7/21/2019 Pdp Context http://slidepdf.com/reader/full/pdp-context-56dcabf6b834d 1/24 7.2PDPContextManagement APDPcontext contains routinginformationfor packet transfer between anMSand aGGSNto have access to an external packet-switching network. It is identified by an exclusive MSPDPaddress (mobile's IPaddress). This means that theMSwillhave as many PDPaddresses as activatedPDP contexts. Aconcept of secondary PDPcontext has been introduced in order to have several PDPcontexts sharingthesame PDPaddress andthesame access to theexternal packet-switchingnetwork. This concept was introduced for multimedia applications where eachmedium type requires specific transport characteristics and is mapped into a specific PDPcontext. It is based on the traffic flow template, which is afiltering mechanism used by theGGSNto route downlinkIPpackets toward the appropriate medium within theMS. Agiven PDPcontext is in the active state when this PDPaddress is activated for data transfer. Before transferringdata between anMSand a GGSN, it is necessary that a PDPcontext be activated. PDPcontext procedures havebeendefined in order to create, modify, and delete PDPcontexts within the MS, SGSN, andGGSNentities. The SM protocol is used betweenthe MSandthe SGSN and theGTPprotocol is used in thecontrollingplane between theSGSNand theGGSNfor PDP context procedures. 7.2.1 PDP Context Defnition APDPcontext provides access to an external packet-switchingnetwork throughthePLMNnetwork. The data associated with thePDPcontext is as follows: • Access point name (APN). This is thereference to a GGSN. • Network serviceaccess point identifier (NSAPI). This is an index of the PDPcontext that uses theservices providedby theSNDCPlayer for GPRSdata transfer. Up to 11 applications over theSNDCPlayer may beidentifiedby theNSAPI parameter. TheNSAPI parameter is present in theSNDCPheader. • LLCserviceaccess point identifier (LLCSAPI). This identifies theSAPused for GPRSdata transfer at the LLClayer. • PDPaddress. This identifies the MSaddress relatedto a particular PDPcontext. This field consists of several fields including the PDPtype (IPor PPP), PDPaddress type (IPv4or IPv6), andaddress information containing the IPaddress. • QoS. This defines the quality of servicerelated to aparticular PDPcontext. Parameters related toQoSare described in Section2.4.
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7.2 PDP Context ManagementA PDP context contains routing information for packet transfer between an MS and a GGSN to have
access to an external packet-switching network. It is identified by an exclusive MS PDP address(mobile's IP address). This means that the MS will have as many PDP addresses as activated PDP
contexts.
A concept of secondary PDP context has been introduced in order to have several PDP contexts
sharing the same PDP address and the same access to the external packet-switching network. This
concept was introduced for multimedia applications where each medium type requires specific
transport characteristics and is mapped into a specific PDP context. It is based on the traffic flow
template, which is a filtering mechanism used by the GGSN to route downlink IP packets toward the
appropriate medium within the MS.
A given PDP context is in the active state when this PDP address is activated for data transfer.Before transferring data between an MS and a GGSN, it is necessary that a PDP context be
activated.
PDP context procedures have been defined in order to create, modify, and delete PDP contexts
within the MS, SGSN, and GGSN entities. The SM protocol is used between the MS and the SGSN
and the GTP protocol is used in the controlling plane between the SGSN and the GGSN for PDP
context procedures.
7.2.1 PDP Context Defnition
A PDP context provides access to an external packet-switching network through the PLMN network.The data associated with the PDP context is as follows:
• Access point name (APN). This is the reference to a GGSN.
• Network service access point identifier (NSAPI). This is an index of the PDP context that
uses the services provided by the SNDCP layer for GPRS data transfer. Up to 11
applications over the SNDCP layer may be identified by the NSAPI parameter. The NSAPI
parameter is present in the SNDCP header.
• LLC service access point identifier (LLC SAPI). This identifies the SAP used for GPRS data
transfer at the LLC layer.
