Vocab Ch. 5-9 Flashcards
1
Q
multiplexing
A
The technique or transmitting multiple signals over a single medium. Makes a connection more efficient by combining the signals from multiple sources.
2
Q
medium division methods
A
1) division of frequencies
2) division of time
3) division of transmission codes
3
Q
Frequency Division Multiplexing
A
(FDM) - The assignment of non-overlapping frequency ranges to each “user” of a medium. Signal is often analog.
Pros -
1) Simple
2) Popular with radio, TV, cable TV
3) All the receivers, such as cellular phones, do not need to be at the same location.
Cons -
1) High overhead because each slot must be allocated to one signal.
2) Uses analog signals so noise is a problem.
4
Q
channel
A
An assigned set of frequencies that is used to transmit the user’s signal.
5
Q
dynamic assigned channels
A
When the users establish a connect, the channels they use as uplink and downlink are assigned based on current network availability.
6
Q
multiplexor
A
The general term used for a device that accepts input from one or more users and transmits it over one medium.
7
Q
demultiplexor
A
Also called the second multiplexor - The general term used for a device that receives the signal and then splits off each signal to deliver it to the appropriate receiver.
8
Q
guard band
A
A set of unused frequencies between two signals that keeps one signal from interfering with another signal.
9
Q
time division multiplexing
A
(TDM) - Allows only one user to transmit at a time, and the sharing of the medium is accomplished by dividing available transmission time among users. The user used the entire bandwidth of the channel, but only for a brief moment.
10
Q
Synchronous time devision multiplexing
A
(Sync TDM) - Gives each incoming source signal a turn to be transmitted, proceeding through the sources in a round-robin fashion.
Pros -
1) digital signals so noise is less of a problem
2) relatively simple
3) commonly used with T-1, SONET
Con -
1) High overhead because each slot must be allocated to one signal.
11
Q
T-1 multiplexing
A
The output stream is divided into 24 separate digitized voice/data channels of 64kbps each. The T-1 can be allocated in full or in part. The T-1 multiplexed stream is a continuous repetition of frames.
12
Q
DS-1 signaling
A
The multiplexing technique used by T-1 telecommunications to provide multiplexing of up to 24 separate channels at a total speed of 1.544 Mbps.
13
Q
256=2^8
A
The telephone system uses 256 quantization levels to digitize the human voice into 8 bits which equals one byte.
14
Q
Synchronous Optical Network & Synchronous Digital Hierarchy
A
(SONET) & (SDH) - Powerful standards for multiplexing data streams over a single medium. They are almost identical standards and for the high-bandwidth transmission of a wide range of data types over fiber-optic cable.
15
Q
synchronous transport signals
A
(STS) - A hierarchy of signaling levels, or data transmission rates. Each STS level supports a particular data rate and is supported by a physical specification called an optical carrier (OC). Note: The data rate of an OC-3 is exactly three times that of an OC-1. Often used by Internet Backbone providers.
16
Q
statistical time division multiplexing
A
(Stat TDM) - Transmits data only for active users and does not transmit empty time slots. The system used a complex frame that contains data only from those input sources that have something to send.
Pros -
1) More efficient use of bandwidth.
2) Frame can contain control and error information
3) packets can be of varying size
Cons -
1) Increase complexity over TDM, so increased initial cost that is often made up due to decrease operational costs.
17
Q
fiber exhaust
A
The inability of a single fiber-optic line to meet a user’s needs.
18
Q
wavelength division multiplexing
A
(WDM) - multiplexes multiple data streams onto a single fiber-optic line. It uses different wavelength (frequency) lasers to transmit multiple signals at the same time over a single medium. Pros - 1) good for transmitting multiple concurrent signals over a fiber-optic line. 2) Signals can have varying speeds 3) Scalable Cons - 1) Equipment is costly. 2) Complexity
19
Q
lambda
A
The wavelengths of each differently colored laser in a WDM multiplexor.
20
Q
dense wavelength division multiplexing
A
(DWDM) - When a WDM multiplexor can support large numbers of lambdas.
21
Q
coarse wavelength division multiplexing
A
(CWDM) - a less expensive variation of WDM that is designed for short-distance connections and has only a few lambdas.
