnect from any PDN as long as it is connected to at least one other PDN.

·        Successful completion of this procedure means that, all EPS bearer contexts established towards this PDN, including the default EPS bearer context, are released.

·        In order to disconnect from the last PDN (the one and the only PDN to which the UE has the connection), the UE should not use PDN disconnect procedure. Instead, it shall use detach procedure

·        In order to request PDN disconnection from a PDN, the UE shall send a PDN DISCONNECT REQUEST message to the MME and start the timer T3492.

·        In this message, The UE shall set the value of Linked EPS Bearer Identity IE as the EPS Bearer Identity of default bearer associated with the PDN for which UE is sending the disconnect request.

·        If the network accepts the PDN DISCONNECT REQUEST sent by the UE, then it shall send the DEACTIVATE EPS BEARER CONTEXT REQUEST message including the linked EPS bearer identity of the default bearer associated with the PDN to disconnect from.

·        If the network doesn’t accept the PDN DISCONNECT REQUEST sent by the UE, the MME shall send a PDN DISCONNECT REJECT message to the UE which shall contain the PTI and an ESM cause IE indicating the cause for the rejection

·        Upon receipt of the DEACTIVATE EPS BEARER CONTEXT REQUEST or PDN DISCONNECT REJECT message, the UE shall stop the timer T3492

·        If there is no response received for the PDN DISCONNECT REQUEST before the expiry of the timer T3492, the UE shall resend the PDN DISCONNECT REQUEST and shall reset and restart timer T3492. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3492, the UE shall abort the procedure and deactivate all EPS bearer contexts for this PDN connection locally without peer-to-peer signalling between the UE and the MME

Reference 3GPP TS 24.301

Example:  PDN DISCONNECT REQUEST message

LTE: PDN Connectivity Reject

·        If the PDN CONNECTIVITY REQUEST cannot be accepted by the network, then the MME shall send a PDN CONNECTIVITY REJECT message to the UE.

·        The PDN CONNECTIVITY REJECT message shall contain the Procedure Transaction Identity (PTI) which should match the PTI value in the PDN CONNECTIVITY REQUEST sent by UE

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

·        The ESM cause IE typically indicates one of the following ESM cause values:

  #8:  operator determined barring

#26:  insufficient resources

#27:  missing or unknown APN

#28:  unknown PDN type

#29:  user authentication failed

#30:  request rejected by Serving GW or PDN GW

#31:  request rejected, unspecified

#32:  service option not supported

#33:  requested service option not subscribed

#34:  service option temporarily out of order

#35:  PTI already in use

#38:  network failure

#50:  PDN type IPv4 only allowed

#51:  PDN type IPv6 only allowed

#53:  ESM information not received

#54:  PDN connection does not exist

#55:  multiple PDN connections for a given APN not allowed

#95 – 111:  protocol errors

#112:  APN restriction value incompatible with active EPS bearer context.

·        If the ESM cause value is #26 "insufficient resources" or #27 "missing or unknown APN", the network may include a value for timer T3396 in the PDN CONNECTIVITY REJECT message. In such a case, the UE should take different actions depending on the timer value and reject cause. Refer to section 6.5.1.4 in the 3GPP TS 24.301 for detailed information

 Reference 3GPP TS 24.301

Example:  PDN CONNECTIVITY REJECT message

LTE: PDN Connectivity Request

·       The PDN connectivity procedure is used by the UE to request the setup of a default EPS bearer to a PDN.

·        The UE requests connectivity to a PDN by sending a PDN CONNECTIVITY REQUEST message to the network. If this request is accepted by the network, then it initiates the establishment of a default EPS bearer context activation procedure.

·        This procedure is used either to establish the first default bearer (PDN CONNECTIVITY REQUEST is sent along with initial attach message), or to establish subsequent default bearers to additional PDNs (a stand-alone PDN CONNECTIVITY REQUEST is sent by the UE).

·        If the UE is in EMM-IDLE mode, the Service Request procedure is performed before the PDN Connectivity procedure can be initiated.

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

·       A UE attached for emergency bearer services shall not request a PDN connection to any other PDN.

·       When the PDN CONNECTIVITY REQUEST message is sent together with an ATTACH REQUEST message, the UE shall not include the APN.

