CS1001CS1001

Lecture 7Lecture 7

OverviewOverview

Computer NetworksComputer Networks The InternetThe Internet Internet ServicesInternet Services Markup LanguagesMarkup Languages

GoalsGoals

Learn fundamentals of networkingLearn fundamentals of networking Understand Internet ServicesUnderstand Internet Services Examine network security issuesExamine network security issues What is a “Markup Language”?What is a “Markup Language”?

AssignmentsAssignments

Brookshear: Ch 3.5, 3.6, 3.7 Brookshear: Ch 3.5, 3.6, 3.7 (Read)(Read)

Know factual material (bolded Know factual material (bolded terms) in 3.5, 3.6, 3.7terms) in 3.5, 3.6, 3.7

Read linked documents on these Read linked documents on these slides (slides will be posted in slides (slides will be posted in courseworks)courseworks)

Figure 3.10: Network Figure 3.10: Network topologiestopologies

Figure 3.10: Network Figure 3.10: Network topologies (continued)topologies (continued)

Figure 3.12: Figure 3.12: A typical A typical approach to approach to connecting to connecting to the the InternetInternet

CentralizationCentralization

Does networking Does networking centralizecentralize or or distributedistribute information? information?– It facilitates It facilitates bothboth

Networking facilitates centralized Networking facilitates centralized storage and remote accessstorage and remote access

Networking Networking alsoalso facilitates the facilitates the interchange of data (distributed interchange of data (distributed data)data)

http://http://www.sei.cmu.edu/str/descriptions/clientserver_body.htmlwww.sei.cmu.edu/str/descriptions/clientserver_body.html

The InternetThe Internet

Initiated in 1973 by DARPA Initiated in 1973 by DARPA (ARPANet)(ARPANet)

Distributes different types of Distributes different types of information across many information across many computers (servers)computers (servers)

Centralizes information published Centralizes information published by one entity (like a company, by one entity (like a company, etc)etc)

Who “Runs” the Who “Runs” the Internet?Internet? Every computer connected to the Every computer connected to the

internet must have a numerical IP internet must have a numerical IP (Internet Protocol) Address(Internet Protocol) Address– These numbers are distributed by a U.S.-These numbers are distributed by a U.S.-

based non-profit company: ICANN.based non-profit company: ICANN. Friendly names map to these numerical Friendly names map to these numerical

addresses (for example: addresses (for example: www.columbia.eduwww.columbia.edu maps to maps to 128.59.59.214) This is DNS (Domain 128.59.59.214) This is DNS (Domain Name System)Name System)

Who “Runs” the Internet Who “Runs” the Internet (2)(2) Only numerical addresses and the Only numerical addresses and the

mappings from names to numbers are mappings from names to numbers are maintained by central bodiesmaintained by central bodies

Connectivity is established by a Connectivity is established by a number of independent bandwidth number of independent bandwidth providersproviders

RoutersRouters direct traffic over the web to direct traffic over the web to their desired destinationtheir desired destination

Correct routingCorrect routing is a is a distributeddistributed responsibilityresponsibility

Network ProtocolsNetwork Protocols

A Protocol is a means for two A Protocol is a means for two parties to exchange data. parties to exchange data. Contains ways of Contains ways of sending/receiving/acknowledging sending/receiving/acknowledging data, error recovery, ability to data, error recovery, ability to switch contextswitch context

Example: HTTP, SMTPExample: HTTP, SMTP

Figure 3.18: The Figure 3.18: The Internet software Internet software layerslayers

Figure 3.19: Figure 3.19: Following a Following a message message through the through the

InternetInternet

Figure Figure 3.19: 3.19: Following a Following a message message through the through the Internet Internet (continued)(continued)

ProtocolsProtocols

There are distinct protocols at There are distinct protocols at eacheach of of the Link, Network, Transport, the Link, Network, Transport, Application layersApplication layers

Protocols establish standards for Protocols establish standards for exchanging binary dataexchanging binary data

Protocols can be optimized for each Protocols can be optimized for each task (some protocols are good for task (some protocols are good for transferring large files… others are transferring large files… others are better for transferring streaming video)better for transferring streaming video)

Figure 3.20: Choosing Figure 3.20: Choosing between TCP and UDPbetween TCP and UDP

Figure 3.17: Package-Figure 3.17: Package-shipping exampleshipping example

Figure 3.13: A typical Figure 3.13: A typical URLURL

Figure 3.14: A simple Figure 3.14: A simple Web page expressed Web page expressed in in HTMLHTML

The InternetThe Internet

HTTP (Hypertext Transfer HTTP (Hypertext Transfer Protocol) is sent OVER TCP/IP Protocol) is sent OVER TCP/IP (Transmission Control (Transmission Control Protocol/Internet Protocol).Protocol/Internet Protocol).

HTTP is a means of efficiently HTTP is a means of efficiently requesting and sending HTML requesting and sending HTML pages/graphics.pages/graphics.

TCP/IP is generic and operates at TCP/IP is generic and operates at the lower “Transport” layerthe lower “Transport” layer

Core Internet ServicesCore Internet Services

DNS – Translates Names to DNS – Translates Names to numerical IP Addressesnumerical IP Addresses

IP Addresses consist of 4 “octets” IP Addresses consist of 4 “octets” of data (a number from 0 to 255)of data (a number from 0 to 255)

Issue – Address shortageIssue – Address shortage