6.10 Multi-RAT Handover Test Model
34.123-33GPPPart 3: Abstract test suite (ATS)TSUser Equipment (UE) conformance specification
6.10.1 Overview
The test model is shown in Figure 6.10.2.9.6. The SS in the model consists of UTRAN emulation part and GERAN emulation part, GERAN emulation part includes protocol emulation modules for GSM CS services and protocol emulation modules for GPRS service. Protocol stack L1 (GERAN), L2 is for GSM CS service function emulation, protocol stack L1, RLC/MAC, LLC, SNDCP is for GPRS service function emulation. SNDCP emulation model and relevant PCO’s can be removed if "traffic channel gets through" is not tested.
L1 (GERAN) provides necessary physical layer functionality for both GSM and GPRS. A control PCO and a set of ASP’s are defined for configuring and controlling its protocol behaviour required in the test cases. L1 (GERAN) provides services to L2 and RLC/MAC emulation modules, the interfaces between them are not specified in this test model, it is implementation dependent and shall follow the relevant GSM and GPRS specifications.
L2 emulates necessary GSM L2 protocol functionality used in testing. A data PCO and a set of ASP’s are defined for this module and used for transmitting and receiving layer 3 signalling messages and use data. The definition of the PCO and these ASP’s are based on the logical channel concept of GSM specification. A control PCO and related ASP’s are also defined for L2, they are used to introduce abnormal layer 2 behaviour required by the test purposes.
RLC/MAC is emulation module for GPRS Radio Link Control/Medium Access Control protocol. Two PCO’s and related ASP’s are defined for the module. Control PCO is used to set TBF and assign physical resources to it, actual physical resources (packet channels) are created by L1 (GERAN) ASP’s beforehand. Data PCO is for transmitting and receiving RLC control messages (RLC control block). Before any RLC data or control block is sent (or received) a proper TBF shall be configured. In addition RLC/MAC module provides service to LLC emulation module, the interface between them is determined by implementation and shall be compliant with relevant core specification.
LLC performs GPRS Logical Link Control protocol emulation. Its data PCO and ASP’s are used for exchange GMM signalling messages between TTCN and the UE under test. The current defined ASP’s on control PCO are subset of the primitives defined in core specification, they are used to assign, un-assign TLLI and ciphering parameters, or get status report.
6.10.2 ASP function description
6.10.2.1 Identities
– Within the SS, a cell is identified by cell identifier (cellId), which is of TTCN type CellId (INTEGER).
– Within a cell, a basic physical channel is identified by physical channel identifier (physicalChId), which is of TTCN type PhysicalChId (INTEGER). In multislot configuration a basic physical channel is identified by physical channel identifier (physicalChId) and timeslot, which is of TTCN type TN (INTEGER).
– Within a physical channel, logical channel is identified by logical channel type (g_LogicChType), which is of TTCN type G_LogicChType (INTEGER). When multiple logical channels of same type are carried by (mapped to) the same basic physical channel, they are differentiated by sub-channel number (subChannel), which is of TTCN type SubChannelNumber (INTEGER).
– At the top boundary of L2 emulation module two service access points (SAP) are available, they are identified by SAPI. SAPI=3 is used for short message service; SAPI=0 is used for L3 signalling messages and user data.
EXAMPLE: If G_L2_DATA_REQ ASP has the following parameter setting:
– cellId = tsc_CellA;
– sAPI = tsc_SAPI_0;
– physicalChId = tsc_PhyCh0;
– g_LogicChType = tsc_SDCCH4; and
– subChannel = tsc_SubChannel1;
it sends PDU on the SDCCH4(1) logical channel which is carried by the physical channel tsc_PhyCh0 in cell A.
6.10.2.2 Cell configuration and control
In GSM each base station has a base station identity code BSIC, it consists of network colour code and base station colour code (NCC + BCC). BSIC is continuously broadcasted on the SCH channel, and it shall be used as the training sequence code for broadcast and common control channels.
In the test model the function of G_CL1_CreateCell_REQ ASP is to create a cell and pass parameter BSIC to it. This ASP establishes the cell identifier which shall be used in the ASP’s related to this cell.