·        When requesting connectivity to an additional PDN, the UE shall include the requested APN (in the stand-alone PDN CONNECTIVITY REQUEST) except for  emergency bearer services

·       The UE may set the ESM information transfer flag in the PDN CONNECTIVITY REQUEST message to indicate that it has ESM information, i.e. protocol configuration options, or APN, or both, that needs to be transferred to the MME after the NAS signalling security has been activated

·        If the  ESM information transfer flag is set in PDN CONNECTIVITY REQUEST message, the MME initiates (after NAS sigalling security is activated) the ESM information request procedure in which the UE can provide the MME with protocol configuration options or APN or both.

·       If the UE wishes to connect to a PDN using default APN, it need not include the APN in the Access Point Name IE in the ESM INFORMATION RESPONSE or PDN CONNECTIVITY REQUEST (stand-alone) message. The only exceptional case is, if the connectivity to a PDN using the default APN requires PAP/CHAP, then the UE should include the APN in the Access point name IE 

·        The UE shall set the Request Type IE to "initial request" when the UE is establishing a new PDN connectivity to a PDN in an attach procedure or in a stand-alone PDN connectivity procedure.

·        The UE shall set the Request Type IE to "emergency" when the UE is requesting a new PDN connectivity for emergency bearer services.

·        The Request Type IE is set to "handover" when the connectivity to a PDN is established upon handover from a non-3GPP access network and the UE was connected to that PDN before the handover to the 3GPP access network

·        The other IEs in the PDN CONNECTIVITY REQUEST message include EPS Bearer Identity, Procedure Transaction Identity, PDN Type, and Device Properties etc…

·       If the UE includes ESM information transfer flag in the PDN CONNECTIVITY REQUEST message, the MME waits for completion of the ESM information request procedure before proceeding with the PDN connectivity procedure. The MME then checks if connectivity with the requested PDN can be established.

·       If requested APN is not included in the PDN CONNECTIVITY REQUEST or the ESM INFORMATION RESPONSE message and the request type is different from "emergency", the MME shall use the default APN as the requested APN. If the request type is "emergency", the MME shall use the APN configured for emergency bearer services

Reference 3GPP TS 24.301

Example1: PDN CONNECTIVITY REQUEST message (sent along with Attach Request)

Example2: Stand-Alone PDN CONNECTIVITY REQUEST message

LTE: Activate Dedicated EPS Bearer Context Accept

·          The ACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT message is sent by the UE to the network to acknowledge the activation of a dedicated EPS bearer context associated with the same PDN address (es) and APN as an already active EPS bearer context

·          Upon receipt of the ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST message, the UE shall stop timer T3396, if it is running for the APN associated with the PDN connection and check the received TFT before taking it into use.

·          The linked EPS Bearer Identity included in the ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST message indicates to the UE to which default bearer, IP address and PDN the dedicated bearer is linked.

·          The UE shall include EPS bearer identity and Procedure transaction identity IEs in the ACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT message.

·          The IE Protocol configuration options is included in the message when the UE wishes to transmit (protocol) data (e.g. configuration parameters, error codes or messages/events) to the network

·           Upon receipt of the Activate Dedicated EPS Bearer Context Accept message, the MME shall stop the timer T3485 

Reference 3GPP TS 24.301

Example: ACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT message

LTE: Activate Dedicated EPS Bearer Context Request

·           The purpose of the dedicated EPS bearer context activation procedure is to establish an EPS bearer context with a specific QoS and TFT between the UE and the EPC.

·           A PDN connection consists of one Default EPS bearer and, depending on the service for which the connection is used, a number of dedicated EPS bearers.

·           FYI.., a default EPS bearer is established during the Attach or Standalone PDN Connectivity procedure. Any additional EPS bearer that is established for the same PDN connection is referred to as a dedicated EPS bearer. Dedicated EPS bearers are activated and deactivated depending on the service used but the default bearer remains established throughout the lifetime of the PDN connection. The network decides if dedicated bearers need to be setup or not and what QoS settings should be applied for the dedicated bearers.

·           The dedicated EPS bearer can be either guaranteed bit rate (GBR) or non-GBR.

