CS105 Introduction to Computer Concepts Computer networks 101 Instructor: Cuong (Charlie) Pham

Computer Network A collection of computing devices connected in order to communicate and share resources Connections between computing devices can be physical using wires or cables or wireless using radio waves or infrared signals Q: What are the devices in a computer network? Repeaters, Hubs, Switches, and Routers CS105 Section 2 - Lecture 10

Network Devices To connect multiple segments of networks into a larger one Hub: A multiport repeater to enhance signal within the same network Switch: Like hub but with intelligent  Better performance Router: Forward packets from one network to another Wireless N and G The best way to answer your question is to state the purpose of a router. A router is designed to connect two different networks together. In your case the LAN, or your local network of computers and the WAN, or the Internet. http://en.wikipedia.org/wiki/Router The wireless speed of your router is the LAN speed. The LAN consists of all the computers and devices connected to your router in your house. Connections will always default to the slowest device. For example if you have a wireless N router (300 Mbps) connected to a wireless G laptop (54 Mbps), then the laptop can communicate with the router at 54 Mbps. If you wanted to copy a file from your laptop to a desktop connected to your router via a Ethernet cable (100 Mbps) connection, then you could do that at the laptop's wireless G speed of 54 Mbps. Now for the DSL speed. The Internet is the other network connected to your router via your DSL modem. The Internet is a Wide Area Network or WAN. Your DSL modem can communicate with your Internet provider at a maximum of around 6 Mbps. This connection bandwidth is shared by your entire LAN via your router. If one user is utilizing 4 Mbps of the bandwidth that only leaves 2 Mbps for the rest of the users on the LAN. Being that your (WAN) Internet connection is less than 6 Mbps and a wireless G router is many times faster at 54 Mbps, there is no advantage in Internet speed by choosing a wireless N router. The only advantage would be in transferring files around between computers on your local LAN. Wireless N also has a larger range, meaning you can get a wireless signal at a larger distance from the router. However, remember to get either the speed or range improvements of wireless N, both devices have to be N. A wireless N router hooked to a wireless G adapter on a laptop computer will have the range and speed of wireless G. I'm not saying not to buy a wireless N router, I use one myself. Just don't expect any improvement in Internet speed. People that recommend N to improve Internet speed don't understand the concept, or they're lucky enough to live in a area and have the money to afford using ungodly fast and expensive Internet connections such as Comcast Cable's Extreme 105 Mbps. Direct CAT5 Ethernet connections are 100 Mbps, there is also a newer Gigabit Ethernet (1000 Mbps) which uses special CAT6 cabling and Gigabit devices and network adapters. As with the wireless devices it will always default to the slowest standard. CS105 Section 2 - Lecture 10

Cabling Coaxial Cable Thinnet looks like regular TV cable. It is about 1/4 inch in diameter and is very flexible and easy to work with. Thicknet is about 1/2 inch in diameter and not very flexible. Thicknet is older and not very common anymore except as a backbone within and between buildings. Coax transmits at 10 Mbps..  Twisted Pair. Twisted pair looks like telephone wire and consists of insulated strands of copper wire twisted together. There are two versions of twisted pair cable: Shielded Twisted Pair (STP). STP is commonly used in Token Ring networks Unshielded Twisted Pair (UTP). UTP is used in Ethernet networks. Transmission rates vary between 10-100-1000-10000 Mbps. Fiber-Optic Cable. Fiber-optic cable consists of a thin cylinder of glass surrounded by glass cladding, encased in protective outer sheath.   Fiber-optic cable is very fast (over 1Gbps).  It can transmit over long distances (2 km +) but is expensive. CS105 Section 2 - Lecture 10

Cabling Top: Unshielded Twisted Pair and Shielded Twisted Pair Cable Bottom: Coaxial and Optical Fiber Cable CS105 Section 2 - Lecture 10

Network Types LAN (Local Area Network) WAN (Wide …) MAN (Metropolitan …) PAN (…) Internet CS105 Section 2 - Lecture 10

LAN A network that connects a relatively small number of machines in a relatively close geographical area E.g., office buildings CS105 Section 2 - Lecture 10

LAN Topologies Ring topology connects all nodes in a closed loop on which messages travel in one direction Star topology centers around one node to which all others are connected and through which all messages are sent Bus topology nodes are connected to a single communication line that carries messages in both directions CS105 Section 2 - Lecture 10

Ethernet The industry standard bus (star) technology for LAN 10BaseT 10Mbps (Mega bits per second) 100BaseT 100Mbps 1000BaseT 1000Mbps or 1Gbps CS105 Section 2 - Lecture 10

WLAN (Wireless LAN) Wi-Fi (Wireless Fidelity) Access Point (AP) A wireless technology that connects computers without cables Access Point (AP) A device (base station) that connects wireless devices together Usually connected to a wired- network SSID (Service Set ID) A “name” for the AP, eg. mobilenet Hotspot The area covered by wireless access points CS105 Section 2 - Lecture 10

WLAN (Wireless LAN) Standard Security 802.11b - 11Mbps 802.11g - 54Mbps 802.11a - 54Mbps Security WEP (Wired Equivalent Privacy) WPA (Wi-Fi Protected Access) To prevent wardriving 2.4G 5G CS105 Section 2 - Lecture 10

