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The 5ESS Switching System is a Class 5 telephone electronic switching system developed by Western Electric for the American Telephone and Telegraph Company (AT&T) and the Bell System in the United States. It came into service in 1982 and the last unit was produced in 2003. [1]
The 5ESS came to market as the Western Electric No. 5 ESS. It commenced service in Seneca, Illinois on March 25, 1982, and was destined to replace the Number One Electronic Switching System (1ESS and 1AESS) and other electromechanical systems in the 1980s and 1990s. The 5ESS was also used as a Class-4 telephone switch or as a hybrid Class 4/Class 5 switch in markets too small for the 4ESS. Approximately half of all US central offices are served by 5ESS switches. The 5ESS was also exported, and manufactured outside the US under license. [2]
The 5ESS–2000 version, introduced in the 1990s, increased the capacity of the switching module (SM), with more peripheral modules and more optical links per SM to the communications module (CM). A follow-on version, the 5ESS–R/E, was in development during the late 1990s but did not reach market. Another version was the 5E–XC.[ citation needed ]
The 5ESS technology was transferred to the AT&T Network Systems division upon the 1984 breakup of the Bell System. The division was divested by AT&T in 1996 as Lucent Technologies, [3] and after becoming Alcatel-Lucent in 2006, [4] it was acquired by Nokia in 2016. [5]
The 5ESS switch is still in widespread use in the public switched telephone network (PSTN) in the United States and elsewhere, but they are being replaced with more modern packet switching systems. 5ESS switches in service in 2021 also included several operated by the United States Navy. [6]
The 5ESS switch has three main types of modules: the Administrative Module (AM) contains the central computers; the Communications Module (CM) is the central time-divided switch of the system; and the Switching Module (SM) makes up the majority of the equipment in most exchanges. The SM performs multiplexing, analog and digital coding, and other work to interface with external equipment. Each has a controller, a small computer with duplicated CPUs and memories, like most common equipment of the exchange, for redundancy. Distributed systems lessen the load on the Central Administrative Module (AM) or main computer.[ citation needed ]
Power for all circuitry is distributed as –48 VDC (nominal), and converted locally to logic levels or telephone signals.[ citation needed ]
Each Switching Module (SM) handles several hundred to a few thousand telephone lines or several hundred trunks or combination thereof. Each has its own processors, also called Module Controllers, which perform most call handling processes, using their own memory boards. Originally the peripheral processors were to be Intel 8086, but those proved inadequate and the system was introduced with Motorola 68000 series processors. The name of the cabinet that houses this equipment was changed at the same time from Interface Module to Switching Module.[ citation needed ]
Peripheral units are on shelves in the SM. In most exchanges the majority are Line Units (LU) and Digital Line Trunk Units (DLTU). Each SM has Local Digital Service Units (LDSU) to provide various services to lines and trunks in the SM, including tone generation and detection. Global Digital Service Units (GDSU) provide less-frequently used services to the entire exchange. The Time Slot Interchanger (TSI) in the SM uses random-access memory to delay each speech sample to fit into a time slot which will carry its call through the exchange to another or, in some cases, the same SM.
T-carrier spans are terminated, originally one per card but in later models usually two, in Digital Line Trunk Units (DLTU) which concentrate their DS0 channels into the TSI. These may serve either interoffice trunks or, using Integrated Subscriber Loop Carrier, subscriber lines. Higher-capacity DS3 signals can also have their DS0 signals switched in Digital Network Unit SONET (DNUS) units, without demultiplexing them into DS1. Newer SM's have DNUS (DS3) and Optical OIU interfaces (OC12) with a large amount of capacity.
SMs have Dual Link Interface (DLI) cards to connect them by multi-mode optical fibers to the Communications Modules for time-divided switching to other SMs. These links may be short, for example within the same building, or may connect to SMs in remote locations. Calls among the lines and trunks of a particular SM needn't go through CM, and an SM located remotely can act as distributed switching, administered from the central AM. Each SM has two Module Controller/Time Slot Interchange (MCTSI) circuits for redundancy.
