CSN08704

Data, Audio, Video and Imageshttp://asecuritysite.com/comms

Telecommunications

Prof Bill Buchanan

Wireless Networks

Wireless Components

Devices

WirelessAccesspoint

WirelessBridge

WirelessClient

Infastructure

Broadcast span

Defined by broadcast domain

IEEE 802.11b networks

IEEE 802.11 - Wireless• IEEE 802.11a. 802.11a deals with communications available in the 5GHz frequency, and

has a maximum data rate of 54 Mbps.• IEEE 802.11b. 802.11b, or Wi-Fi, is the standard that is most commonly used in wireless

LAN communications. It has a maximum bandwidth of 11Mbps, at a frequency of 2.4GHz. • IEEE 802.11g. 802.11g is a proposed standard that hopes to provide 54Mbps maximum

bandwidth over a 2.4GHz connection, the same frequency as the popular 802.11b standard.

• IEEE 802.11c. 802.11c is a group set up to deal with bridging operations when developing access points.

• IEEE 802.11f. 802.11f is concerned with standardising access point roaming which is involved in making sure that interoperability between access points is guaranteed

IEEE 802.11bOperating Channels:11 for N. America, 14 Japan, 13 Europe (ETSI), 2 Spain, 4 FranceOperating Frequency: 2.412-2.462 GHz (North America), 2.412-2.484 GHz (Japan), 2.412-2.472 GHz (Europe ETSI), 2.457-2.462 GHz

(Spain), 2.457-2.472 GHz (France)Data Rate:1, 2, 5.5 or 11MbpsMedia Access Protocol:CSMA/CA, 802.11 CompliantRange:11Mbps: 140m (460 feet)5.5Mbps: 200m (656 feet)2Mbps: 270m (885 feet)1Mbps: 400m (1311 feet)RF Technology:Direct Sequence Spread Spectrum Modulation:CCK (11Mps, 5.5Mbps), DQPSK (2Mbps), DBPSK (1Mbps)

Maximum bandwidth (IEEE 802.11b)

11Mbps

5.5Mbps

2Mbps

1Mbps

400m300m200m100m

Max bandwidthCCK

DQPSK

DBPSK

Ava

ilabl

eba

ndw

idth

Distance

CCK

CCK - Complementary Code KeyingDQPSK - differential quadrature phase shift keyingBPSK - biphase shift keying

Maximum bandwidth (IEEE 802.11b)

11Mbps

5.5Mbps

2Mbps

1Mbps

400m300m200m100m

Max bandwidth

Actual maximum bandwidth

Maximum bandwidth (IEEE 802.11b)

10Mbps8Mbps4Mbps2Mbps

Ava

ilabl

eth

roug

hput

Required data throughput

2Mbps

6Mbps

8Mbps

Linear increase inactual throughputagainst requiredthroughput

More collisionsand errors are occurring, thusdata frames arebeing deleted, causingwasted bandwidth.

Too many errorscauses theTCP windowto close, and reducethroughput.

IEEE 802.11g networks

54Mbps

24Mbps

2Mbps

1Mbps

400m300m200m100m

64-QAM

QPSK

DBPSK

Ava

ilabl

eba

ndw

idth

Distance

16-QAM

QAM – Quadrature Amplitude ModulationCCK - Complementary Code KeyingDQPSK - differential quadrature phase shift keyingBPSK - biphase shift keying

802.11gMbps Modulation6 BPSK9 BPSK12 QPSK18 QPSK24 16-QAM36 16-QAM48 64-QAM54 64-QAM

