03 mn1788eu08mn 0001 air interface um

7/27/2019 03 Mn1788eu08mn 0001 Air Interface Um

http://slidepdf.com/reader/full/03-mn1788eu08mn-0001-air-interface-um 1/98

Air Interface Um Siemens

MN1788EU08MN_00011

Contents

1 Layer 1 of Air Interface - Um 3

1.1 Physics of Layer 1 (Um) 6

1.2 Logic of Layer 1 (Um) 34

2 Layer 2 - Um-Interface 533 Layer 3 - Um 61

3.1 Radio Resource- , Mobility- , Connection Management 62

3.2 Formatting Rules 74

4 Call Sequences on Um 79

4.1 Complete Sequences 80

Air Interface Um



Siemens Air Interface Um

MN1788EU08MN_00012




MN1788EU08MN_00013

1 Layer 1 of Air Interface - Um




MN1788EU08MN_00014

The MS is linked to the fixed PLMN structure via a radio link. The air or radiointerface Um describes the radio link function.

The MS/BSS interface must ensure:

use of the same standard interface by the MS and terminal equipment (TE)

use of MSs from different manufacturers in the whole system area of the GSMnetwork

connection with terminal equipment using the same identifiers and codesindependent of the respective location of the unit

The transmission of speech, data and signaling is carried out on the air interface Umvia radio channels (RFCs). The RFCs form layer 1 of the GSM system air interface.Layer 1 (Um) is described in GSM-Rec. 04.04.




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Layer 3

CC SS SMS

CM MM RR

Layer 2

Layer 1

Logik

Physik

Fig. 1 Layer 1 - 3 of the air interface Um




MN1788EU08MN_00016

1.1 Physics of Layer 1 (Um)

Speech and data transmission on the air interface Um is carried out via the physicalchannels.

A physical channel is defined by a specific carrier pair (RFC = Radio FrequencyChannel) in the UL and DL and the number of the time slot in the TDMA frame. Layer 1 (physical Layer : GSM 04.04) is a physical bi-directional point to point connection inmultiframe mode.

Layer 1 communicates with layer 3 directly according to channel management andmeasurement control. The physical layer will offer layer 2 appropriate channels byusage of the following functions :

l Burst transmission

l Error correction and -detection

l Supervision of RSS Link Control

Furthermore the layer 1 protocol defines the mobile station's search for a suitableBCCH and the seizure of DCCH through the MS (after allocation by the base station)




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RFC

174

RFC

1

RFC

2

7

6

5

4

3

2

1

RFC

3

0

TDMA

UL

FDMA

7

6

5

4

3

2

1

RFC

3

0

7

6

5

4

3

2

1

RFC

2

0

RFC

1

RFC

174

TDMA

FDMA

DL

Fig. 2 Physical channel in the FDMA and TDMA frame




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1.1.1 The TDMA Frame

A TDMA frame is divided into 8 time slots (= TS). The whole TDMA frame lasts4.615 ms, an individual time slot 0.577 ms.

A physical channel is assigned exactly one time slot TS in the TDMA frame. Eachsubscriber receives a time slot and sends all 8 time slots1 once. Transmission is notallowed outside the allocated time slots TS (i.e. after the TS has expired) so other physical channels are not exposed to interference.

1 With full rate transmission; with half rate transmission every 16 time slots; HSCSD and GPRS are not yet taken into

consideration




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TDMA-frame

4,615 ms

0 1 2 3 4 5 6 7

0,577 ms

0 1 26 7

Fig. 3 Assignment / repeat of a TDMA frame




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1.1.2 Burst / Normal Burst

Sending the information in the individual time slot of 0.577 ms with a permanentlydefined bit sequence is called a burst . The burst is realized by the MS by switchingon, transmitting briefly and switching off the transmitter again.




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Power

Time

28 ms

542,80 ms

28 ms

Fig. 4 Time pattern of the resulting transmit power of a burst2

2 Note: the duration of a time slot is 577 ms according to the definition. These 577 ms are not given in descriptions of the

transmit power of a burst and often irritate readers of literature on GSM. The time domain of 542.8 ms shown in fig. 8 and 9(corresponding with 147 bit, also known as „useful part“) is the range where transmit power is required at a constant powerlevel almost as a information transmission platform. Together with the time ranges from the flanks (increase/decrease of

power) of a maximum of 28 ms each this gives 598.8 ms and is thus slightly longer than the duration of the accompanying timeslot. The two 28 ms are however only time maximum limits for the flanks and interference from burst of successive time slots.They are reliable when the power is appropriately low so the duration of the technically realized burst coincides with thedefined duration of a time slot in the 1st approach.




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With base stations the dynamic range is 70 dB, with low power (mobile

phone: 2.5 W) 36 dB. The set tolerance masks for transmitting a burst from a BTSEare shown in the following diagram.




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Time (ms)

Power (dB)

useful part147 bits

10 8 10 T0 10 8 10

40,5

-0,5

-6

-30

-70

0

Fig. 5 Tolerance masks of the TDMA burst




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Time structure of the time frame / bit sequence

A time slot is defined at a time frame of 577ms (to be precise: 576 12/13 ms @ 576.923

ms). This time frame is divided into 156.25 bit. This means an individual bit has aduration of 3.6923 ms.

The 156.25 bits are used as follows:

l 142 bits for information transmission,

l 3 bits each as tail bits (TB) for edge limitation of the time slots. They are alsoused as protection zones if a neighboring channel happens to interfere with thefirst or lasts bits.

l 8.25 bits as a guard period (GP) (exception: the GP for access burst is 68.25 bitslong) for collecting variable run or reception times (determined by the distance

BTSE « MS).




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Burst

. . . 7 0 1 2 3 4 5 6 7 0 1 . . .

TB

3142 “ Information“

TB

3

GP

8,25

Fig. 6 Breaking down a time slot into bits




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Realization of information transmission in the burst

As a rule 142 bits of information transmission are realized in a burst presented as "1"

or "0" as indicated below. They are in the time middle of the burst transmission in the"useful part". The two 3 tail bits (TB) on the edge of the information section providedas security zones are realized as constant transmission of "0".

No information is transmitted in the guard period (GP).

There are 5 different types of burst

l Normal burst

l Frequency correction burst

l Synchronization burst

l Access burstl Dummy burst

Each of these bursts has a different configuration and has a particular purpose.

The normal burst

It contains

l 2 x 3 bits as tail bits (TB);

l

2 x 57 encrypted data bits which carry the actual informationl 2 x 1 bit as a "stealing flag" which tell the receiver that data transmission is being

interrupted briefly and signaling data is being transmitted instead of useful data (or vice versa).

l 26 bits for synchronizing and problem detection (training sequence) which allow both the BS and the MS to synchronize themselves to a burst and allocate thedata bits exactly. Distorted or incomplete received signals can thus bereconstructed.

Now that the contents of the most important burst has been described down to the bitlevel, how information transmission is realized at the level of individual bits in the

burst now has to be described. This means: How is the "0" or "1" presented exactlyon the radio path?




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TB Encrypted Bits S Training Sequence S Encrypted Bits TB

3 57 1 26 1 57 3

Fig. 7 Normal burst




MN1788EU08MN_000118

GMSK - Gaussian Minimum Shift Keying

The information to be transmitted consisting of a sequence of binary data (bit

sequence) must be modulated on an information carrier with a specific rate (bit rate).The receiver must then be able to remove them from this carrier. To obtain the bestpossible bandwidth utilization taking the minimum requirements for transmissionquality into consideration, a frequency modulation method was chosen for theGSM system. It is known as GMSK (Gaussian Minimum Shift Keying).

In principle the bandwidth of a radio channel (RFC) of 200 kHz varies here aroundthe center of the bandwidth (carrier frequency ft) with a maximum frequency

displacement Df = ± 67.7 kHz3 .

MSK - Minimum Shift Keying

MSK is a frequency shifting modulation process which involves the information in theinstantaneous frequency of the HF signal. This process stands out because of thecontinuous phase4 processing of the modulation signal resulting in excellentbandwidth utilization. The binary signal is modulated5 on the carrier using a

modulation index h = Df/f mod = 0.5. The instantaneous frequency of the HF signalchanges with the applied modulation data. When there is a "1", the carrier frequency

f t is increased by Df, when there is a "0" decreased by Df. With a modulation index of

0.5 Df corresponds with the half modulation frequency f mod.

With MSK the phase angle j of the carrier is changed linearly and continually duringthe bit duration T. It is changed by +90° for a logical "1" at the modulator input and by-90° for a "0". The frequency of the HF signal can be seen in the context of the phaserelationship. It is also obtained from the trajectory of the phase path or the phasepath is obtained from the integral of the frequency path.

