CISSP Practice

c. ATM networks use long packets with varying sizes.

d. ATM networks can carry voice communications.

64. c. There are two different kinds of fast packet-switching networks: ATM and PTM. Asynchronous transfer mode (ATM) networks use short packets called “cells” that are always the same length. Packet transfer mode (PTM) does not use short cells but more additional packets that can be longer if necessary. Most packet-switching networks use packets that can be long and vary in size depending on the data being carried. The ATM network can carry data communications where packets are broken into several ATM cells. After travelling through the network, the cells are reassembled into packets. It can also carry video communications where the digital video bits are put in cells and sent through the network. At the destination, the bits are removed from the cells. The ATM also carries voice communications, and the voice is handled in the same way as video.

65. Which of the following effectively facilitates telecommuting?

a. Integrated services digital network

b. Regular modems

c. Facsimile/modems

d. Intelligent modems

65. a. Telecommuting enables employees to work from a remote location. An integrated services digital network (ISDN) can be considered as an “intermediate” step between the current analog local loop and the use of fiber optics. Because of the cost of deploying fiber, it may take a long time before homes are connected. ISDN is cheaper than fiber, can be deployed sooner, and although its capacity is only a fraction of fiber, represents a significant improvement over the current analog local loop. To connect to the office computers, employees need a device called a modem, which enables them to send digital computer data over the analog local loop. ISDN provides higher bits-per-second channels than modems. This would enable videoconferencing of reasonable quality, faster transfer of graphics information, and better quality fax transmission. It would also permit much-improved access to the Internet for home users.

Regular modems, facsimile/modems, and intelligent modems do not have the bits-per-second-channel capacity as that of ISDN. A modem is a device that modulates and demodulates. Modems are primarily used for converting digital signals into quasi-analog signals for transmission over analog communication channels and reconverting the quasi-analog signals into digital signals.

Facsimile/modem combines the features of fax and modem. Intelligent modems are intelligent because they add random-access memory, read-only memory, and erasable programmable read-only memory. Some major functions of intelligent modems include automatic dialing, negotiation of the method of modulation used to communicate with a distant modem, error detection and correction operations to ensure data integrity, and responses to status requests. Regular modems do not have the intelligence so that they cannot perform fax operations.

66. Which of the following information technologies is better equipped to deliver multimedia applications?

a. Integrated services digital network (ISDN) and broadband ISDN

b. Narrowband ISDN, central office switches, and copper-based local loops

c. Narrowband ISDN, fiber optics, and asynchronous transfer mode (ATM)

d. Broadband ISDN, fiber optics, and ATM

66. d. Multimedia applications take advantage of the capability of high-bandwidth integrated services networks to deliver many different kinds of data such as video, image, audio, and text and numerical data. They also take advantage of the processing power of advanced workstations and other devices attached to the network, enabling users to edit, process, and select data arriving from a variety of sources over the network. The capacity of a network, measured as the number of bits it can transmit every second, is called bandwidth. Narrowband networks are low-bandwidth networks, and broadband networks are high-bandwidth networks.

ATM has been chosen as the foundation for the broadband ISDN where the latter is used to carry voice, video, and data traffic to support a range of applications. ATM networks are also suitable for carrying data, video, and voice communications. Fiber optics is an enabling technology for broadband networks. With increased bandwidth, the links can move data more quickly and support the transport of bandwidth-intensive traffic such as video.

Broadband ISDN uses different technology from narrowband (ordinary) ISDN. Narrowband ISDN is best viewed as a digital upgrade of the telephone network’s copper local loop. Broadband ISDN, by contrast, requires fiber optics and ATM, a new approach to network design. ISDN and broadband ISDN have little in common other than their names.