CSIS 321

CSIS 321 Computer Networks: 

CSIS 321 Computer Networks Architecture & Protocols

What is Computer Networking? : 

What is Computer Networking? It is the practice of linking two or more computing devices together for the purpose of sharing data.

: 

So Computer Networks is defined to be an interconnected collection of autonomous computers.

Components in a (simple) network : 

Components in a (simple) network

Uses of Computer Networks : 

Uses of Computer Networks The main purpose of computer Networks is to enable people to exchange data and information

Networking Models : 

Networking Models

1*Client-Server Model : 

1*Client-Server Model client computers (computers forming part of the network ) contact a server , generally a very powerful computer in terms of input/output, which provides services to the client computers. The client sends a request to the server using its IP address and the port , which is reserved for a particular service running on the server. The server receives the request and responds using the client IP address and port

1*Client-Server Model : 

1*Client-Server Model Communication takes the form of: the client process sends a message over the network to the server process. The client process then waits for a reply message. When the server process gets the request, it performs the requested work or looks up the requested data and sends back a reply.

Example of a client-server Network: 

Example of a client-server Network four personal computers in a small company are connected to a network switch that is also connected to a network server, an ADSL modem, and a printer.  Physical resources and information sharing

client-server Network: 

client-server Network Advantages centralised resources improved security server level administration scalable network Disadvantages increased cost a weak link Overloaded server

2*Peer-to-Peer Model: 

2*Peer-to-Peer Model No dedicated server each computer in such a network is part server and part client each computer on the network is free to share its own resources

Example : 

Example Instant messaging or Online chat

2*Peer-to-Peer Network: 

2*Peer-to-Peer Network Advantages reduced cost simplicity Disadvantages lack of security system is not centralised no link in the network is reliable

Client-Server V/S Peer-to-Peer: 

Client-Server V/S Peer-to-Peer Peer-to-Peer only useful for a small number of computers only suitable for applications that do not require a high level of security (it is not advisable in a business network containing sensitive data) each host or instance of the program can simultaneously act as both a client and a server, and each has equivalent responsibilities and status. Is in wide usage today Difficult to manage (Maintenance) Client-Server It functions with multiple different clients of different capabilities All data is stored on the servers, which generally have far greater security controls than most clients client computers (computers forming part of the network ) contact a server, generally a very powerful computer. Is in wide usage today Easy to manage (Maintenance)

Network Applications: 

Network Applications E-mail Web Instant Messaging Remote Login P2P file sharing Multi-user network games resource sharing information sharing

Network Hardware: 

Network Hardware Transmission technology

1) Broadcast networks: 

1) Broadcast networks Broadcast networks are networks with single communication channel shared by all the machines. Short messages (packets) sent by any machine are received by all others. An address field within the packet specifies for whom it is intended .

Example: radio stations. : 

Example: radio stations .

Transmission Types: 

Transmission Types Broadcasting mode of operation in which a packet is sent to every machine using a special code in the address field. Multicasting is sending a packet to a subset of the machines.

2) Point-to-point networks: 

2) Point-to-point networks Point-to-point networks consist of many connections between individual pairs of machines. In these types of networks: A packet on its way from the source to the destination may go through intermediate machines. In general, multiple routes are possible - routing algorithms are necessary

General rule (with many exceptions) in Point-to-point network: : 

General rule (with many exceptions) in Point-to-point network : Smaller geographically localized networks tends to use broadcasting larger networks usually are point-to-point

Example: Video Call : 

Example: Video Call

Unicasting (a type of point-to point transmission.): 

Unicasting (a type of point-to point transmission.) Unicast involves communication between a single sender and a single receiver.

Multiaccess vs. point-to-point: 

Multiaccess vs. point-to-point Multiaccess (shared medium) - Many end-systems share the same physical communication resources ( wire, frequency...). - There must be some arbitration mechanism. Point-to-point: - Only 2 systems involved. - No doubt about where data came from.

Network Hardware: 

Network Hardware Scale

1*Local area network (LAN): 

1*Local area network (LAN) Local area networks (LANs) re privately-owned, within a single building or campus, of up to a few kilometers in size. LANs are: -restricted in size. -consisting a single cable to which all machines are attached. -traditional speed is 10 to 100Mbps. Newer LANs may operate at higher speed. Examples: - 2 or more computers connected. - Small office or an internet café.

LANs Topologies: 

LANs Topologies

2*Metropolitan area network: 

2*Metropolitan area network A metropolitan area network (MAN) is a network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network ( LAN ) but smaller than the area covered by a wide area network (WAN). It might cover a group of nearby corporate offices or a city and might be either private or public. A MAN can support both data and voice, and might even be related to the local cable television network. Example: A chain of community colleges linked by a MAN.

3*Wide area network(WAN): 

3*Wide area network(WAN) A wide area network (WAN): spans a large geographical area contains hosts (or end-systems) intended for running user programs the hosts are connected by a subnet that carries messages from host to host Example: Internet and VPN WAN links

4*Internetworks : 

4*Internetworks Internetwork or internet is a collection of interconnected networks. A common form of internet is a collection of LAN connected by WAN. Connecting incompatible networks together requires using machines called gateways to provide the necessary translation. Example: The worldwide internet.