Df can also be calculated from bit duration T and the change in the phase relationship

(Dj).

Df = (Dj/ Dt) / 2p;

with Dj = p/2 (90°) and Dt = T = 3.6923 ms hence:

Df = 1/(4T) = 1/(4*3.6923ms) = 67.7 kHz

3

Df = 1/(4T) applies; T = duration of a bit = 3.6923 ms4 i.e. there is no phase jittering

5 Df = carrier deviation; fmod = modulation frequency; fmod < 1/2 bit rate fbit




MN1788EU08MN_000119

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MSK Modulation

Phase response

Binary

signal

Frequency

response

Phase

+180°

+90°

t

-90°

-180°

1

0

f f

f

f

f

Fig. 8 Frequency and phase response with the MSK modulation process




MN1788EU08MN_000120

GMSK

Reducing the bandwidth required for MSK can be achieved by prefiltering the data

signal. The "increments" of the data (0 « 1) and thus also frequencies or unsteadiness of the phase path result in a comparably wide spectrum. To reduce thebandwidth requirement by means of improved attenuation of the side bands a low-pass prefilter with the pass through characteristic of a Gaussian bell-shaped curve isused. The filter used with bandwidth B6 has the following impulse answer (Rec.05.04):

H t T e with B T

H f e

t T

B f

( ) / * / *

( )

/

(ln / )*

= =

=

-

-

1 2 2 22 2 2

2 2

2

2 2

P P PI I I

The data signals Gaussian filtered here have "softer" transitions thus affecting the

phase path. A frequency or phase change without jumps (continuous) results.

60.3 was chosen as a standardized filter bandwith for the Gauss filter, i.e. bandwidth B * bit duration T º 0.3; given B = 81.25

kHz




MN1788EU08MN_000121




MN1788EU08MN_000122

1.1.3 Time Organization (Framing)

The transmission of the control and user information (speech/data) takes place inphysical channels. A time slot is available in the TDMA frame every 4.615 ms. Theinformation is transmitted according to specific time schemas, i.e. certain contentsare repeated at specific time intervals. This process, i.e. the periodical repeat of theTDMA frame is called "framing".




MN1788EU08MN_000123

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RFC

1

RFC

2

7

6

5

4

3

2

1

RFC

3

0

TDMA

Frame

FDMA

Time

t

Frequency

0

1

2

3

45

6

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46

47

48

49

50

0

1

2

3

4

5

6

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24

25

BCCH-

Multiframe

TCH-

Multiframe

RFC

174

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Fig. 9 Physical channels / traffic and control channel multiframe




MN1788EU08MN_000124

Multiframe

TDMA frames belonging together in a first framing level are called multiframes.

There are 26 TDMA frames in a user channel7

multiframe, in a control or signaling channel multiframe there are 51 TDMA frames. The control channelmultiframes are transmitted as a rule in time slot 0 of one of the radio channels(RFCs) from a BTSE, the remaining time slots are available for user channelmultiframes.

7Note: Not only subscriber information (speech/data) can be transmitted in a „traffic channel“. If the signaling requirement

increases, signaling can also be transmitted via a traffic channel. A change between subscriber information and signaling isindicated by the so-called „stealing flags“ in the normal burst.




MN1788EU08MN_000125

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0 1 2 49 50

0 1 2 3 4 5 6 7

8 Time slot =1 TDMA frame

4,615 ms

1 Time slot

BURST = Contents of a time slot

156,25 bit = 576,88 ms

(1 bit = 3,692 ms)

0 1 2 24 25

1 Multiframe for Speech/Data 2)

26 TDMA frame = 120 ms

1) Signaling channels

2) User channels andassociated signalingchannels

Time organization of the air interface

1 Multiframe for signaling 1)

51 TDMA frame = 235,38 ms

Fig. 10 Multiframe




MN1788EU08MN_000126

The multiframe for user information (full or half rate transmission) will be used at thispoint as an example of multiframe time organization.

The diagram shows the periodical repeat of the fixed structure of certain "logical

contents" for a user channel with half and full rate transmission. All 26 TDMA framesrepeat specific contents. This is necessary because not only user information (data,speech) is transmitted in the traffic channel connection (called TCH here) but alsofurther specific signaling information (SACCH) has to be transmitted repeatedly atfixed intervals in a traffic channel multiframe. The information (user informationsignaling) is transmitted between MS and BTS as burst in “physical channels“.

To differentiate the contents a division into "logical" channels is useful. These "logicalchannels" specify therefor certain contents of the transmission over the air interface.In particularly for signaling different contents and therefor "logical channels" arerelevant. They are repeated in the signaling channel multiframe every 51 TDMA

frames.




MN1788EU08MN_000127

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26 TDMA frame 120 ms

A full rate TCH

T/t TDMA frame for TCH

A/a = TDMA frame for SACCH/T

Two full rate TCH

UPLINK / DOWNLINK: Traffic Channel (TCH)

T T T T T T T T T T T T A T T T T T T T T T T T T -

T t T t T A T t T at T tt T t T t T t t T t T t T

Fig. 11 Multiframe for a user channel




MN1788EU08MN_000128

Superframe / Hyperframe

The data packets from the time slots are compiled in even higher frame structures in

addition to this first framing level of the merging of the TDMA frames to multiframes.These are called superframes and hyperframes.

A superframe comprises 26 x 51 = 1326 frames and is thus 6.12 s long. Thesuperframe is the smallest common multiple of traffic channel multiframes (26frames) and control or signaling channel multiframes (51 frames). The time window of a superframe is the shortest cycle in which the organization of all channels isrepeated. Some characteristics of the channel organization are excluded from thisrepeat. These are contained in the hyperframe.

The hyperframe is the numbering period. It comprises 2048 superframes and is thusexactly 12,533.760 s or 3 h 28 min 56.76 s long. It is a multiple of all cycles described

up to now and determines all transmission cycles or periods on the air interface inpractice.




MN1788EU08MN_000129

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Hyperframe = 2048 Superframe

Superframe = 26 x 51 (Multi-) Frames

TCH Multiframe

TDMA Frame

BCH Multiframe

0 1 3 24 25 0 1 2 3 4 49 50

0 1 2 3 4 5 6 7

2

Fig. 12 Time organization: multiframe, superframe and hyperframe




MN1788EU08MN_000130

1.1.4 Adaptive Frame Alignment

Adaptive frame alignment is the time condition between uplink (UL) and downlink(DL). The TDMA frames (UL) running from the mobile station (MS) to the base station(BS) or especially the transmission and reception station (BTSE) are delayed by 3time slots (burst periods) compared with the (DL) TDMA frame running in theopposite direction. The BTSE sets the frame (master), the MS has to adapt itself tothe presetting.

The delay of 3 time slots (= 1.73 ms) is GSM-defined. This GSM convention is set upin such a way that the numbering of the time slots can be identical both in the UL andthe DL direction.

The time delay allows the mobile station to avoid sending and receiving at the same

time. This means substantially simpler technical implementation as the MS receiver does not have to be protected against the transmitter from the same MS ("signalisolation"). The so-called "combining" of antennas is thus not necessary.

Timing advance

There is a problem, however, when implementing this convention. If the distancebetween the BTSE and the MS is greater, the delay due to the run time of the signalsmust be taken into consideration. Even at the speed of light (3 x 108 m/s) the radiosignals also require a specific time to bridge the path between the BTSE and the MS.With a maximum cell radius (GSM900) of approx. 35 km this means a delay of

approx. 0.1 ms for the path BTSE - MS or of approx. 0.2 ms for a "round path". Thisdelay in the run time must be taken into consideration when the signal is sent fromthe MS because it is absolutely necessary that the BTSE receives the signals(bursts) from the different MS in the correct time range. Bursts can otherwise overlaptime slots from neighboring time slots and thus reduce the transmission qualitysubstantially or even lead to a communication breakdown.

This problem can be solved by the MS transmitting its signals earlier andcompensating the run time delay. This compensation or its amount is called the"timing advance" (TA). The exact relocation between DL and UL from the viewpointof the MS is 3 time slots minus the timing advance, i.e.: 1.73 ms - TA.

