Ethernet LANs Chapter 4 Copyright 2004 Prentice-Hall Panko’s Business Data Networks and Telecommunications, 5 th edition

Ethernet LANs

Chapter 4

Copyright 2004 Prentice-HallPanko’s Business Data Networks and Telecommunications, 5th edition

2

Perspective

Ethernet is the dominant LAN technology You need to know it well

Basic Ethernet switching is very simple

However, large Ethernet networks require more advanced knowledge

3

Ethernet History

Developed at Xerox Palo Alto Research Center in the 1970s After a trip to the University of Hawai`i’s Alohanet

project

Taken over by the IEEE 802 LAN/MAN Standards Committee is in charge of

LAN Standards

802.3 Working Group develops Ethernet standards

Other working groups create other standards

4

Ethernet Standards are OSI Standards

Ethernet standards are LAN standards

LANs (and WANs) are single networks

Single networks are based on Layer 1 (physical) and Layer 2 (data link) standards

OSI dominates standards at these layers

Ethernet standards are OSI standards Must be ratified by ISO, but this is a mere formality

5

Figure 4-1: Ethernet Physical Layer Standards

PhysicalLayerStandard

MediumMaximumRun

Length

Speed

UTP

100Base-TX 4-pair Category 5 or better

100 meters100 Mbps

1000Base-T 4-pair Category 5or better

100 meters1,000 Mbps

10Base-T 4-pair Category 3 or better

100 meters10 Mbps*

*With autosensing, 100Base-TX NICs and switches will slow to10 Mbps for 10Base-T devices. Often called 10/100 Ethernet

6



MediumMaximumRun

Length

Speed

Optical Fiber

100Base-FX 62.5/125 multimode,1300 nm

2 km100 Mbps

7



MediumMaximumRun

Length

Speed

1000Base-SX 62.5/125 micron multimode,850 nm, 200 MHz-km

275 m1 Gbps

1000Base-SX 50/125 micron multimode,850 nm, 400 MHz-km

500 m1 Gbps

1000Base-SX 62.5/125 micron multimode,850 nm, 160 MHz-kmmodal bandwidth

220 m1 Gbps

Gigabit Ethernet, 850 nm, various core sizes and modal bandwidths

1000Base-SX 50/125 micron multimode,850 nm; 500 MHz-km

550 m1 Gbps

8



MediumMaximumRun

Length

Speed

1000Base-LX 62.5/125 micron multimode,1300 nm

550 m1 Gbps

1000Base-LX 9/125 micron single-mode,1300 nm

5 km1 Gbps

Gigabit Ethernet, 1300 nm, multimode versus single-mode

9

Perspective

Access links to client stations today are dominated by 100Base-TX

Trunk links today are dominated by 100Base-SX Short trunk links, however, use UTP

Longer and faster trunk links use other fiber standards

10



MediumMaximumRun

Length

Speed

10GBase-LX462.5/125 micronmultimode, 1300 nm,WDM with 4 lambdas

300 m10 Gbps

10GBase-SR/SW 62.5/125 micronmultimode, 850 nm

65 m10 Gbps

10 Gbps Ethernet, multimode S = 850 nm, L = 1300 nm R=LAN, W=WAN

11



MediumMaximumRun

Length

Speed

10GBase-LR/LW 9/125 micron singlemode, 1300 nm.

10 km10 Gbps

10GBase-ER/EW 9/125 micron singlemode, 1550 nm.

40 km10 Gbps

10 Gbps Ethernet, for wide area networks L = 1300 nm, E = 1550 nm R = LAN, W = WAN

12



MediumMaximumRun

Length

Speed

40 GbpsEthernet

9/125 micronsingle mode.

