Ericsson AXE HARDWARE EVOLUTION Service Manual

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.

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.

AXE evolution

Extensions

DL2

DL3

GSS64K

DL1

DL2

APT dev

DLMUX

TSM-DL3

APT dev

Generic device

RP4

magazine

RP

RP

RPB-P

RPB-S

RP

RPH-S RPH

CP

IOG

Figure 1

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

AXE evolution

New deliveries

DL2

DL3

DL3

DL2

DL2

DLMUX

GSS64K

DLMUX

APT dev

DL_

IO

APT dev

Generic device

Generic device

RP4

RP4

magazine or

RP

magazine

BYB 202 equipment

RPB-S

RPB-P

RPV2

RPH-S

RPH-P

IOG20

CP

52	Ericsson Review No. 2, 1997

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

Box A Abbreviations

ALI	Alarm interface			EM	Extension module		MW	Megaword
ANSI	American	National	Standards	EMB	Extension module bus		O&M	Operation and maintenance
	Institute			EMC	Electromagnetic compatibility		PCM	Pulse code modulation
ASIC	Application-specific		integrated	EMI	Electromagnetic interference		PDC	Pacific digital cellular
	circuit			ETC5	Exchange	terminal circuit	PROM	Programmable read-only memory
AST-DR-V3	Announcement service terminal				generation 5		PSTN	Public switched telephone network
	version 3			ETSI	European	Telecommunications	RAM	Random access memory
ATM	Asynchronous transfer mode				Standards Institute		RMS	Remote measurement subsystem
BGA	Ball grid array			FSK	Frequency shift keying		ROM	Read-only memory
BM	Building	module (1	BM=40.64	GDM	Generic device magazine (sub-		RP	Regional processor
	mm)				rack)		RP4	Regional processor generation 4
BSC	Base station controller			GS	Group switch		RPB	Regional processor bus
CANS	Code answer			GSM	Global system for mobile commu-		RPD	Regional processor device
CCD	Conference call device				nication		RPG	Regional processor with group
CMOS	Complementary metal-oxide semi-			GSS	Group switch subsystem			switch interface
	conductor			HLR	Home location register		RPV	Regional processor connected to
CP	Central processor			IN	Intelligent network			VME
CSFSK	Code sender for FSK tones			I/O	Input/output		SCP	Service control point
CSK	Code sender for DTMF tones			IOG11	I/O system 11		SCSI	Small computer system interface
CSR	Code sender/receiver			IOG20	I/O system 20		SNT	Switching network terminal
D-AMPS	Digital AMPS			IP	Internet protocol		SPM	Space switch module
DL2	Digital link interface 2			ISDN	Integrated services digital network		STC	Signalling terminal central
DL3	Digital link interface 3			ITU-T	International	Telecommunication	STM	Synchronous transfer mode
DSP	Digital signal processor				Union - Telecommunications Stan-		STP	Signalling transfer point
DTMF	Dual-tone multifrequency				dardization Sector		T1	1.5 Mbit/s digital link
E0	64 kbit/s digital link			IWU	Interworking unit		TCD	Trunk continuity check device
E1	2 Mbit/s digital link			KRD	Keyset receiver device		TSM	Time switch module
ECP 303	Echo canceller in pool			LED	Light-emitting diode		TSM-1	155 Mbit/s time switch module
	generation 3			LUM	Line unit module		VME	Versa Module Eurocard
ECP 404	Echo canceller in pool			MSC	Mobile switching centre
	generation 4			MTBF	Mean time between failures

Ericsson Review No. 2, 1997

53

		DL2	EMB RPB-S		GS		DL2	EMB RPB-S
	CAT								ETCJ32
CSKD									ETC24
KRDD									ETC5
									ETC5	RSM	test
	CCD										phone
											test
				DL3		DL3			DL2_IO	PCD-D
	CSR										instr.
				D			D				test
									DL2_IO	PCD
				D			D
	TCD			L			L				instr.
				L	TSM		L			TRU
				M			M		DL2_IO
				M			M
CSFSK				U			U
				U			U
				L	SPM		L		STC
				L			L
				T			T
ECP404				TI			TI		SS7
				IP			IP
				P			P
	TRA			L			L
				L			L		AUTH
				E			E
				E			E			ETC5 sync.
				X			X
ASTV3	DL2_IO			X			X
				E			E		ICM	external
				E			E
				R			R				sync.
				R			R
	DL2								RCM
					EMB	EMB			CLM	external
											sync.
RP4			RP4			RP4		RP4	RP4
						RPB-S
						RPB-S
					RPB-P
					RPB-P
					Alarm V.24				Terminal V24
									Terminal V24
						Alarm
							IOG20		Billing X.25
RPHP	RPHS	RPHS		RPHP	printer V.24
									OMC X.25
	CP	CP					HD	OD
Cable
Backplane

Figure 2

AXE hardware architecture using new hardware.

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 m) 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