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Introduction to Management Information SystemsChapter 5 Data Communications and Internet Technology HTM 304 Fall 07
Content • 5-layer Architecture for Communication • Internet • Enterprise Network • Wireless
Fundamental Networking Concepts • Computer network – collection of computers that communicate over transmission lines • 3 main type of networks • LANs – Local Area Network • WANs – Wide Area Network • internets – interconnected networks, e.g. the “Internet” • An Internet uses varied communication methods and conventions
PSDN: Packet Switching Data Network Demo: How a file is sent over PSDN
Packet Switching Technology • Packet switching breaks transmissions into messages (or packets, frames) • When a packet arrives at a router, the router must decide which of several paths to use to send the packet on • Complex algorithm • Computation done by each router • Some packets may be lost during transmission. • Only those packets that are lost will be resent • Won’t ruin the whole conversation
Layered Protocol • A set of layered protocols provide seamless communication between computers • What is protocol? -- A standardized means for coordinating an activity between two or more entities.
Computer Protocol • Communications protocolcoordinates activity between two or more computers • Two machines must agree on protocol and follow it to send messages • There are many levels of coordination: e.g. MacOS ↔ Windows, Wireless network ↔ Wired LAN, etc. • A set of layered protocols provide seamless communication
Three different network architectures • 7-layer OSI model (developed by ISO) • ISO (International Organization for Standardization) • OSI (Open System Interconnection) • 4-layer TCP/IP model (developed by IETP) • TCP/IP (Transmission Control Program / Internet Protocol) • IETP (Internet Engineering Task Forece) • 5-layer blend model: TCP/IP – OSI model • The most commonly used model
The 5-Layer Model • Require: • Remember the name of these five layers • Describe the general functions of each layer
Layers, Protocols, and Analogy to Mail Email: How are you doing? Deal with app. software Deal with how to transport (e.g. confirmation?) Deal with how to route packets (e.g. next relay?) Deal with physical transportation (e.g. network medium, CRC)
Layer 1 Physical Layer • Question: what is the very first step to connect two computers? • Concerned with transmitting data bits over a communication circuit. • Example questions concerned: • What voltages to represent 0-1s? • How many bits per seconds to be sent? • What kind of cable to be used? • Reflect to the physical post office example: • The post office vehicle, the staff, the mailbox, the road condition…
The speed measurement • bps: stands for bit per second • Why use bits not bytes? • Other units: • Remember the set of units for capacity storage: B, KB, MB, GB. • Know the difference
Calculation • How long does it take to send 10MB data using dial-up modem? • Speed: 54kbps = 54,000 bit per second • Data amount: 10MB = 10 * 1024 * 1024 * 8 bit = 83,886,080 bit • Time: 83,886,080 bit / 54,000 bit per second 1553.46 second 25.89 minute Why? Ask for effective communication rate! • Revision: take in to account that the effective communication rate is 30% • Effective Speed: 54kbps * 30% = 16,200 bit per second • Data amount: 10MB = 10 * 1024 * 1024 * 8 bit = 83,886,080 bit • Time: 83,886,080 bit / 16,200 bit per second 5178.15 second 86.3 minute
More exercise: • Estimate the time to download the following files under different network conditions: • A) • reported speed: 30kbps, • effective rate: 25% • file size: 204KB – a JPEG file • B) • reported speed: 5.4 mbps, • effective rate: 30% • file size: 4 GB - DVD • C) • reported speed: 100 mbps, • effective rate: 15% • file size: 605MB – a CD
Extended Cable: Hub • Operates on the physical layer: the first layer • A shared bus: an extended cable that physically connects all the computers
Another device - Modem • Stands for: modulator – demodulator • Modulation: • Covert digital signals to analog signals • Demodulation: • Covert analog signals to digital signals Modem converts digital signals to analog signals so that the data can be transferred via the analog cable/equipments.
Types of Modems • Dial-up Modems • Produces analog signals that can be carried on a regular telephone line. • Point – to Point communication circuit switch network • DSL Modems • DSL: digital subscriber line • Operate on the same telephone lines, but do not interfere with voice telephone service. • Cable Modems: • High speed data transmission using cable television lines. • Operate in such a way that their signals do not interfere with TV signals.
How many ways to connect computers? • Three typical topologies • STAR • BUS • RING Pros: easy to add a new node; easy to access the file server; If one node is down, it will not affect others; Cons: the # of nodes has limit; slows down when too many nodes; Pros: in expensive, easy to install, easy to add a new node; can add more nodes; Cons: require coordination among the nodes on when to use the bus Pros: high bandwidth and span large distance; Cons: relatively expensive and hard to install; communication among the computers is difficult (require a token – token ring)
Layer 2: Data Link Layer • Task: to establish a virtual line that appears free of undetected transmission errors to the network layer. • Analogy: • How to send the mail from one station to another. Decision maker on this lever doesn’t consider the physical layer specifics such as what kind of car, road condition, car speed. • Use Google Map to figure out the direction • Traffic Lights • Damage control (car incidence) • Some main function of Data Link Layer: • Traffic control (not sending too fast) • Error control (collision detection, token management)
Frame • Layer 2 receives data packets from above (i.e. layer 3, Internet layer), and breaks them down into frames • A frame can be of a few hundreds or a few thousand bytes. • Frames are transmit sequentially. • Acknowledgement Frames are sent back by the receiver. • Frames contain the MAC address of the sender computer and the receiver computer. • Here, the receiver computer is the computer in the next link (e.g. the next post-office transition station) • MAC address: uniquely assigned with the NIC (network interface card)
Layer 2 Equipment • Network Interface Card (NIC) • Modern motherboard sometimes has NIC built-in • Each NIC has a unique identifier, the MAC address • MAC: Medium Access Control • The MAC address is assigned by the manufacturer, you cannot change it. • Layer 2 protocols recognize the MAC addresses in the network, and determine how to establish data link from one computer to the other.
Some Layer 2 Control Standards • Control error-less communication between two physical computers based on different ways the computers are connected. Two important standards need to know: • Ethernet: IEEE 802.3 • IEEE (pronounced “ I triple E”: stands for the Institute for Electrical and Electronics Engineers. • IEEE 802 committee: LAN standards committee • Used for control communication under bus topology. • Used for most of the PCs. • Token-Ring: IEEE 802.5 • Advocated by IBM. Token circulates around the ring. Whoever gets the ring talks. • Wireless Comm. IEEE 802.11 series • Will talk later in wireless session.
Summary of Today • Basic concepts: • Computer networks • LAN / WAN / internet / Internet • PSDN: explain the difference with circuit switch network • Layered Protocols • What is protocol? Why protocols? • Names of three different architectures • The TCP/IP-OSI blend model: name of 5 layers? • The hardware layers: physical layer and data link layer • Functionalities • Devices: cables, Hub, Modem, NIC • Calculation: How to estimate transmission time?