1. Networking and the Internet
Chapter 4
Networking and the Internet

2. Chapter 4: Networking and the Internet
4.1 Network Fundamentals
4.2 The Internet
4.3 The World Wide Web
4.4 Network Protocols
4.5 Security

3. Network classifications
Networks--Isolated computers can be connected to work together via networking.
Classifications
Local area network (LAN) --on a single building or a group of buildings. Such as university campus, a manufacture plant, or the like.
Wide area network (WAN)—one LANs can be connected to other LANs over any distance through telephone lines or radio waves.
Such as city.

4. Network classifications
Closed, or proprietary--held by an individual corporation like Novell networks.
Open--networks have the ownership in the public domain like the Internet

5. Network classifications
Characteristics of Network
Topology—The geometric arrangement.
Protocols:The rules and encoding specifications for sending data.
Media---Devices are connected by twisted-pair wire, coaxial cables, or fiber optics, or radio waves.

6. Network topologies
Ring
Bus
Star
Irregular

7. Figure 4.1 Network topologies

8. Figure 4.1 Network topologies (cont’d)

9. Connecting networks
Networked computers can be connected in a hierarchical fashion as an internet.
DARPA (Defense Advanced Research Projects Agency) initiated the Internet in 1973.
Interconnection of networks are achieved through routers or proprietary gateways(earlier terms for routers).
Bridge: connects two compatible networks
Router: connects two incompatible networks
Resulting “network” is called an internet

10. Figure 4.2 The distinction between a bridge and a router

11. Inter-process communication
Clients: a client makes requests to servers.􀂄
Servers: a server performs the service and sends replies back to the client (s).
Ex:A machine with high-capacity disk drive contains all the records of other machine
(servers, the others—clients)

12. Figure 4.3 The client/ server model

13. Inter-process communication
Inside the same machine, or among the machines over the networks.
Client-server
One server, many clients
Server must execute continuously
Client initiates communication
Peer-to-peer
Two processes communicating as equals
Peer processes can be short-lived

14. Figure 4.4 The client/server model compared to the peer-to-peer-model

15. Distributed systems Systems with parts that run on different computers
Multiple independent computers communicating over a network to accomplish a common task
Infrastructure usually provided by standardized toolkits
Example: Enterprise Java Beans from Sun Microsystems
Example: .NET framework from Microsoft

16. 1. Which of the following is not a way of classifying networks?
A. WAN versus LAN B. Closed versus open
C. Router versus bridge D. Star versus bus
ANSWER:
2 Which of the following is not a means of performing interprocess communication over a network?
A. Client/server B. ICANN C. Peer-to-peer

17. The Internet The Internet: one internet spanning the world
Started by DARPA in 1973
Today involves millions of machines

18. Internet Architecture
Domain = network or internet controlled by one organization
Gateway = router connecting a domain to the cloud
cloud = the rest of the internet
Domains must be registered by their owners
Internet Corporation for Assigned Names & Numbers (ICANN) serves as registrar

19. Figure 4.5 A typical approach to connecting to the Internet

20. Strategies for connecting to the Internet
Large organization: buy a direct connection
Small organization or individual: link domain to the domain of an ISP
ISP = Internet Service Provider
Individual: temporarily link computer into ISP’s domain

21. Internet Addressing: IP Addresses
IP address = 32 bit identifier for a machine
Network identifier = part assigned by ICANN
Host address = part assigned by domain owner
Dotted decimal notation = standard for displaying IP addresses
Example:

22. Internet addressing: host names
Host name = mnemonic name
Example: mymachine.aw.com
Domain name = part assigned by a registrar
Example: aw.com
Top level domain = classification of domain owner
By usage – Example: .com = commercial
By country – Example: .au = Australia
Subdomains and individual machine names
Assigned by domain owner
Domain owner must run a name server .

23. Connecting networks
InterNIC(Internet Network Information Center) regulates the 32-bit address of domains and thus each machine= network identifier (x-bit) + host address (32–x -bit).􀂄
The network identifier of the mnemonic domain name“nthu.edu.tw” is “ ” determined globally,
while “nyx.cc”is “63.1”assigned locally by the Computer Center of NTHU.⇒
The host machine “nyx.cc.nthu.edu.tw”has an address “ ”.

24. Internet applications
Electronic main ( )
File Transfer Protocol (FTP)
Remote login: telnet, etc.
World Wide Web

25. Electronic mail Mail server: set up by domain owner
Mail sent from domain members goes through mail server
Mail sent to domain members is collected by mail server

26. If the network identifier of a domain in the Internet is 115
If the network identifier of a domain in the Internet is , how many unique IP addresses are available for identifying machines within the domain?
A B. 16,384 C. 32,768 D. 65,536
. Which of the following is not an application of the Internet?
A. FTP B. C. Telnet D. RING

27. World Wide Web
Atop the Internet, the WWW allows the propagation of multimedia documents.
--The hypermedia documents consists of hypertexts: texts, audiovisual contents, links.
Server disseminates hypertext (or hypermedia) documents
Web site = all hypertext documents controlled by one organization or individual
Usually all at same internet address
HTML = language of hypertext documents
Other content can also be disseminated
Example: images

28. World Wide Web implementation
Web server: provides access to documents on its machine as requested
Browser: allows user to access web pages
Hypertext Transfer Protocol (HTTP): communication protocol used by browsers and web servers
Uniform Resource Locator (URL): unique address of a document on the web