The duration of the timing advance is measured by the BTSE and transferred to theMS. This takes it into consideration within the framework of adaptive frame alignmentand signals the total relocation (1.73 ms - TA) to the MS so the MS can take it intoconsideration when sending its bursts.




MN1788EU08MN_000131

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Mobile

station

(MS)

Information for MS on the “Timing Advance“

Transmitter

Receiver

Dt = 3 Time slots

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

2 x Run time (TA)

BS transmission/receive station (BTS)

Fig. 13 Adaptive frame alignment




MN1788EU08MN_000132

1.1.5 Frequency Hopping

Frequency hopping means that RFC physical channels8, therefore the transmitchannel and consequently the transmit frequency are changed to a set algorithm.The time slot is not changed. The logic behind frequency hopping is to guarantee thatall channels have the same high degree of transmission quality by dividing possibleinterference occurring in only one RFC over all available channels.

Frequency hopping is used to reduce or evenly distribute signal losses. These can becaused by screening of an MS in a vehicle or due to multipath propagation (directsignal + on trees, houses, mountains,... reflected signals) as a result of negativeinterference.

As the local occurrence of these signal losses is directly dependent on the wave

length of the radio signal (approx. 33 cm at 900 MHz), changing the transmissionfrequency will also lead to a change in the radio wave propagation. This allows greattransmission losses to be minimized.

As well as reducing interference, frequency hopping also improves protection againsteavesdropping.

The BTSE controls optional frequency hopping. As the MS also has to carry outthese the BTSE also transmits the frequency hopping algorithm via a BCCH. ThisBCCH is therefore not affected by the frequency hopping.

8The exception is the channels of the RFCs on which the BCCH is sent




MN1788EU08MN_000133

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Frame 0 Frame 1 Frame 2 Frame 3 Frame 4 Frame 5TCH

RFC 1

RFC 2

RFC 3

RFC 4

RFC 5

TDMA Frame

Fig. 14 An example of frequency hopping




MN1788EU08MN_000134

1.2 Logic of Layer 1 (Um)

1.2.1 Logical Types - an Overview

A multitude (for signaling in particular) of different "logical channels" or "logicalchannel types" is used in the GSM system for transmission via the air interface.

These logical types:

l traffic channels

l signaling channels




MN1788EU08MN_000135

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CHANNELS

UL

+DL

UL+

DL

DL DL UL

UL + DL

TRAFFICCHANNELS

SIGNALINGCHANNELS

BROADCASTCONTROL

CHANNLES

DEDICATEDCONTROL

CHANNLESFULLRATE

HALFRATE

COMMONCONTROL

CHANNLES

TCH/F TCH/H BCCH FCCH SCH PCH NCH AGCH RACH SACCH SDCCH FACCH

Fig. 15 Hierarchy of the logical channels




MN1788EU08MN_000136

1.2.2 Traffic Channels

Traffic channels TCH

The task of the traffic channels is to transmit coded speech and data information fromthe mobile subscriber.

Two general forms of a traffic channels are defined:

a) Full rate traffic channels (TCH / F)

This channel transmits speech on the air interface Um at a transmission rate of

13 kbit/s (TCH / FS) or data at 9.6 kbit/s (TCH / F9.6), 4.8 kbit/s (TCH / F4.8) or £2.4 kbit/s (TCH / F2.4).

b) Half rate traffic channels (TCH / H)

Speech is transmitted at 6.5 kbit/s (TCH / HS), data is transmitted at 4.8 kbit/s

(TCH / H4.8) or £ 2.4 kbit/s (TCH / H2.4).

1.2.3 Signaling Channels

The signaling channels are organized into 3 types according to their tasks:l Broadcast control channels: BCCH

l Common control channels: CCCH

l Dedicated control channels: DCCH




MN1788EU08MN_000137

Broadcast control channels BCCH

The broadcast control channels BCCH are used for synchronizing and transmitting

the cell-specific data from the BTSE to the MS. They only work in downlink (DL)direction, i.e. from the BS in the direction of the MS.

There are the following according to tasks:

l Frequency correction channel FCCH:

allows exact frequency matching for MS

l Synchronization channel SCH:

after frequency synchronization (by the FCCH) the MS receives further information

via the SCH in order to continue with the check-in procedure. The informationcontains the BSIC and the current TDMA frame number

l Broadcast control channel BCCH:

contains further information which the MS requires as a reference to the cell (e.g.:channel combination, frequency hopping sequence, cell identification CGI)

Common control channels CCCH

The common control channels CCCH are used to control access to the BTSE or the

MS. They are unidirectional channels, i.e. they work in either downlink (DL) or uplink(UL) direction

There are the following according to tasks:

l Paging channel PCH:

used (DL) by the BTSE to call the MS

l Notification Channel NCH:

used (only DL) to notify mobile stations of voice group and voice broadcast calls.

l Random access channel RACH:

used by the MS to request a signaling channel (UL) from the network or to react toa PCH.

l Access grant channel AGCH:

assignment of a signaling channel by the BTSE (network) for the MS (DL).




MN1788EU08MN_000138

Dedicated control channels DCCH

The group of dedicated control channels DCCH also comprises 3 channels:

l Stand alone dedicated control channel SDCCH:

Bi-directional and used for call setup. Authentication and other main signalingfunctions takes place here. The MS is assigned a specific TCH with the help of the SDCCH.

l Slow associated control channel SACCH:

always coupled to an SDCCH or with a TCH. Signaling information (control andmeasuring parameters) is exchanged between the MS and BTSE via theSACCH.

BS: transmits network-specific information using SACCH to keep

the MS up to date on any changes in the cell parameters.Furthermore the control commands for timing advance andpower control are transmitted by the BS to the MS via theSACCH.

MS: transmits measuring results (e.g. receive level) to the BS tosupport them in decisions on the handover. It also informs theBS of the current values of transmission power and timingadvance. This function is known as a measurement report.

l Fast associated control channel) FACCH:activated when the signaling requirement increases in certain situations (e.g.during a handover). The FACCH is transmitted instead of a TCH. The "stealingbits" in the TCH indicate the channel change.




MN1788EU08MN_000139

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MN1788EU08MN_000140

1.2.4 Burst Types

As previously described transmission of the information from an individual time slot with a permanently defined bit sequence is called a burst . There are 5 different typesof bursts:

l Normal burst

l Frequency correction burst

l Synchronization burst

l Access burst

l Dummy burst

Normal burst

The normal burst contains information in traffic and control channels and is structuredas following:

l 2 x 3 bits as tail bits (TB) for edge limitation of the time slot.

l 2 x 57 encrypted bits which carry the actual information / data.

l 2 x 1 bit as a "stealing flag" which tells the receiver that the user data transmissionis interrupted briefly and signaling data is transmitted instead of the user data (or vice versa).

l 26 bits for synchronizing and fault detection (training sequence) allow both theBS and the MS to synchronize itself to a burst and thus assign the data bitsexactly. There are 8 various training sequences in the GSM with a permanentlydefined bit pattern allowing the bit sequence actually received to be compared withthe known bit sequence. This allows distorted or incomplete received signals9 tobe reconstructed.

l 8.25 bits guard period (GP) for collecting run times and reception times

(determined by the distance BTSE « MS).

9Due to multipath propagation, Doppler effect




MN1788EU08MN_000141

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TB Information S Training Sequence S Information TB GP

148 bit = 546,12 ms (+8,25 bit = 30,44 ms )

3 57 1 26 1 57 3 8,25 bit

Fig. 16 Normal burst




MN1788EU08MN_000142

Frequency correction burst

The frequency correction burst is transmitted from the BTS for frequency

synchronization. The bit sequence of the fixed bits corresponds with an unmodulatedcarrier, i.e. a pure sine wave, so the MS can synchronize itself to the presetfrequency. The repeat of frequency correction bursts is also known as the frequencycorrection channel (FCCH).

The frequency correction burst consists of:

l 2 x 3 bit tail bits (TB);

l 142 bit as fixed bits (sine wave10) for frequency synchronization;

l 8.25 bit guard period (GP);

10To be more precise: the fixed bits (142 x signal „0“) lead via this modulation, to a sinusoidal signal for this period with a

frequency being 67,7 kHz above the carrier central frequency




MN1788EU08MN_000143

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TB fixed Bits TB GP

3 142 3 8,25 bits

Fig. 17 Frequency correction burst




MN1788EU08MN_000144

Synchronization burst

The MS receives the first information on the BS from the synchronization burst

allowing it to synchronize time on the base station. The burst contains a longtraining sequence, the TDMA number and the identity code of the BS, BSIC11. TheTDMA frame number is required as one of the parameters for encryption. Thesynchronization burst is transmitted together with the frequency correction burst inthe TDMA time slot zero. The repeat of synchronization bursts is calledsynchronization channel.

