Data CommunicationsDNT 1013

Prepared By:Mdm Noor Suhana Bt SulaimanFKMT-NT, TATiUC

Introduction to Data Communications

Chapter 1

What is data communication?

Not to be confused with telecommunication—– Any process that permits the passage from a sender to

one or more receivers of information of any nature, delivered in any easy to use form by any electromagnetic system.

Data communication-– Defined as a subset of telecommunication involving the

transmission of data to and from computers and components of computer systems.

• More specifically data communication is transmitted via mediums such as wires, coaxial cables, fiber optics, or radiated electromagnetic waves such as broadcast radio, infrared light, microwaves, and satellites.

History of Telecommunications

Invention of telegraph Samuel Morse – 1837

Invention of telephone- Alexander Graham Bell – 1876

Development of wireless By ??? – 1896 Concept of universal access and growth

of AT&T Divestiture of AT&T—what year??

History of Telecommunications Continued…. Telecommunications Act of 1996 Three main developments that led to the

growth of data communications systems:– Large-scale integration of circuits reduced the cost

and size of terminals and comm equipment– Developments of software systems made

establishment of communication networks easy– Competition among providers of transmission

facilities reduced the cost of data circuits

History of Data Communication

Transistor developed by Bell Labs (which is now ???) 1947

Hush-a-Phone Case Carterphone case MCI and Long Distance Creation of networks (LAN’s and WAN’s) Data Link Protocols Microcomputers

Framework for Global Electronic Commerce

A Framework for Global Electronic Commerce was released in 1997

It’s release underscores the importance of Internet-based commerce in the global economy

It outlines several guiding principles for e-commerce planners and strategists

Table 1-3

Table 1-4

Features of Communication

Four things required– Sender, receiver, medium, and message

Types of messages– File– Request– Response– Status– Control– Correspondence

Understandability Error Detection

Network Applications

The network applications environment consists of several important components:– Application programs– Operating systems– Data communication systems– Database management systems

The application environment is illustrated in Figure 1-10

Figure 1-10

Online System Requirements

Response Time Throughput Consistency Flexibility

Online Systems Requirements Continued Availability Reliability

– Mean time between failure (MTBF)– Mean time to repair (MTTR)– Fault Tolerance

Recovery Security

Business Data Communication Applications Major data communication applications

include:– E-mail– Groupware– Knowledge management systems– E-commerce and e-business applications– Wireless applications

Groupware Applications

Group calendar systems

Electronic filing cabinets

Project management software

Group support systems

Electronic meeting and videoconferencing systems

Document management systems (image processing systems)

Other Data Communication Applications Batch applications Data entry

applications Distributed

applications Inquiry/response

applications

Interactive applications

Sensor-based applications

Combined applications

Application Service Providers

Many businesses have turned to third-party services for some or all of their business and data communications applications

Application service providers (ASPs) are third-party organizations that manage and distribute software and services to other companies over the Web

Many ASPs specialize in integrated e-commerce and e-business applications

Business Data Communications Issues Major data communications issues

include:– Cost-effectiveness– The Internet– Bandwidth– Evolving technologies– Convergence– Standards– Privacy and security

Important Standard-Setting OrganizationsTable 1-5

Business Data Communication Careers There are numerous job opportunities and

career paths for individuals interested in data communications and networking

Table 1-6 includes examples of data communication job titles

Table 1-7 summarizes some of the major professional certifications for networking and data communications specialists

Table 1-6

Table 1-7

Introduction to Networks

Can be defined as a single computer , called a host, together with communication circuits, communication equipment, and terminals.

There are many different types of network configurations (see figures1-4 to 1-8)

Key Data Communication Concepts

Session: communication dialog between network users or applications

Network: interconnected group of computers and communication devices

Node: a network-attached computer Link: connects adjacent nodes (see Figure 1-4) Path: end-to-end route within a network Circuit: the conduit over which data travels Packetizing: dividing messages into fixed-length packets prior

to transmission over a network’s communication media Routing: determining a message’s path from sending to

receiving nodes.

