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• Juraid Sadiq• Shahban Iqbal• Raja Faizan Ali• Raja Usman

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Chapter 9

Remote AccessPresentation

Modem Technology

• The easiest way to connect computers over long distances is over telephone lines, you can reach almost anywhere by telephone.

How a Modem Works

• A modem is typically used to send digital data over a phone line. The sending modem modulates the data into a signal that is compatible with the phone line, and the receiving modem demodulates the signal back into digital data. Wireless modems convert digital data into radio signals and back.

Connecting to the Computer

• A modem can be installed internally, in the computer in which case it is called an internal modem, or it can be an external device that is connected to the computer with a serial cable.

Connecting to the Phone System

• You connect a modem to the phone system just as you would a regular telephones or fax machine. The modem should accept a regular telephone cord the kind that connects a telephone to a wall outlet.

Transfer Speed

• Modem speed is often discussed in baud or BPS.

• Baud rate refers to the oscillation of a sound wave on which a single bit of data is carried. BPS, or bits per second, is the amount of data transferred in a second.

• Three common speeds for modems are 9,600 bps, 14,400 bps, and 28,800 bps.

Compression

• In signal processing, data compression, source coding, or bit-rate reduction involves encoding information using fewer bits than the original representation. Compression can be either loss or lossless. Lossless compression reduces bits by identifying and eliminating statistical redundancy.

Error Detection and Correction

• Error detection is the detection of errors caused by noise or other impairments during transmission from the transmitter to the receiver. Error correction is the detection of errors and reconstruction of the original, error-free data.

Types of Modem• There are many types of modems because there

are many different environments over which computer need to send data. Modem are used whenever a computer’s digital signals need to be converted to analog signals to be transmitted.

• the types of modem can be divide into two broad categories, depending on how they coordinate their data transmission.

• Asynchronous• synchronous

synchronous

• A synchronous communication, requires that message begin with a start bit so that the receiving device can synchronize its internal clock with the timing of the message

• A synchronous transmission are normally short, and the end of the message is singled by a stop bit.

Asynchronous

• synchronous communication require that some kind of clocking mechanisms be put into place to keep the clocks of the sender and receiver synchronized.

• One of the three methods are used for synchronous timing coordination.

1. Guaranteed state change2. Separate clock signals3. Over sampling

Digital Modems

• A modem (modulator-demodulator) is a network hardware device that modulates one or more carrier wave signals to encode digital information for transmission and demodulates signals to decode the transmitted information.

• An ISDN (Integrated Services Digital Network) modem is an example of digital modem.

Carriers

• Critical part of remote access, that carriers in remote network access or in wide area networking is the phone company or other entity that carries the telephone connection from one network point to the other.

• We connect computers together using phone company telephone lines into ways.

1. Public dial network lines2. Leased line

Public dial network lines

• Dial-up Internet access is a form of Internet access that uses the facilities of the public switched telephone network (PSTN) to establish a connection to an Internet service provider (ISP) by dialing a telephone number on a conventional telephone line.

Leased line

• A leased line is a private bidirectional or symmetric telecommunications line between two or more locations provided in exchange for a monthly rent. Sometimes known as a private circuit or data line.

Remote Access Software

• Microsoft RAS (Remote Access Service) allows users to connect to a windows NT computers over phone lines. If you have more than one modem attached to yours RAS server, you can have more than one computer connect to it at a time. RAS on a Windows NT server can accept up to 256 simultaneous connection from remote client.

Installing Remote Access Service

• Click Next twice. In the list of role services, select Routing and Remote Access Services to select all of the role services. You can also select individual server roles. Proceed through the steps in the Add Roles Wizard to complete the installation.

Administering Remote Access Service

• Remote Access Service Administration provides a set of functions for administering user permissions and ports on RAS servers. Using these functions, you can develop a RAS server administration application.

Making a Dial-Up Connection

• How to Create a Dial-Up Connection in Windows XP• From the Start menu, choose Control Panel.• Click the Network and Internet Connections icon.• Click the Set up or change your Internet connection icon.• Click the Setup button.• Click the Next button.• Select Connect to the Internet.• Click the Next button