LAST UPDATE: 11/14/06
This will probably always under reconstruction!
This is the most current version of Learning Module II; however, the study guide needs to be written (for the independent learner) and
some of the content sections, links, and assessment tools need to be fine-tuned.  (Nothing is wrong, just imperfect!)
Note that the blinking text designates things that I need to work on; the material is not wrong, but can be improved.
(Don't worry, I don't like blinking text, either, so there will not be any in the finished product!)

LEARNING MODULE II: REVIEW/OVERVIEW OF
COMMUNICATIONS & NETWORKING

    This learning module summarizes concepts, hardware, and software that is involved with communications and networking in general. Because Cyberspace, by definition, involves computer networks, everything in this learning module applies to Cyberspace and consequently to the Internet; however, on the otherhand, the content of this module is perfectly general, applying to all data communications and to any kind of network.  ...before proceeding consult the Study Guide for this learning moduleIf you haven't already done so, read the Introduction to the Study Guide.

The Objectives of this learning module are:

1. To survey the fundamentals of Computer Hardware and Software necessary to understand the concepts of this course.
2. To relate online access to the concept of protocols which will be amplified in Learning Module IV.
3. To survey the basic types of networks and introduce network terminology.

The sequence of presentations is:

1. DATA COMMUNICATIONS, AN OVERVIEW
2. TRANSMISSION CHARACTERISTICS
3. COMMUNICATIONS HARDWARE
4. COMMUNICATIONS MEDIA
5. COMMUNICATIONS SOFTWARE
6. COMMUNICATIONS PROTOCOLS
7. NETWORK ARCHITECUTRE
8. NETWORK TECHNOLOGIES
9. INTERNET CONNCECTIONS
10. SUMMARY

1. DATA COMMUNICATIONS, AN OVERVIEW:

1. An oversimplified generic model of communications (See Figure C&N-1) would have a signal from a source encoded (i.e. the ________(1) signal is __________(2)) for transmission over a communications channel after which it is decoded for the receiver. Four types of transmissions involving different signal/channel combinations are shown in Figure C&N-2.
1. the signal must be protected from corruption by "noise" (interference from the environment)
2. Processing in a distributed environment is based on the client-server model
2. In general, a telecommunication network is a particular arrangement of resources including:
1. computer hardware (host computers, servers, workstations, peripheral devices, etc.)
2. communication hardware (modems, codecs, transmitters, receivers, repeaters, & switching devices) (See section 3, below.)
3. communication media (telephone lines, cables, etc.) (See section 4, below.), and
4. communication software that coordinates the nework components. (See section 5, below.)
3. Types of transmission signals (See Figure C&N-3.):
1. An analog signal is a continuous wave pattern that varied in frequency or amplitude to convey data/information. Most "real-world" data has an analog format, e.g. voice transmission over the telephone.
2. A digital signal is a pattern of discrete high or low amplitude pulses. Such signals can carry __________(3) data without modification (i.e. there is no need for a __________(4)).
3. Analog-to-digital converters convert between types
4. A carrier signal is a base analog signal for transporting data over a communication channel. The actual data is superimposed on the carrier signal by modulating (altering) this carrier signal.  There are several forms of modulation, but the most basic include the following.  (Figure C&N-3 illustrates the three basic techniques, FM, AM, and PM)
1. Amplitue modulation (AM) is a technique that modifies the amplitude (voltage) of an analog carrier wave.  This, the original modulation mechanism of early modems, used a large amplitude for a "1" and small amplitude for "0"; the actual amplitude values are irrelevant, as long as they are clearly distinguishable.  AM transmissions are easy to use but are limited by the carrier channel bandwidth.  Therefore AM is no longer used in modems; however, it is still used in conjunction with other techniques.
2. Frequency modulation (FM) is a technique that modifies the frequency of an analog carrier wave. As with AM, the actual values are irrelevant, as long as they are clearly distinguishable, so in FM the transmission frequencies are different for a "1" and for a "0".  As with AM, FM is limited by the channel bandwith. Also signal distortion makes detection harder than AM, so this technique is currently not used in quality modems.
3. Phase modulation (PM) is a technique that modifies the phase of an analog carrier wave.  A "0" is transmitted as a 0 degrees phase analog signal and a "1" is shifted 180 degrees. Obviously, signal detection depends onphase synchronization between the transmitter and receiver.Variations of PM include:
1. continuous phase modulation( CPM) is a modern adaptation of the basic FM technology. The primary modification is that in the transistion from one bit to another; the phase is changed continuously rather than instantaneously, i.e. there are no phase steps. This results in faster data rates, for the same bandwidth, than FM.
2. differential phase modulation is another modern adaptation of the FM technology. This means that a receiver is designed to detect the difference in phases instead of the absolute phase of each bit; such detection is easier than CPM. Using this technology, the modem shifts the phase of each successive signal in a specific number of degrees for a "0" (e.g. 90 degrees) and a different number for a "1" (e.g. 270 degrees).
A detailed discussion of modulation techniques is given here.

1. Transmission channels:
1. A simplex channel transmits data in only one direction.
2. A half-duplex channel can transmit in either direction, but only one way at a time.
3. A full-duplex channel allows data to transmitted in both directions simultaneously.

1. Transmission parameters:
1. The transmission speed is the amount of data transmitted per unit time, e.g. bits per second, bps (the most commonly used unit), or characters per second, cps (don't confuse with cycles per sec.).
2. The bandwidth, or range of frequencies that can be used with a particular channel, is a measure of the data transmission capacity. Standard telephone lines are "voiceband channels" that have a bandwidth of 3 kilohertz (3000 cycles per second) which is somewhat larger than the range of frequencies of a typical human voice; when used to transmit binary data it can transmit up to about 33 Kbps (kilobits per second) via modems. ISDN, cable, and fiber optics have increasingly higher bandwidth. (See Section 4, below, andFigures C&N-4A and C&N-4B.)

