05_dynamic abis system description for bss10

NOKIA Company Confidential

RAS Dynamic Abis System Description for BSS10 (37)10.9.2004 Version 2.00

Dynamic Abis

System Description for BSS10

Version 2.00

Filename:

Keywords:

Prepared by Reviewed Approved Document NumberHHe, EJä N/A



Document History

Version Date Author(s) Changes and other notes0.01 Edit 9.6.1999 Harri Helminen Document started0.02 Edit 9.7.1999 Esa Järvelä Chapters 4.x.x and part of 5.x.x and 6.x.x added0.03 Edit

0.04 Edit 0.05 Edit

0.06 Edit

19.7.1999

28.7.199930.8.1999

30.8.1999

Esa Järvelä

HHeHHe

EJä

Comments from Leif Friman added to chapter 4.x.xPart of chapters 2.x and 3.x addedChanges from 4.8 meeting and chapters 2 and 3 modified, Dyn Abis simulation added Changes from 4.8 meeting and added chapter 5, edited by Arto Kangas

0.07 Edit 27.9.1999 EJä&HHe Changes from 1.9. meeting0.08 Edit 18.10.1999 EJä Changes after 29.9 and 15.10 meetings1.00 26.10.99 EJä Corrections after 19.10 meeting, first accepted

version1.01Edit 20.3.2000 EJä Updating to semi-dynamic chapters 4 -> 1.02Edit 23.3.2000 HHe Updating to semi chapters 1-31.03Edit 05.04.2000 EJä Updating chapter 42.00 18.04.2000 EJä Comments added, version for BSS102.00 08.05.2000 EJä Comments and corrections



Table of Contents

Page

1 INTRODUCTION......................................................................................................................................... 5

1.1 DOCUMENT OVERVIEW............................................................................................................................... 51.2 SCOPE AND READERSHIP............................................................................................................................. 51.3 DEFINITIONS AND TERMINOLOGY................................................................................................................ 51.4 RELATED DOCUMENTS................................................................................................................................ 6

2 DYNAMIC ABIS OVERVIEW.................................................................................................................... 7

2.1 PRINCIPLE OF SEMI DYNAMIC ABIS............................................................................................................. 72.1.1 Physical Connections........................................................................................................................ 72.1.2 Semi Dynamic Abis........................................................................................................................... 8

2.2 NETWORK ELEMENTS AND ENTITIES INVOLVED.........................................................................................102.3 CALCULATING THE BLOCKING OF SEMI-DYNAMIC ABIS EDAP....................................................................102.4 TOOLS...................................................................................................................................................... 17

2.4.1 Planning Tools................................................................................................................................ 172.4.2 Management Tools.......................................................................................................................... 18

2.5 TRANSMISSION TOPOLOGIES...................................................................................................................... 182.6 TRANSMISSION LINE INTERFACES.............................................................................................................. 22

3 TRANSMISSION IF SPECIFICATION OF DYNAMIC ABIS...............................................................23

3.1 OVERVIEW OF TRANSMISSION SIGNALING LAYERS.....................................................................................233.2 APPLICATION LAYER SPECIFICATION......................................................................................................... 23

3.2.1 Dynamic Abis Transmission Management.......................................................................................233.2.2 Testing of Pool after Commissioning and in Use............................................................................24

3.3 TRUNET SPECIFICATION............................................................................................................................. 243.4 PHYSICAL SPECIFICATION.......................................................................................................................... 24

3.4.1 Additional Physical Requirements to E1, T1, HDSL........................................................................243.4.2 C-type Crossconnections................................................................................................................. 24

4 O&M IF SPECIFICATION OF DYNAMIC ABIS...................................................................................24

4.1 OVERVIEW................................................................................................................................................ 244.2 DYNAMIC ABIS POOL HANDLING............................................................................................................... 24

4.2.1 Creation of the Dynamic Abis Pool.................................................................................................244.2.2 Modification of the Dynamic Abis Pool...........................................................................................244.2.3 Deletion of the Dynamic Abis Pool..................................................................................................244.2.4 BCF/BTS/TRX Creation.................................................................................................................. 24

4.3 ABIS AUTOCONFIGURATION...................................................................................................................... 244.4 ABIS LOOP TEST....................................................................................................................................... 244.5 RADIO NETWORK RECOVERY.................................................................................................................... 24

5 TELECOM IF SPECIFICATION OF DYNAMIC ABIS.........................................................................24

5.1 DYNAMIC ABIS POOL HANDLING............................................................................................................... 245.1.1 Creation of dynamic Abis Pool........................................................................................................245.1.2 EDAP Upgrade............................................................................................................................... 245.1.3 EDAP Downgrade........................................................................................................................... 24

5.2 CIRCUIT SWITCHED SERVICES................................................................................................................... 245.3 PACKET SWITCHED SERVICES.................................................................................................................... 24

5.3.1 Overview of Signaling Layers.......................................................................................................... 245.3.2 GPRS TBF...................................................................................................................................... 245.3.3 EGPRS TBF.................................................................................................................................... 24



5.3.4 L1 Specification.............................................................................................................................. 24

6 USE CASES................................................................................................................................................ 24

7 TESTING.................................................................................................................................................... 24

7.1 TRACE TOOLS (ABIS)................................................................................................................................ 24



1 INTRODUCTION

1.1 Document Overview

This document is a short description of semi dynamic Abis, it's behavior and services. The chapter 2 gives a short overview of the semi dynamic Abis. The chapter 3 describes the transmission-related things and describes shortly possible network configurations. The chapter 4 describes the O&M services of the semi dynamic Abis. The chapter 5 describes PS telecom services related to semi dynamic Abis. The chapter 6 goes through some use cases. Chapter 7 gives some requirements to the trace tools to support semi dynamic Abis.

