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188 Cards in this Set
- Front
- Back
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Convergence
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Convergence is taking all voice, video and data communications whether they are circuit or packet based, coverting them to packet based and putting them all onto one packet based data network using the Internet Protocol (IP). The three key benefits are efficiency, effectiveness and transformation. Simplified network management Chap 1 PG 11
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Unified Communications
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Unified communications is the unification of real time communications with non real time collaboration and business applications combined in an end-user focused set of interfaces. For example a real time communications dashboard that combines instant messaging, email, audio, video, etc into one view for eash and efficiency of the end user Chap 1 PG 13
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voice communications
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Primarly refering to telephone related communications. Voice mail, PBX and Centerex, call forwarding, etc Chap 1 PG 15
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Data Communications
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Virtually any form of information transfer other than voice. Information in terms of text and numerical data Chap 1 PG 16
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image communications
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Best known example is the fax. Optical disk is allowing for massive amounts of data being stored inexpensively allowing the saving and sending of large image files Chap 1 PG 16
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video communications
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In business setting, used for videoconferencing. Chap 1 PG 16
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Client/Server
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Separate copmuters (servers) support database functions, store files, etc on a shared basis for many users (client) (shared drive). Accessed over a LAN Chap 1 PG 18
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Internet
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It's the internet. Allows for marketing and e-commerce, etc Chap 1 PG 18
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TCP/IP
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Transmission Control Protocol/Internet Protocol suite which is used universally for the communications software function across multiple vendor equipment and is the basis for the operation of the internet Chap 1 PG 18
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Distributed Applications
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Applications that are designed to work among a distributed set of computers for both intracompany and intercompany information exchange. Chap 1 PG 19
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Local Area Network (LAN)
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Found in virtually all mediul-large sized office buildings. Common type of network it interconnects a variety of devices and provides a means for information exchange among those devices. LAN is small (single building) WAN is large. LAN is owned by organization that owns the attached dvices, WANs are not usually owned by the users.Data rates for LANs are usually much faster than WANs Chap 1 PG 19
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Circuit Switching
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A dedicated communication path is established between two stations through the nodes of the network. At each node the data are routed or "switched" to the appropriate outgoing channel without delay. Most common is the telephone network. Chap 1 PG 20
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Frame Relay
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With modern day transmissions systems, the packet switching overhead is not needed and is counterproductive, therefore Frame Relay takes out most of the overhead around error control to send packets of data faster. Chap 1 PG 20
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packet switching
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Data is sent out in small chunks called packets and the entire packet is passed from node to node. Commonly used for terminal to computer or computer to computer. Requires a lot of overhead built in to compensate for errors. Chap 1 PG 20
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WAN
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Wide Area Network. Generally cover a large geographic, require the crossing of public right of ways and rely at least in part on circuits provided by a common carrier. Typically a WAN consists of a number of interconnected switching nodes. Generally WAN's are implemented using circuit switching and packet switching although frame relay and ATM have assumed major roles Chap 1 PG 20
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Asynchronous Transfer Mode (ATM)
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ATM is sometimes called Cell relay which is an evolution of frame relay. Frame relay uses variable length packets called frames and ATM uses fixed length packets called cells. Using fixed length packets reduces the overhead even further which allows it to work in the 10s and 100s of Mbps and Gbps range. Chap 1 PG 21
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Metropolitan Area Network (MAN)
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MAN occupies a middle ground between LANs and WANs. Intended to provide the required capacity at a lower cost and greater efficiency than from getting the same service from the phone company. Chap 1 PG 22
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bit
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Fundamental unit of discrete information. Represents the outcome of 1 choice, 1 or 0. Represents 2 possible outcomes. Represent communication rates. Chap 1 PG 29
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byte
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Name given to 8 bits is 2^8 = 256 outcomes. Bytes are representing quantities of storage 1B = 8b. Chap 1 PG 29
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data transmission
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1kbps = 1000bps = 10^3bps Chap 1 PG 30
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computer storage
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1kB = 2^10 bytes = 1024 bytes Chap 1 PG 30
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Analog
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Analog information is a continuous signal (like a voltage) that can take on a continuum of values. Virtually any communication signal can be expressed as a combination of pure oscillations of various frequencies. The higher the frequency allowed, the more accurately a complex signal can be represented. Bandwidth measures the limits on these frequencies. Measured in Hz. 1Hz = 1cycle/sec. Chap 2 PG 33
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audio
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Audio service supports applications based on sound usually of the human voice like over the telephone. Quality is based on bandwidth used. Voice on a telephone is usually limited to 3400Hz of bandwidth where teleconference is 7000 and CD is 20,000 HZ. Chap 2 PG 33
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digital
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Digital information is represented as a sequence of discrete symbols from a finite "alphabet". Examples are text, numerical and binary data. Measured in bps. Chap 2 PG 33
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quantization
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Used to represent audio data digitally. Sampled at a rate of at least twice the maximum frequency and then the signal amplitudes are put into a digital form (quanitization) Chap 2 PG 34
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voice
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Voice over telephone ~ 3400 Hz. Chap 2 PG 34
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centrex
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Provides same sort of service as centrex but the switching facility is done at the telephone companies central office as opposed to the customers premises. IP Centrex is now commmon. Chap 2 PG 35
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Private Branch Exchange (PBX)
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an on-premise switching facility owned or leased by the organization, that interconnects the telephones within the facility and provides access to the public telephone system. Supports voicemail and teleconferencing. IP based PBX is now common as well Chap 2 PG 35
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ASCII
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American Standard Code for Information Interchange. (US version of IRA) Chap 2 PG 36
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byte
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Letter of the alphabet or symbol is represented by a byte or 8 bits. Chap 2 PG 36
