Chapter 7: Wired and Wireless LANs

Most large organizations have numerous wired and wireless LANs connected by …

backbone networks

What are two technologies commonly used in LANs?

1) traditional wired Ethernet
2) wireless Ethernet

What are the six LAN components?

1) Client Computer
2) Server
3) Network interface cards(NICs)
4) Network circuits
5) Hubs/switches/access points
6) The network operating system

What is a network interface card(NIC) used for?

To connect the computer to the network cable in a wired network

In a wireless network the NIC is a _______ that sends and receives messages on a specific radio frequency

radio transmitter

All desktop computers have a wired NIC built in while all laptops have both a wired NIC and a wireless NIC

True

Most LANs are built with one of these three components

1) Unshielded twisted pair (UTP) cable
2) shielded twisted-pair(STP) cable
3) Fiber-optic cable

(Most use UTP cable)
(STP is only used in special areas that produce electrical interference)
(Fiber-optic cable is even thinner than UTP and takes less space)

Wireless LANs (WLANs) use ________ to send data between the NIC and the access point(AP)

radio transmissions

Most countries permit WLANs to operate in ____ frequency ranges

two (may interfere with cordless phones and baby monitors)

Under ideal conditions, radio transmitters in the NICs and Aps can transmit how far?

100-150 meters

As the distance from the AP ____, the maximum speed _____

increases; decreases

When we design a WLAN, what is important to ensure for APs?

It is important to ensure that the APs don’t interfere with each other. To prevent this AP is set to transmit on a different channel.

Network hubs and switches server what two purposes?

1) An easy way to connect network cables
2) They act as repeaters

Network hubs and switches can be thought of as a ______, permitting new computers to be connected to the network

junction box

Each connection point where a cable can be plugged in is called a ____

port; (each port has a unique number)

What is the network operating system(NOS)

the software that controls the network

The NOS provides two sets of software:

1) One that runs on the network server(s)
2) One that runs on the network client(s)

The server version of the NOS provides the software that performs the functions associated with…

1) data link, network, and application layers
2) Computers OS

The client version of the NOS provides the software that performs the functions associated with…

1) data link and network layers
2) application software and computers OS

The NOS server software enables what three servers to operate?

1) file server
2) print server
3) database server

The NOS server acts as the ______ by executing the requests sent to it by the clients

application software

NOS server software replaces the normal operating system on the server

True

Windows provides a built-in software that enables it to act as a client computer with a Windows server.

True

One of the most important functions of a NOS is a ….

directory service (provide information about resources on the network that are available to users

A common example of directory services is…

Microsoft’s Active Directory Service (ADS). Works in the same way as TCP/IPs DNS service but uses LDAP, a standard directory protocol to access/manage directory info across the network

Each branch on the tree contains a ______, a group of related resources

domain

Domains can’t contain other domains

False

The hierarchical tree of domains within one organization can be linked to trees in other organizations to create a…

forest of shared network resources

Within each domain there is a ____ that is responsible for resolving address information

server (the domain controller)

A _______ specified what resources on each server are available on the network for use by other computers and which devices/people are allowed what access to the network

network profile

When is a network profile configured?

When the network is established and remains in place until someone makes a change

There must also be a ____ for each person who uses the LAN

user profile

Almost all LANs installed today use some form of….

Ethernet (layer 2 protocol)

Every Ethernet LAN needs hardware at…

layer 1

Topology

the basic geometric layout of the network

logical topology

is how the network works conceptually

physical topology

how the network is physically installed

Hub-based Ethernet is always used by companies today

False

When we use hubs, Ethernet’s logical topology is a …

bus topology

All frames from any computer flow to all computers on the LAN. This shared multipoint circuit is often called a …

collision domain

Almost all corporate installations of Ethernet today use…

switches (Ethernets topology is a logical star and a physical star)

Each circuit connected to a _____ is not shared with any other devices

switch

When a switch receives a frame, it looks at the address and retransmits the frame only on the ____ connected to that computer

circuit

To know which circuit to use, the switch uses a _____ which is similar to a routing table

forwarding table (called a layer 2 switch)

How do switches build the forwarding table?

By learning addresses

If a switch receives a frame with a destination address that is not in the forwarding table what does it do?

Sends to all ports. WHen the correct computer responds it is added to the forwarding table

What are the three modes that switches operate in?

1) Cut-through switching
2) Store-and forward switching
3) Fragment-free switching

What is 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 (low latency aka better performance)

What is store-and forward switching?

The switch does not begin transmitting the outgoing frame unti; it has received the entire incoming frame and has checked to make sure it contains no errors

What does store-and forward switching prevent?

Prevents an invalid frame from consuming network capacity, but provides higher latency(worse performance)

What is fragment-free switching?