The synchronization burst consists of:

l 2 x 3 bit tail bits (TB);

l 2 x 39 bit which contain the TDMA frame number and the identity code of the BS(BSIC);

l 64 bit training sequence for time synchronization and fault detection;


11BSIC ( Base transceiver Station Identity Code): Identity code of the BTS allowing the MS to distinguish between different

BTS; it consists of 6 characters: 3 characters for the NCC (Network Color Code = PLMN identity) and 3 characters for the BCC(Base Color Code) which allows different RFCs with the same frequency in neighboring clusters to be distinguished.




MN1788EU08MN_000145

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TB Information Training Sequence Information TB GP

3 39 64 39 3 8,25 bits

Fig. 18 Synchronization burst




MN1788EU08MN_000146

Access burst

The access burst is used for the MS contact setup with the BTSE. It is characterized

by a long protection time (GP = 68.25 bits or 252 ms) which takes the signal runtime12 from MS to BTSE into consideration. The MS does not know the distance tothe BTSE first of all and therefore does not know how the transmission has to bestaggered (moved forward).

The access burst consists of:

l 8 + 3 bit tail bits (TB);

l 41 bit synchronization sequence;

l 36 bit information bits;


Dummy burst

The dummy burst is sometimes sent as padding if there is no other information. Itdoes not contain any information but has the same format as the normal burst.

12Note: The length of the access burst is decisive for the maximum cell size of a GSM900 cell. When a contact is setup with an

MS, the 68.25 bits with a duration of 252 ms are sufficient as a security distance for 3 x 108 m/s x 252 ms = 75.6 km. The cell

radius must therefore be less than 37.8 km taking the way BTSE ® MS ® BTSE into consideration




MN1788EU08MN_000147

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TB Synchro.- Sequence Information TB GP

8 41 36 3 68,25 bits

Fig. 19 Access burst




MN1788EU08MN_000148

1.2.5 Multiframe, Channel Combination

The description of the multiframe mentioned that there was only one possibility of arranging the logical channels in multiframes. Moreover there are 7 differentcombinations (channel combinations) for arranging logical channels in multiframes. Inthe channel combinations13 listed below RACH, PCH and AGCH are combined inCCCHs as they all involve the allocation of a channel to a subscriber:

I) TCH/F + FACCH/F + SACCH/F

II) TCH/H(0,1) + FACCH/H(0,1) + SACCH/H(0,1)

III) TCH/H(0) + FACCH/H(0) + SACCH/H(0) +

TCH/H(1) + FACCH/H(1) + SACCH/H(1)

IV) FCCH + SCH + CCCH + BCCHV) FCCH + SCH + CCCH + BCCH + SDCCH/4 + SACCH/4

VI) CCCH + BCCH

VII) SDCCH/8 + SACCH/8

F0

S1

BCCH2 - 5

CCCH6 - 9

F10

S11

CCCH12 - 19

F20

S21

CCCH22 - 29

F30

S31

CCCH32 - 39

F40

S41

CCCH42 - 49

I50

DL: F = FCCH, S = SCH, B = BCCH, C = CCCH, (PCH, AGCH), I = idle

UL: R = RACH

R0

R1

R10

R11

R20

R21

R30

R31

R40

R41

R50

Fig. 20 Multiframe for channel combination IV) FCCH + SCH + CCCH + BCCH

13/4 or /8 means up to 4 / 8 dedicated and associated connections to MS




MN1788EU08MN_000149

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F S B C F S C C F S D0 D1 F S D2 D3 F S A0 A1 I

51 TDMA Rahmen = 235,38 ms

DOWNLINK: Broadcast Control Channel (BCCH), Common Control Channel (CCCH)

+4 Stand Alone Dedicated Control Channels (SDCCH/4)

UPLINK: Common Control Channel (CCCH)

+4 Stand Alone Dedicated Control Channels (SDCCH/4)

D3 R R A2 A3 R R R R R R R R R R R R R R R R R R R R R R R R RD0 D1 D2

D3 R R A0 A1 R R R R R R R R R R R R R R R R R R R R R R R R RD0 D1 D2

F S B C F S C C F S D0 D1 F S D2 D3 F S A2 A3 I

A TMDA frame for SACCHB BCCHC CCCHD SDCCHF frequency correction burstR RACHS synchronized burst

I idle

Fig. 21 Multiframe for channel combination V)




MN1788EU08MN_000150

Purpose / use of the different channel combinations:

I) - III) Call and data transmission in a 26 TCH frame;

I) Combination I) is primarily used to transmit TCH/F (full rate speech). Incombination I) the first 12 frames (0 - 11) are used for call or datatransmission, a SACCH is then transmitted (frame 12) and also 12frames (13 - 24) for call and data transmission. The last frame (25) isnot used (I: idle).

II) III) Combination II) and III) are primarily used for transmitting user data athalf rate. 2 TCH/H have to "share" the 26 multiframe with their associated control channels. Data from the first or second subscriber isalternately filled into the frame. The SACCH of the 1st subscriber is inframe 12, the SACCH of the 2nd subscriber in frame 25. This means

there are no empty (idle) frames.

The FACCH does not have a fixed frame in combination I) to III). If signaling isnecessary, indicated by the "stealing flag" in the normal burst, a 20 ms long part of the multiframe which is 120 ms long in total is occupied with FACCHs instead of TCHs.

V) - VII) BTSE«««« MS signaling:

V) Channel combination V) is the minimum configuration for a basestation. It is mostly used when a BTS is only equipped with 1 or 2RFCs. Channel combination V) may only be used once in a cellbecause the mobile station searches for the frequency correctionchannel FCCH for synchronizing and the channel for timesynchronization SCH. It is transmitted to time slot 0 of an RFCs („basefrequency14“). Channel combination V) and IV) rule each other out.

14The base frequency can be any RFC, it must be sent constantly however




MN1788EU08MN_000151

IV) Channel combination IV) is mainly used for BTS with several RFCs asit provides the common control channels CCCH with a lot of space. Itmay only be used once for the same reasons as with combination V)

(in time slot 0 of one of the RFC). As opposed to combination V) thereare no dedicated channels in combination IV). Channel combination

VII) is thus also required when channel combination IV) is used.

VI) A BTS can contain up to 16 RFCs in the GSM system. When a lot of RFCs are used (corresponding with a very high traffic volume in thecell) further task sharing can be useful in the channel combination.Channel combination VI) which only contains common control channelsCCCH as well as the BCCH is used for this. This means that it isnecessary to also use combination IV) and VII) in addition to channelcombination VI). Combination IV) is in time slot 0 of the base frequencyand VI) going onto 2, 4 and 6.

VII) Channel combination VII) is used to accommodate the dedicatedchannels SDCCH and SACCH each for up to 8 connections betweenBTSE and MS and is used as a supplement to combination IV) and VI).

Remark: Meanwhile there are channel combinations existing, which inhabit theCell Broadcast (for SMS CBS).




MN1788EU08MN_000152




MN1788EU08MN_000153

2 Layer 2 - Um-Interface




MN1788EU08MN_000154

The task of layer 2, the data circuit layer, is so-called "linking", i.e. the safetransmission of signaling messages via an individual signaling link. Layer 2 (linking)protocols in the different GSM interfaces are the same to a great extent, they have

very similar functions. The main tasks of layer 2 are generally the structuring of theinformation to be transmitted on the communication channel:

l Fault detection and correction

l Stable transmission, i.e. guaranteed free of errors; otherwise transmission repeat

l Disassembly of the individual data stream and reconstruction

l Flow control

Layer 2 (Data Link Layer) defines the structure of the 23-byte blocks in the CCM and

in particular the numbering and acknowledgment of the blocks.




MN1788EU08MN_000155

CC

Call

Control

SSS

Supplementary

Services

Support

SMS

Short

Message

Service

CM Connection Management

MM Mobility Management

RR Radio Resource Management

Layer 2 Data Link Layer

Layer 1 Physical Layer

Layer 3 Network Layer

Fig. 22 Layers 1 to 3 at the air interface; the sublayers of layer 3




MN1788EU08MN_000156

The structure of a 23-byte transmission block in the SDCCH, FACCH, PCH, AGCH or BCCH is shown in the adjacent figure. (The block structure in SACCH deviatesslightly from the illustration, whilst a block in the RACH consists of only one byte).

