Lecture 4 Ethernet and Wireless Local Area Networks 4482

8/3/2019 Lecture 4 Ethernet and Wireless Local Area Networks 4482

1/45

Ethernet and Wireless

Local Area Networks


2/45

2

History of Ethernet Standards

Ethernet

The dominant wired LAN technology today

Only competitor is wireless LANs (which actually are

supplementary)

The IEEE 802 Committee

LAN standards development is done primarily by the

Institute for Electrical and Electronics Engineers (IEEE)

IEEE created the 802 LAN/MAN Standards Committeefor LAN standards (the 802 Committee)


3/45

3

History of Ethernet Standards

The 802 Committee creates working groups forspecific types of standards

802.1 for general standards

802.3 for Ethernet standards

The terms 802.3and Ethernetare interchangeable

802.11 for wireless LAN standards

802.16 for WiMax wireless metropolitan area networkstandards


4/45

4

Ethernet Physical Layer Standards

UTP PhysicalLayer

Standards

MediumRequired

MaximumRun

LengthSpeed

100BASE-TX 4-pair Category 5 or higher100 meters100 Mbps

1000BASE-T(GigabitEthernet)

4-pair Category 5 or higher100 meters1,000 Mbps

10BASE-T 4-pair Category 3 or higher100 meters10 Mbps

100BASE-TX dominates access links today.

Although 1000BASE-T is growing in access links today


5/45

5

Fiber PhysicalLayer

Standards

Medium850 nm light (inexpensive)

Multimode fiber

MaximumRun

Length

Speed

1000BASE-SX 275 m1 Gbps


1000BASE-SX

220 m1 Gbps


Ethernet Physical Layer Standards

62.5microns

160MHz-km

62.5 200

50 400

50 500

The 1000BASE-SX standard dominates trunk links today.

Carriers use 1310 and 1550 nm light and single-mode fiber.


6/45

6

Gigabit Ethernet

10 Gbps Ethernet usage is small but growing

Several 10 Gbps 10GBASE-x fiber standards aredefined, but none is dominant

Copper is cheaper than fiber but cannot go as far

100 Gbps has been selected as the next Ethernetspeed

Chosen over 40 Gbps

100 Gbps Ethernet standards development is justgetting underway


7/45

7

Data Link Using Multiple Switches

OriginalSignal

ReceivedSignal

ReceivedSignal

ReceivedSignalRegenerated

SignalRegenerated

Signal

UTP UTP62.5/125Multimode Fiber

100BASE-TX

(100 m maximum)Physical Link

100BASE-TX


1000BASE-SX


Each trunk line along the way has a distance limit


8/45

8

Multi-Switch Ethernet LAN Architecture

Switch 2 (root switch)

Switch 1 Switch 3

Port 5 on Switch 1to Port 3 on Switch 2

Port 7 on Switch 2to Port 4 on Switch 3

C3-2D-55-3B-A9-4FSwitch 2, Port 5

A1-44-D5-1F-AA-4CSwitch 1, Port 2

D4-55-C4-B6-9FSwitch 3, Port 2

B2-CD-13-5B-E4-65Switch 1, Port 7

E5-BB-47-21-D3-56Switch 3, Port 6


9/45

9

Single Point of Failure in a Switch Hierarchy

No CommunicationNo Communication

Switch 1

Switch 2

Switch 3

Switch Fails

A1-44-D5-1F-AA-4C

B2-CD-13-5B-E4-65

C3-2D-55-3B-A9-4F

D4-47-55-C4-B6-9F

E5-BB-47-21-D3-56


10/45

10

Hierarchy Implications

Single possible path between stations.

Makes switching tables very simple because there is only onepossible row for each address. Find the row, send the frame outthe indicated port. Very fast, so minimizes switching cost.

Creates the potential for single points of failure.

Low cost is responsible for Ethernets LAN dominance.

