1. Computer (Transport) Layer
Manages communication between two computers
Platform independence: one computer does not know even what platform the other is (mainframe, PC, etc.)
TCP/IP’s most popular transport standard is TCP

2. Terminal-Host Platform
Processing done at a central host computer
Mainframe (very large)
Minicomputer (mid-size)
Programs
Execute on
the Host
Host

3. PC Network Client PC sits on desks of ordinary users
Receives services from servers
Stand-alone PC with hardware, software added
Client PC
Client PC

4. PC Network Servers Provide services to client PCs
Usually PCs but not always
Server
Service
Service
Service
Server
Server

5. PC Network Servers are Specialized
Optimized for their services for cost, performance, and reliability
File
Server
File Service
Database
Server
Internet Access
Gateway Server

6. File Server Program Access
Programs executed on the client PC
Program and data files downloaded over the network
Program Executed
On Client PC
Downloaded
Over Network
Client PC
Network
Server

7. Client Workstation Workstations are more powerful than PCs
Come in client and server versions
21” display
Powerful RISC
microprocessor
Large, fast RAM,
hard disk
Usually UNIX OS, can be
Windows NT
Client
Workstation

8. Networked PC The Dominant Computer Platform Today is the Networked PC
High penetration of PCs on desktops
Most are already networked
“Legacy” Systems Must be Maintained
Mainframe terminal-host systems
Minicomputer terminal-host systems
Many are being “downsized” to PC networking

9. Managed PCs Designed to be Managed Remotely Slashes maintenance costs
Slashes software upgrade costs
Users have less control over their machines
Company can search for illegal games
Management standards are still immature
Eventually, all networked PCs will be managed

10. NetPC Standard Pushed by Microsoft, Intel
Closed box with limited upgradability
Should ease maintenance by reducing incompatibilities and add-in problems
Will users be content?
Remote management built in

11. Network Computers (NCs)
Designed for Use on the Internet (Java)
Little or no local disk drive storage
Programs downloaded over Internet when needed (or from corporate servers using Internet standards)
User always gets the latest version of the software
Downloading can take time; small applications would load faster but might lack functionality
When the network is down, so are you
The
Internet

12. Low-Cost PCs for the Home
WebTV (Microsoft)
Uses TV for its display
User only needs $500 box
Problem: TV display resolution is far lower than that of a TV screen; webpages look bad
Problem: Need special Internet service provider who cannot work with your regular PC
Problem: No printing
Problem: Limited to WWW and
Sub $1,000 PCs

13. Networks Mix Traffic of Multiple Platforms
(LAN, WAN, internet)
PC network traffic
Terminal-host traffic

14. F2-7: Program Interactions on a Stand-Alone PC
Application Program
Request
Response
Operating System
Commands related to files
Files or error messages
Hardware

15. Client/Server Processing
Client Program
Server Program
Platform independent
TWO programs on
TWO machines
Client Machine
(PC)
Server Machine
(UNIX Minicomputer)

16. Client/Server Processing
Application Layer Protocols
Control the requests and responses
Application independence: any browser can work with any webserver program
Transport Layer Protocols
Allow two computers with different architectures to work together
Brings platform independence

17. Internet Access To connect to the Internet, you must have an ISP
Webserver
Internet
Service
Provider
(ISP)
The Internet
Backbone
Internet
Service
Provider
(ISP)
PC with
browser

18. Internet Service Provider (ISP)
Basic Service: Links You to the Internet
Provides a connection
Pays for your use. (The Internet is NOT Free.)
Most Provide Additional Services
World Wide Web Homepage Hosting
Premium Providers have Specialized Services (America Online, CompuServ, MSN)

19. Internet Access with PPP
ISP
Modem,
TCP/IP software
PPP software
PPP link over telephone line

20. Internet Access with PPP: routers
The Internet:
1. a network of
routers connected
by transmission lines
ISP
Router
2. Subnets connected
by routers
ISP

21. Layered Interactions in Internet Access
User PC
Router
Webserver
Browser
Webserver
Software
TCP
Software
TCP
Software
Subnet
Layer
(PPP) IP
Software IP
Software IP
Software
CSLIP/PPP
Software
PPP
Software
Subnet
Point-to-Point Connection

