Lec9_Network1

Lec9_Network1 - Network Technologies: Infrastructure ISOM...

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Unformatted text preview: Network Technologies: Infrastructure ISOM 101, Spring 2011 Lecture 9 HKUST Business School Overview What are the major components of a computer network? What are the different types of computer networks? What are their respective strengths/weaknesses? What are networking standards? Which standards are the most common (and which is better)? ISOM 101 Raymond G. Sin © 2 HKUST Business School Network Components and Their Functions Transmission media Network Standardized formats for the transmission of data Software Ensuring the data gets to the right place Protocols Sharing data by establishing connections among devices Data communication hardware Sending signals Connecting to the Internet, managing and monitoring the network Services ISOM 101 Adding values to network usage Raymond G. Sin © 3 HKUST Business School Network Components and Their Functions Our current focus Transmission media Network Standardized formats for the transmission of data Software Ensuring the data gets to the right place Protocols Sharing data by establishing connections among devices Data communication hardware Sending signals Connecting to the Internet, managing and monitoring the network Services ISOM 101 Adding values to network usage Raymond G. Sin © 4 HKUST Business School Network Components and Their Functions Transmission media Network Ensuring the data gets to the right place Standardized formats for the transmission of data Software Lecture 10 (the Internet) Protocols Sharing data by establishing connections amongTo be discussed in devices Data communication hardware Sending signals Connecting to the Internet, managing and monitoring the network Services ISOM 101 Adding values to network usage Raymond G. Sin © 5 HKUST Business School Transmission Media (1) The medium through which ______ travel among connected hardware in a telecommunications system What is being “transmitted”? Signals: analog vs. digital Is my voice analog or digital? If my voice is transmitted to you through the microphone and speakers, is it analog or digital? ISOM 101 Raymond G. Sin © 6 HKUST Business School Transmission Media (2) Analog signals are waves They vary in amplitude (power of a signal) and frequency (number of oscillations per second) ISOM 101 Raymond G. Sin © 7 HKUST Business School Transmission Media (3) The “sine curve” looks pretty and fine… what is the problem? computers only understand digital signals – sequences of “on” (1) and “off” (0) signals Most telecommunications systems were originally constructed for voice traffic and rely on analog signaling A “translator” is needed for computer networks Modem – Modulation/demodulation Converts digital signals from a computer to analog – so that it can travel through an analog line (e.g. phone lines) – and back to digital ISOM 101 Raymond G. Sin © 8 HKUST Business School Transmission Media (4) Two main types of media: physical and wireless Measure of capacity of transmission media – bandwidth Analogy: circumference of a garden hose “Bandwidth” can mean different things in different contexts Analog: range of frequencies over which a signal travels Digital: maximum speed of the transmission method, measured in bits per second (bps) or kbps (1,000bps), Mbps (1,000Kbps), Gbps (1,000 Mbps) Early modems: ~1000 bps (compared to the typical network connection speed at 10Mbps/100Mbps today) What are the most common types of physical media (cables)? ISOM 101 A network cable belongs to which of them? Raymond G. Sin © 9 HKUST Business School Transmission Media (5) Three major types of physical media: Twisted pair wire Coaxial cable ISOM 101 Copper wire twisted into pairs Uses electricity to send signals Used in standard telephone systems The good: Inexpensive, already in place in most buildings The bad: Susceptible to interference from other electrical sources (e.g. electronic appliances) Single copper wire surrounded by insulation and a metallic mesh Uses electricity to send signals Used by cable TV industry The good: Metallic mesh minimizes electromagnetic interference from electrical sources; capable of higher transmission speeds (compared to twisted pair wire) The bad: More expensive; multiple layers make the cable thick and difficult to work with Raymond G. Sin © 10 HKUST Business School Transmission Media (6) Fiber optic cable Consists of thousands of individual hair-thin strands of glass with metal coating surrounding each strand Uses lasers to send light signals through glass fibers Usually used to connect multiple networks (or a backbone) on systems that require high transmission rates The good: not susceptible to interference, efficient in connecting remote sites The bad: expensive to buy and install ISOM 101 Raymond G. Sin © 11 HKUST Business School Computer Networks (1) A computer network is the connection of two or more computers for data sharing Network interface card (NIC) – a piece of equipment that allows the device (e.g. desktop, printer, PDA) to send and receive data over the transmission media A node is a piece of device that connects to a network ISOM 101 Raymond G. Sin © 12 HKUST Business School Computer Networks (2) Two main ways for data transmission: Switched circuit network – direct connection between two points (e.g. ?) Packet switched network – breaking down of transmission into “packets”, each containing the destination address (e.g. ?) Additional hardware and software are needed to ensure each packet follows an appropriate route and the receiving device to put them back in order There are many types of networks (e.g. LAN, WAN) and different configurations of network components ISOM 101 Raymond G. Sin © 13 HKUST Business School Computer Networks (3) Network Topology* Bus topology All devices are connected to a common central cable (bus/backbone) *Images are courtesy of Ivy Tech, Indianna and Florida Center for Instructional Technology, College of Education, University of South Florida ISOM 101 Raymond G. Sin © 14 HKUST Business School Computer Networks (4) Star topology Each device is connected to a hub, a hardware that receives data transmissions and sends them to the proper destination ISOM 101 Raymond G. Sin © 15 HKUST Business School Computer Networks (5) Ring topology Each