22
Q
discrete multitone
A
(DMT) - a multiplexing techinique commonly found in DSL systems. It combines hundreds different signals, or sub channels, into one stream; unlike the other multiplexing streams, however, DMT is designed such that all these sub channels are destined for a single user. Each sub channel can perform its own quadrature amplitude modulation (QAM). Pros 1) High speeds Cons - 1) Costly 2) Complex 3) Suffers greatly from too much noise.
23
Q
code division multiplexing
A
(CDM) - A relatively new technology that has been used extensively by both the military and cellular telephone companies. Allows multiple users to share a common set of frequencies by assigning a unique digital code to each user. Based on a class of modulation techniques known as spread spectrum technology. Pros - 1) Large capacities 2) Scalable Cons - 1) Complexity
24
Q
spread spectrum technology
A
A technique used in the communications industry for modulating a signal into a new signal that is more secure and thus more resistant to wiretapping. Falls into two categories:
1) frequency hoping
2) direct sequence
25
chip spreading codes
The binary code, 64 bits in length, assigned to each cell phone on the cellular network so that the network can determine what data is sent by which device.
26
compression
The process of taking data and somehow packing more of it into the same space. whether this is in the form of a storage device such as a hard drive, or a medium such as a fiber-optic line.
27
compression categories
1) lossless compression
| 2) lossy compression
28
lossless compression
No data is lost due to compression. Usually relies on repetitive strings of 1s and 0s.
29
lossy compression
Some data is lost during the process of compression and decompression. Usually, the lost data is data that is designated as less important. Example, frequencies of sound in a song that most humans can not hear.
30
run-lenght encoding
Replaces any repetitions of the same bit or byte that occur in a sequence of data with a single occurrence of the bit/byte and a run count, or simply with a run count.
31
perceptual encoding
Also know as perceptual noise shaping. The process where audio engineers remove the sounds that are at the edge of the normal hearing range.
32
differential encoding
Used in video encoding (MPEG) where only the differences between frames is encoded.
33
error-contol options
1) Ignore the error
2) Return an error message to the transmitter (request the packet again)
3) Correct the error without help from the transmitter.
34
white noise
Also called thermal noise or Gaussian noise, is a relatively continuous type of noise and is much like the static you hear when a radio is being tuned between two stations. It is always present to some degree and is dependent on the temperature of the medium. Because it is relatively continuous, it can be reduced significantly but never completely eliminated. Easier to remove from digital signals.
35
impulse noise
Noise spike, is a noncontinuous noise and one of the most difficult errors to detect because it can occur randomly and it is difficult to separate the noise from the signal. Easier to remove from digital signals but at times the impulse can overwhelm the digital signal.
36
error effect of transmission speed
The higher the transmission speed, the more difficult it is to detect and correct for noise.
37
crosstalk
An unwanted coupling between two different signal paths.Caused when the signal from one wire leaks into another. Can be reduced by twisted pair and shielding.
38
echo
The reflective feedback of a transmitted signal as the signal moves through the medium. The signal will hit the end of a cable, bounce back, and interfere with the original signal. Often found in coaxial systems without endpoint filters.
39
jitter
The result of small timing irregularities that become magnified during the transmission of digital signals as the signals pass from one device to another. Often seen as flickering video in video systems.
40
attenuation
The continuous loss of a signal's strength as it travels through a medium.
41
white noise prevention
Install special filters for analog signals; implement digital signal regeneration for digital signals.
42
impulse noise prevention
Install special filters for analog signals; implement digital signal processing for digital signals.
43
crosstalk prevention
Shielded and twisted pair in addition to fiber.
44
echo prevention
Install proper termination of cables
45
jitter
Use better quality circuitry, use fewer repeaters, slow the transmission speed.
46
attenuation prevention
Install amplifiers on analog signals and repeaters on digital signals.
47
simple parity
(Occasionally known as vertical redundancy check) is the easiest error-detection method to incorporate into a transmission system. It comes in two basic forms:
1) even parity
2) odd parity
A check sum is added to a series of bits to create either odd or even parity.
Does not detect swapped bits.
48
even parity
The 0 or 1 added to the string produces an even number of binary 1s.
49
odd parity
The 0 or 1 added to the string produces an odd number of binary 1s.
50
longitudinal parity
Also called longitudinal redundancy checker horizontal parity, tries to solve the main weakness of simple parity - that all an even number of error can not be detected. Uses additional parity check bits. Better than simple but still a high number to check bits.
51
arithmetic checksum
A sum is added to the data before transmitting and then the receiver adds that same number to the data to check to see if the two sums match.
