Ericsson AXE HARDWARE EVOLUTION Service Manual

The hardware used in the AXE system has
been updated continuously. Initially, all
telephony-related hardware in AXE was ana­logue. Over the years, almost all hardware
has been redesigned to take advantage of the
formidable advances in electronics. This has
been a continuous, ongoing process. Digi­talisation was gradually introduced in the
early 1980s, followed by application­specific integrated circuits (ASIC) in the
mid-1980s. A major breakthrough came in

19861. In the late 1980s and early 1990s, the
evolution continued in small steps. A few
original products have remained, however.
Today, these last remaining products are
being replaced. At the same time, almost all
other hardware products that make up the
basic AXE system are being rationalised.

52

Ericsson Review No. 2, 1997

AXE hardware evolution

Urban Hägg and Tomas Lundqvist

The AXE system is the most widely deployed switching system in the world.
It is used in public telephony-oriented applications of every type, including
traditional fixed network applications in local, transit, international and
combined networks. AXE is also deployed for all major mobile standards –
analogue as well as digital. AXE is very strong in intelligent networks and
other real-time database applications. Recent designs also enable data
communication capabilities to be added to the system.
From its inception, the AXE system was designed to accommodate con­tinuous change. Throughout the years, new applications have been intro­duced, its array of functions has grown, and its hardware has been steadily
updated.
The authors describe how the latest advances in hardware technology have
been brought into the system, thereby dramatically improving such charac­teristics as floor space, power consumption, system handling, and cost of
ownership. As always, backwards compatibility has been maintained to the
greatest possible extent, in order to protect previous investments in AXE.

DL2

DLMUX

APT dev

TSM-DL3

DL3

DL1
DL2

APT dev

RP4

RP

RP

RP

RPB-S

RPH-S

RPH

IOG

CP

Generic device

magazine

AXE evolution

Extensions

GSS64K

RPB-P

DL2

DLMUX

APT dev

DL3 DL2

APT dev

RP4

RP4

RP

RPB-S

RPH-S

RPH-P

CP

Generic device

magazine

GSS64K

AXE evolution

New deliveries

DL3

DLMUX

DL_IO

DL2

Generic device

magazine or

BYB 202 equipment

RPV2

RPB-P

IOG20

Figure 1
The figures show how the new interfaces are
used for extensions and new deliveries.

Ericsson Review No. 2, 1997

53

Architecture

As the AXE system continues to evolve, sys­tem designers ensure that the very solid and
proven system architecture is maintained.
The fundamental principle of a central pro­cessor (CP) that controls regional processors
(RP), which in turn control hardware ser­vices, has proved to be superior. Strict in­terfaces ensure that different system com­ponents can be developed independently. To
ensure non-stop operation, all vital traffic
and operation and maintenance (O&M) sys­tem products are built in duplicated struc­tures.

In order to fully exploit the advantages of
modern electronics, some fundamental sys­tem hardware interfaces are now being im­proved and extended. It goes without say­ing that compatibility is maintained in
AXE.

Traditionally, a parallel bus, or a region­al processor bus (RPB), has been used for
communication between the central and re­gional processors. Now, however, in order
to increase capacity (data transfer rate) and

to decrease the need for interface hardware,
a serial bus is being introduced alongside
the existing RPB (Figure 1). The new RPB
permits single-board regional processors to
be housed in the same subrack as the devices
they control, thus minimising hardware and
cable interconnections between hardware
devices.

In earlier generations of AXE, an ex­tension module (EM) bus and cables were
used to connect regional processors to ap­plication hardware (extension modules). In
the new hardware design, however, most re­gional processors are located in the same
subrack as the extension modules they con­trol. By locating the regional processors in
this way, designers have all but eliminated
the EM bus, except in the backplane. The
new location makes it much easier for
operators to install and extend equipment.

The traditional AXE interface (called the
digital link 2, DL2) between the group
switch (GS) and its connected devices was
at the 2 Mbit/s primary multiplexing pulse
code modulation (PCM) level.

