3GPP TSG-T2 #7 / ETSI SMG4
Ystad, SWEDEN, 22-26 November 1999	TSGT2#7(99)0993	

Agenda Item:	

Source:	Telia AB

Title:	Additional text for Ch. 7 in TR 21.910 “Multi-mode UE issues”

Document for:	Approval

___________________________________________________________________________

Introduction
This input is a suggestion on text to be included in chapter 7 in the report 21.910, Multi-mode UE issues. The text tries to summarise the work done in some of the 3GPP WG:s and if the content in this report is in line with the requirements and procedures stated in the specifications and reports described here.

Proposal
The suggestion is to include the text in the report and when time and resources are available to include more text in the sections, which at present state are stated FFS.

The suggestion of text

Additional abbreviations:
MM	Mobility Management

Additional references:
[9]	3G TS 22.100: “UMTS phase 1 Release 99”
[10]	3G TR 21.904: “Terminal Capability Requirements”
[11]	3G TS 21.111: “USIM and IC Card Requirements”

7	Ongoing work and identified additional work
This section tries to collect all relevant documents related to multi-mode UE issues and reviews the multi-mode UE aspects in them. In some cases additional work has been identified.
The list of document may not be complete but more relevant documents might reside within the group.
7.1	TSG SA
In SA there is one document that collects all requirements for R99 that are set by the different WG:s within SA, TS 3G 22.100 [9]. The requirements on Multi-mode UE:s can be found in ch 8 and reads as follows:
“UMTS phase 1 shall support dual mode UMTS/GSM terminals. At least one Capability Class shall be standardised for mobile terminals supporting the GSM and UTRA modes. It shall support monitoring of cells belonging to the two types of access networks in idle mode (cell reselection procedure) and active mode (handover preparation procedure).”
This corresponds to a type 2 UE as defined in this report. The requirement does not exclude any other types of terminals as those defined in this report 

7.1.1	SA1
7.1.1.1	Service requirements
The service requirements for release 99 is collected in TS 3G 22.101 [8]. The requirement related to Multi-mode UE:s can be found in ch. 17 (Handover requirements) and ch 18 (Network selection). 
The handover requirements are very general and states that:
“Any handover required to maintain an active service while a user is mobile within the coverage area of a given network, shall be seamless from the user’s perspective. However handovers that occur between different radio environments may result in a change of the quality of service experienced by the user.

It shall be possible for users to be handed over between different UMTS networks subject to appropriate roaming/commercial agreements.

Handover between UMTS and GSM systems (in both directions) is required, even if this requires changes to GSM specifications. In addition, a generic solution may be implemented in UMTS which allows calls to be handed over between UMTS and other pre-UMTS systems in both directions.”

The initial requirements for network selection that are relevant for Multi-mode UE:s are:
“Three roles may be involved in UMTS network selection: the home environment, the serving network and the user. Services may be available to the user through a choice of several serving networks in a given location, possibly using different types of Radio Access Network. However it is expected that a user terminal will communicate with one network at a given instant (there may be exceptions such as when an inter-network handover occurs). “

Even more relevant for the UE and user is how the network selection shall be performed. For that three selection procedures are defined: a default automatic procedure, a manual procedure and a home environment specific procedure. The first two shall be implemented in all UMTS UE:s. As the multi-mode UE defined in this report shall include UMTS, these requirements is valid also for a multi-mode UE. This is also stated in this report for all types of UE:s and can be considered to be in line with the requirements.

A requirement that may affect the specified types of UE in this report is:
“If simultaneous access to more than one home environment is required (through a card with multiple USIMs or through several cards in a multi-slot terminal), manual selection shall be invoked.”
The type 3 UE should be able to camp on several cells from different radio access technologies that are belonging to different operators/PLMN:s at the same time and still an automatic switching between modes are defined for this types of terminal. This has to be considered in later releases of the report. Either the definition of this type of terminal has to be changed or the requirement has to change. The type 3 terminal is not of highest priority for R99 and therefore this is lest ffs.

7.1.1.2	Handover requirements
TS 3G 22.129 [4] is a specification that only deals with handover requirements, both within UMTS and between UMTS and GSM. The requirement for handover from UMTS to GSM can be found in clause 6 and the requirements for handover from GSM to UMTS can be found in clause 7. 

The requirements for handover from UMTS to GSM are divided into operational, performance and service requirements. The requirements most affecting the UE are those in the performance clause, which include Detection Time of Potential GSM Handover Candidates, Number of GSM handover candidates to detect, Probability of Connection Loss and Temporary degradation of service caused by handover. As a summary it can be said that the requirements that is set for intra-GSM handover shall be applied even when handover from UMTS to GSM. More stringent requirements than that are not set. These requirements mostly affects the radio part of the Multi-mode UE and some of the specifications for that can be found in clause 7.2 in this report.