1.2 Scope and Readership

The document is written for people in R&D.

1.3 Definitions and Terminology

AC pool Autoconfiguration pool

BSC Base Station Controller

BTS Base Transceiver-Station

BSS Base Station Subsystem

CS-1… CS-4 GPRS channel coding schemes

EDAP EGPRS Dynamic Abis Pool

EDGE Enhanced Data rates for GSM evolution (New modulation scheme for GSM)

EGPRS Enhanced General Packet Radio Service

FC Wireline transmission unit with one line interface to the 2 Mbit/s (E1) or 1.5 Mbit/s (T1) transmission line. FC E1/T1 has no cross-connection capability.

FXC Wireline transmission unit with four line interfaces to the 2 Mbit/s (E1) or 1.5 Mbit/s (T1) transmission line. FXC E1/T1 has cross-connection capability at 8 kbit/s level.

LAPD Link Access Protocol

MCS-1… MCS-9 EGPRS channel coding schemes

SGSN Serving GPRS Support Node



TBF Temporary Block Flow (GPRS data transfer (call))

PCU Packet Control Unit

RR Radio Resource

Master Abis channel 16 kbit/s Abis channel which carries all the information in GMSK and tells the dynamic Abis sub-TSLs in the 8-PSK EGPRS

1.4 Related Documents

EDGE System Requirement Specification RAS/GSM B6S 065833AE

EDGE Transmission System Study

EDGE System Test Plan

Cellular Autoconfiguration System Functional Specification

EGPRS Requirement Specification

GPRS/EGPRS ABIS L1 Interface Specification

BTS SW Telecom Functional Specification(s) for BSS10

EDGE UC/DSP Interface Specification

BSC Dynamic Abis Requirement Specification



2 DYNAMIC ABIS OVERVIEW

2.1 Principle of Semi Dynamic Abis

2.1.1 Physical Connections

The 2M(31*64 kbit/s) Abis channel connections are divided in two different types: TRX dedicated and TRX shared. BSC's dynamic pool must be visible exactly the same as in peer BTS.

TRX dedicated, permanent logical point to point type Abis channel connections are provided between BSC and TRX units of the BTS. The actual implementations are B-type branching in chain, point-to-point and star networks, and protective Y-type connections in the loop networks.

TRX shared, permanent logical point to multipoint type Abis channel connections are provided between BSC and TRX units of the BTS. The actual implementations are digital common channel (C0) connections in all topology networks. See Figure 1

Figure 1 Shared connections principle of usage



Shared pool contains digital common channel connections between BSC and BTS. The BSC grants the permission to use a particular timeslot for each TRX on time domain basis. For example, if lot of transmission capacity is needed at the BTS, the BSC may grant permissions for TRX to start using timeslot(s) and grant permissions for other TRX to start using other timeslot(s) from the shared pool.

Figure 2 C-type pool

2.1.2 Semi Dynamic Abis

Abis PCM has 16 to 64 kbit/s for TRXsigs for each TRX, 16 to 64kbit/s for OMUsig and 16 kbit/s TSL for each TCH in a TRX. Additionally operator can locate EDAP for EGPRS usage. The Abis PCM resources for traffic timeslots, which requires more than 16kbit/s, are hunted dynamically. This implementation enables dimensioning of the Abis transmission by the real traffic amount and can provide great saves for operator transmission costs.



Figure 3 Example Abis PCM with semi dynamic Abis

PS services

For PS services the dynamic Abis implementation means extra signaling between BSC and BTS. In dynamic Abis the 16 kbit/s Master Abis channel for GPRS PDTCH is static and all additional capacity is hunted dynamically when the PDTCH is included in (E)GPRS territory.



2.2 Network Elements and Entities Involved

The dynamic Abis puts requirements to OSS and BSS. Main changes are aimed to BTS and BSC software, see chapters 4 and 5. Network management elements require new way to manage the dynamic Abis pool. Management System shall also show statistic display of the status of dynamic pool, in real time and some kind of long-term statistic.

The dynamic Abis does not cause any requirements to the SGSN or other GPRS backbone network elements or above the BSC (no changes MSC, HLR, VLR).

The network planning tool, Totem will support the dynamic Abis Pool planning. The requirements for Totem are open; e.g. the limits of the dynamic Abis pool and what are the parameters, which have effect to the dynamic Abis pool

2.3 Calculating the blocking of semi-dynamic Abis EDAP

Each EGPRS radio timeslot takes 1 master subtimeslot from the fixed "pool" and 4 slave subtimeslots (=1 64kbit/s timeslot) from the EDAP with the MCS-2 … MCS-9 channel codings. EDAP pool size can be calculated when we know how many TRXs are connected to chosen ET_PCM and what kind of signaling is used in the connected BTSs.