• PDP address. This identifies the MS address related to a particular PDP context. This field
consists of several fields including the PDP type (IP or PPP), PDP address type (IPv4 or
IPv6), and address information containing the IP address.
• QoS. This defines the quality of service related to a particular PDP context. Parameters
mechanism allows for the association of one packet filter with one NSAPI that is the identifier of the
PDP context.
Each packet filter consists of a packet filter identifier within a TFT, a packet filter evaluation
precedence that specifies the precedence for the packet filter among all packet filters in a TFT, and a
list of packet filter attributes. Each packet filter attribute is deduced from IPv4 or IPv6 headers. TheMS will define values related to each packet filter attribute. These may or may not be combined later
in a packet filter. Each packet filter contains at least one of the following packet filter attributes:
• Source address and subnet mask-IPv4 or IPv6 address along with a subnet mask;
• Protocol number/next header-IPv4 protocol number or IPv6 next header value;
• Port numbers-port number or range of port number;
PDP address, protocol configuration options, and APN. The requested NSAPI is provided by the MS
among the ones not currently used by another PDP context in the MS. A PDP address is provided
only if the MS already has a static address.
Security functions may be performed in order to authenticate the MS. The SGSN is able to derive the
GGSN address from the APN identifier in order to forward this request to the GGSN. The SGSNcreates a downlink GTP tunnel to route IP packets from the GGSN to the SGSN. The GGSN creates
a new entry in its PDP context table to route IP packets between the SGSN and the external packet-
switching network. The GGSN creates an uplink GTP tunnel to route IP-PDU from SGSN to GGSN.
The GGSN then sends back to the SGSN the result of the PDP context creation with the negotiated
QoS and if necessary the MS PDP address. Next the SGSN sends an ACTIVATE PDP CONTEXT
ACCEPT to the MS by returning negotiated QoS parameters, radio priority, and if necessary the MS
PDP address.
Figure 7.19 illustrates a PDP context activation procedure initiated by the MS.
Figure 7.19: PDP context activation initiated by MS.
'nitiated (# ))S*
When the network receives an IP packet from an external network, the GGSN checks if a PDPcontext is already established with that PDP address. If not, the GGSN sends a PDU NOTIFICATION
REQUEST to the SGSN in order to initiate a PDP context activation. The GGSN has retrieved the IP
address of the appropriate SGSN address by interrogating the HLR from the IMSI identifier of the
MS. The SGSN then sends to the MS a request to activate the indicated PDP context. Next the PDP
context activation procedure follows the one initiated by the MS. Once the PDP context is activated,
the IP packet can be sent from the GGSN to the MS.
Figure 7.20 illustrates a PDP context activation procedure initiated by the GGSN.
The SGSN acknowledges the delete subscriber data procedure by sending back a MAP DELETE
SUBSCRIBER DATA ACK message to the HLR.
The GGSN deactivates the PDP context upon receipt of the DELETE PDP CONTEXT REQUEST
message from the MS and releases the PDP address if this one was allocated dynamically during
the PDP context activation procedure. When the SGSN receives a PDP context deletionacknowledgment from the GGSN, it initiates the PDP context deactivation in the MS by sending the
DEACTIVATE PDP CONTEXT REQUEST message. When the MS has removed its PDP context, the
MS sends back to the SGSN the DEACTIVATE PDP CONTEXT ACCEPT message.
Figure 7.22 illustrates a PDP context deactivation procedure initiated by the SGSN.
Figure 7.22: PDP context deactivation initiated by SGSN.
'niated (# ))S*
When the PDP context deactivation is initiated by the GGSN, it sends a DELETE PDP CONTEXT
REQUEST message to the SGSN, which then sends to the MS a DEACTIVATE PDP CONTEXT
REQUEST message. After having removed the PDP context, the MS sends a PDP context
deactivation confirmation to the SGSN, which then sends a PDP context deletion acknowledgment to
the GGSN. If the PDP address was requested by the MS during the PDP context activation
procedure, the GGSN releases this PDP address.