In the clause with service requirements there are no specific requirements except for the speech, USSD and data bearer service. These services should be continued after a handover. An example of a service that may be interrupted after a handover is the facsimile service.

For the speech service it is said: 
“any call based on the default UMTS speech codec shall be mapped to the FR GSM speech codec. In the case the terminal and the GSM network support AMR and /or EFR and/or HR, it shall be the operators choice to define the appropriate mapping.”
For USSD it is said:
“The technical standards shall provide means to ensure that any handover that occurs during a USSD interaction need no more affect the service than intra-GSM handover.”

For the data bearer service it is said:
“Standards shall be defined to permit the possibility of handover of a UMTS connection oriented data bearer service to GSM which shall result in an appropriate GSM/GPRS bearer service. The mapping between UMTS data bearer services and appropriate GSM/GPRS data bearer services will depend upon many factors such as data rate, delay constraints, error rate etc. Means shall be provided for the application to indicate minimum acceptable QoS for service continuation after handover.”

In the clause with requirements for handover from GSM to UMTS mostly just requirements for services are dealt with. The services that should continue after a handover are speech, USSD, a circuit switched data service mapped onto a UMTS packet switched data service and a data switched packet service (if not the change of QoS is too big to be accepted by the user).

When using multiple bearer services in GSM/GPRS it is said that:
“Consideration must be given to multimedia services which may involve the use of multiple bearer services. For example Class A GPRS terminals will be capable of simultaneously supporting more than one data bearer services. The mapping between GSM/GPRS data bearer services and UMTS bearer services will depend upon many factors such as data rate, delay constraints, error rate etc. Means shall be provided to allow handover of several data bearer services from GSM to UMTS. Means shall be provided for the application(s) to indicate minimum acceptable QoS for services continuation after handover.”

These service requirements shall apply for all multi-mode UE:s that supports these kind of services. 

6.1.2	SA2
6.1.2.1	Architectural requirements on UMTS for release 99
3G TS 23.121 [6] describes the architectural requirements on UMTS for release 99.
This specification divides connections into if they are in the CS or in the PS domain. The division between GSM and UMTS radio access technology is not so obvious for the core network. From an architectural point of view the division between the CS and PS domain are more important. 

Data retreival between UMTS and GPRS is dealt with in ch. 4.2.2.1. There is even a proposed solution how it shall be done.

The MM procedures for UMTS are described in section 4.3. In section 4.3.1.1 there is a requirement for the R99 UE to support both combined and separate update mechanisms between CS and PS services. The background is that in GSM/GPRS combined updates between RA and LA can be made via the Gs interface between MSC/VLR and SGSN. This possibility is facilitated to optimise the radio resources. As said before, in UMTS it is suggested to use both separate and combined updates for R99 UE:s.

In ch 4.3.14.3 there is a small comparison between MM for UMTS and GSM. The reason for the comparison is to see if the same signalling can be used and how the MM messages should be transferred when handover. If a combined update between GSM and UMTS can be done is in a way studied in [3] as described further down. 

Chapter 6 is totally devoted to the questions on interoperability between GSM and UMTS. In the beginning a recommendation of combined updates if a UE is supporting simultaneous ISDN/PSTN and packet services is made. Otherwise the chapter deals with the signalling procedures for handover between UMTS and GSM. The only thing that is affecting the terminal is where the decision of the handover is performed. For CS services the decision is taken in RNS for UTMS to GSM handover and in BSS for GSM to UMTS handover. For PS services the decision can be made in either the UE, the BSS or in the SRNS. This applies for both directions of handover. In this case the details for how the decision shall be made is FFS.

6.1.2.2	Additional architectural requirements
3G TR 23.920 [3] collects architectural requirements that are not yet accepted or stable enough to be included in the other architectural specification, 23.121. 

A small section on the procedures for ciphering keys is included in ch. 5.5.2 and deals with the case of UMTS-GSM handover. The actual interoperation in the case of different ciphering keys for UMTS and GSM are for further study. This does not directly affect the UE but rather the USIM.

Dual-mode operation between UMTS and GSM when the GSM part of the UE is a MS of GPRS class A is handled in chapter 5.8. The section deals with questions of MM procedures and availability of PS services after a handover of a CS service from one of the radio access technologies to the other. The suggestions include letting the UMTS MM to do distinction between CS and PS services in the registration related procedure. The requirements on the MS/UE are that it must be capable of handling the GSM-UMTS dualism, i.e. to be a multi-mode UE.

