6 Support for packet services

04.083GPPMobile radio interface Layer 3 specificationRelease 1998TS

This chapter contains the description of the procedures for the session management of GPRS point-to-point data services at the radio interface (Reference point Um).

6.1 GPRS Session management

6.1.1 General

The main function of the session management (SM) is to support PDP context handling of the user terminal. The SM comprises procedures for

– identified PDP context activation, deactivation and modification; and

– anonymous PDP context activation and deactivation.

SM procedures for identified access can only be performed if a GMM context has been established between the MS and the network. If no GMM context has been established, the MM sublayer has to initiate the establishment of a GMM context by use of the GMM procedures as described in chapter 4. After GMM context establishment, SM uses services offered by GMM (see 3GPP TS 04.07 [20]). Ongoing SM procedures are suspended during GMM procedure execution.

For anonymous access no GMM context is established.

6.1.1.1 Radio resource sublayer address handling for anonymous access

In the case of anonymous access, no P-TMSI shall be used by the MS or by the network. The MS shall use a randomly selected random TLLI for transmission of the ACTIVATE AA PDP CONTEXT REQUEST message in order to activate the AA PDP context.

Upon receipt of the ACTIVATE AA PDP CONTEXT REQUEST message, the network assigns an auxiliary TLLI (A‑TLLI) to the AA PDP context and transmits the assigned A-TLLI to the MS. After receipt of the assigned A-TLLI, the MS shall use it for further data transmission to the network for the lifetime of the AA PDP context.

6.1.2 Session management states

In this sub-clause, the SM states are described for one SM entity (see 3GPP TS 04.07 [20]). Each SM entity is associated with one PDP context. sub-clause 6.1.2.1 describes the SM states in the MS and sub-clause 6.1.2.2 describes the SM states on the network side.

6.1.2.1 Session management states in the MS

In this sub-clause, the possible states of an SM entity in the mobile station are described. As illustrated in figure 6.1/3GPP TS 04.08 there are four SM states in the MS.

6.1.2.1.1 PDP-INACTIVE

This state indicates that no PDP context exists.

6.1.2.1.2 PDP-ACTIVE-PENDING

This state exists when PDP context activation was requested by the MS.

6.1.2.1.3 PDP-INACTIVE-PENDING

This state exists when deactivation of the PDP contexts was requested by the MS.

6.1.2.1.4 PDP-ACTIVE

This state indicates that the PDP context is active.

Figure 6.1/3GPP TS 04.08: Session management states in the MS (overview)

6.1.2.2 Session management states on the network side

In this sub-clause, the possible states of an SM entity on the network side are described. As illustrated in figure 6.2/3GPP TS 04.08 there are five SM states on the network side.

6.1.2.2.1 PDP-INACTIVE

This state indicates that the PDP context is not active.

6.1.2.2.2 PDP-ACTIVE-PENDING

This state exists when the PDP context activation was initiated by the network.

6.1.2.2.3 PDP-INACTIVE-PENDING

This state exists when deactivation of the PDP context was requested by the network.

6.1.2.2.4 PDP-ACTIVE

This state indicates that the PDP context is active.

6.1.2.2.5 PDP-MODIFY-PENDING

This state exists when modification of the PDP context was requested by the network.

Figure 6.2/3GPP TS 04.08: Session management states on the network side (overview)

6.1.3 Session Management procedures

6.1.3.1 PDP context activation

The purpose of this procedure is to establish a PDP context between the MS and the network for a specific QoS on a specific NSAPI. The PDP context activation may be initiated by the MS or the initiation may be requested by the network.

6.1.3.1.1 Successful PDP context activation initiated by the mobile station

In order to request a PDP context activation, the MS sends an ACTIVATE PDP CONTEXT REQUEST message to the network, enters the state PDP-ACTIVE-PENDING and starts timer T3380. The message contains the selected NSAPI, PDP type and, if the MS requests a static address, the PDP address. The MS shall ensure that the selected NSAPI is not currently being used by another Session Management entity in the MS.

