Remote Login
· Remote
login is a process of logging on to remote site and using the services available
on the remote computer
· With
remote login a user can also transfer the result of processing from remote
computer to local computer
· Remote
login is implemented by using a protocol called TELNET.
TELNET:-
·
Telnet stands for Terminal Network
·
Telnet is a protocol that enables one
computer to connect to remote computer. It is a standard TCP/IP protocol for
virtual terminal service given by ISO.
·
The user`s Computer, which initiates the
connection , is referred to as the local computer.
·
The computer being connected to, which
accepts the connection, is referred to as the remote computer. The remote computer can be physically located
in the next room, the next town or in another country.
·
Once the connection is established
between the local and remote computer, the local computer emulates the remote
computer. The user`s local computer will display what is taking place on the
remote computer during telnet session.
·
Telnet operates on a client/server
principle. The local computer uses a telnet client program to establish the
connection and display data on the local computer`s monitor.
·
The remote computer uses telnet server
program to accept the connection and to send responses to requests for
information back to the local computer.
REMOTE LOGIN PROCEDURE:-
1.
When a user types on local computer ,
the local operating system accepts the character.
2.
The local operating system does not
interpret them rather sends these characters to TELNET client.
3.
Telnet client transforms thesre
characters to a universal character set called network virtual terminal (NVT)
characters and pass them to the local TCP/IP protocol stack.
4.
The commands or text, in NVT form ,
travel through internet and arrive at the TCP/IP stack at remote computer.
5.
Here characters are delivered to the
operating system and passed to the TELNET server.
6.
The TELNET server changes the characters
to the corresponding characters of understandable format by remote computer.
7.
The remote operating system receives the
character from a pseudoterminal driver , which is a piece of software
that pretends that the characters are coming from a terminal.
8.
The operating system then passes the
characters to the appropriate application program.
NVT Character set:-
·
With the network virtual terminal character
set, the client TELNET translates characters that come from the local terminal
into NVT form and delivers them to the network.
·
The server TELNET translates data and
commands from NVT form into the form acceptable by the remote computer.
·
NVT uses two sets of character set in
which the 7 lowest order bits are the same as ASCII and the highest order bit
is 0.
·
For control characters, NVT uses an
8-bit character set in which the highest order bit is set to 1.
Telnet commands:-
·
Telnet commands are identified by a
prefix character, IAC (interpret as command) having code 255.
·
IAC is followed by the command and
option codes.
|
IAC
|
Command code
|
Option code
|
telnet
command format
some of the important
TELNET commands are listed in the table below:
|
Character
|
Decimal
|
Binary
|
Meaning
|
|
WILL
|
251
|
11111011
|
1.
Offering to enable
2.
Accepting a request to enable.
|
|
WON`T
|
252
|
11111100
|
1.
Rejecting a request to enable.
2.
Offering to disable.
3.
Accepting a request to disables
|
|
DO
|
253
|
11111101
|
1.
Approving an offer to enable.
2.
Requesting to enable.
|
|
DON`T
|
254
|
11111110
|
1.
Disapproving an offer to enable.
2.
Approving an offer to disable.
3.
Requesting to disable.
|
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