Computer networking exam preparation- short notes

course code: 403
Course name: Computer Networking

On our next exam (1 December, 2010) we are going to attend the networking exam. We need to study many things, as well as short notes. Some short notes are already in book. But we might not be able to find them. In that case, simply giving the page number is sufficient.

The book we are following is "Data communications and networking" by Behrouza Forouzan.

Starting from Efat's question,

Internet: Page 16

internet: page 15

Intranet: A private network that follows the tcp/ip protocol, where data is securely transferred. Similar to internet, which is used among organizations, intranet is used within an organization.

SMTP: page 834 (section 26.2)

Difference Between URI and URL:

URI is Uniform Resource Identifier
URL is Uniform Resource Locator

URI identifies a resource using meta data of any kind. One thing about URI is that, a URI gives information about exactly one resource. Also more than one URI can describe the same resource.

URL locates the resource on the network, that is if we have URL and the protocols, we can retrieve the resource.

For example:
URL=http://www.example.org
URI=http://www.example.org/pub/WWW.png

So we get URI=URL:http//www.example.org/

good work ^_^

POP3, IAMP4, SSH and SFTP

[POP:
To send messages from server to client we need a message access protocol. One such protocol is the post office protocol or POP3 (version 3). The POP3 client software is installed in the recipient and POP3 server software is installed in the mail server. When a user wants to view her mailbox, she enters the mail address and password. The POP protocol allows one mail to be viewed at a time from the mailbox. POP# has 2 modes: keep mode and delete mode. Keep mode allows mail to be retained after it has been retrieved from the mailbox. Delete mode allows mail to be deleted after it has been retrieved from the mail box.

IMAP4:
Internet Mail Transfer Protocol, version 4 is similar to POP but it has some added features as stated below:
1. IMAP4 allows viewing the header of a mail before downloading.
2. Allows searching a string in a mail before downloading.
3. Allows partial downloading of mail (for slower connections).
4. Helps to create, delete or rename mailboxes for storing mails.
5. Helps to create hierarchy of mailboxes in a folder for e-mail storage.

SSH or SFTP:
Secure Shell (also called Secure File Transfer Protocol) is a established mechanism of TCP/IP to copy the contents of one file from one host to another across a secure channel between the networked devices. The main aim of using this secure channel is to ensure that the data being transferred cannot be intercepted by any device in the middle of transmission and hence unwanted data access, unwanted development or destruction of important data can be prevented. This secure channel is provided by making a virtual abstraction and dedicating a certain capacity of the entire link to the two process that transmit and receive the important files.

Thank you Asif->(Chatur Ramalingom)

thanx both ASIF and AMIT
but, যে বড় বড় জিনিষ দিয়েছে, তা পরতে গেলে তো বাকী সব কিছুই ভুলে যাবো

better I will rather depend on AMIT

Thanks goes to both Asif and Amit
Nice work!
Carry on dude

to this two

The main aim of using this secure channel is to ensure that the data being transferred cannot be intercepted by any device in the middle of transmission and hence unwanted data access, unwanted development or destruction of important data can be prevented.

I won't be so sure about that.

"I have a confuse" about URL and URI. In the class sir told that,
URL = Protocol + host
and URI = protocol + host + path that is for example
URL = [You must be registered and logged in to see this link.]
URI = [You must be registered and logged in to see this link.] full path)
But in the asif's post the thing is just reversed......now who is right??

HTTP
Hyper Text Transfer Protocol is a network protocol for a distributed, collaborative, hypermedia information system It forms the foundation of the data communication for World Wide Web.

All zero subnet:
The first subnet after subnetting contains all bits of the subnet group to be zero so it is called all zero subnetting.

All ones subnet:
The last subnet after subnetting contains all the bits of the subnet group to be 1 so it is called all ones subnetting.

Telnet:
The telnet is a networking protocol that allows bidirectional text-oriented data communication between two networked devices. The user datagram in band with the telnet forms a 8 bit byte-oriented communication protocol for the TCP/IP.

Router:
Electronic device that interconnects two networks and allows inter-exchange of data between two different networks and has packet forwarding capability. It analyzes the address of the packets to determine whether the source and destination are in the same network of different networks and users its packet forwarding capability to transmit data from source to the destination.

Static Router:
Static router is a data communication concept that describes a way to configure the path selection of a router in a network. It is characterized by the lack of communication between routers in terms of topology of the network. Here the routes are entered manually by the system administrator. Static routing can be used to configure the entire network but it is nor error free. If there is a fault between two nodes which are statically routed, then the requests that choose the affected path must wait until the fault is corrected or the system administrator updates the route. Most of the requests would be time out by the time the fault is corrected. However for stub networks and default routes, static router is very useful. In static router, we determine the routes through the network by fixed paths, so the routes are entered into the table statically.

Stub networks:
A network system that does not recognize other networks and relays all data packets to the default route.

Source: WIKIPEDIA

(these are all my opinion)

Actually, URLs are a subset of URI.
lets give a short example.
Say, under [You must be registered and logged in to see this link.] there is a folder called example.
inside example, there is an index.html file
when we put the address

[You must be registered and logged in to see this link.]

It is an URI, which automatically loads index.html, but we didn't specify it. In other words, we are just identifying the resource.
but if we used,

[You must be registered and logged in to see this link.]

It becomes URL, where we located the resource specifically.

The examples Asif gave are both actually URIs, it does not locate any resource explicitly.

All are requested to look here:
[You must be registered and logged in to see this link.]

Lot of thnx for Asif...................................

[You must be registered and logged in to see this image.]

The main differences between the TCP/IP model and OSI are as follows:

1. OSI is a reference model and TCP/IP is an implementation of OSI model.
2.TCP/IP Protocols are considered to be standards around which the internet
has developed. The OSI model however is a "generic, protocol-
independent standard."
3. TCP/IP combines the presentation and session layer issues into its
application layer.
4. TCP/IP combines the OSI data link and physical layers into the network
access layer.
5. TCP/IP appears to be a simpler model and this is mainly due to the fact that
it has fewer layers.

6. TCP/IP is considered to be a more credible model- This is mainly due to the
fact because TCP/IP protocols are the standards around which the internet
was developed therefore it mainly gains creditability due to this
reason. Where as in contrast networks are not usually built around the OSI
model as it is merely used as a guidance tool.
7. The OSI model consists of 7 architectural layers whereas the TCP/IP only
has 4 layers

8. In the TCP/IP model of the Internet, protocols are deliberately not as rigidly
designed into strict layers as the OSI model.[6] RFC 3439 contains a
section entitled "Layering considered harmful." However, TCP/IP does
recognize four broad layers of functionality which are derived from the
operating scope of their contained protocols, namely the scope of the
software application, the end-to-end transport connection, the
internetworking range, and lastly the scope of the direct links to other nodes
on the local network.

9. The presumably strict consumer/producer layering of OSI as it is usually
described does not present contradictions in TCP/IP, as it is permissible that
protocol usage does not follow the hierarchy implied in a layered model.
Such examples exist in some routing protocols (e.g., OSPF), or in the
description of tunneling protocols, which provide a Link Layer for an
application, although the tunnel host protocol may well be a Transport or
even an Application Layer protocol in its own right.

10. The TCP/IP design generally favors decisions based on simplicity,
efficiency and ease of implementation

Erm saiful, if you copy and paste something, please also mention the source. Otherwise, it somewhat looks like you are not giving proper credits to the source