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LAYER 3 MESSAGES

PREPARED BY UMAIR

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LAYER 3 MESSAGES

Mobile station always need information fromthe network in order to be able to get and

provide services. Those information are

broadcast on the Radio Interface and are called

System Information. They are separated in

different types

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TYPES OF LAYER3 MESSAGES

SYSTEM TYPE INFO 1

SYSTEM TYPE INFO 2

SYSTEM TYPE INFO 3

SYSTEM TYPE INFO 4

SYSTEM TYPE INFO 5

SYSTEM TYPE INFO 6

SYSTEM TYPE INFO 7

SYSTEM TYPE INFO 8

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System information can be sent on 2 logical channels:

BCCH or SACCH. The logical

channel used depends on the mobile mode:

in idle mode, BCCH is in use,

in communication mode, SACCH is in use.

Those logical channels are used as following: System Information types 1 to 4 are broadcast on

BCCH,

System Information types 5 to 6 are broadcast on

SACCH, System Information types 7 and are broadcast on

extBCCH

(extBCCH is a logical channel used when BCCH does not

offer a sufficient capacity).

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SYSTEM TYPE INFO 1

WHEN HOPPING IS USED MS NEEDS TO KNOWON WHICH BAND AND WHAT FREQUIENCIESWITHIN THAT BAND ARE ON HOPPING THIS

DETAIL IS PRESENT IN SYSTEM TYPE INFO 1 IT ALSO TELL ABOUT RACH CONTROL

PARAMETER

cellBarred: indicates if the cell is barred or not emergencyCallRestricted: restricts or allows

emergency calls in a cell

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SYSTEM TYPE 1

callReestablishment: indicates if the call re-

establishment is allowed or not,

accessClassCongestion: forbids some

supplementary access classes in a congested

cell

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SYSTEM TYPE INFO 2

The System Information Type 2 message consists of the

DoubleBA list, which defines the BCCH frequencies, used in

the neighboring cells. The MS needs this information to

monitor the system information in neighboring cells. In

addition, the MS uses this frequency list when measuring thesignal strength of the neighboring cells. The Double BA list

provides the MS with the different frequencies on which to

measure, depending on whether the MS is in idle or active

mode. In active mode, the

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SYSTEM TYPE INFO 2

MS should measure on a reduced number of frequencies in order

to improve the accuracy of the measurements. In idle mode, the

MS should measure on a larger number of frequencies, so thatthe

time required for the MS to access the network after power on is

reduced. The MS is also informed which PLMNs it may use.

In addition to System Information Type 2, it is possible to have

System Information Type 2 Bis and System Information Type 2

Ter, depending on the size of the BA list. If it is not possible to

fit the BA list into the first message, then the second (Type 2

Bis) will be used. There may be a large number of frequencies

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SYSTEM TYPE INFO 2

if Multiband Operation is in use, then the frequencies

from other bands will be included in the Type 2 Ter message.

System Information Type 2 Bis/Ter is optional

it tells the MS which Network Color

Codes (NCC) on the BCCH carriers it

is allowed to monitor when in this cell.

ALSO GIVE INFO ABOUT RACH CONTROL PARAMETER

SAME AS TYPE I

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SYSTEM TYPE INFO 3

The System Information Type 3 contains information

on the

identity of the current LA and cell identity. A change

means that the MS must update the network. It also gives info about control channel decription,cell

option,cell selection parameter

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Control channel description

IMSIAttachDetach: allows or not the cell to apply IMSI attach and

detach procedures,

noOfBlocksForAccessGrant: number of blocks reserved for

access grant

total number of CCCH channels used.

transmission period of Paging Request messages,

timeout value for periodic updating (in decihours).

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Cell option

uplinkPowerControl: indicates if power control

is enabled or not for the MS (UL),

dtxMode: indicates the uplink DTX mode use

(mandatory/not mandatory/forbidden),

radioLinkTimeOut: threshold for the radio link

failure declaration.

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Cell selection parameter

The permitted minimum received signal

strength for the MS to access the system.

when accessing the system.

Maximum transmission power an MS may use

when accessing the system.

ALSO GIVE INFO ABOUT RACH CONTROLPARAMETER

SAME AS TYPE I

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System type info 4

The operator can broadcast text messages to all

idle MSs in acell. Each MS knows that if the cell

broadcast function is used,it must listen to this

channel at certain time intervals. However,the MSneeds to know what frequency carries the CBCH.

Thisfrequency is provided in System Information

Type 4. The LAI,

the Cell Selection parameters same as 3 and the

RACH control parameters same as 1

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System type info 5

When the MS is in ACTIVE mode, an SACCH is activated. The

MS sends measurement reports on the up-link and the network

sends output power and TA for the MS on the down-link. In

addition, the MS receives information about the BCCH carrier

in each neighboring cell on the SACCH. The frequencies in the

neighboring cells description may differ from those sent in System Information Type 2.

In addition to System Information Type 5, it is possible to have

System Information Type 5 Bis and System Information Type 5

Ter, depending on the size of the BA list. If it is not possible to

fit the BA list into the first message, the second (Type 5 Bis) will

be used. There may be a large number of frequencies in the lists

if Multiband Operation is in use. The frequencies from other

bands will then be included in the Type 5 Ter message.

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System type info 6

When in active mode, the MS needs to knowif the LAI changes.

If so, it must perform location updating when

the call isreleased. The MS may changebetween cells (within the locationarea) whereRLINKT or DTX conditions differ. ThereforeCellOptions parameters must be sent to theMS. The PLMN permitted is also included inType 6 information

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System type info 6

Also have

Location Area Identity

Cell Identity Cell Options (same as type 3)

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System type info 7&7

System Information Types 7 and 8 contain Cell

Reselect

parameters. Their function is to supplement

System InformationType 4.

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The end