Netperf on a 11g link

Windows IP ConfigurationEthernet adapter Wireless Network Connection 3: Connection-specific DNS Suffix . : IP Address. . . . . . . . . . . . : 192.168.1.100 Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : 192.168.1.1C:\>netperf -H 192.168.1.101 -p 1001TCP STREAM TEST to 192.168.1.101Recv Send SendSocket Socket Message ElapsedSize Size Size Time Throughputbytes bytes bytes secs. 10^6bits/sec 8192 8192 8192 10.00 9.60C:\>netperf -H 192.168.1.101 -p 1001TCP STREAM TEST to 192.168.1.101Recv Send SendSocket Socket Message ElapsedSize Size Size Time Throughputbytes bytes bytes secs. 10^6bits/sec 8192 8192 8192 10.00 7.60c:\>netperf -H 192.168.1.101 -p 1001TCP STREAM TEST to 192.168.1.101Recv Send SendSocket Socket Message ElapsedSize Size Size Time Throughputbytes bytes bytes secs. 10^6bits/sec 8192 8192 8192 10.00 7.60

IEEE 802.11g example

IEEE 802.11g example

IEEE 802.11n

802.11n802.11n

Frequency: 2.4 GHz or 5 GHz Max: 540 Mbit/s

Range: Same as 11b

MIMO (Multiple-in, multiple-out)Sends information on two or more antennas. These signals then reflect off objects, creating multiple paths creating multiple paths. Normally these cause interference and fading, but with MIMO they carry different information, which are recombined on the receiving side.

802.11n

MIMO

IEEE 802.11 networks

CSMA/CA and PCFIEEE 802.11 can use two mechanisms for shared access:

• CSMA/CA. CSMA/CA is, like standard Ethernet (IEEE 802.3) a contention-based protocol, but uses collision avoidance rather than collision detection. It would be impossible to use collision detection as a radio wave is always either sending or receiving and can never do both at the same time. The nodes will thus not be able to listen on the channel while they are transmitting.

• Point Coordination Function (PCF). This is an optional priority-based protocol, which provides contention-free frame transfer for transmission of time-critical data, such as real-time video or audio. With this, the point coordinator (PC) operates in the wireless access point and identifies the devices which are allowed to transmit at any given time. Each PC then, with the contention-free (CF) period, the PC polls each of the enabled PCF to determine if they wish to transmit data frames. No other device is allowed to transmit while a another node is being polled. Thus, PCF will be contention-free and enables devices to transmit data frames synchronously, with defined time delays between data frame transmissions.

CSMA/CD

1

Listen for no activity

ACK

2

2

ACK time-out

• Node has gone.• Data frame has collided with another• Data frame corrupted with noise.

IEEE 802.11 data frameFramecontrol

Duration/ID

Address1

Address2

Address3

Sequencecontrol

Address4

Framebody FCS

2 Bytes 2 6 6 6 2 6 0-2312 4

Frame control. This contains control information.Duration/ID. This contains information on how long the data frame will last.Address fields. This contains different types of address, such as an individual address of group addresses. The two main types of group addresses are broadcast and multicast.Sequence control. This identifies the sequence number of the data frames, and allows the recipient to check for missing or duplicate data frames.Frame body. This part contains the actual data. The maximum amount is 2312 bytes, but most implementations use up to 1500 bytes.FCS (Frame Check Sequence). This is a strong error detection code.

Framecontrol

Duration/ID

Address1

Address2

Address3

Sequencecontrol

Address4

Framebody FCS

2 Bytes 2 6 6 6 2 6 0-2312 4

IEEE 802.11 networks

e0 (or fa0)

dot11radio0(or d0)

bvi 1 port is usedto configure both portswith the same address

# config t(config)# int bvi1(config-if)# ip address 192.168.0.1 255.255.255.0(config-if)# exit

Antenna connector

con

Root

Repeater

# config t(config)# int dot11radio0(config-if)# station role root(config-if)# station role repeater(config-if)# end

Fixed network

Root

Repeater

# config t(config)# ip default-gateway 192.168.1.254(config)# exit

Fixed network

Channel Frequency

Channel. If an ad-hoc network is used, then the nodes which communicate must use the same channel.

channel 1—2412channel 2—2417 channel 3—2422channel 4—2427channel 5—2432 channel 6—2437channel 7—2442channel 8—2447channel 9—2452channel 10—2457channel 11—2462 channel 12—2467channel 13—2472 channel 14—2484

1 6

111

11

6

Channel FrequencyChannel. If an ad-hoc network is used, then the nodes which communicate must use the same channel.

