02 rn28192en20gla0 bss traffic channels

8/10/2019 02 RN28192EN20GLA0 BSS Traffic Channels

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BSS Traffic Channel

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Soc Classification level

RN28192EN20GLA01 N okia Siemens Networks

BSS Traffic Channels (Review)RG20 (BSS)


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Objectives

After this module the participants should be able to:

Name the BSS network elements that are involved in a circuitand packet switched

Name and specify the interfaces that are involved in a call (A,Abis, Gb)

Explain the traffic and signaling flow for the voice in circuitswitched within BSS network elements

Explain the traffic and signaling flow for the packet data inpacket switched within BSS network elements.

Describe the A, Abis and Gb interface over IP concept


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BSS Traffic Channel

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A interface

MGWMSS

A IF

BSCTCSM

User plane: 64kbps traffic channels

Control plane: SS7 signalling

Transcoding functionality implemented in the TCSM, applied to trafficchannels. In the absence of TCSM equipment, transcoding functionality

could be also implemented in MGW. A interface control plane is defined according to signalling standards(SS7/CCIT#7)

Both control plane and user plane can be implemented over severaldifferent transmission medias: PDH, SDH, Ethernet


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1 2 3 4 5 6 7 8TS

TCHTCHTCHTCHTCHTCHTCHTCHTCHTCHTCHTCHTCHTCHTCHSS7TCHTCHTCHTCHTCH

TCHTCHTCHTCHTCHTCHTCHTCHTCHTCH

0123456789101112131415161718192021

22232425262728293031

A interface standard E1 frame example

Synchronism

Traffic channels

SS7 signalling


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Ater

InterfaceA

Interface

E1/T1

E1/T1

E1/T1

E1/T1

BSC TCSM MSC/MGW

Ater Interface

TCSM

Uncompressed 64kbpsspeech channels

Compressed/multiplexedspeech channels


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Transcoding and submultiplexing

3131 3030 2929 2828 2727 2626 2525 2424 2323 2222 2121 2020 1919 1818 1717 1616 1515 1414 1313 1212 1111 1010 99 88 77 66 55 44 33 22 11 00

xxxx xx b1b1 b2b2 xx xx xx

2 Mbit/s frames from the MSC to the transcoder

2 Mbit/s frames, 125 us

B!B! B2B2 B3B3 B4B4 B5B5 B6B6 B7B7 B8B8

20ms sample, 160 x 2 Mbit/s frames

64 kbit/s timeslot, 8 bits

160 x timeslot from the 160 x 2 Mbit/s frames

DSP for TS 1

DSP for TS 31

160 x 2 bits from timeslot

2 Mbit/s frames, 125 us

20 ms sample, 160 2 Mbit/s frames Mbit/s frames from the transcoder to the BSC (SM2M)

77 66 55 44 33 22 11 160160 159159 158158 157157 156156 155155 154154 77 66 55 44 33 22 11 160160 159159 158158 157157 156156 155155 154154

3131 3030 2929 2828 2727 2626 2525 2424 2323 2222 2121 2020 1919 1818 1717 1616 1515 1414 1313 1212 1111 1010 99 88 77 66 55 44 33 22 11 00

77 66 55 44 33 22 11 160160 159159 158158 157157 156156 155155 154154 77 66 55 44 33 22 11 160160 159159 158158 157157 156156 155155 154154

Transcoder TCSM2

The speech signal is divided into 20 ms samples (160 2Mbit/s frames). Each sampleis taken from the MSC and passed into the transcoder where the Digital SignalProcessor (DSP) performs the RPE-LTP coding of the sample (Regular PulseExcitation - Long Term Prediction). The resulting coded sample is known as thevocoded block, which contains 260 bits for full rate traffic channels or 112 bits for halfrate. Each vocoded block is inserted into a TRAU frame, which contains a vocodedblock plus synchronisation bits and control bits giving a total of 320 bits (16 kbit/s)for full rate or 160 bits (8 kbit/s) for half rate. The frame is reassembled in the DSP inthe transceiver unit of the BTS. Each traffic timeslot has its own DSP for transcoding.


