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Purdue University reseachers have developed a miniature device that converts ultrafast laser pulse into radio-frequency signal. The new device will make communication devices in homes, business and cars completely wireless.

The advance could enable all communications, from high-definition television broadcasts to secure computer connections, to be tarnsmitted from a single base station. This base station wold be sort of a computer itself. The centraln computer would take charge of all the information processing, acting as a single point of contact that interacts with the external world in receiving and sending data.

The pulsing nature of the signals produced by the chip-based spectral shaper reduces the interference that normally plagues radio frequency communications.

If you want to know more about the movement towards the wireless world visit here.

If yourn internet connection is currently unavailable, you may try sending data through your body.This has already been tested by researchers at Korea University,Seoul. they trasmitted data through a person's arm at the rate of 10 megabits per second by placing two electrodes 30 cm(12 inches) apart on his skin.

A network trnsmitting through the skin would cut energy needs bu roughly 90 per cent, claim the researchers. The most interesting application would be in the medical field, where it could help measure bllod sugar and electrical activity of the heart.

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What is ISDN?

ISDN stands for Integrated Service Digital Network, and as the name suggests it allows digital communication. This is favourable as digital technology is a lot faster, and more accurate than the old analogue lines as they no longer require the process of modulation and demodulation. ISDN relies on already existing copper cable systems, causing it’s integration into our existing communications system to be smoother and less disruptive.

According to ITU-T(formerly CCITT) "an ISDN is a network, in general evolving from a telephony IDN, that provides end-to-end digital connectivity to support a wide range of services, including voice and non-voice services, to which users have addressed by a limited set of standard multi-purpose user-network interfaces." The key point of this definition is the ability to support voice services adequately, this has not been achieved using any other concept.

ISDN has four major aspects; telephone network; integrated services; digital; network. These will be explored in a little more detail later.

Narrowband ISDN has been designed to operate over the current communications infrastructure, which is heavily dependent on the copper cable. B-ISDN however, relies mainly on the evolution of fibre optics. According to CCITT B-ISDN is best described as ‘a service requiring transmission channels capable of supporting rates greater than the primary rate.’ Behind this statement lies the plan for a network and services that will have far more impact on the world we know today, than ISDN ever would.

When ISDN is referred to as a network it is to be considered a telephone network, not a computer network. Broadband ISDN allows its users to communicate over high speed, high quality digital channels. The media is supports include Telex, fax, voice telephone, video telephone, audio, high definition TV and computer networking.

In the past video, audio, voice and data services needed different types of communication channels. One of the main advantages of ISDN is the ability to integrate these features over the same network and cable plant. Not only is this possible using ISDN technology but the quality of the transmission is better also. In the past four networks were needed and video was distributed on coaxial lines, audio over balanced lines, voice used copper cable pairs and data services required coaxial or twisted pair cables. Using one network allows reductions in installation costs, as well as easier installation. Other features available include demand networking, automatic bandwidth and on the fly connectivity. Advances in the services available are due to ISDN being digital.

Data applications, in particular, seemed to have problems with the old analogue services. This is due to the fact that computers are digital devices and the transmission of data needs to be modified form binary to analogy tones, then changed back to binary when it is received. This process requires a modem, which handles the MODulation and DEModulation of the data. Whilst the data is in transit it is susceptible to outside influences like noise, line spikes and echoes. Bandwidth is also limited, with the speed of modems being close to the maximum possible.

Networks require high speed connectivity if they are going to be useful. ISDN is an excellent vehicle for connecting LANs, because it scales in increments of 64 kilobits per second (kbps). Computers are digital devices, as is ISDN, meaning that no translation of information is required, improving quality and speed. Due to the characteristics of ISDN it can be used, with the same level of performance, across a room or halfway across the continent. This has unlimited benefits.

The class 5 electronic switching system sold by Lucent Technologies. The 5ESS Switch is the digital central office circuit switching system many communication service providers use.

5ESS has three main kinds of Module: AM is Administrative Module, which contains the central computers. CM is Communications Module, which is the central time-divided switch of the system. SM is Switching Module which in most exchanges is the majority of equipment. SM performs multiplexing, analog/digital coding, and other work to interface with the outside world. Each has a controller, a small computer whose CPUs and memories, like most common equipment of the exchange, are duplicated for redundancy.

5ESS runs on a Time-Space-Time (TST) topology. The Time-Slot-Interchangers (TSI) in the Switching Modules (SM) assign each phone call to a time slot for routing through the CM.

Distributed system lessens the load on the Central Administrative Module (AM) or main computer. 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 multiplatter 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.

Power for all circuitry is distributed as -48VDC and converted to logic or telephone voltages as needed by DC to DC converters on each shelf of circuit packs.

Each SM handles several hundred to few thousand telephone lines or several hundred trunks or mixture thereof. Each has its own processors, 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.

T-carrier spans are terminated, one or two per card, in Digital Line Trunk Units (DLTU) which concentrate their DS0 channels into the TSI. Larger DS3 signals can also have their DS0 signals switched in Digital Network Unit SONET (DNUS) units, without demultiplexing them intoDS1. SMs have Dual Link Interface (DLI) cards to connect them by multimode optical fibers to the Communications Modules for time divided switching to other SMs. 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 grid board. Each grid 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 grid boards connecting to the channel boards by shared B links, but in offices with heavier traffic for lines a lesser number of grid boards are equipped.

Since Line Units handle the high voltages and currents of analog lines, their cards fail at higher rates than ones that handle only computer voltages. Some lines, especially ISDN or PBX ones, are served by individual line cards in an Integrated Subscriber Line Unit.

The development effort for 5ESS reached 5000 employees, producing 100 million lines of code, with 100 million lines of header and makefiles. Evolution of the system took place over 20 years, while three releases were often being developed simultaneously (each taking about 3 years to develop).

A 5ESS-2000 version, introduced in the 1990s, increased the capacity of the SM, with more peripheral modules and more optical links per SM to the CM (see below).

The Administrative Module (AM) of the 5ESS Switch 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 required by the AM. 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. Because the processor mirrors its functions, a failure of one side of the processor will not result in a loss of switching.

Communication Module (CM):-

The oddly named Communications Modules form the central time switch of the exchange. 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 screw-on connectors to plug into transceivers mounted in metal cans 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.

Very Compact Digital Exchange:-

The VCDX (Very Compact Digital eXchange) was marketed to small telephone companies and was used in some instances as a large PBX. It consisted of a single Switching Module, had no Communications Module, and used a Sun Microsystems workstation as its Administrative Module.

The 5ESS has two different signaling architectures Common Network Interface (CNI) Ring and Packet Switch Unit (PSU).

Operations, Administration, Maintenance, and Provisioning:-

The system is administered through an assortment of teletypewriter "Channels" (also called the system console) such as the TEST channel and Maintenance channel. Typically provisioning is done using a one of two methods - a command line interface (CLI) called RCV:APPTEXT, and through the menu-driven RCV:MENU,APPRC program. RCV stands for Recent Change/Verification, and can be accessed throughSwitching Control Center System. Most service orders, however, are administered through Recent Change Memory Administration Center(RCMAC).

A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice versa.It is often a part of a rotating wheel (e.g. an eccentric wheel) or shaft (e.g. a cylinder with an irregular shape) that strikes a lever at one or more points on its circular path. The cam can be a simple tooth, as is used to deliver pulses of power to a steam hammer, for example, or an eccentric disc or other shape that produces a smooth reciprocating (back and forth) motion in the follower, which is a lever making contact with the cam.