When we know the pool size and how many air-timeslots are competing of the usage of the pool we can calculate the Abis overflow (blocking) value. Pool overflow (blocking) can be calculated using theorem of binomial distribution.

, Where x is the number of successes in trials, p is the utilization of the slave (E)GPRS channels (CS-1, CS-2, MCS-1 and re-transmission are not included in it), n are the GPRS (air)-timeslots in use. Probability of pool overflow (blocking) will be:

B(n,N,p)=

, Where N is the available pool size.

Block errors and acknowledgement messages are taken into account with the parameter p (slave (E)GPRS channel utilization.)

As said calculation of the pool overflow (blocking) requires the knowledge of the planned 2M path systems. We have to take into account all of the Edge base stations in



the ET_PCM (2M) frame. This will require creation of the 2M path system before we can calculate the blocking. We must get the information what TRXs are connected to chosen 2M frame and what kind of signaling TRXs and base stations are using before we can calculate the blocking. Also the knowledge of the possible link management, Q1 and pilot bit timeslot in ET_PCM (2M) frames is required.

Example 1:

EDGE site configuration 3+3+3 (takes 9*2=18 timeslots from ET_PCM for traffic timeslots)

16kbit/s signaling for both OMUSIG and TRXSIGs (takes 9+1 subtimeslots =3 timeslots from ET_PCM for signaling)

Number of active EGPRS radio timeslots at a time 4+4+3 = 11 (These are estimated values based e.g. simulations in certain type of area).

Maximum size of the EDAP

=32 Timeslots – 'link management timeslot' - 'pilot bit timeslots'-'TRX traffic '-'Signaling timeslots'

=32 TSs – 1TS –1TS – 18TS –3TS = 9 timeslots

How much blocking is this causing?

Each EGPRS radio timeslot takes 1 master subtimeslot from the fixed "pool" and 4 slave subtimeslots (=1 timeslot) from the EDAP. The probability to use these 4 slave timeslots is p.

So, we have 11 traffic channels competing from 9 (64kbit/s) timeslots from the EDAP.

Let the EDAP slave channel usage percent of these competing timeslots be 50 % (with MCS-9 on average 29.6 kbps).

We can calculate the overflow (blocking) of the EDAP with the binomial distribution

Abis overflow (blocking) = 1- Binomdist (pool, number of radio timeslots, usage percent

In this case:

Abis overflow (blocking) = 1- CumulativeBinomdist(9TS, 11TS, 50 %) = 0.005859375 = 0.58 %

If the Abis overflow (blocking) is allowed to be 2% how many radio timeslots can there be:



2% = 1- CumulativeBinomdist(9TS, x TS, 50 %)

x = 12 Timeslots

Figure 4 3+3+3 configuration with the different channel usage %s./2/.

If we would reserve 11 fixed EGPRS channels we would require (Number of TCHs =9*8=72 TCHs) = 16k TCHs+64k Pool size+64k link&pilot bit timeslots(2 timeslots are for link management and pilot bits (usually timeslots 0 and 31))+16k BCF SIG + 16k TRX SIGs = 72+11*4+2*4+1+9*1 subtimeslots = 33.5 timeslots>ET_PCM.



If we allow very small pool overflow (blocking) (0.58%) we can fit this traffic into one ET_PCM.

If you try guarantee MCS-9 access to network with every air-timeslots you'd need up to 3 x 2M lines for 3+3+3 configuration

Fixed Abis (16k)= number of fixed 16k subtimeslots + number of 16k slave subtimeslots + number of 16k signaling subtimeslots + link&pilot bit subtimeslots

= 9 TRX * 8ch subTS + (9TRX * 8ch-3ch)*4subTS + 3*4subTS + 3*2*4subTS=72 + (72-3)*4+12+24=72+276+12+24=384=384 x 16ksubtimeslots=384/4=96 x 64ktimeslots=96 / 32=3 x 2M frames

Now that we use EDAP and allow very small pool overflow (blocking) we can save much transmission capacity. In this example using the dynamic pool versus fixed Abis saves us up to 66 % of transmission capacity!

Table 1 Transmission savings compared to fixed Abis with different pool overflow (blocking) values (example 1.)

EDAP Size - size of the EDAP in 64k timeslots Number of EGPRS radio timeslots - number of EGPRS radio timeslots in use at a time. Minimum savings are calculated – what are the minimum saving when semi-dynamic Abis is used with certain pool overflow (blocking) compared to fixed Abis solution with certain number of EGPRS timeslots 30TS/(number of EGPRS radio timeslots – EDAP Size). Maximum savings in the transmission capacity – maximum savings in the transmission capacity when MCS-9 is guaranteed for all of the TCHs ((1-(semi-dyn capa/fixed dyn cap))*100%)



Maximum required transmission capacity – maximum required transmission capacity when MCS-9 is guaranteed for all of the TCHs.



Example 2:

EDGE Site configurations 1+1 (2 EDGE TRXs) and 1+2+2 (5 EDGE TRXs) in the chain. (takes 7*2=14 timeslots from ET_PCM for traffic timeslots)

16kbit/s signaling for both OMUSIGs and TRXSIGs (takes 2(OMUSIG) +7(TRXSIG) subtimeslots =3 timeslots from ET_PCM for signaling)

2 timeslots are for link management and pilot bits (usually timeslots 0 and 31)

EDGE BTS#1: 1+1

64kTimeslots=2*(2+0.25)+0.25=4.75 timeslots

EDGE BTS#2: 1+2+2

64kTimeslots=5*(2+0.25)+0.25= 11.50 timeslots

Maximum size of the EDAP

= 32 TSs – 2TSs – (2+5)*2TSs - 3TSs= 13 timeslots

How much blocking is this causing?