Upon receipt of an ACTIVATE PDP CONTEXT REQUEST message, the network selects a radio priority level based on the QoS negotiated and may reply with an ACTIVATE PDP CONTEXT ACCEPT message. Upon receipt of the message ACTIVATE PDP CONTEXT ACCEPT the MS shall stop timer T3380, shall enter the state PDP-ACTIVE and shall initiate establishment of the logical link for the LLC SAPI indicated by the network with the offered QoS and selected radio priority level if no logical link has been already established for that SAPI. If the offered QoS parameters received from the network differ from the QoS requested by the MS, the MS shall either accept the negotiated QoS or initiate the PDP context deactivation procedure. If the LLC SAPI indicated by the network can not be supported by the MS, the MS shall initiate the PDP context deactivation procedure.

6.1.3.1.2 Successful PDP context activation requested by the network

In order to request a PDP context activation, the network sends a REQUEST PDP CONTEXT ACTIVATION message to the MS and starts timer T3385. If available, the APN shall be included in the REQUEST PDP CONTEXT ACTIVATION message.

Upon receipt of a REQUEST PDP CONTEXT ACTIVATION message, the MS shall than either initiate the PDP context activation procedure as described in the previous sub-clause or shall reject the activation request by sending a REQUEST PDP CONTEXT ACTIVATION REJECT message as described in sub-clause 6.1.3.1.4. The value of the reject cause IE of the REQUEST PDP CONTEXT ACTIVATION REJECT message shall indicate the reason for rejection, e.g. "insufficient resources to activate another context".

The ACTIVATE PDP CONTEXT REQUEST message sent by the MS in order to initiate the PDP context activation procedure shall contain the PDP address, PDP Type and APN requested by the network in the REQUEST PDP CONTEXT ACTIVATION message.

Upon receipt of the ACTIVATE PDP CONTEXT REQUEST message, the network shall stop timer T3385.

The same procedures then apply as described for MS initiated PDP context activation.

6.1.3.1.3 Unsuccessful PDP context activation initiated by the MS

Upon receipt of an ACTIVATE PDP CONTEXT REQUEST message the network may reject the MS initiated PDP context activation by sending an ACTIVATE PDP CONTEXT REJECT message to the MS. The message shall contain a cause code that typically indicates one of the following causes:

# 26: insufficient resources;

# 27: missing or unknown APN;

# 28: unknown PDP address or PDP type;

# 29: user authentication failed;

# 30: activation rejected by GGSN;

# 31: activation rejected, unspecified;

# 32: service option not supported;

# 33: requested service option not subscribed;

# 34: service option temporarily out of order;

# 35: NSAPI already used; or

# 95 – 111: protocol errors.

Upon receipt of an ACTIVATE PDP CONTEXT REJECT message, the MS shall stop timer T3380 and enter/remain in state PDP-INACTIVE.

6.1.3.1.4 Unsuccessful PDP context activation requested by the network

Upon receipt of the REQUEST PDP CONTEXT ACTIVATION message, the MS may reject the network requested PDP context activation by sending the REQUEST PDP CONTEXT ACTIVATION REJECT message to the network. The message contains the same TI as included in the REQUEST PDP CONTEXT ACTIVATION and an additional cause code that typically indicates one of the following causes:

# 26: insufficient resources;

# 31: activation rejected, unspecified;

# 40: feature not supported; or

# 95 – 111: protocol errors.

The network shall stop timer T3385 and enter state PDP-INACTIVE.

6.1.3.1.5 Abnormal cases

The following abnormal cases can be identified:

a) Expiry of timers

In the mobile station:

On the first expiry of the timer T3380, the MS shall resend the ACTIVATE PDP CONTEXT REQUEST and shall reset and restart timer T3380. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3380, the MS shall release all resources possibly allocated for this invocation and shall abort the procedure; no automatic PDP context activation re-attempt shall be performed.