This is the first step to configure L1 (GERAN) emulation module of the SS.
6.10.2.3 L1 (GERAN) configuration and control
Configuration and control functions identified for L1 (GERAN) of a cell are:
– creation of basic physical channels;
– creation of multislot configuration;
– release of basic physical channel;
– modifications of channel mode, ciphering parameters and transmission power level;
– reporting of L1 header of SACCH channel;
– pickup a frame in near future, which can carry L3 message.
6.10.2.3.1 Basic physical channel configuration
A basic physical channel uses a combination of frequency and time domain resources, therefore, the definition of a particular basic physical channel consists of a description in the frequency domain and a description in the time domain. In time domain the resource is called Time Slot, there are 8 time slots in one frame, numbered from 0 to 7. In frequency domain a basic physical channel may use only one frequency or may use multiple frequencies in frequency hopping.
Basic physical channel carrying FCCH + SCH + BCCH + CCCH (PCH, AGCH, RACH) or FCCH + SCH + BCCH + CCCH + SDCCH4 logical channels shall be located in time slot 0, and uses single frequency (non-hopping). The basic physical channel carrying additional BCCH, CCCH (PCH, AGCH, RACH) logical channels shall be located in time slot 2, 4, 6 and uses the same single frequency as the frequency used by the physical channel carrying FCCH, SCH.
GSM specification defines 24 permitted combinations of different logical channels, which can be mapped on to a basic physical channel. The combination defines which logical channels are carried by a basic physical channel, and it is also an indication of which modulation (GMSK or 8PSK) is used for the basic physical channel.
Training Sequence Code (TSC) is another parameter needed by physical channel. Common control and broadcast channel have to use BCC as its TSC.
Dedicated control channel and dedicated traffic channel need more parameters to configure. Parameter "Channel Mode" is needed to specify channel coding (therefore the user data rate). Ciphering related parameters are required to define the ciphering behaviour of the channel.
Common control channels need parameters to configure where in the 51-multiframe paging and access grant blocks are located.
Transmission power level is provided as per physical channel parameter, power level of each physical channel can be controlled independently.
The function of ASP G_CL1_CreateBasicPhyCh_REQ is to create a basic physical channel which has the required property defined by all the parameters mentioned above.
In the process of L1 (GERAN) configuration, calling the ASP is the next step after calling G_CL1_CreateCell_REQ.
6.10.2.3.2 Multislot configuration for circuit or packet switched channels
Multislot configuration for circuit switched connection consists of multiple circuit switched traffic channels, in L1 point of view these traffic channels are independent basic physical channels with the same frequency parameters (ARFCN or MA, MAIO, HSN) and the same training sequence code but located in different time slots, one of the basic physical channels is the main channel of the configuration carrying the main signalling (FACCH, SACCH, IACCH) for the configuration. The main channel shall be bi-directional channel and with channelCombanition TCH/F+FACCH/F+SACCH/M or E-TCH/F+E-IACCH/F+E-FACCH/F+E-SACCH/M. When transmitting user data (not signalling message) stream is divided into substreams, each substream is transmitted independently on a channel in the configuration. At the receiving side all substreams are combined back to user stream.
According to the test model creation of a multislot configuration for circuit switched connection needs two ASP calls. Firstly, G_L1_CreatedBasicPhyCh_REQ is called to establish the main channel, then G_L1_CreateMultiSlotConfig_REQ is called to allocate more timeslots to the channel established by the previous ASP. A substream of a multislot configuration is identified with the physicalChId and timeslot.
Multislot configuration for packet switched connection consists of multiple PDCHs which can carry PDTCH/Us or PDTCH/Ds. All these PDCHs use the same frequency parameters (ARFCN or MA, MAIO, HSN) and the same training sequence code, but are located on different timeslots.
Similarly, a multislot configuration for packet switched connection is created with two ASP calls. First G_L1_CreatedBasicPhyCh_REQ is called to establish the first PDCH channel, then G_L1_CreateMultiSlotConfig_REQ is called to allocate more timeslots to the channel established by the previous ASP. All data ASP on packet data channel use physicalChId and timeslot to address the physical channels.