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data
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consists of information that can be represented by a finite alphabet of symbols, such as digits 0-9 or symbols on the keyboard. Text is a common example. Chap 2 PG 36
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IRA
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International Reference Alphabet is the most commonly used text code today. Chap 2 PG 36
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image
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Communication of individual pictures, charts or drawings. Chap 2 PG 37
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grayscale
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produced if each pixel is defined by more thank one bit, representing shades of gray. Can be used in vector graphics to define the grayscale of line segments or interior of closed objects. Chap 2 PG 38
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pixel
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or picture element, is the smallest element of a digital image that can be assigned a gray level. An individual dot in a dot-matrix. Chap 2 PG 38
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raster graphics
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Image is represented as a two-dimensional array of pixels (or spots). There is a degradation of image with scaling Chap 2 PG 38
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vector graphics
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image is represented as a collection of straight and curved line segments. No degradation of image with scaling. Chap 2 PG 38
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GIF
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8 bit color format that can display up to 256 colors and is generally useful for non-photographic images in a narrow color range such as a logo. Chap 2 PG 39
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JPEG
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Most widely used Raster image format.Joint Photographic Experts Group - developed set of standards for compression of raster images in grayscale and color. Chap 2 PG 39
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PDF
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widely used on the web. Portable Document Format. Chap 2 PG 39
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postscript
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page description language that is built into many desktop printers and all high end printing systems. Chap 2 PG 40
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video
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Video makes use of a sequence of raster images. Chap 2 PG 40
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interlacing
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Used to eliminate the flicker in a video screen witthout increasing bandwidth. A screen is divided into two fields with even and odd scanned lines scanning each on a field and alternating with each successive scan. This doubles the refresh rate to 60 per second eliminating the flicker that occurs at 30 per second. Chap 2 PG 41
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response time
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The amount of time a system takes to respond or react to an input or particular task. Shorter response time creates greater cost from increase in processing power or competing requirements. Needed response time is balanced with cost to determine necessary response time. Chap 2 PG 43
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protocol
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Is used for communication between entities in different systems. What is communicated, how it is communicated and when it is communicated must conform to a universally agreed convention which is the protocol. Key elements of protocol are Syntax - What is communicated - Data format and signal levels, Semantics - how its communicated Control information and Timing - When is it communicated - Seqeuncing and speed matching. Chap 5 PG 108
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protocol architecture
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a structured set of modules that implements the communication function. Layered architecture with peer entities at each layer performing subtasks appropriate to that layer. Each layer relies on the layers above and below to carry out their function in order to have who system work Chap 5 PG 108
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network layer 3 layer
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In the 3 layer model, the network layer is concerned with the exchange of data between computer and the network for which it's attached Chap 5 PG 110
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application layer - 3 layer
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In the 3 layer model, the application layer contains the logic needed to support the various user applications. For each different application, a separate module is needed that is peculiar to that application Chap 5 PG 111
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port
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Means that each application is individually accessing the services of the transport layer. Each application on a computer has an address that is unique and allows the transport layer to support multiple applications at each computer. Also called Service Access Point Chap 5 PG 111
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Service Access Point (SAP)
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Means that each application is individually accessing the services of the transport layer. Each application on a computer has an address that is unique and allows the transport layer to support multiple applications at each computer. Also called Port Chap 5 PG 111
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Transport Layer 3-layer
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In the 3 layer model, the transport layer is responsible for the mechanisms focused on reliability of the data Chap 5 PG 111
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checksum
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it's the error detection code. The sending transport layer can add a code that is the function of the contents of the segment. The receiving transport protocol uses the same calculation and compares the results to see if there was an error. Also called a frame check sequence Chap 5 PG 113
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frame check sequence (fcs)
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it's the error detection code. The sending transport layer can add a code that is the function of the contents of the segment. The receiving transport protocol uses the same calculation and compares the results to see if there was an error. Also called a checksum Chap 5 PG 113
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header
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contains protocol control information that is applied by each layer Chap 5 PG 113
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packet
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the network access pdu that is appended to the data received from the transport layer Chap 5 PG 113
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protocol data unit (pdu)
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The combination of data from the next higher layer and the control information from current layer. Transport layer PDU's are called segments Chap 5 PG 113
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TCP/IP
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Transmission Control Protocol/Internet Protocol - The TCP is the transport layer and IP is the internet layer. There are 5 layers to this architecture 5) Application Layer, 4) Transport Layer (or Host to Host) 3)Internet layer, 2)Network layer, 1)physical layer. Chap 5 PG 114
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application layer TCP/IP
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In the TCP/IP model, the application layer contains the logic needed to support the various user applications. For each different application, a separate module is needed that is peculiar to that application Chap 5 PG 115
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Internet Protocol (IP)
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The IP is the Internet layer of the TCP/IP. It provides the routing function across multiple networks. This protocol is in the end systems and also the routers. Chap 5 PG 115
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network layer TCP/IP
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In the TCP/IP model, the network layer, from the source computer, provides the attached network with the information neeeded to reach a router that connects this network to the next network on the route to destination. Chap 5 PG 115
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physical layer