The first 64 bytes of the frame are read, stored, and checked.
If all the header data is correct, the switch presumes that the rest of the frame is error free and begins transmitting

When several computers share the same collision domain is it important to…

control their access to the media

Media access control

collisions must be prevented or recovered from

Ethernet uses a contention-based media access control technique called…

Carrier Sense Multiple Access with Collision Detection (CSMA/CD); It waits until the circuit is free and then transmits

The solution to collisions is to listen while transmitting. This is better known as…

collision detection (CD)

If the NIC detects a signal it sends a ____ signal

jamming

______ is the commerical name for a set of standards seveloped by the IEEE 802.11 standards group.

Wireless Ethernet (Wi-Fi)

What are the logical and physical topologies of Wi-Fi?

Physical star and a logical bus

Media access control in Wi-Fi is…

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

Detecting collisions is more ____ in radio transmissions so Wi-Fi attempts to avoid collisions to a greater extent than regular Ethernet

difficult

Before a computer can transmit in a WLAN, it must first establish an association with specific AP

True

Searching for an available AP is called…

scanning

What are the two types of scanning a NIC can engage in?

1) active scanning
2) passive scanning

What is active scanning?

A NIC transmits a special frame called probe frame on all active channels on its frequency range

What is passive scanning?

The NIC listens on all channels for a special frame called a beacon fram that is sent out by an AP

The first media access control method is the…

distributed coordination function (DCF) (Also called the physical carrier sense method)

With DCF, each frame is sent using a stop-and wait ARQ

True

The second media access control technique is…

the point coordination function (PCF) ( Also called the virtual carrier sense method)

What is the hidden node problem?

computers far away may sense the other transmission and transmit at the ame time causing a collision at the AP

How does the AP manage the shared circuit in a point coordination function?

The AP must manage the shared circuit using a controlled-access technique (not contention like regular Ethernet)

Any computer wishing to transmit first sends a ____ to the AP. If no other computer is transmitting, the AP responds with a ______, specifying the amount of time for which the circuit is reserved for the requesting computer

request to send(RTS); clear to send(CTS)

When do controlled-access techniques work best and worst?

best: high traffic WLANs

worst: low-traffic networks

What the three types of wireless ethernet?

1) 802.11n: (obsolete but used because it’s cheap)
2) 802.11ac:(current version)
3) 802.11ax: (newest version(Wi-Fi 6))

____ is important for wireless networks

security

One older wireless security technique is the…

Wired Equivalent Privacy (WEP)

1) AP requires the user to have a key to communicate
2) Keys are produced dynamically
3) users must log in to receive a key

Wi-Fi protected access (WPA)

a newer, more secure security that works similarly to WEP
WPA key is longer than WEP
Key ois changed for every frame transmitted to client

802.11i(WPA2)

The newest, most secure type of WLAN security
User logs in to obtain the master key which uses the AES encryption

MAC address filtering

The AP only processes frames sent by computers whose MAC address is listed
Provides no security against determined hacker

Wi-Fi is considerably cheaper than wired Ethernet. The largest cost of LAN is paying someone to install the cables

True

Most organizations today install wired Ethernet to provide access for desktop users and install Wi-Fi as…

overlay networks

The usual _____ networks are the primary LAN, but they also install Wi-Fi for laptops and mobile devices

switched Ethernet

The cheapest point to install a network cable is during the _____ of the building

construction

Most buildings under construction today have a separate LAN cable plan

True

Designing the physical WLAN is more challenging than designing a w_____

wired LAN

The physical WLAN design begins with a…

site survey

An AP with an omnidirectional antenna broadcasts in ____ direction(s)

all(limit to 50 foot radius)

Most large companies install _______

managed APs

Managed APs are wired into a _____

Wi-FI controller

What do managed APs report to the controller?

What devices are attached to them and how busy they are

Design becomes more difficult in a multistory building. Why?

Because signals from the APs travel up and down as well as left and right so we have to make sure APs on different floors don’t interefere with one another. (floors are thicker than walls too)

Most wireless LAN APs have two separate wireless networks which are?

1) primary password protected one
2) guest network (still has password but not secure/ only used for those that need temporary access)

The data center is where the organization houses its primary servers. Servers are placed in…

server farms / clusters (hugeeee and designing one takes expertise)

A special device called a ______or _____acts as a router at the front of a server farm

load balancer; load balancing switch

When a request hits the load balancer what does it do?

it forwards it to one specific server

If a server crashes, the load balancer stops _____ to it, and the network continues to operate

sending requests

Server virtualization

is the process of creating several logically separate servers on the same physical computer (appear completely separate to the network)

Some operating systems enable virtualization natively

True

A storage area network(SAN)

a LAN devoted solely to data storage

network-attached storage(NAS) devices

Not a general-purpose computer. Has a small processor and a large amount of disk storage and is de

E-commerce edge is a smaller, specialized version of the…

data center(has different security requirements)