2.1 Wired vs. wireless communication:

1. Wired communication requires that the transmitter and receiver be physically connected. There are two basic types of wires, based on the kind of signal they are desigened to transmit analog or digital signals.
1. Analog lines, e.g. "plane ol’ telephone service" ("POTS") which carry analog signals via electrons.  To transmit data, the digital data must be superimposed, by a modem, on the telephone's analog carrier signal.
2. Digital Lines carry digital signals and thus avoid the analog/digital conversions necessary for digital transmission over POTS.
1. The term "digital lines" typically refers to electronic transmissions (See section 4.1.C, below.); however ...
2. Fiber optics are technically "digital lines" that transport digital data via bursts of electormagnetic through glass fibers.  (See section 4.2, below.)
2. Wireless communication uses electormagnetic waves that require no physical medium for transmission.  A common type of wireless technology uses microwaves (electromagnetic waves with frequencies between Radio/TV and light; see Figure C&N - 4A.) or radio waves to provide high-capacity transmission (over 3 million bps) over line-of-sight channels.  If you are interested, check out the description in the interesting Web Site, How Stuff Works.
1. Types of wireless communications:
1. Terrestrial communications involve transmission via repeater stations which form a series of direct line-of-sight links from source to receiver.
2. Satellite communication involves satellites in geosynchronous orbit, which receive data transmitted on an uplink, amplify that signal, and transmit to a receiver station on a downlink.
3. Cellular communications is a form of short-wave wireless technology that is currently used mostly with cellular telephones,  The user connects to a nearby  transmitter.  The land area covered by the transmitter is called its "cell".   As the user travels between adjacent cells, the cellular telephone is automatically passed on to the next local cell transmitter.
4. Wireless network technology is becoming more efficient and cost effective, especially in LAN applications, e.g. wireless routers are now commonly used to share Internet connections, printers, data storage, etc. at home.
2. Wireless categores include the following.
   
1. Fixed wireless involves stationary hardware, e.g. office/home equipment, typically of limited range IR (infared) technology like wireless mice, keyboards, etc.
2. Mobile wireless involves hardware built into vehicles, e.g. cars, boats, airplanes, etc.
3. Portable wireless involves battery powered hardware that is carried by people, e.g.  cell phones, protable communications systems, etc
3. Wireless technologies:
1. 802.11 is a collection of wireless LAN protocols developed by the IEEE that specify communications between a wireless client and a base station or between two wireless clients. There are several variations of the 802.11 technology:
1. 802.11 provides 1 or 2 Mbps transmission in the 2.4 GHz band using either frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS).
2. 802.11a, an extension to 802.11, provides up to 54 Mbps in the 5GHz band.  It uses an orthogonal frequency division multiplexing encoding scheme rather than FHSS or DSSS.
3. 802.11b (also referred to as 802.11 High Rate or Wi-Fi) -- an extension to 802.11 that applies to wireless LANS and provides 11 Mbps transmission (with a fallback to 5.5, 2 and 1 Mbps) in the 2.4 GHz band. 802.11b uses only DSSS. 802.11b was a 1999 ratification to the original 802.11 standard, allowing wireless functionality comparable to Ethernet.  Wi-Fi is a central feature of Microsoft's .Net technology and, as such, is built into Windows XP.
4. 802.11g -- applies to wireless LANs and provides 20+ Mbps in the 2.4 GHz band.
2. Bluetooth is a relatively new technology designed to provide widely available, wireless communication between independent devices, particularly portable devices like notebook computers, PDAs, cell phones, etc.  Each device will be equipped with a microchip tranceiver that transmits and receives in a previously unused frequency band of 2.45 GHz that is available globally (with some variation of bandwidth in different countries). In addition to data, up to three voice channels are available. Each device will have a unique 48-bit address from the IEEE 802 standard. Connections are one-to-one. The maximum range is 10 meters. Data can be exchanged at a rate of 1 megabits per second (up to 2 Mbps in the second generation of the technology). A frequency hop scheme allows devices to communicate even in areas with a great deal of electromagnetic interference. Built-in encryption and verification is provided. (From WhatIs.) There are ambitious plans to develop "personal area networks" (PANs) based on Bluetooth that network the various microprocessor based devices belonging to an individual in the near future.  For more info check out the Bluetooth homepage.

1. Serial transmission sends one bit at a time over a single wire. Telephone lines use serial transmission for digital data, thus modems are connected to the computer via a serial port.
1. A serial port is a socket on a computer used to connect the serial interface to a serial line or bus.
2. A serial interface is a data channel that transfers digital data serially; it is typically implemented as a card that plug into an expansion slot on a computer motherboard. Serial interfaces have multiple lines, but only one is used for data (two must be used for full duplex communication).
3. An external serial bus carries serial data to any device connected to it, e.g. Ethernet.
2. Parallel transmission communicates bits simultaneously over multiple lines; typically the total consists of one or more bytes at a time.  In a manner simialr to serial hardware, a parallel port connects a parallel interface to an exteranal parallel bus.
1. Computers are typically connected to printers and external disk drives via parallel interfaces, ports, and busses (which are analogous to their serial counterparts).
2. SCSI (pronounced "scuzzy"), which stands for Small Computer System Interface, is an example of an external parallel bus; standard SCSI has an 8-bit path and fast SCSI has a 16-bit path.

2.3 Transmission Techniques:

1. Baseband transmission is a communications technique in which digital signals are placed onto the transmission line without change in modulation. In baseband, the full bandwidth of the channel is used and simultaneous transmission of multiple sets of data is accomplished by interleaving pulses using TDM (time division multiplexing).
1. It is usually limited to a few miles and does not require the complex modems used in broadband transmission (See below.)
2. Common baseband LAN techniques are token passing (e.g. Token Ring) and Ethernet.
2. Broadband transmission is a communications technique for sending multimedia over long distances. It propagates data, voice, and video simultaneously by modulating each signal onto a different frequency using FDM (frequency division multiplexing), the same technique used in cable TV.
1. Broadband uses high frequency transmission over coaxial or fiber optic cables.
2. Broadband transmission requires modems to superimpose data onto __________(5) carrier signals.