EDGE BTS#1: 1+1

Number of active EGPRS radio timeslots at a time 3+5 = 8 (These are estimated values based e.g. simulations in certain type of area).

EDGE BTS#2: 1+2+2

Number of active EGPRS radio timeslots at a time 3+4+4 = 11 (These are estimated values based e.g. simulations in certain type of area).

So, we have 8+11=19 traffic channels competing from 13 (64kbit/s) timeslots of the EDAP.

Let the usage percent of these competing timeslots be 50 % (with MCS-9 this corresponds to average throughput of 29.6 kbps).We can calculate the overflow (blocking) of Abis with the binomial distribution.Abis overflow (blocking) = 1- Binomdist (pool, number of radio timeslots, usage percent

In this case



Abis overflow (blocking) = 1- Binomdist(13TS, 19TS, 50 %) = 0.031784 = 3.2 %

If the Abis overflow (blocking) is allowed to be 1% how many radio TS can there be:1% = 1- Binomdist(13TS, x TS, 50 %)x = 17 Timeslots

In the fixed abis we would need:

=32 + 19-13 timeslots = 38 timeslots = 1.1875 x 2M, so 18.75 % more capacity.

Figure 5 Two BTSs in the same 2M line configurations 1+1, 1+2+2. Pool size 13



Figure 6 2M timeslot allocation template for Example 2.

If you try guarantee MCS-9 access to network with every air-timeslots you'd need up to 2.25 x 2M (3 x 2M) lines for 1+1,1+2+2 configuration.

Fixed Abis (16k)= number of fixed 16k subtimeslots + number of 16k slave subtimeslots + number of 16k signaling subtimeslots + link&pilot bit subtimeslots= 7 TRX * 8ch subTS + (7TRX * 8ch-5)*4subTS + 3*4subTS + 3*2*4subTS=56+(56-5)*4+12+24



=56+204+12+24=296 x 16ksubtimeslots=296/4=74 x 64ktimeslots=74 / 32=2.3125 x 2M frames

Now that we use EDAP and allow very small pool overflow (blocking) we can save much transmission capacity. In this example using the EDAP versus fixed Abis saves us upped 56 % of transmission capacity!

Table 2 Transmission savings compared to fixed Abis with different pool overflow (blocking) values (example 2.)

2.4 Tools

2.4.1 Planning Tools

The capacity planning of transmission network is planned with Totem. Before the semi dynamic Abis, Radio network plan tells how much capacity each BTS requires. When semi dynamic Abis pool is taken into use and the transmission capacity is calculated, the amount of the estimated packet data also has to be taken into account. Figure 7 shows simplified activity diagram of the Cellular network planning process.



Customer requirements

TRS Network Dimensioning

TRS Media selections- Topology/capacity for networks-> possible shared Dyn Abis and AC pools

Site HuntingTech. Site survey

MWR link planningby NPS/X, Totem,...

Detailed network planningRouting plans for AC poolsPlans for Shared Dyn Abis poolsby NPS/10

Required capacity

Transmission Network

Plan

Figure 7 Cellular network planning process and semi Dynamic Abis modifications to it

2.4.2 Management Tools

The circuit manager is used to modify dynamic Abis pool through the network. It works with the TruNet. The existing (old) cellular transmission equipment has to be managed by PC-manager (or service terminal). The traffic manager is used to manage Abis allocation in one BTS. It shall also have dynamic Abis support. See also chapter 3.2.1.

2.5 Transmission Topologies

All type of networks are supported (star, chain, loop, mesh). There are some limitations that have to be taken into account when networks are planned.



FXC units can make summing from 7 signals to one signal. Other transmission units have also some limitations, such as the number of signals that they can sum see chapter 3.4.2

The FC cards have not cross connection functions. The FC units connect all signals from the D-bus to the interface (2M or Flexbus) and the unit is always located to the tail site. Thus, the summing function has to be made on next Hub site. Here Hub site does not signify real Hub, all the other FXC units or other cellular transmission units can make the dynamic Abis function (C-type cross connection), see chapter 3.4.2.

Figure 8 FC-units / Dynamic Abis

Example CHAIN network

In Figure 9 there is a basic chain network. All BTSs have a cross connection function, so that it is afterwards easy to continue/branch dynamic Abis pool. BTSs can also be BTSs of previous generation.

Figure 9 Chain network



Example Two chain + hub site

In Figure 10, two new BTSs have been added to the basic chain network. BTS1 has to have at least TRUA or a newer transmission unit, which is able to sum three input signals. All other BTSs could have any transmission unit.

Figure 10 Two chains connected by hub



Example LOOP network

Conditional connections shall be used for the loop network. In Figure 11, DN2 is a loop master. It is also possible that TRUA or FXC work as a loop master.

BTS3

DN2 BTS2

BTS1

= C-type cross connection

Dyn Abis pool

B-type

B-type

BSC

Figure 11 Loop network, normal situation



A failure situation. Units next to the faulty recognize the failure and change connections to B-type and all other units use C-type connections.