On the network side:

On the first expiry of the timer T3385, the network shall resent the message REQUEST PDP CONTEXT ACTIVATION and shall reset and restart timer T3385. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3385, the network shall release possibly allocated resources for this activation and shall abort the procedure.

b) Collision of MS initiated and network requested PDP context activation

Dynamic PDP address collision case:

If the MS uses dynamic PDP addressing that turns out to collide with the network requested PDP address, then there is no detection of collision specified but left for network implementation.

Static PDP address collision detected within the mobile station:

A collision of an MS initiated and a network requested PDP context activation procedure is identified by the MS if a REQUEST PDP CONTEXT ACTIVATION message is received from the network after the MS has sent an ACTIVATE PDP CONTEXT REQUEST message, and the MS has not yet received an ACTIVATE PDP CONTEXT ACCEPT or ACTIVATE PDP CONTEXT REJECT message.

NOTE: In general, the MS is unable to test if the PDP type, PDP address and APN in the REQUEST PDP CONTEXT ACTIVATION message are the same as those for the PDN to which it is attempting to activate a context. This is because the MS may have omitted one or more of the parameters in the ACTIVATE PDP CONTEXT REQUEST message, since it is relying on default values to be provided by the network.

In the case of such a collision, the MS initiated PDP context activation shall take precedence over the network requested PDP context activation. If the MS is able to compare the PDP type, PDP address and APN requested in the ACTIVATE PDP CONTEXT REQUEST message with those requested in the REQUEST PDP CONTEXT ACTIVATION message and these parameters are equal, then the MS shall discard the REQUEST PDP CONTEXT ACTIVATION message and shall wait for the network response to its ACTIVATE PDP CONTEXT REQUEST message. If the MS is not able to compare the PDP type, PDP address, and APN requested in the ACTIVATE PDP CONTEXT REQUEST message with those requested in the REQUEST PDP CONTEXT ACTIVATION message, then the MS shall send a REQUEST PDP CONTEXT ACTIVATION REJECT message with the cause ‘insufficient resources’ to the network, and wait for an ACTIVATE PDP CONTEXT ACCEPT message.

Static PDP address collision detected on the network side:

A collision is detected by the network in the case where the PDP address, PDP type and APN derived (according to 03.60 annex A) from the ACTIVATE PDP CONTEXT REQUEST message received from the MS match those in the REQUEST PDP CONTEXT ACTIVATION message sent to the MS.

In the case of such a collision, the MS initiated PDP context activation shall take precedence over the network requested PDP context activation. The network shall terminate the network requested PDP context activation procedure,and proceed with the MS initiated PDP context activation procedure.

Figure 6.3/3GPP TS 04.08: MS initiated PDP context activation procedure

Figure 6.4/3GPP TS 04.08: Network initiated PDP context activation procedure

6.1.3.2 PDP context modification procedure

The PDP context modification procedure is invoked by the network in order to change the QoS negotiated during the PDP context activation procedure or at previously performed PDP context modification procedures. The procedure can be initiated by the network at any time when a PDP context is active.

In order to initiate the procedure, the network sends the MODIFY PDP CONTEXT REQUEST message to the MS and starts timer T3386. The message shall contain the new QoS and the radio priority level that shall be used by the MS at the lower layers for the transmission of data related to the PDP context.

Upon receipt of this message the MS shall reply with the MODIFY PDP CONTEXT ACCEPT message, if the MS accepts the new QoS and the indicated LLC SAPI.

If the MS does not accept the new QoS or the indicated LLC SAPI, the MS shall initiate the PDP context deactivation procedure for the PDP context – the reject cause IE value of the DEACTIVATE PDP CONTEXT REQUEST message shall indicate "QoS not accepted".

The network shall upon receipt of the MODIFY PDP CONTEXT ACCEPT message stop timer T3386 and shall establish, reconfigure or continue using the logical link with the new QoS for the LLC SAPI indicated in the MODIFY PDP CONTEXT REQUEST message.