3. Multiplicity in transmission governs the number of people involved in a network communication session. The following terms have been defined (and are comming into popular use) in order to distinguish types of communication according to the number and location of receivers of an Internet communication. The new Internet Protocol version 6 (IPv6) supports the packet types for the following categories of multiplicity.  See the excellent illustration FIGURE C&N-5.1, from Byte Magazine, for the pros and cons of the following concepts; the article from which this comes may be accessed at http://www.byte.com/art/9706/sec6/art6.htm.
1. Unicast is network communication between a single sender and a single receiver. . An earlier term, point-to-point communication, is similar in meaning to unicast.
2. Anycast, first defined in IPv6, is network communication between a single sender and the nearest of several receivers of a group.   It is designed to allow a single to host initiate the efficient updating of routing tables for a group of hosts. IPv6 can determine which gateway host is closest and sends the packets to that host as though it were a unicast communication. In turn, that host can anycast to another host in the group until all routing tables are updated.
3. Multicast specifies simultaneously network communication between a single sender and a selected group of receivers.
1. Typical one-to-many examples of multicast is sending an e-mail message to a mailing list or the periodic publication of an online newsletter; teleconferencing and videoconferencing also use multicasting, but require more sophisitcated protocols (like IPv6).
2. Multicast is also used for programming on the Mbone, a system that allows users at high-bandwidth points on the Internet to receive live video and audio . In addition to using a specific high-bandwidth subset of the Internet, Mbone multicast also uses a protocol that allows signals to be encapsulated as TCP/IP packets when passing through parts of the Internet that can not handle the multicast protocol directly.
3. The terms multicast and narrowcast are often used interchangeably, although narrowcast usually refers to the business model whereas multicast refers to the actual technology used to transmit the data.
4. broadcast means to simultaneously send the same message to multiple receivers. Broadcasting is a useful feature in e-mail systems. It is also supported by some fax systems.
5. "datacast" is a new term I first saw on a C|NET TV broadcast about Digital TV.  This refers to computer data that can be downloaded simultaneously with a TV broadcast.  This data can then be processed locally, perhaps by the new DTVs, thus supplementing the broadcast, e.g. up-to-date statistics can be maintained for a sports broadcast.  I suppose this new word will soon become part of our Cyberspace broadcast.

2.4 Digital Signal Classifications and Speeds:

1. DS, a classification of digital circuits used in North America, technically refers to the rate and format of a digital signal. (The "T" designation refers to the equipment carrying such signals; see section 4, below. In practice "DS" and "T" are used synonymously; for example DS1 and T1 or DS3 and T3.)
2. OC (Optical Carrier) speed is a fiber optics classification system that is based on multiples of 51.84 Mbps (OC1) , eg. OC48 = 48 * 51.84 = 2488.3 Mbps, up to a current maximum of 48 Gbps.
3. The table below compares commonly used digital signal classification in the U.S.A. and Europe.

1. A modem (MODulate-DEModulate) is device that superimposed a digital signal on an analog carrier wave (modulates) as well reverses this procedure (demodulates). It is the interface between a computer and a __________(6)communication channel, e.g. __________(7). Modern modems utilize more complex technology so the term "modem" is a bit of a misnomer; however, it will probably always be used to describe a wide varity of equipment used to connect PCs to the the Internet, e.g. the "cable modem".
1. The modem also dials the line, answers the call and controls transmission speed which ranges from .3 to 56 Kbps; the modem can adjust to the optimum speed depending on the communications channel.
2. A Fax/Modem, which includes partial fax capability (See section 3.F, below.), can send a document that is in RAM to any standard fax machine where the document is printed on paper. Fax/Modems can receive fax transmissions which can be viewed on the monitor or printed.
3. A modem requires communication software that allows you enter the settings required to establish communications with other computers. (See section 5, below.)

1. A codec (CODe-DECode) is a device that digitizes an analog signal (code it) and can reproduce (decode) analog signals from those that have been digitized. A codec is the opposite of a __________(8). (Note: this definition specific to computer communications; "codec" has other definitions, even within computer science.)
2. Multiplexers allow several communications to share the same communications channel by interleaving the signals.There are two common multiplexing techniques:
1. FDM (__________(9) dependent multiplexing) which separates signals by modulating the data onto different carrier frequencies, and
2. TDM(__________(10) dependent multiplexing) which separates signals by interleaving the bits of different signals.
3. Controllers supervise data transfer between the CPU and terminals on a multiuser system.
4. Concentrators perform the functions of both controllers and multiplexers among the things.
5. Fax (facsimile machine) transmits images (text, pictures, etc.) over telephone wires.
6. Network hardware (See Network Components, section 7.1, below.)