In contrast to Nortel's DMS-100 which uses individual line cards with a codec, most lines are on two-stage analog space-division concentrators or Line Units, which connect as many as 512 lines, as needed, to the 8 Channel cards that each contain 8 codecs, and to high-level service circuits for ringing and testing. Both stages of concentration are included on the same GDX (Gated Diode Access) board. Each GDX board serves 32 lines, 16 A links and 32 B links. Limited availability saves money with incompletely filled matrixes. The Line Unit can have up to 16 GDX boards connecting to the channel boards by shared B links, but in offices with heavier traffic for lines a lesser number of GDX boards are equipped.
ISDN lines are served by individual line cards in an ISLU (Integrated Services Line Unit).
The Administrative Module (AM) is a dual-processor mini main frame computer of the AT&T 3B series, running UNIX-RTR. AM contains the hard drives and tape drives used to load and backup the central and peripheral processor software and translations. Disk drives were originally several 300 megabyte SMD multi-platter units in a separate frame. Now they consist of several redundant multi-gigabyte SCSI drives that each reside on a card. Tape drives were originally half inch open reel at 6250 bits per inch, which were replaced in the early 1990s with 4 mm Digital Audio Tape cassettes.
The Administrative Module is built on the 3B21D platform and is used to load software to the many microprocessors throughout the switch and to provide high speed control functions. It provides messaging and interface to control terminals. The AM of a 5ESS consists of the 3B20x or 3B21D processor unit, including I/O, disks, and tape drive units. Once the 3B21D has loaded the software into the 5ESS and the switch is activated, packet switching takes place without further action by the 3B21D, except for billing functions requiring records to be transferred to disk for storage. Because the processor has duplex hardware, one active side, and one standby side, a failure of one side of the processor will not necessarily result in a loss of switching.
The Communications Module (CM) forms the central time switch of the exchange. 5ESS uses a time-space-time (TST) topology in which the Time-Slot-Interchangers (TSI) in the Switching Modules assign each phone call to a time slot for routing through the CM.
CMs perform time-divided switching and are provided in pairs; each module (cabinet) belonging to Office Network and Timing Complex (ONTC) 0 or 1, roughly corresponding to the switch planes of other designs. Each SM has four optical fiber links, two connecting to a CM belonging to ONTC 0 and two to ONTC 1. Each optical link consists of two multimode optical fibers with ST connectors to plug into transceivers plugged into backplane wiring at each end. CMs receive time-multiplexed signals on the receive fiber and send them to the appropriate destination SM on the send fiber.
The Very Compact Digital Exchange (VCDX) was developed with the 5ESS-2000, and marketed to mostly non-Bell telephone companies as an inexpensive, effective way to offer ISDN and other digital services in an analog switching center. This avoided the capital expense of retrofitting the entire analog switch into a digital one to serve all of the switch's lines when many wouldn't require it and would remain POTS lines.
An example would be the (former) GTE/Verizon Class-5 telephone switch, the GTD-5 EAX. Like the Western Electric 1ESS/1AESS, it served mostly medium to large wire centers.
The standalone VCDX was also capable of serving as a switch for very small wire centers (a CDX- Community dial office) of fewer than ~400 lines. However, for small wire centers, 400-4000 lines, that function was usually served by RSM's, a 5ESS "Remote SM", ORM's or Wired ORM's. The RSM is controlled by T1 lines connected to a DLTU unit. The first 2 T1's are the control of the RSM and are necessary for any Recent Changes to take place. RSM's can have up to 10 T1's. There can be multiple RSM's in an office. An ORM can be fed via direct fiber or via coax thus called Wired ORM's. An RSM or ORM can have many of the same peripheral units that are part of a full 5ESS switch. An RSM has a limited distance and can serve parts of a larger metro area or rural offices. An ORM or wired ORM can be anywhere technically, and preferred over the RSM once the ORM became available. Both the RSM and ORM is often used as a Class-5 wire center for small to medium towns hosted from a 5ESS located in a larger city. The Wired ORM is connected via coax from a MUX unit and fed to a TRCU which converts the coax to connection to the DLI, There was also a two-mile ORM that was used when an office was broken out or took an area from another office. The distance on this was 2 miles from a host office and fed direct via fiber. As with any SM, the size is dictated by the number of time slots needed for each peripheral unit. ORM's are linked with DS3, RSM's are linked with T1 lines. The VCDX was also used as a large private branch exchange (PBX). Small communities of less than 400 lines or so were also provided with SLC-96 units or Anymedia units.