BTS3

DN2BTS2

BTS1

Loop master

= C-type cross connection

Dyn Abis pool

B-type

B-type

FAILURE

BSC

Figure 12 Loop network, failure situation and new connections

2.6 Transmission Line Interfaces

The dynamic Abis doesn't create additional physical requirements to PDH line interfaces, all kind of PDH interface types are possible. The capacity of dynamic Abis versus line interface has to be taken into account when defining a network and a dynamic Abis pool (T1, HDSL).

It is also possible to use FXC STM-1 when the signal is dropped to 2M level.



3 TRANSMISSION IF SPECIFICATION OF DYNAMIC ABIS

3.1 Overview of Transmission Signaling Layers

This chapter describes management of transmission, which is related to dynamic Abis, and transmission physical interface, which is related to the dynamic Abis.

3.2 Application Layer Specification

3.2.1 Dynamic Abis Transmission Management

3.2.1.1 Co-operation with Autoconfiguration of FXC Units

Release 3 of autoconfiguration will support configuration of dynamic Abis Pool. When new site is taken in use, the Autoconfiguration connects TRXs to the dynamic Abis pool (ref. Cellular autoconfiguration System functional specification)

FXC units (which has TruNet) support Autoconfiguration and circuit manager.

3.2.1.2 Pool Management by Circuit Manager

The circuit manager is a network topology -oriented management application for cellular transmission equipment and it works part of Autoconfiguration concept. The dynamic Abis shall be able to manage by circuit manager.

Dynamic Abis pools or circuits are a bit different than normal point to point connections between TCH and BSC. The type of dynamic Abis pool is point to multi-point. The circuit manager shall have own commands for show, create and edit dynamic Abis. It shall manage complete pool from any point of pool.

3.2.1.3 Pool Management by BTS Traffic Manager

Installation engineer uses traffic manager to manage connections of Abis TS allocation at signal level (TCH, TRXSIG, OMUSIG…). Traffic manager shall have own selection to manage Dynamic Abis pool and connections. Installation engineer shall have possible to define which timeslot is connect permanently and which timeslots are shared and which TRX s used shared timeslots.



3.2.1.4 Pool Management by PC-manager

FXC manager makes C-type connections at 8 kbit/s, 16 kbits, 32 kbit/s, 64 kbit/s or n x 64 kbit/s. FXC manager manages one node and operates at connections level. User could not show/make circuits through the network by FXC manager.

3.2.1.5 Pool Management by Service Terminal

User could use service terminal or service terminal emulator when manages dynamic Abis pool in old cellular transmission units, as DB2, DN2, etc.

It is also possible to manage C-type connections of FXC at 64kbit/s level by using the service terminal (or ST emulator). When it is wanted more accurate/higher level cross connections then the HubMan or DtruMan has to use. (HubMan and DtruMan are manager softwares for FXC units).

3.2.2 Testing of Pool after Commissioning and in Use

It is important that dynamic Abis pool will be tested after commissioning. There will be a few different tests. Test after commissioning will test that BSC has connections to the BTS through the pool (modified Abis loop test). The test will be made so that BSC make Abis loop test for first and last timeslot in EDAP, also it will test permanent connections (master channels) by the normal Abis test. More advanced test shall verify that every TRXs have connections to the BSC or operator could define TRX and timeslot which is under test. This "one timeslot/TRX test" is possible to make when the pool is in use.

After faulty timeslot(s) has been found, this timeslot or these timeslots should be segregated by using Q1 commands. User manuals have to have guide and/or flow charts how to find/block faulty unit. The chapter 4.5 describes BSC's fault counters which helps to find faulty unit.

3.3 Trunet Specification

The dynamic Abis do not cause any changes to the Trunet specifications.

3.4 Physical Specification

3.4.1 Additional Physical Requirements to E1, T1, HDSL

The Dynamic Abis doesn't create additional physical requirements to line interface.



3.4.2 C-type Crossconnections

The dynamic Abis function in transmission units is C-type crossconnection. This feature is supported by following transmission units BIUMD, DB2, DN2, TRUA(A-H) and FXC units (not FC units).

Digital summing is made by using "AND-function" in the crossconnection ASIC. Two or more lines are connected to ASIC's AND-function as inputs. Outline gives "sum" of these lines (free/no signal is continuous 1, active signal is 0). See Table 3

IN1 IN2 OUT

0 0 0

0 1 0

1 0 0

1 1 1

Table 3 Digital summing

DB2 and BIUMD special features related to Dynamic Abis

A digital common channel (C-type connection) can be defined for any 32 kbit/s channel

DN2 special features related to Dynamic Abis

A digital common channel (C-type connection) can be defined for any 64 kbit/s or 32 kbit/s channel. DN2 could combine max 4 incoming signals to one signal (bus).

TRUA – TRUH units special features related to Dynamic Abis

A digital common channel (C-type connection) can be defined for any 64 kbit/s or 32 kbit/s channel.

FXC (FC) – units special features related to Dynamic Abis

A digital common channel (C-type connection) can be defined for any 64 kbit/s, 32 kbit/s or 16 kbit/s channel. All FXC units could combine max. 7 incoming signals to one signal (bus). FC units haven't any cross connection function, so it can not make any C-type connections.