4.1. Electronic Cables transmit data, via electrons, through copper wires:

1. Twisted pair wiring (See Figure C&N -6) is the typical telephone cable. The wires are twisted around each other to minimize interference from other twisted pairs bundled in a cable. Twisted pairs have less bandwidth than coaxial cable or optical fiber.
2. Coaxial cable (See Figure C&N -7) is more expensive than twisted pairs but is stronger and provides more interference protection, i.e. it inhibits "crosstalk". The cable has a solid central conductor surrounded by insulating material and then by a cylindrical shield woven from fine wires. The shield is usually connected to electrical ground to reduce electrical interference.
1. Coaxial cable typically has a bandwidth of100 megahertz or 10Mbps (See Figure C&N-4B.)
2. Ethernet is a standard coaxial cable LAN technology. The typical current bandwidth is 10 Mbps, but the new "Fast Ethernet" has a bandwidth of 100 Mbps and "Gigabit Ethernet" is coming.
3. Cable television (CATV) cables are coaxial cables that have a high capacity bandwidth. They were designed to carry the huge signals that analog TV requires to deliver full-color, full-motion, stereo-sound broadcasts. Currently, transmission is simplex, i.e. there is no signal from your TV back to the cable company (Pay-per-View utilizes your phone lines for feedback to the cable company). However to use CATV for data communication (e.g. to connect to the Internet), full duplex communication is necessary.
1. To facilitate this a cable modem (also called a cable adapter) will be used.  These are relatively new devices and will probably have many different implementations.   In fact, cable modems can be part modem, part tuner, part encryption/decryption device, part bridge, part router, part NIC card, part SNMP agent, and part ethernet hub.  (See Figure C&N-11.)
2. In theory, each TV channel (6 Mhz NTSCband) can carry:
1. one analog video channel
2. five digital video channels
3. one 30 Mbps data stream shared by cable modems. ("Shared" means that actual bandwidth will decrease with the number of users of a common communications channel.)
4. 384 digitized voice conversations.
3. Digital lines are designed to transport digital signals directly, i.e. without having to modulate an analog carrier signal.  They are sometimes referred to as last-mile technologies because they are used only for connections from a telephone switching station to a home or office, not between switching stations.  Digital lines allow the phone company to provide a much wider bandwidth than POTS for transmitting data. Also the signal can be separated so that telephone conversations and computer data can be transmitted simultaneously on the same line.  Digital lines offer more than a bandwidth advatage over POTS in that they can  transmit voice, text, and video as well as computer data.    On the other hand, current disadvantage is that all implementations have a limited maximum distance to the telephone office (< 20,000 ft.)  There are currently two types of digital lines:
1. ISDN (Integrated Services Digital Network) is a circuit-switched, dial-up service for transmitting digital data via a single wire or fiber optics cable. This transmission is completely digital,  It uses  64Kbps bearer channels (B channels) to carry the data and a separate data channel (D channel) for control signals which allows for features such as call forwarding, c all waiting, and advice of charge. Basic Rate service (BRI) provides two B channels (which can be combined to provide 128 Kbps bandwidth) and one 16 Kbps D channel; Primary Rate Service (PRI) in North America provides 23 B channels and one 64 Kbps D channel, equivalent to T1 (See Section 2.4, below.).
2. Digital Subscriber Lines (DSL), an improvement on ISDN,  is also a technology for transmitting high-bandwidth, totally digital data over POTS between end-users and telephone companies.  Unlike ISDN,  DSL is a dedicated point-to-point technology that provides a much higher bandwidth (a practical maximum of over 6 Mbps for current technologies and up to 52 Mbps in the future).  Without doubt, DSL technologies will compete with cable modems for the future last-mile technology; the jury is out.   (See Figure C&N-11.)
1. Because DSL uses packet switching technology that operates independent of the voice telephone system, DSL is  not as well suited to videoconferencing as is ISDN.  ISDN is circuit switched, which keeps the line open and  connected throughout the session.
2. xDSL refers to different variations of DSL that can be categorized under two headings:
1. ADSL (Asymmetrical DSL) technologies prove much higher bandwidth for downloads than for uploads, e.g. 1.5-8 Mbps downloading and .064-1.0 Mbps uploading.
2. Symetric DSL provides the same bandwidth for both uploads and downloads.
3. For more detailed information see About.com's DSL Crib Sheet.
   
3. To read how DSL works or get the details of the different types of xDSL see the excellent article In WhatIs.  To find additional info on DSL and determine whether or not you can receive this service in your area go to 2Wire.com.

1. Fiber optics cables transmit data via concentrated bursts of laser beams which are carried through bundles of hair-thin glass fibers. (See Figure C&N-8.) They have advantages over electronic cables in transmission speed as well as volume. This technology promises to revolutionize telecommunication applications which has used electronic cables.
2. They also minimize interference (because light is not affected by electrical and magnetic fields) and inhibit wire tapping, two critical problems with electronic cable communications.

4.3 Relative Transmission Speeds (Bandwidths):

         The speeds of network traffic vary greatly depending on the components of the network; the network is only as fast as its slowest component (often called a "bottleneck").  The relative speeds depend on both the type of media and type of equipment used.  The relative speeds of current and near-future Internet access technologies are summarized in Figure C&n-11.  (Note that these are theoretical maximum speeds; actual speeds can be considrably less (e.g. cable modems share bandwidth, so transmission speed depends on the number of users)

5. COMMUNICATION SOFTWARE:

1. Communication software controls a computer’s access to system resources and stored data.
2. A communications program manages the transmission of data, in its most basic form, between a computer and another computer or network; it is not needed for data transfers between a computer and its __________(11) devices, which is governed by __________(12) drivers (although these could be classified as communications software).
1. In PCs it manages transmission to and from the computer’s serial port.
2. In multiuser systems (________________(13) and __________(14) with terminals) and networks the communications programs are called "access methods", "network control programs", and "TP monitors".
3. A communications application performs a specific communications service or, in the case of Browsers (often improperly called "Web browsers") several communications services. These include:
1. _____________(15) services, e.g. e-mail, ______(16), ________________(17), and _____(18).
2. _________(19) access, e.g. file transfer (downloading or uploading) and remote _____(20).
3. __________ __________(21) , e.g. Web _________(22), searching, etc.

4. Other types of communication software:
1. Terminal Emulation is the ability of a microcomputer to assume the characteristics of a certain type of mini or mainframe terminal; this is accomplished by software.
2. Data-encryption techniques may be used to scramble data for greater transmission security .

See Learning Module IV, a survey of TCP/IP and the OSI Model of Communications.




1. Communications protocols are sets of hardware and software standards (rules and procedures) that govern the communications (transmission of data ) between two or more computer devices. Protocols govern format, timing, sequencing, and  error control. Without these rules, the computer cannot make sense of the stream of incoming bits. Therefore, two different computer systems can communicate only if they use the same communications protocol. Protocols specify:
1. how the communications link is established (including intermediate connections),
2. how data is transmitted, and
3. how errors are detected and corrected
2. There are, currently, three basic categories of protocols:
1. Basic protocols specify whether communication is synchronous or asynchronous, govern error detection and correction ("parity"), etc.
2. Modem protocols: On PCs communications programs offer a variety of protocols (e.g. Kermit, Xmodem, Ymodem, Zmodem, etc.) that facilitate transfer of files via modem and SLIP and PPP which facilitate modem connections to the Internet.
3. Network protocols:
1. WAN protocols govern communications of complex distributed systems involving disparate architectures, operating systems, and applications, e.g. TCP/IP, the protocol (actually ________(23) of protocols), of the Internet. Note that there is often much overlap of LAN and WAN protocols, e.g. TCP/IP is used in intranets (corporate networks) as well as the Internet; on the other hand, Ethernet is not applicable to WANs.
2. LAN protocols are simpler than WAN protocols because the do not involve different kinds of networks and thus do not have to govern complex gateways or routers; see section 7.1.B, below. On LANs, data link protocols such as Ethernet, Token Ring, and FDDI provide the access method to the Internet.
3. The OSI model is the standard with which networks are analyzed and developed. It has seven layers, each with a specific translation task that is needed to transmit data between to different nodes (computers) of a network.