Now, a new high-speed interface is being

ALI Alarm interface
ANSI American National Standards

Institute

ASIC Application-specific integrated

circuit

AST-DR-V3 Announcement service terminal

version 3
ATM Asynchronous transfer mode
BGA Ball grid array
BM Building module (1 BM=40.64

mm)
BSC Base station controller
CANS Code answer
CCD Conference call device
CMOS Complementary metal-oxide semi-

conductor
CP Central processor
CSFSK Code sender for FSK tones
CSK Code sender for DTMF tones
CSR Code sender/receiver
D-AMPS Digital AMPS
DL2 Digital link interface 2
DL3 Digital link interface 3
DSP Digital signal processor
DTMF Dual-tone multifrequency
E0 64 kbit/s digital link
E1 2 Mbit/s digital link
ECP 303 Echo canceller in pool

generation 3
ECP 404 Echo canceller in pool

generation 4

EM Extension module
EMB Extension module bus
EMC Electromagnetic compatibility
EMI Electromagnetic interference
ETC5 Exchange terminal circuit

generation 5

ETSI European Telecommunications

Standards Institute
FSK Frequency shift keying
GDM Generic device magazine (sub-

rack)
GS Group switch
GSM Global system for mobile commu-

nication
GSS Group switch subsystem
HLR Home location register
IN Intelligent network
I/O Input/output
IOG11 I/O system 11
IOG20 I/O system 20
IP Internet protocol
ISDN Integrated services digital network
ITU-T International Telecommunication

Union - Telecommunications Stan-

dardization Sector
IWU Interworking unit
KRD Keyset receiver device
LED Light-emitting diode
LUM Line unit module
MSC Mobile switching centre
MTBF Mean time between failures

MW Megaword
O&M Operation and maintenance
PCM Pulse code modulation
PDC Pacific digital cellular
PROM Programmable read-only memory
PSTN Public switched telephone network
RAM Random access memory
RMS Remote measurement subsystem
ROM Read-only memory
RP Regional processor
RP4 Regional processor generation 4
RPB Regional processor bus
RPD Regional processor device
RPG Regional processor with group

switch interface

RPV Regional processor connected to

VME
SCP Service control point
SCSI Small computer system interface
SNT Switching network terminal
SPM Space switch module
STC Signalling terminal central
STM Synchronous transfer mode
STP Signalling transfer point
T1 1.5 Mbit/s digital link
TCD Trunk continuity check device
TSM Time switch module
TSM-1 155 Mbit/s time switch module
VME Versa Module Eurocard

Box A Abbreviations

introduced at the third level in the basic
PCM hierarchy. The interface, which is
called DL3 (digital link 3), works at the
32 Mbit/s level (overhead excluded).

The introduction of the DL3 interface dra­matically decreases group switch and device
hardware. Equally important, it removes
massive amounts of internal system cabling.
The DL2 interface has been retained to en­sure compatibility.

Each DL3 interface contains 16 multi­plexed DL2 interfaces. In fact, the DL2s run
in the backplane of the new device subracks,
which means that only one sixteenth of the
cabling is needed between the group switch
and the devices that are connected to it.

Basic technology

In general, designers taking part in the AXE
hardware evolution programme have used
ASICs, high-performance microprocessors,
digital signal processors (DSP) and faster in­terfaces to improve AXE hardware. ASICs
were chosen where volumes of circuits are
very high or where performance is critical.
Commercial microprocessors, which are be­coming commonplace for more and more
applications, have also been integrated into
the hardware. These changes allow design­ers to integrate commercial operating sys­tems and software – especially at the re­gional processor level.

Also, inasmuch as the processing capaci­ty of regional processors has kept pace with
developments in general-purpose processor
technology, the new AXE hardware requires
fewer processors than were used before. This
was another important factor in reducing
the size of the exchange.

The most common type of processor in
AXE systems today is the digital signal pro­cessor. DSPs, which are used in many kinds
of application, are flexible platforms that
may easily be programmed to provide new
functions. Moreover, software at the DSP
level may be sourced from other manufac­turers, which allows designers to introduce
new functionality with shorter time to mar­ket.