Store-and-Forward Systems

Messages may be stored at intermediate nodes along the transmission path between sender and receiver in store-and-forward systems– This helps ensure message delivery without

obligating the sender to wait until a message is delivered before transmitting other messages

– It also helps ensure message delivery in the case of link or destination failure while the message is in transit

– Store-and forward algorithms are valuable in time-staged delivery systems and in networks that assign priorities to different messages

Network Topology, Architecture, and Complexity Network topology refers to the physical layout

of a network, the way that nodes attach to the communication medium

Network architecture refers to the way in which media, hardware, and software are integrated to form a network

Network complexity is concerned with extent to which network architectures are simple or diverse in their make– Figures 1-5, 1-6, and 1-7 illustrate various levels of complexity

Figure 1-5

Figure 1-6

Figure 1-7

Data Communication Frameworks Two major data communication

frameworks have been developed to help ensure that networks meet business and communication requirements:– Open Systems Interconnection (OSI)

reference model developed by the International Standards Organization (ISO)

– Transmission Control Protocol/Internet Protocol (TCP/IP) suite

History of the OSI Model

Open Systems Interconnected Model– was created in the 70’s by the ISO (although the

CCITT came up with their own model)• 10 different people got together and considered all

functions of communications

– was created because people realized that our computers needed to talk to each other(and there was no one dominant computer system)

– ISDN was a big factor– 7 layers = 4 upper and 3 lower

OSI Reference Model in Practice

The OSI reference model is used in many ways:– To provide assistance when troubleshooting network

problems

– To provide a common terminology and framework for networking technology developers

– To facilitate the development of connectivity standards needed for flexible open architectures

– To enable the development of protocol stacks that allow network nodes to communicate with one another

Network Models

Using a formal model allows us to deal with various aspects of Networks abstractly.

We will look at a popular model (OSI reference model).

The OSI reference model is a layered model.

Layering

Divide a task into pieces and then solve each piece independently (or nearly so).

Establishing a well defined interface between layers makes porting easier.

Major Advantages: Code Reuse Extensibility

Layering Example: Federal Express

Letter in envelope, address on outside FedX guy adds addressing information,

barcode. Local office drives to airport and

delivers to hub. Sent via airplane to nearest city. Delivered to right office Delivered to right person

FedX Layers

Letter

Letter Addressed Envelope

Addressed Envelope

OSI MODEL

Established in 1947, the International Standards Organization (ISO) is a multinational body dedicated to worldwide agreement on international standards. An ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI) model. It was first introduced in the late 1970s.

ISO is the organization.OSI is the model

Why the structure

of network need

Network Model

-OSI Model?

Cont..

The OSI model describes how information or data makes its way from application programmes (such as spreadsheets) through a network medium (such as wire) to another application programme located on another network.

The OSI reference model divides the problem of moving information between computers over a network medium into SEVEN smaller and more manageable problems .

This separation into smaller more manageable functions is known as layering.

Cont.. The OSI Reference Model is composed of 7 layers, each

specifying particular network functions. The process of breaking up the functions or tasks of

networking into layers reduces complexity. Each layer provides a service to the layer above it in the

protocol specification. Each layer communicates with the same layer’s software or

hardware on other computers. The lower 4 layers (transport, network, data link and physical

—Layers 4, 3, 2, and 1) are concerned with the flow of data from end to end through the network.

The upper four layers of the OSI model (application, presentation and session—Layers 7, 6 and 5) are orientated more toward services to the applications.

Data is Encapsulated with the necessary protocol information as it moves down the layers before network transit.

Figure 1.0: OSI Model

Layer 7: Application The application layer is the OSI layer that is closest to

the user. It provides network services to the user’s applications. It differs from the other layers in that it does not

provide services to any other OSI layer, but rather, only to applications outside the OSI model.

Examples of such applications are spreadsheet programs, word processing programs, and bank terminal programs.

The application layer establishes the availability of intended communication partners, synchronizes and establishes agreement on procedures for error recovery and control of data integrity.

Layer 6: Presentation

The presentation layer ensures that the information that the application layer of one system sends out is readable by the application layer of another system.

If necessary, the presentation layer translates between multiple data formats by using a common format.

Provides encryption and compression of data. Examples :- JPEG, MPEG, ASCII, EBCDIC,

HTML.

Layer 5: Session The session layer defines how to start, control and

end conversations (called sessions) between applications.

This includes the control and management of multiple bi-directional messages using dialogue control.

It also synchronizes dialogue between two hosts' presentation layers and manages their data exchange.

The session layer offers provisions for efficient data transfer.