A block of this type (known also as layer 2 frame) begins with an address field (1byte), a control field (1 byte) and a length indicator (1 byte). The subsequentinformation field contains the layer 3 data. If the 20 bytes available for this data arenot completely used, the residual bytes are filled with the fill bit pattern "00101011"("11111111" also permissible in uplink direction) in order to attain a total length of 23bytes.

Address field contents:

l Link Protocol Discriminator (LPD) for discriminating between the GSM protocol

and other protocols (national or manufacturer-specific)l Service Access Point Identifier (SAPI) for discriminating between short message

service (SMS) and other layer 3 parts (RR, MM, CC or SSS) in the informationfield. (A special layer 3 format is used for SMS, and the SMS messages arenumbered independently of the other messages in the control field).

l Command/Response Field bit (C/R) for discriminating between commands(messages transmitted on own initiative) and responses (reactions to receivedcommands).

The control field is used to number and acknowledge the frames. Its structure isshown in the next figure.

The length indicator specifies the length in bytes of the information field. The indicator additionally contains the More Data bit (M) specifying whether the layer 3 messageextends to the follow-on layer 2 frame. It may be the case that a layer 3 message islonger than 20 bytes and must therefore be distributed over several layer 2 frames. Inthis case, the last frame is transmitted with M = 0 and all preceding frames with M = 1("Continuation in the next issue"). If the layer 3 messages fits into one layer 2 frame,the More-Data bit of the latter is set to 0 ("End").




MN1788EU08MN_000157

LPD SAPI C/R

see next figure

1

2

Length M

Address Field

Control Field

Length Indicator

Layer 3

Fill bits

3

n

23

Fig. 23 Structure of a Layer 2 frame (acc. to GSM 04.06)




MN1788EU08MN_000158

The control field differentiates the following three frame types: Information Frames(I-frames), Supervisory Frames (S-frames) and Unnumbered Frames (U-frames).

Information frames are identified by the digit 0 in the least significant bit in the control

field. These frames are used for error-protected message transmission. "Error protection" means in this context that the messages are individually numbered andacknowledged, thus allowing the receiver the opportunity to request a repeattransmission in the event of a transmission error or reception fault. Accordingly, thecontrol field in the I-frame contains one send number N(S) and one receptionnumber N(R), each 3 bits in length. The send number numbers consecutively all I-frames running in the same direction on one CCH, whereby short message service(SMS) messages and other layer 3 part messages are counted separately. Thereception number specifies which I-frame is next expected in the counterdirection;thus, the number is that of the last correctly-received I-frame + 1. I-frames are alwayscommands and always include an information field.

Supervisory frames are identified by the bit combination "01" in the two leastsignificant bits in the control field. These frames are used for acknowledgment of received information frames without simultaneously supplying new information.Therefore, the S-frame control fields have only a reception number N(R) indicatingthe next anticipated I-frame in the counterdirection. Three types of S-frame aredistinguished:

l Receive Ready (RR): positive acknowledgment in normal operation

l Receive Not Ready (RNR): positive acknowledgment simultaneously declaringthat due to overload no further I-frames can currently be accepted

l Reject (REJ): negative acknowledgment (i.e. repeat request)

Supervisory frames can occur as commands or responses; they never include aninformation field.

If information and supervisory frames are exchanged between MS and BSS in aCCH, a layer 2 connection is said to exist in this CCH. The set up of such a layer 2connection means that both sides allocate storage space for the valid send andreception numbers as well as for the buffering of as yet unacknowledged I-frames(which must possibly be retransmitted). This storage space is released when the

layer 2 connection is cleared down.




MN1788EU08MN_000159

both

both

Command

Response

Command

Command

Response

Frame Format bit patternCommand

Response

Inform.

Field

I Command yes

no

no

no

possible

no

yes

no

possible

S

U

RR

RNR

REJ

SABM

DM

UI

DISC

UA

N(R) P/F 0 0 0 1

N(R) P/F 0 1 0 1

N(R) P/F 1 0 0 1

0 0 1 P 1 1 1 1

0 0 0 F 1 1 1 1

0 0 0 P 0 0 1 1

0 1 0 P 0 0 1 1

0 1 1 F 0 0 1 1

both

N(R) P N(S) 0

Fig. 24 Control Field Structure (acc. to GSM 04.06)




MN1788EU08MN_000160

As SMS messages are numbered separately from other messages, two independentlayer 2 connections can exist in the same CCH: one layer 2 connection for SMS, onefor all other layer 3 messages.

Layer 2 connections may only be established in SDCCH and FACCH. For thisreason, only unnumbered frames are used in all other CCH (i.e. BCCH, AGCH, PCHand SACCH).

Unnumbered frames are identified by the digit 1 in the two least significant bits in thecontrol field. These frames contain like their name suggests neither a send number nor reception number. The frames are not acknowledged, therefore, and the receiver cannot request a retransmission. A distinction is made between the following types of unnumbered frames:

l Set Asynchronous Balanced Mode (SABM): layer 2 connection set up

l Disconnect (DISC): layer 2 connection cleardownl Unnumbered acknowledge (UA): positive acknowledgment for SABM

l Disconnect Mode (DM): negative acknowledgment for SABM; is also used incases where an I-frame or S-frame arrives without a layer 2 connection havingbeen established

l Unnumbered Information (UI): transmission of an information field without layer 2 connection.

SABM, DISC and UI are commands; UA and DM are responses. An information field

is always included in the UI, but never in the DISC or DM. SABM and UA mayoptionally contain an information field.

As layer 2 connections exist only in the SDCCH and FACCH, UI-frames are usedexclusively in the BCCH, AGCH, PCH and SACCH.

The P, F or P/F bits shown in table 3 are known as poll bits in commands and finalbits in responses. Their standard value is 0. By transmitting a command with P = 1,one side (MS or BSS) can specially request the opposite side to send a responselabeled with F = 1. This polling method is used for set up and cleardown of the layer 2 connection (SABM or DISC with P = 1, UA with F = 1). The BSS likewise polls theMS to ascertain whether the latter is still accessible. Polling is additionally used when

one side reports overload with RNR: the opposite side regularly queries (commandRR with P = 1) whether the overload still exists (response RNR with F = 1) or not(response RR with F = 1).

For all details of the Layer 2 protocol release refer to GSM Guideline 04.06




MN1788EU08MN_000161

3 Layer 3 - Um




MN1788EU08MN_000162

3.1 Radio Resource- , Mobility- , ConnectionManagement

The layer 3 is composed of three sublayers comprising :

l the Radio Resource Management (RR) functions

l the Mobility Management (MM) functions

l the Connection Management (CM) functions.

The Layer 3 messages can only contain maximal 249 Bytes.




MN1788EU08MN_000163


CC

Call

Control

SSS

Suplementary

Services

Support

SMS

Short

Message

Service

CM Connectioon Management

MM Mobility Management

RR Radio Resuorce Management



Fig. 25 Layers to 3 at the air interface; the sublayers of layer 3




MN1788EU08MN_000164

3.1.1 Radio Resource Management (RR)

The Radio Resource management (GSM 04.08) messages will be sent between MSand BTS / BSC. Many RR messages will be transported over the Abis Interface

within the RSL / DTAP to the BSC.

Radio Resource management procedures include the functions related to themanagement of the common transmission resources, e.g. the physical channels andthe data link connections on control channels.

The general purpose of Radio Resource procedures is to establish, maintain andrelease RR connections that allow a point-to-point dialogue between the network anda Mobile Station. This includes the cell selection/reselection and the handover procedures. Moreover, Radio Resource management procedures include the

reception of the uni-directional BCCH and CCCH when no RR connection isestablished. This permits automatic cell selection/reselection.




