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Agenda
• Last class: Network Hardware
• Today: Network Protocols
– How do computers talk to each other?
– Needs?
• Same hardware
• Same rules (protocols) for encoding data
• “Standards of Interoperability”
Protocol for Data Encoding
• Sending data: flashing light in cable
Light = 1
No light = 0
What
• Need same way to talk
does that
so all computers know
mean?
001001011110101010
101011100100100110
Protocol for Data Encoding
• Ex: You want to send 0010010111101…
from Shanghia to Beijing
– What info do you need to include?
0010
0101
1110
1010
1010
1001
1110
0010
0101
1110
1010
1010
1001
1110
Protocol for Data Encoding
• Ex: You want to send 0010010111101…
from Shanghai to Beijing
– What info do you need to include?
• Address (IP address)
• Where to start and end, other RULES to read it
0010
0101
1110
1010
0010
0101
1110
1010
TCP/IP
• TCP = transmission control protocol
• IP = Internet Protocol
Coded
with
TCP/IP
rules
TCP/IP are
communication rules
so computers can
understand each other
001001011110101010
101011100100100110
Using
TCP/IP, I
can read
it!
TCP / IP and How Internet works
• Ex: You want to send an email from
Shanghai to a friend in Beijing
1. The email is cut into small ~1kb packets (TCP)
2. Each packet has the (IP) address and goes
there using any route
3. The packets are put together again (TCP)
Analogy
• Cut e-mail up
• Code it (address,
order)
• Send it in many
ways
• Decode it
0011101
010110
101011
101110
1111100
010010
Packet 2
Packet 1
Packet 3
name is
Hi my
Mr Y
To Mr Z,
Hi my name is Mr Y
Packet 1
Packet 2
Packet 3
To Mr Z
Hi my
To Mr Z
name is
To Mr Z
Mr Y
101011
101110
0011101
010110
1111100
010010
Order
Hi my name is Mr Y
Assignment
•
•
•
•
•
•
We are going to copy this process!
I wrote an “email” to each student
Then I cut it up into packets
Then I coded it
Then I send it many ways (to YOU)
Your job: Find your message and decode
it
TCP: What do the numbers
mean???
001001011110101010
101011100100100110
Coded
with
TCP/IP
rules
Using
TCP/IP,
it makes
sense!
001001011110101010
101011100100100110
???
TCP/IP Rules (just for this)
• HEXADECIMAL, ASCII
• All packets follow this rule for order:
– IP address
– Total number of packets (1 bit)
– Packet number (1 bit)
– Start message character (1 bit)
– Message (2 bits each character)
– End of message character
Example: 1154AF22ECD987625417