Networking between husband and wife

Sreedevi joined our group today..

So my mail communications to her paid off !! I tried freshening her network knowledge through my mails..!

Hope my managers and sreedevi dont see this blog:

-----Original Message-----
From: Anoop G []
Sent: Wednesday, June 21, 2006 3:18 PM
To: 'Anoop G'; 'Sreedevi V'
Subject: RE: OSI layers - addressing

IP address can be used to identify the Network and Host. Port will be used for identifying the receiving process.

http://172.16.100.20:80

172.16.100.20 is the IP address
80 is the port for WebServer residing in 172.16.100.20


-----Original Message-----
From: Anoop G []
Sent: Wednesday, June 21, 2006 3:11 PM
To: 'Anoop G'; 'Sreedevi V'
Subject: RE: OSI layers - socket

A process sends messages into, and receives messages from, the network through its socket. A process is analogous to a house and its socket is analogous to the door.

Socket is the interface between the application layer and the transport layer within a host.

-----Original Message-----
From: Anoop G []
Sent: Wednesday, June 21, 2006 2:59 PM
To: 'Anoop G'; 'Sreedevi V'
Subject: RE: OSI layers - client/server

In the context of communication session between a pair of processes, the process that initiates the communication ( that is, initially contacts the other process at the beginning of the session) is labeled as a client. The process that waits to be contacted to begin the session is the Server.

-----Original Message-----
From: Anoop G []
Sent: Friday, June 16, 2006 12:18 PM
To: 'Anoop G'; 'Sreedevi V'
Subject: RE: OSI layers - Higher layers

Example of session layer may be FTP session… for FTP we have to enter username/password and it gets authenticated to the server and a session is formed.

Example of presentation layer is HTML. HTML defines how to present Web pages

Example of application layer protocols are FTP, HTTP etc.. examples of applications browser, FTP client

-----Original Message-----
From: Anoop G []
Sent: Friday, June 16, 2006 12:16 PM
To: 'Anoop G'; 'Sreedevi V'
Subject: RE: OSI layers - TCP/UDP

UDP is User datagram protocol. UDP uses Ports to communicate from application to application. UDP provides no reliability.

TCP – Transmission Control Protocol is a more reliable protocol. TCP needs connection establishment before starting to send packets.

TCP uses a three way handshake for connection establishment
1. application sends a SYN message to the server
2. in response, server replies with a SYN-ACK
3. Finally the client sends an ACK to the Server

After this data can be send. For each TCP data packet, and acknowledgement is given back. If acknowledgement is not received back, it indicates error and re-transmission will occur.

Examples where UDP protocol can be used – hearing music over network…
Examples where TCP protocol can be used – transferring files across network

-----Original Message-----
From: Anoop G []
Sent: Friday, June 16, 2006 12:10 PM
To: 'Anoop G'; 'Sreedevi V'
Subject: RE: OSI layers - How to identify application?

We discussed about IP address, MAC address…

But how to identify an application… ?

For that Port is used. It is just a number..

For standard applications it is defined… say for Telnet 23, HTTP – 80 etc


-----Original Message-----
From: Anoop G []
Sent: Friday, June 16, 2006 12:06 PM
To: 'Anoop G'; 'Sreedevi V'
Subject: RE: OSI layers - Hub/Bridge

So Router is a network layer device .. !

What is Hub and Bridge ?

Hub is just a repeater, in the sense that it just amplifies signals … it can be used to extend physical layer. So it is a physical layer device.

Bridge is a more sophiscated device than Hub


a---------b--------c--------------d
|
B
|
e-------f-----------g---------------h

see eight computers connected… 4 ( a,b,c,d) to one side of bridge, and the rest to other side of bridge.

Bridge brings some sort of segmentation……… While a talks with d, e can talk with g. It separates the collision domain.

But still all these will be in the same network.. If a broadcast is send , it will reach all the computers from a-h

Router is more sophiscated.. It separates network.. Broadcasts will not pass to the other side of the router.

-----Original Message-----
From: Anoop G []
Sent: Friday, June 16, 2006 11:35 AM
To: 'Anoop G'; 'Sreedevi V'
Subject: RE: OSI layers - Router

What happens if B is in separate network………..

Say A’s IP address is 172.16.100.20/255.255.0.0

And B’s IP address is 10.1.30.25/255.255.0.0.

So these are in different networks.. and there may be atleat one Router in between these two networks…..

Router is a device for connecting different networks…………

--------- So now coming to the point ----------------------------

A needs to send a packet to B

A sees address of B, and it understands that it is in different network… Now what to do ?

A can only send the packet to the gateway ( which will be the router’s IP address )

And Router will route the packet to the 10.1.x.x network where B resides.

A(172.16.100.20) ----------------------------( say 172.16.1.1)Router (say 10.1.1.1) --------------------------B ( 10.1.30.25)



-----Original Message-----
From: Anoop G []
Sent: Friday, June 16, 2006 11:26 AM
To: 'Anoop G'; 'Sreedevi V'
Subject: RE: OSI layers - ARP

Suppose there are two machines A and B

IP address of A is 172.16.100.20/255.255.0.0, and MAC address is A
IP address of B is 172.16.100.21/255.255.0.0, and MAC address is B

A want to communicate to B>

Seeing the IP address A will find that B is in the same network.

But A does not know the MAC address of B.

So A will send an ARP ( Address Resolution Protocol )

That is very simple --- A will ask – “Anybody has 172.16.100.21 IP address – it will broadcast that “

B knows B has – 172.16.100.21 – So B will send reply

Now A knows B’s MAC address…

A will send packet to B/

-----Original Message-----
From: Anoop G []
Sent: Friday, June 16, 2006 11:15 AM
To: 'Anoop G'; 'Sreedevi V'
Subject: RE: OSI layers

Data link uses MAC address – 48 bit long – say 00:00:00:45:56:65

The data link layer technologies can be different – say Token ring, Ethernet etc etc..

How to handle these ?

Network layer abstracts the data link layer technologies… Network layer uses different address – IP address

IP address has two parts – Network address and host address

If my IP address is 172.16.100.20, and my subnet address is 255.255.0.0. That means 172.16.x.x is the network address 172.16.100.20 is specific address of my machine.

-----Original Message-----
From: Anoop G []
Sent: Wednesday, May 31, 2006 1:38 PM
To: 'Sreedevi V'
Subject: OSI layers

What are the different OSI layers ?

Application layer
Presentation layer
Session layer
Transport layer
Network layer
Data link layer
Physical layer

What is physical layer ?

Physical layer defines the medium of communication – say cables, connectors etc

What is data link layer ?

Data link layer defines communication between two nodes.

Let us take example of Ethernet which is the most common. ( Ethernet defines datalink layer and physical layer). Ethernet uses MAC address for addressing. Each node or netword card has a MAC address which is 48 bit long.

When node A sends data to Node B, MAC address of Node A will be the source address in the packet and MAC address of Node B will be the destination address in the packet.

Ethernet is a shared medium. Anybody can talk at the same time. If multiple persons talk at the same time, what happens ? collisions might occur and the packets will be lost. So there has to be some protocol for avoiding collisions. Ethernet uses CSMA/CD – carrier sense multiple access/collision avoidance