TCP/IP Protocol

4. Application	DNS, TFTP, TLS/SSL, FTP, Gopher, HTTP, IMAP, IRC, NNTP, POP3, SIP, SMTP, SNMP, SSH, TELNET, ECHO, BitTorrent, RTP, PNRP, rlogin, ENRP, …
	Routing protocols like BGP, which for a variety of reasons run over TCP, may also be considered part of the application or network layer.
3. Transport	TCP, UDP, DCCP, SCTP, IL, RUDP, …
2. Internet	Routing protocols like OSPF, which run over IP, are also to be considered part of the network layer, as they provide path selection. ICMP and IGMP run over IP and are considered part of the network layer, as they provide control information.
	IP (IPv4, IPv6)
	ARP and RARP operate underneath IP but above the link layer so they belong somewhere in between.
1. Network access	Ethernet, Wi-Fi, token ring, PPP, SLIP, FDDI, ATM, Frame Relay, SMDS, …

OSI

OSI Model
	Data unit	Layer	Function
Host layers	Data	7. Application	Network process to application
		6. Presentation	Data representation and encryption
		5. Session	Interhost communication
	Segments	4. Transport	End-to-end connections and reliability (TCP)
Media layers	Packets	3. Network	Path determination and logical addressing (IP)
	Frames	2. Data link	Physical addressing (MAC & LLC)
	Bits	1. Physical	Media, signal and binary transmission

TCP/IP & Internet

1969 ARPA (Advanced Research Projects Agency) funded a research and development project to create ARPAnet network.
1975 Converted from an experimental network to an operational network.
1983 TCP/IP protocols were adopted as Military Standards (MIL STD)
Internet: MILNET plus ARPAnet

Convert string to html table

#!/bin/sh
sed -e '/^[A-Za-z0-9]*[^\:]$/{
d
}' < source_file > tmp_file
echo "<table>" > destination_file.html
sed -e '/:/{
s/^/<tr><td>/g
s/\:/<\/td><td>/g
s/$/<\/td><\/tr>/g
}' < tmp_file >> destination_file.html
echo "</table>" >> destination_file.html

Replace file contents by perl

#!/usr/bin/perl -w
# use strict;

sub replace_str($$$)
{
my $line = shift;
my $old_string = shift;
my $new_string = shift;

if($line =~ m/($old_string)/)
{
$line =~ s/$old_string/$new_string/;
}
return $line;
}

open (SOURCE_FILE, "source.txt");
open (DESTINATION_FILE, '>>destination.txt');

while ($line = <source_file>) {
$line = replace_str($line,"2","3");
print DESTINATION_FILE $line;
}

close(SOURCE_FILE);
close (DESTINATION_FILE);

SED notes

Replace in sed
sed -e '/pattern/{
s/old1/new1/g
s/old2/new2/g
}' < source_file > destination_file