1 6

111

11

6

channel 1—2412channel 2—2417 channel 3—2422channel 4—2427channel 5—2432 channel 6—2437channel 7—2442channel 8—2447channel 9—2452channel 10—2457channel 11—2462 channel 12—2467channel 13—2472 channel 14—2484

(config)# int dot11radio0(config-if)# channel 7(config-if)# no shutdown(config)# int fa0(config-if)# no shutdown

Fragmentation thresholdFragmentation threshold. This can be used to split large data frames into smaller fragments. The value can range from 64 to 1500 bytes. This is used to improve the efficiency when there is a high amount of traffic on the wireless network, as smaller frames make more efficient usage of the network.

Data packets are split into 1500 byte data frames (MTU)

The large data frames may allow nodes to ‘hog’ the airwave

Fragmentation thresholdFragmentation threshold. This can be used to split large data frames into smaller fragments. The value can range from 64 to 1500 bytes. This is used to improve the efficiency when there is a high amount of traffic on the wireless network, as smaller frames make more efficient usage of the network.

Data frames are fragmented into smaller frames

Possibly allows for a smoother and fairer transmission.

Network settingsFragmentation threshold. This can be used to split large data frames into smaller fragments. The value can range from 64 to 1500 bytes. This is used to improve the efficiency when there is a high amount of traffic on the wireless network, as smaller frames make more efficient usage of the network.

Data frames are fragmented into smaller frames

Possibly allows for a smoother and fairer transmission.

# config t(config)# int dot11radio0(config-if)# fragment-threshold ? <256-2346>(config-if)# fragment-threshold 700(config-if)# end

Infrastructure or ad-hocNetwork type. This can either be set to an infrastructure network (which use access points, or wireless hubs) or Ad-hoc, which allows nodes to interconnect without the need for an access point.

Infrastructure

Ad-hoc

Infrastructure or ad-hoc

Infrastructure

Ad-hoc

SSIDdefines the connected nodes

SSIDdefines the connected nodes

Infrastructure or ad-hoc

Infrastructure

Ad-hoc

SSIDdefines the connected nodes

SSIDdefines the connected nodes

# config t(config-if)# dot11 ssid fred(config-ssid)# guest-mode(config-ssid)# exit(config)# int dot11radio0(config-if)# ssid fred(config-if-ssid)# end

Span of network

LL

L

Network settings

Authentication algorithm. This sets whether the adapter to use an open system (where other nodes can listen to the communications), or uses encryption (using either a WEP key, or a shared key).

# config t(config)# dot11 ssid fred(config-ssid)# authentication ?client LEAP client informationkey-management key managementnetwork-eap leap methodopen open methodshared shared method(config-ssid)# authentication open(config-ssid)# exit(config)# exit

Authentication isa key issue, andwill be covered laterin the module. At present the authenticationis open, so that any userand device can connect without authenticating itself.

Other Factors

Network settingsPreamble mode. This can either be set to Long (which is the default) or short. A long preamble allows for interoperatively with 1Mbps and 2Mbps DSSS specifications. The shorter allows for faster operations (as the preamble is kept to a minimum) and can be used where the transmission parameters must be maximized, and that there are no interoperatablity problems.

Preamble – this is sentbefore the start of the data transmission so that nodes can detect that it is about to transmit.

Network settingsPreamble mode. This can either be set to Long (which is the default) or short. A long preamble allows for interoperatively with 1Mbps and 2Mbps DSSS specifications. The shorter allows for faster operations (as the preamble is kept to a minimum) and can be used where the transmission parameters must be maximized, and that there are no interoperatablity problems.

Preamble – this is sentbefore the start of the data transmission so that nodes can detect that it is about to transmit.

