es/eg 4546 a local area network is simple low cost local ...es/eg 4546 the ethernet local area...

ES/EG 4546 The Ethernet

Local Area Network

G. Fairhurst

r48 2019

What is a LAN?

local (one building, group of buildings, etc)

always controlled by one administrative authority

usually high speed and is always shared

often assumes other users of the LAN are trusted

either planned (structured ) or unstructured

A Local Area Network is....

Ethernet

Simple low cost Local Area Network (LAN)

Shared or Switched Access

Supports: Unicast (1 to 1) Broadcast (1 to all) Multicast (1 to some)

Divided into Two Layers Link Layer - Medium Access Control (protocol) Physical Layer - Transmission Control (cabling)

What is Ethernet?

First LAN designed at Xerox "PARC" (1972)2 Mbps 75 Ohm Coaxial cableTo share expensive laser printers

File sharing followed later

Ethernetv2 - Blue Book (1980)Digital, Intel, Xerox (DIX) 10 Mbps 50 Ohm Coaxial cable

Printer PC PC PC

What is Ethernet?

Standardised by IEEE in 1985:IEEE 802.3 Two variants: Thick Ethernet and Thin Ethernet

Various speeds now available:10 Mbps (original IEEE spec)100 Mbps (Fast Ethernet)1000 Mbps (1 Gbps)10000 Mbps (10 Gbps)40 Gbps, 100 Gbps, …

First LAN designed at Xerox "PARC" in 1972

Ethernet v2 followed from Digital, Intel, Xerox (DIX) in 1980

IEEE 802.X Protocol Suite

IEEE 802 Committees

802.1Arch.

802.3CSMA/

CD LAN

802.4TokenBus

802.5TokenRing

802.6DQDBMAN

802.2Logical

LinkControl

802.7Broad-band

802.8Fibre

10B5 (Thick Ethernet)!Yellow PVC Outer Coating (0.5")

Dielectric Insulation50 Ohm

CopperConductor

Braided Outer Conductor

High performance co-axial cableSegment length ≤ 500mGood noise immunityN-Type connector used

In-Line or Vampire external transceiver

Ethernet Bus

Bus Topology

Network medium (cable)Terminator

Host Computer(station)

Network Interface

Transceiver(Attachment Unit)

Attachment UnitInterface Cable

Ethernet 10B5 Cabling

Ethernet trunk cable

AUI drop cable to each room50 Ohmterminator(one end earthed)

Wiring cabinet

RepeaterBridgeor Router

10B5 (Thick Ethernet Transceiver)50 ohmterminator

Attachment Unit Interface(AUI) Drop Cable

0 - 50 m

Host AUI Port

N-type Connectors

In-LineTransceiver

15 pin AUID-Connector

Host AUI Port

VampireTransceiver

Vampire Cable Tap

10B5 (Thick Ethernet Vampire Transceiver)

2-Part BlockHolds Cable

InsulatedSpike Pierces Centre Core

Shorter SpikesCut into Outer Conductor

Cable

Transceiver Block

MAU

Bolt to Tighten Block

Thick Wire(Yellow)

Ethernet Cable

10B2 (Thin Ethernet)!White, Grey or Black PVC Outer Coating

CopperConductor

Dielectric Insulation50 Ohm

Braided Outer Conductor

Low cost co-axial cableSegment length ≤ 185 mFlexible, easy installationBNC connector and “T” joiner

In-built or external transceiverdifficult to manage (unstructured)

Ethernet 10B2 Cabling

Wiring cabinet

Repeater Bridge or Router

Terminator

Terminator

One bus: No loops or stubs!

10 Base Fibre

Fibre Optic Cable

Used for pt-to-pt linksSegment length ≤1 km (or more)

Two diameters of fibre:Multimode (Thicker, Local networks)Single Mode (Thin, Longer distance)

All types of fibre provide:High noise immunityNo electrical path

(protected from lightning)(secure, hard to tap-into)

Uses external transceiver(i.e. connects a pair of repeaters)Easy to upgrade transceiver speed

10 Base FibreAUI connectoron equipment

10BFtransceiver

Pair of fibres(62.5/125 )

LED laser transmitterPhoto diode detector

Ethernet Success Story

Cost-Effective

Simple to use

Familiarity to customers

Standard for Internet LANs

Medium Access Control

FramesAddressingShared Access

CRCpreamble

8 bytes 4 bytes

packet of data to be sent

46 -1500 bytes

destination address

sourceaddress type

14 bytes

Link Layer

MACMedium Access Control

Frames- Data is sent on an Ethernet Network in Frames

Addressing- All End Systems have an Ethernet MAC Address (In their “PROM”)- Each frame sent with this source address

- Frames also carry a Destination Address, used in three ways:Broadcast, Unicast, and Multicast

Shared Access- Sharing network cost- Sharing the reachability

CRCpreamble

8 bytes 4 bytes


46 -1500 bytes

destination address

sourceaddress type

14 bytes

Ethernet Frames

Protocol Data Unit, PDU (Internet Packets)

Encapsulated by Ethernet Frames to cross the LANAdds 26 bytes of overhead to each PDU

CRCpreamble

8 bytes 4 bytes


46 -1500 bytes

destination address

sourceaddress type

14 bytes


46 -1500 bytes

e.g. a 46 byte packet is carried in a 72 byte framea 1200 byte PDU is carried in a 1226 byte frame.

Ethernet MAC Address

Each Network Interface Card (NIC) has a MAC Address

Held in a manufacturer-configured PROM

Addresses are globally unique

A MAC Vendor Code (OUI) + Number

About 1% of OUIs have been used.

IEEE sells the blocks of addresses to manufacturers

Each block has 256 cubed addresses

That is 16 Million!!

08:00:20:00:00:01

MAC Vendor Codes (OUIs)

08:00:20:00:00:01

080002 3Com (Formerly Bridge) 080003 ACC (Advanced Computer Communications) 080005 Symbolics Symbolics LISP machines 080008 BBN 080009 Hewlett-Packard 08000A Nestar Systems 08000B Unisys 080011 Tektronix, Inc. 080014 Excelan BBN Butterfly, Masscomp, Silicon Graphics 080017 NSC 08001A Data General 08001B Data General 08001E Apollo 080020 Sun Sun machines 080022 NBI 080025 CDC 080026 Norsk Data (Nord)

The first 3B of address tells you the manufacturer

Shared Access to Ethernet Medium

Sender Intended Recipient

Shared medium delivers all frames to all computers

Each computer discards frames intended for other computers

Using the Destination MAC address

A D BC

Source: A Destination: B

A sends a frame to Bwhich is broadcast to all stations

All stations receivethe frame, but discardthe frame if the destinationaddress does not matchthe local address

The destination stationreceives the frame andforwards it to host B

This assume that a sender knows the value of the MAC address in the destination’s PROM (we’ll find out how it does this later!)

CRCpreamble

8 bytes 4 bytes

Ethernet Frame Structure


46 -1500 bytes

destination address

sourceaddress type

14 bytes

first bit = 0 indicates point to pointfirst bit = 1 indicates broadcast or multicast

LAN address of intended recipient

48 bits, expressed as 12 hexadecimal digits e.g., 12:34:56:78:9A:BC

A theoretical 200,000,000,000 addressesActually 70,000,000,000... (2 bits are used)

20,000 MAC addresses for each person on the planet!

Special MAC Addresses

The all 1’s Address is used to send to all NICsKnown as the broadcast destination addressOnly ever used as destination address

FF:FF:FF:FF:FF:FF

The all 0’s Address is specialKnown as the unknown addressOnly ever used as source address

00:00:00:00:00:00

Group MAC Addresses

Groups addresses Have the least significant bit of the first byte to 1The remainder of the address carries the specific group address

01:00:5E:00:00:FF

NICs need to “register” to receive from a groupA computer may “register” several group addressesThe NIC passes all frames with group addresses that match

Group addresses identify “channels” not ReceiversSender chooses a group address to usee.g. one channel may carry a specific Internet TV station

Multicast on EthernetServer

Client(destination

address matches)

1 Receiver

Server

Client(registered)

Client(registered)

Client(registered)

NotRegistered

3 Multicast Receivers

TV/Radio/etc Transmission (several receivers)

Addressing SummaryAll NICs have a MAC Address

- Also provides an income stream to the IEEE :-)

All NICs receive:Every frame with a broadcast MAC destination address ff:ff:ff:ff:ff:ff

Every frame with a destination address that matches its PROM

Every frame with a destination address that matches a registered multicast group address (i.e. used by a program on the computer)

All filtering is performed within the NIC

Computer does not know about discarded frames

A computer can override filtering, by placing NIC into promiscuous mode - where all frames are received

Ethernet Transmit

Sharing the Media shared physical bus

shared wireless channel

Link Layer

There is only one medium (cable)

All NICs should be able to use the cable

Clearly only one should send at a time

How does a NIC know if it may send?