52
cyclic redundancy checksum
(CRS) or cyclic checksum, method typically adds 8 to 32 check bits to potentially large data packets and yields an error-detection capability approaching 100 percent.
53
generating polynomial
An industry-approved bit string used to create the cyclic checksum remainder.
54
error control
The action the receiver takes once an error is detected.
55
stop-and-wait error control
A workstation (Station A) transmits one packet of data to another workstation (Station B), and then stops and waits for a reply from Station B. Four possible outcomes:
1) Station B gets a good packet and send back a positive acknowledgement (ACK), Station A transmits the next packet.
2) If the data has an error, Station B responds with a negative acknowledgment (NAK) or (REJ). If Station A receives a (NAK) or (REJ), Station A retransmits the packet.
3) The packet arrives at Station B, B sends an ACK but Station A does not get it. After a timeout, Station A resends the last packet.
4) Station A sends a packet but the packet is lost. Station A waits for the response, times out, and resends.
56
sliding window protocol
A flow control scheme that allows a station to transmit a number of data packets before receiving some form of acknowledgement.
57
piggybacking
When a receiver includes an ACK with other data that it needs to transmit to the other station.
58
forward error correction
Redundant data is sent so that the receiver can correct the errors.
59
Hamming code
A specially designed code in which special check bits have been added to data bits such that, if an error occurs during transmission, the receiver might be able to correct the error using the included check and data bits.
60
Hamming distance
The characteristic of a code. The smallest number of bits by which character codes differ. If the character set has a Hamming distance of 1, it is not possible to detect errors, nor correct them. Hamming distance of 2, you can detect errors but not correct them. Hamming distance of 3 allows for single-bit error correction and double-bit error detection.
61
local area network
(LAN) - A communications network that interconnects a variety of data communications devices within a small geographic area and transmits data at high data transfer rates.
62
primary function of a LAN
1) file serving
2) database and application serving
3) print serving
4) Internet accessing
5) e-mailing
6) video & music transfers
7) process control and monitoring
8) distributed processing
63
file server
A workstation with a large storage disk drive that acts as a central storage repository.
64
print server
Software that provides workstations with the authorization to access a particular printer, accepts and queues print jobs, prints cover sheets, and allows users access to the job queue for routine administrative functions.
65
common applications for a LAN
1) office environment
2) academic environment
3) manufacturing
66
LAN advantages/disadvantages
Pros:
- The ability to share resources in an economical and efficient manner.
- component evolution can be independent of system evolution
Cons:
- expensive to implement
- expensive to maintain
- all devices are not always interoperable
- user licensing issues
- maintenance and control requires many hours of dedication and service
67
bus/tree area network
(bus LAN) - The first physical designs, it is simply a linear coaxial cable into which multiple devices or workstations tap.
Difficult to add a workstation unless a tap already exists.
68
passive device
A tap in the network that does not alter the signal and does not require electricity to operate.
69
network interface card
(NIC) - An electronic device, sometimes in the form of a computer circuit board or part of a larger circuit board, that performs the necessary signal conversions and protocol operations that allow the workstation to send and receive data on the network.
70
types of signaling technologies
1) baseband - typically uses a single digital signal to transmit over the bus, which uses the entire spectrum of the cable so only one signal can be transmitted at a time. It is also bidirectional, so when a signal is introduced in the line, it propagates away from the source in both directions on the cable.
2) broadband - Uses analog signaling in the form of frequency division multiplexing to divide the available medium into multiple channels. It is also possible to split and join broadband cables and signals to create configurations more complex than a single linear bus.
71
star-wired bus LAN
Looks like a star. Today's modern version looks like a star but acts logically like a bus.
72
logical design
The design of the network, it determines how the data moves around the network from workstation to workstation.
73
physical design
The design of the network that refers to the pattern formed by the locations of the elements of the network, as it would appear if drawn on a sheet of paper.
74
hub
A relatively non-intelegent device that simply and immediately retransmits the data it receives from any workstation out to all other workstations (or devices) connected to the hub.
75
medium access control protocol
Software that allows a device to place data onto a hub-based local area network (as well as other networks that require their workstations to compete for access to the network). Because a LAN is essentially a single bus using baseband technology, it is imperative that only one workstation at a time be allowed to transmit its data onto the network.
76
medium access control protocol categories
1) Contention-based protocols, such as carrier sense multiple access with collision detection.
