Revolution of Telephone Switching

 

Manual Switch – In the telephone exchange all subscribers are connected to a central switch and it is manually operated by an operator. If a person want to call another person first he or she should call to telephone exchange. There is a person who can connect the two subscribers together by plugging in the exchange.

Strowger Switch - Every subscriber line ended at the Strowger switch with a relay, referred to as line relay. This switch had stepping relays that worked according to the dial pulses. Upon completing one digit, the first stepping relay would activate another stepping relay. Complete connection was achieved by serial activation of several stepping relays. The line relays were connected to an electromechanical device called line finder.

Crossbar switch - Crossbar switch employed centralized common control equipment which encompassed a group of equipment engaged in establishing call set up. The equipment was released and was available for setting up other calls once setting up phase of a call was over. Crossbar switch replaced the line finder with line scanner, to check when a telephone line connected to a line link frame was off hook.

SPC switch – After the evolution of electronics, especially the invention of the transistor, SPC switches came into use. The SPC switch entirely replaced the electromechanical common control equipment of the cross bar switch with electronic circuits, while retaining the same switching matrices. These systems employ memories based on RAM (Random Access Memory) technology, tape and disk storage. SPC switching system was space division switching systems.

Cisco Router Configuration

Router Configuration

Date                                          3/2/2010

Objective                                  Configure a new Cisco Router

Aim                                           Understand how to use the Cisco IOS command line interface (CLI) to        configure and manage a Cisco router.

Cisco Router

                   Cisco Router is a network hardware device which we can use to interconnect different networks to communicate with each other. It is running under Network Layer (layer 3) in OSI model and uses many protocols to communicate. Cisco Router contains several interfaces. They are,

Console and auxiliary-             used to configure the device.

Auxiliary -                                 used to configure the router from remote area via dial-up connection.

                        Router has its own operating system which is called as Internetwork operating system. And its main components are Ram, Rom, Flash, NV Ram, Interfaces and CPU.

Equipment List

Cisco router

Personal computer

PC and router arrangement

            We can also configure the when we connect with a LAN. Initially we can connect with Router & can configure.

Procedure:

Initially we will probably configure our router from a terminal. If the router is already configured and at least one port is configured with an IP address and it has a physical connection to the network. If it is not already configured, then you will have to directly connect to it with a terminal and a serial cable. Plug a serial cable into a serial (COM) port on the PC and the other end into the console port on the Cisco router. Start HyperTerminal, tell it which COM port to use and click OK. If the router is not on, turn it on. Then Run the Cisco IOS software. Using that Prompt we can configure the Router from giving following commands.

If the router is configured before.

First we can see,

Password:

After giving the password & press enter

cisco>?

 We can see name of the router as “Cisco”.

If the router is not configured before we can see,

Router>?

Optical Fiber Communication

Type of optical fiber

            When we are selecting optical fiber for a specific application we have two types of optical fibers. They are Single mode and multi mode. The mode structure depends on the wavelength of the light used, so that this fiber actually supports a small number of additional modes at visible wavelengths. Multi-mode fiber is a type of fiber optic cable which is thick enough for light to follow several paths through the code. Multi-mode fiber is best suited for use in short lengths, such as those used in Local Area Networks (LANs). But single modes are standard choice for high data rates or long distance telecommunications which use laser diode based fiber optic transmission equipment. 

Dispersion

When we discuses about dispersion of fiber. Ever fiber has Inter modal or chromatic dispersion. Multi mode dispersion only occurs in multimode fibers. . But single mode fibers are having lower dispersion than multi mode fibers. Therefore we can use single mode fibers for long haul repeater/amplifier less optical communication links. 

Fiber non linearity

In this system it is difficult to maintain a linear fiber connection. The system has bending losses and signal transmitting distance may reduce. So, it is important to try to design a linear fiber optic transmission system as possible.

Operating wavelength

When we are selecting a suitable wave length for optical fiber communication we have to analyze the Optical window graph. In optical window there are three windows. We have  820 nm to 900 nm(1^st window), 1280 nm to 1350 nm (2^nd  window), and 1450 to 1650 nm(3^rdwindow) But 3^rd window is enhanced for long distance communication for the reason that, the attenuation is varying 0.15 - 0.25 dB/Km which is very low compare to other two windows.

Transmitting power