Sharing the media

Printer PC PC PC

ALOHA Collision

AB

Idle

B does not notice that

A is already sending

A, B will both need to send again at a later time

Maximum ALOHA Channel Throughput

kmax= (2eLd)-1

L = average number of frames/sec

Assumes a poisson distribution

d = duration of each frame

Maximum at 1/2e, i.e., 18.4%

Listen-Before-Talk

Also called Carrier Sense Multiple Access

AB

Idle

B hears A and waits

B sends

Back-off with Carrier Sense

Chances of a collision are small, but still need to share mediumBack-off detects when medium used and coordinates access

(1) There were no collisions. (2) How much do we backoff?

Consider a BUSY network with four nodes each trying to send:

1 2 3 4

3 Waits

From 1

1 Transmits

2 Tries and waits

2 Backoff

3 Backoff

From 2

2 Retries

4 Tries & waits

4 Backoff

3 Backoff

3 Backoff

From 4 From 3

3 Tries and waits

3 Waits

Ethernet Medium Access

Ethernet needs to solve the challenges:

- how to scale to large numbers of active nodes- how to deal with propagation delay

Collisions and Collision Detection

A B

A starts transmissiont=0

A B

B starts transmissiont=∂t

A B

B detects collisiont=tp

A B

A detects collisiont=2tp

Suggests a minimum frame size

Slot Time

All senders need to know when a collision occurs.

The sharing in a CSMA/CD system is controlled by the slot time.

The slot time In a IEEE 802.3 LAN is 51.2 µs (i.e. 64 B).

This limits the maximum distance to 3km at 10 Mbps.

This defines the minimum Ethernet frame size (60 bytes+CRC32)

A B


Slot Time (Example)

Sum less than Slot Time of system < 51.2 microsecs

Component Properties Delay (microsec)

AUI Cable 6x 50m , 0.65c 3.08Transceiver 3 transceivers (6x 1.2 micosec) 7.2

3xCoax Medium e.g. 1500m, 0.77c 13

2xOther Media e.g.1000m, 0.65c 10.26

Repeater delay Propagation delay 2

Signal Rise Time 8.4

Elec Circuit Propagation delay 1.05

Total 44.99

Random Backoff

Senders need to back-off different periods.

Each sender waits for a random period of time

Senders choose a random number from a set of values [0...t]

Value is multiplied by the Ethernet Slot Time (51.2 microsecs)

Each attempt the sender exponentially increases t ([0..1], [0..3],[0..7]...)

A B


Retransmission

Retransmit[0,1]

A picks 0 from the

set of [0,1]

AB

Retransmit[0,1]

50% probability the two NICs choose different numbers

AB

Exponential Back-Off

Retransmit[0,1,2,3]

Retransmit[0,1,2,3]

IdleRetransmit[0,1]

Retransmit[0,1]

Idle

Random Backoff

[0,1] First Retx

Randomnumber at

A

Randomnumber at

BResult

0 0 Collision

0 1A sends

first

1 0B sends

first

1 1Collision after 1

slot time

[0,1,2,3] Second RetxA B Result0 0 Collision0 1 A sends0 2 A sends0 3 A sends1 0 B sends1 1 Collision1 2 A sends1 3 A sends2 0 B sends2 1 B sends2 2 Collision2 3 A sends3 0 B sends3 1 B sends3 2 B sends3 3 Collision

Transmit4B Jam

Select Random IntegerR: = (0 and 2K)

Increment Retry Count

TestCount

Defer between (0 and 2K)x 51.2 µSwhere K=N, K≤10

N < 15N=15

N++

N≤10?

K:= N K:= 10

Defer R x 51.2 µS

N > 10N ≤ 10

Collision

Done

idle

no

yes

wait 9.6 µS

Inter frame gapallows receiverstime to settle

TransmitFrame

CSMA/CDSend Frame

DeferCarrierSense

busy

N:= 0

Aborted

R = {0 …2^(k)-1}

Ethernet Utilisation

Utilisation

100%

0Offered Load

0

Congestioncollapse

Maximum (random retransmission)

Maximum(Ethernet)

Performance degrades with increasing load- when there are many NICs with data to send

AB

Capture by A

Retransmit[0,1]

Retransmit [0,1,2,3, 4,5,6,7]

Retransmit[0,1]

Retransmit[0,1,2,3]

Idle(A,B wait)

Retransmit[0,1]

Retransmit[0,1]

Multiple Access - SummaryALOHA

Requires Checksum (CRC)Problem: Many collisions when many nodesEfficiency: 100% (1 node) 18% (many)

Listen-Before-Talk (CSMA)Requires Carrier Sense (CS)Problem: Collisions still possible

Collision Detection (CSMA/CD)Requires Collision Detect (CD) with Back-OffProblem: Capture possibleEfficiency: 100% (1 node) higher (many)

Recap: Strengths v Weakness of CSMA/CD

StrengthsNo controlling system neededEasy to add new systems (NICs)Performance “reasonably fair”

WeaknessPerformance degrades with increasing loadOne “busy” system can “capture” capacity

- more of a problem for “upstream”(e.g. wifi base station, router)

On balance good design!

Wireless Ethernet

Wire-less physical layerNo cable

Gorry Fairhurst (c) 2003

Standardised by IEEE 802.11 Committee

Radio Link

2.4-2.485 GHz Industrial Science & Medicine (ISM) Band 14 channels available worldwide (fewer channels available in some countries)

Only 3 non-overlapping 20 MHz channels

Uses spread spectrum channels First used by military ~ 50 years ago Very high immunity to noise

RF Power 802.11b 100mW Mobile Phone 600 mW CB Radio 5W Microwave Radio 2W

5.15-5.825 GHz Band also used for 802.11n (3 channels)

100m

Radio Technologies

0.001

0.01

0.1

1

10

100

100 1000 10000 100000 1000000 10000000 100000000

Watt

Bandwidth bps

SensorISM

Zigbee6lowpan

BT

DECT

802.11b

UWB

802.11aGSM GPRS

3G LTE

802.11n

802.11 Success

WiFi deployment~500,000 Hotspots in 144 countries! 1,000,000,000 chipsets since 20002.5 GHz, 5 GHz, 60 GHz

Speeds Initial 11 Mbps Grew to 300 Mbps in a decadeSince 2011, looking at 1 Gbps at short distances ~ 10m(rate reduces with distance at 100m or so, still only 11 Mbps)

Frequency Channel Re-use

The ISM frequency band allows several WiFi channels All systems using a basestation use the same channelThis forms a logical network

X BY A

X BY A

P

Can be interferencefrom adjacent networks!

!!!

Base Stations and Beacon Frame

How do you know which network you are using? The WiFi access point sends periodic beacon frames

can also identify the network (ssid)

A APWiFi basestation

The WiFi base station forms the logical centre of the network

Wireless (802.11)

Each wireless node has a rangeA is an end system; AP is a an access point

A needs to be able to receive signal from AP (and AP from A)

A AP

When A sends to AP it can first sense the medium(i.e. check if any system is sending)

Wireless (802.11)

A and AP can no longer communicate (signal strength)A AP

A and AP can no longer communicate (interference)

A AP

Hidden Node Problem

Some nodes may not be able to “see” other transmissions e.g.C does not know if A is sending C may try to send to AP (causing a collision)

Note 1: Wireless propagation can be very variable!Note 2: By definition AP sees signal from all nodes using AP

A AP C

Virtual Carrier Detect

C first sends a Clear To Send frame to ask if it can transmit- received by all nodes in range (i.e. Pink)

AP responds with an Ready To Send frame- received by all nodes in range (i.e. Pink & Yellow) both now know the “channel is in use”

When Ready To Send is not receivedsender must defer (“back-off”) before repeating Clear To Send

A AP C

Hidden Node Problem and CTS/RTS

CTS

RTS

Data from C

RTS

mediabusy

Note: If C needs to talk to A, it would rely on AP to relay (or repeat) the signal so that A can receive it.

time

A AP C

transmissionstarts

Collision Avoidance

WiFi uses CSMA with Collision Avoidance

Three important changes:

1. A sender attempts to avoid causing a collision

2. A sender cannot monitor the wireless mediumReceivers acknowledge (after a short delay) if they receive a frame.If no ACK is received within a timeout, the sender backs-off (as in CSMA/CD). Backoff increases for 5-7 attempts

3. A procedure known as CTS/RTS is used to detect hidden nodes.

Ethernet Transmit

Sending Frames

The Physical Layer

Synchronous Serial Communications

serial bit stream

Byte

Byte

Tx Clock

Rx Clock

Uses two shift registers (both clocks must be the same)- Note that bytes are sent l.s.b. first!