2) Round-robin protocols, such as token passing.
77
contention-based protocol
Basically, a first-come, first-served protocol.
78
carrier sense multiple access with collision detection
(CSMA/CD) - Was found almost exclusively on star-wired bus and bus LANs, and was the most widely used medium access control protocol.
Basically, a half-duplex protocol, the workstations listen to the network waiting for a clear network, and then transmits. While it is transmitting, it continues to listen, normally only hearing its own transmission.
79
collision
When two or more workstations listen to the medium at the same moment, hear nothing, and then transmit data at the same moment.
80
collision window
The interval of time that it takes for the signal from the work station to travel, on average, halfway down the bus, collide with the other workstation's signal, and then propagate back down the bus to the first station.
81
nondeterministic protocol
A protocol in which you cannot calculate the time at which a workstation will transmit.
82
switch
A device that uses addresses and processing power to direct a frame out of a particular port, thus reducing the amount of traffic on the network. The switch acts as a filter, instead of sending it out to all locations on the bus, it sends it only to the device it is addressed to.
83
filter
Examines the destination address of a frame and forwards the frame appropriately, depending on some address information stored in the switch.
84
transparent
Switches usually learn by themselves, so once installed, they monitor the traffic on the network and learn where packets come from and where they go. Eventually, they create an internal table for directing traffic, all transparently.
85
backward learning
The switch observes the location from where a frame comes.
86
backplane
The main hardware of the switch, must be fast enough to support the aggregate or total bandwidth of all the ports.
87
hot swappable
Devices that can be inserted and removed while the power to the unit is still on.
88
cut-through architecture
The data frame begins to exit the switch almost as soon as it begins to enter the switch. The switch does not store a data frame.
89
store-and-forward device
Holds the entire frame for a small amount of time while various field of frame are examined, a procedure that diminishes the overall network throughput.
90
shared segment network
A switch may be connected to a hub (or several hubs), which then connects multiple workstations. Because the workstations are first connected to a hub, they all share the one channel, or bandwidth, of the hub, which limits the transfer speeds of individual stations.
91
dedicated segment network
A switch may be directly connected to one or more workstations. Each workstation then has a private or dedicated a connection. This increase bandwidth to each workstation.
92
full-duplex switch
Allows for a CSMA/CD network to simultaneously transmit and receive data to and from a workstation. This requires:
1) A NIC capable of supporting, and then configured to support, a full-duplex connection.
2) A switch must be configured for a full-duplex connection.
3) The cable connecting components must be capable of supporting a full-duplex connection.
93
virtual LAN
A logical subgroup within a LAN created via switches and software rather than manually moving wiring from one network device to another. Allows you to create a network within a network to allow certain workstations to communicate and share data faster.
94
link aggregation
Allows you to combine two or more data paths, or links, into one higher-speed link.
95
Spanning Tree Protocol
(STP) - A protocol that finds the circular interconnections of LANs and switches and then break the loop by modifying the forwarding tables. Essentially consists of four steps:
1) Designate a root switch
2) Visti each switch (except the root switch) and identify the port/connection that leads you back to the root switch in the fewest number of hops. Mark each with RP (for root port).
3) Visit each LAN and identify the port/connection that leads you back to the root switch in the fewest number of hops. Mark each with DP (for designated port).
4) Remove all the ports that do not have either an RP or DP designation.
96
Rapid Spanning Tree Protocol
(RSTP) - Recomputes the spanning tree algorithm in approximately 6 seconds.
97
quality of service
An element that is supported by LAN network switches that is relatively new. Allows you to select priority codes for different types of traffic. Essentially, bits for streaming video need to continuously flow to prevent disruptions in the video where as bits for email traffic can be delayed without a significant impact.
98
Ethernet
First commercially available and most popular LAN system. The wired version is based primarily on the star-wired bus topology and uses essentially the CSMA/CD medium access protocol. There were multiple versions, most recent versions are known as Gigabit Ethernet and have transmission speeds of 1 gigabit (1 billion bits) per second. There are higher speed versions, the most recent operational version is 10-Gbps Ethernet
99
Power over Ethernet
(PoE) - Allows the devices connected to the network go get power over the Ethernet connection.
100
medium accès control sublayer
(MAC) - works more closely with the physical layer and contains a header, computer (physical) address, error-detection codes, and control information.
101
logical link control sublayer
(LLC) - Primarily responsible for logical addressing and providing error control and flow control information.
