We will discuss several aspects of networks in this lecture. First the communications channels, the transmission medium that the data is transferred over. The transmission medium consists of materials or techniques capable of carrying a signal. Then we will discuss transmission characteristics, which includes things like the transmission mode, transmission direction, and transmission rates. Then we will discuss transmission software, and finally transmission devices any type of  hardware capable of transmitting data, instructions, and information between a sending device and a receiving device. The last thing we will cover is types of networks, such as LAN, and WAN.

TRANSMISSION MEDIUMS

We have two groups of mediums to cover, physical and wireless.

Physical Transmission media

These are cables usually used in buildings, or underground. The three main types of physical transmission mediums I will cover are twisted pair lines, coaxial cable, and fiber-optic cable

• Channel's capacity is rated by the number of bits it can transmit per second
  • Modems often have a bps rating - 28bps, 33bps, 54bps
  • To the average user the baud rate is basically the same thing as bps rating
• Twisted pair wire
  • One of the most commonly used transmissions medias
  • Link your telephone with the telephone system
  • Two insulated copper wires twisted together
• Coaxial cable
  • Copper wire that permits high-speed transmissions with a minimal signal distortion
  • Hooked up any stereos, VCRs, or TVs lately?
  • Not used much today because other transmission media such as fiber-optic cable transmit signals at faster rates.
• Fiber optic cable
  • Glass fibers thinner than a strand of hair
  • Carry data faster, are lighter, less expensive (sorta)
  • Twisted pair and coaxial cable carry data as electrical signals
  • Fiber optic carries data as laser-generated pulses of light
  • Harder to intercept pulses of light than electrical signals

Wireless Transmission Media

Wireless transmission is becoming more and more popular these days. One of the leading protocols that is being used is called 802.11b. The sub and a few other buildings on campus are talking about putting in a wireless network using 802.11, this means that if you turn on your laptop in the sub and you have a 802.11 modem you will have Internet access without plugging in a cable. The third floor of EPS has 802.11 wireless Internet Access, bring your laptop and sit on the comfy chairs and you can have unlimited Internet access.

Here are some other wireless protocols:

• Broadcast Radio
  • Wireless transmission medium that distributes radio signals through the air over long distances such as between cities, regions, and countries.
  • AM/FM radio is broadcast radio.
  • Slower and more susceptble to noise than physical transmission media.
  • Provides flexibility and portability
• BlueTooth
  • Proposed radio frequency
  • Short range wireless communications
  • Range is from 10 to 100 meters
  • Wireless mice and keyboards are beginning to use this technology. 
• Cellular Radio
  • Broadcast Radio
  • Cell phones are the same
• Microwaves
  • Radio waves that provide a high-speed signal transmission.
  • Limited to line-of-site
• Communications Satellite
  • Space station that recieves microwave signals from an Earth-based station
  • 22,300 miles above the Earth's equator
  • These satelites orbit at the same rate as the Earth, they are considered geosynchronous satelites
• Infared
  • Wireless transmission media that sends signals using infrared light waves.
  • Requires line of site.

TRANSMISSION CHARACTERISTICS

Characteristics include signal type, transmission mode, transmission direction, and transmission rate.

Signal Type

• Analog - continuous electrical wave
• Digital - individual electrical pulses that represent the bits grouped together into bytes.

Transmission Modes

How the bits are moved between devices

• Asynchronous - send at anytime, no synchronization needed.
• Synchronous - sending large blocks of bytes at regular intervals, everything is synchronized.

Transmission direction

• simplex - sends only in one direction (mouse only needs to send the signal one direction).
• half-duplex -  Data can flow in both directions, just not at the same time.(walkie-talkie).
• full-duplex - Data can flow both directions at the same time. (phone line).
  

Transmission rate

• The speed in which a transmission medium can carry data
• expressed in bits per second
• Bandwidth - The quantity of information which can be transferred through a connection. This is generally measured in bits-per-second.
• Broadband vs. Baseband
  • Baseband - Some types of media can transmit only one signal at a time.
    • Phone lines
  • Broadband -  Some types of media can transmit multiple signals simultaneously
    • CableTV - all the channels you receive come across the line at the same time.

