Computer networks -- 2007-2008 -- info.uvt.ro/Course 1
Quick links:
- front;
- courses 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13;
- laboratories agenda, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, evaluation, tools, repository.
Course notes and contacts
edit- http://web.info.uvt.ro/~ccraciun
- http://beta.wikiversity.org/wiki/Computer_networks_--_2007-2008_--_info.uvt.ro
- conf. dr. Victoria Iordan -- iordan@info.uvt.ro
- Ciprian Crăciun -- ccraciun@info.uvt.ro
- please use your @info address to send emails;
Bibliography
editBooks
editIn English:
- Computer Networks -- Andrew Tanenbaum
- Complete Guide to Networking -- Peter Norton
- TCP/IP Ilustrated (Volume 1 and 2) -- Richard Stevens
In Romanian:
- Bazele reţelelor de calculatoare -- Manual pentru administrarea retelelor LAN si WAN -- Editura Teora, 1999
- Reţele locale de calculatoare -- Valentin Cristea, Editura Teora, Bucuresti, 1995
- Sisteme cu prelucrare distribuită si aplicaţiile lor -- Păunescu F., Golesteanu D.P., Editura tehnică, Bucuresti, 1993
- Reţele locale de calculatoare -- Bulăceanu C., Editura Tehnică, Bucureşti, 1995
- Reţele de calculatoare -- A. Stepan, Gh. Petrov, V. Iordan, Editura Mirton, 1998
On-line material
editPlease consult: Computer networks -- 2007-2008 -- info.uvt.ro#References.
Course structure
edit- general characteristics;
- topologies;
- protocols;
- architectural models: OSI, TCP/IP, etc. -- introduction + detailed;
- network devices / hardware;
- VPN;
- security;
What networking stands for
edit- a computing / processing and resource access model;
- a way to transport information;
- it involves:
- standardization;
- organizations backing-up the standards -- IETF, ITU, IEEE;
- important services (DNS, NTP);
Concepts
edit- network element:
- computing unit;
- networking device;
- network topology;
- transmission medium;
- medium access;
- frames, packets;
- bandwidth (GPS, MPS, PPS);
- errors:
- bit error rate (for telephony: 10^-4 is faulty, 10^-5 should be corrected; for data: between 10^-9, 10^-12);
- packet loss (TCP stops working correctly below 0.1%, that is 10^-3);
Network types
editCategorized by computational / resource usage
edit- centralized:
- all users work on the same machine;
- terminals based;
- thin clients;
- low cost;
- very secure;
- easy to administer and recover;
- less flexible;
- applications: accounting, financial transactions;
- descentralized / distributed:
- each user works on its own machine;
- local processing;
- off-line working;
- software incompatibilities;
- less secure;
- collaborative / distributed:
- the same application is run on multiple computers;
- GRID;
- client-server:
- there is a hierarchy;
- the resources are accessed directly only by a server;
- the clients access resources through a server;
- security is high;
- more easy to administer;
- ActiveDirectory;
- spooling;
- peer-to-peer:
- each computer is at the same time a client or a server;
- only applicable for very small networks;
- security is low;
- more flexible and cheap, but less performant;
Categorized by spatial spread
edit- LAN -- Local Area Network:
- small spread;
- high bandwidth;
- small error rate;
- cheap equipments;
- Ethernet;
- MAN -- Metropolitan Area Network:
- medium spread -- towns;
- usually a group of LANs;
- medium bandwidth;
- medium error rates;
- expensive equipments;
- WAN -- Wide Area Networks:
- large coverage;
- low speeds;
- high error rate;
- very expensive equipment;
- WLAN -- Wireless LAN;
- WiFi, WiMAX;
- fixed (wired) vs mobile (wireless) networks;
- VPN -- Virtual Private Network;
- Internet;
Network topology
edit- physical layout of the computers, links and network specific devices;
- it affects:
- spread;
- performance;
- equipment cost;
- administration and security;
- physical topology:
- the way the network elements are layed-out and connected;
- logical topology:
- the way in which they communicate;
- the physical and logical topologies might be differ for an implementation;
- we can see the network topology as a graph, thus any graph algorithm applies to it;
Bus
edit- all computers are connected through a single segment;
- each packet is seen by all computers, but only the target one uses it;
- the computers are passive -- they are not involved in the transmission process;
- the bandwidth is shared;
- the cable length is limited;
- it usually implies using a terminator to stop signals from reflecting at the end of the segment;
- low resiliency -- if a link is broken the entire network is broken;
- security concerns;
Star
edit- each computer is connected through a link to a device -- hub or switch;
- there is a single failure point -- the hub;
- the hub can be passive (it only serves as junction point) or active (it repeats and enhances the signal, or it sends the message to an specified target);
- the bandwidth is limited by the hub processing capacity and the link bandwidth;
- the total cable length is high;
- high resiliency -- if a link is broken only that computer will be disconnected;
- security concerns;
Ring
edit- all computers are connected through a single segment that is closed / circular;
- the data flows into a single direction;
- each computer acts as a repeater relaying the message to it's neighbors -- as a repeater;
- low resiliency -- the breaking of a link breaks the entire network;
Other
edit- mesh (partial or fully connected);
- hierarchical (tree);
Token ring
edit- token bus -- the adaptation for bus topology;
- when the network is idle a token passes through the network from computer to computer in a circular model;
- if a computer wants to send data it waits to the token, replaces it with a data frame, and sends it as in the case of the token;
- each computer passes the frame if it is not addressed to it;
- if the frame is addressed to a computer, it uses the data, and replaces it with a token, thus the cycle is closed;
Network advantages and disadvantages
editUsage and advantages
edit- Internet: it is part of our lives;
- communication (VoIP), coordination, collaboration;
- information dissemination -- education;
- resource sharing;
- remote control / remote access;
- high resiliency;
- anonymity -- if careful enough;
Disadvantages
edit- vulnerabilities;
- data loss;
- downtime causes huge loses;