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The physical layer is the physical interface between a data transmission device and a transmission medium or network. This layer is concerned with specifying the characteristics of the transmission medium, the nature of the signals and the data rate. Chap 5 PG 115
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Transport layer TCP/IP
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In the TCP/IP model, the transport layer is responsible for the mechanisms focused on reliability of the data. The TCP is the transport layer. Chap 5 PG 115
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IP datagram
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The combination of header that IP adds to the control information of each Transport Layer (TCP) segment. Chap 5 PG 117
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Transmission Control Protocol (TCP)
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TCP is the transport layer protocol. It provides a reliable connection for the transfer of data between applications Chap 5 PG 117
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TCP Segment
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The TCP Segment is the PDU for the transport layer (Combination of data from next higher level and control information from TCP) Chap 5 PG 117
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User datagram Protocol
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UDP is another transport level protocol that is used, but UDP does not guarantee delivery, preservation of sequence or protection against duplication. UDP enables a process to send messages to tother processes with a minimum of protocol mechanism. It adds a port addressing capability to IP. UDP is fixed at 8 octets where as TCP is a minimum of 20 octets and is variable. Chap 5 PG 117
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IPv4
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Uses a header format that is 20 octets and combined with the TCP segment forms an IP PDU or IP Datagram or IP Packet. The source and destination address field is 32 bits Chap 5 PG 118
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IPv6
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Uses a header format that is 40 octets and combined with the TCP segment forms an IP PDU or IP Datagram or IP Packet. The source and destination address field is 1 bits Chap 5 PG 118
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end system
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The devices attached to a subnetwork. (Each constituent subnetwork in an internet supports communication among the devices attached to that subnetwork) Chap 5 PG 121
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extranet
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Organization extending intranet across the internet to selected customers or suppliers. Chap 5 PG 121
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Intermediate System
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devices that connect subnetworks. They provide a communications path and perform the necessary relaying and routing functions so that data can be exchanged between devices attached to different subnetworks in the internet. Chap 5 PG 121
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Internet
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The entire configuration of constituent networks that retain their indentity and special mechanisms for communicating across mulitple networks. Chap 5 PG 121
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Internetworking
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Achieved by using routers to interconnect a number of independent Chap 5 PG 121
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intranet
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private internet in an organization Chap 5 PG 121
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Subnetwork
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Each of the constituent networks that retain their identity in the internet Chap 5 PG 121
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router
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A type of Intermediate System (the other is bridge). It provides links between networks that nmay or may not be similar, provide for the routing and delivery of data between end systems attached to different networks, provide these functions so as to not require the modification of the networking architecture of any of the attached networks. Chap 5 PG 122
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bridge
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An Intermediate System used to connect two LANs that use similar protocols. Operates at layer 2 of the OSI model. Chap 5 PG 122
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Open systems Interconnections (OSI)
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Developed as a model for computer protocol and as a framework for developing protocol standards. Seven layers 1) Physical, 2) Data Link 3)Network, 4) Transport, 5) Session, 6) Presentation, 7) Application. Not widely used, the TCP/IP accomplishes the same in 5 layers compared to 7. The PDU process is still used and at the Data link level its called a frame and that is passed to the physical layer for transmission Chap 5 PG 125
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IP Sec
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IP Security. Provides the capability to secure communications across a LAN, private and public WANs and the internet. It can encrypt all traffic at the IP level. Chap 5 PG 130
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Analog data
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takes on continuous values on some interval. For example, voice and video are continuously varying patterns of intensity. Ch 16 PG 459
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Analog signal
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a continuously varying electromagnetic wave that may be transmitted over a variey of media depending on frequency Ch 16 PG 460
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digital data
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takes on discrete values; examples are text, integers and binary data Ch 16 PG 460
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digital signal
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a sequence of voltage pulses that may be transmitted over a wire medium (constant positive voltage represents 0 where constant negative represents 1). Digital signal is cheaper than analog and is less susceptible to noise interference. Ch 16 PG 460
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Analog transmission
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a means of transmitting analog signals without regard to their content; the signals may represent analog data (voice) or digital data (data that passes through a modem) The analog signal will suffer attenuation which limits the length of the transmission link. To achieve longer distances the signal includes an amplifier. Amplifiers boost the energy in the signal but also boosts the noise components, for analog data it's ok, for digital data it increases the number of errors. Ch 16 PG 461
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Digital Data, Digital Signal
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The equipment for encoding digital data into a digital signal is less complex and less expensive then digital to analog equipment Ch 16 PG 461
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Analog Data, Digital Signal
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Conversion of analog data to digital form permits the use of modern digital transmission and switching equipment Ch 16 PG 461
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Digital Data, Analog Signal
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Some transmission media, such as satellite and optical fiber will only propagate analog signals Ch 16 PG 461
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Analog Data, Analog Signal
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Analog data is easily converted to an analog signal Ch 16 PG 461
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codec
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The device that permits analog data to be represented by a digital signal. It takes an analog signal and approximates the bit stream and then reconstructs the analog data on the other end Ch 16 PG 461
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modem
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Device that allows digital data to be represented by analog signals. Converts a series of binary voltage pulses into an analog signal by modulating a carrier frequency. Most modems represent data in the voice spectrum so that it can be propagated over normal voice grade telephone lines. Ch 16 PG 461
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digital transmission
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Unlike Analog transmission, Digital transmission is concerned with the content of the signal. Since transmission distance causes attenuation which reduces the integrity of the data, greater distance can be achieved by using repeaters. Repeaters receive the digital signal, recovers the pattern of 1's and 0's and then retransmits. The same technique can be used for analog signal with digital data. Digital transmission is preferred (lower cost, better data integrity, greater capacity, easier to encrypt and easier integration. Ch 16 PG 462
