Transcript Document
Tunneling Protocol Support for 1x CSFB from
E-UTRAN
Source:
Qualcomm Inc: Masa Shirota([email protected]), Ravindra Patwardhan,
Peerapol Tinnakornsrisuphap, George Cherian, David Ott and Jun Wang
China Telecom: Mei Cheng Li ([email protected])
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1
Introduction
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1x CSFB (Circuit Switched FallBack) from E-UTRAN has been defined in 3GPP as
one of the Release 8 features. Stage 2 requirements can be found in TS23.272.
Major Stage 3 requirements can be found in TS36.331 (RRC), TS36.413 (S1),
TS29.274 (GTPv2) and TS29.277 (S102).
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1x CSFB Design Principles in 3GPP specifications:
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The UE can perform the 1x registration and receive the 1x page message while it stays in
E-UTRAN.
1x messages (LAC PDUs) are exchanged between the UE and the MME over the
transports provided by RRC and S1.
The MME interfaces to the 1x IWS though S102. S102 is defined as a subset of A21
interface.
E-UTRAN directs the UE when it should fall back to an 1x.
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When the UE performs an 1x call origination, it firstly connects E-UTRAN by initiating the CSFB
service request to get the redirection. After the UE receives the redirection, it tunes to an 1x based
on the information (Band Class and Frequency number) in the redirection information. Then, it
sends an ORM.
When the UE receives an 1x page message, it initiates the CSFB service request to get the
redirection. After the UE receives the redirection, it tunes to 1x based on the information (Band
Class and Frequency number) in the redirection information. Then, it sends a PRM.
E-UTRAN may require the UE to measure 1x network during the measurement gaps.
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1x CSFB Architecture
1xCS
CSFB
UE
1xRTT CS
Access
1xRTT
MSC
A1
A1
1xCS IWS
S102
MME
S1-MME
1xCS
CSFB
UE
S11
Serving/PDN
GW
E-UTRAN
SGi
S1-U
Tunnelled 1xRTT messages
Reference: 3GPP TS23.272
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Issues with current 3GPP 1x CSFB Design
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No tunneling protocol (similar to CSNA) is used to transport 1x
Encapsulated LAC PDU between the cdma2000 upper layer in
UE and MME (endpoint for A21 interface).
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RRC provides a tunnel between UE and eNB. S1 provides a tunnel
between eNB and MME.
Some parameters, such as RAND, Cell ID, Mobile Subscription
Information, etc., can be exchanged over those interfaces.
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No clear requirements for how to populate LAC fields, e.g.,
ARQ fields and Radio Environment Report fields, are defined.
1x Message control is not supported.
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An IWS and UE cannot understand if LAC PDU is formed as for common
channel or dedicated channel.
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If the logical channel is not identified, the message cannot be parsed as the format of the
LAC PDU changes depending on the logical channel.
1x CSFB uses common channel messages basically. But, SRVCC uses dedicated channel
messages (handoff direction, see annex Stage 2 call flow from 3GPP document).
Layer 2 ack is not supported. Some 1x messages, such as the
Registration Message, require L2 ack. If the cdma2000 LAC layer does
not receive L2 ack, it continues to resend the message.
These issues occur due to lack of CSNA-like tunneling protocol to
exchange 1x messages.
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Proposal for New Tunneling Protocol
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Define a CSNA-Lite tunneling protocol to be used between
A21 endpoint and cdma2000 upper layer.
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This new tunneling protocol can be used for any interworking scenarios
between 1x and non-3GPP2 technologies.
This new protocol will have subset of functions from CSNA. Other Access
Technologies need to provide a transport channel for this tunneling
protocol. (We do not intend to change 1x CSFB design in 3GPP. Only
message encapsulation and L2 ack defined by the new protocol can
apply.) Thus, major changes are not expected in 3GPP documents for 1x
CSFB.
Updates A.S0008 to support this new generic tunneling protocol by A21
interface in addition to CSNA.
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Functions for CSNA-Lite Protocol
• CSNA-Lite tunneling protocol supports:
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1x LAC PDU encapsulation
Message control (L2 acknowledgement, Protocol Revision, and Logical
Channel Indication)
1x parameters provisioning
• 1x message filter negotiation between AT and A21 end
point will not be defined. Protocol revision of CSNA-Lite
Protocol will indicate which 1x messages can be
exchanged.
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Recommendations
• Define a CSNA-Lite tunneling protocol which can
generally apply to interworking any access technologies
(except for HRPD).
• Primarily to support 1x CSFB from E-UTRAN. But, it is
not limited to it. (This tunneling protocol can be used for
SRVCC as well.)
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Annex A: A21 and CSNA Brief Overview
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A21 assumes the AN supports CSNA.
A21 supports:
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1x LAC PDU encapsulation (AN and IWS can exchange 1x message over
A21.)
Message control
L2 acknowledgement
1x parameters provisioning
Event Notification
Service Request (for HRPD page delivery)
Radio Parameter Update
CSNA supports:
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1x LAC PDU encapsulation (AT and AN can exchange 1x message over
HRPD.)
Message control (L2 acknowledgement, Protocol Revision, Logical
Channel Indication)
1x parameters provisioning
1x message filter negotiation
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Annex B: SRVCC Call Flow
1xCS
SRVCC
UE
eNB
MME
S-GW
1xCS
IWS
1xRTT
MSC
1xRTT
CS
access
1. Ongoing VoIP session over the IMS access leg established over E-UTRA access
2.Measurement Reports
3. Handover decision
- from EUTRA preparation
4. .HO
request (3G1x Parameters)
5. UL info transfer
(MEID, 1x Origination)
6. UL S1 cdma2000 tunnelling
(MEID, RAND, 1x Origination)
7. S102 Direct Transfer (1x Air
Interface Signalling (Origination))
8. 1x traffic assignment/handoff initiation
9. S102 Direct Transfer (1x Air Interface
Signalling (Handoff Direction))
10. DL cdma2000 tunnelling
(Handoff Direction)
11. Mobility from EUTRA
command (Handoff Direction)
12. 1x radio interface procedures to acquire a traffic channel
13. 1x handoff completion message
14. 1x handoff done
15. Ongoing voice call over the CS access leg established over 1xRTT access
16. S1 UE Context
Release Request
17. Suspend Request/Ack
18. S1 UE Context Release
Reference: 3GPP TS23.216
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