UnderDevelopment

40 Gbps

13


Notes:

For 10GBase-x, LAN versions (R) transmit at 10 Gbps. WAN versions (W) transmit at 9.95328 Gbps for carriage over SONET/SDH links (see Chapter 6)

The 40 Gbps Ethernet standards are still under preliminary development

14

Figure 4-2: Baseband Versus Broadband Transmission

Baseband Transmission

Source

Signal Transmitted Signal (Same)

Transmission Medium

Signal is injected directly into the transmission medium(wire, optical fiber)

Inexpensive, so dominates wired LAN transmission technology

15

Figure 4-2: Baseband Versus Broadband Transmission

Broadband Transmission

SourceRadioTuner

Modulated Signal

Radio Channel

Signal is first modulated to a higher frequency,then sent in a radio channel

Expensive but needed for radio-based networks

16

Figure 4-3: Link Aggregation (Trunking)

UTPCordUTP

Cord

100Base-TX Switch

100Base-TX Switch

Two links provide 200 Mbps of trunkcapacity between the switches

No need to buy a more expensiveGigabit Ethernet port

Switch must support link aggregation(trunking)

17

Figure 4-4: Data Link Using Multiple Switches

OriginalSignal

ReceivedSignal

RegeneratedSignal

Switches regenerate signals before sending them out;This removes errors

18


OriginalSignal

ReceivedSignal

ReceivedSignal

ReceivedSignalRegenerated

Signal RegeneratedSignal

Thanks to regeneration, signals can travel far acrossa series of switches

19


OriginalSignal

ReceivedSignal

ReceivedSignal



UTP UTP62.5/125Multimode Fiber

100Base-TX(100 m maximum)

Physical Link


Physical Link

1000Base-SX(220 m maximum)

Physical Link

Each transmission line along the way has a distance limit.

20


Data Link Does Not Have a Maximum Distance(420 m distance spanned in this example)

OriginalSignal

ReceivedSignal

ReceivedSignal



UTP UTP62.5/125Multimode Fiber


Physical Link


Physical Link

1000Base-SX(220 m maximum)

Physical Link

21

Figure 4-5: Layering in 802 Networks

Governs aspects of the communicationNeeded by all LANs, e.g., error correction.

These functions not used in practice.

Governs aspects of the communicationSpecific to a particular LAN technology,

e.g., Ethernet, 802.11 wireless LANs, etc.

Physical Layer

MediaAccessControlLayer

LogicalLink

ControlLayerData

LinkLayer

Internet Layer

22

Figure 4-5: Layering in 802 Networks

TCP/IP InternetLayer Standards(IP, ARP, etc.)

Other InternetLayer Standards

(IPX, etc.)

802.2

Ethernet 802.3 MAC LayerStandard

Physical Layer

MediaAccessControlLayer

Other MACStandards

(802.5,802.11, etc.)

10Base-T1000Base-

SX…

LogicalLink

ControlLayer

Other PhysicalLayer

Standards(802.11, etc.)

DataLink

Layer

Internet Layer

23

Figure 4-6: The Ethernet Frame

Preamble (7 Octets)10101010 …

Start-of-Frame Delimiter (1 Octet)10101011

Destination MAC Address (48 bits)

Source MAC Address (48 bits)

Field

Computers use raw48-bit MAC addresses;Humans useHexadecimal notation(A1-23-9C-AB-33-53),Which is discussedLater.

24

Figure 4-6: The Ethernet Frame

Length (2 Octets)

PAD Field

Field

Packet(VariableLength)

LLC Subheader(Usually 7

Octets)Data Field

(VariableLength)

Frame Check Sequence (4 Octets)

Added if data fieldIs less than 46 octets;Length set to makedata filed plus PADfield 46 octets; Not added if data fieldis greater than 46octets long.

If an error is found,the frame isdiscarded.

