Mobile station side
In idle mode, the mobile station listens to the BCCH and to the paging sub-channel for the paging group the mobile station belongs to it measures the radio propagation to connect with other cells. When the decision to change cells is made, the mobile station switches to the BCCH of the new cell. The broadcast information is then checked to verify the allowance to camp on this cell. If allowed, the cell change is confirmed, and the broadcast information is then treated for Mobility Management actions. Similarly, physical contexts are updated for example: Neighboring cells frequencies, thresholds Margins for some actions liken Handovers, etc.
Network side
System information broadcasting
Based on this information from SYSTEM INFORMATION TYPE 2 to 4 messages, and optionally TYPE 1, 2bis, 2ter 7 and 8 the mobile station is able to decide whether and how it may gain access to the system via the current cell. All these information are regularly broadcast by the network on the BCCH. The SYSTEM INFORMATION TYPE 2bis message shall be sent if and only if the EXT-IND bit in the Neighbor Cells Description IE in both the TYPE 2 and TYPE 2bis messages indicates that each IE only carries part of the BA. SYSTEM INFORMATION TYPE 2ter message shall be sent if and only if this is indicated in SYSTEM INFORMATION TYPE 3 message.
The information broadcast may be grouped in the following classes:
- Giving unique identification of the current network, location area and cell
- Used for candidate cell measurements for handover and cell selection procedures
- Describing the current control channel structure
- Controlling the random access channel utilization
- Defining different options supported within the cell
Paging:
network need to provide all valid layer 3 messages to all paging sub channels continuosly.
RR Connection establishment State:
(i) Initiated by Mobile Station or Immediate Assignment procedure
The purpose of the immediate assignment procedure is to establish an RR connection between the mobile station and the network. The immediate assignment procedure can only be initiated by the RR entity of the mobile station. Initiation is triggered by request from the MM sublayer to establish an RR connection or by the RR entity in response to a PAGING REQUEST message. On these kind of PAGING REQUEST
if access to the network is allowed the RR entity of the mobile station initiates the immediate assignment procedure otherwise, it rejects the request.
The request from the MM sublayer to establish an RR connection specifies an establishment cause.
Similarly, the request from the RR entity to establish a RR connection in response to a PAGING
REQUEST 1, 2 or 3 message specifies one of the establishment causes "answer to paging".
Permission to access the network
All SIM are members of one out of 10 access classes numbered 0 to 9.In addition, SIM cards may also be members of one or more out of 5 special access classes (access classes 11 to 15).The system info messages on BCCH broadcast the authorized access classes and special classes. This determines whether emergency calls are allowed with this SIM card or not.
If the establishment cause for the request of the MM sublayer is not "emergency call", access to the
Network is allowed if and only if the mobile station is a member of at least one authorized
Access class or Special access class.
If the establishment cause for the request of the MM sublayer is "emergency call", access to the network
Is allowed if and only if emergency calls are allowed to all mobile stations in the cell or the mobile station is a member of at least one authorized special access class
Initiation of the immediate assignment procedure
The RR entity of the mobile station initiates the immediate assignment procedure by scheduling the sending on the RACH and leaving idle mode. It sends maximum of M + 1 CHANNEL REQUEST messages on the RACH in a way such that
· the number of slots belonging to the mobile station's RACH between initiation of the immediate
assignment procedure and the first CHANNEL REQUEST message (excluding the slot containing the message itself) is a random value drawn randomly for each new initial assignment initiation with uniform probability distribution in the set {0, 1, ..., max (T,8) - 1}
· the number of slots belonging to the mobile station's RACH between two successive CHANNEL
REQUEST messages (excluding the slots containing the messages themselves) are a random value
drawn randomly for each new transmission with uniform probability distribution in the set {S,S + 1,
..., S +T - 1}
Here, T is the value of the parameter "Tx-integer" broadcast on the BCCH
M is the value of the parameter "max retrans" broadcast on the BCCH
S is a parameter depending on the CCCH configuration and on the value of Tx-integer as defined in table
After sending the first CHANNEL REQUEST message, the mobile station shall start listening to the BCCH. It shall also listen to the full downlink CCCH timeslot corresponding to its CCCH group.
Having sent M + 1 CHANNEL REQUEST messages, the RR entity of the mobile station starts timer T3126. At expiry of timer T3126, the immediate assignment procedure is aborted; if the immediate assignment procedure was triggered by a request from the MM sublayer, a random access failure is indicated to the MM sublayer.
Answer from the network
On receipt of a CHANNEL REQUEST message
The network may allocate a dedicated channel to the mobile station by sending an IMMEDIATE
ASSIGNMENT message or IMMEDIATE ASSIGNMENT EXTENDED message in unacknowledged mode
on the same CCCH timeslot on which it has received the CHANNEL REQUEST. The type of channel allocated (SDCCH or TCH; the channel mode shall be set to signaling only) is a network operator decision. Timer T3101 is then started on the network side.