The standalone VCDX has a single Switching Module, and no Communications Module. Its Sun Microsystems SPARC workstation runs the UNIX-based Solaris (operating system) that executes a 3B20/21D processor MERT OS emulation system, acting as the VCDX's Administrative Module. The VCDX uses the CO's normal telephone power sources (which are very large uninterruptible power supplies), and has connections to the CO Digital cross connect system for T1 access, etc.
The 5ESS has two different signaling architectures: Common Network Interface (CNI) Ring and Packet Switching Unit (PSU)-based SS7 Signaling.
The development effort for 5ESS required five thousand employees, producing 100 million lines of system source code, mostly in the C language, with 100 million lines of header files and makefiles. Evolution of the system took place over 20 years, while three releases were often being developed simultaneously, each taking about three years to complete. The 5ESS was originally U.S.-only and the international sales resulted in a complete development system and team, in parallel to the U.S. version.
The development systems were Unix-based mainframe systems. There were around 15 of these systems active at the peak. There were development machines, simulator machines, and build machines, etc. Developers' desktops were multi-window terminals (versions of the Blit developed by Bell Labs) until the mid 1990s, when Sun workstations were deployed. Developers continued to login into the servers for their work, using X11 on their workstations as a multi-window environment.
Source code management was based on SCCS and utilized "#feature" lines to separate source code between releases, between features specific to US or Intl, and the like. Customisation around the vi and Emacs text editors allowed developers to work with the appropriate view of a file, hiding the parts that were not applicable to their current project.
The change request system used the SCCS MR to create named change sets, tied into the IMR (initial modification request) system which had purely numeric identifiers. An MR name was created with subsystem prefix, IMR number, MR sequence characters, and a character for the release or "load". So, for the gr (generic retrofit) subsystem, the first MR created for the 2371242 IMR, destined for the 'F' load, would be gr2371242aF.
The build system used a simple mechanism of build configuration that would cause makefile generation to occur. The system always built everything, but used checksum results to decide if a file had actually changed, before updating the build output directory tree. This provided a huge reduction in build time when a core library or header was being edited. A developer could add values to an enum, but if that did not change the build output, then subsequent dependencies on that output would not have to be relinked or libraries built.
The system is administered through an assortment of teletypewriter "channels", also called the system console, such as the TEST channel and the Maintenance channel. Typically provisioning is done either through a command line interface (CLI) called RCV:APPTEXT, or through the menu-driven RCV:MENU,APPRC program. RCV stands for Recent Change/Verification, and can be accessed through the Switching Control Center System. Most service orders, however, are administered through the Recent Change Memory Administration Center (RCMAC). In the international market, this terminal interface has localization to provide locale-specific language and command name variations on the screen and printer output.
Bell Labs is an American industrial research and scientific development company credited with the development of radio astronomy, the transistor, the laser, the photovoltaic cell, the charge-coupled device (CCD), information theory, the Unix operating system, and the programming languages B, C, C++, S, SNOBOL, AWK, AMPL, and others. Ten Nobel Prizes and five Turing Awards have been awarded for work completed at Bell Laboratories.
Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Work on the standard began in 1980 at Bell Labs and was formally standardized in 1988 in the CCITT "Red Book". By the time the standard was released, newer networking systems with much greater speeds were available, and ISDN saw relatively little uptake in the wider market. One estimate suggests ISDN use peaked at a worldwide total of 25 million subscribers at a time when 1.3 billion analog lines were in use. ISDN has largely been replaced with digital subscriber line (DSL) systems of much higher performance.
Digital subscriber line is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line (ADSL), the most commonly installed DSL technology, for Internet access.
In telecommunications, a four-wire circuit is a two-way circuit using two paths so arranged that the respective signals are transmitted in one direction only by one path and in the other direction by the other path. The four-wire circuit gets its name from the fact that is uses four conductors to create two complete electrical circuits, one for each direction. The two separate circuits (channels) allow full-duplex operation with low crosstalk.
Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fraction of time according to agreed rules, e.g. with each transmitter working in turn. It can be used when the bit rate of the transmission medium exceeds that of the signal to be transmitted. This form of signal multiplexing was developed in telecommunications for telegraphy systems in the late 19th century but found its most common application in digital telephony in the second half of the 20th century.
In modern telephony a remote concentrator, remote concentrator unit (RCU), or remote line concentrator (RLC) is a concentrator at the lowest level in the telephone switch hierarchy.
System X is the digital switching system installed in almost all telephone exchanges throughout the United Kingdom, from 1980 onwards.
The DMS-100 is a member of the Digital Multiplex System (DMS) product line of telephone exchange switches manufactured by Northern Telecom. Designed during the 1970s and released in 1979, it can control 100,000 telephone lines.
Multi-Environment Real-Time (MERT), later renamed UNIX Real-Time (UNIX-RT), is a hybrid time-sharing and real-time operating system developed in the 1970s at Bell Labs for use in embedded minicomputers. A version named Duplex Multi Environment Real Time (DMERT) was the operating system for the AT&T 3B20D telephone switching minicomputer, designed for high availability; DMERT was later renamed Unix RTR.
A Class-5 telephone switch is a telephone exchange in the public switched telephone network (PSTN) that directly serves subscribers and manages subscriber calling features. Class-5 services include basic dial-tone, calling features, and additional digital and data services to subscribers connected to a local loop.
The Elektronisches Wählsystem Digital (EWSD), translated to Electronic Digital Switching System in English, is a widely installed German telephone exchange system, originally introduced in 1975 by Siemens AG, but discontinued in 2017.
Alcatel–Lucent S.A. was a multinational telecommunications equipment company, headquartered in Boulogne-Billancourt, Paris France. It was formed in 2006 by the merger of France-based Alcatel SA and U.S.-based Lucent Technologies, the latter being a successor of AT&T's Western Electric and a holding company of Bell Labs.
Telecom Valley was an area located in Sonoma County, California specifically the Redwood Business Park of Petaluma, California.
40 Gigabit Ethernet (40GbE) and 100 Gigabit Ethernet (100GbE) are groups of computer networking technologies for transmitting Ethernet frames at rates of 40 and 100 gigabits per second (Gbit/s), respectively. These technologies offer significantly higher speeds than 10 Gigabit Ethernet. The technology was first defined by the IEEE 802.3ba-2010 standard and later by the 802.3bg-2011, 802.3bj-2014, 802.3bm-2015, and 802.3cd-2018 standards. The first succeeding Terabit Ethernet specifications were approved in 2017.
A class-4, or tandem, telephone switch is a U.S. telephone company central office telephone exchange used to interconnect local exchange carrier offices for long distance communications in the public switched telephone network.
The Number One Electronic Switching System (1ESS) was the first large-scale stored program control (SPC) telephone exchange or electronic switching system in the Bell System. It was manufactured by Western Electric and first placed into service in Succasunna, New Jersey, in May 1965. The switching fabric was composed of a reed relay matrix controlled by wire spring relays which in turn were controlled by a central processing unit (CPU).
The GTD-5 EAX is the Class 5 telephone switch developed by GTE Automatic Electric Laboratories. This digital central office telephone circuit switching system is used in the former GTE service areas and by many smaller telecommunications service providers.
The No. 4 Electronic Switching System (4ESS) is a class 4 telephone electronic switching system that was the first digital electronic toll switch introduced by Western Electric for long-distance switching. It was introduced in Chicago in January 1976, to replace the 4A crossbar switch. The last of the 145 systems in the AT&T network was installed in 1999 in Atlanta. Approximately half of the switches were manufactured in Lisle, Illinois, and the other half in Oklahoma City, Oklahoma. At the time of the Bell System divestiture, most of the 4ESS switches became assets of AT&T as part of the long-distance network, while others remained in the RBOC networks. Over 140 4ESS switches remained in service in the United States in 2007.
A telephone exchange, also known as a telephone switch or central office, is a crucial component in the public switched telephone network (PSTN) or large enterprise telecommunications systems. It facilitates the interconnection of telephone subscriber lines or digital system virtual circuits, enabling telephone calls between subscribers.
NANP telephone switches | |
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| Early automatic & crossbar switches | |
| Electronic switching systems | |
