osi model international organization for standardization (1984): the model modulizes a sequence of...
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OSI Model
International Organization for Standardization (1984):
The model modulizes a sequence of tasks for inter-exchanged information between computers into 7 layers:
• Application layer (7)• Presentation layer (6)• Session layer (5)• Transport layer (4)• Network layer (3)• Data Link layer (2)• Physical layer (1)
• Each layer should be viewed as a job (task) description but not the actual rules or methods to do the job
Open Systems Interconnection reference model.
OSI Model Analogy
Secretary
Servant
Captain
Secretary
Servant
Captain
King ArthurKnight Lancelot
OSI, Peer-Layer Communication
John
IE 7. Application
Win
2K
6. Presentation
5. Session
Server
4. Transport
3. Network
2. Data Link
Tok
en
Rin
g 1. Physical
Mary
7. Application
Netscap
e
6. Presentation Un
ix
5. Session
4. Transport Server
3. Network
2. Data Link
Eth
ernet1. Physical
Head
er1
Data
Header
2
Data2
H3 Data 3
H4 Data 4
H5 Data 5
H6 Data 7
H7 Data 8
Packet Switching Data Link Layer
A
BA I LOVE YOU.. I LOVE YOU.. I LOVE YOU.. I LOVE YOU!
1 2 3 4 5 6 7 8 9 10 11 12 13
I_LO VE_Y OU.. _I_L OVE_ YOU. ._I_ LOVE _YOU .._I _LOV E_YO U!__
7,8,11,13,1,2,9,10,5,6,4,6,12,3
1, 13 5 10
2 3
8 6 6, 4 7
9
11 12
B
This can be a LAN or Internet.
In addition to the sequence number, a packet should contain information about the sender and receiver.
The packet that transmitted across the Internet is call IP Datagram.
Internet and Routers
Chicago
Denver
CNY
NYC
LA
SF
Seattle
Houston
Boston
UCLA
Colgate
SU
Yale
A routers is a special purposedComputer that receives and forwards datagrams from and to the Internet.
In fact, it is router that connects networks together.
Price? $10,000,000 to $69.
Address
Post Office as the Router
MailmanLocal
Post Office
Air Port
Regional Post Office
Air Port
RegionalPost Office
LocalPost Office
Mailman
Mailman
Internet and Routers
Chicago
Denver
CNY
NYC
LA
SF
Seattle
Houston
Boston
UCLA
Colgate
SU
Yale
Colgate
CS
CSLab
Lib
UCLA CS at Colgate
TCP/IP Transmission Control Protocol / Internet Protocol
IP Address: (4 bytes) 0 0 0
255
0
255 255255256 256 256
256 = 4,294,967,296
128.10.2.1128.230.208.46128.230.18.55149.43.80.141149.43.3.23
Chung-Chih Li
48 Payne Street
Hamilton, NY
USA
• TCP tells how to break the information into packets.• IP tells how to send packets across the Internet
DNS Domain Name System
128.10.2.1128.230.208.46128.230.18.55149.43.3.23149.43.1.7…………..( some IP may not have a domain name)
arthur.cs.purdue.eduapollo.syr.edurodan.syr.educs.colgate.edu colgate.edu…………..………….
Domain Name Server : • A computer that provides DNS services.• One can let his/her computer uses a specific DNS or let it
arbitrarily use an available one.
The table is huge, we don’t want to maintain this table in every computer.
IP address Domain Name
Routers and IP Address
Chicago
Denver
CNY
NYC
LA
SF
Seattle
Houston
Boston
UCLA
128.230
Yale
………..cs.colgate.edu = 149.43.3.23
………..
………..cs.colgate.edu = 149.43.3.23
………..
DNS
DNS149.43.1.7149.43.3.23149.43.2.1………….
………….131.179.128.25………….
cs.ucla.edu/~xxx http://cs.colgate.edu/~chungli
131.179.128.25/~xxx http://cs.colgate.edu/~chungli
1
2
3
We need a DNS to translate this domain name so the router knows how to forward the message.
Traveling trough the Internet
Chicago
Denver
CNY
NYC
LA
SF
Seattle
Houston
Boston
UCLA
128.230
Yale
………..cs.colgate.edu = 149.43.3.23
………..
………..cs.colgate.edu = 149.43.3.23
………..
DNS
DNS149.43.1.7149.43.3.23149.43.2.1………….
………….131.179.128.25………….
131.179.128.25/~xxx http://cs.colgate.edu/~chungli
131.179.128.25/~xxx http://149.43.3.23/~chungli
45 6
7
8
1
2
3
Traveling trough the Internet (2)
Chicago
Denver
CNY
NYC
LA
SF
Seattle
Houston
Boston
UCLA
128.230
Yale
149.43.1.7149.43.3.23149.43.2.1………….
………….131.179.128.25………….
131.179.128.25/~xxx (index.html)
45 6
7
8
1
2
3
9
10
11
12
13
14
Dynamic IP addresses
CNY
twcny.rr.com24.24.1.140
home.twcny.rr.com207.211.212.39.
………………………dennisliattwcny………………………………………………………………………….
dli : ([email protected])seanyboy : ([email protected])gbush : ([email protected])…………………………..…………………………..
66.24.3.190
66.24.2.170
66.24.3.180
192.168.0.188 192.168.0.190192.168.0.196