Chapter 2: How LAN and WAN Communications Work TRUE/FALSE Analog signals are the basis of the most common signaling method used on LANs and high-speed WANs ANS: F PTS: REF: 37 In a connectionless service, there is no acknowledgment that a frame has been received ANS: T PTS: REF: 41 The Ethernet protocol permits only one node to transmit at a time ANS: T PTS: REF: 53 Class A nodes in FDDI networks are servers or workstations ANS: F PTS: REF: 60 The upstream and downstream frequencies used by cable modems may be the same ANS: T PTS: REF: 63 MULTIPLE CHOICE The OSI model consists of distinct layers stacked on one another a two c five b three d seven ANS: D PTS: REF: 35 A(n) signal can vary continuously, as in a wave pattern with positive and negative voltage levels a discrete c digital b analog d binary ANS: B PTS: REF: 36 The task of the layer in a LAN is to organize bits so that they are formatted into frames a Network c Data Link b Transport d Physical ANS: C PTS: REF: 39 circuits are logical communication paths set up to send and receive data a Electric c Closed b Physical d Virtual ANS: D PTS: REF: 42 A(n) is a connection identification assigned by the Session layer a MAC address c port b IP address ANS: C d network id PTS: REF: 42 A Class protocol within the Transport layer provides an option to recover lost packets in certain situations a c b d ANS: D PTS: REF: 43 Two-way alternate (TWA) mode for dialog control is used in communications a simplex c half duplex b complex d full duplex ANS: C PTS: REF: 43 is a process that scrambles the data so that it cannot be read if intercepted by unauthorized users a Encryption c Deciphering b Decryption d Decoding ANS: A PTS: REF: 44 Computer programmers use the layer to connect workstations to network services, such as linking an application into electronic mail a Presentation c Session b Application d Transport ANS: B PTS: REF: 46 10 The term refers to wrapping the information in one layer inside the information within the next layer a encase c encapsulate b enclose d envelope ANS: C PTS: REF: 49 11 Information from one layer is transferred to the next by means of commands called a primitives c primaries b pointers d messages ANS: A PTS: REF: 50 12 Ethernet transport (the IEEE 802.3 specification), takes advantage of the and star topologies a bus c mesh b torus d tree ANS: A PTS: REF: 53 13 The field in an Ethernet frame synchronizes frame transmission and consists of an alternating pattern of zeroes and ones a data and pad c start of frame delimiter (SOF) b frame check sequence (FCS) d preamble ANS: D PTS: REF: 54 14 Both standard 802.3 and Ethernet II can have optional field(s) between the length or type field and the data field a one c three b two d four ANS: C PTS: REF: 55 15 The token ring transport method uses a physical topology along with the logic of a ring topology a bus c mesh b star d grid ANS: B PTS: REF: 56 16 The field of a token identifies the frame as a data frame or as a frame used for network management, such as reporting network errors a access control c frame status b frame check sequence d frame control ANS: D PTS: REF: 57 17 If no broadcasts are detected from the active monitor or any one of the standby monitors, a ring goes into a condition a signaling c messaging b beaconing d broadcasting ANS: B PTS: REF: 58 18 communications in FDDI networks are used for time-sensitive transmissions requiring continuous transmission a Synchronous c Modulated b Asynchronous d Amplified ANS: A PTS: REF: 59 19 A(n) line is a dedicated telephone line that can be used for data communications to connect two different locations for continuous point-to-point communications a DSL c T-carrier b LATA d IXC ANS: C PTS: REF: 61 20 In the switching technique, the bandwidth of communications medium is dynamically allocated based on application need a Time Division Multiple Access c circuit b Frequency Division Multiple Access d Statistical multiple access ANS: D PTS: REF: 65 21 switching establishes a dedicated circuit between the two transmitting nodes, but the circuit is a logical connection and not a physical one a Packet c Circuit b Frame d Message ANS: A COMPLETION PTS: REF: 66 LAN and WAN communications have been generally guided by a network communications model called the _ reference model ANS: Open Systems Interconnection OSI Open Systems Interconnection (OSI) OSI (Open Systems Interconnection) PTS: REF: 34 The layer of the OSI model controls the passage of packets along routes on the network ANS: Network PTS: REF: 41 The Microsoft Windows is a service that makes one computer visible to another for access through the network ANS: redirector PTS: REF: 46 is the process of checking communication media for a specific voltage level indicating the presence of a data-carrying signal ANS: Carrier sense PTS: REF: 53 The switching technique divides channels into distinct time slots ANS: Time Division Multiple Access TDMA Time Division Multiple Access (TDMA) TDMA (Time Division Multiple Access) PTS: REF: 65 MATCHING Match each term with the correct statement below a discovery f b peer protocols g c digital signal h d message switching i e Service access point (SAP) frame packet radio point of presence (POP) simplex communications uses distinct voltages to generate binary ones or zeroes discrete unit of data containing control and address information corresponding to OSI Data Link layer process by which Network layer constantly gathers metrics about the location of networks and nodes allows a signal to travel in only one direction on a medium enable an OSI layer on a sending node to communicate with the same layer on the receiving node enables Network layer to determine which network process at the destination should accept a frame a junction at which LATA lines are connected to IXC lines form of wireless WAN communication that takes place at very high radio frequencies uses a store-and-forward communication method to transmit data from sending to receiving node ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: C F A I B E H G D PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: 1 1 1 1 REF: REF: REF: REF: REF: REF: REF: REF: REF: 37 39 42 44 49 55 60 64 66 SHORT ANSWER Provide a high-level description of the bottom, middle, and top layers of the OSI model ANS: The bottom layers perform functions, such as constructing frames and transmitting packet-containing signals, related to physical communications The middle