Recall the Ethernet broadcast/unicast address bit?

Non Return to Zero

0 encoded: 1 encoded:

2 signal levels usedThe level indicates the value of each bit- a low level indicates 0- a high level indicates 1The bandwidth of NRZ is approx 1 Hz / bit

NOT USED IN ETHERNET! Traditional Synchronous Transmission

DriverData

Clock

Data

Clock

Data

Clock

Clock signal transitions indicate centre of each bitRequires two wires (clock & data)

Driver

Data

Clock

Non Return to Zero

Data

NRZ

The receiver needs some way of determining the clock...

NOT USED IN ETHERNET! Manchester Encoding

1 00 1

0 encoded: 1 encoded:

2 signal levels usedTransition in the centre of each bit- down-wards transition indicates 0- up-wards transition indicates 1Double the bandwidth compared to NRZ

Encoded Data

EncoderData

Clock

Decoder Data

ClockDPLL

EncodedData

Digital Phase Locked Loop (DPLL) regenerates clockCombined clock & data signal

What no clock wire?

Manchester Encoded Signal

Data

NRZ

Ethernet Waveform

0 1 10 1 1 1

0 V-0.225 V

-1.825 V

0.1 0.2 0.3 0.4 0.5 0.6 0.7

0

Time ( uS)

Waveform as seen on an oscilloscope may be inverted!

Transitionsat centre of bits

Can you decode this?

Manchester Encoding

2-signal levels usedNo DC component (even for long runs of 0‘s or 1’s)Timing component at fundamental clock frequency (10 MHz)Double bandwidth of NRZ (but Ethernet uses RF cable!)

Ethernet Reception

Three parts to decoding each bit of data

1) We need a clock signal at the receiver

2) We need to know the start of the data (and polarity of a ‘1’)

3) We need to identify the end of frame

Ethernet Clock Recovery

0 1 10 1 1 1

0 V-0.225 V

-1.825 V

0.1 0.2 0.3 0.4 0.5 0.6 0.7

0

Time ( uS)

Clock

EncodedData

DPLL

DPLL contains a clock (oscillator)Uses the phase transitions to lock oscillator frequencyIf transition late, decreases period (increases frequency)If early, increases period (decreases the frequency)

After many transitions frequency matches original clock

Ethernet Clock Recovery by DPLL

0 1 10 1 1 1

0 V-0.225 V

-1.825 V

0.1 0.2 0.3 0.4 0.5 0.6 0.7

0

Time ( uS)

AlignedLeading Lagging

Carrier Detected

Value in “window” looking at each bit period:

Digital Phase-Locked Loop (DPLL)

Clock

EncodedData

Bit Sample

Rx DataCentre of bit

Correction Logicx8 Clock

÷ 8 Divider

Regenerated Clock

One bit sample

You do not need to

reproduce this!

Preamble Sequence

destination address

sourceaddress packet of data to be sent CRCtypepreamble

46 -1500 bytes14 bytes8 bytes 4 bytes

Ethernet Inter-Frame Gap / Spacing

A silent time between frames (no carrier on medium)

Allows electronics to recover after end of previous frame

20 byte periods (measured from end to next SFD)

10 Mbps: > 9.6 microsecs between frames (at sender)

(some descriptions say 10.4 microsecs)

Carrier Detected

Ethernet Frame

Carrier Detected

DPLLLock

Start of Frame

Delimiter

CarrierEnd

More bitsin preamble

Manchesterdecode each bitto form bytes

More bitsin frame

Ethernet Preamble Sequence

1 0 1 0 1 0 1 ....

Sequence of 62 alternating 1 and 0’sForms a square wave when encoded!Start of frame delimiter (11 in m.s.b. position of last byte)

Strictly speaking the preamble is 7B and the SFD is (1B)

Loss of the start of the preamble

NOTE:(1) Each sender will have a slightly different clock signal(2) Not all bits of the preamble are “received”

0 1 10 1 1 1

0 V-0.225 V

-1.825 V

0.1 0.2 0.3 0.4 0.5 0.6 0.7

0

Time ( uS)

“LOST”

DPLLLock

SummaryIFG between each frame

All Ethernet frames have a preamble

62 bits with value 10

First bits used to detect carrier

Remainder allow DPLL to gain lock (takes time)

Not all preamble bits are “received”

Start/polarity of MAC header detected by 2 bits, with 11

Final bit in frame detected by absence of carrier

CRC-32 used to verify the process

Ethernet Receive

Transmit CRC& Receiving

Frames

Receive Frame

addrmatch

Forward

IncrementError Count

no

yes

Startof frame

Discard

Carrier Detect

Error

OK

CRC &size

no

yes

Wait for DPLL lock

Address matchesLocal addressBroadcast addressMulticast address

Length ≥ 64 BLength ≤ 1518 BIntegral No BytesCRC = OK

data =11?

LAN (MAC) address





Cyclic Redundancy Check (CRC)

CRC is a form of digital signature (32 bit hash)

Calculated at the sender & sent

Re-calculated at the receiver

Two values compared at receiver

Able to verify the integrity of the frame

CRC detects:

Frames that have been corrupted

Frames where the DPLL failed

destination address



Division

! ! ! ! !quotientdivisor !) dividend

! ! ! !___________! ! ! !! ! ! ! !remainder

content offrame

generatorpolynomial

fixed size (<divisor)used for checksum

not used

Why Modulo 2 Division?

• CRC calculations ignore the carry

Because the hardware solution is simple!!!!!

Truth Table for Modulo-2 Division (XOR)

0 ⊕ 0 = 00 ⊕ 1 = 11 ⊕ 0 = 11 ⊕ 1 = 0

Modulo 2 Division

1 1 1 1 0 0 1 0 1 0 0 0 0⊕ 1 1 0 0 1 0|1 1 0 1

11001 )

Divisor(Generator Polynomial)

First digitmust be '1'

0's are appenedto the dividend(flush bits)

This digit must always be 0

Modulo 2 division replaces additionin BCC calculation

Example simplified to generate a short (4 bit) CRC

Modulo Division

1 0 1 1 1 0 0 1 0 1 0 0 0 0⊕ 1 1 0 0 1 0|0 1 0 1 1 ⊕ 0 0 0 0 0 0|1 0 1 1

11001 )¨

1 Bring next digit of dividend down2 Copy msb of value to quotient3 Insert 0 (if quotient 0) or divisor (if quotient 1)4 Calculate XOR sum5 Discard msb of value (always 0)

Revise yournotes from

Level 3 course!!!

CRC Value 1 0 1 1 0 1 0 0 1 1 1 0 0 1 0 1 0 0 0 0⊕ 1 1 0 0 1 0|0 1 0 1 1 ⊕ 0 0 0 0 0 0|1 0 1 1 0 ⊕ 1 1 0 0 1 0|1 1 1 1 1 ⊕ 1 1 0 0 1 0|0 1 1 0 0 ⊕ 0 0 0 0 0 0|1 1 0 0 0 ⊕ 1 1 0 0 1 0|0 0 0 1 0

⊕ 0 0 0 0 0 0|0 0 1 0 0 ⊕ 0 0 0 0 0 0| 0 1 0 0

11001 )

CRC value = RemainderYou do not need to

reproduce this!

CRC Value after an Error 1 0 1 1 0 1 1 1 1 1 1 0 0 1 1 1 0 0 0 0⊕ 1 1 0 0 1 0|0 1 0 1 1 ⊕ 0 0 0 0 0 0|1 0 1 1 1 ⊕ 1 1 0 0 1 0|1 1 1 0 1 ⊕ 1 1 0 0 1 0|0 1 0 0 0 ⊕ 0 0 0 0 0 0|1 0 0 0 0 ⊕ 1 1 0 0 1 0|1 0 0 1 0

⊕ 1 1 0 0 1 0|1 0 1 1 0 ⊕ 1 1 0 0 1 0| 1 1 1 1

11001 )

CRC value = Remainder

Received CRCreplace by 0's

Bit error in frame

0 1 0 0

Received CRC≠

Calculated CRC⇒ ERROR !!!!!

You do not need to

reproduce this!

Hardware Example: CRC-32Sum = x32 + x26 + x23 + x22

+ x16 + x12 + x11 + x10

+ x8 + x7 + x5 + x4 + x2 + x + 1

+ +++ + +

+ + + +

+ + +

+Data In

32 1-bit shift register elements


Discard

ErrorCRC OK?

Length ≥ 64 BLength ≤ 1518 BIntegral No Bytes

Receive Frame

sizeOK?


