Networking Key Terms Ch 6

hub

A hub or a switch can be thought of as a junction box, permitting new computers to be connected to the network as easily as plugging a power cord into an electrical socket. #

logical topology

A logical topology is how the network works conceptually, much like a logical data flow diagram (DFD) or logical entity relation diagram (ERD) in systems analysis and design or database design.#

overlay network

A network (usually a WLAN) used to supplement a primary network (usually a wired LAN).#

peer-to-peer network

A peer-to-peer network, therefore, is one in which each computer node has equal abilities. #

physical topology

A physical topology is how the network is physically installed, much like a physical DFD or physical ERD.#

redundant array of inexpensive disk (RAID)

A special type of disk drive called RAID (redundant array of inexpensive disks) builds on this concept and is typically used in applications requiring very fast processing of large volumes of data, such as multimedia. Of course, RAID is more expensive than traditional disk drives, but costs have been shrinking. RAID can also provide fault tolerance#

storage area network (SAN)

A storage area network (SAN) is a LAN devoted solely to data storage. When the amount of data to be stored exceeds the practical limits of servers, the SAN plays a critical role. The SAN has a set of high-speed storage devices and servers that are networked together using a very high speed net- work (often using a technology called fiber channel that runs over a series of multi-gigabit point-to-point fiber-optic circuits).#

switch

A switch is an intelligent device with a small computer built-in that is designed to manage a set of separate point-to-point circuits.#

omnidirectional antenna

An access point with an omnidirectional antenna broadcasts in all directions. Its coverage area is a circle with a certain radius.#

layer-2 switch

Because the switch uses the Ethernet address to decide which port to use and because Ethernet is a data link layer or layer-2 protocol, this type of switch is called a layer-2 switch.#

shared Ethernet

Ethernet is a layer 2 protocol, which means it operates at the data link layer;we describe traditional Ethernet which is sometimes called shared Ethernet.#

file server

File servers allow many users to share the same set of files on a common, shared disk drive. #

wardriving

Finding WLANs is quite simple. You just walk or drive around different office buildings with your WLAN-equipped client computer and see if it picks up a signal. There are also many special-purpose software tools available on the Internet that will enable you to learn more about the WLANs you discover, with the intent of helping you to break into them. This type of wireless reconnaissance is often called wardriving#

association

However, before a computer can transmit in a WLAN is must first establish an association with a specific AP, so that the AP will accept its transmissions. #

802.11a

IEEE 802.11a is an obsolete, legacy technology, and no new products are being developed. Under perfect conditions, it provides eight channels of 54 Mbps each with a maximum range of 50 meters or 150 feet. Speeds of 20 Mbps at 50 foot ranges are more common in the face of interference such as drywall or brick walls.#

802.11b

IEEE 802.11b is another obsolete, legacy technology. Under perfect conditions, it provides three channels of 11 Mbps each with a maximum range of 150 meters or 450 feet, although in practice both the speed and range are lower.#

802.11g

IEEE 802.11g is another obsolete, legacy technology, but many organizations still use it. Under perfect conditions, it provides three channels of 54 Mbps each with a maximum range of 150 meters or 450 feet, although in practice both the speed and range are lower.#

802.11n

IEEE 802.11n is the latest version of Wi-Fi that most firms use (or are in the process of installing). Under perfect conditions, it provides three channels of about 200 Mbps each with a maximum range of 150 meters or 450 feet, although in practice both the speed and range are lower. It is also possible to configure APs to use different frequency ranges to provide fewer channels that run at higher speeds up to 600 Mbps each.

clear to transmit (CTS)

If no other computer is transmitting, the AP responds with a clear to transmit (CTS), specifying the amount of time for which the circuit is reserved for the requesting computer. #

network segmentation

If there is more traffic on a LAN than it can handle, you can divide the LAN into several smaller segments. Breaking a network into smaller parts is called network segmentation.#

latency

Most devices are rated for their speed in converting input packets to output packets (called latency).#

resource sharing

Resource sharing refers to one computer sharing a hardware device (e.g., printer, an Internet connection) or software package with other computers on the network to save costs. #

LAN metering software

One approach to controlling the number of copies of a particular software package is to use LAN metering software that prohibits using more copies of a package than there are installed licenses. #

Wired Equivalent Privacy (WEP)

One wireless security technique is Wired Equivalent Privacy (WEP). With WEP, the AP requires the user to have a key in order to communicate with it.#

network-attached storage (NAS)

A NAS is not a general-purpose computer like a server that runs a server operating system (e.g., Windows, Linux); it has a small processor and a large amount of disk storage and is designed solely to respond to requests for files and data. NAS can also be attached to LANs where they function as a fast file server.#

small office, home office (SOHO)