Today almost all AXE hardware uses a

3.3 V power supply. This change and the
use of submicron technology (0.25-0.5 µm)

have reduced power consumption to levels
far below that of previous hardware genera­tions.

Equipment practice

Owing to the introduction of high-speed in­terfaces and tougher requirements for elec­tromagnetic compatibility (EMC), AXE
hardware designers constructed a new
equipment practice, called the BYB 5012.
The BYB 501 has excellent EMC character­istics and fulfils Class B requirements with
good margin. Compared with the BYB 202,
whose cabinet shields against electromag­netic interference (EMI), the new equip­ment practice provides shielding at the sub­rack level. Note: the standard on which the
BYB 501 is based uses the term subrack.
However, in AXE terminology, the word
magazine is often used.

The equipment practice supports multi­point and single-point earthing. The multi-

54

Ericsson Review No. 2, 1997

D
L

M
U
L
T

I
P
L
E
X
E
R

D
L

M
U
L
T

I
P
L
E
X
E
R

CAT

CSKD

KRDD

CCD

CSR

TCD

CSFSK

ECP404

TRA

ASTV3

ETCJ32

ETC24

ETC5

ETC5
DL2_IO
DL2_IO
DL2_IO

STC
SS7

AUTH

DL2_IO

ICM

RCM

CLM

RP4

RP4 RP4 RP4 RP4

external

sync.

external

sync.

ETC5 sync.

test
phone

test
instr.

test
instr.

RSM

PCD-D

PCD
TRU

RPHP RPHS RPHS RPHP

CP

CP

Terminal V24
Terminal V24

Billing X.25
OMC X.25

Alarm V.24

Alarm

printer V.24

OD

HD

IOG20

RPB-P

RPB-P

TSM

DL3

DL3

D
L

M

U
L
T

I
P
L
E
X
E
R

D
L

M
U
L
T

I
P
L
E
X
E
R

SPM

RPB-S

RPB-S

DL2

DL2

EMB

RPB-S

DL2

EMB

RPB-S

GS

EMB

EMB

Cable
Backplane

Figure 2
AXE hardware architecture using new hard­ware.

Ericsson Review No. 2, 1997

55

point earthing concept will be used in all
new AXE deliveries. The equipment prac­tice also supports several different sizes of
board and cabinet. However, for use with
AXE, two main board sizes are used: 115 x
175 mm, and 265 x 175 mm. The standard
dimensions of the cabinet are as follows:
Height: 1800 mm
Width: 600 mm
Depth : 400 mm
Normally, no backplane cabling is needed
on the subracks. Consequently, the cabinets
may be placed back-to-back, giving the ex­change a very small footprint and allowing
a flexible cabinet arrangement against walls.
The cabinets will also be delivered fully
equipped, their hardware tested and cabled
at the factory – a feature that greatly reduces
installation time and other time-to­customer-related activities.

Group switch

The group switch3has been the subject of
far-reaching rationalisation. For example,
a configuration for 65,536 group switch
ports is now contained in two cabinets
(Figure 3). What is more, the new group
switch consumes 95% less power than its
predecessor. Nevertheless, the basic struc­ture of the switch – that is, the time-space­time (T-S-T) switching architecture, the
time switch, the space switch, the clock
module, and system concepts such as the
switching network terminal maintenance
(SNT) and DL2 hardware interface – has
been maintained, which facilitates hard­ware and software design and preserves
compatibility.

In improving the group switch, designers

made the following changes:

• A 32 Mbit/s DL3 interface replaces six­teen 2 Mbit/s DL2 switch interfaces.

• Four time switch module (TSM) functions
are grouped onto one board, yielding
2,048 ports per board (Figure 4).

• A space switch module (SPM) function for
16,384 ports now fits on a single board
(Figure 5).

• Switching equipment and the RPs that
control the equipment are co-located in
the same subrack.

These design changes gave rise to a switch
subrack that contains eight TSM boards,
providing a total of 16,384 switch ports; one
SPM board; and four RP boards. Since the
switch is duplicated, another plane is locat­ed in a second subrack with exactly the same
configuration.