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Amplitude Shift Keying
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Method of analog encoding for digital data (Modulation of data) ASK - 2 binary values are represented by two different amplitudes of the carrier frequency. The presence of the carrier is one digit and the absence is the other digit. Not an efficient modulation technique. Ch 16 PG 463
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frequency shift keying
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Method of analog encoding for digital data (Modulation of data) FSK - 2 binary values are represented by two different frequencies near the carrier frequency. Less susceptible to error than ASK Ch 16 PG 464
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phase shift keying
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Method of analog encoding for digital data (Modulation of data) PSK - phase of the carrier is shifted to encode data. A 0 is represented by a signal burst of the same phase as preceding signal and a 1 is represented by a signal burst of opposite phase as preceding one. More efficient than FSK. Can be combined with ASK called multilevel signaling. Ch 16 PG 464
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baud
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In multilevel signaling (ASK and PSK combined) data rate and modulation rate (Signaling rate) are measured. Baud is the modulation rate. Ch 16 PG 465
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pulse code modulation
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Method of digital encoding of analog information PCM - samples the analog signal ar regular intervals of time at a rate higher than twice the highest significant signal frequency. The analog samples are converted to digital by assigning them a binary code. PCM can be used for any analog signal. Ch 16 PG 468
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NRZ-L and NRZI
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Digital Encoding of Digital Data - Non return to Zero Level and Non return to zero, invert on ones Ch 16 PG 469
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Manchester and differential Manchester
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Digital Encoding of Digital Data - biphase coding that overcomes the problem of synchronization loss of NRZ-L. Requires greater bandwidth but have 2 advantages 1) Synchronization (self clocking codes) 2) Error detection (absence of expected transition). Ch 16 PG 470
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Amplitude Modulation
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Analog encoding of Analog information - AM - the amplitude of the carrier varies with the pattern of the modulating signal Ch 16 PG 471
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frequency modulation
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Analog encoding of Analog information - FM - the frequency of the carrier varies with the pattern of the modulating signal Ch 16 PG 471
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phase modulation
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Analog encoding of Analog information - PM - the phase of the carrier varies with the pattern of the modulating signal Ch 16 PG 471
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asynchronous transmission
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In order to achieve desired synchronization - data are transmitted one character at a time, where each character is 5 to 8 bits in length. Thus timing only has to be maintained per character. A start bit (0) initiates, then the 5-8 bits of data, then a parity bit for error detection and then the stop bit (1). Ch 16 PG 473
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synchronous transmission
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In order to achieve desired synchronization - a block of bits is transmitted in a steady stream without start and stop codes. Manchester and differential Manchester can act as the synchronization(timing) on one level, but there is another level of synchronization needed to determine beginning and end of the multiple character transmission. Thus each block begins with a preamble bit pattern and ends with a postamble bit pattern. The data plus the preamble, postamble and control information are called a frame. Ch 16 PG 475
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error detection
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Error control involves 2 elements - error detection (redundancy is introduced into the data stream so that occurrence of an error will be detected) and Error correction (once detected the receiver and transmitter cooperate to retransmit the data) Ch 16 PG 476
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parity bit
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A check bit appended to an array of binary digits to make the sum of all the binary digits, including the check bit, always odd or even. Used in error detection and synchronization. Ch 16 PG 476
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cyclical redundancy check
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Most common and most powerful error detecting codes. Message to be transmitted is treated as a long binary number, is divided by a unique prime binary number and the receiver performs the same division and compares the calculated remainer with the remainder in the frame. 17 bit divisors which produce 16 bit remainder and 33 bit divisors with 32 bit remainders are most common. Ch 16 PG 477
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error-detecting code
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Also known as the frame check sequence(fcs) Calculation is performed on the bits of the frame to be transmitted; the result is inserted as an additional field to the frame. On reciept the same calculation is performed and results compared. A discrepancy assumes error. Ch 16 PG 477
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flow control
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A function of the Data link control layer (OSI layer 2) which is responsible for regulating the flow and compensating for transmission errors. Flow control is a technique for assuring that a transmitting entity does not overwhelm a receiving entity with data. In data link control, Flow control is accomplished by sequentially numbering each frame. The receiving entity allocates a buffer of agreed size and as the frames arrive and are processed and sent up to the higher levels, the receiver sends an acknowledgement of which frames have been received and if its ok to send more frames. Ch 17 PG 485
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Automatic repeat request (ARQ)
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Most common ingredients for common error control techniques 1) Error detection - destination detects bad frames and discards them 2) Positive Acknowledgement - destination sends message that they recieved the frames error free 3)Retransmission after time out - If no acknowledgement, source retransmits frame. 4) Negative acknowledgment and retransmission - destination returns a negative acknowledgement for error frame and source retransmits. Collectively these are called ARQ. The effect of ARQ is to turn unreliable data link into a reliable data link. Ch 17 PG 486
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error control
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The detection and correction of errors in the process of transmission and reception. Since data is sent as a sequence of frames, Data link control focuses on two types of errors, Lost frame (doesn't get to the receiver) and Damaged Frame (arrives but some bits are in error). Most common ingredients for common error control techniques 1) Error detection - destination detects bad frames and discards them 2) Positive Acknowledgement - destination sends message that they recieved the frames error free 3)Retransmission after time out - If no acknowledgement, source retransmits frame. 4) Negative acknowledgment and retransmission - destination returns a negative acknowledgement for error frame and source retransmits Ch 17 PG 486
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High Level data link control (HDLC)
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Most important data link control protocol. HDLC consists of the sending of I Frames, S Frames and U Frames. The frame in HLDC is made up of the following fields : Flag - used for synchronization, Address - indicates the secondary station for this transmission (usually 8 bits long but can be extended), Control - Identifies the purpose of function of frame (S,I,U), Information - the user data to be transmitted, and Frame check sequence (checksum) with 16 bit or 32 bit cyclic redundancy check, used for error detection. The three phases of HDLC is Initialization, Data Transfer, and Disconnect. In initialization Either side issues one of 6 set mode comands. If the other side accepts by sending an Unnumbered Acknowledgement (UA) then they're off, otherwise they send a Disconnected Mode (DM Message). In data transfer the data starts to be sent. I frams are for information, S frames (supervisory) are used for flow control and error control and U frames (Unnumbered) are used for supplemental features. (RR) is