SOHO environments can be small versions of enterprise designs, or can take a very different approach;For SOHO networks, the best LAN choice may be wireless; shows an AP for use in SOHO (small office, home office) environments. This AP is wired into the regular Ethernet LAN and has a separate power supply that is plugged into a normal electrical outlet; Many wireless routers are sold for use in SOHO environments. #

server farm

Sometimes servers are organized into a large set of servers on one part of the network called a cluster or server farm. Server farms can range from tens to thousands of servers.#

fragment-free switching

The final mode, called fragment-free switching, lies between the extremes of cut-through switching and store and forward switching. With fragment-free switching, the first 64 bytes of the frame are read and stored. The switch examines the first 64 bytes (which contain all the header information for the frame) and if all the header data appears correct, the switch presumes that the rest of the frame is error free and begins transmitting.#

distributed coordination function (DCF)

The first media access control method is the distributed coordination function (DCF) (also called physical carrier sense method because it relies on the ability of computers to physically listen before they transmit). With DCF, each frame in CSMA/CA is sent using stop-and-wait ARQ. #

network interface card (NIC)

The network interface card (NIC) is used to connect the computer to the network cable in a wired network and is one part of the physical layer connection among the computers in the network. In a wireless network, the NIC is a radio transmitter that sends and receives messages on a specific radio frequency. #

site survey

The physical WLAN design begins with a site survey. The site survey determines the feasibility of the desired coverage, the potential sources of interference, the current locations of the wired network into which the WLAN will connect, and an estimate of the number of APs required to provide coverage. #

print server

The print server, which is connected to a printer, manages all printing requests from the clients on the network#

point coordination function (PCF)

The second media access control technique is called the point coordination function (PCF) (also called the virtual carrier sense method); The virtual carrier sense method is optional. It can always be used, never used, or used just for frames exceeding a certain size, as set by the WLAN manager.#

network server

The server version of the NOS provides the software that performs the functions associated with the data link, network, and application layers and usually the computer's own operating system.#

collision detection (CD)

The solution to this is to listen while transmitting; If the NIC detects any signal other than its own, it presumes that a collision has occurred and sends a jamming signal. All computers stop transmitting and wait for the circuit to become free before trying to retransmit. #

unshielded twisted-pair (UTP) cable

The type of wiring used in 10Base-T Ethernet networks. Same as twisted pair; A pair of wires used in standard telephone wiring. They are twisted to reduce interference caused by the other twisted pairs in the same cable bundle. Twisted-pair wires go from homes and offices to the telephone company end office.#

virtual carrier sense

The virtual carrier sense method is optional. It can always be used, never used, or used just for frames exceeding a certain size, as set by the WLAN manager.#

channel

Therefore, each AP is set to transmit on a different channel, very much like the different channels on your TV. Each channel uses a different part of the 2.4 GHz or 5 GHz frequency range so that there is no interference among the different channels. #

switched Ethernet

They build the usual switched Ethernet networks as the primary LAN,#

Carrier Sense Multiple Access with Collision Avoidance (CSMA/ CA)

This protocol is similar to the Carrier Sense Multiple Access (CSMA) with Collision Detection (CD) protocol. Whereas CSMA/CD sends a data packet and then reports back if it collides with another packet, CSMA/CA sends a small preliminary packet to determine whether the network is busy. If there is a collision, it is with the small packet rather than with the entire message. CA is thought to be more efficient because it reduces the time required to recover from collisions. #

topology

Topology is the basic geometric layout of the network—the way in which the computers on the network are interconnected.#

Wireless LAN (WLAN)

WLANs use radio transmissions to send data between the NIC and the AP; A wireless local area network (WLAN) is a wireless computer network that links two or more devices using a wireless distribution method (often spread-spectrum or OFDM radio) within a limited area such as a home, school, computer laboratory, or office building. #

warchalking

Warchalking refers to the practice of writing symbols in chalk on sidewalks and walls to indicate the presence of an unsecured WLAN (see www.warchalking.org).#

lightweight directory services (LDAP)

When a client computer wishes to view available resources or access them, it sends a message using an industry standard directory protocol called lightweight directory services (LDAP) to the ADS domain controller. The ADS domain controller resolves the textual name in the LDAP request to a network address and—if the user is authorized to access the resource—provides contact information for the resource. #

bus topology

When we use hubs, Ethernet's logical topology is a bus topology. All computers are connected to one half-duplex circuit running the length of the network that is called the bus.#

Software Publishers Association (SPA)