6.10.2.3.3 Frame in the near future
ASP G_CL1_ComingFN_REQ is defined to request L1 (GERAN) return the reduced frame number (FN modulo 42432) which is far enough in the future from current frame number and is able to carry L3 message on the specified channel. "far enough" means that there is enough time left for TTCN to prepare a L3 message to be sent on that frame. When calculating startingTime, this ASP could be useful. The starting time usually is set to a frame number in a time distance from current frame number. TTCN writer can use G_CL1_ComingFN_REQ to get a frame number in the future then add a certain number of frames as time distance to it and use the result as the value for startingTime.
6.10.2.3.4 L1 header
The layer 1 header of SACCH from UE to network carries information of timing advance and UE uplink transmission power level, verifying L1 header contents is required in some test cases, ASP G_CL1_L1Header_REQ and G_CL1_L1Header_CNF are defined for fulfilling this requirement.
6.10.2.4 L2 configuration and control
For normal operation there is no parameter configurable in L2. Some abnormal L2 behaviours are required in test cases. In the test model two ASP’s are currently defined to introduce abnormal L2 behaviour. When creating a dedicated channel the initial SACCH header is set to the values in powerLevel and timingAdvance fields of DedCH_Info.
6.10.2.4.1 Don’t response to some handover access bursts
In non-synchronized handover procedure UE/MS, having received handover command, sends handover access bursts on the target channel repeatedly till it receives PHYSICAL INFORMATION message from network or T3124 times out. Normally network replies PHYSICAL INFORMATION as soon as it receives handover access burst. Some test cases require that the SS ignores several incoming handover access bursts then responses to the one that follows. ASP G_CL2_HoldPhyInfo_REQ is defined for fulfilling this requirement. It is used together with and before a data ASP sending PHYSICAL INFORMATION message. When SS receives the G_CL2_HoldPhyInfo_REQ, it does not transmit the PHYSICAL INFORMATION message until n handover access bursts have been received.
6.10.2.4.2 No UA reply to SABM
GSM L2 protocol is adapted from LAPD (HDLC subset). The multiframe operation mode is established through exchange of supervisory frame SABM and unnumbered frame UA between peer entities, and SABM is always sent by UE/MS, UA is always sent by network. UE/MS will repeatedly transmit SABM till it receives UA or retransmission counter is reached. Some handover test cases require that the SS does not response to the incoming SABM, so handover fails. G_CL2_NoUAforSABM_REQ is used for such purpose, it commands the SS not to send UA response to the UE when SABM is received.
6.10.2.5 System Information sending
There are 17 different SYSTEM INFORMATION messages on BCCH and 4 different SYSTEM INFORMATION messages on SACCH defined for circuit switched services in GSM specification. In a particular test case not all of them are required. SYSTEM INFORMATION messages on BCCH shall be broadcasted periodically by the SS, SYSTEM INFORMATION TYPE 5, 6 and optionally 5bis and 5ter messages shall be sent on SACCH by the SS when nothing else has to be sent on that channel.
G_L2_SYSINFO_REQ is defined to deliver a SYSTEM INFORMATION message and its type SysInfoType to the SS, SS shall store the SYSTEM INFORMATION and transmit it periodically according to the scheduling rules specified in 3GPP TS 45.002 [31], clause 6.3.1.3. SYSTEM INFORMATION message newly delivered shall override the same type SYSTEM IFORMATION message previously stored in the SS.
SYSTEM INFORMATION message type 18, 19, 20 are scheduled by scheduling information in SYSTEM INFORMATION type 9. ASP for scheduling these messages has not been defined yet because these messages are not required in current test cases.
6.10.2.6 Paging
Paging message for a particular UE/MS shall be sent on the right CCCH_GROUP and PAGING_GROUP which are determined by IMSI of the UE/MS and other parameters. In the test model TTCN code is responsible to calculate the value of CCCH_GROUP and the value of PAGING_GROUP.