The UMTS Mobility Management (UMM) for R99 shall use packet anchoring at the GGSN. This implies that some changes have to be introduced in GPRS.  In section 5.9.5.4 the affects the requirements of QoS when using the anchor concept and the UE/MS described above (a dual-mode UE with a UMTS part that supports simultaneous CS and PS services combined with a GPRS class A MS) is described. There are no specific requirements on the multi-mode UE and all suggested changes reside in the network. 

A definition on simultaneous mode has been made in chapter 5.17. It is defined as:
“Simultaneous mode is defined as the support of active parallel CS and PS communications. 
The UE has simultaneous PS MM Connected and CS MM Connected states when in UE simultaneous mode.”
In this section it is also stated that it is important that from day one of UMTS launch supply terminals that supports simultaneous active communication with both the CS and the PS domain. This requirement only applies for and within UMTS but puts special requirements on the UE in respect to terminal capabilities.

Chapter 5.18 deals with the question on GSM and UMTS cells in the same registration area. This could save a lot of signalling when changing between UMTS and GSM, as also described and asked for in the scenarios (chapter 5.1.5). One reason for introducing this is, as stated in [3], that: 
“Third generation needs to offer higher quality (eg higher MT call success rate) than second generation. Hence the capability to have GSM and UMTS cells in the same Registration Area is needed for at least CS traffic.”

Some open issues still reside for implementing GSM and UMTS in the same registration area and these are questions on security, network service capabilities, terminal capabilities, idle mode control and the capacity of paging channels, as described in [3].

7.1.3	SA3
FFS
7.1.4	SA4
FFS
7.1.5	SA5
FFS
7.2	TSG RAN

7.2.1	RAN1
FFS
7.2.2	RAN2
7.2.2.1	UE functions and Interlayer procedures in Connected Mode
In 3G TS 25.303 [2] the functions and Interlayer procedures for a UE in connected mode are described. It starts with defining the UE states and states transitions. The states and states transitions are divided according to if a the UE is utilising the CS GSM domain (PSTN/ISDN only) or the GSM/GPRS domain (IP only). 

Section 5.6 shortly describes the inter-system handover between UMTS and GSM when simultaneous services in the IP and the PSTN/ISDN domain are used. This procedure requires a terminal with GPRS class A capabilities and no other inter-system procedures for terminals not capable of simultaneous services are described. A GPRS class A MS is not thought to be produced in the nearer future and therefore procedures for other GPRS classes are also needed. Possibly these procedures can be used even if the UE is not connected to both domains at the same time.

The RRC mobility procedures are described not just for FDD and TDD but also for inter-system handover between UMTS and GSM. These procedures are just described for the PSTN/ISDN domain and the procedures for the IP domain are lacking. 

7.2.2.2	UE Procedures in Idle mode
In RAN2 another specification dealing with procedures for a UE, 3G TS 25.304 “UE Procedures in Idle Mode” [5], is produced.

The specification shall, according to the scope, include examples of inter-layer procedures related to the idle mode processes and describes idle mode functionality of a dual-mode UMTS/GSM UE. Even so there is no description on how radio access technology shall be chosen. The specification only talks about PLMN selection and reselection. In the section with PLMN selection and reselection (5.1) it is stated:
“Selection of the radio access system may be part of the PLMN selection and reselection process or it may be a separate process inside NAS [FFS].
[Note: Details of the possible NAS process of the radio access system selection are out of the scope of TSG-RAN WG2.]”

The Non Access Stratum (NAS) and the Access Stratum (AS) is a functional division to serve as a basis for the work division between SMG2 UMTS L23 and other groups.

The present report recommends that a specific procedure for choice of radio access technology should be implemented. Some suggestions on how this procedure could be outlined can be found in section 5.1.1.

7.2.3	RAN3
FFS
7.2.4	RAN4
FFS
7.3	TSG CN

7.3.1	CN1
FFS
7.3.2	CN2
FFS
7.3.3	CN3
FFS
7.4	TSG T

7.4.1	T1

7.4.2	T2
In the report 3G TR 21.904 [10], the choice of radio access technology is introduced in a diagram in achapter 4 where the baseline definitions for a UE are described. The diagram makes the choice of radio access technology before searching for networks to register on. If no network is found within the radio access technology chosen, a new radio access thechnology is chosen and the procedure is performed once again.
This procedure is the in line with what is proposed by this report.
7.4.3	T3
The requirement document for T3, 21.111 [11], collects all relevant requirements for the USIM and the IC Card. One section, section 11, is concerned with 3GPP/GSM interworking. The requirements deal with GSM subscribers in a 3GPP network and 3GPP subscribers in a GSM network.