102
network operating system
Essential for the network to operate, it is the programming that provides user password protection, network administer access to the network, and devices with the protocol for communication.
103
wireless LAN
A LAN that is not based primarily on physical wiring but uses wireless transmissions between workstations. Essentially, configured in a star topology.
104
access point
Usually a wireless router, it is the component of a wireless LAN that communicates with the wireless user device. It is the interface device between the wireless user device and the wired LAN. Also acts as a switch/bridge and supports a medium access control protocol.
105
Basic Service Set
(BSS) - All user devices communicate with one access point and compete for the same set of frequencies.
106
Extended Service Set
(ESS) - The wireless LAN term for a collection of multiple Basic Service Sets (BSS). Configured similar to a mobile telephone cellular network with each cell using a different set of frequencies for communication between user device and the access point.
107
IEEE 802
The suite of protocols used for wireless LANs.
108
Multiple Input Multiple Output
(MIMO) - A technique in which both the mobile device and the access point have multiple, smart antennae that help to reduce signal interference and reflections.
109
5 GHz wireless LAN
Pros:
- Greater bandwidth
Cons:
- Requires more power from the device
- Shorter range (2.4 GHz - 150' indoors, 5 GHz - 50' indoors)
- Has Difficulty transmitting through doors and walls.
110
Wired Equivalent Privacy
(WEP) - Original security provided on a wireless LAN. Now known to be extremely vulnerable to attack.
111
Wi-Fi Protected Access
(WPA) - A temporary security standard created to improve on WEP.
112
Temporal Key Integrity Program
(TKIP) - Uses a 128-bit key one each packet and it changes with each packet transmitted, making it nearly impossible for an unauthorized user with a wireless device to connect to a WPA-protected signal and eventually figure out the transmission scheme.
113
Wi-Fi Protected Access II
(WPA2) - The latest encryption standard to support wireless LANs and has replaced TKIP with an even more robust encryption technique called CCMP.
114
hidden workstation (WiFi)
When workstations are so far apart that they will not hear each signals in order to detect collisions.
115
multiple access with collision avoidance
(CSMA/CA) - A algorithm type that tries to avoid collisions.
116
interframe space
(IFS) - The small amount of time that a device must wait before it can transmit after ensuring that no other device is transmitting.
117
operating system
The program initially loaded into computer memory when a computer is turned on; it manages all the other programs and resources in a computer.
118
application programming interface
(API) - A defined interface that enables the applications to make use of the operating system by making service requests.
119
multitasking operating system
An operation system that allows multiple programs run at the same time.
120
network operating system
(NOS) - A large, complex program that can manage the common resources on most LAN.
121
NetWare Directory Services
(NDS) - An intelligent system that authenticates users and includes a distributed database of information about every application, user, server, and resources on a network.
122
organizational unit
(OU) - An object that is further composed of additional objects (examples of which include servers, printers, users, or groups of users).
123
Leaf objects
Not composed of any objects and are usually entities such as the users, peripherals, servers, printers, queues, and other network resources.
124
hierarchical tree
A network plan put together by network administrators to help them build and manage a network. It resembles an inverted tree with the root at the top and the "leaf objects" at the bottom. The root connects to OUs which uses branches to connect to other OUs that provide services to the individual devices and users, "Leaf objects."
125
UNIX
A popular operating system that can be found on single-user workstations as well as on mainframe computers. It is most often found with a text-based interface, although GUIs are available.
126
Linux
Based on UNIX, it is a complete rewrite of the UNIX kraal and borrows additional functions from the well-established Free Software Foundation's GNU toast and from the even larger free software community.
127
Mac OS X
Based on the UNIX concept, and thus shares some characteristics with both the UNIX and Linux operating systems, such as fast efficient, and stable core.
128
server
The host machine on which the network operating system operates.
129
Redundant Array of Independent Disks
(RAID) - A collection of techniques for interfacing multiple hard disk drives to a computer.
130
server virtualization
A technology that allows one computer (or server) act as if it were multiple computers (or servers).
131
server appliance
A single unit or box that supports many networking functions such as Internet sharing, intranet We serving, firewall security, FTP services, file and print serving, e-mail service, and virtual private network configurations.
132
server blade
A server that has no cabinet or box, but resides on a single printed circuit card.
133
peer-to-peer network
May not have servers but allows communications between workstations, as if the workstations were all equals.