Error

OK

CRC received= CRC calculated?

Ethernet ReceiverReceive Frame

no

yes

Startof frame

?

Wait for DPLL lock

Carrier Detect

addrmatch

Forward

OKno

yes

Address matchesLocal addressBroadcast addressMulticast address

Transceiver Interface

EthernetController

Attachment UnitInterface (AUI)

Rx CSTxJabber

Control

Medium Attachment Unit (MAU)

or Transceiver

Media Interface

MAUControl

* Jabber is transmission of a frame longer than the maximum allowed.

AUI drop cable(0 -50m)

5 shielded pairsPower &Ground

MAC FunctionsGain access to medium by listening for activity (e.g. CSMA/CD)

Co-ordinate sharing of the medium between users

Address single and groups of stations (i) Static address of each computer (copied from PROM) (ii) 1 or more dynamic group addresses (e.g. multicast) (iii) Broadcast address to send to every computer

Diagnose failures (i) transmission errors (detected by CRC-32) (i) protocol errors (e.g. jabber (too long) , runt (too short)) (ii) cabling (e.g. loss of carrier, reflection from a cable break)

Questions?

(i) What is the Ethernet destination address used for?(ii) Why is the first bit never set in an Ethernet source address?

There are two types of anti-social Ethernet frame: Jabber and Runts

(i) What are the minimum and maximum Ethernet frame sizes?(ii) Why does Jabber impact performance?(iii) Why do Runts impact reliability?

Connecting LAN Segments

LAN A

LAN B

ConnectingDevice

Ethernet framesreceived here

... are retransmitted here

Repeater

Physical Physical

Identical physical interfaces

Similar or different media (cabling)

Isolation of cabling faults (partitioning)

Repeater

Repeaters

Uses:Extends media length and number of NICsAllows conversion between media typesAllows for more flexible cable routing

Function:Connect segments and regenerate signal

N.B. All interfaces must operate at same speed!

Part 1 Regeneration of Clock and Data

Repeater regenerate signal to all output ports

Receive “poor” signal

Lock to clock (using DPLL)

Decode bits using Manchester Decoder

Reconstruct 0’s and 1’s of frame

MUST also regenerate full preamble

Re-encode bits using Manchester Encoder

Send “good” signal

Clock Regeneration Minimum Frame Size - LAN slot-time

Sender

Minimum Frame size needed

Signal must reach all nodes before sender finishes

Ethernet defines a minimum payload of 46B

(64B including MAC header and CRC)

Regeneration to all parts of the LAN

Repeaters

Ethernet LANs

Sender

Sender

Assume one NIC sends

Reaching 2-3 km (5.1 km using fibre)

10B5 ”thick” cable segments may be joined to 500m

AUI cable up to 50m at each transceiver

“Repeaters” needed to get further

3 Copper segments (“ACTIVE”) end-to-end

1 fibre segment (“INACTIVE”) 1km

Total = 0.5 x 3+1+.05 x8 = 2.9 km !!!

Part 2 : Repeaters must participate in CSMA/CD

Connecting LAN Segments

LAN A

LAN B

ConnectingDevice

Repeaters

Ethernet LANs

Sender Sender

Assume both senders transmit at same time

Participation in CSMA/CD

All need to see each other signals

Repeater Network (1)1.

Sender Sender

Jam Jam2.

Repeater Network (2)3.

1 collision domain

4.

Back-Off Back-Off

CSMA/CD determines maximum number of repeaters

• Repeaters need to:

• Detect Collisions

• “regenerate” collisions on all output ports

• This takes time...

• Limits maximum number of repeaters in series

5-4-3 Repeater RuleMost LANs assign one segmentas a "backbone" LAN interconnection device

Inactivesegments

Not more than 5 segments in seriesNot more than 4 repeatersNot more than 3 active segments

Repeater Network

a

b

c

d

e

f

a

b

c

d

e

f

a

b

c

d

e

f

a

b

c

d

f

a

b

c

d

e

e

f

g

1 3

2 4

5


Repeater Networka

b

c

d

e

f

a

b

c

d

e

f

a

b

c

d

e

f

a

b

c

d

f

a

b

c

d

e

e

f

g

1 3

2 4

5


Repeater Network

a

b

c

d

e

f

a

b

c

d

e

f

a

b

c

d

e

f

a

b

c

d

f

a

b

c

d

e

e

f

g

1 3

2 4

5


Repeater Network

a

b

c

d

e

f

a

b

c

d

e

f

a

b

c

d

e

f

a

b

c

d

f

a

b

c

d

e

e

f

g

1 3

2 4

5


Repeater Network

a

b

c

d

e

f

a

b

c

d

e

f

a

b

c

d

e

f

a

b

c

d

f

a

b

c

d

e

e

f

g

1 3

2 4

5


Unshielded Twisted Pair Cabling

EthernetCabling

10B5 (Thick Ethernet)

10B2 (Thin Ethernet)

10BT (Unshielded Twisted Pair)

10BF (Fibre Optic Pair)

Reaching 2-3 km (5.1 km using fibre)

10B5 ”thick” cable segments may be joined to 500m

AUI cable up to 50m at each transceiver

“Repeaters” needed to get further

3 Copper segments (“ACTIVE”) end-to-end

1 fibre segment (“INACTIVE”) 1km

Total = 0.5 x 3+1+.05 x8 = 2.9 km !!!

10BT or UTP (Unshielded Twisted Pair)

Segment length 0.6m – 100mCable flexible and very cheapRJ-45 connector usedEasy to manage / install

Integrated or external transceiver

10BT or UTP (Connectors)8-pin RJ-45 Connector

Unshielded Twisted Pair cable to hub(2 Pairs)

10BT Port

AlternativeAUI Port

Cable has 4 twisted pairs2 are used in 10 BT:

Pins 1,2 (white+orange/orange)and

Pins 3,6 (white+green/green)

Ethernet 10BT Cabling

Wiring cabinet

Wiring centre & 10BT Hub

2 or more UTP pairs to each room

10BT Equipment 10 BT just two pairs

One pair for transmissionOne pair for reception

Basic CSMA/CD algorithm means use one direction at a time

Differential Transmission

Uses 2 wires TWISTED to form a PAIR

0 Signal sent +ve on one wire, -ve on other

1 Signal sent -ve on one wire, +ve on other

100 Ohm terminationEIA/TIA TS 568 wiring

28/08/2011 08:17TIA/EIA-568 - Wikipedia, the free encyclopedia

Page 3 of 5http://en.wikipedia.org/wiki/TIA/EIA-568-B

pin/pair assignments for eight-conductor 100-ohm balanced twisted-pair cabling, such as Category 3,Category 5 and Category 6 unshielded twisted-pair (UTP) cables. These assignments are named T568A andT568B and they define the pinout, or order of connections, for wires in 8P8C (often incorrectly referred toas RJ45) eight-pin modular connector plugs and sockets. Although these definitions consume only one ofthe 468 pages in the standards documents, a disproportionate amount of attention is paid to them. This isbecause cables that are terminated with differing standards on each end will not function normally.

TIA/EIA-568-B specifies that horizontal cables should be terminated using the T568A pin/pairassignments, "or, optionally, per [T568B] if necessary to accommodate certain 8-pin cabling systems."Despite this instruction, many organizations continue to implement T568B for various reasons, chieflyassociated with tradition (T568B is equivalent to AT&T 258A). The United States NationalCommunication Systems Federal Telecommunications Recommendations do not recognize T568B.

The primary color of pair one is blue, pair two is orange, pair three is green and pair four is brown. Eachpair consists of one conductor of solid color, and a second conductor which is white with a stripe of thesame color. The specific assignments of pairs to connector pins varies between the T568A and T568Bstandards.