22. Point-to-Point Connection
Physical Layer
Serial Port
Modem
Telephone Transmission
Data Link Layer
Packaging of data for delivery over line
Error detection and correction
CSLIP or PPP standard

23. Layered Interactions in Internet Access
User PC
Routers
Webserver
Browser
Webserver
Software
Internet Layer Governs
Routing Across Multiple Routers
On the Internet
TCP
Software
TCP
Software IP IP IP
Software IP
Software IP
Software
PPP
Software
Subnet
Software
Subnet

24. Routing Across the Internet
Message (packet) must travel over a network of routers
The user PC tells the first router the destination address of the webserver (e.g., voyager.cba.hawaii.edu)
Working together, routers route the packet to its destination host

25. Layered Interactions in Internet Access
User PC
Routers
Webserver
Browser
Webserver
Software
Transport Layer
(TCP)
TCP
Software
TCP
Software IP
Software IP
Software IP
Software
PPP
Software
Subnet
Software
Subnet

26. Transport Layer Connects the Two Computers
Establishes a temporary connection
Breaks connection when transmission ends
Asks for the retransmission of damaged packets
Asks for the retransmission of lost packets
Flow control: tell the other computer to pause
Platform independence: connects computers from different vendors

27. Layered Interactions in Internet Access
User PC
Routers
Webserver
Browser
Webserver
Software
Application Layer
(HTTP, HTML)
TCP
Software
TCP
Software IP
Software IP
Software IP
Software
PPP
Software
Subnet
Subnet

28. Protocol Data Units (PDUs)
At each layer, messages are strings of 1s and 0s
These messages are organized
Called protocol data units (PDUs)
Each layer (except Physical) has a PDU
E.g., Application PDU or APDU
E.g., Computer (Transport) PDU or CPDU
PDU

29. Organization of PDU Header (delivery information)
Trailer (sometimes present for error handling)
Data Field
Often PDU of next higher layer
PDU at Layer N+1
PDU at Layer N
Trailer
Data Field
Header

30. PDU Transmissions from the PC
User PC
Application Layer
Browser
Application PDU
APDU
Computer (Transport) Layer
TCP
Software
APDU CH
(CPDU) TCP PDU
Internet Layer IP
Software
CPDU IH
Internet PDU (IPDU)
Subnet Layer
CSLIP/PPP
Or Other
Subnet
Software
SnT
IPDU
SnH
Subnet PDU (SnPDU)
CSLIP or PPP

31. At Each Router
2. Subnet process removes IP PDU from SnPDU, delivers it to the IP process.
3. IP process
considers
best route
Router
4. IP process delivers the IP PDU to the subnet process IP
Software
IP PDU
IP PDU
Subnet
Process
SnPDU for
Subnet A
SnPDU on
Subnet B
SnA
SnB
1. Router subnet process accepts the SnPDU
Subnet A
Subnet B

32. At the Webserver Webserver 4. TCP Software delivers APDU
to Webserver Program
Webserver
Software
APDU
3. IP Software delivers CPDU
to Transport Process
TCP
Software
CPDU
2. delivers IPDU
to IP Software Process IP
Software
IPDU
Subnet
Software
1. accepts SnPDU
SnPDU
Subnet

33. Intranets Use of Internet Technology within Firms Standards are mature
Standards for many applications
Security is good for internal use
Platform independent: No need to create separate applications for PCs, Macs, Unix
Browser runs software: no need to install software on PCs
Major concern of corporations today

34. Intranets Must keep out hackers
Yet users need access to Internet services outside the Internet
Solution: create a firewall to limit access from the outside
Firewall OK
Intranet No
Hacker

35. Extranets Give Buyers or Suppliers Access
Limited to certain resources, such as inventory and pricing databases
Uses the Internet for transmission
Extranet
Resource
Internal OK
Customer No
Any Other Resource

36. Extranets Tunneling Extranet transmission uses the unsecure Internet
Add secure transmission through the Internet by means of encryption, other measures
Creates a secure “tunnel” through the Internet
Tunnel