What is the difference between taking a backup(or copying a file over network) using SCP and SSH.If u can copy a file over network using SSH what is the need for SCP.Can any one explain

One is a secure shell (SSH), the other a secure copy (SCP). To my knowledge you cannot copy (secure or not) with SSH.

See man ssh and man scp.

scp (on Linux, any way) is part of the OpenSSH suite of tools. Basically it's an encrypted/strongly authenticated version of rcp (one of those nasty "r protocols").

ssh is a secure remote shell mechanism, so it doesn't have any kind of way to copy files between hosts. The whole job of ssh is to make you session act like a local shell on the remote box (like telnet).

We should be clear about what we are discussing, though. SSH (big letters) is the Secure SHell protocol. SSH.com has a commercial suite of products based on it (and I believe they also copyrighted "SSH"), and many other companies (such as Van Dyke) also make SSH tools. ssh (little letters) is the client program that implements SSH on most UNIX systems. In *BSD and Linux it's OpenSSH. OpenSSH is not just ssh though, there are scp, sftp, ssh-keygen, ssh-agent, sshd, etc, etc all of which do different things, but they use the same encryption and key handling techniques.

You can with sftp.

Isn't it possible to ssh into a box, the run ftp from there back into your own?

You can setup a ssh tunnel between to machines and use that to run a (insecure) tcp connection.

I believe that's exactly what sftp does. It uses an ftp-like program through an encrypted SSH tunnel. That saves you the effort of having to manually setup an SSH tunnel and then turn on the ftp client/server.

I disgree with u ppl.U can copy using ssh.
U can copy using ssh.The command is
ssh -e none -T user@xxx.xxx.xxx.xxx cat /tmp/somefile_tobe_transferred > /tmp/test
I Tried it in my network.

Yep, I just transfered an .rtf file that way and it is readable.