Wiring

See modular connector for numbering of the pins

Pin T568APair

T568BPair Wire T568A Color T568B Color Pins on plug face (socket is

reversed)

1 3 2 tip white/greenstripe

white/orangestripe

2 3 2 ring green solid orange solid

3 2 3 tip white/orangestripe

white/greenstripe

4 1 1 ring blue solid blue solid

5 1 1 tip white/bluestripe

white/bluestripe

6 2 3 ring orange solid green solid

7 4 4 tip white/brownstripe

white/brownstripe

8 4 4 ring brown solid brown solid






Wiring


Pin T568APair


reversed)


white/orangestripe



white/greenstripe



white/bluestripe



white/brownstripe







Wiring


Pin T568APair


reversed)


white/orangestripe



white/greenstripe



white/bluestripe



white/brownstripe







Wiring


Pin T568APair


reversed)


white/orangestripe



white/greenstripe



white/bluestripe



white/brownstripe







Wiring


Pin T568APair


reversed)


white/orangestripe



white/greenstripe



white/bluestripe



white/brownstripe







Wiring


Pin T568APair


reversed)


white/orangestripe



white/greenstripe



white/bluestripe



white/brownstripe







Wiring


Pin T568APair


reversed)


white/orangestripe



white/greenstripe



white/bluestripe



white/brownstripe







Wiring


Pin T568APair


reversed)


white/orangestripe



white/greenstripe



white/bluestripe



white/brownstripe







Wiring


Pin T568APair


reversed)


white/orangestripe



white/greenstripe



white/bluestripe



white/brownstripe







Wiring


Pin T568APair


reversed)


white/orangestripe



white/greenstripe



white/bluestripe



white/brownstripe







Wiring


Pin T568APair


reversed)


white/orangestripe



white/greenstripe



white/bluestripe



white/brownstripe







Wiring


Pin T568APair


reversed)


white/orangestripe



white/greenstripe



white/bluestripe



white/brownstripe







Wiring


Pin T568APair


reversed)


white/orangestripe



white/greenstripe



white/bluestripe



white/brownstripe







Wiring


Pin T568APair


reversed)


white/orangestripe



white/greenstripe



white/bluestripe



white/brownstripe







Wiring


Pin T568APair


reversed)


white/orangestripe



white/greenstripe



white/bluestripe



white/brownstripe







Wiring


Pin T568APair


reversed)


white/orangestripe



white/greenstripe



white/bluestripe



white/brownstripe


Pin T568APair

T568BPair Signal T568A Colour

OLDT568B/C Colour

NEW

1 3 2 + white/green white/orange

2 3 2 - green orange

3 2 3 + white/orange white/green

4 1 1 - blue blue

5 1 1 + white/blue white/blue

6 2 3 - orange green

7 4 4 + white/brown white/brown

8 4 4 - brown brown

10BT Hub

Power Supply AUI port 10B2 Port 8 10BT Ports using RJ-45 Connectors

Indicator lights for each segmentVLSI repeater20 MHz Crystal

Bridges & Switches

LAN 1 LAN 2

Control

When Do We Need A Bridge?Bridges

Bridges are needed to:Connect > 1024 nodesExtend total network diameterConnect more than 5 segments in series

Bridges also:Increase maximum capacity of networkDeny unauthorised use of the network

Bridge

Physical Physical

Data Link

Similar or different subnetworks

Address Table Filter Table

Different subnetwork hardware addresses

Address Table

Use of the Ethernet Destination Address

destination address



NIC inserts a destination address in each frameSwitches can now “see” where to send the frame

- i.e. using the “topology” information in the address table

- switches do this for each frame

Address Table

Bridge 1

Address Table

00:EF:15:13:03:41

One entry for each MAC Address, indicating port used

MAC Address Static Port

00:11:00:02:03:04 Yes I

00:EF:15:13:03:41 Yes II

00:11:00:02:03:04 1

1I

Frames sent to “correct” port

Filter

Switch

Filter

Filter

Filter

Each port is a seperate LAN

Ports

Frames are forwarded based on MAC destination address

Forwarding (I)

Unicast frames sent only if destination is on another port

(reads frame destination address & uses address table)

Sent only to specific port

Unknown destinations flooded

(reads frame destination address, but not in address table)

Sent to all ports except the receiving port

Broadcast “flooded”

Multicast also “flooded” (unless configured group addresses)

Is frame destination address in table?NO - forward to all ports EXCEPT incoming port (flood)YES - Look-up address and find table port

Is table port == incoming port?NO - forward only to table portYES - discard the frame


00:11:00:02:03:04 Yes I

00:EF:15:13:03:41 Yes II

Forwarding (II)

Flooding addresses not in Address Table

Filter

Switch

Filter

Filter

Filter


Ports

Frames are flooded if not found in the address table“Flooding” sends to all ports except the received port(Almost the same as a “repeater/hub”!)

Example Network

Bridges

Ethernet LANs

Sender

Sender and Receiver on the same LAN segment

Receiver

Example Network

Sender Sender

Assume both senders transmit at same time

Bridges

Ethernet LANs

red sends to greengreen sends to red

Bridged Network (1)

Sender Sender

Buffered

Bridged Network (2)

No frames sent here

Separate collision domains

How many bytes need to be read?

destination address



The first 6 bytes identify the destination!However, it is important to read at least first 64B

- collisions, etc result in frames less than 64B- “runt” frames MUST NOT be forwarded

Cut-Through Forwarding

Simple bridges receive a frame in full before forwardingThis lets the bridge check the frame is valid

Frame Header contains all addressesCould start to forward as soon as 64 bytes are receivedThis eliminates some of the delay in storing data1.2 ms lower transit delay!

DisadvantagesCould start to forward an oversize frame :-(Could start to forward a frame with a bad CRC :-(These frames are forwarded by CRC invalidated.

•Known as “cut-through”

Enterprise Stage 1

ServerHub /Repeater

Server

Server

Each workgroup has own server

All connected via backboneto form one network(10B5 or 10BF with repeaters)

Repeaters / Hubs isolate faults

Hub /Repeater

Hub /Repeater

Enterprise Stage 2

Stage 2

Server Bridge

Server Bridge

Server Bridge

Each workgroup has own server

Most traffic only local

LANs connected via backbone(typically 10B5 or 10BF)

Summary of Bridge ForwardingNIC operates in promiscuous mode

(receives all frames ignoring destination address)

Bridge checks frame Check length and CRCStores in internal memoryCut-Through can forward before receiving CRC !

Examine address table for destination addressForward if matches different port to output portDiscard if matches same port as output portOtherwise, flood to all ports (except input)

Examine filter table for an address matchDiscard if matches filter tableMay also send “traps” to alert network manager

Bridges are “smart”

Part II - Dynamic Learning of Addresses

Dynamic learning

LAN 1 LAN 2

Control

Static Entries in tables

Static Tables are fine....Can also fix the MAC address to a specific port (useful in “public areas” to prevent hacking)

BUT!Someone needs to keep address tables correctAddress Table usually generated automaticallyMakes bridges “Plug & Play

Difficult to track 100’s, 1000’s of addressesAn automated method is required...

Use of the Ethernet Source Address

destination address



NIC inserts its own address in each frame!Switches can now “see” where a source is

- i.e. dynamically assign port & MAC in address table

- actually switches do this for every frame

“Learning” entries in the Address Table

Bridge 1

Address Table

00:EF:15:13:03:41

Entries made for each new (unicast) MAC Address


00:11:00:02:03:04 Yes I

00:EF:15:13:03:41 Yes II

00:11:00:02:03:04 1

1I

00:01:00:02:03:FF

00:01:00:02:03:FF No I

00:02:00:02:03:FE

00:02:00:02:03:FE No II

Dynamic Learning of Addresses in the Table

Age updated as frames arrive from a src addressEach second, all ages reduceZero entries are deleted

MAC Address Static Port Expires00:11:00:02:03:04 Yes I never

00:EF:15:13:03:41 Yes II never

00:01:00:02:03:FF No I 2 secs

00:02:00:02:03:FE No II 3 mins

Each entry is ”aged”old entries are deleted.

Denial Attack on the Address Table

Address Table

Bridge 1

A denial-of-service attack could be made against a MAC address

Suppose a malicious computer sends packets with another computer’s source address (there are programs that do this)

Updates address table (preventing destination receiving traffic)

Denial attack on Address Table

Filter

Switch

Filter

Filter

Filter


Ports

DestinationMAC 00:48:64:01:0C:FE

Attacker sends with srcMAC 00:48:64:01:0C:FE

Destination portAttack updates Address Table, stealing traffic from intended destination Attacker must keep doing this, (the real destination will also update the table next time it sends)Managed switches can detect this attack

Idiot-proof plug&play?

Bridge 1

Connecting two networks needs a bridge

First deployed bridge did not work :-(

You need to connect a port to each network :-)

Forwarding loops - Unicast

Bridge 1 Bridge 2

Connecting two bridges in parallel may cause duplication ofunicast frames

Can cause incorrect learning of source address - and black-holing of frames.

Bridges MUST NOT forward in loops!

Forwarding loops - Broadcast

Bridge 1 Bridge 2

Connecting two bridges in parallel may cause looping ofbroadcast (or flooded) frames

Bridges MUST NOT forward in loops!

The Spanning Tree Algorithm (STA) provides an automatic way to ensure this (not in current course!).

Exponential proliferation of frames in the LAN

Loops between bridges/switches?

