CPSC 353 Data Communications and Computer Networks
OSI Protocol
- Application - Provides access to the OSI environment for users and also provides distributed information services.
- Presentation - Provides independence to the application processes from differences in data representation (syntax).
- Session - Provides the control structure for communication between applications; establishes, manages, and terminates connections(sessions) between cooperating applications.
- Transport - Provides reliable, transparent transfer of data between end points; provides end-to-end error recovery and flow control.
- Network - Provides upper layers with independence from the data transmission and switching technologies used to connect systems; responsible for establishing, maintaining, and terminating connections.
- Data Link - Provides for the reliable transfer of information across the physical link; sends block (frames) with the necessary synchronization, error control, and flow control.
- Physical - Concerned with transmission of unstructured bit stream over physical medium; deals with the mechanical, electrical, functional, and procedural characteristics to access the physical medium.
TCP/IP Protocol
- Application layer - Provides communication between processes or applications on separate hosts.
- End-to-end or Transport layer - Provides end-to-end data transfer service. This layer may include reliability mechanisms. It hides the details of the underlying network or networks from the application layer.
- Internet layer - Concerned with routing data from source to destination host through one or more networks connected by routers.
- Network access layer - Concerned with the logical interface between an end system and a network.
- Physical layer - Defines characteristics of the transmission medium, signaling rate, and signal encoding scheme.
January 9, 2002
Quiz 6 (Courtesy of Tony)
Bus In this topology, all stations attach, through appropriate hardware interfacing known as a tap, directly to a linear transmission medium.
Tree This topology is a generalization of the bus topology. The transmission medium is a branching cable with no closed loops.
Ring In this topology, the network consist of a set of repeaters joined by point-to-point links in a closed loop.
Star In this topology, each station is directly connected to a common central node. Typically, each station attaches to a central node via two point-to-point links, one for transmission and one for reception.
Round Robin With this technique each station in turn is given the opportunity to transmit. During that opportunity, the station may also decline to transmit. The station, when it is finished, relinquishes its turn, and the right to transmit passes to the next station in a logical sequence.
Broadband Coaxial Cable Is the type of cable used in cable television systems. This type of system is more expensive and more difficult to install and maintain.
Baseband Coaxial Cable Is the type of cable that make use of digital signaling.
Choice A The four alternatives media that can be used for a bus LAN are.
True There are a number of potential problems with the ring topology. A break in any link of the failure of a repeater disables the entire network.
Hub The products on the market use a scheme in which the central element of the star is an active element, referred to as the.
Cut-through Switch In this type of switch, the hub begins repeating the incoming frame onto the appropriate output line as soon as the hub recognizes the destination address.
Store-and-Forward Switch In this type of switch, the hub accepts a frame on an input line, buffers it briefly, and then routes it to the appropriate output line.
Wireless LANS This type of LAN are an indispensable adjunct to traditional LANs by satisfying requirements for mobility, relocation, ad hoc networking and coverage of locations difficult to wire.
Ad Hoc Network A peer-to-peer network (no centralized server) set up temporarily to meet some immediate need.
(B) Satellite All current wireless LAN products fall into one of the following categories except for:.
Bridge Provides an extension to the LAN that requires no modification to the communications software in the stations attached to the LANs.
Passive threats, sometimes referred to as eavesdropping, involve attempts by an attacker to obtain information relating to a communication.
Active threats involve some modification of the transmitted data or the creation of false transmissions.
Public-key An encryption scheme that involves two keys, one for encryption and a paired key for decryption.
Conventional With this type of encryption, two parties share a single encryption/decryption key. The principal challenge with this type of encryption is the distribution and protection of the keys.
Network Security The measures that are needed to protect data during their transmission and to guarantee that data transmissions are authentic.
Computer Security The generic name for the collection of tools designed to protect data and to thwart hackers.
Information Security The use of automated tools for protecting files and other information stored on the computer.
True Conventional encryption and public-key encryption are often combined in secure networking applications.
Masquerade and Replay Which of the following is not a category of Passive threats.
