Computer Networks Modulewise Short Notes Free PDF and Doc Download

Welcome. I have uploaded some short notes (lecture notes) and slides for CN (Computer networks). Computer Networks is a subject taught for Computer Science and Engineering Branches and Information technology Branches. The notes for Computer networks are available for download. There are different notes from different sources. We have also included slideshows (slides). The note full set is complete. You can compare and study. Computer networks slides are specially mentioned as slides. MGU (MG university) Computer networks syllabus is available here.

Module 1:

Network requirements, Network Architecture, Layering and Protocols, OSI Architecture, Internet Architecture, Performance - bandwidth and latency, Delay bandwdith product, high speed networks.

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Module 2:

Direct Link network, hardware Building Block, Framing - Byte Oriented protocol, Bit oriented protocol, Clock based framing, Reliable transmission- stop and wait, sliding windows, Ethernet (802.3)- physical properties, Access protocol, wireless-bluetooth, wifi, Wimax

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Download Module 2 Slides -Ethernet onwards

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Module 3:

Packet switching-switching and forwarding-Datagram,  virtual circuit switching, source routing bridges and LAN switches - Learning bridges, Spanning tree algorithms, Broadcast and multicast, Limitations of bridges, simple internetworking - service model, global address, datagram forwarding in IP, address translation, Routing - network as graph, distance vector, link state, matrix.

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Module 4

End to End protocol, simple de-multiplexer, reliable byte stream, TCP - Issues, segment format,connection establishment and termination, sliding window revisited, triggering transmission,, adaptive retransmission, RPC- fundamentals, TCP congestion control, - additive increase, slow start, fast retransmit and fast recovery, congestion avoidance mechanism, DEC bit, Randomearly detection bit, source based congestion avoidance.

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Module 5

Applications -WWW, Email, name service, network management, web services custom application protocol, generic application protocol, overlay networks - peer to peer networks.

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How Block Websites on a Windows Computer

We will see how to block websites on a computer. There is a fine trick to block websites on any computer. This is done by editing the hosts file. The 'hosts' file is used to map host names to given IP addresses. The 'hosts' file is a plain text file that can be edited using text editors. Each line is a redirection entry. Each line should be an IP address followed by a space followed by a host name. When any application software (including browsers) try to connect to a host name (or website) which has an entry in the 'hosts' file, instead of using the domain name service, the IP address is taken from the corresponding entry in 'hosts' file. Then the connection goes to that IP address.

So, if we want to block any website, we only need add an entry for that website in the hosts file with a different IP address. By 'different IP address', i mean any IP other than the original IP of the website. The IP 127.0.0.1 is IP of your own computer. It is called loop back address. You can use this IP to block any website. If you use this IP, the application will try to connect to your own computer on its attempt to access the blocked website and thereby will fail to load the website.

hosts File in Windows

In Windows 7, Windows 8 or 8.1 and Windows 10, the hosts file can be found in the folder:

C:\Windows\System32\drivers\etc\

Here, C: is Windows installation drive.

How to Edit 'hosts' File in Windows - Why to Edit It?

Windows host file screenshot

There is a file named 'hosts' located in the following path: C:\Windows\System32\drivers\etc. For me, C is the Windows installation drive. Replace it with your Windows installation drive. The file can be found in the same path in Windows 7, Windows 8 and Windows 10. This file is used to map host names to IP addresses.

Why use hosts file

As said earlier, the hosts file is used to map domain name (actually host names) to IP some address. The file contains many lines starting with # symbol. Those lines are comments. Within the comments you can see some examples showing how to use the hosts file. Each line (not comments) should contain an IP address followed by a space and a host name. The format is:

IP_address<space>Host_name

When you access the host with given host name using your browser or any other application, before looking for the host name in your Internet Domain Name Service (DNS), your computer looks in the hosts file first. If there is an entry for the hostname the IP address provided in its line is used to access the website.

In the example given by Microsoft, rhino.acme.com is redirected to 102.54.95.97. Similarly x.acme.com is redirected to some other IP.

Why 127.0.0.1 ?

127.0.0.1 is the loop back address. It is the IP of your own computer. It is corresponding IP for localhost. localhost is the host name used to represent the computer from which we are accessing network (means our own computer). It is same to use 127.0.0.1 or localhost. But you cannot redirect a host name to another host name in hosts file. You should use an IP. When you redirect some host name to 127.0.0.1, actually you are redirecting the access to your own computer, which means blocking access to that host name

Uses of hosts file

As we have seen, the uses of hosts file are:

• Redirecting one host (or website) to another using an IP
• Blocking websites completely (by redirecting to 127.0.0.1)

Some people use hosts file to prevent pirate software accessing the vendors website to avoid auto update. We won't recommend piracy. Find a free software alternative if you cannot afford buying it.