Chapter 4 Networking and the Internet
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
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.
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
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.
Network topologies • Ring • Bus • Star • Irregular
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
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)
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
Figure 4.4 The client/server model compared to the peer-to-peer-model
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
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 ANSWER:
The Internet • The Internet: one internet spanning the world • Started by DARPA in 1973 • Today involves millions of machines
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
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
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: 184.108.40.206
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 .
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 “140.114” 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 “220.127.116.11”.
Internet applications • Electronic main (e-mail) • File Transfer Protocol (FTP) • Remote login: telnet, etc. • World Wide Web
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
If the network identifier of a domain in the Internet is 115.48, how many unique IP addresses are available for identifying machines within the domain? A. 4096 B. 16,384 C. 32,768 D. 65,536 . Which of the following is not an application of the Internet? A. FTP B. Email C. Telnet D. RING
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
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
Hypertext document format • Entire document is printable characters • Contains tags to control display • Display appearance • Links to other documents and content • Dynamic functions
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
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)
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
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
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.
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.
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.
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? A. Application B. Transport C. Network D. Link Which layer of the TCP/IP hierarchy decides the direction in which message segments are transferred across the Internet? A. Application B. Transport C. Network D. Link Which layer of the TCP/IP hierarchy presents incoming messages to the computer user? A. Application B. Transport C. Network D. Link
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.