WAN/MAN Wide-area network (WAN) A network that connects local-area networks over a potentially large geographic distance Metropolitan-area network (MAN) The communication infrastructures that have been developed in and around large cities Internet A wide area network that spans the planet CS105 Section 2 - Lecture 10

Gateway One particular set up to handle all communication going between that LAN and other networks Figure 15.1 Local-area networks connected across a distance to create a wide-area network CS105 Section 2 - Lecture 10

Internet Connections Internet backbone A set of high-speed networks that carry Internet traffic, provided by companies such as AT&T, Verizon, GTE, British Telecom, and IBM Internet service provider (ISP) A company that provides other companies or individuals with access to the Internet CS105 Section 2 - Lecture 10

Dial-up Services Modem Modulator/demodulator A device that converts analog signal to digital (modulation) and vice versa (demodulation) Speed 1200/2400/9600 bps 14.4/28.8/33.6 Kbps 56 Kbps CS105 Section 2 - Lecture 10

Dial-up Services ISDN Integrated Services Digital Network 2 data channel (56K each) 1 voice channel CS105 Section 2 - Lecture 10

Broadband Services xDSL (Digital Subscriber Line) Speed A technology that provides digital data transmission over unused frequencies on traditional telephone lines For example, ADSL (Asymmetric DSL) Speed Downlink 128Kbps - 4Mbps Uplink 64Kbps - 800Kbps Need a DSL modem Splitters are needed to separate the voice and data signal CS105 Section 2 - Lecture 10

Broadband Services Cable Need a cable modem A technology that provides digital data transmission over cable TV infrastructure Speed Downlink 128Kbps - 3~5Mbps Uplink 64Kbps - 128Kbps~1Mbps Need a cable modem http://www.dish.com/entertainment/internet-phone/#internet http://www22.verizon.com/home/fiosinternet/#plans http://www.comcast.com/internet-service.html?CMP=KNC-IQ_ID_48056930-VQ2-g-VQ3--VQ6-23367977128&iq_id=48056930 CS105 Section 2 - Lecture 10

Broadband Services Satellite Need a satellite dish A technology that provide digital data transmission over satellites Speed Downlink 500Kbps - 1Mbps Uplink 50Kbps - 100Kbps Need a satellite dish CS105 Section 2 - Lecture 10

Home Network (single machine) Wall Jack DSL/Cable Modem USB/Ethernet Cable CS105 Section 2 - Lecture 10

Home Network (multiple machines) Wall Jack DSL/Cable Modem Hub/Switch/Router USB/Ethernet Cable CS105 Section 2 - Lecture 10

Home Network (multiple machines) Wall Jack Ethernet Cable DSL/Cable Modem Hub/Switch/Router CS105 Section 2 - Lecture 10

Home Wireless Network Wall Jack Ethernet Cable DSL/Cable Modem Hub/Switch/Router CS105 Section 2 - Lecture 10

Network Security Firewall A gateway machine and its software that protects a network by filtering the traffic it allows CS105 Section 2 - Lecture 10

Network Addresses Hostname A name made up of words separated by dots that uniquely identifies a computer on the Internet IP address An address made up of four one-byte numeric values separated by dots that uniquely identifies a computer on the Internet CS105 Section 2 - Lecture 10

Where does the host number Network Addresses Figure 15.9 An IP address is stored in four bytes Class A: first byte for network address and three remaining bytes for host number Class B: first two bytes for network address and the last two bytes for host number Class C: first three bytes for network address and the last byte for host number Where does the host number come from? CS105 Section 2 - Lecture 10

Domain Name System Host number The part of the IP address that specifies a particular host (machine) on the network Yes, but what is it? Domain name The part of a hostname that specifies a specific organization or group Top-level domain (TLD) The last section of a domain name that specifies the type of organization or its country of origin CS105 Section 2 - Lecture 10

Domain Name System matisse.csc.villanova.edu Domain name TLD Computer CS105 Section 2 - Lecture 10

Domain Name System Figure 15.10 Top-level domains, including some relatively new ones CS105 Section 2 - Lecture 10

Domain Name System Organizations based in countries other than the United States use a top-level domain that corresponds to their two-letter country codes Do you email someone in another country? Figure 15.11 Some of the top-level domain names based on country codes CS105 Section 2 - Lecture 10

Domain Name System Domain name system (DNS) A distributed system for managing hostname resolution Domain name server A computer that attempts to translate a hostname into an IP address CS105 Section 2 - Lecture 10

References Computer Science Illuminated Ch 15 Slides Modem Cabling http://en.wikipedia.org/wiki/Modem DSL http://en.wikipedia.org/wiki/Digital_subscriber_line Cabling http://ww2.it.nuigalway.ie/.../ct101/CT101_Introductio nToNetworking.ppt Basic Computer Network by Weesan Lee http://www.cs.ucr.edu/~weesan/cs6/03_basic_computer _network.ppt CS105 Section 2 - Lecture 10

References (cont) Domain Names http://www.icann.org/topics/new-gtld-strategy- faq.htm http://www.iana.org/root-whois/index.html CS105 Section 2 - Lecture 10