Upload
michaelmccabe18
View
219
Download
0
Embed Size (px)
Citation preview
7/28/2019 6 Topics in Networking (2)
1/56
Copyright 2006 by The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill Technology Education
Lecture 6
Advance Topics inNetworking
7/28/2019 6 Topics in Networking (2)
2/56
Overview
Wireless LAN Standards
Wireless LAN Components Access Points, Bridges and Antennas
WLANs and the SSID
IBSS, BSS and ESS
Wireless Channel Setting up Ad hoc Network on WinXP
7/28/2019 6 Topics in Networking (2)
3/56
Wireless LAN Standards
A number of standards have beendeveloped to ensure that wireless
devices can communicate.
They specify the RF spectrum used,data rates, how the information is
transmitted, and more.
The main organization responsible forthe creation of wireless technical
standards is the IEEE.
7/28/2019 6 Topics in Networking (2)
4/56
7/28/2019 6 Topics in Networking (2)
5/56
Wireless LAN Standards
The IEEE 802.11 standard governs theWLAN environment.
There are four amendments to the IEEE802.11 standard that describe different
characteristics for wirelesscommunications.
The currently available amendments are802.11a, 802.11b, 802.11g and 802.11n
(802.11n is currently not ratified) Collectively these technologies are
referred to as Wi-Fi, Wireless Fidelity.
7/28/2019 6 Topics in Networking (2)
6/56
Wireless LAN Standards
Another organization, known as theWi-Fi Alliance, is responsible fortesting wireless LAN devices from
different manufacturers. The Wi-Fi logo on a device means
that this equipment meets the
standards and should interoperatewith other devices of the samestandard.
7/28/2019 6 Topics in Networking (2)
7/56
Wireless LAN Standards
802.11a: Uses 5 GHz RF spectrum
Not compatible with 2.4 GHz spectrum, i.e.
802.11b/g/n devices Range is approximately 33% that of the
802.11 b/g
Relatively expensive to implement
compared to other technologies.
Increasingly difficult to find 802.11a
compliant equipment
7/28/2019 6 Topics in Networking (2)
8/56
Wireless LAN Standards
802.11b: First of the 2.4 GHz technologies
Maximum data-rate of 11 Mbps
Range of approximately 46 m (150 ft)indoors/96 m (300 ft.) outdoors
7/28/2019 6 Topics in Networking (2)
9/56
Wireless LAN Standards
802.11g: 2.4 GHz technologies
Maximum data-rate increase to 54 Mbps
Same range as the 802.11b
Backwards compatible with 802.11b
7/28/2019 6 Topics in Networking (2)
10/56
Wireless LAN Standards
802.11n: Newest standard in development
2.4 GHz technologies (draft standard
specifies support for 5 GHz) Extends the range and data throughput
Backwards compatible with existing
802.11g and 802.11b equipment (draft
standard specifies 802.11a support)
7/28/2019 6 Topics in Networking (2)
11/56
Wireless LAN Standards
7/28/2019 6 Topics in Networking (2)
12/56
Wireless LAN Components
Once a standard is adopted, it isimportant that all components within the
WLAN adhere to the standard, or are at
least compatible with the standard. There are various components that must
be considered in a WLAN including:
an Access Point, a wireless client or STA,
a Wireless Bridge and
an Antenna
7/28/2019 6 Topics in Networking (2)
13/56
Wireless LAN Components
Wireless Access Point Controls access between a wired and a wireless
network. I.E. allows wireless clients to gain accessto a wired network and vice versa.
Acts as a media converter accepting the Ethernetframes from the wired network and convertingthem to 802.11 compliant frames beforetransmitting them on the WLAN.
Accepts 802.11 frames from the WLAN and
converts them into Ethernet frames before placingthem onto the wired network.
APs support wireless connections within a limitedarea, known as a cell or Basic Service Set (BSS)
7/28/2019 6 Topics in Networking (2)
14/56
Wireless Access Point
7/28/2019 6 Topics in Networking (2)
15/56
Wireless LAN Components
Wireless Clients Any host device that can participate in a wireless
network.
