CS245 - CS II Chapter 10 - Communications
10.1 Communications Basics
telecommunications - long-distance electronic communications
communications channel - path over which data travels from its source to the destination
ex. electrical wires, fiberoptic cables, microwave links, other radio frequencies
properties of channel:
- type of signal (digital vs. analog)
- modem (modulator-demodulator) - internal vs. external modems
- speed at which the signal is transmitted
- bps - bits per second (300, 1200, 2400, 9600, 14.4Kbps, 28.8K, 36.6K, 56K, 1.44Mbps, 10/100 Mbps, 1 Gbps)
- baud rate - number of signal changes per second
- type of data movement
- simplex - TV transmission (one-way only)
- half-duplex - Bank ATM (two-way but only one way at a time)
- full-duplex - telephone conversation (two-way)
- method of data movement
- asynchronous - requires start & stop bits (cheaper but slower)
- synchronous - data sent in large blocks (requires that both ends are syncronized - each know what bits compose a byte and how it is organized)
10.2 Communications Media
Linking Up: Network Basics
computer network - computer system that links together two or more computers
Why network? - share hardware resources, share data & software, communicate with others
The Network Advantage
- Share hardware (reduces costs & increases access)
- Share data & software (increases efficiency & productivity)
- People can work together (groupware, e-mail)
Basic Network Anatomy
ports - sockets that allow data to pass in/out
parallel port vs. serial port
network interface card (NIC)
transmission media: cable - twisted pair, coaxial cable, fiber-optic
network software
Understanding the Components of a LAN
- Computers
- WorkStations(Clients) & Servers
- LAN cables
- Thinnet (thin coaxial wire)
- Thicknet (thick coaxial wire)
- STP (shielded twisted pair)
- UTP (unshielded twisted pair)
- fiber optic
Network interface cards
- Ethernet cards: BNC (T) connector; DB15; RJ-type - 10 Mbit/sec
- uses Carrier Sense, Multiple Access/Collision Detection
- Token Ring cards: DB9 or RJ-type - 4 - 16 Mbit/sec
- ArcNet - 2.5 Mbit/sec
- LANtastic (proprietary system) - 2 Mbit/sec
Data Transfer Speeds on a LAN
- 10 Mbit/sec = 1.2 Mbyte/sec
- LAN speed < speed of slowest component
Networks Near and Far
Different Topologies star, ring, star, and bus topologies
node - device found in a network
Local area networks or LANs, are networks that are limited geographically to a single site. Most local area networks of microcomputers employ the "client-server" architecture. Most computers in the network are client workstations; a few are servers. The server computers provide various services to the clients. These servers usually include shared disk storage, shared printers, and shared wide-area-network (WAN) access.
Hardware Devices
- REPEATERS - used to boost the signal on a network (used in 10Base2 & 10Base5 networks)
- HUBS - multiport repeater used in 10BaseT, ARCnet & Token Ring networks
- BRIDGES - used to connect two different types of networks and to partition a network
- ROUTERS - devices that route LAN traffic between logically separate networks
- GATEWAYS - used to allow two or more dissimilar networks to communicate as a single logical network
| A file server is a computer dedicated to providing files to
other computers on the network. |
Distributed processing involves using a network to allow a single
entity to decentralize its computing needs over several networked computers
|
Client Server Computing - A computer containing the resource responds to requests from other machines
Communications Software
protocol - set of rules for exchange of data between terminal & computer or 2 computers;
- peer-to-peer LAN vs. client-server LAN
- IBM's NetBIOS - Network Basic Input Output System
- Novell's IPX - Internetwork Packet Exchange
- Microsoft's NetBEUI -
- TCP/IP - Transmission Control Protocol / Internet Protocol
- ftp, telnet, http
network operating system (NOS) - Novell's Netware, WFWG, Windows NT, OS/2, Macintosh