MN1788EU08MN_000165

The elementary procedures for Radio Resource management are as follows :

l

Idle mode procedures:System information broadcasting

Paging

l RR connection establishment procedures:

Entering the dedicated mode: immediate assignment procedure

Entering the group transmit mode: uplink access procedure

Paging procedure for RR connection establishment

Notification procedure

l Procedures in dedicated mode and in group transmit mode:

SACCH procedures

Channel assignment procedure

Handover procedure

Frequency redefinition procedure

Channel mode modify procedure

Ciphering mode setting procedure

Additional channel assignment procedurePartial channel release procedure

Classmark change procedure

Classmark interrogation procedure

RR connection release procedure

Group receive mode procedures

Configuration change procedure

The following table summarizes Radio Resource Management messages:




MN1788EU08MN_000166

RR Management Messages Remarks

channel establishment messages: ADDITIONAL ASSIGNMENT

IMMEDIATE ASSIGNMENT

IMMEDIATE ASSIGNMENT EXTENDED

IMMEDIATE ASSIGNMENT REJECT

Ciphering messages:

CIPHERING MODE COMMAND

CIPHERING MODE COMPLETE

Handover messages:

ASSIGNMENT COMMAND

ASSIGNMENT COMPLETE

ASSIGNMENT FAILURE

PDCH ASSIGNMENT COMMAND

HANDOVER ACCESS

HANDOVER COMMAND

HANDOVER COMPLETE

HANDOVER FAILURE

RR-CELL CHANGE ORDER

PHYSICAL INFORMATION

RR INITIALISATION REQUEST

HANDOVER ACCESS

HANDOVER COMMAND

HANDOVER COMPLETE

HANDOVER FAILURE

PHYSICAL INFORMATION

Channel release messages:

CHANNEL RELEASE

PARTIAL RELEASE

PARTIAL RELEASE COMPLETE




MN1788EU08MN_000167

Paging messages:

PAGING REQUEST TYPE 1PAGING REQUEST TYPE 2

PAGING REQUEST TYPE 3

PAGING RESPONSE

System information messages:

SYSTEM INFORMATION TYPE 1


SYSTEM INFORMATION TYPE 2bis

SYSTEM INFORMATION TYPE 2ter




SYSTEM INFORMATION TYPE 5bis

SYSTEM INFORMATION TYPE 5ter








Specific messages for VBS/VGCS:

NOTIFICATION/FACCH

NOTIFICATION/NCH

TALKER INDICATION

UPLINK ACCESS

UPLINK BUSY

UPLINK FREE

UPLINK RELEASE




MN1788EU08MN_000168

VGCS UPLINK GRANT

EXTENDED MEASUREMENT ORDEREXTENDED MEASUREMENT REPORT

Miscellaneous messages:

CHANNEL MODE MODIFY

CHANNEL MODE MODIFY ACKNOWLEDGE

CHANNEL REQUEST

CLASSMARK CHANGE

CLASSMARK ENQUIRY

FREQUENCY REDEFINTION

MEASUREMENT REPORT

SYNCHRONIZATION CHANNELINFORMATION

RR STATUS

GPRS SUSPENSION REQUEST

Configuration Change messages:CONFIGURATION CHANGE COMMAND

CONFIGURATION CHANGE ACKNOWLEDGE

CONFIGURATION CHANGE REJECT

Application messages:

APPLICATION INFORMATION




MN1788EU08MN_000169

3.1.2 Mobility Management (MM)

The Mobility Management (GSM 04.08) messages will be sent between MS andMSC and have no influences to the BSS. The MM messages will be transported over the Abis and A-Interface within the RSL / DTAP and DTAP to the BSC.

The main function of the Mobility Management sublayer (GSM 04.08) is to supportthe mobility of user terminals, such as informing the network of its present locationand providing user identity confidentiality.

A further function of the MM sublayer is to provide connection management servicesto the different entities of the upper Connection Management (CM) sublayer.

The elementary procedures for Mobility Management are as follows :

l MM common procedures:

TMSI reallocation procedure

Authentication procedure

Identification procedure

IMSI detach procedure

Abort procedure

MM information procedure

l MM specific procedures:

Location updating procedure

Periodic updating

IMSI attach procedure

Generic Location Updating procedure

l Connection management sublayer service provision:

MM connection establishment

MM connection information transfer phase

MM connection release

The following table summarizes Mobility Management messages:




MN1788EU08MN_000170

MM Management messages Remarks

Registration messages:IMSI DETACH INDICATION

LOCATION UPDATING ACCEPT

LOCATION UPDATING REJECT

LOCATION UPDATING REQUEST

Security messages:

AUTHENTICATION REJECT

AUTHENTICATION REQUEST

AUTHENTICATION RESPONSE

IDENTITY REQUEST

IDENTITY RESPONSE

TMSI REALLOCATION COMMAND

TMSI REALLOCATION COMPLETE

Connection management messages:

CM SERVICE ACCEPT

CM SERVICE REJECT

CM SERVICE ABORT

CM SERVICE REQUEST

CM RE-ESTABLISHMENT REQUEST

ABORT


MM INFORMATION

MM STATUS

MM NULL




MN1788EU08MN_000171

3.1.3 Connection Management (CM)

The Connection Management (CM) sublayer is composed of :

l Call Control (CC)

l Short Message Service Support (SMS)

l Supplementary Services Support (SS)

The CC messages will be sent between the MS and the MSC and will therefore beconsidered mainly. Every mobile station must support the call control protocol. If amobile station does not support any bearer capability at all then it shall respond to aSETUP message with a RELEASE COMPLETE message.

In the call control protocol, more than one CC entity are defined. Each CC entity is

independent from each other and shall communicate with the correspondent peer entity using its own MM connection. Different CC entities use different transactionidentifiers.

The elementary procedures for circuit switched Call Control are as follows:

l Call establishment procedures:

Mobile originating call establishment

Mobile terminating call establishment

l Signaling procedures during the "active" state

User notification procedureCall rearrangements

User initiated level up- and downgrading

l Call clearing

Clearing initiated by the mobile station

Clearing initiated by the network

Clear collision

l Miscellaneous procedures

In-band tones and announcements

Call collisions

Status procedures

Call re-establishment, mobile station side

Call re-establishment, network side

DTMF protocol control procedure

The following table summarizes Call Control messages:




MN1788EU08MN_000172

CC messages Remarks

Call establishment messages: ALERTING

CALL CONFIRMED

CALL PROCEEDING

CONNECT

CONNECT ACKNOWLEDGE

EMERGENCY SETUP

PROGRESS

SETUP

Call information phase messages:

MODIFY

MODIFY COMPLETE

MODIFY REJECT

USER INFORMATION

Call clearing messages:

DISCONNECT

RELEASE

RELEASE COMPLETE

Messages for supplementary servicecontrol:

FACILITY

HOLD

HOLD ACKNOWLEDGEHOLD REJECT

RETRIEVE

RETRIEVE ACKNOWLEDGE

RETRIEVE REJECT




MN1788EU08MN_000173


CONGESTION CONTROLNOTIFY

START DTMF

START DTMF ACKNOWLEDGE

START DTMF REJECT

STATUS

STATUS ENQUIRY

STOP DTMF

STOP DTMF ACKNOWLEDGE


CC

Call

Control

SSS

Supplementary

Services

Support

SMS

Short

Message

Service

CM Connection Management

MMMobility Management

RRRadio Resource Management



Fig. 26 Layers to 3 at the air interface; the sublayers of layer 3




MN1788EU08MN_000174

3.2 Formatting Rules

Every layer 3 message is comprised of several parameters, also known asinformation elements. Section 9 of GSM Guideline 04.08 defines the mandatory andoptional parameters for every message. The same parameter may be mandatory for one message and optional for another. Optional parameters bear an identifier (Information Element Identifier, IEI) to designate their presence. The identifier isalways located at the beginning of the parameter. Mandatory parameters, bycontrast, include sometimes - dependent on the position - an identifier.

The parameters are sub-divided into 5 parameter formats (described in GSM 04.07):

V (value only) parameters have neither an identifier (IEI) nor a length indicator;they are mandatory parameters of fixed length. The length is either an integer

amount of bytes or 1/2 byte. In the last case, V-parameters of 1/2 byte lengthare combined to form pairs whenever possible. The first parameter in thecombination encompasses the 4 least significant bits, the second parameter the 4 most significant bits. If the total number of V-parameters of 1/2 byte isodd, the 4 most significant bits of the last byte are filled with 0000.

