Integrated Services Digital Network You do not need a modem but instead need a device called an ISDN terminal adapter. In this network sending voice, video and computer data and user can receive telephone calls using the one line. Conduct videoconferencing easily. Designed to replace public telecom system Wide variety of services Entirely digital domain First generation ( narrowband ISDN ) –64 kbps channel is the basic unit –Circuit-switching orientation –Contributed to frame relay Second generation ( broadband ISDN ) –100s of mbps –Packet-switching orientation –Contributed to ATM ( cell relay )

Disadvantages Your main telephone socket has to be changed to an ISDN box by an engineer. Your computer has to be fitted with an ISDN modem which is more expensive than a standard modem. It is more expensive than Dial-up on a monthly basis. Should you move house, you have to pay for your telephone line to be converted back again to a normal line.

Asymmetric Digital Subscriber Line A technology that turns traditional copper wires into fast data pipes. This offers internet connections up to 30 times faster than the fastest dial up modem. The connections work by splitting your phone line into two separate channels, one for data (internet) and one for voice (phone calls) which means you can talk on the phone and be connected to the internet at the same time.

Advantages Faster downloads compared to dial-up or ISDN No need for a second phone line - by allowing voice and data transfer at the same time (you can use the phone as normal while connected to the internet). Because ADSL transfers data digitally it doesn't need to convert the data from digital to analogue and back again. ADSL connections are Always on, which makes the usual long wait to connect a thing of the past

Disadvantages ADSL connections are not available to everyone, you need to be within 3 miles of an ADSL enabled exchange. The hardware costs can be quite significant as you will need a special ADSL modem and ADSL filters to use the service, most ISPs allow you to hire these items which can reduce the initial cost. Because ADSL connections are Always on you will need a firewall to protect your PC

OSI( Open Systems Interconnection Layers Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer

The Physical Layer Deals with transmitting raw bits over a communication channel. How many volts for 1 or 0. How many microseconds a bit lasts.

Data link Layer Break the input data up into data frames. Process the acknowledgement frames sent back by the receiver. Solve the problems caused by damaged, lost and duplicate frames. Full duplex transmission Physical details of interfacing with the cable. Handles data flow control. It can support Ethernet, Token Ring.

Network Layer Routing packets from source to destination. Routes can be static or dynamic In broadcast networks, routing problem is simple, so the network layer is thin. It contain IP address which is connectionless Datagram protocol.

Transport Layer Accept data from the session layer, split it up into smaller units if needed, pass these to the network layer and ensure that the all pieces arrive correctly at the other end The transport layer is a true end-to-end layer, from source to destination Establishing and deleting connections across the network. what type of service to provide the session layer with and ultimately, the users of the entire network TCP and UDP protocols

Session Layer Allows users on different machines to establish sessions between them A session might be used to allow a user to log into a remote timesharing system or to transfer a file between two machines Example: token management. Only the side holding the token may perform the critical operation. The Session Layer adds traffic flow and control information, such as establishing and terminating connections between host computers

Presentation Layer Concerned with the syntax and semantics of the information transmitted. The Presentation Layer adds formatting, display and encryption information, such as helping to maintain compatibility with different coding methods and file types used on computer systems. A typical example of a presentation service is encoding data in a standard agreed upon way. [Character strings, integers, floating-point numbers…].

Application Layer The application layer contains a variety of protocols that are commonly needed. The application sends the continuous data stream. Example: incompatible terminal type. Other application is file transfer (ftp),HTTP

TCP/IP Protocol Stack The most standard protocol is the transmission control protocol/Internet Protocol (TCP/IP). It has the similar protocols and functions. The TCP/IP protocol allows different computers from many different suppliers which is running different operating system. It is the protocol where internet is based. More correctly it is referred to as a protocol suite because it is a collection of protocols

TCP/IP and OSI Protocol Stack application: supporting network applications –ftp, smtp, http transport: host-host data transfer –tcp, udp network: routing of datagrams from source to destination –ip, routing protocols link: data transfer between neighboring network elements –ppp, ethernet, ATM physical: bits “on the wire” Application Layer Transport Layer Network Layer Data link Layer Physical

Sockets The combination of IP Address and port number. This is used in a similar way to a file, giving programs the opportunity to exchange data across the network. Allows programmers to establish communication between process running on computers There are two types pf sockets Datagram: Allow a computer to send a single message Stream: Supports ongoing data exchange between participating processes. It has two components IP Address Port Number Example: : 80

IP address Internet Protocol Address –4 groups of numbers ranging from 0-255,separated by full stop. –Every web site has a unique address known as IP Address –32 bit (4-byte) binary number –Like Domain Name : IP address: Identify the network Identify the specific computer

Hands-on: Find Your PC’s IP Click the “start” button on the taskbar Click “Run” Type in “cmd” to display a MS-DOS window Type “ipconfig /all” at the prompt and press enter key See who “owns” your IP address – Trace a route to your PC –

Ethernet Ethernet uses a system of sending signals called ‘Carrier Sense Multiple Access / Collision Detect’ CSMA/CD. When a piece of data is to be sent, it is broken into smaller packets, then data to be sent waits until the communication line is clear, and then sends. If two different devices send at exactly the same time, there will be a collision and the packet will become corrupted. The system detects the collision and puts a stop to all signals being sent until the communication line is clear, devices are then able to send at random intervals, and the destroyed packet can be resent. If the communication line is very busy some signals never make it and have to be resent by the operator. Ethernet speeds are about 10 Mbps.

Token Ring A ring network may use a Token to carry a message from one device to another. The sender waits for the Token to arrive, sticks the message on to it and the Token goes around the ring visiting every device until the message finds its destination. Occasionally the Token may get lost and if it travels around the ring a second time it gets destroyed and a new one created. The system avoids collisions as only one Token is allowed on the network, it is also fair as busy devices are serviced the same as less busy ones.