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TCSM BSC

BTS

64 kb

Inband Signallingwithin the TRAU Frame

16 kb

2 Mb/s 2 Mb/s 2 Mb/sETDSP1

DSP90

16 kb16 kb

ET

G

S

W

TRU

TRX

16 kb

DSP

MS

33.8 kb

Inband Signalling between TCSM2 and BTS

Inband signalling between TCSM2 and TRX in the BTS

The bit rate after transcoding is 16 kbit/s for full rate traffic channels, which includes13 kbit/s of transcoded speech/data and 3 kbit/s of control data. For half rate the bitrate is 8 kbit/s, which includes 5.6 kbit/s of speech/data and 2.4 kbit/s of control data.This control data is used for inband signalling between the DSP in the Transcoderand the DSP in the Transceiver Unit of the BTS.

The BTS controls the transcoder with this signalling information for the followingpurposes:

shifting between speech and data,- shifting between half and full rate radio channels,

- controlling rate adaptation functions for data calls,- timing down link frames for speech frames, and- transferring DTX (discontinuous transmission) information.


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Ater

InterfaceA

Interface

Example of Channel allocation for TCSM on Ater IF

2726252431

2322212030

1918171629

1514131228

11109827

765426

32125

31302928242726252423

2322212022

1918171621

1514131220

11109819

765418

32117

3130292816

2726252415

2322212014

1918171613

1514131212

11109811

765410

3219

313029288

272625247

232221206

191817165

151413124

1110983 76542

321LAPD1

Synchronization0

87654321TS

Bits

E1/T1

TCSM

E1/T1

TS 1 2 3 4 5 6 7 8

0

1

23

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31 TCH 31

Bits

Synchronization

TCH 1

TCH 2TCH 3

TCH 4

TCH 5

TCH 6

TCH 7

TCH 8

TCH 27

TCH 28

TCH 29

TCH 30

TCH 23

TCH 24

TCH 25

TCH 26

TCH 19

TCH 20

TCH 21

TCH 22

TCH 15

TCH 16

TCH 17

TCH 18

TCH 11

TCH 12

TCH 13

TCH 14

TCH 9

TCH 10

1

2

3

4

0


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RN28192EN20GLA010 N okia Siemens Netw orks

Gb interface

Transmission

Network

BSC

TCSM

MSC

Frame Relay

Network

SGSN

1

2

3

ET

ET

ET

ET

ET

ET

ESBxx

4

ESBxxIP

Network

Gb interface

The Gb interface is located between the BSC and the SGSN, and it is implementedusing either Frame Relay (FR) or IP.

The Frame Relay can be either point-to-point (PCU SGSN) or there can be aFrame Relay network located between the BSC and the SGSN. The Frame Relaynetwork will be comprised of third-party off-the-shelf products. The following figuredisplays examples of the Gb interface transmission solutions:

In the first solution (1) spare capacity of the Ater and the A interfaces is used for theGb interface. The Gb timeslots are transparently through connected in the TCSM andin the MSC. The second solution (2) represents a transmission network that providesa point-to-point connection between the BSC and the SGSN. In the third solution (3)the Frame Relay network is used.

Gb interface allows many users to be multiplexed over the same physical link usingFrame Relay. Bandwidth is allocated to a user upon activity (when data is sent orreceived) and is reallocated immediately thereafter. This is in contrast to the Ainterface, where a single user has the exclusive use of a dedicated physical resourcethroughout the lifetime of a call irrespective of activity.

A Gb interface Bearer channel can use 1 to 30 64kbit/s timeslots.

Solution (4) illustrates the Gb over IP connection.


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GSW

PCU

BCSU

AS7

MSC/TCSM

SGSN

BTS

MCMU

TCH (Circuit Switched) TCH (Circuit Switched)

Data (Packet Switched) Data (Packet Switched)

Signalling (CCS7)Signalling (LAPD)

ET

ET

ET

Base Station Controller (BSC)

Speech/ HSCSD:The traffic channels in the Ater interface coming from the transcoder are connected

to the BSC Exchange Terminal (ET), and from there to the Group Switch (GSW). TheGSW connects the traffic channel to the correct time slot which is then sent to the ETand further on to the base station (BS). The GSW is controlled by the Marker andCellular Management Unit (MCMU).