Some mobile systems employ subrate
switching to handle bit rates below 64 kbit/s
(8 kbit/s; 16 kbit/s; 24 kbit/s ... 64 kbit/s).
In its maximum configuration, which has
4,096 ports, the subrate switch is housed in
two small subracks: the A-plane is located
in one subrack and the B-plane is located in
the other.

As in earlier versions of the group switch
subsystem (GSS), wideband (n x 64 kbit/s)
is supported up to 2 Mbit/s.

The synchronisation equipment, which
occupies another two small subracks, con­sists of:

16K plane A

16K plane A

16K plane B

16K plane B

16K plane A

16K plane A

16K plane B

16K plane B

CLM, RCM

The 64K group switch

Figure 3
The new group switch in a 64K configuration,
including synchronisation equipment.

Figure 4
The new time switch module board, which
contains 2,048 ports, replaces four BYB 202
subracks.

Figure 5
The space switch module board, which han­dles 16,384 ports, replaces one subrack in
the BYB 202.

• three clock modules;

• two highly accurate reference clock mod­ules;

• two incoming clock reference boards (for
connecting additional clock references);

• regional processors for controlling the
synchronisation equipment.

Designers have also constructed a compact
switch subrack for switching applications
that require less than 4,096 ports. This sub­rack contains a 4,096-port switch, three
clock boards for synchronisation, 1,024
ports for subrate data transfer, and regional
processors for controlling the equipment.
The two switch planes are co-located in one
subrack.

The new group switch was designed to

provide backward compatibility. Accord­ingly, a DL3-to-DL2 converter subrack has
been developed. The converter connects
hardware that uses a DL2 cable interface to
a new switch that uses the DL3 interface.
Another way of connecting an old switch to
hardware that uses the new DL3 interface is
to add an interface board (which supports a
DL3 cable interface) in existing TSM64C
subracks.

The new design concept also allows the

GSS switch to be extended to up to
131,072 ports.

Central processor

Designers of the AXE central processor have
always emphasised high processing capaci­ty. This holds true even today. Nonetheless,
while developing the next generation high­capacity central processor (APZ 212 30),
AXE designers also produced a smaller,
power-efficient processor (APZ 212 25) for
switching applications that require moder­ate processing capacity.

The APZ 212 25 has a very small foot-

print (Figure 6) and consumes only 75 W of
power. Designers reduced power consump­tion by replacing the 5 V supply voltage
with 3.3 V, and by using 0.5 µm comple­mentary metal-oxide semiconductor
(CMOS) ASIC technology with ball grid
array (BGA) packaging. The maximum
memory capacity of the APZ 212 25 is
64 Megawords (MW), program store; and
256 MW, data store. Despite its small size,
this computer processor is 1.5 to 1.7 times
more powerful than its much larger prede­cessor, the APZ 212 11.

Although it was designed for use in the

BYB 501, where it uses the serial RP bus,
the APZ 212 25 is fully compatible with the

parallel bus used in earlier versions of AXE
switching equipment. In a minimum con­figuration, the APZ 212 25 may connect
four of the new serial RP buses, controlling
up to 128 regional processors. If more re­gional processors are required, or if parallel
and serial RP buses must be used simulta­neously, then extension subracks may be
added that allow up to 512 regional proces­sors to be connected.

Regional processors

A new regional processor, called the RPG
(regional processor with group switch in­terface, Figure 7) has been introduced for ap­plications that require high processing ca­pacity. Most applications that previously
ran on the regional processor device (RPD
– Motorola 68020) have been transferred to
the RPG, which has at least four times as
much processing capacity as the RPD. The
RPG is a single-board processor based on
the general-purpose Motorola 68060 run­ning at 50 MHz. On the same board is a
communications processor (a Motorola

68360) for handling the switch interface and
a 10 Mbit/s Ethernet interface. Although it
may be used for any application that requires
high processing power, the RPG will ini­tially be used with the following applica­tions:

• signalling system no. 7 – signalling ter­minal according to ANSI;

• signalling system no. 7 – signalling ter­minal according to ITU-T;

• signalling terminal central (STC) – sig­nalling terminal for base stations and re­mote subscriber switches;

• transceiver handler – base station sig­nalling in GSM;

• authentication in all mobile systems;

• integrated services digital network
(ISDN) Internet access server (IP routing
function).

