computer networking

Category: Education

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A presentation on computer networking


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WHAT DOES NETWORKING MEAN A computer network - a collection of computers and other hardware interconnected by communication channels that allow sharing of resources. Networks may be classified according to a wide variety of characteristics, such as the medium used to transport the data, communications protocol used


Network Includes Computers Servers Routers Wireless devices Etc. Purpose is to transmit data

Packet Switched Network:

Packet Switched Network Usual telephone network is circuit switched For each call, a dedicated circuit is established Dedicated bandwidth Modern data networks are packet switched Data is chopped up into discrete packets Packets are transmitted independently No real circuit is established More efficient bandwidth usage But more complex than circuit switched

Network Protocols:

Network Protocols Study of networking focused on protocols Networking protocols precisely specify the communication rules Stateless protocols don’t remember Stateful protocols do remember Many security problems related to state

Protocol Stack:

Protocol Stack Application layer protocols HTTP, FTP, SMTP, etc. Transport layer protocols TCP, UDP Network layer protocols IP, routing protocols Link layer protocols Ethernet, PPP Physical layer application transport network link physical user space OS NIC card

Layering in Action:

Layering in Action At source, data goes down the protocol stack Each router processes packet up to network layer That’s where routing info lives Router then passes packet down the protocol stack Destination processes up to application layer That’s where the data lives application transport network link physical application transport network link physical network link physical data data host host router

Application Layer:

Application Layer Applications Web browsing, email, P2P, etc. Run on hosts Hosts want network to be transparent Application layer protocols HTTP, SMTP, IMAP, Gnutella, etc., etc. Protocol is one part of an application For example, HTTP only part of Web browsing

Peer-to-Peer (P2P) Model:

Peer-to-Peer (P2P) Model Hosts act as clients and servers For example, when sharing music You are client when requesting a file You are a server when someone downloads a file from you In P2P model, more difficult for client to find a server Many different P2P models exisits .

HTTP Example:

HTTP Example HTTP --- HyperText Transfer Protocol Client (We) request a web page Server responds to our request HTTP request HTTP response


SMTP SMTP - used to send email from sender to recipient’s mail server Then use POP3, IMAP or HTTP (Web mail) to get messages from server As with many application protocols, SMTP commands are human readable SMTP POP3 Sender Recipient SMTP

Transport Layer:

Transport Layer The network layer offers unreliable, “best effort” delivery of packets Any improved service must be provided by the hosts Transport layer has two protocols TCP  better service, more overhead UDP  minimal service, minimal overhead TCP and UDP run on hosts, not routers


TCP TCP assures that packets Arrive at destination Are processed in order Are not sent too fast for receiver (flow control) TCP also provides Network-wide congestion control TCP is “connection-oriented” TCP contacts server before sending data Orderly setup and take down of “connection” But no true connection, only a logical connection

TCP Three Way Handshake:

TCP Three Way Handshake SYN: synchronization requested SYN-ACK: acknowledge SYN request ACK: acknowledge msg 2 and send data Then TCP “connection” established Connection terminated by FIN or RST packet SYN request SYN-ACK ACK (and data)


UDP UDP is minimalist, “no frills” service No assurance that packets arrive No assurance packets are in order, etc., etc. Why does UDP exist? More efficient (smaller header) No flow control to slow down sender No congestion control to slow down sender Packets sent too fast, they will be dropped Either at intermediate router or at destination But in some apps this is OK (audio/video)

IP Addresses:

IP Addresses IP address is 32 bits Every host has an IP address Not enough IP addresses! Lots of tricks to extend address space IP addresses given in dotted decimal notation For example: Each number is between 0 and 255 Host’s IP address can change


Socket Each host has a 32 bit IP address But many processes on one host You can browse web, send email at same time How to distinguish processes on a host? Each process has a 16 bit port number Port numbers < 1024 are “well-known” ports (HTTP port 80, POP3 port 110, etc.) Port numbers above 1024 are dynamic (as needed) IP address and port number define a socket Socket uniquely identifies a process


CONCLUSION Computer networks -makes our life easier to communicate with each other Networks and Protocols have forever changed the way humans will work, play, and communicate. Digital networking will further empower us for the future. New protocols and standards will emerge, new applications will be conceived, and our lives will be further changed and enhanced.

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