Most devices that can be connected to a traditional
wired network can be connected to a WLAN ifequipped with the proper wireless NIC and
software.
Can either be stationary or mobile.
Commonly referred to as a STA, short for station. Examples include: Laptops, PDAs, printers,
projectors and storage devices.
7/28/2019 6 Topics in Networking (2)
16/56
Wireless Bridges
7/28/2019 6 Topics in Networking (2)
17/56
Wireless LAN Components
Wireless Bridge Used to connect two wired networks
through a wireless link
Allows Long-range point-to-pointconnections between networks
Using the unlicensed RF frequencies,
networks 20 to 40 Km (25 Miles) or more
can be connected without the use of wires
7/28/2019 6 Topics in Networking (2)
18/56
Wireless Antennas
7/28/2019 6 Topics in Networking (2)
19/56
Wireless LAN Components
Wireless Antennas Used on APs and Wireless bridges
Increases the output signal strength from awireless device
Receives wireless signals from otherdevices such as STAs
Increase in signal strength from an antennais known as the gain
Higher gains usually translate intoincreased transmission distances
7/28/2019 6 Topics in Networking (2)
20/56
Wireless LAN Components
Antennas are classified according to the way theyradiate the signal.
Directional antennas concentrate the signal
strength into one direction.
Omni-directional antennas are designed to emitequally in all directions.
By concentrating all of the signal into one direction,
directional antennas can achieve great transmission
distances. Directional antennas are normally used in bridging
applications while omni-directional antennas are
found on APs.
7/28/2019 6 Topics in Networking (2)
21/56
WLANs and the SSID
7/28/2019 6 Topics in Networking (2)
22/56
WLANs and the SSID
When building a wireless network, it is important that thewireless components connect to the appropriate WLAN.
This is done using a Service Set Identifier (SSID).
The SSID is a case-sensitive, alpha-numeric string that is up to32-characters. It is sent in the header of all frames transmittedover the WLAN.
The SSID is used to tell wireless devices which WLAN theybelong to and with which other devices they can communicate.
Regardless of the type of WLAN installation, all wireless devicesin a WLAN must be configured with the same SSID in order tocommunicate.
7/28/2019 6 Topics in Networking (2)
23/56
WLANs and the SSID
There are two basic forms of WLANinstallations:
Ad-hoc and
Infrastructure mode
7/28/2019 6 Topics in Networking (2)
24/56
WLANs and the SSID
Ad-hoc The simplest form of a wireless network is created
by connecting two or more wireless clientstogether in a peer-to-peer network.
A wireless network established in this manner isknown as an ad-hoc network and does not includean AP.
All clients within an ad-hoc network are equal.
The area covered by this network is known as an
Independent Basic Service Set (IBSS). A simple ad-hoc network can be used to exchange
files and information between devices without theexpense and complexity of purchasing andconfiguring an AP.
7/28/2019 6 Topics in Networking (2)
25/56
WLANs and the SSID
Infrastructure Mode Although an ad-hoc arrangement may be good for small
networks, larger networks require a single device thatcontrols communications in the wireless cell.
If present, an AP will take over this role and control who cantalk and when.
This is known as infrastructure mode and is the mode ofwireless communication most often used in the home andbusiness environment.
In this form of WLAN, individual STAs can not communicatedirectly with each other.
To communicate, each device must obtain permission fromthe AP.
The AP controls all communications and ensures that allSTAs have equal access to the medium.
The area covered by a single AP is known as a BasicService Set (BSS) or cell.
7/28/2019 6 Topics in Networking (2)
26/56
WLANs and the SSID
The Basic Service Set (BSS) is the smallest building block of aWLAN.
The area of coverage of a single AP is limited.
To expand the coverage area, it is possible to connect multipleBSSs through a Distribution System (DS).
This forms an Extended Service Set (ESS).
An ESS uses multiple APs. Each AP is in a separate BSS.
In order to allow movement between the cells without the loss ofsignal, BSSs must overlap by approximately 10%.
This allows the client to connect to the second AP before
disconnecting from the first AP.
Most home and small business environments consist of a singleBSS.
However, as the required coverage area and number hostsneeding to connect increases it becomes necessary to create an
ESS.