Traffic Analysis Which of the the following is not a category of Active threats.
Availability This requirement of computer and network security requires that data are available to authorized parties only.
Confidentiality This requirement of computer and network security requires that data only be accessible for reading by authorized parties. This type of access includes printing, displaying, and other forms of disclosure, including simply revealing the existence of an object.
Integrity This requirement of computer and network security requires that data can be modified only by authorized parties. Modification includes writing, changing, changing status, deleting, and creating.
802.3 - Ethernet
802.4 - Token Bus
802.5 - Token Ring
802.7 - Broadband
802.8 - Fiber Optic
Quiz 5
Congestion Control The amount of traffic entering and transiting the network must be regulated for efficient, stable, and fair performance. What provides this function?
Routing Because the source and destination station are not directly connected, the network must route each packet, from node to node, through the network. What provides this function?
Circuit Switching This is used in public telephone networks and is the basis for the private networks built on leased lines and using on-site circuit switches.
Stations The end devices that wish to communicate on a communications network may be referred to as?
Nodes Switching devices whose purpose is to provide communication on a communications network are?
Subscribers The devices that attach to the network.
Subscribers line The link between the subscriber and the network; also referred to as the subscriber loop or local loop.
Exchanges The switching centers in the network.
End Office A switching center that directly supports subscribers is known as an?
Trunks The branches between exchanges that carry multiple voice-frequency circuits using either FDM or synchronous TDM.
Packet Switching Was designed to provide a more efficient facility than circuit switching for bursty data traffic.
False With internal datagrams, a route is defined between two endpoints and all packets for that datagram follow the same route.
True With internal virtual circuits, a route is defined between two endpoints and all packets for that virtual circuit follow the same route.
True With internal datagrams, each packet is treated independently, and packets intended for the same destination may follow different routes.
Packet switching The routing function of this type of network attempts to find the least-cost route through the network, with cost based on number of hops, expected delay, or other metrics.
X.25 Is the standard protocol for the interface between an end system and a packet switching network.
Datagram In this approach, each packet is treated independently, with no reference to packets that have gone before.
Virtual Circuit In this approach, a preplanned route is established before any packets are sent.
Datagrams follow a predefined route is not an advantage of the datagram approach.
External virtual circuit, internal virtual circuit. When the user requests a virtual circuit, a dedicated route through the network is constructed. All packets follow that same route.
Eternal virtual circuit, internal datagram. The network handles each packet separately. Thus, different packets for the same external virtual circuit may take different routes.
External datagram, internal datagram. Each packet is treated independently from both the user's and the network's point of view.
External datagram, internal virtual circuit. The external user does not see any connections, simply sending packets one at a time. The network, however, sets up a logical connection between stations for packet delivery.
Adaptive Routing When the routing decisions that are made change as conditions on the network change.
Random routing This form of routing has the simplicity and robustness of flooding with far less traffic load. With this form of routing, a node selects only one outgoing path for retransmission of an incoming packet.
Flooding This technique requires no network information whatsoever and works as follows. A packet is sent by a source node to every one of its neighbors.
Fixed Routing For this type of routing, a single, permanent route is configured for each source-destination pair of nodes in the network.
ATM Makes use of fixed-size packet, called cells. In this interface the use of a fixed size and fixed format results in an efficient scheme for transmission over high-speed networks.
Frame Relay With this network interface, a single user data frame is sent from source to destination, and an acknowledgement, generated at a higher layer, is carried back in a frame.
Frame Relay Like ATM, this interface is designed to provide a more efficient transmission scheme than X.25.
Source generates the data to be transmitted; examples are telephones and personal computers.
Transmitter transforms and encodes the information in such a way as to produce electromagnetic signals that can be transmitted across some sort of transmission system.
Modem takes a digital bit stream from an attached device such as a personal computer and transforms the bit stream into an analog signal that can be handled by the telephone network.
Transmission system can be a single transmission line or a complex network connecting source and destination.
Receiver accepts the signal from the transmission system and converts it into a form that can be handled by the destination device.
Destination takes the incoming data from the receiver.