Port Station2 A1-44-D5-1F-AA-4C7 B2-CD-13-5B-E4-655 E5-BB-47-21-D3-56


11/45

11

Switch Operation in Ethernet

Today, Switches Dominate in Ethernet A frame comes in one port

The switch looks up the frames destination MAC

address in the switchingtable

The switch sends the frameout a single port

Only two ports are tied up

Other conversations cantake place on other portpairs simultaneously


12/45

12

Ethernet 802.3 10Base2

Ethernet 10Base2

To NextStation

T-Connector to Link NIC to next segments

NIC


13/45

13

Ethernet 802.3 10Base2

Ethernet 10Base2

BNC connector

T-connectorTo nextstation


14/45

14

Client A

Client B

Client C

Server D Server E

Serverbroadcast

Virtual LAN with Ethernet Switches

Server broadcasting without VLANS

Frame is BroadcastGoes to all other stationsCreates congestion


15/45

15

Virtual LAN with Ethernet Switches

Server multicasting with VLANS

Client Aon VLAN1

Client Bon VLAN2

Client Con VLAN1

Server Don VLAN2

Serverbroadcast

With VLANs,broadcasts go to a

servers VLAN

clients; less latency

Multicasting(some), notBroadcasting (all)

NONO

Server E

on VLAN1


16/45

16

Handling Momentary Traffic Peaks withOverprovisioning and Priority

Traffic

Network capacity

Momentary traffic peak:

Congestion and latency

Time

Momentary traffic peak:Congestion and latency

Momentary traffic peaks usually last fraction of a second;They occasionally exceed the networks capacity.

When they do, frames will be delayed, even dropped.


17/45

17


Traffic

Overprovisioned network capacity Momentary peak:No congestion

Time

Overprovisioned traffic capacity in Ethernet

Overprovisioning:Build high capacity than will rarely if ever be exceeded.This wastes capacity. But cheaper than using priority.


18/45

18


Traffic

Network capacity

Momentarypeak

Time

Priority in Ethernet

High-priority traffic goes

Low-priority waits

Priority: During momentary peaks, give priority totraffic that is intolerant of delay, such as voice.

No need to overprovision, but expensive to implement.Ongoing management is very expensive.


19/45

19

Routed LAN with Ethernet Subnets

If a routed LAN links multiple Ethernet switched

networks, the switched networks are called subnets


20/45

Wireless LANs


21/45

21

Local Wireless Technologies

802.11 Wireless LANs (Wi-Fi)

Today, mostly speeds of tens of megabits per secondwith distances of 30 to 100 meters or more

Can serve many users in a home or office

Increasingly,100 Mbps to 600 Mbps with 802.11n

Organizations can provide coverage throughout abuilding or a university campus by installing manyaccess points


22/45

22

802.11 Wireless LANs (WLANs)

Wireless hosts connectby radio to access points

Transmission speed: up to 300 Mbps but usually 10 Mbps to 100 Mbps.

Distances between station and access point: 300 to 100 meters.


23/45

23

Wireless Access Points and NICs


24/45

24

Typical 802.11 Wireless LAN Operation withWireless Access Points

802.11 uses a differentframe format than 802.3

The access point translatesbetween the two frame formats

However, the packet goes all theway between the two hosts


25/45

25

Hosts and Access Points Transmitin a Single Channel

The access point and all the hosts it serverstransmit in a single channel

If two devices transmit at the same time,their signals will collide, becoming unreasonable

Media access control (MAC) methodsgovern when a device may transmit;

It only lets one device transmit at a time


26/45

26

Media Access Control (MAC)

MAC methods govern when devices transmit sothat only one station or the access point cantransmit at a time

To control access (transmission), two methodscan be used

CSMA/CA+ACK (mandatory)

RTS/CTS (optional unless 802.11b and g stationsshare an 802.11g access point)


27/45

27

CSMA/CA+ACK in 802.11 Wireless LANs

CSMA/CA (Carrier Sense Multiple Access withCollision Avoidance)

Sender listens for traffic

1. If there is traffic, waits

2. If there is no traffic:

2a. If there has been no traffic for less than the criticaltime value, waits a random amount of time, then returnsto Step 1.

2b, If there has been no traffic for more than the criticalvalue for time, sends without waiting

This avoids collision that would result if hosts couldtransmit as soon as one host finishes transmitting


28/45

28

CSMA/CA + ACK in 802.11 Wireless LANs

ACK (Acknowledgement)

Receiver immediately sends back anacknowledgement; no waiting because ACKs have

highest priority.

If sender does not receive the acknowledgement,retransmits the frame using CSMA/CA.

802.11 with CSMA/CA+ACK is a reliable protocol!