7/28/2019 6 Topics in Networking (2)
27/56
WLANs and the SSID (ESS)
7/28/2019 6 Topics in Networking (2)
28/56
Wireless Channel
Regardless if the wireless clients are communicating
within an IBSS, BSS or ESS the conversationbetween sender and receiver must be controlled.
One way this is accomplished is through the use of
Channels.
Channels are created by dividing up the available RF
spectrum.
Each channel is capable of carrying a different
conversation.
This is similar to the way that multiple television
channels are transmitted across a single medium.
Multiple APs can function in close proximity to one
another as long as they use different channels for
communication.
7/28/2019 6 Topics in Networking (2)
29/56
Wireless Channel
Unfortunately it is possible for the frequencies used bysome channels to overlap with those used by others.
Different conversations must be carried on non-overlapping channels.
The number and distribution of channels vary by
region and technology.
The selection of channel used for a specificconversation can be set manually or automatically,based on factors such as current usage and available
throughput. Normally each wireless conversation makes use of a
separate channel.
Some of the newer technologies combine the channelsto create a single wide channel, which provides morebandwidth and increases the data rate.
7/28/2019 6 Topics in Networking (2)
30/56
Wireless Channel
Within a WLAN, the lack of well-defined boundaries
makes it impossible to detect if collisions occur during
transmission.
Therefore, it is necessary to use an access method on
a wireless network that ensures collisions do not
occur.
Wireless technology uses an access method called
Carrier Sense Multiple Access with Collision
Avoidance (CSMA/CA).
CSMA/CA creates a reservation on the channel for
use by a specific conversation.
While a reservation is in place, no other device may
transmit on the channel thus possible collisions are
avoided.
7/28/2019 6 Topics in Networking (2)
31/56
Wireless Channel
How does this reservation process work? If a devicerequires use of a specific communication channel in a
BSS, it must ask permission from the AP.
This is known as a Request to Send (RTS).
If the channel is available, the AP will respond to thedevice with a Clear to Send (CTS) message indicating
that the device may transmit on the channel.
A CTS is broadcast to all devices within the BSS.
Therefore, all devices in the BSS know that therequested channel is now in use.
7/28/2019 6 Topics in Networking (2)
32/56
Wireless Channel
Once the conversation is complete, the device thatrequested the channel sends another message to the
AP known as an Acknowledgement (ACK).
The ACK indicates to the AP that the channel can be
released. This message is also broadcast to all devices on the
WLAN.
All devices within the BSS receive the ACK and know
that the channel is once again available.
7/28/2019 6 Topics in Networking (2)
33/56
7/28/2019 6 Topics in Networking (2)
34/56
Setting up Ad hoc Network on WinXP
Wireless networks are helpful because they let youuse your computer and connect to the Internetanywhere in your home or office.
However, most wireless networks use a wirelessrouter, which can be expensive.
If you have more than one computer, you can set up awireless network without buying a wireless router andsave yourself some money.
In a traditional wireless network, a wireless router acts
as a base station, much like the base station forcordless phones.
All wireless communications go through the wirelessrouter, allowing nearby computers to connect to the
Internet or to each other.
7/28/2019 6 Topics in Networking (2)
35/56
Setting up Ad hoc Network on WinXP
7/28/2019 6 Topics in Networking (2)
36/56
Setting up Ad hoc Network on WinXP
Ad hoc wireless networks work more like walkie-talkies, because the computers communicate directly
with each other.
By enabling Internet Connection Sharing on one of
the computers, you can share Internet access. Ad hoc networking might seem like a much smarter
alternative to using a wireless router, but it does have
a couple of disadvantages:
If the computer connected to the Internet is shutdown, all computers that are part of the ad hoc
network lose their Internet access.
To connect to the Internet, one computer always
needs a wired network connection.
7/28/2019 6 Topics in Networking (2)
37/56
Setting up Ad hoc Network on WinXP
To connect your computers to the Internetusing an ad hoc wireless network, follow
these high-level steps:
1. Enable Internet Connection Sharing on the
Internet-connected computer. You can skip thisstep if you don't need to access the Web.
2. Set up the ad hoc wireless network on the
Internet-connected computer.