WAN generally covers a large geographical area, requiring the crossing of public right-of-ways, and relying at least in part on circuits provided by a common carrier.
Circuit switching is a dedicated communications path is established between two stations through the nodes of the network.
LAN is a communications network that interconnects a variety of devices and provides a means for information exchange among thoses devices typically in a small building or a cluster of buildings.
Packet switching data are sent in a sequence of small chunks which pass through the network from node to node along some path leading from source to destination.
Frame relay is developed to take advantage of the high data rates and low error rates of modern packet switching networks.
ATM or cell relay extends circuit switching to allow multiple channels with the data rate on each channel dynamically set on demand.
ISDN is designed to replace existing public telecommunications networks and deliver a wide variety or services.
Narrowband ISDN is based on the use of a 64-kbps channel as the basic unit of switching and has a circuit-switching orientation.
Broadband ISDN supports very high data rates (100s of Mbps) and has a packet switching orientation.
MAN is a high speed intra-city/campus data network.
Dynamic routing is a way of moving data across an internet; when one path is unavailable, it can use an alternate one.
Node is one of the many packet switches which form the network's backbone.
Multiplexer is an electronic equipment which allows two or more signals to pass over one communications circuit. That "circuit" may be a phone line, a microwave circuit, or a through-the-air TV signal. That circuit may be analog or digital.
Digital transmission is a form of transmission that the signal is reconstructed to what it was identically and then amplified and sent along its way.
Signals are electric or electromagnetic representation of data.
Digital is a sequence of voltage pulses that may be transmitted over a wire medium; for example, a constant positive voltage level may represent binary 1 and a constant negative voltage level may represent binary 0.
Point-to-point is a guided transmission medium providing a direct link between two devices and those are the only two devices sharing the medium.
FTP stands for File Transfer Protocol.
Guided media are electromagnetic waves which are guided along a physical path. Examples: twisted pair, coaxial cable, and optical fiber.
Analog is a continuously varying electromagnetic wave that may be propagated over a variety of media, depending on spectrum; examples are wire media, such as twisted pair and coaxial cable, fiber optic cable, and atmosphere or space propagation.
HTTP is the TCP/IP protocol for transferring World Wide Web pages across the Internet or Intranet.
Analog is a form of transmission, the signal, along with all the garbage it picked up, is simply amplified.
Multipoint is when two devices share the same medium.
Backbone is the physical cable in a building from which network segments radiate. 10Base5(thickwire Ethernet) and fiber optic cable are two popular backbone media.
Unguided media provides a means for transmitting electromagnetic waves but do not guide them. Examples: air, vacuum, and sea water.
SNMP is the protocol used by management stations (computers that monitor network activity and performance) to communicate with one another and the computer (agents) they are monitoring.
TCP/IP is a set of protocol developed by the Department of Defense to link dissimilar computers across many kind of networks, including unreliable ones and connected to dissimilar LANs.
MIME stands for Multipurpose Internet Mail Extensions.
Repeater receives the digital signal, recovers the pattern of 1s and 0s, and retransmits a new signal.
Digital represents dta with a sequence of voltage pulses.
TCP/IP stands for Transmission Control Protocol/Internet Protocol.
SMTP stands for Simple Mail Transfer Protocol.
MIME are the extensions to the standard SMTP e-mail message body to support attachments and other nontext data.
SMTP provides basic electronic mail facility. It provides a mechanism for transferring messages among separate hosts.
HTTP stands for HyperText Transfer Protocol.
Delay distortion is a phenomenon peculiar to guided transmission media where distortion is caused by the fact that the velocity of propagation of a signal through a guided medium varies with frequency.
Attenuation is when the strength of a signal falls off with distance over any transmission medium.
FTP is used to send files from one system to another under user command. Both text and binary files are accommodated, and the protocol provides features for controlling user access.
Amplifier to achieve longer distances, the analog transmission system includes devices that boosts the energy in the signal. Unfortunately, this device will also boost the noise components.
TELNET provides a remote logon capability, which enables a user at a terminal or personal computer to logon to remote computer and function as if directly connected to that computer.