GPRS Data:In the BSC, the physical connection to the Gb interface is made through the 2Mbit/slinks (ET2E) and the Group Switch (GSWB), while the PCU unit implements theBSSGP protocol in the Gb interface. The PCU unit receives and transmits TRAUframes to the BS and Frame Relay packets to the Serving GPRS Support Node(SGSN).

Signalling:Signalling data from the MSC (CCS7) and from the base stations (LAPD) is handledby the BCSU.


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XXXXXXXX

OMU12TRX12OMU11TRX11

OMU10TRX10OMU9TRX9

OMU8TRX8OMU7TRX7

OMU6TRX6OMU5TRX5

OMU4TRX4OMU3TRX3

OMU2TRX2OMU1TRX1

TCH3TCH2TCH1TCH0

TCH7TCH6TCH5TCH4

TCH3TCH2TCH1TCH0

TCH7TCH6TCH5TCH4

TCH3TCH2TCH1TCH0

TCH7TCH6TCH5TCH4

TCH3TCH2TCH1TCH0

TCH7TCH6TCH5TCH4

TCH3TCH2TCH1TCH0

TCH7TCH6TCH5TCH4

TCH3TCH2TCH1TCH0

TCH7TCH6TCH5TCH4

TCH3TCH2TCH1TCH0

TCH7TCH6TCH5TCH4

TCH3TCH2TCH1TCH0

TCH7TCH6TCH5TCH4

TCH3TCH2TCH1TCH0

TCH7TCH6TCH5TCH4

TCH3TCH2TCH1TCH0

DYNAMIC ABIS

POOL

0

1

2

3

4

56

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

2223

24

25

26

27

28

29

30

31

1 2 3 4 5 6 7 8Abis interface

TRX-1

TRX-2

TRX-3

TRX-10

(E)DAP

TRXSIG 1 - 10

OMUSIG

Abis interface

The Abis is the interface between the BSC and the BTS. It is a 2 Mbit/s interfacewhich can carry up to 96 channels. The capacity of the Abis interface depends on thetype of signalling (16kbit/s, 32kbit/s, 64kbit/s) used between the BSC and the BTS.The allocation of the channels within the Abis interface is free (TCH must occupy twosuccessive timeslots). For EDGE configuration its possible to define dynamically

Abis pools in 64 kbit/s steps.


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Abis interface

TRU BCF

BTS

BSC

TRX 2

BBTX

RX

BB TXRX

Couplingunit

MS

TRX 1

OMUSIG (LAPD)

TRXSIG 1 (LAPD)

TRXSIG 2 (LAPD)

Transmission Unit (TRU):

- The transmission unit provides the Abis interface to the BSC. The traffic channels andsignalling channels are reallocated in the transmission unit and connected to the correct unit(BCFU or TRX).

Base Controller Function Unit (BCFU):

- Controls the connection between the BSC and the BTS (O/M)

Transceiver (TRX):

The transceiver unit contains two main parts, the base band part (BB) and the radio part(TX/RX).

The base band part of the transceiver unit is responsible for:(in the downlink direction)

block coding

convolutional coding

interleaving

encryption

TDMA formatting

The transmitter (Tx) part of the TRX is responsible for:

(in down link direction)

GMSK modulation

Power amplification

Signalling on Abis interface

LAPD is the protocol used for communication between BSC and the BTS elements. There are

2 kinds of LAPD links:

OMUSIG (or BCFSIG): for O&M purposes, provides communication from the BSC to the BCF.Only one OMUSIG channel per site.

TRXSIG: for call-related signalling and for measurements. Theres one TRXSIG per TRX, andthis link will carry all signalling messages originated by the MSs allocated to this TRX.