·           The dedicated EPS bearer context activation procedure is initiated by the NW, but may be requested by the UE by means of the UE requested bearer resource allocation/modification procedure.

·           This procedure can be part of the attach procedure or be initiated together with the Default EPS bearer context activation procedure when the UE initiates a stand-alone PDN connectivity procedure.

·           If the attach procedure or the Default EPS bearer context activation procedure fails, then the UE shall consider that the dedicated bearer activation has implicitly failed.

·           The MME shall initiate the dedicated bearer context activation procedure by sending an ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST message and start the timer T3485

·           The MME allocates and includes the EPS Bearer Identity in the ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST message.

·           The MME shall include the EPS bearer identity of the associated default bearer as the Linked EPS Bearer Identity in the ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST message.

·           If this procedure was initiated by a UE requested bearer resource allocation/modification procedure, the ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST message shall contain the Procedure Transaction Identity (PTI) value received by the MME from the UE

·           The other IEs in the ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST include EPS QoS, Traffic Flow Template (TFT), Transaction Id, Negotiated QoS, Negotiated LLC SAPI, Radio Priority, Packet flow Id, Protocol configuration options etc…

Reference 3GPP TS 24.301

Example: ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST message

LTE: Activate Default EPS Bearer Context Accept

·           After receiving the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message, the UE shall stop timer T3396 if it is running for the APN indicated in the message and send an ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT message.

·           The UE should check the Procedure transaction identity (PTI) in the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message to identify the UE requested PDN connectivity procedure to which this default bearer context activation is related.

·           When the default bearer is activated as part of the attach procedure, the UE shall send the ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT message together with ATTACH COMPLETE message.

·           When the default bearer is activated in response to the stand-alone PDN CONNECTIVITY REQUEST message, the UE shall send the ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT message alone.

·           The UE shall include EPS bearer identity and Procedure transaction identity IEs in the ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT message

·           The IE Protocol configuration options is included in the message when the UE wishes to transmit (protocol) data (e.g. configuration parameters, error codes or messages/events) to the network

·           Upon receipt of the ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT message, the MME shall stop the timer T3485, if the timer is running

Reference 3GPP TS 24.301

Example: ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT with Attach Complete message

LTE: Activate Default EPS Bearer Context Request

·          The purpose of the default bearer context activation procedure is to establish a default EPS bearer context between the UE and the EPC.

·           The default EPS bearer context activation procedure is initiated by the network as a response to the PDN CONNECTIVITY REQUEST message from the UE.

·          The default bearer is a non-Guaranteed Bit Rate (GBR) bearer. A dedicated bearer can be either a GBR or a non-GBR bearer.

·           The default bearer remains established throughout the lifetime of the PDN connection to provide the UE with IP connectivity to the PDN

·           The default bearer context activation procedure can be part of the Attach procedure, and if the attach procedure fails, the UE shall consider that the default bearer activation has implicitly failed

·           Once the UE is successfully attached, the UE can request the MME to set up connections to additional PDNs. For each additional connection, the MME will activate a separate default EPS bearer context

·           The MME shall initiate the default bearer context activation procedure by sending an ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message

·           When the default bearer is activated as part of the attach procedure, the MME shall send the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message together with ATTACH ACCEPT

·           When the default bearer is activated as the response to a stand-alone PDN CONNECTIVITY REQUEST message apart from the attach procedure, the MME shall send the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message alone, and start the timer T3485

·           The MME shall assign and include an EPS bearer identity in the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message.

·           The MME shall retrieve the PTI (Procedure Transaction Identity) from the PDN CONNECTIVITY REQUEST message and include it in the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message

·           Typical IEs in  ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message include EPS bearer identity, Procedure transaction identity (PTI), EPS QoS, Access point name (APN), PDN address, Negotiated QoS, Negotiated LLC SAPI, Packet flow Identifier, APN-AMBR (APN aggregate maximum bit rate), ESM cause, and Protocol configuration options etc…

·           The network shall include the IE ESM cause, if the network allocated a PDN address of a PDN type which is different from the PDN type requested by the UE

Reference 3GPP TS 24.301

Example: ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST with Attach Accept message