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Chapter 5
Network Protocols
Eng. Ahmed Khaled

Main RR procedures:
Power control
Channel quality monitoring
Handover
Frequency hopping
Discontinuous transmission
Timing advance.
MS, BTS and BSC are
Concerned with
transmission

Power Control:
Enables power adaptation of MS and BTS.
Main reasons for power control:
Saving MS battery Power
Improve CIR.
Can be enabled or disabled.
Performed separately for uplink and DL.
Measurements on UL and DL are sent to BSC every 480 ms.
Measurements in terms of:
Signal strength in dBm.
Signal quality in BER.

Power Control:
Distance
Power Increase Step
MS Power (dBm)
Max. Transmitted Power
Distance
Upper Threshold
Lower Threshold
Power Control
Increase Command
Signal Strength
Measured at BTS

Handover Control:
Automatic switching of a call from one TCH to another.
Can be within the cell or between cells.
Reasons for intra-cell handover:
reduction of co-channel interference.
Maintenance activity
Handover occurs on TCH when call is in speech stage.
Only started if power control is not helpful. Unique feature of
mobile network.

Handover:
Handover types:
 Inter cell handover: Involves change of carrier and BTS.
Intra-cell handover: Involves change of carrier in same cell.
MS MS MS MS
BTS BTS BTS BTS
BSC BSC BSC
MSC MSC
1 2 3 4

Handover:
BSC
MSC-A
BSC
BSC
MSC-B
Inter-MSC HO
Intra-Cell HO
Inter-BSC HO
Intra-MSC HO
Intra-BSC HO

Handover:
Requirements for Handover
Execution speed
Reliability
• No excessive HO
• No delayed HO
• No early HO
Transparent to users (not aware)
Service-dependent (voice, data)

Handover:
Criteria for Handover
BSC receives measurement data from BTS and MS.
The MS measures DL:
Signal strength (dBm)
Signal quality (BER)
Signal strength of neighboring BTSs downlink
The BTS measures UL:
Signal strength received from MS.
Signal quality received from MS.
Distance between BTS and MS.

1
2
𝐍 𝐜
𝐍
Handling of Handover:
Reserved channel concept
Some channels are reserved for HO
New Calls
Handover

Handover:
N times retry
Multiple request for Handover
Handover queue
HO wait for a free channel.
Sub-rating algorithm
Full rate TCH is split into 2 half rate TCHs.

Intra-BSC (Inter-cell) HO:
Old BTS
New BTS
2
34
5
6
1
5
2
BSC

Inter-BSC (Intra-MSC) Handover:
MSC
New
BSC
Old
BSCOld BTS
New BTS
2
4
7
4
9
3
7
1
4
8
4
56
7

Inter-MSC Handover:
MSC-A
Old
BSC
MSC-B
New
BSC
1
5
99
4 3
5
8
852
5
8
6
7
New BTS
Old BTS
PSTN
GSM PLMN

Mobility Management (MM):
Main task of MM is to support mobility.
MM activities include:
Location update
Update HLR/VLR
TMSI re-allocation.
Authentication of MS.

Location Update in same MSC/VLR:
HLR
VLR
MSCBSC
1
2
3
4
2
3
4
BTS

Location Update with New MSC/VLR:
New
VLR
New
MSC
BSC
Old
VLR
HLR
4
2
3 4
Old
MSC
5
BTS
When MS enters into new LA, location update.
LA may belong to new MSC/VLR.

IMSI Attach:
BSC MSC / VLR
4
2 3
4
1
BTS

Mobile Originated Call:
BSC MSC / VLR
4
3
2
4 4 5
3
2
1
BTS
1

BSC
GMSCHLR
MSC
VLR
Local
Exchange
MSRN
PSTN
MSISDN
MSISDN
MSISDN
GSM PLMN
Telephone
BTSBTS
1
15
2
54
TMSI 11
7
8
8
10
11
9
8
11
8
9
10
6
Call Scenario:

PCH
RACH
AGCH
SDCCH
SDCCH
SDCCH
SDCCH
SDCCH
SDCCH
SDCCH
FACCH
FACCH
FACCH
FACCH
TCH
SDCCH
Paging Request
Immediate Assignment
Authentication Request
Cipher Mode Command
Setup
Assignment Command
Connect Acknowledge
Data
Channel Request
Paging Response
Auth. Response
Cipher Mode Comp.
Call Confirmed
Assignment Complete
Alert
BSS/MSC
Data
Connect
MS

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