Bridges 1,2,3 receive the frame

A sends to C

Bridge 2Bridge 1 Bridge 3

End System A

End System C

Bridges 1 forwards the frame, Bridges 2,3 receive the frame

There are now three frames that have been forwarded

Bridges 2,3 also forward a copy of the frame

The Spanning Tree Algorithm

Bridge 1 Bridge 2

Connecting two bridges in parallel may cause looping

Therefore need Spanning Tree Algorithm (STA)

Each bridge is either: Blocked, Learning or ForwardingThere is only one active forwarding path to each LAN

One bridge (the root) co-ordinates the other bridges - Bridge with the lowest MAC becomes the Root

X

The Spanning Tree Algorithm

Bridge 1 Bridge 2

Connecting two bridges in parallel may cause looping

Therefore need Spanning Tree Algorithm (STA)

Each bridge is either: Blocked, Learning or ForwardingThere is only one active forwarding path to each LAN

One bridge (the root) co-ordinates the other bridges - Bridge with the lowest MAC becomes the Root

X

33

93

4

117

10

14

2 5

6

2,0,2

2,0,2

2,1,142,1,5

2,1,7

2,1,6

2,2,4

2,2,4

2,3,3

2,2,11

A

X

34

Bother with spanning tree?

• Maybe just tell customers “don’t do loops”• First bridge sold...

ST Bridges form a least-cost tree that links all segmentsFrames not necessarily forwarded along an optimal pathX->A is rather longer than necessary

(Note: IP Routers do more optimal forwarding)

The Spanning Tree

Thinking about the Address Table

An end system that only listens (never sends) - Frames are broadcast to all ports - Could configure a static entry

An end system is turned off- Address entry will age and be deleted

An end system moves to another collision domain- Bridge will have learned the wrong port- End system will not receive unicast frames- Entry updated when end system sends

Things to think about:

Summary of Bridge Learning

Bridges Learns form Source Address of Frames Need to send to “create” entry in the Address TableAddress associated with a port

Address aged (old entries deleted)Unknown destination addresses flooded

Simple Plug and PlayMust not form loops!

Examine filter table for an address matchDiscard if matches filter tableMay also send “traps” to alert network managerCan also send the “frame contents!”

Bridges are “smart”

Address Table (II)

Address Table

Bridge 1

Two types of table entry: Static addresses to forward (set by administrator) Learned address to forward (dynamic entries)

Table COULD be implemented as an array- may be a software “Tree” structure- usually a Contents-Addressable Memory (CAM)

A CAM will be needed for high-speed switches!

Physical Physical

Data Link

Similar or different subnetworks

Address Table Filter Table

Different subnetwork hardware addresses

Address Table

Bridges also check filter table BEFORE forwardingDiscard if matches filter tableMay also send “traps” to alert network manager

Bridge/Switch Filter TableGood to set policies Prevent frames from being forwarded to specific portsLog/track users as they use the network

Part III - Hardware support for Addresses

Contents Addressable Memory (CAM)

LAN 1 LAN 2

Control

Bridges & SwitchesAddress Table

Bridges

Ethernet Collision Domains

II

IAddress Table

MAC address Static Port

00:5E:45:23:12:01:03 YES I00:EF:15:13:03:41:55 YES II

00:5E:45:23:12:01

00:EF:15:13:03:41

How do you stored the address table?

Using a linear list it takes (n) attempts at max to find a match, or (n/2) on average

A binary tree can decrease search toLOG2(n).

Using a CAM for the Address Table

Address Lookup can be time consuming in software- even with one network processor/state machine per port!- This problem is faced by each generation of equipment, as

speed of network increases it is still a challenge

Ordering the Address Table as a tree or sorted list helps (a bit)

This really needs hardware support if we have lots of addresses- for a “home”/“office” switch could manage without- for a campus/enterprise network need 10,000+ addresses!

Content Addressable Memory (CAM)CAM are much more expensive than static RAM~twice as complex as SRAM (2x area on chip)

Simplified CAM Design714 IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 41, NO. 3, MARCH 2006

Fig. 4. Simple schematic of a model CAM with 4 words having 3 bitseach. The schematic shows individual core cells, differential searchlines, andmatchline sense amplifiers (MLSAs).

miss condition. Finally, the encoder maps the matchline of thematching location to its encoded address.

We organize the remainder of this paper by expanding uponthe structure of the model in Fig. 4. In the next section, Sec-tion II, we begin our survey by looking at the two commonCAM cells, the NOR cell and the NAND cell, each of which canbe used as the basic building block in Fig. 4. The section con-tinues by examining the combination of CAM cells to constructa full matchline. Section III describes techniques for detectingwhether a matchline has a match or a miss. This section alsodiscusses matchline power consumption, and compares the re-viewed techniques in terms of the power savings they provide.In Section IV, we turn our attention to the searchlines, and ex-amine proposals that save searchline power. Section V reviewsthree architectural techniques that save power. Finally, in Sec-tion VII, we explore future directions for CAM research.

II. CORE CELLS AND MATCHLINE STRUCTURE

A CAM cell serves two basic functions: bit storage (as inRAM) and bit comparison (unique to CAM). Fig. 5 shows aNOR-type CAM cell [Fig. 5(a)] and the NAND-type CAM cell[Fig. 5(b)]. The bit storage in both cases is an SRAM cell wherecross-coupled inverters implement the bit-storage nodes D and

. To simplify the schematic, we omit the nMOS access tran-sistors and bitlines which are used to read and write the SRAMstorage bit. Although some CAM cell implementations use lowerarea DRAM cells [27], [30], typically, CAM cells use SRAMstorage. The bit comparison, which is logically equivalent toan XOR of the stored bit and the search bit is implemented in asomewhat different fashion in the NOR and the NAND cells.

A. NOR Cell

The NOR cell implements the comparison between the com-plementary stored bit, D (and ), and the complementary searchdata on the complementary searchline, SL (and ), using fourcomparison transistors, through , which are all typicallyminimum-size to maintain high cell density. These transistorsimplement the pulldown path of a dynamic XNOR logic gate withinputs SL and D. Each pair of transistors, and ,forms a pulldown path from the matchline, ML, such that a mis-match of SL and D activates least one of the pulldown paths,

Fig. 5. CAM core cells for (a) 10-T NOR-type CAM and (b) 9-T NAND-typeCAM [26]. The cells are shown using SRAM-based data-storage cells. Forsimplicity, the figure omits the usual SRAM access transistors and associatedbitlines. The SRAM storage and access transistors account for six of the celltransistors.

connecting ML to ground. A match of SL and D disables bothpulldown paths, disconnecting ML from ground. The NOR na-ture of this cell becomes clear when multiple cells are connectedin parallel to form a CAM word by shorting the ML of each cellto the ML of adjacent cells. The pulldown paths connect in par-allel resembling the pulldown path of a CMOS NOR logic gate.There is a match condition on a given ML only if every indi-vidual cell in the word has a match.

B. NAND Cell

The NAND cell implements the comparison between the storedbit, D, and corresponding search data on the correspondingsearchlines, (SL, ), using the three comparison transistors

, , and , which are all typically minimum-size tomaintain high cell density. We illustrate the bit-comparisonoperation of a NAND cell through an example. Consider thecase of a match when and . Pass transistoris ON and passes the logic “1” on the SL to node B. Node Bis the bit-match node which is logic “1” if there is a match inthe cell. The logic “1” on node B turns ON transistor . Notethat is also turned ON in the other match case whenand . In this case, the transistor passes a logichigh to raise node B. The remaining cases, where ,result in a miss condition, and accordingly node B is logic“0” and the transistor is OFF. Node B is a pass-transistorimplementation of the XNOR function . The NAND natureof this cell becomes clear when multiple NAND cells are seriallyconnected. In this case, the and nodes are joinedto form a word. A serial nMOS chain of all the transistorsresembles the pulldown path of a CMOS NAND logic gate. Amatch condition for the entire word occurs only if every cell ina word is in the match condition.

An important property of the NOR cell is that it provides a fullrail voltage at the gates of all comparison transistors. On theother hand, a deficiency of the NAND cell is that it provides onlya reduced logic “1” voltage at node B, which can reach only

when the searchlines are driven to (whereis the supply voltage and is the nMOS threshold voltage).

C. Cell Variants

Fig. 6 shows a variant of the NOR cell [Fig. 6(a)] and a variantof the NAND cell [Fig. 6(b)]. The NOR cell variant uses only9-transistors compared to the previous 10-T NOR cell. The bitcomparison uses pass transistors (as in the previous 9-T NAND

CAM are much more expensive than static RAM~twice as complex as SRAM (2x area on chip)

Basic CAM consists of cells, and sense amps to detect a match

Using a CAM for the Address Table

1000100 etc 0

1000110 etc 1

1010110 etc 1

MACAddress

Port

Each cell stores one value together with an index

To Read the CAM you apply a “value” not an address- Switches use this to search for a MAC address - CAM returns the “index” associated with the value (or “none”)

Each read/write access performed in one cycle (e.g 50 ns)

1000110 etc Matches 1

search Input match output

Storing Addresses in the CAM

1 A D B9 C

1725 F33 E41 G

...… I

48b MACAddress

Any cell can be used to store the valueSo, which cell does the CAM choose?