Common carriers that you can get from the phone companies

• Private line - dedicated channel between two points
  • Pay for it whether you use it or not
  • More reliable
  • More secure
• Switched line
  • Pay for only the time you use it
  • Greater flexibility
• ISDN - Integrated Services Digital Network
  • Source-to-destination digital channel
  • No need for modems
• DSL -Digital Subscriber Line
• Uses sophisticated techniques to transmit a greater number of bytes over your normal phone lines.
• Changes a baseband phone line to Broadband.
• Bridgeband and Multiband are two companies that provide DSL in Bozeman.
• T - lines
  • T1 lines are much more expensive, they are equivalent to 24 phone lines.
  • MSU used to have five T1 lines connecting to Spokane (we switched to a different technology Spring 03).
  • T3 lines are even more expensive, usually just for very large Internet companies, these lines are equivalent to 28 T-1 lines

TRANSMISSION SOFTWARE

• Telnet
• FTP - a protocol for transferring files from one computer to another computer.
• Terminal emulation mode - allows a personal computer to act as a specific type of terminal, allows the PC to access data and resources on a server or mainframe computer.

COMMUNICATION DEVICES

The hardware that allows or helps allow the transmitting of data, instructions, and information between a sending device and a receiving device.

• Modem - modulator/demodulator
  • Changes digital signals from computers to analog signals that telephone lines can carry
  • Changes analog signals back to digital signals that computer can understand
• Cable Modem
  • a modem that sends and receives data over the cable television network, usually coaxial cable.
• Network Interface Card
  • an expansion card that you insert into an expansion slot of a personal computer or other device, such as a printer, enabling the device to connect to a network.

Connecting Networks

• Hub (Switch)
  •  is a device that provides a central point for connections in a network, can use cables or can be a wireless hub.
• Front-end processor
  • Sometimes the host computer on a large network gets overloaded processing data, monitoring transmissions, controlling the system, etc
  • Install another computer that does nothing but process the electronic transmissions between computers
  • Each computer system and terminal/PC has a network address
  • Addresses are used to route transmissions to the right place
  • My experiences in Oklahoma
• Multiplexer -
  • a device that combines two or more input signals from various devices into a single stream of data and then transmits it over a single transmission medium.
  • Collects data from several devices
  • Sends a consolidated transmission over a single communications channel to front-end processor
• Router
  • Bridge gap between incompatible networks
  • Converts protocols and routes message to its destination
  • Backbone - a system of routers and associated transmission media
• Repeater
  • A device that accepts a signal from a transmission medium, amplifies it, and retransmits it over the medium.
  • As a signal travels over a long distance the signal undergoes a reduction in strength, an occurrence called attenuation.
  • Repeaters regenerate analog or digital signals that can be distorted by attenuation.
• Bridge
  • A device that connects two LAN's using the same protocol, such as Ethernet.

Networks

• WANS - wide area networks
• LANS - local area networks
• All of them include hardware, software, and channels
• Hardware sharing
  • Several users accessing & using single device - printers, communication channels
• Software sharing
  • Store frequently used software on server so that more than one person can use it
  • Don't have to load it on each individual client
  • Available when needed
  • The idea behind NetPCs
• Information sharing
  • Put data on server - whoever needs it can get it
  • Limit access to data - read only; read/write
  • Limit use of data
• Necessary hardware for a LAN
  • Network interface cards (NIC)
    • Add on card that facilitates and controls exchange of data
  • Transmission media
    • Cables (twisted pair, coaxial, fiber optic) or wireless transceivers are connected to NIC
  • Servers
    • File server, print server, communications server
    • Single PC or distributed among the computers within the network

Network Line control

Ya gotta have rules!

• Protocols
  • Describe how data are transmitted in a network
  • Set of rules and procedures for exchanging information between computers
  • Define how comm link is established, how info is transmitted, and how errors are detected and correct
  • Use of protocols allow different makes and types of computers to talk to each other
  • Usually embedded in the software for particular applications
  • Two types of protocols
  • Proprietary
  • Open
  • Ethernet is an example of an open protocol that is used in the dorms and most labs on campus
    • It works on a competitive process, each PC competes for network access when needed
    • Developed at Palo Alto by Xerox, they didn't find it useful kind of like the mouse and GUI they also developed and abandoned.
    • It is inexpensive and easy to maintain since there is no synchronization, just competition.
    • When you see a computer that has a network interface card(NIC) that says 10/100, this means it's an Ethernet card that can cary data at rates of 10mbps or 100mbps (fast ethernet).
    • Gigabit Ethernet can transfer rates of 1000 mbps, it is the newest technology.
  • TCP/IP is an example of an open protocol used to manage transmission of data by breaking it up into packets
    • TCP/IP was developed in 1973 for use in the ARPANET
    • It is the Internet standard
    •  

  Intranets

  • This is essentially a small version of the Internet used within an organization.
  • Supports all the same protocols that the Internet uses, but it is set up to allow insiders of the organization in, but not the rest of the World.
  • A firewall is a general term that refers to both hardware and software that restricts access to the Intranet from people outside the organization. It is a security wall that can be made up of software or hardware.