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EG19: Abis InterfaceLM: 4

Engineering Guideline

401 - 380 - 349Version 0.9February 1998

Lucent Technologies — ProprietaryThis document contains proprietary information of Lucent Technologies and is not to be

disclosed or used except in accordance with applicable agreements.Copyright © 1998 by Lucent Technologies

Unpublished and Not for PublicationAll Rights Reserved

Engineering Guideline EG19: Abis Interface

Lucent Technologies PROPRIETARYSee notice on first page

2 Version: 0.9 LM: 4



Version: 0.9 LM: 4 3

This material is protected by the copyright and trade secret laws of the United States andother countries. It may not be reproduced, distributed or altered in any fashion by anyentity, including other Lucent Technologies Business Units or Divisions, without theexpressed written consent of the Customer Technical Support and Informationorganisation.

Notice

Every effort was made to ensure that the information in this document was complete andaccurate at the time of printing. However, information is subject to change.




Table of Contents

1.1 About this Guideline 7

1.2 Overview 7

1.3 Dimensioning the Abis Interface 81.3.1 LM4 Abis Interface timeslot allocation 91.3.2 LM5 Abis Interface timeslot allocation 101.3.3 Example 1 111.3.4 Example 2 12

1.4 References 13




1.1 About this GuidelineThis Engineering Guideline provides a description of the physical characteristics of theAbis interface and defines how the Abis interface is dimensioned within the “LucentGSM Network”.

1.2 OverviewThe Abis Interface supports signalling and traffic circuits between the Base TransceiverStation(BTS) and the Base Station Controller Frame (BCF). The Abis Interface is basedon the PCM30 transmission principles of the ITU-T at a data rate of 2.048 Mbit/s. ThePCM30 interface carries 32 x 64 Kbit/s channels.

Functions implemented at the Abis Interface are:

• Voice/Data traffic exchange

• Signalling exchange between the BCF and BTS

• Transport of O&M information between the BTS and the BCF.

The bandwidth of each Abis interface is shared by31 timeslots1. Some timeslots areallocated to carry traffic and others to carry signalling information.

“Traffic” timeslots are subdivided into 4 x 16 Kbit/s subrate GSM1800/GSM900 traffic .channels.2 The situation is shown schematically in

BTS-2000 BCF-2000

TS0 TS1 TS31

64Kbit/s

16Kbit

16Kbit

16Kbit

16Kbit

13Kbit

3Kbit

4 Sub-rate Trafficchannels in every

timeslot

Ove

r-he

ad

Voc

oded

Spe

ech

Bit transferRate

8 Bitframes

2.048 Mb/s

either or

64Kbit

Signallinglink

16Kbit

16Kbit

16Kbit

16Kbit

Lucent LM4 method

Lucent LM5 methodLAPD signalling concentration

function

Abis PhysicalCharacteristics

Figure 1:Physical characteristics of the Abis Interface.

1 E1 has 32 timeslots but timeslot 0 is utilised for frame synchronisation.2 These are termed “full-rate” 16 Kbit/s traffic channels. “Half-rate” 8kbit/s traffic channels will beavailable in the future.




1.3 Dimensioning the Abis InterfaceLucent BTS-2000 products can have up to 3 Abis interface connections. (e.g. 3 x E12.048Mbit/s links)3

• 2 Abis interfaces to a BCF

• 1 Abis link output to provide the multidrop capability

Alternatively

• 1 Abis interface to a BCF

• 2 Abis interface outputs to provide the multidrop capability

One exception is the Lucent BTS-Compact which has a maximum of 2 Abis interfaces.

• 1 Abis interface to a BCF

• 1 Abis link output to provide the multidrop capability.

3 Lucent also supports the T1 transmission system. This is not detailed in this document but may beincluded at a later date.




1.3.1 LM4 Abis Interface timeslot allocationEach TRX connected via the Abis interface requires three timeslots.

• 2 for voice traffic/data

• 1 for signalling

Each Cell/Sector connected via the Abis interface requires 1 timeslot for O&M signalling.

Example: for a 3-sectored (3,3,3) site

# Timeslots = 3 x # TRXs + # Cells

= 3 x 9 + 3 = 30 timeslots required.

The Lucent BSS configuration allows a maximum of 7 multidropped BTSs on a singleAbis Interface connection.4

The maximum number of TRXs which can be placed on a single Abis is 10.

i.e. 3 x # TRXs + # Cells

= 3 x 10 + 1

= 31 (Max. No. of timeslots available on a single Abis.