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frame
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A group of bits that includes data plus one or more addresses and other protocol control information. Generally refers to the link layer (OSI2) Ch 17 PG 487
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Multiplexing
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Sharing the capacity of a data link with two or more communicating stations. The multiplexer accepts n number of inputs and carriers n number of channels across one data link to a demultiplexer which accepts the data stream and separates out the data by channel and delivers it to the proper output. Ch 17 PG 492
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frequency division multiplexing (fdm)
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A widely used form of multiplexing. Used with Analog signals. (Cable TV) FDM is possible when the useful bandwidth of the transmission medium exceeds the required bandwidth of signals to be transmitted. A number of signals can be carried simultaneously if each signal is modulated onto a different carrier frequency and the carrier frequencies are separated enough by un used spectrum known as guard bands so that the signals don't overlap. Each modulated signal requires a certain bandwidth centered on its carrier frequency referred to as a channel. FDM was the mainstay of telephone transmission for many years and is more efficient in terms of bandwidth than digital. But noise is amplified as well. Ch 17 PG 493
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Wavlength Division Multiplexing (WDM)
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Multiple beams of light at different frequencies are transmitted on the same fiber. It's a form of FDM but is called WDM. The WDM has the same architecture as the FDM. A number of sources generate a laser beam at different wavelengths. These are sent to the multiplexer which consolidates the sources for transmission over a single fiber line. Commercial systems with 10gbps and 160 channels are available. Ch 17 PG 496
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Asymmetric digital subscriber line (ADSL)
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provides more capacity downstream then upstream. Uses FDM with 3 elements 1) Reserve lowest 25 kHz for voice. Additional band (voice is 0-4kHz) is to prevent crosstalk between voice and data. 2) Use either echo cancellation or FDM to allocate two bands (smaller upstream and larger downstream). 3) Use FDM within the upstream and downstream bands.(a single bit stream is split into multiple parallel bit streams and each portion is carried on a separate frequency band. Ch 17 PG 497
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Dense Wavelength division Multiplexing (DWDM)
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Denotes the use of more channels more closely spaced than WDM. A channel spacing of 200 GHZ or less could be considered dense. Ch 17 PG 497
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echo cancellation
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A signal processing techniqe that alows transmission of signals in both directions in the same frequency band on a single transmission line simultaneously. The transmitter subtracts the the echo from its own transmission from the incoming signal to recover the signal sent. When used, the entire frequency band for the upstream overlaps the lower portion of the downstream channel. Since higher frequency yields greater attenuation, the lower frequency puts the downstream into the "good" part. It provides for more flexibility with the upstream to extend into the downstream if necessary. The disadvantage is that both ends of the line need echo cancellation logic for it to work. Ch 17 PG 498
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Discrete Multitone
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DMT uses multiple carrier signals at different frequencies sending some of the bits on each channel. The DMT modem sends out test signals on the line and sends more bits to the channels with better signal transmission(less noise) and less bits to the ones with poorer signal transmission (more noise). Sub channel can carry data rate from 0-60Hz. Present ADSL/DMT designs employ 256 downstream subchannels. This works out to be 1.5-9Mbps. Ch 17 PG 499
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Synchronous TDM
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STDM is refered to as TDM. Synchronous TDM is called synchronous because the time slots are preassigned to sources and are fixed NOT because of synchronous transmission. Capacity is wasted to achieve ease of implementation. T-1 is a popular form Ch 17 PG 500
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Time Division Multiplexing (TDM)
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Possible when the data rate of the transmission exceeds the required data rate of the transmission. TDM works by a number of data signals are sent simultaneously over a transmission medium. The signals are all buffered and then scanned in a "round robin" format (1,2,3,1,2,3,etc). Then it is multiplexed into a composite digital data stream. Thus, the rate transmitted must at least equal the sum of the data rates of the 3 inputs. The digital data stream is sent, either digitallyor analog via modem transmission is synchronous to the destination where the data is demultiplexed into destination buffers equal to the number of data signals. (3 data signals to the multiplexer then 3 buffers,etc) Used with digital signals or analog signals carrying digital data. Ch 17 PG 500
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TDM Channel
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The set of timeslots dedicated to one source from frame to frame. (a portion of the transmission capacity is dedicated to signals from a single source - that source sees a constant data rate (tdm) or constant bandwidth channel (fdm) for transmission. Ch 17 PG 501
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TDM frame
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The data of TDM is organized into frames which each contain a cycle of time slots and in each frame one or more slots are dedicated to each data source. Ch 17 PG 501
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Synchronous digital Hierarchy (SDH)
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A compatible version of SONET Ch 17 PG 504
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Synchronous optical network (SONET)
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an optical transmission interface originally proposed by BellCore. Intended to provide the specification for taking advantage of high speed digital transmission capability of optical fiber. The basic SONET building block is the STS-1 frame which is 810 octets transmitted once every 125 us for overall data rate of 51.84Mbps. Ch 17 PG 504
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data link control protocol
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The layer of control in each communication device that provides functions such as flow control, error detection, and error control. The most common Data link control protocol is the HDLC. Ch 17 PG 507
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digital Subscriber Line (DSL)
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Ch 17 PG
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What three kinds of basic organizational difficulties can communications technology help companies overcome?
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Communications technology can assist companies in:1) Overcoming operational silos by reducing communication barriers between departments2) Reducing the amount of Middle Management in companies with too many managers3) Managing a geographically diverse company RQ1 PG 1.1
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Name four types of information that are found on networks
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The four types of information found on networks are:1) Data communications2) Voice communications3) Video communications4) Image communications RQ1 PG 1.2
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Briefly define convergence and unified communications
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Convergence is taking all voice, video and data communications whether they are circuit or packet based, converting them to packet based and putting them all onto one packet based data network. The three key benefits are efficiency, effectiveness and transformation. Unified Communications is the unification of real time communications with non-real time communications and business applications combined in an end-user focused set of interfaces. For example a real time communications dashboard that combine instant messaging, email, audio, video, etc into one view for the ease and efficiency of the end user RQ1 PG 1.3
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How has the technology of the compact disc used in the music industry been used in image communications?