134
Utilities
Software programs that operate in the background and support one or more functions to keep the network running at optimal performance.
135
Antivirus software
Software designed to detect and remove viruses that have infected the computer's memory, disks, or operation system.
136
Spam
Unsolicited commercial bulk e-mail.
137
Anti-spam software
Used to block Spam.
138
Spyware
Software that a user unknowingly downloads from the Internet, and when this software is executed on the user's machine, it begins spying on the user.
139
Anti-spyware software
Locates and cleans the spyware programs found in a computer's memory and hard disk drive.
140
Backup software
Allows network administrators to back up data files currently stored on a server's hard drive.
141
crash protection software
Software which performs crash stalling, or tries to keep the operating system running long enough to perform a graceful exit.
142
Network-monitoring software
Incorporates a fairly large number of network support tools.
143
Sniffers
"Listen" for traffic on a network and determines if invalid messages are being transmitted, report network problems such as malfunctioning NICs, and detect traffic congestion problems.
144
Remote access software
Allows users to access all of the possible functions of a personal computer workstation from a mobile or remote location.
145
Security assessment software
Designed to scan an IP address or a range of IP addresses for any type of security weakness.
146
Uninstall software
Works with the user to locate and remove applications that are no longer desired.
147
Internet software
The toolset to support Internet-related services.
148
Web server software
The application or set of programs that stores Web pages and allows browsers from anywhere in the world to access those Web pages.
149
licensing agreement
A legal contract that accompanies a software product and describes a number of conditions that must be upheld for proper use of the software package.
150
singler-user-single-station license
The software package may be installed on a single machine and then only a single user at one time may use that machine.
151
singler-user-multiple-station license
The software package may be installed on a multiple machines and then only a single user at one time may use that software.
152
interactive user license
A user license which allows for a controlled number of concurrent users license. These usually have a system that keeps track of the number of users and once a limit is reached, prevents the addition of more users.
153
server license
System-based or cluster wide licenses which usually do not have software controlling the current number of users.
154
site license
Allows a software package to be installed on any and all workstations and servers at a given site.
155
corporate license
Allows a software package to be installed on any and all workstations and servers belonging to a given corporation, even if they are at different sites.
156
General Public License
(GPL) - Associated with software that is free to share and change.
157
uninterruptible power supply
(UPS) - A device that provides power to one or more pieces of equipment when the power goes out. Typically designed to provide for short periods of time to allow emergency power to be available or to allow the equipment enough time to shutdown safely.
158
Network attached storage
(NAS) - A computer-based device that provides a large amount of storage to users on a network.
159
storage area network
(SAN) - A simpler version of a NAS with less capabilities.
160
Media converter
Allows you to connect one medium to another.
161
thin client
A computer with no disk drives of any sort. Any software that operates on the thin client is downloaded from the server to the thin client.
162
metropolitan area network
(MAN) - A network that expands into a metropolitan area and exhibits high data rates, high reliability, and low data loss.
MANs can recover very quickly form a switch/router failure.
Most MANs are based on a ring design.
Has the ability to allow a user to dynamically allocate more bandwidth on demand.
163
wide area networks
(WAN) - Networks that expand beyond a metropolitan area. They share a few characteristics with LANs:
1) They interconnect computers
2) Use some form of medium for the interconnections
3) Support network applications
Differences:
1) LANs don't do routing, WANs do.
2) WANs interconnect large numbers of computers.
3) WANs cover large areas.
164
failover
The ability of a MAN to reroute in the event of a failure.
165
failover time
The time it takes a MAN to reroute in the event of a failure.
166
Metro Ethernet
A data transfer service that can connect your business to another business (or businesses) using a standard Ethernet connection.
167
bandwidth profile
Describes various characteristics about the connection, such as basic data transfer rates, basic burst rates, excess data transfer rates, and excess burst rates.
168
mesh network
A network where neighbors are connected only to neighbors. Thus, to be transmitted across a mesh network, the data has to be passed along a route from workstation to workstation.
169
station
A device that a user interacts with to access a network, and it contains the software application that allows someone to use the network for a particular purpose.
170
node
A device that allows one or more stations to access the physical network, and is a transfer point for passing information through a network, the information is transferred from node to node through the network.
171
subnetwork
Or network cloud, is a collection of nodes and interconnecting telecommunications links.
172
circuit-switched network
A network cloud in which a dedicated circuit is established between the sender and receiver, and all data passes over this circuit.
