10 direct tunnel signalling procedures
TRANSCRIPT
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PCNSIG
Direct Tunnel
Signalling procedures
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Objectives
After the module, the participants will be able to:
• Describe the Direct Tunnel Signalling procedures and messages
• Explain the new Information Elements in Direct Tunnel Signalling procedure messages
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Signalling procedures – PDP context activation (1/5)
1. Activate PDP context request
2. Create PDP context request (SGSN IP address and TEID)
8. Update PDP context response 9. Activate PDP context accept
SGSN informs GGSN about RNC IP and TEID and if the QoS attributes
are downgraded
7. Update PDP context request (RAN IP address and TEID)
4. RAB assignment request (GGSN IP address and TEID)
5. RAB establishment response (RAN IP address and TEID)
6. Invoke trace
3. Create PDP context response (GGSN IP address and TEID)
RAB establishment
SGSN GGSN RAN
node
GTP-U
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Signalling procedures – Intra SGSN SRNS relocation (2/5)
SGSN GGSN Target
RAN
node
3. Relocation Request (IMSI, Cause, CN Domain Indicator, S- RNC, RAB to be set up)
2. Relocation Required (Cause, S-RNC Id, T-RNC Id, used RAB)
6. Relocation Command (RAB to be released)
10. Relocation Detect
7c. Forward SRNS Context (seq nbr of GTP-PDUs to be transmitted next in UL and DL)
7d. Forward SRNS Context (seq nbr of GTP-PDUs to be transmitted next
in UL and DL )
)
8. RRC message
11. RRC message
13a. Update PDP Context Request
14a. Iu Release Command
14b. Iu Release Complete
7. Forwarding of data (session context data, seq nbr of GTP-PDUs to be transmitted next in UL and DL )
5. Relocation Request Acknowledge (RAB id)
Source
RAN
node
1. Relocation Decision
9. UE detected
12. Relocation Complete
13b. Update PDP Context Response
)
Needed for hard handover
(No Iur available)
GTP-U
GTP-U
7a. SRNS Context Request (session context data req )
7b. SRNS Context Response (session context data provided )
4. RAB establishment
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Signalling procedures – RAB (Iu) release (3/5) RNC releases PDP context (inactivity timer expires)
1. RAB release request
2. Update PDP context request (SGSN IP address and TEID)
3. Update PDP context response (GGSN IP address and TEID)
SGSN GGSN RAN
node
GTP-U
GTP-U
Note: After RAB release the GTP user plane needs to be established between SGSN and GGSN, so that the
dowlink data packets are not lost
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Signalling procedures – Service request (4/5)
Subsriber in idle state
1. Service request
5. Update PDP context request (RAN IP address and TEID)
2. Service accept
6. Update PDP context response
SGSN GGSN RAN
node
GTP-U
3. RAB assignment request (GGSN IP address and TEID)
4. RAB assignment response (RAN IP address and TEID)
GTP-U
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Signalling procedures – Downlink data (5/5) Subscriber in idle state
3. Service request (Paging response)
7. Update PDP context request (RAN IP address and TEID)
4. Service accept
8. Update PDP context response
SGSN GGSN RAN
node
GTP-U
5. RAB assignment request (GGSN IP address and TEID)
6. RAB assignment response (RAN IP address and TEID)
GTP-U
1. GTP PDU 2. Paging request
9. GTP PDU
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Direct Tunnel – 3GPP support
DT-flag:
• DTI-flag indicates to the GGSN that this is a DT context
• In case the RNC has lost the RABs then it sends an “Error indication” of this to the GGSN. GGSN marks the tunnel unavailable and inform SGSN of the EI. SGSN starts an Update PDP context (DT flag=EI).
• If DT is used in a network where the GGSN does not support the feature, it is possible to lose the DT PDP context. This happen in uncrontrolled situation such as RAN node failure where the RAB is dropped during data transmission. N this case, GGSN receives an “Error indication” from RAN node and deletes the related PDP context.
3GPP Rel-7 introduced two new fields in the ”Update PDP context” message for the DT usage.
No-Qos-flag:
• No-QoS-flag indicates that the GGSN will accept the QoS received from SGSN. This verifies
that the Update PDP context message related to DT shall not initiate QoS re-negotiation. This will not prevent GGSN from re-negotiating the QoS later for some other reason.
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Direct Tunnel Flags IE (3GPP 29.060 section 7.7.81)
Update PDP Context Request The Direct Tunnel Flags information element is used to hold values for multiple bit flags related to the GTP direct tunnel
feature.
