lecture 4: ethernet and wireless local area networks

Ethernet and WirelessLocal Area Networks

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 Committee for LAN standards (the 802 Committee)

3

History of Ethernet Standards

The 802 Committee creates working groups for specific types of standards

802.1 for general standards

802.3 for Ethernet standardsThe terms 802.3 and Ethernet are interchangeable

802.11 for wireless LAN standards

802.16 for WiMax wireless metropolitan area network standards

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

Fiber PhysicalLayer

Standards

Medium850 nm light (inexpensive)

Multimode fiber

MaximumRun

Length

Speed

1000BASE-SX 275 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

Gigabit Ethernet

10 Gbps Ethernet usage is small but growing Several 10 Gbps 10GBASE-x fiber standards are

defined, but none is dominant

Copper is cheaper than fiber but cannot go as far

100 Gbps has been selected as the next Ethernet speed Chosen over 40 Gbps

100 Gbps Ethernet standards development is just getting underway

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(100 m maximum)

Physical Link

1000BASE-SX(220 m maximum)

Physical Link

Each trunk line along the way has a distance limit

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

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

Hierarchy Implications

Single possible path between stations.

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

Creates the potential for single points of failure.

Low cost is responsible for Ethernet’s LAN dominance.

Port Station 2 A1-44-D5-1F-AA-4C7 B2-CD-13-5B-E4-655 E5-BB-47-21-D3-56

11

Switch Operation in Ethernet

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

The switch looks up the frame’s destination MAC address in the switching table

The switch sends the frame out a single port

Only two ports are tied up

Other conversations can take place on other port pairs simultaneously

12

Ethernet 802.3 10Base2

Ethernet 10Base2

To NextStation

T-Connector to Link NIC to next segments

NIC

13

Ethernet 802.3 10Base2

Ethernet 10Base2

BNC connector

T-connectorTo nextstation

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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

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

server’s VLAN clients; less latency

Multicasting (some), not Broadcasting (all)

NONO

Server Eon VLAN1

16

Handling Momentary Traffic Peaks with Overprovisioning 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 network’s capacity.

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

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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.

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Traffic

Network capacity

Momentarypeak

Time

Priority in Ethernet

High-priority traffic goesLow-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

Routed LAN with Ethernet Subnets

If a routed LAN links multiple Ethernet switched

networks, the switched networks are called subnets

Wireless LANs

21

Local Wireless Technologies

802.11 Wireless LANs (Wi-Fi)

Today, mostly speeds of tens of megabits per second with 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 a building or a university campus by installing many access points

22

802.11 Wireless LANs (WLANs)

Wireless hosts connectby radio to access pointsWireless hosts connect

by 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.

Transmission speed: up to 300 Mbps but usually 10 Mbps to 100 Mbps.Distances between station and access point: 300 to 100 meters.

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Wireless Access Points and NICs

24

Typical 802.11 Wireless LAN Operation with Wireless Access Points

802.11 uses a different frame format than 802.3

The access point translatesbetween the two frame formats

However, the packet goes all theway between the two hosts

25

Hosts and Access Points Transmit in 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

Media Access Control (MAC)

MAC methods govern when devices transmit so that only one station or the access point can transmit at a time

To control access (transmission), two methods can be used

CSMA/CA+ACK (mandatory)

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

27

CSMA/CA+ACK in 802.11 Wireless LANs

CSMA/CA (Carrier Sense Multiple Access with Collision 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 critical time value, waits a random amount of time, then returns to Step 1.

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

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

28

CSMA/CA + ACK in 802.11 Wireless LANs

ACK (Acknowledgement)

Receiver immediately sends back an acknowledgement; 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!

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Request to Send/Clear to Send

30

Specific 802.11 Wireless LAN Standards

Characteristic 802.11

802.11a 802.11b 802.11g 802.11g with

802.11b

802.11n

Rated Speed 2 Mbps

54 Mbps

11 Mbps

54 Mbps

Not Speci-

fied

100 Mbps to

300 MbpsActual Throughput, 3 m

1 Mbps

25 Mbps

6 Mbps 25 Mbps

12 Mbps

Closer to rated speed than

earlier standards

Actual Throughput, 30 m

? 12 Mbps

6 Mbps 20 Mbps

11 Mbps

High at longer

distances

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Characteristic 802.11 802.11a 802.11b 802.11g 802.11g with

802.11b

802.11n

Unlicensed Band

2.4 GHz

5 GHz

2.4 GHz

2.4 GHz 2.4 GHz

2.4 GHz and

5 GHzRemarks Dead

and gone

Little market accep-tance

Bloomed briefly

Today’s dominant 802.11

standard

Get rid of old

802.11b

equip.

Greater speed and

distance

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

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 (~20 MHz) to roughly double speed

Currently a draft standard

A bit of overkill for most users

34

Bluetooth Personal Area Networks (PANs)

Bluetooth is standardized by a consortium

Connect devices on or near a single user’s desk PC, Printer, PDA, Laptop, Cellphone

Connect devices on or near a single user’s body Laptop, Printer, PDA, Cellphone

The goal is cable elimination

35

Bluetooth PANs

There may be multiple PANs in an area May overlap

PANs are called piconets

36

Bluetooth PAN Operation

File synchronization

Client PCslave

Notebookmaster

Printer slavePrinting

Call through companyphone System

Cellphonemaster

Telephone slave

Piconet 1

Piconet 2

Note: Printeris in bothpiconets;Slave has

two masters.

37

802.11 versus Bluetooth PANs

Focus

Speed

802.11 Bluetooth

Large WLANs Personal Area Network

11 Mbps to 54 MbpsIn 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

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 profiles for printing, cordless telephones, headsets, etc. Must be implemented on both master and slave.

39

Bluetooth PANS

Trends

Bluetooth Alliance is enhancing Bluetooth

The next version of Bluetooth is likely to grow to use ultrawideband 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

Emerging Local Wireless Technologies

In mesh wireless networks, the access points do all routingThere is no need for a wired network

The 802.11s standard for mesh networking is under developmentThis P2P networking needs high density of devices

In mesh wireless networks, the access points do all routingThere is no need for a wired network

The 802.11s standard for mesh networking is under developmentThis P2P networking needs high density of devices

41


Can be focused electronically to give better receptionCan be focused electronically to give better reception

42


Ultrawideband (UWB)

Uses channels that are several gigahertz wide

Each UWB channel spans multiple frequency bands

Low power per hertz to avoid interference with other services

Wide bandwidth gives very high speeds

But limited to short distance and ideal for video networking at home

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

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 from UWB

44


RFID (Radio Frequency Identification) Tags Like UPC tags but readable remotely

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

The RFID tag uses this power to send information about itself

Battery-operated RFID tags can send farther and send more information

30-500 KHz, short distances, for supermarket scanning and inventory control

850-950 MHz, large distances, higher speed, for automated toll collection

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

lecture 4: ethernet and wireless local area networks

Documents

root switch switch

f switch

ethernet overprovisioning

c switch

communication switch

switch hierarchy

ethernet highpriority

switch operation