Whistleblowers receive rewards from SPA, and the violating organizations and employees are brought to court. SPA will work with companies that voluntarily submit to an audit, and it offers an audit kit that scrutinizes networks in search of software sold by SPA members (see www .spa.org).#

cable plan

cable plan, as they have plans for telephone cables and electrical cables. Each floor has a telecommunications wiring closet that contains one or more network hubs or switches. Cables are run from each room on the floor to this wiring closet. #

fiber-optic cable

designed for digital transmission; fiber-optic cable is even thinner than UTP wire and therefore takes far less space when cabled throughout a building. It also is much lighter, weighing less than 10 pounds per 1,000 feet. Because of its high capacity, fiber-optic cabling is perfect for BNs, although it is beginning to be used in LANs.#

dedicated-server LAN

has one or more computers that are permanently assigned as network servers. These servers enable users to share files and often are also used to share printers. A dedicated-server LAN can connect with almost any other network, can handle very large files and databases, and uses sophisticated LAN software. Moreover, high-end dedicated-server LANs can be easily interconnected to form enterprisewide networks or, in some cases, can replace a host mainframe computer. #

bottleneck

he part of the network that is restricting the data flow. Generally speaking, the bottleneck will lie in one of two places. The first is the network server. In this case, the client computers have no difficulty sending requests to the network server, but the server lacks sufficient capacity to process all the requests it receives in a timely manner. The second location is the network circuit, connecting the LAN to the corporate BN. #

twisted-pair cable

insulated pairs of wires that can be packed quite close together (Figure 3.9). The wires usually are twisted to minimize the electromagnetic interference between one pair and any other pair in the bundle.#

Ethernet

is a very popular LAN protocol; Ethernet has been further refined and developed into a formal standard called IEEE 802.3ac. There are several versions of Ethernet in use today. Ethernet uses a contention media access protocol.#

network operating system (NOS)

is the software that controls the network. Every NOS provides two sets of software: one that runs on the network server(s) and one that runs on the network client(s). #

collision

it is possible that two computers located some distance from one another can both listen to the circuit, find it empty, and begin simultaneously. This simultaneous transmission is called a collision. The two frames collide and destroy each other.#

1000Base-T

max data rate: 1 Gbps#

10 GbE

max data rate: 10 Gbps

10Base- T

max data rate: 10 Mbp; standard that revolutionized Ethernet and made it the most popular type of LAN in the world.

100Base-T

max data rate: 100 Mbps#

40 GbE

max data rate: 40 Gbps

network profile

network profile specifies what resources on each server are available on the network for use by other computers and which devices or people are allowed what access to the network. The network profile is normally configured when the network is established and remains in place until someone makes a change.#

Power over Ethernet (POE)

power over Ethernet (POE) so it needs no external power; the power is provided from a POE switch over the unused wires in a category 5/5e cable. POE APs are more expensive, but can be located anywhere you can run Cat 5/5e cable, even if there are no power outlets nearby. #

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

A system used in contention networks. The network interface unit listens for the presence of a carrier before attempting to send and detects the presence of a collision by monitoring for a distorted pulse;Ethernet uses a contention-based media access control technique called Carrier Sense Multiple Access with Collision Detection (CSMA/CD). CSMA/CD, like all contention-based techniques, is very simple in concept: wait until the circuit is free and then transmit. #

domain controller

Active Directory Service works in much the same manner as TCP/IP's DNS service, and in fact ADS servers, called domain controllers, can also act as DNS servers; The domain controller is also responsible for managing authorization information (e.g., who is permitted to use each resource) and making sure that resources are available only to authorized users. #

frame

All frames from any computer flow onto the central cable (or bus) and through it to all computers on the LAN. Every computer on the bus receives all frames sent on the bus, even those intended for other computers. Before processing incoming frames, the Ethernet software on each computer checks the data link layer address and processes only those frames addressed to that computer.#

Active Directory Service (ADS)

Directory services provide information about resources on the network that are available to the users, such as shared printers, shared file servers, and application software. A common example of directory services is Microsoft's Active Directory Service (ADS). Active Directory Service works in much the same manner as TCP/IP's DNS service #

probe frame

During active scanning, a NIC transmits a special frame called probe frame on all active channels on its frequency range. When an AP receives a probe frame, it responds with a probe response that contains all the necessary information for a NIC to associate with it.#

port

Each connection point where a cable can be plugged in is called a port. Each port has a unique number.#

information sharing

Information sharing refers to having users access the same data files, exchange information via email, or use the Internet. #

shielded twisted-pair (STP)

TP is only used in special areas that produce electrical interference, such as factories near heavy machinery or hospitals near MRI scanners.#

software audit

The SPA has recently undertaken an aggressive software audit program to check the number of illegal software copies on LANs. #

Wi-Fi Protected Access (WPA)