A single cell cannot be split across different Abis links. An omni 11 or omni 12 cannot besupported with LM4 software release. A 3-sectored 4,4,4 or 4,4,3 can be supported byplacing the 3rd cell on a second Abis.

Timeslot allocation summary (LM4)

Number of Multidrops1 2 3 4 5 6 7

Maximum TRXs 10 9 9 9 8 8 8Timeslots 31 29 30 31 29 30 28

SYNC ST T T ST T T ST T T ST T T ST T T

ST T T ST T T ST T TT orS07

T orS05

T orS04

T orS03

T orS04

S01T orS06

TR

X1

TR

X2

TR

X3

TR

X4

TR

X5

TR

X6

TR

X7

TR

X8

TR

X9

TR

X10

Where T =Traffic Channel ST = TRX Signalling

S0n = Signalling for Cell n

Figure 2: Timeslot allocation with LM4 software release.

4 Multidrop indicates that more that one BTS can utilise the same Abis interfaceconnection




1.3.2 LM5 Abis Interface timeslot allocationLM5 provides the LAPD Link Concentrator Function. This allows the concentration of 4logical signalling links onto one physical timeslot on the Abis Interface. (i.e. .4 x 16Kbit/ssubrate slots). This allows a more economical use of the Abis transmission capacity. BothTRX related signalling and cell(O&M) related signalling can be combined into a singletimeslot, but all signalling channels sharing a timeslot must be in the same cell.

Each TRX connected via the Abis interface requires:

• 2 timeslots for voice traffic/data

• 1 timeslot for signalling . 1 timeslot can accommodate signalling for:

• up to 4 TRXs (all TRXs must be in the same cell) OR

• 3 TRXs + 1 O&M ( all TRXs must be in the same cell and O&Mmust relate to that cell).

With these capacity increases, a single Abis interface can support up to 12 TRXs inmulticell or single cell configurations




1.3.3 Example 1For a 3-sectored (4,4,4) site:

Traffic Timeslots required = 2 x # TRXs = 2 x 12 = 24

Perform the signalling timeslot calculation on a per cell basis.

# Signalling Timeslots for cell A = # TRX + 1 = 4 + 1 = 2 4 4

Signalling Timeslots required for cell B and C are the same in this example.

Total # signalling channels required = 3 x 2 = 6

Total # Timeslots required = # Signalling timeslots + # Traffic timeslots = 6 + 24 = 30.

The situation is shown schematically in Figure 3.

SYNC S01 S4T T T T T T T T T S02 S4T T T T T

T T T T S03 S4T T T T T T T TT

TR

X3

Where T =Traffic Channel SnT = Signalling for n TRXs


TR

X1

TR

X2

TR

X4

TR

X11

TR

X9

TR

X10

TR

X12

TR

X7

TR

X8

TR

X5

TR

X6

Cell 1

Cell 3Cell 2

Cell 2

Figure 3:Timeslot allocation for 4,4,4 configuration, with LM5 release.




1.3.4 Example 2For a 2 x 2-sectored 3,3 on a single Abis:

Traffic Timeslots required = 2 x # TRXs = 2 x 12 = 24

Perform the signalling timeslot calculation on a per cell basis.

# Signalling Timeslots for cell A = # TRX + 1 = 3 + 1 therefore 1 timeslot required

4 4

Signalling Timeslots required for cell B and C are the same in this example.

Total # signalling channels required = 4 x 1 = 4

Total # Timeslots required = # Signalling timeslots + # Traffic timeslots = 4 + 24 = 28

SYNCS3T+S01 T T T T T T

S3T+S02 T T T T T T

S3T+S03

T T T T T TS3T+S04

T T T T TT

TR

X3

Where T =Traffic Chanel SnT = Signalling for n TRXs


TR

X1

TR

X2

TR

X4

TR

X11

TR

X9

TR

X10

TR

X12

TR

X7

TR

X8

TR

X5

TR

X6

Cell 1

Cell 4Cell 3

Cell 2

Figure 4: Timeslot allocation for 2 x 2 sectored 3,3 on a single Abis, using release LM5 software.

The Lucent BSS configuration at LM5 allows a maximum of 7 multidropped BTSs on asingle Abis Interface connection.




1.4 References

[Ref. 1] BSS Network Configuration Training Course (WL9011), Issue A, June 19 1997[Ref. 2] Lucent Network Design Tool (NDT). Available through Offer Engineering, Swindon, England

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