25

Figure 4-7: Hexadecimal Notation

4 Bits(Base 2)*

Decimal(Base 10)

Hexadecimal(Base 16)

0000 0 0 hex

0001 1 1 hex

0010 2 2 hex

* 2^4=16 combinations

0011 3 3 hex

0100 4 4 hex

0101 5 5 hex

0110 6 6 hex

0111 7 7 hex

BeginCounting atZero

26


4 Bits(Base 2)

Decimal(Base 10)

Hexadecimal(Base 16)

1000 8 8 hex

1001 9 9 hex

1010 10 A hex

1011 11 B hex

1100 12 C hex

1101 13 D hex

1110 14 E hex

1111 15 F hex

After 9,Count AThrough F

27


Converting 48-Bit MAC Addresses to Hex Start with the 48-bit MAC Address

1010000110111011 …

Break the MAC address into twelve 4-bit “nibbles”1010 0001 1101 1101 …

Convert each nibble to a hex symbol A 1 D D

Write the hex symbols in pairs (each pair is an octet) and put a dash between each pair

A1-BB-3C-D7-23-FF

28

Figure 4-8: Multi-Switch Ethernet LAN

Switch 2

Switch 1 Switch 3

Port 5 on Switch 1to Port 3 on Switch 2 Port 7 on Switch 2

to Port 4 on Switch 3

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

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

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

D4-47-C4-B6-9FSwitch 3, Port 2

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

The Situation:A1… Sends to E5…

29


Switching Table Switch 1Port Station

2 A1-44-D5-1F-AA-4C7 B2-CD-13-5B-E4-655 C3-2D-55-3B-A9-4F5 D4-47-55-C4-B6-9F5 E5-BB-47-21-D3-56

Switch 2

Switch 1

Port 5 on Switch 1to Port 3 on Switch 2


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


On Switch 1

30


Switch 2

Switch 1 Switch 3



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


3 A1-44-D5-1F-AA-4C3 B2-CD-13-5B-E4-655 C3-2D-55-3B-A9-4F7 D4-47-55-C4-B6-9F7 E5-BB-47-21-D3-56 E5-BB-47-21-D3-56

Switch 3, Port 6

On Switch 2

31


Switch 2

Switch 3



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


4 A1-44-D5-1F-AA-4C4 B2-CD-13-5B-E4-654 C3-2D-55-3B-A9-4F2 D4-47-55-C4-B6-9F6 E5-BB-47-21-D3-56


On Switch 3

32

Figure 4-9: Hub Versus Switch Operation

A B C D

EthernetHub

Hub Broadcasts Each BitIf A Is Transmitting to C,B Must Wait to Transmit

33


A B C D

EthernetSwitch

Switch Sends Frame Out One Port;If A Is Transmitting to C,

Frame Only Goes OutC’s Port.

34


A B C D

EthernetSwitch

Switch Sends Frame Out One PortIf A Is Transmitting to C,

B Can Transmit to DSimultaneously

35

Figure 4-10: Hierarchical Ethernet LAN

EthernetSwitch F

Server YServer X

Client PC1

SinglePossible Path

BetweenClient PC 1

and Server Y

EthernetSwitch E

EthernetSwitch D

EthernetSwitch B

EthernetSwitch A

EthernetSwitch C

36


Only one possible path between stations Therefore only one entry per MAC address in

switching table

The switch can find the one address quickly, with little effort

This makes Ethernet switches inexpensive per frame handled

Low cost has ledto Ethernet’sLAN dominance

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

37


Workgroup EthernetSwitch F

Core andWorkgroupSwitches

WorkgroupEthernetSwitch E

WorkgroupEthernetSwitch D

Core EthernetSwitch B

Core EthernetSwitch A

Core EthernetSwitch C

Core

38


Workgroup switches connect to stations via access lines

Core switches higher in the hierarchy connect switches to other switches via trunk lines

The core is the collection of all core switches

Core switches need more capacity than workgroup switches because they have to handle the traffic of many conversations instead of just a few

