WAN Technology

M Tanvir IrfanM Tanvir Irfan

WAN TechnologyWAN TechnologyPhysical and Data Link LayerPhysical and Data Link Layer

M Tanvir IrfanM Tanvir [email protected]@yahoo.com

Lecture 9, Lecture 9, IICTIICT

To the memory of Moslehuddin BhaiYou still live in my heart


What is WAN?What is WAN?

Basically, WAN is a networking technology. Basically, WAN is a networking technology. Its full name is Its full name is Wide Area NetworkWide Area Network..

WAN spans a large geographical area, often WAN spans a large geographical area, often a country or even a continent.a country or even a continent.

Example: the Example: the InternetInternet

WAN consists of a large number of WAN consists of a large number of computers. Each computer is called computers. Each computer is called HostHost..

Hosts are connected by Hosts are connected by subnetsubnet..

As you already know, a subnet consists of 2 As you already know, a subnet consists of 2 elements – 1. elements – 1. Transmission linesTransmission lines (circuits/ (circuits/ channels/ trunks) and 2. channels/ trunks) and 2. Switching elementsSwitching elements (e.g. routers).(e.g. routers).


What is WAN?What is WAN?

subnet

A simple overview of WAN

Host

Can you find the hosts, routers and subnet in the followingDiagram? [You need spectacles if you can’t find ]

Host


WAN StandardsWAN Standards

A WAN standard usually gives a description of WAN physical layer and WAN data link layer.

A number of organizations have given their standards:

ITU–T – International Telecommunication Union –

Telecommunication Standardization Sector

ISO – International Organization for Standardization

IETF – Internet Engineering Task Force

EIA – Electronic Industries Association


WAN Physical LayerWAN Physical Layer

WAN Physical Layer protocols describe how to provide electrical, mechanical, operational and functional connections for WAN services.

The WAN physical layer describes the interface between

Data Terminal Equipment (DTE) Data Communicating Equipment (DCE)


WAN Physical Layer:WAN Physical Layer:DTE & DCEDTE & DCE

Data Terminal Equipment (DTE) Device at the user end of a user-network interface that serves as a data source, destination, or both. Examples: computers, printers, faxes

Data Communicating Equipment (DCE) Device that helps DTE (user computer) to connect to the network. DCE provides a physical connection to the network DCE transmits and receives data in the form of an analog or digital signal through a network Examples: Modems and Interface Cards


WAN Physical Layer:WAN Physical Layer:DTE & DCEDTE & DCE

Communication through DTE and DCECommunication through DTE and DCE

DTE (your computer) wants to get connected to DTE (your computer) wants to get connected to the WAN (the Internet) by using DCE (modem).the WAN (the Internet) by using DCE (modem). DCE (modem) takes data generated by DCE (modem) takes data generated by DTE(computer), converts them to an appropriate DTE(computer), converts them to an appropriate signal and sends that signal to another DCE signal and sends that signal to another DCE through the physical (telecom) link.through the physical (telecom) link. The second DCE (modem) takes the signal off The second DCE (modem) takes the signal off the line, convert it to a form usable by its DTE the line, convert it to a form usable by its DTE (computer)(computer) To make the communication possible, both the To make the communication possible, both the sending and the receiving DCEs must use the sending and the receiving DCEs must use the same modulating methodsame modulating method


You didn’t understand so far if You didn’t understand so far if you can’t answer these you can’t answer these

questions:questions:1. True/False: WAN spreads over a large

geographical area.

2. True/False: WAN = Wiring And Networking

3. Real Life Example: Mr. T. I. connects to the Internet using a US Robotics 56 Kbps modem with his HP notebook computer. Identify the following objects:

WAN:

DTE:

DCE:


WAN Data Link LayerWAN Data Link Layer

WAN Data link Layer protocols describe how frames are WAN Data link Layer protocols describe how frames are transmitted in the Data Link Layer.transmitted in the Data Link Layer. Several common Data Link Layer standards [only for Several common Data Link Layer standards [only for reference]:reference]:

High Level Data Link Control (HDLC)High Level Data Link Control (HDLC) Frame RelayFrame Relay Point to Point Protocol (PPP)Point to Point Protocol (PPP) Integrated Service Digital Network (ISDN)Integrated Service Digital Network (ISDN) Simple Data Link Control Protocol (SDLC)Simple Data Link Control Protocol (SDLC) Serial Line Interface Protocol (SLIP)Serial Line Interface Protocol (SLIP) Link Access Procedure Balance (LAPB)Link Access Procedure Balance (LAPB) Link Access Procedure D-channel (LAPD)Link Access Procedure D-channel (LAPD) Link Access Procedure Frame (LAPF)Link Access Procedure Frame (LAPF) Asynchronous Transfer Mode (ATM)Asynchronous Transfer Mode (ATM)

We will studyThe star-marked topics


WAN Data Link Layer:WAN Data Link Layer:PPP (Point-to-Point PPP (Point-to-Point

Protocol)Protocol) IETF took the initiative to design PPP as the data link layer protocol for point-to-point lines. Their goal was to use it as the official Internet Standard.

Q: What’s Point-to-Point? A: A point-to-point network may consist of more than one connection between two machines: source and destination. A packet sent from source to destination may have to visit one or more intermediate machines. But the source and destination will think that they are connected by a single wire.