4 O&M IF SPECIFICATION OF DYNAMIC ABIS

4.1 Overview

The semi dynamic Abis approach means that the normal signaling links (TRXSIG and OMUSIG) and Abis channel allocation for TCHs are allocated from the Abis fixedly as previously. The Abis channel allocation for EGPRS demand will be made by BSC on a call basis from the transmission pool (EDAP).

Only the new 5th generation BTSs (DINO2, (E)PUMA, and (E)CATS) are able to use Dynamic Abis allocation.

OMU & n*TRXSIGs

n*TCH

EDAP

ETPCM1

OMU & n*TRXSIG

n*TCH

EDAP1

OMU & TRXSIG

n*TCH

EDAP2

EDAP can be used by TRXs of ETPCM1

SIGNALLING

16kbit/s fixed Abis traffic timeslotsEGPRS dynamic Abis poolETPCM2

O&M and TRX Sign. TSs of one or more site(BCF)

Fixedly definedtraffic TSs of one or more site(BCF)

O&M and TRX Sign. TSs of one or more site(BCF)

Fixedly definedtraffic TSs of one or more site(BCF)

EDAP1 can be used by theseTRXs

EDAP2 can be used by theseTRXs

Figure 13 Dynamic Abis pool example

Figure 13 describe two examples of dynamic Abis allocation. ETPCM1 has one dynamic Abis pool EDAP. The capacity of EDAP can be dynamically allocated for EGPRS use of TRXs defined to ETPCM1.

ETPCM2 has two dynamic Abis pools, EDAP1 and EDAP2. The capacity of EDAP1 can be dynamically allocated for EGPRS use of TRXs, which are defined to use EDAP1. The capacity of EDAP2 can be dynamically allocated for EGPRS use of TRXs, which are defined to use EDAP2. In the TRX creation is defined, which EDAP pool is used.



The master Abis channel is allocated from the fixed Abis traffic timeslots. The allocations from the EDAP to EGPRS purposes are handled by inband signaling in the master Abis channel.

4.2 Dynamic Abis Pool Handling

The following chapters describe how pools are handled at the BSC O&M.

4.2.1 Creation of the Dynamic Abis Pool

User creates the EDAP into the Abis PCM timeslots. The size of the pool can be 1 – 24 TSLs (ETSI and ANSI). Several pools can be created to the same PCM. In the creation the user must also give the controlling PCU unit. The pool is created as continuous block of 64k timeslots. BSC reserves the circuits so that they can not be used to other purposes without deleting the pool first and makes the necessary routings.

The BSC checks that the given PCM is connected to the Abis and the circuits to be reserved are free. If reservation of the circuits, the updating of the program block which handles the EDAPs, updating of the Radio network database fails or the PCU unit does not exist, the BSC gives an error indication to the user and releases the already reserved circuits.

4.2.2 Modification of the Dynamic Abis Pool

The user can modify the EDAP by adding timeslots to the beginning or to the end of the pool, deleting timeslots from the beginning or from the end of the pool and changing the PCU unit controlling the EGPRS timeslots. The BSC makes the necessary modifications and updatings. If the PCU is changed, there can be no TRXs attached to that pool with GPRS enabled on. BSC also updates the new pool information to the BTSs that use this pool.

The BSC checks that the given the circuits to be reserved are free. If reservation of the circuits, updating of the Radio network database fails or the updating of the controlling PCU units fails, the BSC gives an error indication to the user and cancels the already made circuit operations.

4.2.3 Deletion of the Dynamic Abis Pool

The user deletes the EDAP with the pool id. The BSC checks that there are no TRXs attached to the pool with the GPRS enabled on. The BSC deletes the pool and releases the circuits from the pool and updates the BTSs that used this pool.



If the releasing of the pool circuits fails, the pool is seen as deleted and the user has to release/clean the pool circuits manually.

4.2.4 BCF/BTS/TRX Creation

The EDAP is created first. The radio network is planned. The signalling links are created (unless Abis autoconfiguration is used).

The creation of the BCF, BTS, power control and handover parameters, neighbouring cell information, BCF SW package handling and BTS definition at the MSC are handled as currently.

The creation of the TRXs and logical radio channel configuration: In the TRX creation the user can define whether or not the Dynamic Abis is used with optional parameter. If the dynamic Abis is used, the operator must define the pool to be used by the TRX. It must locate on the same PCM than TRXSIG and fixed traffic timeslots. Dynamic Abis usage can not be modified later. If the operator wants to change the TRX's usage of Dynamic Abis, the TRX must be deleted and created again.

If creation of the radio network object fails, the BSC returns an error code. If the Dynamic Abis is used, and given pool does not exist or it locates on different PCM, where the TRX signalling link locates, the BSC prevents TRX creation and returns appropriate error code.

4.3 Abis Autoconfiguration

The Autoconfiguration pool, dynamic Abis pool and radio network objects must be created first.

The installation engineer connects 5th generation BTS (DINO2, (E)CATS, (E)PUMA) to the "Network-end" connection port and gives parameters required for Abis Autoconfiguration. BTS sends Abis Autoconfiguration request to the BSC via Access Channel. BSC makes required allocations from the AC Pool to the O&M and TRX signaling links and TRX's traffic channels. If the Dynamic Abis is used, the BSC informs the BTS of what timeslots it may use for EGPRS purposes (from EDAP). The EDAP, TRX signaling links and TRX traffic timeslots must exist on the same PCM. If the TRXs of the one BTS are located in the different PCMs, the PCU that controls the dynamic pools of these PCMs must be same. I.e. one PCU can control several pools.