17b hash

CAM cells

+15b Other data(VLAN, etc)

Writing to a CAM is like writing to a static RAM- Write a value in a cell together with an index.

Choosing the cell to store the address

MACAddress Cell

position

A

Addresses are stored in cells

Cell position chosen by hashing the address to a smaller value(a hash is rather like a CRC)

1000110 etc+ Other Information(e.g. VLAN) HASH

If cell at the hash value is already used, use next cell


1 A D B9 C

1725 F33 E41 G

...… I

48b MACAddress

Which cell do you use?Many systems use a “hash” of the value to determine cell address(CISCO uses a 63b hash resulting a 17b value) A=1; B=4; C=10; D=3; E=33; F=26; G=41

17b hash

CAM cells


2 3 4

Removing entries from the Address Table

1000100 etc 0

1000110 etc 1

1010110 etc 1

MACAddress

Each cell associated with a timestampTimestamp updated when cell matched Values not recently used are deleted from the CAM

This can be done in hardwareCan automatically handle purging of old addressesWhole process may be performed in one cycle (e.g 50 ns)

search Input

Overflow Attack on the Address Table

Address Table

Bridge 1

A flooding denial-of-service attack could be made against the table

Suppose a malicious computer sends frames with lots of source addresses (there are programs that override the source address)

- Table could overflow

Later traffic is flooded to all ports

The hash used to store in the CAM increases the vulnerability- requires only small number of carefully chosen addresses


1 A D B9 C

1725 F33 E41 G H J K L M N O

...… I

48b MACAddress

What if values hash to same cell?H=41;J=41; K=41 etc … P=41If cell at the hash value is already used, use next cell

If next 8 cells are all full, then flood the frame

PFlooded!

17b hash

CAM cells


2 3 4

Practical CAM Design

CAM design (often implemented inside an ASIC)

Ternary CAM (TCAM)

A TCAM can match more than one set of non-contiguous bits

i.e. matches 0,1 and don’t care (X)

100XX matches 10000, 10010 etc

More than one cell can match the input (unlike CAM)

Often uses a priority encoder to determine a single output

Mid-high-range switches and routers use TCAMs to implement:

Access Control Lists (filter tables)

QoS classification

IP forwarding (in routers)

sh mac add Mac Address Table---------å---------------------------------

Vlan Mac Address Type Ports---- ----------- -------- ----- All 0016.4718.e680 STATIC CPU All 0100.0ccc.cccc STATIC CPU All 0100.0ccc.cccd STATIC CPU All 0100.0cdd.dddd STATIC CPU 1 0002.b302.72b9 DYNAMIC Gi0/1 1 0003.ba9a.8c9b DYNAMIC Gi0/1 1 0004.23b5.9b36 DYNAMIC Gi0/1 1 0004.76dd.bb0a DYNAMIC Gi0/1 1 0007.e9bd.5d1f DYNAMIC Gi0/1 1 0008.a334.7018 DYNAMIC Fa0/24 1 000e.0cea.1ff8 DYNAMIC Gi0/1 1 0010.6026.1436 DYNAMIC Gi0/1 1 0011.43e1.9fdf DYNAMIC Gi0/1 1 0013.80b1.e216 DYNAMIC Gi0/1

Bridge/Switch Question

W X Y Z

R BA B C

Four computers (W,X,Y,Z) are connected by 3 Ethernet segments (A,B,C) using a Repeater (R) and a Bridge (B).

(a) Which computers receive (at the network level) the followingframes (show also which LAN segments carry each frame)

W -> BroadcastX -> ZY -> ZY -> Broadcast

(b) W, X are members of the multicast group 0x23. W = 0x00102030 and X = 0x00102040. Sketch the MAC header for a multicast frame sent from X.Which segments carry this frame?

Thinking about the Address Table

An end system that only listens (never sends) - Frames are broadcast to all ports - Could configure a static entry

An end system is turned off- Address entry will age and be deleted

An end system moves to another collision domain- Bridge will have learned the wrong port- End system will not receive unicast frames- Entry updated when end system sends

Things to think about:Fast Ethernet

100 Mbps

Collision Domains

Broadcast Domains

Faster Transmission Speeds

Full Duplex [& Half Duplex]

100B-FX

Fast (100 Mbps) Ethernet

Two Media:

100 Mbps Copper (UTP)

100 Mbps Fibre

Two Modes:

Half Duplex (CSMA/CD) - Little used

Full Duplex (to switch ports)

•

System SystemUTP cable

System SystemFibre

Physical Layer for 10BT

Copper (Unshielded Twisted Pair)

Uses 2 of the 4 twisted pairs in in CAT5 UTP

Pins 1 & 2 for Transmit; Pins 3,6 for Receive

CAT 5 UTP has a bandwidth of 100 MHz

CAT 5e UTP has a bandwidth of 125 MHz

100Mbps Manchester Encoded waveform

Power

Frequency

20 MHz 200 MHz

Frequency response for Cat5 UTP

100 MHz UTP cable bandwidth

Manchester Encoding

~ 20 MHz bandwidth (Carrier 10 MHz)

~200 MHz bandwidth (Carrier 100 MHz)

Manc’ not work over CAT-5 UTP!

125 MHz

4b/5b Encoding

4b/5b

5 bits

4b/5b Encoding4 bits have 2^4 (16) values5 bits have 2^5 (32) values

Chooses an encoding rule that has:2 changes/4bit (ensures sufficient timing for DPLL)≤ a sequence of 3 bits changed in 5 bits

4 bits 4b/5b Encoding

Decimal Binary Encoded0 0000 111101 0001 010012 0010 101003 0011 101014 0100 010105 0101 010116 0110 011107 0111 011118 1000 100109 1001 10011A 1010 10110B 1011 10111C 1100 11010D 1101 11011E 1110 11100F 1111 11101

Signaling Codes

There are 16 unused encoded values

Some of these are used for signaling special events:

Quiet (00000) Idle (11111) Halt (00100)

Starting delimiters J (11000) K (10001)

Ending Delimiter T (01101)

Control Reset (00111) Set (11001)

The remaining should never be sent

Reception of these indicates an error

4b5b Encoded waveformEncode and send least significant 4b first

Encode and send most significant 4b

4b/5b output includes transitions needed for receiver DPLL

Stream contains start, end and other control signals

However, spectral bandwidth is > 100 MHz!

Power

Frequency

20 MHz 125 MHz

Frequency response for Cat5 UTP

MLT-3 Encoding

MLT-3 EncodingLevels -1, 0, +10 data sent as no change1 data sent as next value in a sequence:

(0) -> (1) -> (0) -> (-1) -> (0) ...

125 Mbps

MLT-3

31.2 MHz

NRZ 0 0 0 1 0 0 1 0 1 1 1 0 1 0MLT-3 0 0 0 + + + 0 0 - 0 + + 0 0

31.25Mps ~ 62.5 MHz bandwidth for 4b/5b+MLT-3 :-)

Example encoding

Clock

MLT-3signal

1 0 1 0 1Data 1

2ns/Division

MLT-3 Encoder

AMD

3Implementing FDDI Over Copper; The ANSI X3T9.5 Standard

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 241 2

1 1 1 0 0 1 1 1 0 1 0 0 1 0 1 0 0 1 1 1 1 01 1

Data to be Transmitted (After 4B/5B Encoding and Scrambling)

Line Bit Clock at the Baud Rate

NRZI Waveform

MLT-3 Waveform

18258A-3Figure 3. Waveforms of NRZI and MLT-3 Line Signals

18258A-4

10.0 dBm

0 dBm

-10 dBm

-20 dBm

-30 dBm

-40 dBm

-50 dBm

-60 dBm

-70 dBm10 25 40 55 70 85 100 115 130 145 160

Frequency – MHz

Figure 4. Typical MLT-3 Spectrum at the Transmitter Output

Adaptive EqualizationAdaptive equalization is necessary to compensate for thecable attenuation and phase distortion that is encoun-tered at various lengths of STP and UTP cable. STP ca-ble has a characteristic impedance of 150 Ω. 100 metersof this cable will attenuate a transmitted signal by 12 dB (afactor of 4) at 62.5 MHz. 100 meters of UTP-5 cable, suchas AT&T 1061 (ZO = 100 Ω), attenuates the signal by 18dB at 62.5 MHz. Should the channel be equalized for themaximum length of either cable, it would be over-equal-ized for the shorter and intermediate lengths. Over-equalization results in excessive signal jitter. Withadaptive equalization, the receiver frequency response isoptimized for any given segment of cable. In order toachieve this, the equalizer is constantly adjusted by afeedback loop.