The Direct Tunnel Indicator (DTI) bit field is relevant only for the Update PDP Context procedure to indicate whether the
procedure is being used for the establishment of a direct GTP-U tunnel between the GGSN and the RNC.
The GPRS-CSI (GCSI) bit field is relevant only for the SRNS Relocation procedure and Inter-RAT handover procedure
and is used to indicate to the new SGSN whether the subscriber's profile in the old SGSN contained a GCSI.
The Error Indication (EI) bit is relevant only for the case when a direct tunnel is used and the GGSN receives an Error
Indication message from the RNC.
Bits marked as "Spare" shall be assigned the value 0 by the sending node and shall not be evaluated by the receiving
node.
Bits
Octet
s
8 7 6 5 4 3 2 1
1 Type=182 (Decimal)
2-3 Length
4 – n Spare Spare Spare Spare Spare EI GCSI DTI
NOTE:In the present release of the present document, n=4 in the above figure. In future releases of the present document, may be
greater.
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Direct Tunnel Establishment – PDP Context Activation procedure
GGSN
8. Activate PDP Context Accept
3. Create PDP Context Response
(GGSN IP address, TEID)
2. Create PDP Context Request
(SGSN GTP-U IP address, TEID)
1. Activate PDP Context Request
SGSN RNC
7. Update PDP Context Response
6. Update PDP Context Request
(RNC GTP-U IP address and TEID, DTI flag + No QoS negot. flag)
4. RAB Assignment Request
(GGSN IP address, TEID)
5. RAB Assignment Response
(RNC GTP-U IP address and TEID)
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New Information Element messages in PDP Context activation procedure
On Iu-PS Control Plane interface (between RNC and SGSN), no message or Information Element is modified, only the Transport Layer address of GGSN is used instead of SGSN.
On the Gn Control Plane interface (GTP-C between SGSN and GGSN), Update PDP Context request/response messages are added.
Update PDP Context request contains a new Information Element (Direct Tunnel Flag) and the Transport Layer address of RNC is used instead of SGSN.
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Signalling procedures – RNC failure (RANAP or RNC node reset)
1. Update PDP context request (SGSN IP address and TEID)
2. Update PDP context response
SGSN GGSN RAN
node
GTP-U
GTP-U
Iu guard timer
SCTP link lost
Iu connection lost for that UE!
RAN failure or broken cable
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Error Handling with Direct Tunnel (1/2)
GGSN
3. Update PDP context request
EI (Error Indication) flag
2. Error Indication
SGSN RNC
7. Update PDP Context Response
4. Update PDP Context Response
(SGSN GTP-U IP address and TEID, EI flag)
5. RAB Establishment
RNC failure
1. GTP PDU
6. Update PDP Context Request
(RNC GTP-U IP address and TEID, DTI flag + No QoS negot. flag)
8. GTP PDU
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New Information Element messages in Error Handling procedure (2/2)
• Error Indication message is sent over the GTP-U (between RNC and GGSN)
• Update PDP Context request sent over GTP-C (between GGSN and SGSN) contains EI (Error Indication) flag.
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Direct Tunnel impacts for Iu-PS Interface
• no new messages or new Information Elements on Iu-PS interface introduced by Direct Tunnel.
• different Transport Layer Address value (the GGSN IP Address instead of SGSN IP Address) is the only visible effect on Iu-PS interface.
There is no impact on Iu-PS interface.
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Direct Tunnel impacts for Gn/Gp Interface
• One new Information Element (Direct Tunnel Flags) on Gn interface introduced by Direct Tunnel. The Direct Tunnel Flags IE is used in the Update PDP Context Request message.
• The signalling flow on Gn interface is affected by one additional Update PDP Context Request/Response between SGSN and GGSN during PDP Context activation (without QoS change) when Direct Tunnel is used.
The Gn interface is impacted by the Direct Tunnel feature.
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Direct Tunnel PDP Context Activation messages
Create PDP Context Request message (1/2)
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Create PDP Context Request message (1/2)
Direct Tunnel PDP Context Activation messages
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Direct Tunnel PDP Context Activation messages
Create PDP Context Response message (1/2)
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Direct Tunnel PDP Context Activation messages
Create PDP Context Response message (2/2)
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Direct Tunnel PDP Context Activation messages
Update PDP Context Request message
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Direct Tunnel PDP Context Activation messages
Update PDP Context Response message