node is connected to two other nodes forming a closed-loop ISOM 101 Raymond G. Sin © 16 HKUST Business School Computer Networks (6) Mesh topology Each node is connected to every other node on the network ISOM 101 Raymond G. Sin © 17 HKUST Business School Computer Networks (7) Tree topology Combination of a bus and a star topology – two or more star networks connected through a bus network The good: Point-to-point wiring between individual segments The bad: If the backbone cable breaks, communications across segments go down; more difficult to configure and wire ISOM 101 Raymond G. Sin © 18 HKUST Business School Computer Networks (8) Oh my goodness… more topologies?! Hybrid topologies Combinations of various topologies (e.g. bus+ring) Application 1: which topology (or combination of topologies) does HKUST use for connecting computer barns to the local area network? Why? Application 2: How should an organization decide which topology to adopt? ISOM 101 Raymond G. Sin © 19 HKUST Business School Computer Networks (9) Network Architecture Client-Server Peer-to-peer All computers on the network are both clients and servers Local Area Network (LAN) Servers: providers of services; clients: requesters of services A computer network that is contained within a geographic location (e.g. HKUST) To share resources (e.g. printers, software) so that users do not have to acquire their own Wide Area Network (WAN) ISOM 101 Consists of at least two LANs that are geographically separate but linked together Raymond G. Sin © 20 HKUST Business School Data Communication Hardware Hub Connecting point for devices on a network; it receives incoming data from one device and sends it out to other devices What is the difference between a hub and a switch? Router “Passive” vs. “Intelligent” – simply passing along/repeating data (disadvantages?) vs. delivering to the intended audience an intelligent hub is often referred to as “switching hub”/“switch” If one is more sophisticated than the other, why do both exist? Determines the appropriate route for data to get from one network to another Gateway ISOM 101 Converts data from one standard to another so that networks using different standards can “talk” to each other Raymond G. Sin © 21 HKUST Business School ISOM 101 Raymond G. Sin © 22 HKUST Business School Standards and Protocols (1) Networking standards (protocols) are a format for transmitting data that has been agreed to by a standards organization or industry consortium What is the importance of networking standards? It serves as a “universal language” for different systems Three common protocols: TCP/IP (transmission control protocol and Internet protocol), Ethernet, Token Ring ISOM 101 Raymond G. Sin © 23 HKUST Business School Standards and Protocols (2) Ethernet ISOM 101 Invented by Bob Metcalfe and David Boggs in early 70’s @ Xerox’s Palo Alto Research Center most common protocol for LANs, also known as the IEEE 802.3 standard a local area technology that connect devices in close proximity Operates at speeds of 100mbps to >1gbps it specifies a set of rules for constructing frames (short messages that nodes communicate with each other), e.g. minimum and maximum lengths, a set of required pieces of information such as destination address and source address Each address identifies a unique node – no two Ethernet devices should ever share the same address Raymond G. Sin © 24 HKUST Business School Standards and Protocols (3) How does Ethernet work? (like postal service) A Ethernet Medium B ISOM 101 C Raymond G. Sin © 25 HKUST Business School Standards and Protocols (4) Ethernet nodes “listen” to the medium while they transmit to ensure that they are the only device transmitting at that time What if both computers B and C are trying to “speak to” the printer at the same time? COLLISION! The Ethernet protocols ensures that the issue is resolved in a gentle and graceful fashion Image what is going to happen if both students are trying to answer a question at the same time ISOM 101 Raymond G. Sin © 26 HKUST Business School Standards and Protocols (5) Ethernet (continued) If another device attempts to transmit at the same time, both devices will hear their own transmission returning in a garbled form They both cease transmission, wait a random amount of time, and attempt to transmit when they again detect silence on the medium. The random pause and retry is an important part of the protocol (why?) the random delay makes it unlikely that any two stations will collide more than a few times in a row. ISOM 101 Raymond G. Sin © 27 HKUST Business School Standards and Protocols (6) What are the major limitations of Ethernet? Electrical signals move quickly, but weaken as they travel and is subject to electrical interference from neighboring devices A network cable must be short enough to ensure clarity and minimal delay of signals between the devices Limitation on the maximum distance between two devices (a.k.a. network diameter) Only a single device can transmit at a given time This sets practical limits to the number of devices that can coexist in a single network Any ISOM 101 Alternative? Raymond G. Sin © 28 HKUST Business School Standards and Protocols (7) Token Ring Invented by IBM in the 70’s Connects devices in a closed loop Allows only one device to transmit at a time (no collision problem) A “token” passes from device to device Only the device that currently holds the token may transmit Operates at speeds of 4, 16, 100mbps ISOM 101 Raymond G. Sin © 29 HKUST Business School Standards and Protocols (8) Token Ring (cont’d) The good: If network traffic is light, little difference in speed between Ethernet and Token Ring; if traffic is high, Token Ring networks are much faster The bad: requires more expensive hardware, careful planning, and difficult to troubleshoot An alternative technology: Asynchronous transfer mode (ATM) ATM networks can attach many different devices with high reliability and at high speeds, even across the country. Versatile and expandable: ATM networks are suitable for carrying voice and video traffic as well ISOM 101 Raymond G. Sin © 30 ...
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This note was uploaded on 01/10/2012 for the course ISOM 101 taught by Professor Chanriki during the Spring '10 term at HKUST.

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