SNMP stands for Simple Network Management Protocol.
Packet is a network message that includes data, a header, error control data, and addressing information.
Crosstalk is a category of noise which has been experienced by anyone who, will using the telephone, has been able to hear another conversation; it is an unwanted coupling between signal paths.
Modem stands for modulator/demodulator.
Codec stands for coder-decoder.
Noise are additional unwanted signals that are inserted somewhere between transmission and reception.
Simplex are systems in which data only travel in one direction.
Half duplex are systems in which data can travel in either direction, but not simultaneously.
Duplex are systems in which data travels in both directions at once.
Propagation time is the time required for an electrical wave to travel between two points on a transmission line.
Propagation delay is the time it takes for signal to travel from one point on a circuit to another.
Transmission is the communication of data by the propagation and processing of signals.
Signaling is the physical propagation of the signal along a suitable medium.
Channel capacity is the maximum rate at which data can be transmitted over a given communication path, or channel, under given conditions.
Quiz 3
True The atmosphere and outer space are examples of unguided media, which provide a means of transmitting electromagnetic signals but do not guide them; this form of transmission is usually referred to as wireless transmission.
Twisted pair is the least expensive and most widely used guided transmission medium.
Unshielded twisted pair This transmission medium is ordinary telephone wire. It is the least expensive of all the transmission media commonly used for local area networks and is easy to work with and easy to install.
Category 5 UTP cables and associated connecting hardware whose transmission characteristics are specified up to 100 Mhz. It is a data-grade cable that is becoming increasingly common for preinstallation in new office buildings.
Shielded twisted pair Provides better performance and higher data rates. However, it is more expensive and more difficult to work with than UTP.
Category 3 UTP cables and associated connecting hardware whose transmission characteristics are specified up to 16 Mhz. It corresponds to the voice-grade cable found in abundance in most office buildings.
Twisted pair Traditionally has been the workhorse for communications of all sorts.
True Higher data rates over longer distances can be achieved with coaxial cable and so coaxial cable has often been used for high-speed local area network and for high-capacity long-distance trunk applications.
Large size and weight is not an attribute of optical fiber.
False Within an office building, each telephone is also connected to a twisted pair, which goes to the in-house Centrex system or to a private branch exchange (PBX) facility at the end office. (Note: Centrex goes to office and PBX goes to in house.)
Coaxial cable Can be used over longer distances and support more stations on a shared line than twisted pair. Like twisted pair, consists of two conductors, but is constructed differently to permit it to operate over a wider range of frequencies.
Optical fiber The tremendous capacity of this medium has made it more attractive than coaxial cable, and thus it has taken over much of the market for high-speed LAN's and for long-distance applications.
Optical fiber Is a thin, flexible medium capable of guiding an optical ray.
Directional In this form of unguided media transmission configuration, the transmitting antenna puts out a focused electromagnetic beam; the transmitting and receiving antennas must therefore be carefully aligned.
True The most common type of microwave antenna is the parabolic dish. The antenna is fixed rigidly and focuses a narrow beam to achieve line-of-sight transmission to the receiving antenna.
Omnidirectional In this form of unguided media transmission configuration, the transmitted signal spreads out in all directions and can be received by many antennas.
False In general, the higher the frequency of a signal, the more it is possible to focus it into an omnidirectional beam.
True A communications satellite is, in effect, a microwave relay station. It is used to link two or more ground-based microwave transmitter/receivers, known as earth stations, or ground stations. The satellite receives transmission on one frequency band(uplink), amplifies or repeats the signal, and transmits it on another frequency(downlink).
Broadcast radio The principal difference between this transmission medium and microwave is that the former is omnidirectional and the latter is directional. Thus it does not require dish-shaped antennas, and the antennas need not be rigidly mounted to a precise alignment.
Infrared This form of communications is achieved using transmitters/receivers (transceivers) that modulate noncoherent infrared light. Transceivers must be within the line of sight of each other either directly or via reflection from a light-colored surface such as the ceiling of a room.