39

Figure 4-11: 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

40

Figure 4-12: 802.1D Spanning Tree Protocol

Switch 1

Switch 2

Switch 3

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

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

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

D4-47-55-C4-B6-9FE5-BB-47-21-D3-56

Activated

Activated

Deactivated

Normal OperationLoop, but Spanning Tree ProtocolDeactivates One Link

41

Figure 4-12: 802.1D Spanning Tree Protocol

Switch 1

Switch 2

Switch 3

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

Deactivated Deactivated

Reactivated

Switch 2 Fails

42

Figure 4-13: Virtual LAN (VLAN) with Ethernet Switches

Client A

Client B

Client C

Server D Server E

ServerBroadcast

Server Broadcasting without VLANS

Servers SometimesBroadcast; GoesTo All Stations;Latency Results

43

Figure 4-13: Virtual LAN (VLAN) with Ethernet Switches

Server Broadcasting with VLANS

Client Aon VLAN1

Client Bon VLAN2

Client Con VLAN1

Server Don VLAN2

Server Eon VLAN1

ServerBroadcast

NoNo

With VLANs,Broadcasts Only GoTo a Server’s VLAN

Clients; LessLatency

44

Figure 4-14: Tagged Ethernet Frame (Governed By 802.1Q)

Destination Address(6 Octets)

Destination Address(6 Octets)

Source Address (6 Octets)

Length (2 Octets)Length of Data Field in

Octets1,500 (Decimal) Maximum

Tag Protocol ID (2 Octets)1000000100000000

81-00 hex; 33,024 decimal,So Tagged.

Larger than 1,500, So nota Length Field

By lookingat the value

in the 2octets after

theaddresses,the switchcan tell ifthis frameis a basic

frame(value lessthan 1,500)or a tagged(value is 33,024).

Basic 802.3 MAC Frame Tagged 802.3 MAC Frame

Start-of-Frame Delimiter(1 Octet)

Preamble (7 octets)

Start-of-Frame Delimiter(1 Octet)

Preamble (7 octets)

Source Address (6 Octets)

45

Figure 4-14: Tagged Ethernet Frame (Governed By 802.1Q)

Tag Control Information(2 Octets) Priority Level (0-7)

(3 bits); VLAN ID (12 bits)1 other bit

Basic 802.3 MAC Frame Tagged 802.3 MAC Frame

Length (2 Octets)

Data Field (variable)

Data Field (variable)

PAD (If Needed)

Frame Check Sequence(4 Octets)

PAD (If Needed)

Frame Check Sequence(4 Octets)

46

Figure 4-15: Handling Momentary Traffic Peaks with Overprovisioning and Priority

Traffic

Network Capacity

Momentary Traffic Peak:Congestion and Latency

Time

Congestion and Latency

47


Traffic

Overprovisioned Network Capacity Momentary Peak:No Congestion

Time

Overprovisioned Traffic Capacity in Ethernet

48


Traffic

Network Capacity

MomentaryPeak

Time

Priority in Ethernet

High-Priority Traffic GoesLow-Priority Waits

49

Figure 4-16: Switch Purchasing Considerations

Number and Speeds of Ports

Decide on the number of ports needed and the speed of each

Often can by a prebuilt switch with the right configuration

Modular switches can be configured with appropriate port modules before or after purchase

50


Switching Matrix Throughput (Figure 4-17)

Aggregate throughput: total speed of switching matrix

Nonblocking capacity: switching matrix sufficient even if there is maximum input on all ports

Less than nonblocking capacity is workable For core switches, at least 80% For workgroup switches, at least 20%

51

Figure 4-17: Switching Matrix

1

2

3

4

100 Mbps

100 Mbps

100 Mbps

100 Mbps

1 2 3 4

Port 1to

Port 3400 MbpsAggregateCapacity

to BeNonblocking

InputQueue(s)

100Base-TXInput Ports

100Base-TXOutput Ports

Any-to-AnySwitching

Matrix

Note: Input Port 1 and Output Port 1 are the same port

52


Store-and-Forward Versus Cut-Through Switching (Figure 4-18)

Store-and-forward Ethernet switches read whole frame before passing it on

Cut-through Ethernet switches read only some fields before passing it on

Perspective: Cut-through switches have less latency, but this is rarely important

53

Figure 4-18: Store-and-Forward Versus Cut-Through Switching

Preamble

Start-of-Frame Delimiter

Destination Address

Source Address

Tag Fields if Present

Length

Cyclical Redundancy Check

Data (and Perhaps PAD)

Cut-Through BasedOn MAC DestinationAddress (14 Octets)

Cut-Through forPriority or VLANs(24 Octets)