29. Figure 4.6 A typical URL

30. Hypertext document format
Entire document is printable characters
Contains tags to control display
Display appearance
Links to other documents and content
Dynamic functions

31. Figure 4.7 A simple Web page

32. Figure 4.7 A simple Web page (cont’d)

33. Figure 4.8 An enhanced simple Web page

34. Figure 4.8 An enhanced simple Web page (cont’d)

35. Extensible Markup Language (XML)
XML: a language for constructing markup languages similar to HTML
A descendant of SGML(Standard Generalized Markup Language)
For math, multimedia, music and Web pages

36. Figure 4.9 The first two bars of Beethoven’s Fifth Symphony

37. Dynamic web pages(i.e. search)
Client-side(specifies topic of interest)
Examples: java applets, java script, Macromedia Flash
Server-side(identifying documents)
Common Gateway Interface (CGI)
Servlets—allow clients to execute programs units in servers
PHP(personal home page)

38. Network protocols: transmission control
Token ring: one-way communication around ring network
Ethernet:
Uses carrier sense, multiple access with collision detection (CSMA/CD)
Popular for bus networks
Like a conversation in small group

39. Figure 4.10 Communication over a ring network

40. Figure 4.11 Communication over a bus network

41. Figure 4.12 Package-shipping example

42. Figure 4.13 The Internet software layers

43. Figure 4.14 Following a message through the Internet

44. Internet software layers
Application layer:
Example: browser
Transport layer: TCP/IP, UDP
Network layer: handles routing through the internet
Link layer: handles actual transmission of packets
Token ring or Ethernet

45. Delivery of messages
The transport layer takes the message from the application layer, packages them with additional tags (50+bytes including sequence #, …) into packets of a size compatible with the beneath network layer, and hands over to the network layer.􀂄
The network layer will properly forward these packets to the very network specified by the application layer.􀂄
The same prefix of both addresses ⇔on the same network.􀂄
Different ⇒the network layer appending the address of a router in the current network sends the packets to that router. (maybe, intermediate routers) 􀂄
The link layer does the actual transmission between machines and routers by local addressing system with additional wrapping. ⇒striped off at the message destination.

46. TCP/IP Protocol Suite
It is the network layer to determine the destination of the next hop (network).􀂄
The routing table in the network layer contains the final destination addresses and intermediate addresses. [NAT: IP address vs. Link address]􀂄
The information in this table routinely exchanges and propagate through the Internet.􀂄
Packets of the same message may travel along different paths.􀂄
Once all packets of the message are received (using sequence #), the target transport layer hands it over to its application layer. [complete delivery]􀂄
The response time of the Internet is rather instant in milliseconds.􀂄

47. TCP/IP Protocol Suite
�The TCP/IP protocol suite defines a collection of protocols beside TCP and IP.􀂄
IP(Internet Protocol) defines the network layer service.􀂄
--Hop count, TTL (time to live, 64): decrement per hop forwarding, avoiding circling.􀂄
TCP(Transmission Control Protocol) defines a reliable transport service.􀂄
--Two ends first build an acknowledged connection and confirms each subsequent packet delivery in sequence.􀂄
UDP(User Datagram Protocol) defines a more efficient but less reliable transport service.􀂄
One end sends the data merely to the destination address regardless of its reception.􀂄
ISO (International Organization for Standardization) develops the OSI (Open System Interconnection) reference model using 7 layers –Application, Presentation, Session, Transport, Network, Data Link, & Physical.

48. Figure 4.15 Choosing between TCP and UDP

49. A. Application B. Transport C. Network D. Link
Which layer of the TCP/IP hierarchy actually transmits a message?
A. Application B. Transport C. Network D. Link
Which layer of the TCP/IP hierarchy chops messages into units whose size is compatible with the Internet?
Which layer of the TCP/IP hierarchy decides the direction in which message segments are transferred across the Internet?
Which layer of the TCP/IP hierarchy presents incoming messages to the computer user?

50. Network security
Connecting to the networks, a machine becomes accessible to the general public.􀂄
Unauthorized access: attack on confidentiality.􀂄
Protection on personal information
Vandalism: malicious acts from hackers, computer viruses, or network worms.
Computer Virus—a program segment that attaches itself to other programs in computer systems.
Worms—an autonomous program that transfers itself through a network, taking up residence in machines and forwarding copies of itself through network. 􀂄

51. Network security Privacy of communication Public-key encryption
Public key and private key: (asymmetric)􀂄
A and B each have pairs of public key and private key: PA, pA, and PB, pB.􀂄
--Private keys are held by individuals, while public keys are known to the party.􀂄
Authenticated receiver: (only B has pB to decrypt the received data)􀂄�
Authenticated sender: (only A has pA to send that encrypted data)􀂄

52. Integrity of machine exposed to internet
Network security
Integrity of machine exposed to internet
Attacks: viruses and worms
Defense: firewall
Firewall software that filters the traffic entering or passing through a machine(network layer to reject traffics from an entire domain or a specific IP)

53. A. ICANN B. Firewall C. Encryption D. Public key
The primary purpose of which of the following is not the enhancement of security?
A. ICANN B. Firewall C. Encryption D. Public key   
Which of the following is not a means of referencing entities on the Internet?
A. URL B. IP address C. Anonymous FTP D. Host address