TTCN selects the right channel according to the value of CCCH_GROUP, then PAGING REQUEST message and the value of PAGING_GROUP are passed to the SS by using:
– ASP G_L2_Paging_REQ in case of UE/MS in idle mode or the UE/MS not supporting SPLIT_PG_CYCLE on CCCH when it is in GPRS attached mode.
The SS shall determine the position where the paging block is located using the value PAGING_GROUP and other CCCH parameters configured by G_CL1_CreateBasicPhyCH_REQ, then send the PAGING REQUEST message according the parameter pagingMode in the ASP:
– send the message on the paging block determined by PAGING_GROUP if pagingMode = "normal paging";
– send the message on the paging block determined by PAGING_GROUP and the "next but one" position on the PCH if pagingMode = "extended paging";
– send the message on all paging blocks if pagingMode ="paging reorganization".
6.10.2.7 Generic procedures for GPRS signalling
Two channel combinations are applied to configure a GERAN cell for the GPRS signalling:
– The channel combinations 5 + 13, (FCCH + SCH + BCCH + CCCH + SDCCH/4(0..3) + SACCH/C4(0..3)) + (PDTCH/F+PACCH/F+PTCCH/F), are considered as default at the interRAT tests and GERAN to UTRAN Inter-RAT test cases in clause 42.4.7 of TS 51.010-1.
The following generic procedures show the usages of GPRS ASP’s for the GPRS generic attach procedures, the generic cell change order within a TBF and the GSM ciphering procedure.
6.10.2.7.1 GPRS generic attach procedures and ciphering mode control
6.10.2.7.1.1 GPRS attach procedure in channel combinations 5 and 13
|
Direction |
ASP |
message |
Comments |
|---|---|---|---|
|
SS |
G_CL1_CreateCell_REQ |
Create the cell |
|
|
SS |
G_CL1_CreateBasicPhyCh_REQ |
Create the physical channel combination 5 for FCCH+SCH+BCCH+CCCH+SDCCH/4(0..3)+SACCH/C4(0..3) |
|
|
SS |
G_CL1_CreateBasicPhyCh_REQ |
Create the physical channel combination 13 for PDTCH/F+PACCH/F+PTCCH/F |
|
|
SS -> MS |
G_L2_SYSINFO_REQ |
SYSTEM INFORMATION TYPE1, SYSTEM INFORMATION TYPE2, SYSTEM INFORMATION TYPE2quater, SYSTEM INFORMATION TYPE3, SYSTEM INFORMATION TYPE4, SYSTEM INFORMATION TYPE13 |
Broadcast system information messages : SI 1~4; SI 13 |
|
SS |
G_CRLC_CreateRLC_MAC_REQ |
Create RLC/MAC emulation entity |
|
|
SS |
G_CLLC_CreateLLE_REQ |
Create LLC emulation entity |
|
|
SS |
MMI_CmdReq |
Power on the UE/MS |
|
|
MS-> SS |
G_L2_ACCESS_IND |
CHANNEL REQUEST |
RACH, TBF establishment with Establishment Cause = one phase packet access. |
|
SS |
G_CRLC_UL_TBF_Config_REQ |
Set up uplink TBF in RLC/MAC entity in SS, this TBF is corresponding to what indicated in IMMEDIATE ASSIGNMENT. |
|
|
SS -> MS |
G_L2_UNITDATA_REQ |
IMMEDIATE ASSIGNMENT |
Assign the uplink resources (uplink TBF) to MS. Polling bit and Starting Time are set |
|
MS -> SS |
G_RLC_ControlMsg_IND |
PACKET CONTROL ACKNOWLEDGEMENT |
|
|
SS |
G_CLLC_Assign_REQ |
Assign TLLI, ciphering key and algorithm. The ciphering algorithm = "ciphering not used". The value of ciphering key shall be the one generated in the following authentication procedure. If there is no user data traffic in acknowledged mode before authentication procedure the ciphering algorithm may be set to one of the GPRS ciphering algorithm, and the late G_CLLC_Assign_REQ shall be not used. |
|
|
MS -> SS |
G_LLC_UNITDATA_IND |
ATTACH REQUEST |