In future all the ISP’s (Internet Service Provider) will support PPP.

PPP Frame Format

011111101111111100000011 variable 01111110


How it works:How it works:PPP (Point-to-Point PPP (Point-to-Point

Protocol)Protocol)The Story of Mr. T. I. Connecting to the InternetThe Story of Mr. T. I. Connecting to the Internet

1. Mr. TI calls the ISP using his telephone and modem.2. The modem connected to the router of the ISP answers Mr. TI’s

call. This establishes a physical layer connection.3. Now Mr. TI’s PC sends PPP frames to the ISP’s router.4. The router sends back replies to Mr. TI’s PC.5. Thus a PPP (data link layer) connection is established.

Second Part of the StorySecond Part of the Story6. Now a network layer connection is required. This is done by

sending & receiving NCP(Network Control Protocol) packets.

7. Mr. TI needs an IP address. The ISP has n IP addresses. It gives Mr. TI an IP address dynamically.

8. Thus Mr. TI is connected to the Internet. He can browse (i.e. send and receive IP packets) happily.


ISDN (Integrated Service ISDN (Integrated Service Digital Network)Digital Network)

History: For more than 100 years, the international telecommunication infrastructure has been public circuit-switched telephone system. It can support only analog voice transmission. Hence it is not enough for modern communication. So the telephone companies of the world decided to design a new, fully digital telephone system. The main goal was to integrate voice and non-voice service. This new system is called ISDN.

Features of ISDN: 1. Voice (the main service)

2. Intercom button for calling secretaries instantly3. Multiple hotkeys for instantly calling (no

delay for call setup) anywhere in the world4. Caller ID display 5. Telephone can be connected to computer

so that caller’s tel. no + name + address can be displayed from database 6. Call forwarding

7. Conferencing worldwide. There are more…


How it works: ISDNHow it works: ISDN

Key Idea: Digital Bit Pipe means a conceptual pipe between the customer and the carrier through which bits flow. ISDN configuration for home/small office is: -

NT

ISDNExchange

Customer’s office Carrier’s officeKm’s away

Digital bit pipeISDN telephone ISDN Terminal


How it works: ISDNHow it works: ISDN

In the customer’s office up to 8 telephones, computers and other devices can be connected. Similar to LAN.

NT: This is the Network Terminator placed in the customer’s office. It is responsible to send signals to the ISDN Exchange, in the carrier’s office, many kilometers away.

Digital signal is processed inside the carrier’s office and then sent to the destination customer.Now we would like to look inside the Digital Bit Pipe


How it works: ISDNHow it works: ISDNThe ISDN InterfaceThe ISDN Interface

Inside the digital bit pipe: It’s a wonderful world! There is Time Division Multiplexing (TDM)

inside the bit pipe. Don’t tell me you don’t know what is TDM!

Three types of bit pipes have been standardized on the basis of TDM:

1. Basic Rate

2. Primary Rate

3. Hybrid The Basic Rate digital bit pipe is the replacement for POTS (Plain Old Telephone Service). Let’s examine it.


How it works: ISDNHow it works: ISDNBasic Rate Digital PipeBasic Rate Digital Pipe

64 kbps digital PCM channel for voice or data

16-kbps out-of-band signal


ATM ATM (Asynchronous Transfer (Asynchronous Transfer

Mode)Mode) This is a connection-oriented network. Hope you know what’s connection-oriented and what’s connectionless.

ATM: This strange name is due to the fact that most transmission is synchronous (closely related to a clock) and ATM is not.

ATM Craze: During 1990s it was believed that ATM was going to solve all the networking problems by merging – voice, data, cable TV, telex, telegraph etc. etc. Did not work because of politics

Internet (connectionless) versus Telephone companies (connection-oriented)

Don’t think ATM is dead. It is still alive deep inside the telephone network, mostly used by carriers for internal transport.


How it works: ATM How it works: ATM Virtual CircuitsVirtual Circuits

ATM is connection-oriented. So before sending data a connection has to be set up. To set up a connection the source sends a setup-packet to the destination. As this packet moves through the subnet, it sets up the path from source to destination. Routers in subnet updates their routing table, when they get this packet. This kind of connection is called virtual circuits, similar to how electricity passes through an actual circuit.


How it works: ATM How it works: ATM Virtual CircuitsVirtual Circuits

As you can see, the sending host sends a setup packet to the receiving host through the subnet. This packet sets up the connection. Then data can be transmitted.

ATM Virtual Circuit


You didn’t understand so far if You didn’t understand so far if you can’t answer these you can’t answer these

questions:questions:1. What protocol is used to connect to the Internet?

A. PPP

B. ISDN

C. ATM

D. I don’t care

2. What is a digital bit pipe?

3. True/False: There is no need for connection set up in ATM.

4. Who is Mr. T. I.?


That’s the end of That’s the end of today’s storiestoday’s stories

This presentation is prepared from the following references: Computer Networks, A. S. Tanenbaum, 3rd Edition Data and Computer Communications, W. Stalling, 6th Edition Computer Networks, A. S. Tanenbaum, 4th Edition

Documents

WAN Technology