During Autoconfiguration start-up scenario, the BTS informs BSC that this is Autoconfiguration start-up and asks BSC to execute TRX and Abis loop tests. If the dynamic Abis allocation is used, BSC executes the Abis loop test for every channel of the dynamic Abis pools first and last timeslot. If the dynamic Abis pool is already in use in some other BTSs, possible ongoing calls cleared before the test.



4.4 Abis Loop Test

The user starts Abis loop test for some TRX. If the TRX is using Dynamic Abis allocation, the user can (not necessary) also give timeslot that is going to be tested (this way testing the Dynamic Abis pool channels). The timeslot must be on Dynamic Abis pool the TRX is using.

If the TRX uses permanent Abis allocation, the timeslot can not be given. If the timeslot to be tested already carries traffic and calls can not be handed over to other timeslots of the pool, the testing can not be done and BSC returns an error code to the operator.

4.5 Radio Network Recovery

When the system detects the PCM fault, the actions concerning it are similar whether or not the TRX has dynamic or permanent Abis allocation. All TRXs of the PCM are blocked to the call control and thus no calls can be made on those TRXs. At the same time dynamic Abis pool of that PCM can not be used (No working TRXs on that PCM) and thus no dynamic Abis pool recovery is required. The dynamic Abis does not cause changes to the general error cases, as signal lost, frame lost sync. error etc. These are handled in the same way as before dynamic Abis.

BSC shall find basic error cases. It is possible that one unit (or BTS) could confuse dynamic Abis pool (one or more bits are constant zero/one). BSC shall have counters for failed calls to recognize faulty timeslot, what is load of pool (per cent), what is peak load of pool, what is relation between packet calls and circuit switched calls. The BSC has own counters for every BTS.



5 TELECOM IF SPECIFICATION OF DYNAMIC ABIS

5.1 Dynamic Abis Pool Handling

This chapter describes the dynamic Abis pool handling in the BSC Telecom point of view.

5.1.1 Creation of dynamic Abis Pool

EGPRS Dynamic Abis Pool (EDAP) is created as defined in 4.2.1.

BSC telecom receives the Dynamic Abis information, including the PCM TSLs belonging to the EDAP. Figure 13 Error: Reference source not foundgives an example of ET_PCM configuration with EDAP.

Circuit switched (CS) connections and master Abis channel in EGPRS (see chapter 5.3.3) are connected to fixed 16 kbit/s Abis channels. Only additional Abis transmission needed for EGPRS is using EDAP.

When EDAP is created the PCU that handles the pool must also be defined. BSC telecom hunts Abis PCM TSLs and PCU PCM TSLs for the EDAP and makes the connection between ETPCM and PCUPCM. BSC telecom informs the EDAP configuration to the PCU.

PCU can handle traffic from several Abis PCMs. In PCU PCM there can be several EDAPs. There are two PCU PCMs per PCU. One EDAP can not be divided to separate PCU PCMs.

There are no PDTCH related to an EDAP TSLs. There will be no PCU-frame synchronization on those TSLs. Error: Reference source not found

PCU unit can handle 256 TCHs. Those TCHs are switched through GSWB by two PCMs offering 256 16 kbit/s TSLs. When certain amount of the PCU PCM transmission is used for the EDAP the number of served TCHs decreases. If six 64 kbit/s TSL are in EDAP. You can have 24 16 kbit/s TCHs in six TSLs. The PCU unit TCH capacity has decreased to (256 – 24) 232 TCHs.

5.1.2 EDAP Upgrade

EDAP upgrade is initiated by O&M; i.e. size of EDAP is increased.

PCM TSLs belonging to EDAP are from consecutive TSLs. When EDAP upgrade is initiated BSC telecom marks the upgraded TSL as 'to be included to EDAP'. PCU PCM



TSL is hunted and the EDAP TSL is switched to the PCU PCM after all the connections using the TSL have been disconnected.

5.1.3 EDAP Downgrade

EDAP downgrade is initiated by O&M; i.e. size of EDAP is decreased.

BSC telecom commands PCU to stop using either the first or last EDAP TSL. PCU stops scheduling the deleted EDAP TSL and acknowledges to BSC telecom. BSC telecom releases the switch.

5.2 Circuit Switched Services

CS calls are handled as before. Abis capacity is allocated fixedly.



5.3 Packet Switched Services

5.3.1 Overview of Signaling Layers

LAPD

GMM/SM

LLC

RLC

MAC

GSM RF GSM RF

L1Abis

Abis Relay

UmMS BTS

L3 AbisL3Abis

LAPD

L1 Abis L1 bis

LLC Relay

BSCPCU

BSSGP

Abis

GMM/SM

LLC

BSSGP

L1bis

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NS NS

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Figure 14 GPRS signaling model

In a GPRS system, signaling messages can be transmitted over Abis using ordinary LAPD TRXSIG channels but also using PCU frames. GPRS signaling information data packets can be transmitted on TRXSIG channel (16 kbit/s LAPD) and on PDTCH/PACCH traffic channel (16 kbit/s PCU frames, a derivative of TRAU frames). PCU frames are modified TRAU frames. They are used for carrying RLC/MAC frames (data and signaling) and some "inband" PCU-BTS signaling bits in the PCU frame overhead.



