Transcript Slide-8-GSM-Overview

Slide 8 –
Global System for Mobile
Communication
(GSM)
GSM Architecture
Base Station Subsystem(BSS)
BSS terdiri dari dua buah perangkat :
 Base Transceiver Station (BTS)
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BTS merupakan tranceiver yang mendefinisikan sebuah
sel dan menangani hubungan link radio dengan MS.
BTS terdiri dari perangkat pemancar dan penerima,
seperti antenna dan pemroses sinyal untuk sebuah
interface.
 Base Station Controller (BSC)
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BSC mengatur sumber radio untuk sebuah BTS atau lebih.
BSC menangani radio-channel setup, frequency hopping,
and handover intern BSC.
Network Sub-system (NSS)
NSS terdiri dari :
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Mobile Switching Center (MSC).
Home Location Register (HLR).
Visitor Location Register (VLR).
Authentication Center (AuC).
Equipment Identity Register (EIR).
Mobile Switching Center (MSC)
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Melakukan fungsi switching dasar
Sebagai penghubung antara satu jaringan GSM
dengan jaringan lainnya melalui Internetworking
Function (IWF)
Authentication Center (AuC)
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Berisi parameter authentikasi pelanggan untuk
mengakses jaringan GSM.
AuC mekanisme authentication.
Home Location Register (HLR)
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HLR berisi rekaman database permanen dari
pelanggandan merupakan database user yang
utama.
HLR juga berisi rekaman lengkap lokasi terkini
dari user.
Visitor Location Register (VLR)
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VLR berisi database smentara dari pelanggan, digunakan
untuk pelanggan lokal dan yang sedang melakukan
roaming.
VLR memiliki pertukaran data yang luas daripada HLR dan
diakses oleh MSC untuk setiap panggilan, dan MSC
dihubungkan dengan VLR.
Setiap MSC terhubung dengan sebuah VLR, tetapi satu VLR
dapat terhubung dengan beberapa MSC.
Equipment Identity Register
(EIR)
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EIR merupakan register penyimpan data seluruh
mobile stations
EIR berisi IMEIs (international Mobile Equipment
Identities), yang merupakan nomor seri perangkat +
tipe code tertentu.
Operation Sub-system (OSS)
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Operation and Maintenance Jaringan.
Pengaturan pelanggan dan tagihan.
Pengaturan Mobile Equipment.
Kanal Pada GSM (1)
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Struktur kanal pada GSM, terbagi menjadi dua, yaitu kanal
fisik dan kanal logik.
Kanal fisik berhubungan dengan kanal frekuensi radio dan
time slot, sedangkan kanal logik berhubungan dengan
informasi dan kontrol data pensinyalan.
Seperti yang telah dibahas pada pertemuan sebelumnya,
bahwa teknik multiplexing GSM menggunakan TDMA &
FDMA.
Kanal Pada GSM (2)
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FDMA membagi kanal menjadi 125 kanal, dimana 124 kanal
merupakan kanal komunikasi, dan 1 kanal untuk keperluan
pensinyalan.
Tiap kanal pada GSM memiliki lebar 200kHz, dimana setiap
kanal dibagi lagi menjadi 8 time slot, dengan setiap slot
memiliki durasi 576,9 µs.
Sehingga 8 slot memiliki durasi 4,615 ms.
MS (Mobile Station) States (1)
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The mobile station does not answer paging messages,
therefore there is no contact between the MS and the
network. The network does not get any information on where
the MS is. This state is considered as MS detached.
When the MS is turned on – or MS attached – it can be in two
states : MS Idle & MS Active.
MS (Mobile Station) States (2)
~ MS Idle
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While moving around - roaming - the mobile station listens to
the ”best” cell for paging messages.
The MS decides by itself which cell is the best one. This is
done by comparing own cell to neighboring cells.
If a neighboring cell is considered better, the MS will change
cells and, if necessary, inform the system about the new
Location Area (LA).
This is called location updating. In idle state the MS can
receive short messages or cell broadcast messages.
MS (Mobile Station) States (3)
~ MS Active
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MS is considered active (or busy) when there is a call (speech,
fax or data), or a call set up procedure, going on.
In this state the MS does not decide by itself if it is necessary
to change cell.
Based on measurements provided by the MS and the BTS, the
BSC makes the decision on change of cell. The decision
making is considered as locating, while the actual change of
cells is considered as handover.
In active state the MS can at the same time receive short
messages, but not cell broadcast messages.
Handover Between Cell, Controlled by
The Same BSC
1. BSC orders to the new BTS to activate a
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TCH (Traffic Channel).
BSC sends a message to the MS via the
old BTS containing information about the
frequency and time slot to change to,
and also what output power to use. This
information is sent over FACCH (Fast
Associated Control Channel).
MS tunes to the new frequency, and
transmits Handover (HO) access bursts in
the correct time slot.
When the new BTS detects the HO bursts
it sends information about timing
advance. This is sent on FACCH.
MS sends a Handover Complete message
to BSC via new BTS.
BSC tells the old BTS to release the old
TCH.
Handover Between Cell : The Different
BSC, Same MSC/VLR (1)
1. The serving (old) BSC sends a Handover
required message to the MSC together with
the identity of the target cell.
2. MSC knows which BSC that controls this BTS
and sends a Handover request to this BSC.
3. New BSC orders target BTS to activate a TCH.
4. New BSC sends a message to the MS via MSC,
old BSC and old BTS containing information
about the frequency and time slot to change
to, and what output power to use. This
information is sent over FACCH (Fast
Associated Control Channel).
5. MS tunes to the new frequency, and transmits
Handover (HO) access bursts in the correct
time slot.
6. When the new BTS detects the HO bursts it
sends information about timing advance. This
is sent on FACCH.
7. MS sends Handover Complete message to
MSC via new BSC.
8. The MSC sends an order to old BSC
previously to release the old TCH.
9. The old BSC tells the old BTS to release the
previously used TCH.
Handover Between Cell : The Different
MSC/VLR (1)
1. The serving (old) BSC sends a Handover
required message to the serving MSC, MSC–A,
together with the identity of the target cell.
2. MSC–A realizes that this cell belongs to another
MSC, MSC–B, and asks for help.
3. MSC–B allocates a handover number in order to
reroute the call. A Handover request is then
sent to the new BSC.
4. New BSC orders target BTS to activate a TCH.
5. MSC–B receives the information, and passes it
on to MSC–A together with the handover
number.
6. A link is set up to MSC–B, possibly via PSTN.
7. MSC–A sends a HO command to MS, via old BSC
containing information on which frequency and
time slot to use, and what output power to use.
This information is sent over FACCH (Fast
Associated Control Channel).
8. MS tunes to the new frequency, and transmits
Handover (HO) access bursts in the correct time
slot. The HO bursts are transmitted on FACCH.
9. When the new BTS detects the HO bursts it
sends information about timing advance.
This is sent on FACCH.
10. MS sends Handover Complete message to
old MSC via new BSC and new MSC/VLR.
11. A new path in the group switch in MSC–A is
established, and the call is switched
through.