System 7, UNIX, DECNET
10.3 How are Networks Used?
Internet: ARPANET, NSFNET
- e-mail
- telnet
- ftp
- Usenet (NetNews)
- gopher
- world-wide web
Electronic Mail and Teleconferencing: Interpersonal Computing
e-mail
delayed teleconference (ListServ)
real-time teleconference (phone on VAX, chat on WFWG, talk on UNIX)
The postal Alternative
- e-mail is fast
- e-mail doesn't depend on location
- e-mail facilitates group communication (allows aliases & group lists)
- e-mail messages are digital (easy to appnd, forward & reply to)
- e-mail is less intrusive than the telephone
- e-mail allows time shifting
- e-mail & teleconferencing makes long-distance meetings possible
- e-mail & teleconferencing emphasize the message over the messenger
On-line Problems
- vulnerable to machine failures & human errors
- can pose a threat to privacy
- users need to read & respond regularly
- many human components of communication are filtered out
- not available everywhere yet
Rules of Thumb
- If you're using a metered service, do your homework offline
- Let your system do as much of the work as possible
- Say what you mean, and say it with care
- Learn the nonverbal language of the network (smileys)
- Avoid lynch-mob mentality ("flaming")
- Don't be a source of electronic junk mail
- Avoid information overload
- Practice Netiquette
BBS (Bulletin Board System)
- Freeware - software that is free
- Public Domain software - similar to Freeware
- Shareware - software that is free to copy, but the author expects a token payment for its use
- Download - process of copying software from one computer to another
Conferencing Systems
- Usenet (Netnews)
- teleconferencing
- IRC
- Collabra
ATMs & EFT
10.4 The Matrix: Internet, Bitnet, Usenet and Others
Some of the Networks in the Matrix
- 1973 - Internet
- 1979 - UseNet
- 1979 - CompuServ
- 1981 - BITNET (Because It's Time)
- 1983 - FidoNet
- 1988 - Prodigy
- 1989 - AOL
- 1990s - Intranets
- originated in early 70s (e-mail & ftp)
- uses TCP/IP protocols
- Gopher @ UMN developed 1988
- www @ CERN developed by Tim Berners-Lee in 1989 to allow communications via hypertext
- uses HTTP protocol for transmission and HTML for development
- exists in a Client/Server environment
Terms:
- Internet - worldwide collection of computers and computer networks
- TCP/IP (Transmission Control Protocol/Internet Protocol) - rules for transmitting data between computers across a network.
- IP address - Internet address in the form of four period-delimited octets of numerals (ex. 192.132.89.65)
- Domain name - name corresponding to an IP address (ex. frodo.nmhu.edu)
- DNS (Domain Name System) server - resolves domain names to IP addresses
- Internet gateway - network device needed to connect to the Internet
- SMTP (Simple Mail Transfer Protocol) - transports a mail message across a TCP/IP-based network.
- POP3 (Post Office Protocol version 3) - standard for using mailboxes and forwarding mail message to a user's local computer.
- HTML (HyperText Markup Language) - language for creating "web" documents
- HTTP (HyperText Transfer Protocol) - a set of rules for transferring documents across the Internet
- WWW (World Wide Web) - collection of computers that share HTML documents using the TCP/IP and HTTP protocols
- Client/Server Architecture - distributed computing environment where one or more server computers provide access to data from one or more client computers
Benefits of a "Global Electronic Village" by Jean Jipguep
- More fluid, global markets
- Shared research work and findings
- Worldwide creative and intellectual contributors
- No geographic barriers
- Wide range of available entertainment
Barriers to a "Global Electronic Village" by Jean Jipguep
- Cultural pluralism
- Conflicting values
- No universal digital policing
- National legislative actions
- Lack of standards' enforcement
Travels on the Internet (The Past, Present and Future)
- Draw diagrams of the networks in LH2 and SCA205 and discuss the connections from the computers in the labs to the Internet
- Be sure to discuss the properties of the communications channel from the labs to the Internet.
- for your e-journal this week, find a discussion of local area networks and describe it.
- Describe your e-mail address and the address where the notes for this chapter are kept on my computer
- Use Word & Internet Assistant or Word '97 or HomeSite to build your personal homepage (view the HTML code with Netscape or IE)
- for your e-journal this week, find a discussion of the Internet and describe it.