It has two key disadvantages:
1) Each circuit is dedicated to only one connection.
2) When the circuit is used to transfer data (as apposed to voice), it is probably not being utilized fully because computer data transfer is often sporadic.
173
packet-switched network
A network cloud in which all data messages are transmitted using fixed-sized packages, called packets, and no unique dedicated physical path is established to transmit data packets across the subnetwork.
174
datagram packet-switched network
A packet-switched network where each data packet can follow its own, possibly unique, course through the cloud. The problem is that this dynamic routing can cause latency.
175
virtual circuit packet-switched network
A packet-switched network where all packets that belong to a logical connection can follow the same path through the network.
176
broadcast network
When a node on this type of network transmits data, the data is received by all the other nodes on the network.
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connection-oriented network application
Such as the one that performs a file transfer using FTP, provides some guarantee that information traveling through the network will not be lost and that the information packets will be delivered to the intended receiver in the same order in which they were transmitted.
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reliable service
A network that provides some guarantee that information traveling through the network will not be lost and that the information packets will be delivered to the intended receiver in the same order in which they were transmitted.
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connectionless network application
Does not require a logical connection to be made before the transfer of data. Thus, it does not guarantee the delivery of any information or data.
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weighted network graph
A network graph where the edge between each pair of nodes can be assigned a weight or associated cost.
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weight (for edge rating)
Could be determined by dollar cost of data transmission, time-delay of transfer, or the size of the queue that has backed up while waiting for a packet to be transmitted onto a link.
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Dijkstra's least-cost algorithm
A classic algorithm that calculates a least-cost path through a network.
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flooding technique
Each node takes the incoming packet and retransmits it onto every outgoing link.
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hop limit
A network limit placed on how many times a packet is copied.
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hop count
A counter associated with the packet that increases by 1 each time the packet is copied.
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centralized routing
Involves storing all the routing information at one central location. Whenever a counter in a network needs routing information, this central location is queried and the routing results are returned.
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distributed routing
A technique that uses a routing algorithm, such as a least-cost algorithm, to generate routing information and dictates that this information be stored (in the form of routing tables) at distributed locations.
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adaptive routing
A dynamic technique in which routing tables react to network fluctuations, such as congestion and node/link failure. This can lead to network congestion though.
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fixed routing
Routing tables are created once, typically when the network is installed, and then never updated again.
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Routing Information Protocol
(RIP) - An adaptive, distributed algorithm that updates each nodes own vector with the least-cost values of all the neighbors.
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Open Shortest Path First protocol
(OSPF) - A link stat algorithm where networks are divided into areas (collection of networks, routers, and hosts). All routers inside an area flood all other routers in the same area. Special areas called area border routers interconnect areas.
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network congestion
When a network or a part of a network becomes so saturated with data packets that packet transfer is noticeably impeded.
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implicit congestion control
The application simply observes its own throughput and does not rely on any special types of signals coming from the network.
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explicit congestion control
When the network signals the transmitting station to slow down.
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forward explicit congestion notification
(FECN) - When a frame relay router experiences congestion, it sends a congestion signal (inside the data frames) forward to the destination station, which in turn tells the originating station to slow down the transfer of data.
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backward explicit congestion notification
(BECM) - The frame relay router experiencing congestion sends a signal back to the origination station, which then slows down its transmission.
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buffer preallocation
Before one node sends a series of n packets to another node, the sending node inquires in advance whether the receiving node has enough buffer spaces for the n packets.
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connection admission control
Avoids congestion by requiring users to negotiate with the network regarding how much traffic they will be sending, or what resources the network must provide to satisfy the user's need before the user sends any data.
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service level agreement
A legally binding, written document that can include service parameters offered in the service, and penalties if service levels are not met.
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Internet Protocol Layers
```
From top down:
Application Layer
Transport Layer
Network Layer
Network Access Layer
```
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TCP/IP
Two protocols used for the interconnection of internal networks and connection on the internet.
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Internet Protocol
(IP) - Provides a connectionless data transfer service over heterogeneous networks by passing and routing IP datagrams.
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IP datagram
Essentially, another name for a data packet.
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IPv4 address length
32 bits
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IP multicasting
The capability of a network server to transmit a data stream to more than one host at a time.
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subnet masking
The practice of taking the host ID portion of an IP address and further dividing it into a subnet ID and a host ID.