6.1.3.2.1 Abnormal cases

On the first expiry of timer T3386, the network shall resend the MODIFY PDP CONTEXT REQUEST message reset and restart timer T3386. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3386, the network may continue to use the previously negotiated QoS or it may initiate the PDP context deactivation procedure.

Figure 6.5/3GPP TS 04.08: PDP context modification procedure

6.1.3.3 PDP context deactivation procedure

The purpose of this procedure is to deactivate an existing PDP context between the MS and the network. The PDP context deactivation may be initiated by the MS or by the network.

6.1.3.3.1 PDP context deactivation initiated by the MS

In order to deactivate a PDP context, the MS sends a DEACTIVATE PDP CONTEXT REQUEST message to the network, enters the state PDP-INACTIVE-PENDING and starts timer T3390. The message contains the transaction identifier in use for the PDP context to be deactivated and a cause code that typically indicates one of the following causes:

# 25: LLC or SNDCP failure;

# 26: insufficient resources;

# 36: regular PDP context deactivation; or

# 37: QoS not accepted.

The network shall reply with the DEACTIVATE PDP CONTEXT ACCEPT message. Upon receipt of the DEACTIVATE PDP CONTEXT ACCEPT message, the MS shall stop timer T3390. Both the MS and the network shall initiate local release of the logical link if it is not used by another PDP context.

6.1.3.3.2 PDP context deactivation initiated by the network

In order to deactivate a PDP context, the network sends a DEACTIVATE PDP CONTEXT REQUEST message to the MS and starts timer T3395. The message contains the transaction identifier in use for the PDP context to be deactivated and a cause code that typically indicates one of the following causes:

# 25: LLC or SNDCP failure;

# 36: regular PDP context deactivation;

# 38: network failure; or

# 39: reactivation requested.

The MS shall, upon receipt of this message, reply with a DEACTIVATE PDP CONTEXT ACCEPT message. Upon receipt of the DEACTIVATE PDP CONTEXT ACCEPT message, the network shall stop the timer T3395. Both the MS and the network shall initiate local release of the logical link if it is not used by another PDP context.

6.1.3.3.3 Abnormal cases

The following abnormal cases can be identified:

a) Expiry of timers

In the mobile station:

On the first expiry of timer T3390, the MS shall resent the message DEACTIVATE PDP CONTEXT REQUEST and shall reset and restart the timer T3390. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3390, the MS shall release all resources allocated and shall erase the PDP context related data.

On the network side:

On the first expiry of timer T3395, the network shall resent the message DEACTIVATE PDP CONTEXT REQUEST and shall reset and restart timer T3395. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3395, the network shall erase the PDP context related data for that MS.

b) Collision of MS and network initiated PDP context deactivation requests

If the MS and the network initiated PDP context deactivation requests collide, the MS and the network shall each reply with the messages DEACTIVATE PDP CONTEXT ACCEPT and shall stop timer T3390 and T3395, respectively.

Figure 6.6/3GPP TS 04.08: MS initiated PDP context deactivation procedure

Figure 6.7/3GPP TS 04.08: Network initiated PDP context deactivation procedure

6.1.3.4 AA PDP context activation

The purpose of this procedure is to anonymously establish a PDP context between the MS and the network for a specific QoS on a specific NSAPI. The AA PDP context activation shall only be initiated by the MS.

6.1.3.4.1 Successful AA PDP context activation initiated by the mobile station

In order to activate an anonymous PDP context, the MS sends an ACTIVATE AA PDP CONTEXT REQUEST message to the network, enters the state PDP-ACTIVE-PENDING and starts timer T3380. As long as no auxiliary TLLI is allocated to the MS, a random TLLI is used for addressing on lower layers.