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The same technology that was used to create the compact disc of the music industry was used to create the optical disc which allows for the storing of large amounts of information cheaply. RQ1 PG 1.4
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Why are the burdens on the manager greater today than in the previous years when it comes to using new technology efficiently?
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With the ever changing and rapid improvement of old and development of new technology, the manager needs to understand the basics behind each of the improvements or foundations of the new in order to make the most cost- effective and apt solution for their business. The improvement and development of technology has created a multitude of decisions where in the past it was much more limited. RQ1 PG 1.5
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Why has optical fiber transmission become popular in the past few years?
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Optical fiber transmission has become so popular due to the decrease in cost and serious increase in capacity. Fiber optic cable is also very secure since it is difficult to tap into. RQ1 PG 1.6
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What types of communications can be carried by satellite transmission?
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All four types of information (data communications, voice communications, video communications and image communications) can be carried by satellite transmission. RQ1 PG 1.7
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Name two approaches that can be used for increasing the efficiency of transmission services.
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1) Multiplexing – sharing a transmission facility across a number of devices which allows for sharing the cost over those devices. 2) Compression – consolidation of data for the ability to use a less costly and reduced capacity transmission facility RQ1 PG 1.8
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Contrast the function of application software with that of interconnection software.
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For a business, application software is the software that is distributed and used throughout the business PC's and terminals to communicate or accomplish business. Interconnection software is the software that allows for all of the PC's and terminals to transmit messages or work together so that the application software can work effectively. RQ1 PG 1.9
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What are the two different interpretations of the prefixes kilo, mega, and giga? Define a context in which each interpretation is used.
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Kilo, mega and giga have different interpretations depending on if they are expressing data transmission or computer storage. Data Transmission uses the international standard which is defined by the powers of 10. Bandwidth is an example of data transmission measurement and is measured in bps. So 1,000,000 bps is = 106 bps = 1mbps.Computer storage is based on bytes so therefore measurement is based on the power of 2 (the potential outcomes). So 1MB = 2 20 = 1,048,576 bytes. RQ2 PG 2.1
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What is the bandwidth of telephone voice?
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Limited to 3400 Hz of bandwidth. RQ2 PG 2.2
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The process that takes advantage of redundancy to reduce the number of bits sent for a given piece of data is called what?
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Compression. RQ2 PG 2.3
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What is the difference between Centrex and PBX?
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PBX (private branch exchange) is a telephone switching facility that is owned by(or leased) and located on-site of the company. It allows for the interconnection of all the phones in the facility and allows for access to the public telephone system. Centrex is an option provided by the phone company. It provides the same functionality as PBX, but the switching facility is at the phone company's main office and is owned by the phone company. RQ2 PG 2.4
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What is the difference between a printable character and a control character?
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A printable character is one that is seen on the screen (text) or in printed form. A control character is not seen but is used (return, backspace, etc). RQ2 PG 2.5
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Explain the basic principles of vector graphics and raster graphics.
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Vector Graphics are images that are made up of a group of straight and curved line segments. Vector graphics are used with many advanced graphic software development programs such as Adobe illustrator. Vector graphics quality also does not degrade with scaling. Raster Graphics are images that are created by grouping pixels together on a grid. A Raster graphic will degrade with scaling. Raster Graphics are widely used and is usually seen in the JPEG format. RQ2 PG 2.6
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List two common image formats
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JPEG (Joint Photographic Experts Group) and GIF(Graphics Interchange Format). JPEG is the more commonly used image format since it is designed for common general use and can be used for high quality images. GIF is primarily used on the web and can only display up to 256 colors making it not suitable for photographic images. RQ2 PG 2.7
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List two common document formats.
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PDF (Portable Document Format) and Postscript. PDF is widely used for protecting documents and free readers are available on the web. Postscript is in most printers, desktop and high-end, and is a page description language. RQ2 PG 2.8
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Describe the process used to prevent flicker in a video screen.
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Interlacing is the process used to eliminate flicker without increasing bandwidth. A screen is divided into two fields with the even and odd scanned lines scanning each on a field and alternating with each successive scan. At the bottom, the scan is repositioned to the top and done again allowing for a doubling of the refresh rate to 60 per second. This removes the flicker from the screen that is evident with a refresh of 30 per second. RQ2 PG 2.9
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Define Response Time
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The amount of time a system takes to respond or react to an input or particular task. Shorter response time creates greater cost from an increase in the computer processing power or the competing requirements. Needed response time and cost are examined to determine necessary response time. RQ2 PG 2.1
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What is considered an acceptable system response time for interactive applications and how does this response time relate to acceptable response time for Web Sites?
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The old school thought was that response time for interactive applications of up to 2 seconds was acceptable since people had to think about the next task. New research has suggested that faster response times increase productivity. Response times of under a second (.25 to .75) yield a significantly higher productivity level than anything above 1 second. For the Web, response times that are within 3 seconds yield a higher level of user attention than response times greater than that with 10 seconds or greater actually discouraging the user from using the site. RQ2 PG 2.11
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What is the major function of the network access layer?
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The major function of the network access layer is to manage the exchange of data from the computer to the communication network with which it is attached. The network access protocol uses control information to present data to the network for transmission. RQ2 PG 5.1
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What tasks are performed by the transport layer?
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The transport layer is made up of the mechanisms that ensure that the data that is transmitted arrives at the destination complete and in the same order that it was sent. The transport layer accepts the data from the next higher level and adds a transport header that contains the protocol control information which may include the source port, destination port, sequence number and error-detection code. Then the transport layer sends the information (each segment) to the network access layer. RQ2 PG 5.2
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What is a protocol?