TV (type and value) parameters have an identifier (IEI) but no length indicator. If the length of the contents is an integer amount of bytes, then the IEI is 1 bytein length, and the most significant IEI bit is 0. If the length of the contents is 1/2byte, then the IEI is likewise 1/2 byte in length. The most significant bit is 1,and the succeeding bits must not be 010 (to distinguish them from T-

parameters, see below).T (type only) parameters have 0 byte content. The communicated information

consists solely in the presence or absence of the parameter. Obviously, suchparameters can only be considered as optional. The identifier (IEI) is 1 byte inlength and begins with 1010 (so that no confusion with TV-parameters ispossible). One example of a type-2 parameter is the authorization given in"Location Update Accept" for the Mobile Station to set up a MM connectiondirectly after the location update (i.e. in the same RR connection). Thisauthorization may, or may not, be present.

LV (length and value) parameters have a length indicator but no identifier (IEI);

they are mandatory parameters of variable length. The length indicator is thefirst byte and indicates how many bytes of contents follow.

TLV (type, length and value) parameters have an identifier (IEI) and a lengthindicator. The IEI is the first byte of the parameter; its most significant bit is 0.The length indicator is the second byte of the parameter and indicates how many bytes of contents follow.




MN1788EU08MN_000175

Layer 3 parameters (GSM 04.07)

Parameter Format Length integer amount of Bytes Length of 1/2 Bytes

Example: 5 parameters

V alue

T ype,

V alue

T ype

L ength,

V alue

T ype,

L ength,V alue

content

content

0 IEI

content

Length indicator

content

Length indicator

0 IEI

0 contentIEI¹ 010

IEI1 0 1 0

content 1

content 3content 4

content 5

content 2

0 0 0 0

Fig. 27 Parameter formats




MN1788EU08MN_000176

Each message begins with the same three V-parameters:

The protocol discriminator specifies the layer 3 part to which the message belongs.It is a parameter of 1/2 byte length.

The transaction identifier (TI) characterizes the transaction ( = CM connection, cf.2.3). It is a V-parameter of 1/2 byte, too; in conformity with the rules, the protocoldiscriminator and the TI together fill 1 byte. For RR and MM messages (protocoldiscriminator = 0110 or 0101), no CM connection is established; for this reason, theTI is replaced by the skip indicator whose value is 0.

With a proper TI, the most significant bit serves as TI flag in messages for other TIparts; it is 0 in messages from the side which set up the transaction, and 1 inmessages to the side which set up the transaction. The three remaining bits form theTI value are freely selected by the initiating side in a transaction set up; the value 111is not permissible.

The message type identifies the nature of the message (e.g. "Handover Command","Location Update Request", "Setup" and many other examples). It is a V-parameter

with a length of 1 byte. The second bit is the send sequence number N(SD). In allmessages from the Base Station, as well as in RR messages from the MobileStation, this bit is 0. In MM and CM messages from the Mobile Station the bitalternately has the values 0 and 1.

For the remaining parameters, the protocol may define three different presencerequirements: M (mandatory), C (conditional) or O (optional). An M-parameter must

always be included in a message of a given type; its absence is reason enough for the receiver to reject the whole message. A C-parameter must be present under certain conditions, but can be absent under other conditions. An O-parameter, finally,is never bound to be present; its absence is never sufficient reason for the receiver toreject the message.




MN1788EU08MN_000177

TI-

flagTI-Value

0 N(SD)

Message Type

Transaction identifier

or Skip indicator Protocol discriminator

Protocol

discriminator

Message

type

Fig. 28 Layer 3 message header (GSM 04.07)

Value

0110

0101

0011

1011

1001

1111

Layer 3 part

Radio Resource Management (RR)

Mobility Management (MM)

Call Control (CC)

Supplementary Services Support (SSS)

Short Message Service (SMS)

reserved for tests

Fig. 29 Protocol discriminator




MN1788EU08MN_000178

Some examples of layer 3 messages will now be examined. First we shall consider aRadio Resource Management message the "Handover Command" from BaseStation to Mobile Station. Apart from the parameters in the message header, the

mandatory parameters are the description of the new cell (Cell Description), thespecification of the new speech channel (Description of the First Channel) and therequired power of the Mobile Station in the new cell (Power Command). Severalconditional and optional parameters exist which depend on the cell synchronizationor on whether frequency hopping is employed in the new cell.

The length specifications indicate the total parameter lengths, i.e. inclusive of identifier and length indicator, where applicable. Thus, V-parameters have the length1/2 or an integer value. With TV-parameters, the length is 1 if they have 1/2 bytecontents and 1/2 byte identifier; otherwise, the length of the contents is 1 byte lessthan the indicated length (because the first byte is the IEI). T-parameters alwayshave a length of 1 byte. LV-parameters have a length of the contents which is 1 byteless than the indicated length (here, the first byte is the length indicator). Finally, withTLV-parameters, the length of the contents is 2 bytes less than the indicated length,since the first byte is the IEI and the second byte is the length indicator.

For example, the parameter "Real Time Difference" (TLV) has a total length of 3bytes. When 1 byte is subtracted for identifier and length indicator respectively, 1byte remains for the content.




MN1788EU08MN_000179

4 Call Sequences on Um




MN1788EU08MN_000180

4.1 Complete Sequences

Our consideration of a location update will be confined to the following case: aMobile Station, which is in service but without an existing user connection, changesits location area. As soon as the Mobile Station has tuned itself to the new BaseStation and recognizes the new LAI in the BCCH, it requests (via the RACH) asignaling channel (SDCCH). After being assigned a signaling channel (in the AGCH),the Mobile Station sets up a layer 2 connection with the "Contention Resolution"procedure, including in the SABM the layer 3 message "Location Update Request"along with the old CKSN, the prior TMSI and previous LAI. The Mobile Stationadditionally indicates that the requested location update is a normal one (and not aperiodic one or an IMSI Attach). The Base Station acknowledges the SABM with UA.

The VLR determines the IMSI on the basis of the TMSI and LAI (and possibly byquerying the previous VLR), and notifies (if necessary) the HLR. Before confirmingthe location update and assigning a new TMSI to the Mobile Station, the VLRperforms the authentication (I-frames "Authentication Request" and "AuthenticationResponse") and the ciphering activation (I-frames "Ciphering Mode Command" and"Ciphering Mode Complete").

After this, a new TMSI can be allocated with the enciphered message "LocationUpdate Accept"; the Mobile Station responds with "TMSI Reallocation Complete".The Base Station then clears down the RR connection.




MN1788EU08MN_000181

Location update

RACH Channel Request

(Reason = Loc. Upd., Random Reference)

UI (Immediate Assignment)

(Request Reference, SDCCH-No.) AGCH

SDCCHSABM (Location Update Request)

(TMSI + old LAI, CKSN, loc upd. type)

SDCCHUA

SDCCHI (Authentication Request)

(RAND, CKSN)

SDCCHI (Authentication Response)

(SRES)

SDCCHI (Ciphering Mode Command)

SDCCHI (Ciphering Mode Complete)

SDCCHI (Location Update Accept)

(new TMSI, new LAI)

SDCCHI (TMSI Reallocation Complete)

SDCCHI (Channel Release)

SDCCHDISC

SDCCHUA

Fig. 30 Location Update




MN1788EU08MN_000182

For a mobile originating call (MOC) we will consider the case that a Mobile Station, whose current location is already updated, sets up an outgoing call. Therefore, alocation update with directly following MM connection set up is not required first of all;

instead, a RR connection must be set up specifically for the MOC. For this, theMobile Station requests a SDCCH (in the RACH; reason for request = MOC set up).

After allocation of the SDCCH (via the AGCH), the Mobile Station sets up the layer 2connection and conveys in the SABM the message "CM Service Request", whichincludes the CKSN of the last authentication and the information that a MMconnection for call control (CC) is to be set up. The Base Station acknowledges theSABM with UA.

The Base Station now performs the authentication (I-frames "Authentication Request"and "Authentication Response") and ciphering activation (I-frames "Ciphering ModeCommand" and "Ciphering Mode Complete"). With this, the MM connection is set upand the Mobile Station for its part can establish a CC connection with the message"Setup". This message contains a new transaction identifier (TI; selected by theMobile Station) as well as all information required for a network call set up (inparticular the bearer capability and the called party number).

The Base Station answers with the I-frame "Call Proceeding", to which the MobileStation responds with "Receive Ready".