       Theoretically a network is simply a collection of linked "nodes", the components of the network. In communications, a network consists of the transmission channels, clients, servers as well as all supporting hardware and software. Collectively the client sees the network as a collection of resources and services. Networks provide the infrastructure for a distributed computing environment with its client/server processing model. This is the origin of the futuristic statement, by Sun Microsystems, "The network IS the computer".

NOTE: A more detailed treatment of the following material can be found in the networking "primer" from Bay Networks at http://www.baynetworks.com/products/Papers/wp-primer.html.  This is NOT required reading, but may amplify the your understanding the following complex concepts.

SAQ 9: Explain what is meant by the current buzzwords ,"The network is the computer".

7.1 Network Components ("Nodes") :

1. End nodes:
1. A terminal is any end point of the network, e.g. a user station, printer, disk drive, etc. A ______(24)is a terminal that uses client/server software to share the resources of the network which are managed by a __________(25).
2. A server is a device that connects a peripheral to a network and allows other network nodes to share it. Examples include file servers, print servers, database servers, etc.
3. A host computer is multiuser computer that coordinates terminals connected to it. It is the host that is connected to a network thus enabling its terminals to communicate with other nodes.
2. Connection hardware:
1. Multiplexers (MUX) allow several communications to share the same communications channel by interleaving the signals. See illustration.  There are two common multiplexing techniques:
1. FDM (__________(24) dependent multiplexing) which separates signals by modulating the data onto different carrier frequencies, and
2. TDM(__________(25) dependent multiplexing) which separates signals by interleaving the bits of different signals.
2. A hub is a device that connects several network nodes together.  Devices on a hub-based network share the total bandwidth.  Compare with the switch.
3. A switch is a device that allows a non-shared connection between two network devices to be selected.  The network software can select one of several links between two network nodes. (Compare with a hub.) A switch with added functionality becomes a router or gateway. (See below.)
3. Intermediate nodes (not end nodes, but nodes that are within a network):
1. A repeater is a device which propagates electrical signals betweem remote network devices.  It is used to regenerate an analog or digital signals distorted by transmission loss.  Analog repeaters typically only amplify  the signal, but digital repeaters can reconstruct a signal almost to its original quality.  Repeaters are less intelligent than a bridge, router, or gateway (See below) which are successively more sophisticated.
2. A bridge is an interface linking two similar LANs located in different buildings.
3. A router is a computer system in a network that stores and forwards data packets between LANs and WANs. They see the network as network addresses and all the possible paths between them. They read the network address in a transmitted message and can make a decision on how to send it based on the most expedient rout (taking into account traffic load, line costs, speed, bad lines, etc.)
4. A gateway is an interface device (computer) that provides the translations necessary to link two different types of networks.
4. A firewall is a node set up as a betwork boundary that controls access to that network in order to maintain its security.
5. Communication hardware (See Section 4.1, above.)

7.2 Generic Network Organizations

3. topology, the pattern of a network:
1. In a star network all hardware is connected to a central unit which controls all communication.
2. In a bus network all hardware is interfaced to a common bus; anything placed on the bus may be accessed by any terminal.
3. In a ring network each hardware device is connected to two neighbor forming a communications circle.
4. In a hierarchical (also called hybrid) network two or more networks using preceding topologies may be linked to form a larger network.  For example a ring of hubs can form thecenter of a star network.
4. Network access methods:
1. Polling is a technique in which the central controller sequentially asks each network device if it wishes to transmit. It is primarily used on the __________(26) network.  Polling is the least costly access method since "intelligence" need reside only in the network controller; it also has limited growth potential due to its high overhead.
2. In the token technique, a network node may only transmit if there is an available software "data container" that is circulated through the network.  It is primarily used with __________(27) networks.  A simplified description of the process is as follows:
1. Empty data containers are continuously circulated on the network.
2. When a node transmits a message, it inserts, into the empty container, a token (perhaps as simple as switching a single bit) the message, and the network address of the destination .
3. The data container is then examined by each network node. The desitnation node recognizes its identifier and copies the message and resets the token back to its original state.
4. When the container returns to the sender, it sees that the token has been reset and that the message has been received. The sender then removes the message from the container.
5. The container continues to circulate the network available for the next transmission.
Actually the token passing technique can be used with star and bus technologies as well.
3. In the contention technique any device may transmit at any time that the network is idle, i.e. it is first come first served unless their is a priority system imposed. It is primarily used with __________(28) networks.  The contention ;method provides the most flexibility, but has less capacity than token passing.
5. Comparative utility of different topologies:
1. The bus network provides the most flexibility, capacity, and growth potential.
2. The ring topology occupies the middle ground on all network evaluation criteria. It is more fair than the bus topology because it ensures that all users get regular turns at transmitting their data.  With a bus, all users compete to get onto the network.
3. The star network is the least costly and least sophisticated because all networking facilities reside on a single, central computer.

8.  NETWORK TECHNOLOGIES:

        In section 7 we discussed theoretical models of generic computer networks.  In this section we will consider actual technologies in use today; we will focus on some of the most popular technologies that are currently employed as well as projections for the future.  These can be classified either as LAN technologies or WAN technologies. The chronological evolution of networking technologies is graphically illustrated in Figure C&N-10 from PC Magazine, March 1997.