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A protocol is a set of rules that govern the exchange of data between two entities. The key elements include: Syntax (data format and signal levels), Timing (sequencing and speed matching) and Semantics (error handling and control information for coordination). RQ2 PG 5.3
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What is a protocol data unit (PDU)?
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The protocol data unit (PDU) is the combination of the data from the previous layer and the control information that the current layer adds to it. For example, the control information that the transport layer adds to the data from the previous layer would be called a transport PDU. When the data is sent to the network access layer and the new control information is added, that creates a network access PDU (also known as a packet). RQ2 PG 5.4
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What is a protocol architecture?
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A protocol architecture is the structured set of modules that implement the communication function. For example, a File transfer architecture can consist of a File transfer module, a Communications service module and a network access module. These modules have peers at each layer to perform the appropriate subtasks. These peer modules communicate on the same level even though they are in different systems. RQ2 PG 5.5
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What is TCP/IP?
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TCP/IP is a protocol suite that performs the communication task by using a five layer approach (based on protocol standards). The layers consist of: Application layer, transport layer, internet layer, network access layer and physical layer. TCP/IP is the standard for the internet communications. RQ3 PG 5.6
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There are several protocol models that have been developed. Examples of these include SNA, Appletalk, OSI, and TCP/IP as well as more general models such as three-layer models. What model is actually used for communications that travel over the internet?
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The TCP/IP model is the standard for internet communications RQ3 PG 5.7
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What are some advantages of layering as seen in the TCP/IP architecture?
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First it is used to create a standardized set of communication protocols. Second, it's more effective and efficient for design and implementation as each layer can be tested and then combined with other layers and tested again. Third, it allows for a complex system to be broken down into manageable sections for design, troubleshooting and/or implementation. RQ3 PG 5.8
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Which version of IP is most prevalent today?
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Today, IPv4 is the most prevalent. Although IPv6 is ready, will accommodate faster speeds and mix of data streams, IPv4 is the maintained standard. This is expected to change over the next few years. RQ3 PG 5.9
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Does all traffic running on the internet use TCP?
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No. Some applications do not need to use TCP to function. SNMP (Simple Network Management Protocol) uses UDP (User Datagram Protocol) and others like ICMP (Internet Control Message Protocol) and IGMP (Internet Group Management Protocol) interact directly with IP. RQ3 PG 5.1
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Compare the address space between IPv4 and IPv6. How many bits are used in each?
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IPv4 uses a 32 bit address space for source and destination. IPv6 uses a 128 bit address space for source and destination. RQ3 PG 5.11
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Large files sent over the network must be broken up into smaller packets. How does the IP layer keep the packets from getting misplaced or collected out of order?
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The IP adds a header of control information to each segment received from the TCP in order to form the IP datagram (or IP Packet). The IP can fragment the data into smaller packets if necessary and indicates the order in the fragment offset field of the header. Then it is passed down to the network access layer. Upon receipt the IP layer at destination will use the fragment offset for reassembly. RQ3 PG 5.12
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What is a router?
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A router is a device that connects two networks and is designed to send data from one network to the other from the source system to the destination. Its essential functions are: a) provide a link between networks b) the routing and delivery of data between end systems c) work with various networks to complete its purpose without modifying the network architecture RQ3 PG 5.13
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Does a router require that all attached layer 2 protocols are the same?
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No. The router will connect two networks that don't have to be similar. For example, packet sizes on Ethernet and Frame Relay networks can be different and the router needs to be able to accommodate those differences. RQ3 PG 5.14
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Define flow control.
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Flow control is a procedure that prevents a faster transmitting entity from overwhelming the receiver with data. In the absence of flow control data can be lost. For data link control, flow control is accomplished by sequentially numbering each frame. The receiving entity sends acknowledgements to the sender stating which frames have been received and if it's ok to send more. RQ4 PG 17.1
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Define error control.
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Error control is the detection and correction of errors in the process of transmission and reception. Since data is sent as a sequence of frames, data link control focuses on two types of errors: Lost frame and damaged frame. RQ4 PG 17.2
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List common ingredients for error control for a link control protocol.
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The following ingredients are used for error control in a link control protocol: Error detection – receiving entity detects frames in error and discards ; Positive acknowledgment – Receiving entity sends a positive acknowledgment that the frame was received without error. ; Retransmission after timeout – If the receiving entity does not send a positive acknowledgment to the sender then after a predetermined amount of time the sender will send again. ; Negative acknowledgment and retransmission - The receiving entity sends a negative acknowledgment for frames that have an error and the sending entity will retransmit those frames. RQ4 PG 17.3
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What is the purpose of the flag field in HDLC?
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The flag field is used for synchronization. It always contains a standard pattern and appears at the beginning and the end of the frame. RQ4 PG 17.4
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What type of error detection is used in the HDLC frame check sequence field?
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16 or 32-bit cyclic redundancy check. RQ4 PG 17.5
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What are the three frame types supported by HDLC? Describe each.
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Information Frames (I) – they carry the data for transmission as well as the control information for flow and error control. Supervisory Frames (S) – another means of control for flow and error control. Unnumbered Frames (U) – provide for the supplemental link control functions. RQ4 PG 17.6
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What is multiplexing?
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Multiplexing is the sharing the capacity of a data link with two or more data sources. The Multiplexer accepts x number of inputs and carries x number of channels across one data link to a demultiplexer which accepts the data stream and separates out the data by channel and delivers it to the proper output. RQ4 PG 17.7
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The set of time slots or the frequency allocated to a single source is called what?
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Channel. RQ4 PG 17.8
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Why is multiplexing so cost effective?