MS uses the assigned uplink TBF to transmit the L3 message to SS, the SS manages the operation of the TBF without TTCN intervention and releases the TBF automatically according the countdown procedure. The SS reassembles the received data blocks into the L3 message and passes it to the LLC DATA PCO G_LLC. |
|
SS |
G_CRLC_DL_TBF_Config_REQ |
Set up downlink TBF in RLC/MAC entity in SS |
|
|
SS -> MS |
G_L2_Paging_REQ |
IMMEDIATE ASSIGNMENT |
Downlink TBF establishment |
|
SS -> MS |
G_LLC_UNITDATA_REQ |
AUTHENTICATION AND CIPHERING REQUEST |
|
|
MS-> SS |
G_L2_ACCESS_IND |
CHANNEL REQUEST |
RACH, TBF establishment with Establishment Cause = one phase packet access. |
|
SS |
G_CRLC_UL_TBF_Config_REQ |
Set up uplink TBF in RLC/MAC entity in SS, this TBF is corresponding to what indicated in IMMEDIATE ASSIGNMENT. |
|
|
SS -> MS |
G_L2_UNITDATA_REQ |
IMMEDIATE ASSIGNMENT |
Assign the uplink resources (uplink TBF) to MS. Polling bit and Starting Time are set |
|
MS -> SS |
G_RLC_ControlMsg_IND |
PACKET CONTROL ACKNOWLEDGEMENT |
|
|
SS |
G_CLLC_Assign_REQ |
Assign TLLI, if changed |
|
|
MS -> SS |
G_LLC_UNITDATA_IND |
AUTHENTICATION AND CIPHERING RESPONSE |
|
|
SS |
G_CLLC_Assign_REQ |
Keep TLLI unchanged, ciphering algorithm = one of the GPRS ciphering algorithm. The value of ciphering key shall be the one generated in the authentication procedure. If no user data traffic in acknowledged mode before authentication procedure, this ASP is not needed. |
|
|
SS |
G_CRLC_DL_TBF_Config_REQ |
Set up downlink TBF in RLC/MAC entity in SS |
|
|
SS -> MS |
G_L2_Paging_REQ |
IMMEDIATE ASSIGNMENT |
Downlink TBF establishment |
|
SS -> MS |
G_LLC_UNITDATA_REQ |
ATTACH ACCEPT |
SS uses the established downlink TBF to transmit the L3 message to MS, the SS manages the operation of the TBF without TTCN intervention and releases the TBF automatically after all data blocks of the L3 message are transmitted |
|
MS-> SS |
G_L2_ACCESS_IND |
CHANNEL REQUEST |
RACH, TBF establishment with Establishment Cause = one phase packet access. |
|
SS |
G_CRLC_UL_TBF_Config_REQ |
Set up uplink TBF in RLC/MAC entity in SS |
|
|
SS -> MS |
G_L2_UNITDATA_REQ |
IMMEDIATE ASSIGNMENT |
Assign the uplink resources (uplink TBF) to MS. Polling bit and Starting Time are set |
|
MS -> SS |
G_RLC_ControlMsg_IND |
PACKET CONTROL ACKNOWLEDGEMENT |
|
|
SS |
G_CLLC_Assign_REQ |
Assign new TLLI |
|
|
MS -> SS |
G_LLC_UNITDATA_IND |
ATTACH COMPLETE |
MS uses the assigned uplink TBF to transmit the L3 message to SS, the SS manages the operation of the TBF without TTCN intervention and releases the TBF automatically according the countdown procedure |
|
SS |
G_CRLC_DeleteRLC_MAC_REQ |
Release resources in the SS for RLC/MAC emulation entity |
|
|
SS |
G_CLLC_DeleteLLE_REQ |
Release resources in the SS for LLC emulation entity |
|
|
SS |
G_CL1_DeleteChannel_REQ |
Release SS resources of channel combination 13 |
|
|
SS |
G_CL1_DeleteChannel_REQ |
Release SS resources of channel combination 5 |
|
|
SS |
G_CL1_DeleteCell_REQ |
6.10.2.7.1.2 Void
6.10.2.7.2 Cell change order within a TBF
6.10.2.7.2.1 Cell change order procedure in channel combinations 5 and 13
|
Direction |
ASP |
message |
Comments |
|---|---|---|---|
|
SS |
G_CL1_CreateCell_REQ |
||
|
SS |
G_CL1_CreateBasicPhyCh_REQ |
Create the physical channel combination 5 for FCCH+SCH+BCCH+CCCH+SDCCH/4(0..3)+SACCH/C4(0..3) |
|
|
SS |
G_CL1_CreateBasicPhyCh_REQ |
Create the physical channel combination 13 for PDTCH/F+PACCH/F+PTCCH/F |
|
|
SS -> MS |
