6 topics in networking (2)

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    Copyright 2006 by The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill Technology Education

    Lecture 6

    Advance Topics inNetworking

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    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

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    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.

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    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.

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    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.

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    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

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    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

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    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

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    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)

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    Wireless LAN Standards

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    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

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    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)

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    Wireless Access Point

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    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.

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    Wireless Bridges

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    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

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    Wireless Antennas

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    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

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    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.

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    WLANs and the SSID

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    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.

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    WLANs and the SSID

    There are two basic forms of WLANinstallations:

    Ad-hoc and

    Infrastructure mode

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    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.

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    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.

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    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.

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    WLANs and the SSID (ESS)

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    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.

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    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.

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    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.

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    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.

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    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.

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    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.

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    Setting up Ad hoc Network on WinXP

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    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.

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    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.

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    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.

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    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.

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    Setting up the First Computer (Router)

    2. Click Start, and

    then click Control

    Panel.

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    Setting up the First Computer (Router)

    3. UnderPick a

    category, click

    Network and

    Internet

    Connections.

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    Setting up the First Computer (Router)

    4. Underor pick a

    Control Panel

    icon, click

    Network

    Connections.

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    Setting up the First Computer (Router)

    5. Right-click your

    wireless network

    connection, and

    then click

    Properties.

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    Setting up the First Computer (Router)

    6. In the Wireless

    Network

    Connection

    Properties

    dialog box, click

    the Wireless

    Networks tab.

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    Setting up the First Computer (Router)

    7. On the

    Wireless

    Networks tab,

    under

    Preferred

    networks,

    click Add

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    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.

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    Setting up the First Computer (Router)

    11. Click OK again to

    save your changes.

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    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.

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    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.

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    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.

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    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.

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    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

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    Q&A

    ?

    A i

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    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

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    The End

    Questions?