In AXE, the RPG is the platform for hand­ling packet switched data communication.
With respect to traffic handling, these types
of regional processor have a more indepen­dent role, relative to the CP, than traditional
AXE regional processors.

A new version of the traditional regional

processor, called RP4 (regional processor
generation 4), is used for controlling exten­sion modules. The RP4 is compatible with
earlier versions of the regional processor. A
prime benefit of the RP4 is that it is co­located in a subrack with the extension mod­ules it controls. This design does away with

56

Ericsson Review No. 2, 1997

Figure 6
The APZ 212 25 occupies only half a subrack
in the BYB 501.

Figure 7
The RPG consists of two boards mounted
together into one plug-in unit. Every interface
is to the backplane.

Ericsson Review No. 2, 1997

57

a large amount of cable, reduces size, and
simplifies equipment handling consider­ably.

Earlier versions of the central processor
may not be connected to new hardware with­out first modifying their side of the RP bus
interface.

The regional processor bus interface VME
(RPV) is a conversion product for the con­nection from the CP to the Versa Module
Eurocard-based IOG20, through the RP
bus. There are two RPVs: the first, known
simply as RPV, is used for the parallel bus
connection; the second, called the RPV2, is
used for the serial bus connection.

IOG20, the AXE I/O
system

A duplicated input/output (I/O) system,
known as the IOG20, handles data transport
to and from an AXE exchange. Communi­cation to and from the AXE I/O system may
be broken down into customer administra­tion and element handling.

The IOG20 is much smaller than the
IOG11 – the previous generation I/O sys­tem. For example, whereas the IOG11 fills
a whole cabinet in the BYB 202 equipment
practice, the IOG20 fits into a single sub-

rack. Moreover, the IOG20 outperforms the
IOG11 by as much as four to five times but
consumes only one third as much power.

The new I/O system, whose design is char­acterised by modern technology and greater
integration, contains relatively few printed
circuit board types (seven instead of 25). In
taking steps to make the system open to
commercially available components, de­signers used the industry standards Versa
Module Eurocard (VME) bus, Ethernet, and
small computer system interface (SCSI).
Similarly, they implemented Ethernet for
connections between nodes and as a line in­terface. The IOG20 is currently available in
three configurations:

• IOG20 – a fully compatible version of the

twin-subrack configuration with an in-

terface to a parallel RP bus;

• IOG20B – a twin-subrack version with

one node in each subrack (maximum con-

figuration);

• IOG20C – a single-subrack version with

two nodes (minimum configuration).
The IOG20B and the IOG20C are designed
to operate with the new serial RP bus.
The IOG20C is probably the most compact
and powerful I/O system ever produced
for telecommunications applications
(Figure 8).

Figure 8
The IOG20C with A- and B-sides in one sub­rack. With its daughter boards, the line unit
module can handle four different interfaces.

In its maximum configuration, the

IOG20 stores data on three duplicated

3.5 inch/4 Gbyte hard disks and one dupli­cated 3.5 inch/640 Mbyte magneto-optical
disk. In the compact version, the IOG20
stores data on one duplicated 3.5 inch/
4 Gbyte hard disk and one duplicated

3.5 inch/640 Mbyte magneto-optical disk.
To connect data communication inter-

faces to the I/O system, the twin-subrack
version may contain up to four duplicated
line unit module (LUM) boards. Likewise,
the compact version may contain up to three
duplicated LUM boards. A LUM board con­sists of a main board and as many as four in­dependent line module daughter boards for
almost any type of line interface, including
V.24, V.28, V.35, V.36, X.21, G.703 E0,
G.703 E1, and Ethernet.

An alarm interface (ALI) function consists

of two boards: one for supervising fans and
external alarm input/output, and another for
displaying alarms.

In terms of software and applications, the

IOG20 is fully compatible with its prede­cessor, the IOG11.