G_L2_SYSINFO_REQ |
SYSTEM INFORMATION TYPE1, SYSTEM INFORMATION TYPE2, SYSTEM INFORMATION TYPE2quater, SYSTEM INFORMATION TYPE3, SYSTEM INFORMATION TYPE4, SYSTEM INFORMATION TYPE13 |
Broadcast system information messages: SI 1~4; SI 13 |
|
SS |
G_CRLC_CreateRLC_MAC_REQ |
Create RLC/MAC emulation entity |
|
|
SS |
G_CLLC_CreateLLE_REQ |
Create LLC emulation entity |
|
|
SS |
G_CLLC_Assign_REQ |
Assign TLLI, ciphering key and algorithm |
|
|
MS |
MS is GPRS attached, PDP context activated, then trigger MS to send two SNDCP PDU on LLC SAPI 3, each with 500 bytes user data. |
||
|
MS-> SS |
G_L2_ACCESS_IND |
CHANNEL REQUEST |
RACH, TBF establishment with Establishment Cause = one phase packet access. |
|
SS |
G_CRLC_UL_TBF_Config_REQ |
Set up uplink TBF in RLC/MAC entity in SS, this TBF is corresponding to what indicated in the next IMMEDIATE ASSIGNMENT. The USFRate is set to 5 USF per second. |
|
|
SS -> MS |
G_L2_UNITDATA_REQ |
IMMEDIATE ASSIGNMENT |
Assign the uplink resources (uplink TBF) to MS |
|
MS -> SS |
G_LLC_UNITDATA_IND |
User data on SAPI 3, the first SNDCP PDU |
The TBF shall not be in countdown process |
|
SS -> MS |
G_RLC_ControlMsg_REQ |
PACKET MEASUREMENT ORDER |
This is within the TBF established above, which is in the process handling the second SNDCP PDU REPORT_TYPE = 1 |
|
MS -> SS |
G_RLC_ControlMsg_IND |
PACKET MEASUREMENT REPORT |
MS sends the PACKET MEASUREMENT REPORT |
|
SS -> MS |
G_RLC_ControlMsg_REQ |
PACKET CELL CHANGE ORDER |
This is within the TBF established above |
|
what follows are in UTRAN cell, not present here |
6.10.2.7.2.2 Void
6.10.2.8 Generic configuration procedure for GSM ciphering mode control
|
Direction |
ASP |
message |
Comments |
|---|---|---|---|
|
. . . |
Other necessary configuration ASP’s |
||
|
SS |
G_CL1_CreateBasicPhyCh_REQ |
Create a dedicated physical channel, e.g. combination 1 with ciphering not started: This ASP download Kc and ciphering algorithm to the SS with startingCiph = 0 in cipherMode. If there is no authentication procedure before CIPHERING MODE COMMAND, the value of Kc in this ASP shall be the one generated in previous authentication procedure, otherwise the value of Kc shall be the one generated by forthcoming authentication procedure. |
|
|
. . . |
Any other signalling message sending/receiving or configuration ASP’s |
||
|
SS |
G_CL1_CipheringControl_REQ |
rcvCipherMode =’1′ , the SS starts ciphering on receiving |
|
|
SS |
G_CL1_CipheringControl_CNF |
||
|
SS -> MS |
G_L2_DATA_REQ |
CIPHERING MODE COMMAND |
Sent without ciphering |
|
SS |
Before this point both transmitting and receiving in the SS are not ciphered. |
||
|
MS -> SS |
G_L2_DATA_IND |
CIPHERING MODE COMPLETE |
After receiving this message the SS shall start ciphering on transmitting, The CIPHERING MODE COMPLETE is ciphered |
|
. . . |
Any signalling message or user data sending/receiving in ciphered mode |
6.10.2.9 L|H bits convention and bit padding in DL
6.10.2.9.1 GERAN DL RLC/MAC message bit padding
The length of a GPRS RLC/MAC control messages is an integer number of RLC/MAC control blocks. Padding bits are necessary to fill the message up to the desired length. The padding bits may be the ‘null’ string. Otherwise, the padding bits starts with bit ‘0’, followed by "spare padding". The padding sequence used for "spare padding" in the present document, is a repetition of octet ‘00101011’, starting on an octet boundary.