29/45

29

Request to Send/Clear to Send


30/45

30

Specific 802.11 Wireless LAN Standards

Characteristic 802.11 802.11a 802.11b 802.11g 802.11gwith

802.11b

802.11n

Rated Speed 2Mbps

54Mbps

11Mbps

54Mbps

NotSpeci-

fied

100 Mbpsto

300 MbpsActualThroughput,3 m

1Mbps

25Mbps

6 Mbps 25Mbps

12Mbps

Closer toratedspeedthan

earlierstandardsActualThroughput,30 m

? 12Mbps

6 Mbps 20Mbps

11Mbps

High atlonger

distances


31/45

31


Characteristic 802.11 802.11a 802.11b 802.11g 802.11gwith

802.11b

802.11n

UnlicensedBand

2.4GHz

5GHz

2.4GHz

2.4 GHz 2.4GHz

2.4 GHzand

5 GHzRemarks Dead

andgone

Littlemarketaccep-tance

Bloomedbriefly

Todays

dominant802.11

standard

Get rid ofold

802.11b

equip.

Greaterspeedand

distance


32/45

32


802.11g

Most popular 802.11 standard today

54 Mbps rated speed with much slower throughput

Generally sufficient for Web browsing

Inexpensive

All access points support it


33/45

33

802.11n

Under development

Rated speeds of 100 Mbps to 600 Mbps

Will operate in both the 2.4 GHz and 5 GHz bands

May use twice current bandwidth per channel (~20MHz) to roughly double speed

Currently a draft standard

A bit of overkill for most users


34/45

34

Bluetooth Personal Area Networks (PANs)

Bluetooth is standardized by a consortium

Connect devices on or near a single usersdesk

PC, Printer, PDA, Laptop, Cellphone Connect devices on or near a single users

body

Laptop, Printer, PDA, Cellphone

The goal is cable elimination
https://www.bluetooth.org/


35/45

35

Bluetooth PANs

There may be multiple PANs in an area

May overlap

PANs are called piconets


36/45

36

Bluetooth PAN Operation

File synchronization

Client PC

slave

Notebookmaster

Printer slavePrinting

Call through companyphone System

Cellphonemaster

Telephone slave

Piconet 1

Piconet 2

Note: Printeris in bothpiconets;

Slave hastwo masters.


37/45

37

802.11 versus Bluetooth PANs

Focus

Speed

802.11 Bluetooth

Large WLANs Personal Area Network

11 Mbps to 54 Mbps

In both directions

722 kbps with backchannel of 56 kbps.

May increase.

Distance100 meters for 802.11b(but shorter in reality)

Even shorter of 802.11a

Numberof devices in

an area

Limited in practice onlyby bandwidth and traffic

Only 10 piconets,each with8 devicesmaximum

10 meters.May increase


38/45

38

802.11 versus Bluetooth PANs

Scalability

Cost

Battery Drain

802.11 Bluetooth

Good through havingmultiple access points

Poor(but may get

access points)

Probably higher Probably Lower

Higher Lower

Profiles No Yes

Profiles allow specific products to work together. Different profilesfor printing, cordless telephones, headsets, etc. Must beimplemented on both master and slave.


39/45

39

Bluetooth PANS

Trends

Bluetooth Alliance is enhancing Bluetooth

The next version of Bluetooth is likely to grow to useultrawideband transmission

This should raise speed to 100 Mbps (or more)

Transmission distance will remain limited to 10

meters

Good for distributing television within a house


40/45

40

Emerging Local Wireless Technologies

In mesh wireless networks, the access points do all routing

There is no need for a wired networkThe 802.11s standard for mesh networking is under developmentThis P2P networking needs high density of devices


41/45

41


Can be focused electronically to give better reception


42/45

42


Ultrawideband (UWB) Uses channels that are several gigahertzwide

Each UWB channel spans multiple frequency bands

Low power per hertz to avoid interference with otherservices

Wide bandwidth gives very high speeds

But limited to short distance and ideal for video networkingat home

Wireless USB provides 480 Mbps up to 3 meters, 110Mbps up to 10 meters


43/45

43


ZigBee for almost-always-off sensor networks

Very low speeds (250 kbps maximum)

Very long battery life (months or years)

At the other end of the performance spectrum fromUWB


44/45

44


RFID (Radio Frequency Identification) Tags

Like UPC tags but readable remotely

In most cases, the radio signal from the reader provides powerfor the RFID tag

The RFID tag uses this power to send information about itself

Battery-operated RFID tags can send farther and send moreinformation

30-500 KHz, short distances, for supermarket scanning andinventory control

850-950 MHz, large distances, higher speed, for automated tollcollection


45/45


Software-Defined Radio

Can implement multiple wireless protocols

No need to have separate radio circuits for each

protocol

Reduces the cost of multi-protocol devices

Documents

Lecture 4 Ethernet and Wireless Local Area Networks 4482