Wi-Fi Protected Access (WPA) is a newer, more secure type of security. WPA works in ways similar to WEP and EAP: every frame is encrypted using a key, and the key can be fixed in the AP like WEP or can be assigned dynamically as users login like EAP. The difference is that the WPA key is longer than the WEP key and thus is harder to break. More importantly, the key is changed for every frame that is transmitted to the client. Each time a frame is transmitted, the key is changed.#

cut- through switching

With cut-through switching, the switch begins to transmit the incoming packet on the proper outgoing circuit as soon as it has read the destination address in the frame. In other words, the switch begins transmitting before it has received the entire frame. The advantage of this is low latency (the time it takes a device from receiving a frame to transmitting it) and results in a very fast network. The disadvantage is that the switch begins transmitting before it has read and processed the frame check sequence at the end of the frame; the frame may contain an error, but the switch will not notice until after almost all of the frame has been transmitted. Cut-through switching can only be used when the incoming data circuit has the same data rate as the outgoing circuit.#

store and forward switching

With the second switching mode, called store and forward switching, the switch does not begin transmitting the outgoing frame until it has received the entire incoming frame and has checked to make sure it contains no errors; Store and forward switching can be used regardless of whether the incoming data circuit has the same data rate as the outgoing circuit because the entire frame must be stored in the switch before it is forwarded on its way.#

request to transmit (RTS)

With this approach, any computer wishing to transmit first sends a request to transmit (RTS) to the AP, which may or may not be heard by all computers. The RTS requests permission to transmit and to reserve the circuit for the sole use of the requesting computer for a specified time period.#

access point (AP)

access point (AP) is a radio transceiver that plays the same role as a hub or switch in wired Ethernet LANs. It enables the computers near it to communicate with each other and it also connects them into wired LANs, typically using 100Base-T.#

1 GbE

also called 1000Base-F at max data rate: 1 Gbps

802.11i

also called WPA2) is the newest, most secure type of WLAN security. It uses EAP to obtain a master key—in other words, the user logs in to a login server to obtain the master key. Armed with this master key, the user's computer and the AP negotiate a new key that will be used for this session until the users leaves the WLAN. 802.11i uses the Advanced Encryption Standard (AES) discussed in Chapter 10 as its encryption method.

directional antenna

projects a signal only in one direction. Because the signal is concentrated in a narrower, focused area, the signal is stronger and therefore will carry farther than the signal from an AP using an omnidirectional antenna. Directional antennas are most often used on the inside of an exterior wall of a building, pointing to the inside of the building. This keeps the signal inside the building (to reduce security issues) and also has the benefit of increasing the range of the AP.#

switching

s a form of packet switching used in local area networks. Switching technologies are crucial to network design, as they allow traffic to be sent only where it is needed in most cases, using fast, hardware-based methods.#

software piracy

software used illegally#

symmetric multi-processing (SMP)

that enables one server to use up to 16 CPUs. Such servers provide excellent performance but cost more (often $5,000 to $15,000).#

Extensible Authentication Protocol (EAP)

the WEP keys are produced dynamically, much like the way in which a DHCP server is used to dynamically produce IP addresses. #

cabling

the cheapest point at which to install network cable is during the construction of the building; adding cable to an existing building can cost significantly more. Indeed, the costs to install cable (i.e., paying those doing the installation and additional construction) are usually substantially more than the cost of the hubs and switches, making it expensive to reinstall the cable if the cable plan does not meet the organization's needs.#

IEEE 802.3

traditional wired Ethernet (IEEE 802.3) that is commonly used to network desktop computers#

beacon frame

uring passive scanning, the NIC listens on all channels for a special frame called beacon frame that is sent out by an access point. The beacon frame contains all the necessary information for a NIC to associate with it.#

forwarding table

used by a switch to know which circuit is connected to what computer; he table lists the Ethernet address of the computer connected to each port on the switch. When the switch receives a frame, it compares the destination address on the frame to the addresses in its forwarding table to find the port number on which it needs to transmit the frame. #

10/100/1000 Ethernet

which is a hybrid that can run at any of these three speeds.#

IEEE 802.11

wireless Ethernet (IEEE 802.11, commonly called Wi-Fi) that often is used to network laptop computers and mobile devices.#

Wi-Fi

wireless Ethernet (IEEE 802.11, commonly called Wi-Fi) that often is used to network laptop computers and mobile devices; Wireless Ethernet (commonly called Wi-Fi) is the commercial name for a set of standards developed by the IEEE 802.11 standards group. #

MAC address filtering

with MAC address filtering, the AP permits the owner to provide a list of MAC addresses (i.e., layer-2 addresses). The AP only processes frames sent by computers whose MAC address is in the address list; if a computer with a MAC address not in the list sends a frame, the AP ignores it.#