Networking And Internet

Networking and Internet Tian-Li Yu [email_address] Department of Electrical Engineering National Taiwan University

Network classifications Scope LAN: local area network MAN: metropolitan area network WAN: wide area network Ownership Closed Open Topology

Network topology Ring Bus Star hub

Protocols Token ring Popular in ring topology. Token and messages are passed in one direction. Only the machine that gets the token can transmit its own message. CSMA/CD Carrier sense, multiple access with collision detection. Popular in bus topology (Ethernet). Broadcasting. When collision, both machines wait for a brief random time before trying again.

Dilbert on token ring Dilbert, Scott Adams

Connecting compatible networks Repeater Simply passing through messages. Connecting two compatible networks. Bridge Only passing those messages addressed to the other side. Connecting two compatible networks more efficiently. Switch A bridge with multiple connections. Connecting several compatible networks more efficiently.

Repeater, bridge, and switch Textbook, Figure 4.4

Connecting incompatible networks Router Building a network of networks, known as an internet . Textbook, Figure 4.5

Interprocess communication Server-client One server, several clients. Clients initiate communications by sending requests. Server serves. P2P (peer-to-peer) Two processes communicating as equals. The most popular distribution mode nowadays.

Interprocess communication (contd.) Textbook, Figure 4.6

Distributed systems Infrastructure can be provided by standardized toolkits. Enterprise Java Beans by Sun Microsytems .NET framework by Microsoft

The I nternet The most notable example of an internet is the Internet. Original goal was to prevent disruptions caused by local disaster. Now it’s a commercial undertaking.

Internet architecture Domain a network or an internet controlled by one single authority. ICANN (Internet corporation for assigned names and numbers) Oversee the registration of domains. Registrar Gateway A router that connects a domain to the rest of the Internet (the Internet cloud).

Domains, gateway, and the Internet Textbook, Figure 4.7

Connecting to the Internet ISP (Internet service provider) Allow customers to connect their domain to the ISP’s equipment or join the domain already established by the ISP. Different means Telephone (dial-up) Cable DSL Wireless

IP addresses IP (Internet protocol) addresses 32 bit in IPv4 128 in IPv6 Network identifier (by ICANN) Host address (domain administrator) Dotted decimal 140.112.18.33

Host names Mnemonic address made up of two parts Domain name Assigned by a registrar edu.tw Top-level domain By usage: .edu = education By country: .tw = Taiwan Subdomains and individual host names Assigned by domain owner www.ee.ntu .edu.tw Name server & domain name server (DNS) www.ee.ntu.edu.tw  140.112.18.33

Internet applications VoIP (voice over Internet protocol) email (electronic mail) FTP (file transfer protocol) telnet & ssh (secure shell) p2p: bittorrent, edonkey, emule…

World wide web www, w3, web hypertext, hyperlink, hypermedia. Web page: hypertext document Website: a collection of closely related web pages.

Browsers Presenting the web pages downloaded from the Internet. HTTP (hypertext transfer protocol) URL (uniform resource locator) Textbook, Figure 4.8

Hypertext markup language Textbook, Figure 4.10

eXtensible markup language XML Standard style to represent data as text. Restricted mapping each opening to each ending. <x property=“yyy”> …… </x> XHTML HTML that follows XML format. <name code=“ISO-8859-1”> Tian-Li Yu </name> <name code=“Big5”> 于天立 </name> <education> <BS> NTUEE, 1997</BS> <MS> UIUCCS, 2003 </MS> <PhD> UIUCCS, 2006 </PhD> </education>

Client-side & server-side Client-side Java applets Java scripts Flash Server-side CGI Servlets (jsp, asp) PHP (Personal Home Page, PHP Hypertext Processor)

Internet protocol Layers Application: constructs message with address Transport: chops message into packets Network: handles routing through the Internet Link: handles actual transmission of packets Port (not the I/O port)

TCP/IP suite TCP and IP are two protocols, TCP/IP refers to a collection of protocols more than just TCP and IP. TCP (transmission control protocol) UDP (user datagram protocol) No notification before sending message, no retransmission service, no acknowledge of receiving message. TCP: more reliable, less efficient UDP: more efficient, less reliable

Security Attacks Malware (malicious software) Virus, worm, Trojan horse, spyware, phishing) Denial of service Spam Protections Firewall Spam filter Proxy Antivirus, antispyware

Encryption sftp (ftps as in the textbook) , https, ssh, ssl Public/private keys Public key  encryption Private key  decryption Textbook Figure 4.16

Public/private key issues Certificate authority Ensure the public key is given by the trusted one. Authentication Make sure the author of a message is, in fact, the party it claims to be. Use private key to encrypt; public key to decrypt.

Exercises Chapter 4: 1, 7, 8, 12, 20, 26, 27, 35, 37, 39, 40, 43, 46.

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