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The greater number of channels that a single transmission facility can transmit, the more cost effective it is. The higher the data rate the cost per kbps decreases. Since many voice and data communications require a limited amount of data rate support, multiplexing allows for more efficient and cost effective approach in sharing the capacity of the data link. RQ4 PG 17.9
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How is interference avoided by using frequency division multiplexing?
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The channels (carrier frequencies) are separated by portions of the unused spectrum know as "guard bands". This prevents or lessens overlap which prevents or limits interference. RQ4 PG 17.1
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What is echo cancellation?
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Echo cancellation is a process that allows for simultaneous transmission of signals in both directions in the same frequency band on a lone transmission line. The transmitter will remove the echo of its own transmission from that of the transmission it is receiving in order to retrieve the signal from the sender. Echo Cancellation is used in ADSL to improve the downstream channel and extend the upstream channel as long as there is echo cancellation logic on both ends. RQ4 PG 17.11
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"Define upstream and downstream with respect to subscriber lines.
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Downstream is flow of data from the “carrier’s central office” to the users site. Upstream is the opposite (user to carrier).
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Explain how synchronous time division multiplexing (TDM) works.
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TDM works by a number of data signals are simultaneously sent over a transmission medium. The signals are all buffered and then scanned in a "round robin" format (1, 2, 3, 1, 2, 3, etc). Then it is multiplexed into a composite digital data stream. In order to successfully complete the multiplexing, the multiplexer must have an equal or greater data rate than the sum of the source data rates. The digital data stream is sent, either digitally or analog via modem, to the receiver who demultiplexes the data into three destination buffers. RQ4 PG 17.13
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What are some of the major uses of T-1 lines?
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The major external use is for T-1 facilities to lease a dedicated transmission to a customer who uses it to set up private networks for their organization. Some examples of these private networks are: Private voice networks, private data networks, video conferencing, High Speed Digital Fax and internet access. RQ4 PG 17.14
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Why is the use of private T-1 lines attractive to companies?
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T-1 allows for one system for configuration rather than a cacophony of other lower speed choices. T-1 transmissions are also cheaper. T-1 also allows for high speed access from the users location to the telephone network. RQ4 PG 17.15
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Distinguish among analog data, analog signaling, and analog transmission
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Analog data takes on continuous values on some interval ; Analog signaling is a continuously varying electromagnetic wave that may be transmitted over a variety of media depending on the frequency ; Analog transmission is a means of transmitting analog signals without regard to their content - could be analog or digital data. The analog signal suffers attenuation which limits the length RQ5 PG 16.1
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Distinguish among digital data, digital signaling, and digital transmission
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Digital Data take on discrete values ; Digital signal is a sequence of voltage pulses that may be transmitted over a wire medium. It's generally cheaper than analog signalling and is less suceptible to noise interference ; Digital transmission is concerned with the content of the sgnal and can only be sent a limited distance before attenuation threatens integrity so repeaters are used RQ5 PG 16.2
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What is the difference between amplification and retransmission?
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Amplification boosts the energy of the signal, but also boosts the noise. For analog it will work, but for digital it increases the number of errors. Retransmission is done with repeaters in digital transmission. Repeaters recieves the digital signal, recovers the binary pattern and re transmits a new signal. RQ5 PG 16.3
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What is differential encoding?
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In differetial encoding, the signal is decoded by comparing the polarity of adjacent signal elements rather than determining the absolute value of a signal element. This is more reliable to detect a transition in the presence of noise. Digital encoding of digital data. RQ5 PG 16.4
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What function does a modem perform?
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Modems encode digital data to produce an analog signal RQ5 PG 16.5
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Are the modem and the codec functions inverses? Could an inverted modem function as a codec and vice versa?
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No. A modem encodes digital data to produce an analog signal and a codec encodes analog data to create a digital signal. The inverse of the modem would create digital data and the inverse of the codec would create analog data. RQ5 PG 16.6
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Indicate three major advantages of digital transmission over analog transmission
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Cost, data integrity, capacity utilization, security and privacy and integration RQ5 PG 16.7
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How are binary values represented in ASK and what is the limitation to this approach?
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In ASK the binary values are represented by two different amplitudes. One is represented by a constant amplitude and the other by the absence of the amplitude. ASK is susceptible to sudden gain changes and is rather inefficient and is used up to only 1200bps. RQ5 PG 16.8
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Indicate the major categories into which modems may be classified based on their data rates
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Dial up modem - 33.6Kbs Up and 56kbs down. ISDN basic rate 2 channels 128kbs up and 128kbs down. ADSL 16-640kbs up and 1.5-9Mbs down. Cable modem - 400kbs up and 10-30Mbs down. RQ5 PG 16.9
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What is NRZL? What is a major disadvantage of this data encoding approach?
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Digital encoding of digital data. NRZL is Nonreturn to zero level. Easiest way to transmit digital signals is to use two different voltage levels for the two binary digits. A negative voltage is binary 1 and positive is binary 0. This means that the voltage is never 0. It can be difficult to determine where the stream ends and where it begins. Also, if the leads in the twisted cable are reversed, it inverts the 1's and 0's. This doesn't happen in differential encoding NRZI. RQ5 PG 16.1
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How is the transmission of a single character differentiated from the transmission of the next character in asynchronous transmission?
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Following the data bits of the character there is a parity bit that is used for error detection and then a stop element which signals the end of the character. The stop element is continually transmitted until the transmitter is ready to send the next character. RQ5 PG 16.11
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What is a major disadvantage of asynchronous communication?
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A major disadvantage to asynchronous communciation is that there is a large amound of overhead that is transmitted as well. The overhead is reduced withlarger blocks of bits but that results in a greater timing error. RQ5 PG 16.12
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