3. Add your other computers on the wirelessnetwork.
7/28/2019 6 Topics in Networking (2)
38/56
Enabling Internet Connection Sharing
On networks with wireless routers, the routerhas the important job of forwarding
communications from the computers on your
home network to the Internet.
On ad hoc networks, you must designateone computer to serve this role.
The computer you choose must have a wired
connection to the Internet, and it should be
left on whenever you want to be able to use
your other computers.
Enable Internet Connection Sharing on the
Internet-connected computer.
7/28/2019 6 Topics in Networking (2)
39/56
Setting up the First Computer (Router)
To set up an ad hoc wireless network thatallows computers to share an Internet
connection without a router.
1. If necessary, install a wireless network adapter.
7/28/2019 6 Topics in Networking (2)
40/56
Setting up the First Computer (Router)
2. Click Start, and
then click Control
Panel.
7/28/2019 6 Topics in Networking (2)
41/56
Setting up the First Computer (Router)
3. UnderPick a
category, click
Network and
Internet
Connections.
7/28/2019 6 Topics in Networking (2)
42/56
Setting up the First Computer (Router)
4. Underor pick a
Control Panel
icon, click
Network
Connections.
7/28/2019 6 Topics in Networking (2)
43/56
Setting up the First Computer (Router)
5. Right-click your
wireless network
connection, and
then click
Properties.
7/28/2019 6 Topics in Networking (2)
44/56
Setting up the First Computer (Router)
6. In the Wireless
Network
Connection
Properties
dialog box, click
the Wireless
Networks tab.
7/28/2019 6 Topics in Networking (2)
45/56
Setting up the First Computer (Router)
7. On the
Wireless
Networks tab,
under
Preferred
networks,
click Add
7/28/2019 6 Topics in Networking (2)
46/56
7/28/2019 6 Topics in Networking (2)
47/56
Setting up the First Computer (Router)
10. Create a 13-digit
password and type it
in both the Network
key and Confirm
network key boxes.For the best security,
include letters,
numbers, and
punctuation. Then
click OK.
7/28/2019 6 Topics in Networking (2)
48/56
Setting up the First Computer (Router)
11. Click OK again to
save your changes.
7/28/2019 6 Topics in Networking (2)
49/56
Setting up additional Computers (Client)
If the computer you want to add to your network
does not have built-in wireless network support,
install a wireless network adapter.
Windows XP automatically detects the newadapter and notifies you that it found a wireless
network.
7/28/2019 6 Topics in Networking (2)
50/56
Setting up additional Computers (Client)
Now connect your computer to your wireless
network.
Note: These steps apply only if you're using
Windows XP Service Pack 2 (SP2). If you haven't installed SP2, visit Microsoft
Update website to install it before connecting
to the ad hoc network.
7/28/2019 6 Topics in Networking (2)
51/56
Setting up additional Computers (Client)
Right-click the Wireless Network icon in the
lower right corner of your screen, and then click
View Available Wireless Networks.
7/28/2019 6 Topics in Networking (2)
52/56
Setting up additional Computers (Client)
The Wireless Network Connection window appears and displays your
wireless network listed with the SSID you chose. If you don't see your network, click Refresh Network List in the upper left
corner.
Click your network, and then click Connect in the lower right corner.
7/28/2019 6 Topics in Networking (2)
53/56
Setting up additional Computers (Client)
Windows XP prompts you to enter a key.Type your encryption key in both the Network
key and Confirm network key boxes, and then
click Connect.
Q
7/28/2019 6 Topics in Networking (2)
54/56
Q&A
?
A i
7/28/2019 6 Topics in Networking (2)
55/56
Assignment
Answer the questions below: Name Services run on the first Machine (that acts as
Internet Router) in Ad hoc Network on Windows XP
Which TCP/IP Settings does the first Machine sets for
each client in Ad hoc Network on Win XP What are the IP Addresses of first Machine and Other
Clients in Ad hoc Wireless Network on XP
How many Network interfaces are required on the first
Machine acting as router in Ad hoc Network
Th E d
7/28/2019 6 Topics in Networking (2)
56/56
The End
Questions?