Figure 7.23 illustrates a PDP context deactivation procedure initiated by the GGSN.
Figure 7.23: PDP context deactivation initiated by GGSN.
7.2.$.3 PDP Context !odifcation Proced%re
The PDP context modification procedure is used to change the negotiated QoS, the radio priority
level, or the TFT parameters negotiated during the PDP context activation procedure. This procedure
may also be used to change the MS PDP address by the GGSN. The PDP context modification may
be initiated by the MS, the SGSN, or the GGSN. The PDP context modification procedure initiated by
the MS or GGSN was introduced in Release 99 of the GPRS recommendations, even though the
PDP context modification procedure initiated by the SGSN was already introduced in Release 97 of
the GPRS recommendations.
'nitiated (# S)S*
The PDP context modification initiated by the SGSN may occur after an inter-SGSN RA updateprocedure to change the negotiated QoS, the radio priority level, or the TFT negotiated during the
PDP context activation procedure.
The SGSN sends an UPDATE PDP CONTEXT REQUEST message to the GGSN with a new QoS.
The GGSN then checks if the new QoS is compliant with its capabilities and sends back to the
SGSN in an UPDATE PDP CONTEXT RESPONSE message the negotiated QoS that takes into
account if necessary some restrictions. The SGSN then sends new QoS parameters and a new
radio priority parameter to the MS in a MODIFY PDP CONTEXT REQUEST message. If the MS
accepts the new QoS parameters, it acknowledges the MODIFY PDP CONTEXT REQUEST
message by sending to the SGSN a MODIFY PDP CONTEXT ACCEPT message.
Figure 7.24 illustrates a PDP context modification procedure initiated by the SGSN.
Figure 7.24: PDP context modification initiated by SGSN.
Note that if the new QoS is not accepted by the MS during the PDP context modification initiated by
the SGSN, the MS will deactivate the PDP context by initiating the PDP context deactivation
procedure.
'nitiated (# !S
The PDP context modification procedure initiated by the MS allows for a change in the negotiated
QoS, the radio priority level, or the TFT negotiated during the PDP context activation procedure. The
MS initiates the procedure by sending to the SGSN a MODIFY PDP CONTEXT REQUEST
message, which may include a new requested QoS or new TFT parameters.
Next, the SGSN sends the new characteristics proposed for that PDP context to the GGSN by
restricting if necessary the requested QoS in the UPDATE PDP CONTEXT REQUEST message.
The GGSN then checks if the new QoS or TFT parameters are compliant with its capabilities and
sends back to the SGSN in the UPDATE PDP CONTEXT RESPONSE message the negotiated QoS.
When the SGSN receives the acknowledgment of the PDP context update from the GGSN, it sends
to the MS a new radio priority and a packet flow ID on the QoS negotiated in a MODIFY PDP
CONTEXT ACCEPT message.
Figure 7.25 illustrates a PDP context modification procedure initiated by the MS.
When an MS wishes to create a secondary PDP context in order to reuse the same PDP address
and the same APN, it sends a secondary PDP context activation request to the SGSN with the
requested QoS and TFT. Security functions may be performed in order to authenticate the MS. The
SGSN creates a downlink GTP tunnel to route IP packets from GGSN to SGSN. It then sends the
requested QoS and TFT parameters to the GGSN in the CREATE PDP CONTEXT REQUEST
message while indicating the NSAPI assigned to the already activated PDP context with this PDP
address.
The GGSN creates a new entry in its PDP context table to route IP packets between the SGSN andthe external packet-switching network, which stores the TFT. The GGSN creates an uplink GTP
tunnel to route IP-PDU from SGSN to GGSN. It then sends back to the SGSN the result of the
secondary PDP context creation with a negotiated QoS. Next the SGSN sends an ACTIVATE
SECONDARY PDP CONTEXT ACCEPT message to the MS by adding NSAPI and by returning QoS
parameters and radio priority.
Figure 7.27 illustrates a secondary PDP context activation procedure initiated by the MS.