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Exercise

MSC

---

----

----

--

--

--

--

--

--

--

--

-- --

--

---- ----

--

--- --- ---

SGSN

MS

Label the network elements and their interfaces

1

TS 1 2 3 4 5 6 7 801 TCH2 TCH3 TCH4 TCH5 TCH6 TCH7 TCH8 TCH9 TCH

10 TCH11 TCH12 TCH13 TCH14 TCH15 TCH16 CCS717 TCH18 TCH19 TCH20 TCH21 TCH22 TCH23 TCH24 TCH25 TCH26 TCH27 TCH28 TCH29 TCH30 TCH31 TCH

2

CCS7

CCS7

CCS7

3

TS 1 2 3 4 5 6 7 80

1 TCH0 TCH1 TCH2 TCH32 TCH4 TCH5 TCH6 TCH73 TCH0 TCH1 TCH2 TCH34 TCH4 TCH5 TCH6 TCH75 TCH0 TCH1 TCH2 TCH36 TCH4 TCH5 TCH6 TCH77 TCH0 TCH1 TCH2 TCH38 TCH4 TCH5 TCH6 TCH79 TCH0 TCH1 TCH2 TCH3

10 TCH4 TCH5 TCH6 TCH711 TCH0 TCH1 TCH2 TCH312 TCH4 TCH5 TCH6 TCH713 TCH0 TCH1 TCH2 TCH314 TCH4 TCH5 TCH6 TCH715 TCH0 TCH1 TCH2 TCH316 TCH4 TCH5 TCH6 TCH717 TCH0 TCH1 TCH2 TCH318 TCH4 TCH5 TCH6 TCH719 TCH0 TCH1 TCH2 TCH320 TCH4 TCH5 TCH6 TCH721 TCH0 TCH1 TCH2 TCH322 TCH4 TCH5 TCH6 TCH723 TCH0 TCH1 TCH2 TCH324 TCH4 TCH5 TCH6 TCH725 TRX1 OMU1 TRX2 OMU226 TRX3 OMU3 TRX4 OMU427 TRX5 OMU5 TRX6 OMU628 TRX7 OMU7 TRX8 OMU829 TRX9 OMU9 TRX10 OMU1030 TRX11 OMU11 TRX12 OMU1231 XX XX XX XX


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BSS Traffic Channel



Exercise

Identify the interfaces of the Base Station Subsystem:

_______ Interface _______ Interface_______ Interface

Check the three frame structures in the diagram above and identify which interfacesof the BSS are they representing.

1

TS 1 2 3 4 5 6 7 801 TCH2 TCH3 TCH4 TCH5 TCH6 TCH7 TCH8 TCH9 TCH

10 TCH11 TCH12 TCH13 TCH14 TCH15 TCH16 CCS717 TCH18 TCH19 TCH20 TCH21 TCH22 TCH23 TCH24 TCH25 TCH26 TCH27 TCH28 TCH29 TCH30 TCH31 TCH

2

CCS7

CCS7

CCS7

3

TS 1 2 3 4 5 6 7 80

1 TCH0 TCH1 TCH2 TCH32 TCH4 TCH5 TCH6 TCH73 TCH0 TCH1 TCH2 TCH34 TCH4 TCH5 TCH6 TCH75 TCH0 TCH1 TCH2 TCH36 TCH4 TCH5 TCH6 TCH77 TCH0 TCH1 TCH2 TCH38 TCH4 TCH5 TCH6 TCH79 TCH0 TCH1 TCH2 TCH3

10 TCH4 TCH5 TCH6 TCH711 TCH0 TCH1 TCH2 TCH312 TCH4 TCH5 TCH6 TCH713 TCH0 TCH1 TCH2 TCH314 TCH4 TCH5 TCH6 TCH715 TCH0 TCH1 TCH2 TCH316 TCH4 TCH5 TCH6 TCH717 TCH0 TCH1 TCH2 TCH318 TCH4 TCH5 TCH6 TCH719 TCH0 TCH1 TCH2 TCH320 TCH4 TCH5 TCH6 TCH721 TCH0 TCH1 TCH2 TCH322 TCH4 TCH5 TCH6 TCH723 TCH0 TCH1 TCH2 TCH324 TCH4 TCH5 TCH6 TCH725 TRX1 OMU1 TRX2 OMU226 TRX3 OMU3 TRX4 OMU427 TRX5 OMU5 TRX6 OMU628 TRX7 OMU7 TRX8 OMU829 TRX9 OMU9 TRX10 OMU1030 TRX11 OMU11 TRX12 OMU1231 XX XX XX XX

02 rn28192en20gla0 bss traffic channels

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