8.1 LAN Technologies:

1. Ethernet is a bus technology that has several varieties, including:
1. Twisted-pair Ethernet, currently the most commonly used LAN technology, utilizeshubs to connect network devices.  In this technology, all network nodes of a segment share the total bandwidth, which can be 10  Mbps (10BASE-T Ethernet), 100 Mbps (100BASE-T10 Fast Ethernet) or 1000 Mbps  (Gigabit Ethernet).   10BaseT uses standard RJ-45 connectors and inexpensive telephone wiring (thus being able to use existing wires in a building); it is configured in a star topology with the hub as its center.
1. 10BASE-T Ethernet is typically used to connect LANs to backbones that implement Fast or Gigabit Ethernet.
2. Since twisted-pair Ethernet is a bus technology, network access is managed via contention;in particular it uses a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol.
3. Normally twisted-pair Ethernet utilizes special grades of twisted pair lines, but coaxial cable can also be used.
4. Computers are typically connected to an Ethernet network using Ethernet cards that plug into expansion slots.
2. Switched Ethernet manage network connections via a switch  (rather than the _____(29) used with standard Ethernet).  With switch technology each connection has the full bandwidth of the network, instead of having to share it as in Twisted-pair Ethernet.
3. Fiber Optic Ethernet (10BaseF) provides all the advantages of fiber optics.Since it is uaffected by electrical interference so it is often used to extend Ethernet segments over long distances (up to 1.2 miles without a repeater). Specifications exist for complete fiber optic networks as well as backbone implementations.
2. Token Ring networks, that implement the token passing technique described in section 7.2.B.b, are avaiable in two types.
1. Type 1 Token Ring networks allow up to 255 nodes per segment.   Since they use shielded twisted pair wires with IBM style Type 1 connectors they are often called IBM token rings.
2. Type 3 Token Rings allow up to 72 nodess per segment; they use unshielded twisted pair wiring with RJ-45 connectors.
3. Fiber Distributed Data Interface (FDDI) is a standard data transmission architecture for fiber optic LANs that is based on a dual token ring technology; it can support thousands of users. (There is a copper cable based equivalent called CDDI.)
1. The "dual" designation means that such networks contains two token rings;this facilitates fault tolerance because the secondary ring can take over network management if the primary ring fails.The primary ring has a bandwidth of 100 Mbps, but, if the secondary ring is not being used for fault tolerance, it can be utilized, doubling the transmission capacity. However, the dual ring has half the range (64 miles instead of 124 miles) of the primary ring.
2. FDDI can be used to interconnect LANs that are based on different protocols.
4. ATM (Asychoronous Transfer Mode) is a dedicated-connection switching technology, available for LANs as well as WANs, that supports realtime voice and video as well as data.
   
1. ATM is a special case of cell relay, a method of statistically multiplexing fixed-length cells (53 byte data packets) in order to transmit them over networks  via digital signal technology. Individually, a packet is processed asynchronously relative to other related packets and is queued before being multiplexed over the transmission channel.  For more details see Cell Relay in Wikipedia.
2. (From Wikipedia) ATM is most commonly used for home DSL connections, which often runs between 128 kbit/s and 1.544 Mbit/s (DS1), and for high-speed backbone connections (OC-3 and faster).
3. For more details see Asynchronous Transfer Mode in Wikipedia.
4. ATM network architectures utilize a switching technology to establish a dedicated point-to-point circuit; thus guaranteeing quality of service (QOS) which is essential to realtime voice and video transmission.
5. Unlike telephone switching technology, ATM appropriates unused bandwidth, e.g. idle bandwidth in a videoconference circuit can be used to transfer data.
6. ATM is implemented in hardware (rather than software), thus providing scalable high bandwidths of 1.5, 25, 100, 155, 622 and 2488 Mbps with 10 Gbps projected in the near future.
7. ATM based networks are easily modified because when a new switch is added, the network is automatically updated usingATM's PNNI routing protocol.
8. ATM is a key component of broadband ISDN (BISDN) and DSL.

1. Unswitched technologies: The T-carrier system is entirely digital, using pulse code modulation and TDM (time-division multiplexing). It uses four wires and provides full-duplex capability (two wires for receiving and two for sending at the same time). The four wires were originally a pair of twisted-pair copper wires, but can now also include coaxial cable, optical fiber, digital microwave, and other media. A number of variations on the number and use of channels are possible.
1. The T-1 digital stream consists of 24 64-Kbps multiplexed channels that are multiplexed plus 8,000 signalling bits give a maximum throughput of ______(30) Mbps.
2. The T-3 line, providing ______(31) Mbps, is commonly leased by ISPs to connect to the Internet.
3. Fractional T-carrier systems provide less than full bandwidth.  Fractional T-1 provides increments of 64 Kbps and fractiona T-3 provides increments of 3 Mbps.
2. Switched sevrices:
1. Modem dial-up is the least sophisticated but most common service.
2. X.25 is an old packet switching service designed for transmitting analog signals such as voice conversations.
3. ISDN (See section 2.1.C.a. )
4. Frame relay is a new technology designed for cost-efficient packet switching of intermittent transmissions.   It is optimized for WANs at bandwidths between .065-45 Mbps, thus providing a mid-range service between ISDN (128 Kbps) and ATM (up to __________(32) Mbps).  The name is derived from the fact that data is compartmentalized in variable-sized  "frames" (of up to thousands of bytes) that are "relayed" through WAN routers at high speeds.
1. Frame relay is associated with the data-link layer of the OSI model, which is explained in LM IV, AN OVERVIEW OF TCP/IP, PROTOCOLS, and the OSI MODEL.
2. Normally a Frame relay provides a permanent virtual circuit (PVC), which appears, to the network user, as a continous, dedicated connection. (It requires a dedicated connection throughout the transmission period.) Thus frame relay is a cost efficient alternative to a full-time leased line.
3. Because frame relay is a fast-packet technology, it does not attempt to correct errors.When an error is detected (a rare occurance), the frame in which it occurs, is simply dropped. The receiver is responsible for notifying the sender to retransmit that dropped frame.
4. Frame relay allows relative priorities to be assigned to frames.
5. Frame relay is often used to connect LANs to backbones, WANs, or T-1 lines. .
6. Because Frame relay is a packet-switching, frame dropping technology, it is not suited for realtime voice or video transmission.
7. A frame can incapsulate packets from different protocols such as Ethernet, X.25, etc.
8. For more details see Frame Relay in Wikipedia.
5. SMDS (Switched Multimegabit Data Service) is a new, public, packet-switching technology,offered by the local telephone companies, for interconnecting LANs.  It is specifically designed for large bandwidth connections via a WAN using "bursty" (not continuous) transmissions, typical of LANs.  Thus SMDS extends the facilities of a local LAN to include those of an external WAN providing bandwidth on demand. It was introduced in 1992 and became generally available nationwide by 1995.
1. SMDS is connectionless, i.e. it is unnecessary to establish a complete network connection before sending data.
2. Since SMDS is a public service, any SMDS customer can exchange data with any other customer.
6. ATM (See section 8.1.D.) for WANs is the same technology as that for LANs; it is similar to (but faster than) __________(33).