Examples :- SQL, ASP(AppleTalk Session Protocol).

Layer 4: Transport

The transport layer regulates information flow to ensure end-to-end connectivity between host applications reliably and accurately.

The transport layer segments data from the sending host's system and reassembles the data into a data stream on the receiving host's system.

The boundary between the transport layer and the session layer can be thought of as the boundary between application protocols and data-flow protocols. Whereas the application, presentation, and session layers are concerned with application issues, the lower four layers are concerned with data transport issues.

Layer 4 protocols include TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).

Layer 3: Network

Defines end-to-end delivery of packets. Defines logical addressing so that any

endpoint can be identified. Defines how routing works and how routes are

learned so that the packets can be delivered. The network layer also defines how to

fragment a packet into smaller packets to accommodate different media.

Routers operate at Layer 3. Examples :- IP, IPX, AppleTalk.

Layer 2: Data Link

The data link layer provides access to the networking media and physical transmission across the media and this enables the data to locate its intended destination on a network.

The data link layer provides reliable transit of data across a physical link by using the Media Access Control (MAC) addresses.

The data link layer uses the MAC address to define a hardware or data link address in order for multiple stations to share the same medium and still uniquely identify each other.

Concerned with network topology, network access, error notification, ordered delivery of frames, and flow control.

Examples :- Ethernet, Frame Relay, FDDI.

Layer 1: Physical

The physical layer deals with the physical characteristics of the transmission medium.

It defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems.

Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors, and other similar attributes are defined by physical layer specifications.

Examples :RJ45

TCP/IP Protocol Suite

The TCP/IP suite provides insights into the inner workings of the Internet

Like the OSI model, the TCP/IP suite is layered– Because the protocols found at each layer are

independent of those at the other layers, a given protocol can be modified without affecting those found at other layers

– TCP/IP layers and layer-specific protocols are illustrated in Figure 1-9

TCP/IP TCP-Transmission Control Protocol In OSI reference model terminology -the TCP/IP

protocol suite covers the network and transport layers. TCP/IP can be used on many data-link layers (can

support many network hardware implementations). The TCP/IP protocol suite is made of five layers:

physical, data link, network, transport, and application. The first four layers provide physical standards,

network interface, internetworking, and transport functions that correspond to the first four layers of the OSI model.

The three topmost layers in the OSI model, however, are represented in TCP/IP by a single layer called the application layer.

Cont..

Relationship of layers and address in TCP/IP

Cont..

TCP/IP is the basic communication language or protocol of the Internet.

It can also be used as a communications protocol in a private network (either an intranet or an extranet).

When user are set up with direct access to the Internet, your computer is provided with a copy of the TCP/IP program just as every other computer that you may send messages to or get information from also has a copy of TCP/IP.

Cont..

TCP/IP is a two-layer program. The higher layer, Transmission Control Protocol, manages the assembling of a message or file into smaller packets that are transmitted over the Internet and received by a TCP layer that reassembles the packets into the original message.

The lower layer, Internet Protocol, handles the address part of each packet so that it gets to the right destination.

Each gateway computer on the network checks this address to see where to forward the message. Even though some packets from the same message are routed differently than others, they'll be reassembled at the destination.

Cont..

Many Internet users are familiar with the even higher layer application protocols that use TCP/IP to get to the Internet.

These include the World Wide Web's Hypertext Transfer Protocol (HTTP), the File Transfer Protocol (FTP), Telnet (Telnet) which lets you logon to remote computers, and the Simple Mail Transfer Protocol (SMTP).

These and other protocols are often packaged together with TCP/IP as a "suite."

The IP in TCP/IP

IP is the network layer– packet delivery service (host-to-host).– translation between different data-link protocols.

IP provides connectionless, unreliable delivery of IP datagrams.– Connectionless: each datagram is independent of

all others.– Unreliable: there is no guarantee that datagrams

are delivered correctly or even delivered at all.

Moving Bits through the NetworkAnalog Signal

1

0

Digital Signal

1 1 1

0 0 0

digital analog digital Computer Modem Modem Computer

telephone lines

Putting It all Together

Data Communications Supports Applications The Operating System manages the

resources of the computer. There must however, be a system that

provides a bridge between applications and the devices so they can communicate—this is called a Transaction Control Process (TCP)