N ETWORK P ROGRAMMING CSC- 341 Instructor: Junaid Tariq, Lecturer, Department of Computer Science

Lecture 3

N ETWORK C OMPONENTS Physical Media Interconnecting Devices Computers Networking Software Applications

N ETWORKING M EDIA Networking media can be defined simply as the means by which signals (data) are sent from one computer to another (either by cable or wireless means). Wide variety of transmission links: Copper Twisted pair Coaxial Cable Optical Fiber Wireless media Introduction to Computer Networks

N ETWORKING D EVICES HUB, Switches, Routers, Wireless Access Points, Modems etc. Introduction to Compute Networks

C OMPUTERS : C LIENTS AND S ERVERS In a client/server network arrangement, network services are located in a dedicated computer whose only function is to respond to the requests of clients. The server contains the file, print services, application, security, and other services in a central computer that is continuously available to respond to client requests. Introduction to Computer Networks

A PPLICATIONS Searchable Data (Web Sites) E-Commerce News Groups Internet Telephony (VoIP) Video Conferencing Chat Groups Instant Messengers Internet Radio

A DDRESSING AND R OUTING Address: byte-string that identifies a node usually unique Routing: forwarding decisions process of determining how to forward messages to the destination node based on its address Types of addresses unicast: node-specific broadcast: all nodes on the network multicast: some subset of nodes on the network

W RAP - UP A network can be constructed from nesting of networks An address is required for each node that is reachable on the network Address is used to route messages toward appropriate destination

LAYERED TASKS LAYERED TASKS We use the concept of layers in our daily life. As an example, let us consider two friends who communicate through postal mail. The process of sending a letter to a friend would be complex if there were no services available from the post office.

L AYERED T ASKS Sender, Receiver and Carrier

L AYERED T ASKS Hierarchy  Higher Layer  Middle Layer  Lower Layer Services  The Each layer uses the services of the layer immediately below it.

O RGANIZATION OF AIR TRAVEL ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing Although this course is about network programming (and not about networking in general), an understanding of a complete network model is essential.

O RGANIZATION OF AIR TRAVEL : A DIFFERENT VIEW Layers: each layer implements a service  via its own internal-layer actions  relying on services provided by layer below ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing

D ISTRIBUTED IMPLEMENTATION OF LAYER FUNCTIONALITY ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing Departing airport arriving airport intermediate air traffic sites airplane routing

THE 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.

L AYERED A RCHITECTURE The OSI model is composed of seven layers ; Physical (layer1), Data link (layer2), Network (layer3) Transport (layer4), Session (layer5), Presentation (layer6), Application (layer7) Layer  Designer identified which networking functions had related uses and collected those functions into discrete groups that became the layers.  The OSI model allows complete interoperability between layers.  The Each layer uses the services of the layer immediately below it.

Figure 2.2 Seven layers of the OSI model Layered Architecture (cont’d) All People Seem ToTo Need Data Processing

P EER - TO - PEER P ROCESSES Layer x on one machine communicates with layer x on another machine - called Peer-to-Peer Processes. Interfaces between Layers Each interface defines what information and services a layer must provide for the layer above it. Well defined interfaces and layer functions provide modularity to a network Organizations of the layers  Network support layers : Layers 1, 2, 3  User support layer : Layer 5, 6, 7 It allows interoperability among unrelated software systems  Transport layer (Layer 4) : links the two subgroups

OSI A RCHITECTURE

Figure 2.3 The interaction between layers in the OSI model Peer-to-peer Processes (cont’d)

Figure 2.4 An exchange using the OSI model  The data portion of a packet at level N-1 carries the whole packet from level N. – The concept is called encapsulation. Peer-to-peer Processes (cont’d)

LAYERS IN THE OSI MODEL In this section we briefly describe the functions of each layer in the OSI model. Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer Topics discussed in this section:

 OSI Model Physical Layer

P HYSICAL L AYER Physical layer coordinates the functions required transmit a bit stream over a physical medium. The physical layer is responsible for movements of individual bits from one hop (node) to the next.

P HYSICAL L AYER Physical layer is concerned with the following: (deal with the mechanical and electrical specification of the primary connections: cable, connector)  Physical characteristics of interfaces and medium  Representation of bits  Data rate : transmission rate  Synchronization of bits  Line configuration  Physical topology  Transmission mode

 OSI Model Data Link Layer

D ATA L INK L AYER The data link layer is responsible for moving frames from one hop (node) to the next.

D ATA L INK L AYER Major duties  Framing  Physical addressing  Flow control  Error control  Access control

D ATA L INK L AYER Hop-to-hop (node-to-node) delivery