9.  INTERNET CONNCECTIONS:

1. There are two basic access methods that allow users to connect to the Internet..
1. Dial-up connections require accounts with an ISP who provides an on-demand connection to the Internet.  Modem connections, using SLIP or PPP, are the most commonly used, but cable modem and DSL connections are rapidly replacing modem access via POTS.  Access via Online Services fall into this category because the Online Service is actually the ISP even though it typically provides other services in addition to Internet connection.
1. advantages: free or minimal cost access; simple configuration via software.
2. disadvantages: relatively slow, temporary connections to the Internet.
2. LAN-based connections, like those of FSU dorms, corporation intranets, etc., provide permanent, fast access to an enterprise intranets as well as the Internet.  Network adapters, e.g. Ethernet cards, connect a PC to a LAN running TCP/IP; this LAN is typically linked to the Internet via a T1 line. .
1. advantages: high bandwidth connections that are permanent
2. disadvantages: too expensive for home implementation; requires some expertise (but not much) to install.
Older technologies like Unix Shell Connections (which do not handle multimedia) are being superceeded by LAN-based connections.
2. Private networks can restrict access to their networks.
1. Intranets are private networks that are restricted to users inside an enterprise; firewalls allow insiders to access the Internet while controlling outside access to the facilities of the private network.
2. Extranets are private networks that are restricted to outside organizations that are associated with an enterprise, e.g. people and corporations that do business with the enterprise like customers, suppliers, etc.

• "Communications" is a general word for the transmission of signals between two or more points.

1. "Data communications" refers to computer data.
2. "Telecommunications" pertains to transmissions over a distance in one of two forms:
1. electronic transmission (via electrons) occurs through physical media such as wires and
2. electromagnetic wave transmission (via laser, radio, TV, microwave, etc.) requires no media, except in the case of fiber optics in which light carries data through cables.
3. Networking links computers so they can communicate, as well as share hardware and software, thus uniting processing power. This leads to the goal of distributed computing, which is the optimum spread of computing resources among users.
1. DATA COMMUNICATIONS, AN OVERVIEW:
1. Types of transmission signals (See Figure C&N-3.):
1. An analog signal is a continuous wave pattern that varied in frequency or amplitude to convey data. Most "real-world" data has an analog format.
2. A digital signal is a pattern of discrete high or low amplitude pulses that represents binary data and are therefore used to transmit computer data.
2. A carrier signal is a base signal for transporting data, superimposed on the carrier signal by modulation (altering) the carrier signal.  The most basic forms include Amplitude modulation (AM), Frequency modulation (FM), and Phase modulation (PM).  (Figure C&N-3 illustrates the AM and FM concepts)
1. Transmission channels include simplex, half-duplex, and full-duplex
2. Transmission parameters:
1. The transmission speed is the amount of data transmitted per unit time, e.g. bits per second, bps.
2. TRANSMISSION CHARACTERISTICS:
1.  Wired vs. wireless communication:
1. Analog lines, e.g. "plane ol’ telephone service" ("POTS") which carry analog signals via electrons.  To transmit data, the digital data must be superimposed, by a modem, on the telephone's analog carrier signal.
2. Digital Lines carry digital signals and thus avoid the analog/digital conversions necessary for digital transmission over POTS.  There are currently two types of digital lines:
1. ISDN (Integrated Services Digital Network) is a circuit-switched, dial-up service for transmitting digital data via a single wire or fiber optics cable.   Basic Rate service (BRI) can provide 128 Kbps bandwidth); Primary Rate Service (PRI) can provide 1.5 Mbps, equivalent to T1 transmissions.
2. Digital Subscriber Lines (DSL) also transmits completely digital data over POTS.  It is a dedicated point-to-point technology that provides a practical maximum of over 6 Mbps using current technologies and up to 52 Mbps in the future.
3. Wireless communication typically uses microwaves (electromagnetic waves with frequencies between Radio/TV and light; see Figure C&N - 4A.) or radio waves to provide high-capacity transmission (over 3 million bps) over line-of-sight channels.
2. Serial vs. Parallel transmission:
1. Serial transmission sends one bit at a time over a single wire.
1. A serial port is plug that links the serial interface card to a serial line or bus.
2. A serial interface is a card that plugs into an expansion slot on a computer motherboard that sequences data for transmission, via the serial port, to peripheral devices.
3. An external serial bus carries serial data to any device connected to it, e.g. Ethernet.
2. Parallel transmission communicates bits simultaneously over multiple lines; a parallel port connects a parallel interface to an external parallel bus. SCSI (Small Computer System Interface) is an example of an external parallel bus; standard SCSI has an 8-bit path and fast SCSI has a 16-bit path.
3. Transmission Techniques: *See FIGURE C&N-5 for a comparison of Baseband and Broadband
1. Baseband transmission provides digital transmission without change in modulation; simultaneous transmission of multiple sets of data is accomplished by interleaving pulses using TDM (time division multiplexing).
2. Broadband transmission is used to send multimedia over long distances. It modulates data, voice, and video onto a different frequencies using FDM (frequency division multiplexing).
3. Multiplicity governs the number of people involved in a network communication session.  There are five categories: Unicast (1 to 1), .Anycast (to the nearest of several receivers),  Multicast (to a selected group of receivers), Broadcast  (to multiple receivers), and Datacast (allows computer data to transmitted simultaneously with a TV broadcast).
5. Digital Signal Classifications and Speeds:
1. DS is a data transmission classification system based on multiples of 64 Kbps.
2. OC (Optical Carrier) speed is a fiber optics classification system that is based on multiples of 51.84 Mbps.
3. COMMUNICATION HARDWARE:
1. A modem is a device that transmits digital data over an analog channel by modulating the analog carrier signal.
1. A codec transmits analog data over a digital channel.
2. Multiplexers interleaves multiple communications so that can share a single communications channel. The two common multiplexing techniques are FDM and TDM.
3. Controllers supervise data transfer between the CPU and terminals on a multiuser system.
4. Concentrators perform the functions of both controllers and multiplexers among the things.
5. Fax (facsimile machine) transmits images (text, pictures, etc.) over telephone wires.
4. COMMUNICATION MEDIA :
1. Electronic Cables transmit data, via electrons, through copper wires. These include Twisted pair wiring, Coaxial cable, and Cable television (CATV) cables which can be used with cable modems to rival  DSL technology for the future of high bandwidth data transmission for the general public.
2. Fiber Optics Cables transmit data, via light, through glass wire bundles; they outperform electronic cables in transmission speed, bandwidth, interference avoidance, and inhibition of wire tapping.
3. The  network is only as fast as its slowest component (often called a "bottleneck").  The relative speeds depend on both the type of media and type of equipment used.
5. Communication software controls a computer’s access to system resources and stored data.
1. A communications program manages the transmission of data, between a computer and another computer or network