# config t(config)# int dot11radio0(config-if)# preamble-short(config-if)# end

Hidden node problem

The hidden node problemoccurs when two nodes transmitto an access point, but they are notin communication range, thus theirsignals can collide, and cause errors.

These nodes cannot hear each other.

Network settings (cont.)RTS/CTS threshold. The RTS Threshold prevents the Hidden Node problem, where two wireless nodes are within range of the same access point, but are not within range of each other. As they do not know that they both exist on the network, they may try to communicate with the access point at the same time. When they do, their data frames may collide when arriving simultaneously at the Access Point, which causes a loss of data frames from the nodes. The RTS threshold tries to overcome this by enabling the handshaking signals of Ready To Send (RTS) and Clear To Send (CTS). When a node wishes to communicate with the access point it sends a RTS signal to the access point. Once the access point defines that it can then communicate, the access point sends a CTS message. The node can then send its data.

Hidden node problemRTS (Ready To Send)

RTS (Ready To Send)

CTS (Clear To Send)

Data transmitted

RTS

CTS

Data

CTS

Data

RTS

Hidden node problemRTS (Ready To Send)

RTS (Ready To Send)

CTS (Clear To Send)

Data transmitted

RTS thresholdRTS threshold determines the data frame size that is required, in order for it send an RTS to the WAP. The default value is 4000.

# config t(config)# int dot11radio0(config-if)# rts threshold 8000(config-if)# end

Hidden node problemRTS (Ready To Send)

RTS (Ready To Send)

CTS (Clear To Send)

Data transmitted

RTS retriesRTS Retries defines the number of times that an access point will transmit an RTS before it stops sending the data frame. Values range from 1 to 128.

# config t(config)# int dot11radio0(config-if)# rts retries 10(config-if)# end

Power management

The power of the access point and alsoof the client are important as they will define the coverage of the signal, and mustalso be within the required safety limits.

The higher thetransmitting power,the wider the coverage.

Power management

The power of the access point and alsoof the client are important as they will define the coverage of the signal, and mustalso be within the required safety limits.

The higher thetransmitting power,the wider the coverage.

# config t(config)# int dot11radio0(config-if)# power ?(config-if)# power local ?(config-if)# power local 30(config-if)# power client 10(config-if)# speed ?(config-if)# speed 1.0(config-if)# exit(config)# exit

[1.0] [11.0] [2.0] [5.5][basic-1.0] [basic-11.0] [basic-2.0] [basic-5.5] | range | throughput

Power managementPower saving modes:

CAM (Constant awake mode). Used when powerusage is not a problem.PSP (Power save mode). Power is conservedas much as possible. The card will typically goto sleep, and will only be awoken by the accesspoint, or if there is activity.FastPSP (Fast power save mode). This usesboth CAM and PSP, and is a compromise betweenthe two.

Maximum bandwidth (IEEE 802.11b) 11Mbps

5.5Mbps

2Mbps

1Mbps

400m300m200m100m

Max bandwidthCCK

DQPSK

DBPSK

(config)# int dot11radio0(config-if)# speed 1.0(config-if)# exit(config)# exit

Maximum associations

A particular problem in wireless networksis that the access point may becomeoverburdened with connected clients...

... this could be due to an attack, such asDoS (Denial of Service), or due to poorplanning.

Maximum associations

For example:

Max bandwidth = 25MbpsAv rate = 0.5MbpsMax. associations = 50

Maximum associations

A particular problem in wireless networksis that the access point may becomeoverburdened with connected clients...

... this could be due to an attack, such asDoS (Denial of Service), or due to poorplanning.

# config t(config)# dot11 ssid fred(config-ssid)# max ? <1-255> association limit(config-ssid)# max 100(config-ssid)# exit(config)# int dot11radio0(config-if)# ssid fred(config)# exit

# show dot11 association# show dot11 statistics client-traffic

# show dot11 adjacent-ap

CSN08704

Data, Audio, Video and Imageshttp://asecuritysite.com/comms

Telecommunications

Prof Bill Buchanan

Wireless Networks