Connecting hardware to
the group switch

Hardware is connected to the switch either
by a trunk (for example, exchange terminals)
or by means of pooling (for example, of echo
cancellers). In AXE, only exchange terminals
and some signalling terminals are connected
by trunks. All other equipment is connected
in pool, which heightens reliability, flexi­bility, economy, and maintainability.

Announcement machines

Designers have also developed a new gener­ation of system-integrated announcement
machines – AST-DR-V3. The new ma­chines are substantially smaller than their
predecessors, but have more capacity for
speech storage and for a larger number of
dual-tone multifrequency (DTMF) re­ceivers. The announcement machines are
available in different sizes (configurations).
The largest machine has capacity for
256 DTMF receivers, up to eight hours of
stored speech, and provisions for backing up
speech on the hard disk.

The smallest configuration has capacity

for 32 DTMF receivers and two hours of
stored speech. Depending on how often
stored phrases are changed, speech may be
stored in either random access memory
(RAM) or in read-only memory (ROM) on

memory boards that support up to one hour
of speech per board. The high-capacity an­nouncement machine occupies one and a
half subracks: one subrack for the control
subrack that contains the DTMF receivers,
and half a subrack for the memory boards
and hard disk. The smallest machine occu­pies only half a subrack. As many as 20 sys­tems may be run in parallel, providing a
total of 5,120 ports. The systems may also
be used in large intelligent network (IN)
nodes or in other service-providing func­tions. The AST-DR-V3 forms a powerful
voice-response system that may be used as a
base product for the future development of
such applications as voice or fax mail, cash­less calling, and the virtual telephone.

Exchange terminals

AXE supports every kind of trunk interface
that has been incorporated into the new
equipment practice. By integrating all func­tionality into one ASIC, designers were able
to fit the 32-channel E1 (2 Mbit/s digital
link) interface onto one small board
(Figure 9). New versions of the 24-channel
T1 and the Japanese 32-channel interface
have also been designed.

In time, STM-1 (155 Mbit/s synchronous
transfer mode) terminations will be de­signed in AXE for each relevant standard.
Once they become available, the termina­tions will greatly reduce (possibly com­pletely eliminating) operator requirements
for transmission equipment and generally
simplify system handling.

DSP platform

To date, much of the telephony devices in
AXE – conference call device (CCD); trunk
continuity check device (TCD); code
sender/receiver (CSR) for R1, R2, and no. 5
code; code sender for DTMF (CSK); code
sender for FSK tones (CSFSK); code answer
(CANS); keyset receiver device (KRD); and
several maintenance functions – is delivered
from separate subracks that range in size
from 3 to 12 building modules (BM) in the
BYB 202 equipment practice. Nonetheless,
designers have developed a new digital sig­nal processor platform board that can be pro­grammed to provide the functionality of any
one of these applications. Initially the boards
will be programmed at the factory. In a sec­ond step, operators will be able to change
the onboard software from the AXE system,
giving them tremendous flexibility and ex­cellent means with which to handle redun­dancy and spare parts. Should a fault occur

58

Ericsson Review No. 2, 1997

Figure 9
The 32-channel E1 interface is now made on
one small board.

Ericsson Review No. 2, 1997

59

on a board that provides the functions de­scribed above, then an operator can remote­ly activate an unprogrammed standby board
by command, taking it into operation. This
feature will simplify maintenance and re­duce operating costs.

Echo cancellers

The ECP 3034has been replaced with a new
echo canceller, called the ECP 404. The ECP
404 has a capacity of 512 channels per sub­rack, which is twice the capacity of the ECP

303. As with its predecessor, the ECP 404
is connected to the group switch by means
of pooling.

Transcoders

Transcoders, which are included in all dig­ital mobile telephony systems, are used for
speech compression – from 64 kbit/s to bit
rates below 16 kbit/s in the downlink di­rection, and from bit rates below 16 kbit/s
to 64 kbit/s in the uplink direction. Limit­ed bandwidth in the air interface, which is
a major challenge of mobile telephony sys­tems, requires that speech be compressed be­fore it can be sent over the interface.

As with all other devices, the transcoders
are connected to the switch and supervised
by AXE. The capacity of each board differs
depending on the mobile standard for which
it has been deployed (for example, D-AMPS,
GSM or PDC). Each standard uses unique
algorithms that require different processing
capacity.