Cut-Through at64 Bytes (Not a Runt)

Store-and-ForwardProcessingEnds Here(OftenHundredsOf Bytes)

54

Figure 4-19: Jitter

Jitter Variability in latency from cell to cell. Makes voice

sound jittery (Figure 4-19)

High Jitter (High Variability in Latency)

Low Jitter (Low Variability in Latency)

55


Manageability

Manager controls many managed switches (Figure 4-20: Managed Switches)

Polling to collect data and problem diagnosis

Fixing switches remotely by changing their configurations

Providing network administrator with summary performance data

56

Figure 4-20: Manageable Switches

Manager

Commandto Change

Configuration

Get Data

Data Requested

Managed Switch

Managed Switch

57


Manageability

Managed switches are substantially more expensive than unmanageable switches

To purchase and even more to operate

However, in large networks, the savings in labor costs and rapid response are worth it

58

Figure 4-21: Physical and Electrical Features

Form Factor

Switches fit into standard 19 in (48 cm) wide equipment racks

Sometimes, racks are built into enclosed equipment cabinets

Switch heights usually are multiples of 1U (1.75 inches or 4.4 cm)

19 inches(48 cm)

59


Port Flexibility Fixed-port switches

No flexibility: number of ports is fixed

1U or 2U tall

Most workgroup switches are fixed-port switches

60


Port Flexibility Stackable Switches

Fixed number of ports

1U or 2U tall

High-speed interconnect bus connects stacked switches

Ports can be added in as few as 12

61


Port Flexibility Modular Switches

1U or 2U tall Contain one or a few modules Each module contains 1 to 4 ports

62


Port Flexibility Chassis switches

Several U tall

Contain several expansion slots

Each expansion board contains 6 to 12 slots

Most core switches are chassis switches

63


UTP Uplink Ports Normal Ethernet RJ-45 switch ports transmit on

Pins 3 and 6 and listen on Pins 1 and 2 (NICs do the reverse)

If you connect two normal ports on different switches, they will not be able to communicate

Most switches have an uplink port, which transmits on Pins 1 and 2. You can connect a UTP uplink port on one switch to any normal port on a parent switch

64


802.3af brings electrical power over the station’s ordinary UTP cord Limited to 12.95 watts (at 48 volts)

Sufficient for wireless access points (Chapter 5)

Sufficient for IP telephones (Chapter 6)

Not sufficient for computers

Automatic detection of compatible devices; will not send power to incompatible devices

65

Topics Covered

Who develops Ethernet standards?

Many physical layer standards (100Base-TX, 1000Base-SX, etc.)

Baseband versus broadband transmission

Link aggregation

Switch signal regeneration allows maximum distances spanning several UTP and fiber links

66

Topics Covered

MAC and LLC layers

Ethernet Frame Preamble and Start of Frame Delimiter fields 48-bit Source and Destination Address fields Length field (length of data field) Data field

LLC subheaderPacket

PAD if needed to make data field + PAD 64 bits long

67

Topics Covered

Ethernet Frame Frame check sequence field

Discard if detect error: unreliable

Hexadecimal Notation For humans, not computers

Multi-Switch LAN Operation with Switching Tables

68

Topics Covered

Hubs versus Switches

Hierarchical Topology Only one possible path between any two end

stations

Makes switching decisions easy and fast

This makes the cost per frame handled low

Key to Ethernet’s LAN dominance

Core and Workgroup Switches

69

Topics Covered

VLANs to reduce congestion due to server broadcasting

Handling Momentary Traffic Peaks Overprovisioning—least expensive Ethernet choice

today

Priority is more efficient but more expensive to do

Tagged Frames for VLANs and Priority

70

Topics Covered

Switch Purchasing Decisions Number and speeds of ports Switch matrix capacity and nonblocking switches Store-and-forward versus cut-though switches Jitter Manageability Form factor (U) Port flexibility UTP uplink ports 802.3af for electrical power

Documents

Ethernet LANs Chapter 4 Copyright 2004 Prentice-Hall Panko’s Business Data Networks and Telecommunications, 5 th edition