5.3.2 GPRS TBF

Nokia supports only coding schemes CS-1 and CS-2 in standard GPRS service. This means the master Abis channels (see chapter 5.3.3) are only used for GPRS. EDAP is not used by GPRS. GPRS release 1 procedures apply for GPRS.

5.3.3 EGPRS TBF

The GPRS RR procedures apply in EGPRS also. The difference comes from the EGPRS need for more than 16 kbit/s Abis channels.

The master Abis channel is always linked to a PDTCH. The rest of the needed Abis transmission is allocated from the EDAP in the in the 64kbit/s blocks. That is told to BTS by inband signaling in master Abis channel PCU frame with every RLC block. So there will be two new PCU frame formats: one for master Abis channel and one for EGPRS slave channel.

PCU schedules the use of PDTCHs shared by multiple MSs. The PCU must in the case of EGPRS using more 16 kbit/s Abis schedule also Abis sub-TSL transmission turns from the EDAP. The same EDAP 16 kbit/s sub-TSL can be allocated to different PDTCH in the succeeding PCU frames (Figure 15).



Figure 15 EDAP scheduling example

5.3.4 L1 Specification

PCU frame formats, inband signaling synchronization and other L1 functions are described in GPRS/EGPRS Abis L1 Interface Specification.



6 USE CASES

Fixed CS with free allocated EGPRS mastersand free allocated EDAPs

ET_PCM 1 ET_PCM 2 ET_PCM 3 PCU PCM 1 PCU PCM 2

OMU&TRX sig

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BTS1 TRX1

BTS1 TRX2

BTS1 TRX3

BTS2 TRX1

BTS2 TRX2

BTS2 TRX3

BTS4 TRX1

BTS4 TRX2

BTS4 TRX3

BTS4 TRX4

BTS4 TRX6

BTS4 TRX7

BTS4 TRX8

BTS4 TRX9

BTS4 TRX10

BTS7 TRX1

BTS7 TRX2

BTS7 TRX3

BTS7 TRX4

BTS7 TRX5

BTS3 TRX1

OMU&TRX sig

BTS3 TRX2

BTS4 TRX5

OMU&TRX sig OMU&TRX sig

BTS4 TRX11

BTS4 TRX12

BTS7 TRX6

BTS7 TRX7

BTS7 TRX8

BTS7 TRX9

BTS7 TRX10M

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ETPCM1_EDAP1

ETPCM1_EDAP2ETPCM2_EDAP1

ETPCM3_EDAP1

Figure 16 Dynamic Abis configuration example

Figure 16 gives an example of the dynamic Abis allocation at the ETPCMs and PCUPCMs. The allocations of the ETPCMs for signaling, TCH channels and EDAP pools can be done manually or by Autoconfiguration.

OMUSIG and TRXSIGs of BTSs are defined fixedly in ET_PCM1, ETPCM2 and ETPCM3. TCHs timeslots of BTSs are defined fixedly.

ETPCM1_EDAP1 timeslots can be allocated dynamically to EGPRS use of BTS1 TRXs. The size of the ETPCM1_EDAP1 is 8*64kbit/s. It means that there can be 8 simultaneous EGPRS allocations at the same time with the MCS-2 to MCS-9 coding (capacity of one EGPRS TRX).

ETPCM1_EDAP2 timeslots can be allocated dynamically to EGPRS use of BTS2 and BTS3 TRXs. The size of ETPCM1_EDAP2 is 4*64kbit/s. It means that there can be 4 simultaneous EGPRS allocations at the same time with the MCS-2 to MCS-9 coding (capacity of 4 timeslot from one EGPRS TRX).

ETPCM2_EDAP1 timeslots can be allocated dynamically to EGPRS use of BTS4 TRXs. The size of the ETPCM2_EDAP1 is 3*64kbit/s. It means that there can be 3 simultaneous EGPRS allocations at the same time with the MCS-2 to MCS-9 coding (capacity of 3 timeslots from one EGPRS TRX or 1 timeslot from 3 EGPRS TRX).



ETPCM3_EDAP1 timeslots can be allocated dynamically to EGPRS use of BTS7 TRXs. The size of the ETPCM3_EDAP1 is 8*64kbit/s. It means that there can be 8 simultaneous EGPRS allocations at the same time with the MCS-2 to MCS-9 coding (capasity of 1 EGPRS TRX).

At the ETPCMs the EGPRS master channels are reserved from the TCH timeslots of TRXs.

One PCU can handle two PCMs. PCU PCM1 and PCU PCM2 show how the EGPRS traffic is shared between PCU PCMs and PCU DSPs. At the PCU the EDAPs are allocated starting from the end of the second PCU_PCM. EGPRS master channels are reserved from the beginning of the first PCU PCM. See Figure 16.

7 TESTING

7.1 Trace Tools (Abis)

The Abis trace tools must have BSS10 support for tracing O&M, Telecom and TRAU signaling.

In the packet services the tool must be capable to trace the DSPSIG from the master Abis channel and to trace the traffic also from all sub channels which are related to master Abis channel.