Broadcast radio A prime source of impairment for this form of transmission is multipath interference. Reflection from land, water, and natural or human-made object can create multiple paths between antennas. This effect is frequently evident when TV reception displays multiple images as an airplane passes by.
True One important difference between infrared and microwave transmission is that the former does not penetrate walls. Thus the security and interference problems encountered in microwave systems are not present.
Usually installed in building after construction is not an attribute of Twisted Pair.
Inner conductor is braided shield is not an attribute of coaxial cable.
Pulse-shift keying is not one of the three basic encoding or modulation technique for transforming digital data into analog signals.
ASK Is used to transmit digital data over optical fiber.
FSK Is less susceptible to error than ASK. On voice-grade lines, it is typically used up to 1200 bps. It can also be used at even higher frequencies on local area network that use coaxial cable.
Spread Spectrum The technique developed initially for military and intelligence requirements. The essential idea is to spread the information signal over a wider bandwith to make jamming and interception more difficult.
Asynchronous Transmission In this form of transmission each character of data is treated independently.
Synchronous Transmission In this form of transmission each block of data is formatted as a frame that includes a starting and an ending flag.
Quiz 4
Interface defines not only the electrical characteristics of the signal but also the physical means of attachment and the procedures for sending and receiving bits of data.
Synchronous Transmission is where each block of data is formatted as a frame that includes a starting and an ending flag.
Asynchronous Transmission this technique would not work well for long blocks of data because the receiver's clock might eventually drift out of synchronization with the transmitter's clock.
Synchronization is where the receiver must know the rate at which bits are being received so that it can sample the line at regular intervals to determine the value of each received bit.
Topology refers to the physical arrangement of stations on a transmission medium.
DTE includes terminals and computers.
V.24/EIA-232-F is the most widely used interface specified in the ITU-T standard.
DCE is responsible for transmitting and receiving bits, one at a time, over a transmission medium or network.
Mechanical interface characteristic pertains to the actual physical connection of the DTE to the DCE.
Electrical interface characteristic has to do with the voltage levels and timing of voltage changes.
Functional interface characteristic specifies the functions that are performed by assigning meanings to each of the interchange circuits.
Procedural interface characteristic specifies the sequence of events for transmitting data, based on the functional characteristics of the interface.
Interchange Circuits is a set of wires that allow the DCE to interact with the DTE.
True because of the possibility of transmission errors, and because the receiver of data may need to requlate the rate at which data arrive, synchronization and interfacing techniques are insufficient by themselves.
Error Control is achieved by retransmission of damaged frames that have not been acknowledge or for which the other side requests a retransmission.
Flow Control enables a receiver to regulate the flow of data from a sender so that the receiver's buffers do not overflow.
Error Detection is performed by calculating an error-detecting code that is a function of the bits being transmitted. The code is appended to the transmission bits. The receiver calculates the code based on the incoming bits and compares it to the incoming code to check for errors.
Lost Frame a frame fails to arrive at the other side. For example, a noise burst may damage a frame to the extent that the receiver is not aware that a frame has been transmitted.
Damaged Frame a recognizable frame does arrive, but some of the bits are in error (have been altered during transmission).
FDM is a form of multiplexing, a number of signals are carried simultaneously on the same medium by allocating to each signal a different frequency band.
Synchronous TDM in this form of multiplexing, data from various sources are carried in repetitive frames. Each frame consists of a set of time slots, and each source is assigned one or more time slots per frame. The effect is to interleave bits of data from the various sources.
Statistical TDM in this form of multiplexing, the time slots are not pre-assigned to particular data sources. Rather, user data are buffered and transmitted as rapidly as possible using available time slots.
Sonet is intended to provide a specification for taking advantage of the high-speed digital transmission capability of optical fiber.
Synchronous TDM and FDM (page 246) in this form of multiplexing, the time slots for each source are transmitted whether or not the source has data to send.
True the multiplexer combines(multiplexes) data from the input lines and transmits over a higher-capacity data link. The demultiplexer accepts the multiplexed data stream, separates(demultiplexes) the data according to the channel, and delivers them to the appropriate output lines.