Upon receipt of an ACTIVATE AA PDP CONTEXT REQUEST message, the network selects a radio priority level based on the QoS negotiated, assigns a AA-TID to the PDP context and sends an ACTIVATE AA PDP CONTEXT ACCEPT message to the MS. The message shall contain a the selected radio priority level and negotiated QoS allocated by the network. If the offered QoS parameters received from the network differ from the QoS requested by the MS, the MS shall accept the QoS offered by the network. If the LLC SAPI indicated by the network can not be supported by the MS, the MS shall initiate the implicit AA PDP context deactivation procedure. Upon receipt of the message ACTIVATE AA PDP CONTEXT ACCEPT, the MS shall stop timer T3380, shall enter the state PDP-ACTIVE and shall initiate establishment of the logical link for the LLC SAPI indicated by the network with the negotiated QoS.

6.1.3.4.2 Unsuccessful AA PDP context activation

Upon receipt of the ACTIVATE AA PDP CONTEXT REQUEST message the network may indicate the failure of the MS initiated AA PDP context activation by sending the ACTIVATE AA PDP CONTEXT REJECT message to the MS. The message contains a cause code that typically indicates one of the following causes:

# 32: service option not supported;

# 34: service option temporarily out of order;

# 90 – 111: protocol errors.

The MS shall stop the timer T3380.

6.1.3.4.3 Abnormal cases

a) Expiry of timers

On the first expiry of timer T3380, the MS shall retransmit the ACTIVATE AA PDP CONTEXT REQUEST message and shall reset and restart timer T3380.

This retransmission is repeated four times, i.e. on the fifth expiry of timer T3380, the MS shall indicate the failure of the AA PDP context activation procedure to the register functions, shall release all resources possibly allocated for this invocation and shall abort the procedure; no automatic AA PDP context activation re-attempt shall be performed.

Figure 6.8 3GPP TS 04.08: MS initiated AA PDP context activation procedure

6.1.3.5 AA PDP context deactivation

6.1.3.5.1 Implicit AA PDP context deactivation

The implicit deactivation is performed without signalling message exchange as specified below.

The AA PDP context on the network side shall be deactivated when:

– the AA READY timer expires in the GMM-AA entity.

The AA PDP context in the MS shall be deactivated when:

– the AA READY timer expires in the GMM-AA entity;

– the MS changes the routing area;

– the LLC SAPI indicated by the network can not be supported by the MS during activation; or

– user requested.

6.1.3.5.2 Explicit AA PDP context deactivation

An explicit AA PDP context deactivation shall only be initiated by the network. The procedure shall be performed when a misuse of the anonymous PDP context has been detected.

In order to deactivate the AA PDP context, the network sends the message DEACTIVATE AA PDP CONTEXT REQUEST and starts timer T3397. The message shall contain the transaction identifier in use for the AA PDP context to be deactivated. After sending the message the network initiates the release of the logical link.

The MS shall, upon receipt of this message, reply with the DEACTIVATE AA PDP CONTEXT ACCEPT message after the logical link has been released.

Upon receipt of the DEACTIVATE AA PDP CONTEXT ACCEPT message, the network shall stop the timer T3397.

6.1.3.5.3 Abnormal cases

a) Expiry of timers

On the first expiry of timer T3397, the network shall retransmit the message DEACTIVATE AA PDP CONTEXT REQUEST and shall reset and restart timer T3397.

This retransmission is repeated four times, i.e. on the fifth expiry of timer T3397, the network shall release all remaining resources allocated for that MS and shall erase the AA PDP context related data for that MS.

Figure 6.9/3GPP TS 04.08: Network initiated AA PDP context deactivation procedure

b) Lower layer failure

If a lower layer failure is indicated before the DEACTIVATE AA PDP CONTEXT ACCEPT message is sent, the MS shall abort the procedure and shall locally de-allocate the P-TMSI from the LLC sublayer.

If a lower layer failure is indicated before the DEACTIVATE AA PDP CONTEXT ACCEPT message is received, the network shall abort the procedure and shall locally de-allocate the P-TMSI from the LLC sublayer.

6.1.3.6 Receiving a SM STATUS message by a SM entity

If the SM entity of the MS receives a SM STATUS message no state transition and no specific action shall be taken as seen from the radio interface, i.e. local actions are possible.

The actions to be taken on receiving a SM STATUS message in the network are an implementation dependent option.