5-tcsm2e

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BSSSYS CourseBSSSYS Course

TCSM2ETCSM2E

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TTCSM2ECSM2E functions functions Transcoder is responsible of the speech coding in the

downlink direction; it provides the de-transcoding in the uplink direction

Transcoders are always used between the MSC and the BSC.

1 time slot, TS, always through connected carrying:

• CCS7

• X.25 between OMC and BSC

• no information

The submultiplexing function is used to reduce the number of links between MSC and BSC.

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TCSM2ETCSM2E

TCSM2E = TC + SM

TC SM

2 Mbit/s

2 Mbit/s

2 Mbit/s

2 Mbit/s

BSCMSC

A I/F Ater’ I/F Ater I/F

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TranscodingTranscoding 20 ms samples of the speech

• 160 A-law PCM samples of 8 bits

• Linear Predictive Coding - Long Term Prediction - Regular Pulse Excited, LPC-LTP-RPE vocoder is used for speech coding

• Speech information sent in vocoder blocks of 260 bits

• Digital Signal Processor, DSP, for each speech channel

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TRAU frameTRAU frame

• Created in the TC

• Used between the DSP in the Transcoder and the DSP in the Frame Unit in the BTS

• Carrying the vocoder traffic channel blocks when the call is on

• TRAU frame is transmitted "on top" of the 2 Mbit/s frame.

• 260 bits carry the vocoder block (13 kbit/s) and

• 60 bits (3 kbit/s) are used for in band signalling

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TRAU TRAU frameframe

TS0 TS1 = frame alignment word

C1-C4 = frame type

C5 = channel type

C6-C11 = time alignment info.

C12-C16 = frame indicator

C17 = DTX ON/OFF

C18-C21 = spare bits

T1-T4 = time alignment

0 0 0 0 0 0 0 0

1 C1 C2 C3 C4 C5 C6 C7C8 C9 C10 C11 C12 C13 C14 C151 D1 D7

D81

D231

D381

D531

D681

D831

D981

D1131

D1281

D1431

D1581

D1731

D1881

D2031

D2181

D233

1 C16 C17C18 C19 C20 C21 T1 T2 T3 T4

0 0 0 0 0 0 0 0

1D248

TS 0

TS 39

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Inband signalling between Inband signalling between TCSM2E and TRX in the BTSTCSM2E and TRX in the BTS

TCSM

BSC

GS

W

BTS

TRX

DSP2Mb 2Mb2Mb

MS

64 Kbit/s 16 Kbit/s 16 Kbit/s 33.8 Kbit/s

DSP1

DSP90ET

ET

ET

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Inband Inband SSignallingignalling::

Shifting between speech and data

Shifting between half and full rate radio channels

Controlling rate adaptaion functions for data calls

Timing down link frames

Transferring DTX information

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Discontinous transmission, DTXDiscontinous transmission, DTX

SID

DSP

VAD

VAD

DSP

TC BSC BTS MS

Ater Interface

Air Interface

Abis Interface

SID

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Discontinous transmission, DTXDiscontinous transmission, DTX (cont.) (cont.)

Transmission alternates between:

• Speech active phases: one speech frame every 20 ms

• Speech inactive phases: one frame every 480 ms

Down link the speech activity detection is performed by TC

• no speech detected ---> Silence Descriptor, SID, frames to MS

characteristics of the backround noise MS generates the comfort noise

Implemented to reduce interference in the Air interface

Up link DTX is used to save the batteries of the MS and to reduce interference between the TDMA frame time slots in the Air interface

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Submultiplexer functionsSubmultiplexer functions

• The submultiplexer is integrated in the transcoder

• To reduce the number of the 2 Mbit/s links between the MSC and the BSC

• The routing of signals between the MSC side and the BSC side is controlled by the chosen timeslot allocation. The allocation is programmed and loaded into the TRCO

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Submultiplexing - timeslot allocation FRSubmultiplexing - timeslot allocation FR