< padding bits > ::= { null | 0 < spare padding >
"<spare padding> ::= <spare L> {null | < spare padding>}"
In the TTCN a specific encoding variation – encoding rule 1 – is defined according to the rules described above. This shall be used in the definition of the message itself. No ‘padding bits’ field will be defined in the TTCN. The implementation shall ensure that after encoding the message contents defined in the TTCN, the remainder of the message shall be filled with ‘padding bits’.
6.10.2.9.2 GSM DL message spare padding
A number of GPRS information elements are defined in the rest octets of certain GSM DL messages, for instance, IA Rest Octets, SI 2quater Rest Octets, SI 3 Rest Octets, SI 4 Rest Octets, SI 13 Rest Octets, etc. These rest octets were filled in a repetition of bit padding ‘00101011’ or ‘2B’O, starting on an octet boundary to a certain length.
In the TTCN, a second encoding variation – encoding rule 2 – shall be used in the definition of the message itself, which shall be of a fixed length (always 23 octets). No "spare padding" field will be defined in the TTCN. The implementation shall ensure that after encoding the message contents defined in the TTCN, the remainder of the message, up to the defined fixed length, shall be filled with "spare padding".
6.10.2.9.3 L | H convention in rest octets of GSM DL messages
A number of GPRS information elements are defined in the rest octets of certain GSM DL messages. The special notations "L" and "H" are used to denote respectively the bit’s logical value corresponding to the padding spare bit for that position, and the other value. The actual value of the bit transmitted by SS therefore depends upon its position within the octet – this involves counting bits.
In the TTCN a third encoding variation – encoding rule 3 – is defined for this purpose. This encoding variation is applied to those specific TTCN Rest Octets definitions which contain the L|H convention.
6.10.2.9.4 Spare Bits
Where the IE definition of RLC/MAC blocks contains bits defined to be ‘spare bits’, these bits shall set to the value ‘0’ by the TTCN writers, according to the defined length indicator.
6.10.2.9.5 GSM System Information messages on SACCH
Certain GSM System Information messages, for instance, SI 5 and SI 6 are sent as a B4 frame on the SACCH. These messages are defined in 3GPP TS 44.006 [42], clause 8.8.3, to have a maximum of 19 octets.
In the TTCN a fourth encoding variation – encoding rule 4 – shall be used in the definition of the message itself. The implementation shall ensure that after encoding the message contents defined in the TTCN, the remainder of the message, up to the fixed length of 19 octets, shall be filled with "spare padding".
6.10.2.9.6 GSM Measurement Information messages on SACCH
The GSM Measurement Information message is sent as a Bter UI frame on the SACCH. This messages is defined in 3GPP TS 44.006 [42], clause 8.8.3 to have a maximum of 21 octets.
In the TTCN a fifth encoding variation – encoding rule 5 – shall be used in the definition of the message itself. The implementation shall ensure that after encoding the message contents defined in the TTCN, the remainder of the message, up to the fixed length of 21 octets, shall be filled with "spare padding".
Figure 6.10.2.9.6: The model of multi-RAT handover testing