By employing the latest techniques in dig­ital signal processing, designers have been
able to more than double the capacity of the
transcoder boards. This represents a signifi­cant achievement since the transcoders make
up a large part of mobile exchanges.

Data transmission interworking unit

Interworking functions are needed to provide
the digital transmission of data services with­in mobile networks as well as between them
and other networks. This is because protocols
for the standard network use analogue tones,
which are not suitable for transmission over
the radio interface to mobile terminals.

An interworking unit (IWU) extracts
analogue information received from a pub­lic switched telephone network (PSTN)
modem and sends it to the mobile terminal
by means of a digital protocol. The opposite
function is performed for signals from the
mobile terminal to the PSTN modem. The
interworking function is implemented in a

7.5 BM subrack, which can handle up to 32

simultaneous data or fax calls. The subrack
fits in the new equipment practice.

This function was previously used as a
stand-alone product in the Ericsson GSM
system, but it will now be integrated into
the system and supervised by AXE.

Remote measurement subsystem

The AXE remote measurement subsystem
(RMS) measures characteristics and trans­mission quality between telephony ex­changes. It performs digital, analogue and
signalling tests. To date, this function –
which occupies one subrack in the BYB 202
equipment practice – has been used solely
in transit exchanges. In the new rationalised
version of the RMS, the function will be con­structed from powerful DSPs on a single
board.

Subracks for switch­connected hardware

Nearly all telephony devices in AXE are now
single-board applications, giving rise to the
development of a new concept for generic
device magazines (subracks). The concept is
based on a subrack with 16 slots for device
boards. From the backplane, the boards are
connected to a duplicated group-switch in­terface, a duplicated RP bus interface, a du­plicated EM bus interface, and a mainte­nance bus. Moreover, each board is given an
EM bus address and supplied with dupli­cated –48 V (Figure 10).

Besides the 16 device boards, two multi­plexers on the front of the board are connect-

Group
switch

A

B

A

B

A

B

DL3

DL2

DL

multiplexer

Maintenance

bus

Generic device

magazine

EM bus

RPB-S

-48V-A

-48V-B
Maintenance

bus

RP4

RPB-S

-48V

CP

A

B

1

0

15

Device

-48V

Figure 10
Hardware architecture of the generic device
magazine (subrack).

ed to the switch by means of a DL3 interface.
The multiplexers split the DL3 interface into
16 DL2 connections in the backplane, one
connection per board. The other interfaces are
connected to a pair of regional processors, one
at each end of the subrack. Moreover, since
the RP bus is also distributed in the back­plane, it is possible to mix – in the same sub­rack – boards that use the EM bus with boards
that use the RP bus. Because some applica-

tions require a large board size while others
require a small one, two versions of the gener­ic subrack have been constructed.

Product identification

A new function has been introduced for
checking the hardware of an AXE exchange.
Each board contains a small programmable
read-only memory (PROM) that stores the
unique serial number, product number, re­vision state and manufacturing date of that
board. Operators may fetch and read this in­formation by command (on site or remote­ly), which enables them to check:

• hardware when replacing faulty units;

• revision states when upgrading hardware;

• for compatibility when introducing new
software.

Visual indication

Most boards in the new AXE system con­tain a light-emitting diode (LED) on their
front. The LEDs help operators in various
maintenance situations; for example, when
locating boards that need to be removed for
repair or for upgrade.

The indicator does not necessarily indi-

cate that a board is faulty. Instead, it indi­cates whether or not a board may be removed
without disturbing traffic.

Power supply

An optional battery backup and modular
power supply are offered for exchanges
whose power consumption is below 6 kW.
The batteries and rectifiers are housed to­gether with the switching equipment. A

60

Ericsson Review No. 2, 1997

T

R

H

T
R
H

S
S
7

S
S
7

FAN

CP

IOG20C

TRA

ETC
ETC

GS16

GS16

SYNC

SUBRATE

TRA

TRA

TRH

AC/DC

AC/DC

Battery

Battery

ETC

ETC

Top view

or

2400 mm

400 mm

600 mm

800 mm

1200 mm

Total area = 0.96 m

2

Figure 12
A complete AXE exchange in one cabinet.
This configuration can be used for any of the
following applications: HLR, STP, SCP, or
BSC (more than 120 transceivers).