00010203

24252627

08091011121314151617181920212223

04050607

28293031

0 1 2 3 4 5 6 7

LAPD 1 2 34 5 6 78 9 10 11

12 13 14 15- 17 18 19

20 21 22 2324 25 26 2728 29 30 31

SYNC

- 1 2 34 5 6 78 9 10 11

12 13 14 15- 17 18 19

20 21 22 2324 25 26 2728 29 30 31

- 1 2 34 5 6 78 9 10 11

12 13 14 15- 17 18 19

20 21 22 2324 25 26 2728 29 30 31

64 Kbit/s64 Kbit/s64 Kbit/s

TSLBits

TCH of

Trunk 1

TCH of

Trunk 2

TCH of

Trunk 3

00010203

24252627

08091011121314151617181920212223

04050607

28293031

0 1 2 3 4 5 6 7

LAPD 1 2 34 5 6 78 9 10 11

12 13 14 1516 17 18 1920 21 22 2324 25 26 2728 29 30 31

SYNC

- 1 2 34 5 6 78 9 10 11

12 13 14 1516 17 18 1920 21 22 2324 25 26 2728 29 30 31

- 1 2 34 5 6 78 9 10 11

12 13 14 1516 17 18 1920 21 22 2324 25 26 2728 29 30 31

TSLBits

- 1 2 34 5 6 78 9 10 11

12 13 14 1516 17 18 1920 21 22 2324 25 26 27

TCH of

Trunk 3

TCH of

Trunk 2

TCH of

Trunk 4

TCH of

Trunk 1

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Submultiplexing – timeslotSubmultiplexing – timeslot allocation HRallocation HR

Allocation of different channels on the A-ter interface in case of 8 kbit/s TRAU frame submultiplexing

00010203

24252627

08091011121314151617181920212223

04050607

28293031

TSLBits

0 1 32 4 5 6 7

21 3 4 5 67 8 109 11 12 13 14

15 17 1918 20 21 22 2324 25 2726 28 29 30 31

LAPD

21 3 4 5 67 8 109 11 12 13 14

15 17 1918 20 21 22 2324 25 2726 28 29 30 31

-

21 3 4 5 67 8 109 11 12 13 14

15 17 1918 20 21 22 2324 25 2726 28 29 30 31

-

21 3 4 5 67 8 109 11 12 13 14

15 17 1918 20 21 22 2324 25 2726 28 29 30 31

-

21 3 4 5 67 8 109 11 12 13 14

15 17 1918 20 21 22 2324 25 2726 28 29 30 31

-

21 3 4 5 67 8 109 11 12 13 14

15 17 1918 20 21 22 2324 25 2726 28 29 30 31

-

21 3 4 5 67 8 109 11 12 13 14

15 17 1918 20 21 22 2324 25 2726 28 29 30 31

-

64 Kbit/s64 Kbit/s64 Kbit/s

SYNC

TCH of Trunks 1

TCH of Trunks 2

TCH of Trunks 3

TCH of Trunks 4

TCH of Trunks 5TCH of Trunks 6

TCH of Trunks 7

7 A I/F x Ater

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Nokia DX200 TCSM2ENokia DX200 TCSM2E

• Easy upgrading for future transcoding improvements (software changes are included in BSC software package)

• Software downloadable via BSC

• High performance DX200 technology

• Central supervision and configuration management via the BSC (NMS/2000)

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Transcoder TCSM2E Transcoder TCSM2E functional unitsfunctional units (1) (1)

One to four ET2E cards for providing two to eight 2 Mbits/s interfaces

• one towards BSC, Ater interface

• three towards MSC, A interface

One TRCO unit for providing the storage of the SW and all common functions

• it provides interfaces towards ET2E and TR16-S

• the TRC0 includes 5 LAPD functions: four controls ET2E and one communicates with the BSC

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Transcoder TCSM2E Transcoder TCSM2E functional unitsfunctional units (2) (2)

1 to 14 TR16 units for providing the transcoding function

• Each traffic channel’s TRAU block is realized with one digital signal processor (DSP)

• A DSP can alternatively perform the switching-through of a 64 kbit/s timeslot between the BSC side and MSC side PCM lines

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ET1TC ET1TC CartridgeCartridge

• One ET2E handles two 2 Mbit/s link

• The first (N. 0) PCM interface of ET2E N. 0 is the Ater interface, while the subsequent PCM interfaces are the MSC side PCM line interfaces.

DN9834218

4 x ET2E

4 x ET2E

0 1 2 3

4 5 6 7

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Network Interface (access functionality) Network Interface (access functionality) Exchange Terminal Exchange Terminal ETET

Main tasks: Each ET connects the TCSM2E to a 2 Mbyte/s PCM transmission line

Incoming:• HDB3-decodind• clock extraction• alarm-handling

Outgoing:• HDB3-coding• add alarm bits • Create frame-structure

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TCSM2E CapacityTCSM2E Capacity

TR16-S 2...6 *)

2...82...14

ET2E 1…2 *)

1...31...4

TCH 29…90 *)

or 29...12029...210

*) If BSC-side submultiplexing is carried out by the SMUX unit and three PCMs are multiplexed onto Ater.

Plug-in unit 16 kbit/s 8 kbit/s

SubmultiplexSubmultiplex

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SoftwareSoftware

• The TRCO keeps in non volatile memory

• TRCO programs

• Et2E programs (downloadable from TRCO)

• TR16-S programs (downloadable from TRCO)

• TCSM2E configurations data (including time slot allocation)

• The entire software can be downloaded from a PC (Kermit protocol)

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