MN1788EU08MN_000183

Mobile originating call (MOC), beginning

RACHChannel Request

(Reason = MOC, Random Reference)

UI (Immediate Assignment)

(Request Reference, SDCCH-No.) AGCH

SDCCH SABM (CM Service Request)

(CC, CKSN)

SDCCHUA


(RAND, CKSN)


(SRES)


SDCCHI (Ciphering Mode Complete)

SDCCHReceive Ready

SDCCHI (Setup)

(bearer capability, compatibility,

called party number, features)

SDCCHI (Call Proceeding)

SDCCHReceive Ready

Fig. 31 Mobile originating call, part 1




MN1788EU08MN_000184

At this stage, if Off-Air Call Set up (OACSU) is not active, the network side assigns aspeech channel by sending an "Assignment Command" I-frame with the TCHnumber. The Mobile Station responds with "Receive Ready", whereupon the layer 2

connection in the SDCCH can be cleared down locally, and a new layer 2 connectionis set up in the FACCH. The Mobile Station uses this new FACCH to acknowledgethe received "Assignment Command" with "Assignment Complete".

As soon as ringing begins for the called party, the network side sends to the MobileStation the I-frame "Alerting", to which the Mobile Station responds with "ReceiveReady".

Once the called party answers, the network side sends the I-frame "Connect" to theMobile Station; the latter responds with I-frame "Connect Acknowledge". Finally, theBase Station acknowledges the MS response with "Receive Ready", thus completingthe connection set up.




MN1788EU08MN_000185

Mobile originating call (MOC),

continuation without OACSU

SDCCHI (Assignment Command)

(TCH-No.)

Receive ReadySDCCH

FACCHSABM

FACCHUA

FACCHI (Assignment Complete)

FACCHReceive Ready

FACCHI (Alerting)

FACCHReceive Ready

FACCH

FACCHI (Connect Acknowledge)

FACCHReceive Ready

I (Connect)

Fig. 32 Mobile originating call, part 2a




MN1788EU08MN_000186

If Off-Air Call Set up (OACSU) is active, the speech channel is first assigned whenthe called party answers (i.e. directly before the "Connect"). The transmission of "Alerting" and the associated "Receive Ready" continues in the SDCCH.




MN1788EU08MN_000187

Mobile originating call (MOC),

continuation with OACSU

I (Alerting)SDCCH

SDCCHReceive Ready


(TCH-No.)

SDCCHReceive Ready

FACCHSABM

FACCHUA


FACCH


FACCHReceive Ready

I (Connect)

Fig. 33 Mobile originating call, part 2b




MN1788EU08MN_000188

The Base Station initiates a mobile terminating call (MTC) by paging. For this, itsends in the PCH a UI-frame "Paging Request" including the TMSI. The calledMobile Station requests ("Channel Request" in RACH, Reason = Answer to paging)

and obtains ("Immediate Assignment" in AGCH) a channel, in which it sets up a layer 2 connection. The SABM for this set up includes the message "Paging Response"along with the last CKSN and the TMSI. The network recognizes the positive pagingresult and answers the SABM with UA.

The Base Station now performs the authentication (I-frames "Authentication Request"and "Authentication Response") and ciphering activation (I-frames "Ciphering ModeCommand" and "Ciphering Mode Complete"). With this, the MM connection is set upand the Base Station can establish a CC connection with the message "Setup". Thismessage contains a new transaction identifier (TI; selected by Base Station) as wellas all information required for a call set up (in particular the bearer capability).

The Mobile Station answers with the I-frame "Call Confirmed", to which the BaseStation responds with "Receive Ready".




MN1788EU08MN_000189

Mobile terminating call (MTC), beginning

I (Setup)

(bearer capability, compatibility,

calling party number, features)

PCHUI (Paging Request)

(Mobile Identity)

Channel Request

(Reason = Answer to Paging, Random Reference)

RACH

AGCHUI (Immediate Assignment)

(Request Reference, SDCCH-No.)

SDCCHSABM (Paging Response)

(TMSI, CKSN)

SDCCHUA


(RAND, CKSN)


(SRES)


SDCCH

SDCCH

SDCCH I (Call Confirmed)

I (Ciphering Mode Complete)

SDCCHReceive Ready

Fig. 34 Mobile terminating call, part 1




MN1788EU08MN_000190

If Off-Air Call Set up (OACSU) is not active, the Base Station assigns the speechchannel at this point. The procedure is identical with that for a mobile originating call(see above). Most importantly, the remaining RR connection in the SDCCH is

replaced by a new one in the FACCH. As soon as ringing begins for the called party, the Mobile Station sends the I-frame"Alerting", to which the Base Station responds with "Receive Ready".

If the called party answers, the Mobile Station notifies the Base Station with the I-frame "Connect". The Base Station responds with "Connect Acknowledge". Finally,the Mobile Station acknowledges the Base Station response with "Receive Ready",thus completing the connection set up for a mobile terminating call.




MN1788EU08MN_000191

Mobile terminating call (MTC),

continuation without OACSU


(TCH-No.)

Receive ReadySDCCH

FACCHSABM

FACCHUA


FACCHReceive Ready

FACCHI (Alerting)

FACCHReceive Ready

FACCH


FACCHReceive Ready

I (Connect)

Fig. 35 Mobile terminating call, part 2a




MN1788EU08MN_000192

If Off-Air Call Set up (OACSU) is active, the speech channel is first assigned whenthe called party answers (i.e. after the "Connect"). The transmission of "Alerting", theassociated "Receive Ready", and "Connect" continue in the SDCCH.




MN1788EU08MN_000193

Mobile terminating call (MTC),

continuation with OACSU

I (Alerting)SDCCH

SDCCHReceive Ready

SDCCH


(TCH-No.)

SDCCHReceive Ready

FACCHSABM

FACCHUA

FACCH


FACCHReceive Ready

I (Assignment Complete)

I (Connect)

Fig. 36 Mobile terminating call, part 2b




MN1788EU08MN_000194

From the view of the Mobile Station, the Handover procedure begins when the BaseStation sends an I-frame with a "Handover Command" message in the FACCH validup to that point. The message contains specifications of the new cell (e.g. color code,

channel structure, timing advance), of the new speech channel (TCH) and a new Handover reference number. The Mobile Station acknowledges this I-frame with"Receive Ready". With this, the layer 2 connection in the remaining FACCH iscleared down locally. The old speech channel (TCH), together with its associatedsignaling channels (FACCH and SACCH), is now idle once more.

The Mobile Station now logs-on in the new cell by transmitting four separate"Handover Access" messages in the FACCH of the new TCH. This message doesnot conform to the standard format of 23 Byte length; it is one byte long andcomprises only the Handover reference number. The Mobile Station subsequentlysets up with SABM the layer 2 connection in the new FACCH and, after receiving theUA, transmits the message "Handover Complete" in the first I-frame to the new BaseStation. This Base Station responds with "Receive Ready". From the viewpoint of theMobile Station, the handover is now completed.




MN1788EU08MN_000195

Handover

I (Handover Command)

(data about new cell, new

TCH-No., handover reference)

FACCH old

FACCH oldReceive Ready

FACCH new

FACCH new

FACCH new

FACCH new

Handover Access

(Handover Reference)

FACCH new

FACCH new UA

FACCH new I (Handover Complete)

SABM

FACCH new Receive Ready

Handover Access


Handover Access


Handover Access


Fig. 37 Handover




MN1788EU08MN_000196

The call cleardown can be initiated by either the Mobile Station or network side (i.e.the partner side). Here, only the cleardown of an established useful connection willbe considered.

If the Mobile Station initiates the cleardown, it sends the I-frame "Disconnect". TheBase Station responds by clearing down the CM connection with the I-frame"Release", which is answered by "Release Complete".

If the partner side initiates the cleardown, the Base Station transmits "Release"immediately. Again, the Mobile Station answers with "Release Complete".

The MM connection is cleared down only locally. The RR connection, however mustbe cleared down explicitly. The Base Station must initiate the RR cleardown(irrespective of the initiating side for the user connection cleardown) by sending the I-frame "Channel Release".

Finally, the Mobile Station clears down the layer 2 connection with DISC, which theBase Station acknowledges with UA. With this, all seized resources are released,and the connection cleardown is completed.




MN1788EU08MN_000197

Call cleardown

FACCHI (Disconnect)

I (Release)

FACCH

FACCHI (Release Complete)

FACCHI (Channel Release)

FACCHDISC

FACCHUA

FACCHI (Release)

FACCHI (Release Complete)

FACCH

FACCHDISC

FACCHUA

I (Channel Release)

Initiated by partner side

Initiated by mobile station

Fig. 38 Call clear down

03 mn1788eu08mn 0001 air interface um

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