Figure 11
A powerful BSC with capacity for more than
300 transceivers including power supply and
batteries. The configuration is similar to a
small local exchange (subscriber stage
excluded) or to a small MSC.

Ericsson Review No. 2, 1997

61

single cabinet with battery backup can pro­vide a 3 kW power supply for nearly two
hours. A 6 kW power supply is sufficient to
operate approximately 15 AXE cabinets,
which more or less corresponds to a high­end mobile switching centre (MSC) in a mo­bile telephony system.

Most hardware in the BYB 501 equip­ment practice is fed with a redundant power
supply to each subrack through two branch­es of –48 V. Each branch of power is filtered
and distributed to the subrack backplane,
from which each board is supplied through
a double-diode configuration. This arrange­ment increases reliability, since the subrack
continues to work even if one branch of the
power supply is lost.

The power distribution system also allows
boards to be inserted into a subrack that is
in service, which greatly simplifies proce­dures when boards in the subracks must be
replaced.

Results

At the system level, recent developments
in the AXE hardware evolution pro­gramme have reduced the number of board
types used in AXE and made them small­er and much more power-efficient. For ex­ample, it was possible to reduce the size of
a base station controller (BSC) for a GSM
configuration that supports approximate­ly 300 transceivers by nearly 90% – in­cluding power supply, battery backup
(Figure 11) and transcoders. Today, power
consumption for a complete base station
controller of this type is less than 1500 W.
Moreover, when the BSC is delivered for
installation, very little additional work is
required, since the cabinets are equipped
with subracks and internal system cables at
the factory.

For the first time, a complete AXE ex­change fits into a single cabinet (Figure 12).
This configuration can be used for a home
location register (HLR), signalling transfer
point (STP), service control point (SCP), or
for a base station controller application.

Conclusion

The AXE hardware evolution programme
has successfully reduced the size of hardware
by between 70% and 90%; cabling in the
exchange has been reduced by 90%, and
power has been reduced by 75%. Therefore,
operators can expect that the time and re-

sources needed for installing the hardware
will also decrease by between 70% and 90%.
The delivery of fully equipped and tested ex­changes will further simplify installation.

The following aspects contribute towards
reducing operator costs for running the new
exchanges:

• smaller footprints require less floor space

(reduced overhead);

• costs of power (batteries, rectifiers and

kW) and cooling are reduced (reduced

overhead);

• fewer spare parts are needed (smaller

facilities, smaller stores);

• operations have been simplified (less staff,

less training);

• less hardware implies that the mean time

between failures (MTBF) increases, while

the repair time decreases – in that way,

the total down time, due to hardware fail-

ures, will decrease;

• pooled devices;

• programmable platforms.
The hardware evolution described in this ar­ticle represents only a first step in Ericsson’s
AXE hardware evolution programme. In
subsequent phases of the programme, AXE
will be migrated towards an open hardware
architecture that supports datacom func­tionality, asynchronous transfer mode
(ATM) switching, high-speed interfaces and
multiprocessor configurations.

References

1 Hägg, U., Persson, K.: New hardware

in AXE 10. Ericsson Review
63(1986):2, pp 86-92.

2 Stockman, B. and Wallers, A.:

BYB 501 metric equipment practice.
Ericsson Review 74(97):2, pp. 62-67.

3 Hansson, U., Paone, T.: The group

switch subsystem – an enhanced com­petitive group switch. Ericsson Review
74(1997):2, pp 68-73.

4 Eriksson, A., Eriksson, G., Karlsen, J.,

Roxström, A., Vallon Hulth, T.:
Ericsson echo cancellors – a key to
improved speech quality. Ericsson
Review 73(1996):1, pp 25-33.

100%

100% 100%

30%

40%

35%

Footprint Power Board types

Average exchange reduction

Figure 13
Average reduction in footprint, power, and
board type for an AXE exchange.