A communications application performs a specific communications service or, in the case of Browsers, several communications services.
1. Other types of communication software include Terminal Emulation and Data-encryption.
6. COMMUNICATIONS PROTOCOLS (a preview of LM IV):
1. Communications protocols are standards  that govern the communications between computing devices.
2. There are, currently, three basic categories of protocols:
1. Basic protocols are either synchronous or asynchronous and govern error detection and correction ("parity"), etc.
2. Modem protocols govern transfer of files via modem.
3. Network protocols include WAN protocols (communications within complex distributed systems) and LAN protocols.
3. The OSI model is a standard, seven layer, network model.
7. GENERIC NETWORK ARCHITECTURE  is  a collection of linked "nodes" that form channels, clients, servers and supporting hardware/software. They provide the infrastructure for a distributed computing environment with its client/server processing model. This is the essence of the provocative statement,  "The network IS the computer".
1. Network Components ("Nodes") :
1. A terminal is any end point of the network.
2. A server is a computer that provides network services.
3. A host computer coordinates terminals connected to it.
4. A hub connects several network nodes together, sharing the total bandwidth.
5. A switch allows a non-shared connection between two network devices.
6. A repeater facilitates data transfer between distant devices by regenerating an attenuated or distorted signal.
7. A bridge is an interface linking two similar networks.
8. A router is a computer manages the efficient routing of a transmission by selecting the "fastest" link to the destination.
9. A gateway is a network computer that links two different types of networks.
10. A firewall is a computer that controls access to a private network in order to maintain security.
2. Basic network topologies includethe star (uses polling), bus (uses contention), ring (uses token passing), and hierarchical.
8. NETWORK TECHNOLOGIES
1. LAN Technologies:
1. Ethernet is a bus technology that comes in several varieties:  twisted-pair, switched, and fiber optic.
2. Token Ring networks implement ring technologies that are avaiable in two types: Type 1  connects up to 255 stations via shielded twisted pair wiring;  Type 3 connects up to 72 devices via unshielded twisted pair.
3. FDDI is a ring technology for fiber optics LANs that has a range of 124 miles and can support thousands of users.
4. ATM (Asychoronous Transfer Mode) is a dedicated-connection switchingtechnology available for LANs as well as WANs that provides realtime multimedia transmission.
2. WAN Technologies:
1. Unswitched technologies: The T-carrier system is entirely digital and provides full-duplex capability via coaxial cable, optical fiber, digital microwave, and other media. The most common are the T-1 line that provides 1.5 Mbps  and the T-3 line, that provides almost 45 Mbps.
2. Switched services:
1. Modem dial-up is the least sophisticated but most common service.
2. Packet Switched (X.25), an old service designed voice conversations.
3. ISDN
4. Frame relay is a new technology optimized for cost-efficient packet switching for intermittent telecommunications throughout WANs atbandwidths between .065-45 Mbps.
5. SMDS is a newpublic, connectionless, packet-switched service offered by telephone companies for interconnecting LANs in different locations, providing large bandwidth exchanges between enterprises over a WAN.
6. ATM  for WANs is the same technology as that for LANs.
9. INTERNET CONNECTIONS:
1. There are four basic Internet access methods, via modem, LAN, Online Service, or Unix Shell.
2. Private networks can restrict access to their networks.
1. Intranets are private networks that are restricted to users inside an enterprise.
2. Extranets are private networks that are restricted to outside organization that are associated with an enterprise, e.g. people and corporations that doe with the enterprise like customers, suppliers, etc.

 
 

FIGURE C&N-2: CATEGORIES OF COMMUNICATION CHANNELS

 

FIGURE C&N-3: DIGITAL VS. ANALOG

 

FIGURE C&N-4A:  BANDWIDTH & THE ELECTORMAGENTIC SPECTURM

 

FIGURE C&N-4B: BANDWIDTH AND ITS APPLICATIONS

 

FIGURE C&N-5: BASEBAND VS. BROADBAND

 

FIGURE C&N-5.1: UNICAST, BROADCAST, AND MULTICAST:

 

FIGURE C&N-6 through 8: TYPES OF COMMUNICATION MEDIA

 

FIGURE C&N-10 A & B: NETWORK COMPONENTS

 

FIGURE C&N-11: PRACTICAL COMPARISON OF INTERNET ACCESS POSSIBILITIES

 

FIGURE C&N-12:  HOW INTERNET ACCESS VIA SATELLITE WORKS

(Illustration comes from maxim PC magazine, November, 1999.)

 

FIGURE C&N-13: HOW DSL WORKS

(Illustration comes from maxim PC magazine, November, 1999.)

 

FIGURE C&N-14: HOW CABLE MODEMS WORK

(Illustration comes from maxim PC magazine, November, 1999.)