There are two types of immediate assignment messages:
· IMMEDIATE ASSIGNMENT message, containing assignment information for one
Mobile station only;
· IMMEDIATE ASSIGNMENT EXTENDED message, containing assignment
information for two mobile stations at the same time.
The IMMEDIATE ASSIGNMENT or IMMEDIATE ASSIGNMENT EXTENDED message contains
· the description of the assigned channel
· the information field of the CHANNEL REQUEST message and the frame number of the frame in
which the CHANNEL REQUEST message was received
· the initial timing advance
· A starting time indication (optional)
If frequency hopping is applied, the mobile station uses the last CA received on the BCCH to decode the
Mobile allocation.
On receipt of an IMMEDIATE ASSIGNMENT or IMMEDIATE ASSIGNMENT EXTENDED message
Corresponding to one of its 3 last CHANNEL REQUEST messages, the mobile station stops T3126 (if running), stops sending CHANNEL REQUEST messages, switches to the assigned channels, sets the channel mode to signaling only and activates the assigned channels. It then establishes the main signaling link with an SABM containing an information field.
An IMMEDIATE ASSIGNMENT or IMMEDIATE ASSIGNMENT EXTENDED message may indicate a frequency change in progress, with a starting time and possibly alternative channel descriptions. In the case of the reception of an IMMEDIATE ASSIGNMENT EXTENDED message, or of an IMMEDIATE ASSIGNMENT message which contains only the description of a channel to be used after the starting time, the mobile station shall wait up to the starting time before accessing the channel. If the starting time has already elapsed, the mobile shall access the channel as an immediate reaction to the reception of the message .
If the message contains both the description of a channel to be used after the indicated time and of a channel to be used before, the mobile station accesses a channel as an immediate reaction to the reception of the message. If the moment the mobile station is ready to access is before the indicated time, the mobile station accesses the channels described for before the starting time. The mobile station then changes to the channel described for after the starting time at the indicated time. New parameters can be frequency list and MAIO. Other parameters describing the channel to be used before the starting time are taken from the description of the channel defined for use after the starting time. If the moment the mobile station is ready to access is after the starting time, the mobile station accesses the channel described for after the starting time. If frequency hopping is applied, the Mobile Station uses the last CA received on the BCCH.
Assignment rejection Procedure
If no channel is available for assignment, the network may send to the mobile station an IMMEDIATE
ASSIGNMENT REJECT message in unacknowledged mode on the same CCCH timeslot on which the
channel request message was received. This message contains the request reference and a wait indication.
On receipt of an IMMEDIATE ASSIGNMENT REJECT message corresponding to one of its 3 last CHANNEL REQUEST messages, the mobile station, stops sending CHANNEL REQUEST messages, starts timer T3122 with the indicated value, ("wait indication" information element), starts T3126 if it has not already been started, and listens to the downlink CCCH until T3126 expires. During this time, additional IMMEDIATE ASSIGNMENT REJECT messages are ignored, but any immediate assignment
corresponding to any other of its 3 last CHANNEL REQUEST messages make the mobile station follow the Immediate assignment procedure. If no such immediate assignment is received, the mobile station returns to CCCH idle mode (listening to its paging channel). The mobile station is not allowed to make a new attempt to establish a non emergency RR connection in the same cell until T3122 expires. Provided that an IMMEDIATE ASSIGNMENT REJECT message has not been received for an emergency RR connection attempt, the mobile station may attempt to establish an RR connection for an emergency call in the same cell before T3122 has expired. The Wait Indication IE (i.e. T3122) relates to the cell from which it was received.
After T3122 expiry, no CHANNEL REQUEST message shall be sent as a response to a page until a
PAGING REQUEST message for the mobile station is received.
Assignment completion
The immediate assignment procedure is terminated on the network side when the main signalling link is
established. Timer T3101 is stopped and the MM sublayer on the network side is informed that an RR
connection exists.
On the mobile station side, the procedure is terminated when the establishment of the main signalling link is
confirmed. The MM sublayer is informed that an RR connection exists.
Early classmark sending consists in the Mobile Station sending as early as possible after access a
CLASSMARK CHANGE message to provide the network with additional classmark information.
A Mobile Station which implements the ® Controlled Early Classmark Sending ¯ option shall perform the
early classmark sending if and only if explicitly accepted by the network, as indicated in the last reception
in the accessed cell of the SYSTEM INFORMATION TYPE 3 message.
A Mobile Station which implements one of the ® multiple band support ¯ option shall also implement the ®
Controlled Early Classmark Sending ¯ option.
A Mobile Station which implements the ® Controlled Early Classmark Sending ¯ option shall indicate it in
the classmark (ES IND bit).