layers coordinate network communications between nodes, ensuring that a communication session continues without interruptions or errors, for example The top layers perform work that directly affects software applications and data presentation, including data formatting, encryption, and data and file transfer management Taken together, the set of layers is called a stack PTS: REF: 36 What are electromagnetic interference (EMI) and radio frequency interference (RFI)? ANS: Electromagnetic interference (EMI) and radio frequency interference (RFI) are two sources of Physical layer interference.EMI is caused by magnetic force fields that are generated by electrical devices such as fans, elevator motors, portable heaters, and air-conditioning units RFI is caused by electrical devices that emit radio waves at the same frequency used by network signal transmissions These transmissions include cable TV components, radio and television stations, nearby amateur radio operators, ballast devices in fluorescent lights, inexpensively built computer or TV equipment, and CB radios PTS: REF: 38 What is the role of the media access control (MAC) sublayer of the Data Link layer? ANS: The MAC sublayer examines the physical address or device address—sometimes called the MAC address—information contained in each frame.For example, the MAC sublayer on a workstation examines each frame received by the workstation and sends the frame to the next higher layer, if the address matches The frame is discarded if the address is not a match The MAC sublayer also regulates how multiple devices share communications on the same network PTS: REF: 39 Explain how TWS (two-way simultaneous) dialog control and buffering enable full duplex communications ANS: TWS enables full duplex communications in which the network interface can send and receive at the same time, because there are two channels created over the same medium, one for receiving and one for sending Besides the TWS capability, full duplex is possible because of buffering at the network interface Buffering means that the NIC is equipped with memory to temporarily store information that it is not currently processing PTS: REF: 44 Describe the relationship between the service data unit (SDU) and protocol data unit (PDU) ANS: At each OSI layer,an SDU is encapsulated with control and transfer information to form a PDU After the PDU is formed at a particular layer on computer A, for instance, it is then sent to the same layer on computer B Also, if the layered communications are going down the stack on computer A, for example, then the PDU is sent to the next lower layer in the stack The control and transfer information is stripped out of the PDU to leave only the SDU That layer then adds control and transfer information PTS: REF: 50 What is a Request for Comment (RFC)? ANS: An RFC is a document prepared and distributed by any individual or group as a way to further networking, Internet, and computer communications RFCs help ensure that network standards and conventions are provided so one network can talk to another Every RFC is assigned a number to distinguish it from other RFCs and to provide a way to track it Older RFCs are sometimes clarified, built upon, or replaced by newer ones RFCs build cooperation in a community of equals and play a significant role in advancing network technologies PTS: REF: 52 Describe the role of the active monitor in a token ring network ANS: Each token ring network designates one node as the active monitor Usually this is the first station recognized when the network is brought up The active monitor is responsible for packet timing on the network and for issuing new token frames if problems occur.Every few seconds, the active monitor broadcasts a MAC sublayer frame to show it is functioning properly A broadcast frame or broadcast packet is one that is sent to all points on the network The other workstation nodes are standby monitors.Periodically, they broadcast frames called “standby monitor present” frames to show they are working normally and are available to replace the active monitor should it malfunction PTS: REF: 57 Compare and contrast FDDI to the token ring access method ANS: FDDI is similar to the token ring access method because it uses token passing for network communications It differs from standard token ring in that it uses a timed token access method An FDDI token travels along the network ring from node to node If a node does not need to transmit data, it picks up the token and sends it to the next node If the node possessing the token does need to transmit, it can send as many frames as desired for a fixed amount of time, called the target token rotation time (TTRT) Because FDDI uses a timed token method, it is possible for several frames from several nodes to be on the network at a given time, providing high-capacity communications PTS: REF: 59 Describe the role of the headend in the star topology of a Cable TV WAN ANS: The focal point in the star is the headend, which is the central receiving point for signals from various sources, including satellite, other major cable sources, and local television sources The headend is a grouping of antennas, cable connections, microwave towers, and satellite dishes, and it distills all incoming signal sources and transfers them to remote distribution centers through trunk lines PTS: REF: 62 10 Describe the topology of wireless WANs using radio communications ANS: The topology of radio communications requires connecting a LAN to a wireless bridge or switch, for example, which in turn is connected to an antenna The antenna transmits a radio wave to a distant antenna, which is also connected to a bridge, switch, or router that receives packets and places them on the local LAN This type of communications is called packet radio and takes place at very high radio frequencies PTS: REF: 64 ... Interconnection OSI Open Systems Interconnection (OSI) OSI (Open Systems Interconnection) PTS: REF: 34 The layer of the OSI model controls the passage of packets along routes on the... by which Network layer constantly gathers metrics about the location of networks and nodes allows a signal to travel in only one direction on a medium enable an OSI layer on a sending node to communicate... into a condition a signaling c messaging b beaconing d broadcasting ANS: B PTS: REF: 58 18 communications in FDDI networks are used for time-sensitive transmissions requiring continuous