TP-PMD CircuitThe copper solution described in this application note hasbeen based on three functional blocks: AMD’sSUPERNET® 2 PHY (Am79C864A PLC-S, Am79865PDT and Am79866A PDR), Micro Linear’s MLT-3 Trans-ceiver (ML6671) and Pulse Engineering’s Filter/MagneticModule (PE68502). An application circuit of the TP-PMDis shown in Figure 5. This is a UTP-5 implementation util-izing an RJ-45 connector at the media interface. A 13-pinconnection is shown at the PHY-PMD interface which ispin compatible with the footprint of the Sumitomo ODL. A9- or 22-pin footprint could also be used for compatibilitywith other common ODL configurations from AT&T,Siemens and HP.

AMD


3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 241 2

1 1 1 0 0 1 1 1 0 1 0 0 1 0 1 0 0 1 1 1 1 01 1



NRZI Waveform

MLT-3 Waveform


18258A-4

10.0 dBm

0 dBm

-10 dBm

-20 dBm

-30 dBm

-40 dBm

-50 dBm

-60 dBm

-70 dBm10 25 40 55 70 85 100 115 130 145 160

Frequency – MHz




AMD


3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 241 2

1 1 1 0 0 1 1 1 0 1 0 0 1 0 1 0 0 1 1 1 1 01 1



NRZI Waveform

MLT-3 Waveform


18258A-4

10.0 dBm

0 dBm

-10 dBm

-20 dBm

-30 dBm

-40 dBm

-50 dBm

-60 dBm

-70 dBm10 25 40 55 70 85 100 115 130 145 160

Frequency – MHz




MLT-3 Encoding

Eye Diagram

2ns/Division

<1 bit >

+1

0

-1

10Mb/s SPE PHY Technical Feasibility

• First we consider 10Base-T v 100Base-TX

• 10BT

• Separate TX/RX pairs (4 wire)

• Differential voltage, NRZ coding

• Manchester encoding to guarantee transitions

• Relatively simple design

• 100BTX – increasing complexity

• Separate TX/RX pairs (4 wire)

• MLT3 coded signaling, +1,0,-1V

• DSP and ADC/DAC’S

• 4B/5B encoding

• Point to point

• 10BT silicon area << 0.5x of 100BTX

NRZ

MLT3

How does MLT-3 Encoding compress the frequency?Fastest change results when sending 1,1,1,1 etc

Manchester

baud x 2

MLT-3

baud / 4

1 1 1 1 1Data2ns/Division

Max fundamental frequency = 100*5/4*1/4 = 31.25 MHz

MLT-3 Encoding

AMD


3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 241 2

1 1 1 0 0 1 1 1 0 1 0 0 1 0 1 0 0 1 1 1 1 01 1



NRZI Waveform

MLT-3 Waveform


18258A-4

10.0 dBm

0 dBm

-10 dBm

-20 dBm

-30 dBm

-40 dBm

-50 dBm

-60 dBm

-70 dBm10 25 40 55 70 85 100 115 130 145 160

Frequency – MHz




AMD


3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 241 2

1 1 1 0 0 1 1 1 0 1 0 0 1 0 1 0 0 1 1 1 1 01 1



NRZI Waveform

MLT-3 Waveform


18258A-4

10.0 dBm

0 dBm

-10 dBm

-20 dBm

-30 dBm

-40 dBm

-50 dBm

-60 dBm

-70 dBm10 25 40 55 70 85 100 115 130 145 160

Frequency – MHz




AMD


3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 241 2

1 1 1 0 0 1 1 1 0 1 0 0 1 0 1 0 0 1 1 1 1 01 1



NRZI Waveform

MLT-3 Waveform


18258A-4

10.0 dBm

0 dBm

-10 dBm

-20 dBm

-30 dBm

-40 dBm

-50 dBm

-60 dBm

-70 dBm10 25 40 55 70 85 100 115 130 145 160

Frequency – MHz




AMD


Transmit CircuitThe Am79865 PDT sends scrambled NRZI data to theCDL at PECL signal levels. The ML6671 converts theNRZI data to three level, MLT-3 code. In MLT-3 coding,ones are represented by transitions and zeros are repre-sented by a lack of transitions. The transitions are alwaysbetween two adjacent levels.

The transmit level is set to 2 V peak-to-peak by placing a2 KΩ resistor between pins 17 and 18 of the ML6671. Therise time between adjacent levels (10% to 90%) out of theML6671 is less than 1.0 ns. A low pass filter on thePE68502 increases the rise time to 3.0 ns, prior to launch-ing the signal onto the cable. A fast rise time maintains aclean eye pattern, but it also creates unnecessary over-shoot and EMI that can develop when the signal encoun-ters punch down blocks in the wiring closet and cableimbalances. The 3.0 ns rise time has been found empiri-cally to be the optimum value for the application. The Fil-ter/Magnetics module also provides AC Coupling,Ground Isolation and reduces radiated emissions by pro-viding Common Mode Filtering. In the transmit channel, itis recommended that the transformer center tap be ACcoupled to ground for added Common Mode Filtering.Figure 6 shows the MLT-3 eye pattern at the transmitteroutput into a 100 Ω resistive load. The output jitter of thetransmitter is typically less than 2.5 ns.

Receive CircuitThe receive section consists of a differential EqualizationAmplifier, Signal Detect Circuitry and an MLT-3 to NRZIDecoder. Again, the signal is AC coupled from the mediathrough a transformer in the PE68502 module. Two 50 Ωresistors from pins 1 and 3 of the PE68502 to CMREF (pin32 of the ML6671) are part of the cable termination andalso set a DC bias for the receive amplifier input. Pin 4 ofthe module should also be connected to CMREF. As withthe transmit channel, AC coupling the center tap (pin 4) ofthe Filter/Magnetics module to ground improves commonmode rejection of the channel and reduces noisesusceptibility.

It was found in early implementations of MLT-3 overUTP-5 that fixed equalization cannot be optimized for allcombinations of distances and cable performance.Adaptive equalization changes the receiver gain and fre-quency response as a function of the received signal. Thereceiver amplifier has a dynamic range of 20:1, from100 mVPP to 2.0 VPP. The equalizer boosts the high fre-quency content of the signal in order to compensate forcable filtering and/or distortion. Equalization is adaptiveand the receiver can compensate for lengths of UTP-5between 0 and 100 meters.

Figures 7 and 8 show the typical eye patterns of the NRZIsignal recovered by the receiver (at RD+/–) after 10 and100 meters of UTP-5, respectively. In both cases, the jit-ter is held below 3.0 ns. Figure 9 shows the jitter at thePHY/PMD interface plotted as a function of cable length.

50 mV/Div

2 ns/Div 18258A-6Figure 6. MLT-3 Eye Pattern of the Transmitter

150 mV/Div

2 ns/Div 18258A-7Figure 7. NRZI Eye Pattern Out of the Receiver,

10 Meters UTP-5 Cable

150 mV/Div

2 ns/Div 18258A-8Figure 8. NRZI Eye Pattern Out of the Receiver,

100 Meters UTP-5 Cable

Eye Diagram

2ns/Division

< 1 bit >

+1

0

-1

100BT Transmission

bit/clock encoding (4b5b)

scrambling

level encoding (MLT-3)

Fast Ethernet MLT transmission - Data patternsA problem occurs when same set of bytes are repeated over the cable

Results in a repetitive waveform with distinct frequency components (resulting in interference)

111111 = results in power concentrated at 31.25 MHz, 52.5 MHz, etc

10101 = results in power concentrated at 16.13 MHz, 31.25 MHz, etc

... clearly the spectrum is a function of the payload data!

Power

Frequency

MLT-3

63 MHz

Power

Frequency

11111 encodedIDEALMax Power

MLT transmission - Interference

A repetitive waveform causes distinct frequency components

The peaks exceed the permitted power density allowed for the cable

Causes interference to other cables and equipment!

The spectrum must not be a function of the payload data!

Power

Frequency

MLT-3

63 MHz

Power

Frequency

MLT-3

63 MHz

Effect of repetitionwithout scramblerIDEAL

Max Power

MLT transmission - Scrambler

Scrambling is needed to ensure a smooth spectral response

A scrambler changes the output of the 4b/5B encoder in some determibistic way, that may be restored at the receiver prior to decoding.

Data appears random to the MLT-3 encoded, and power is ideally spread rather than focussed at particular frequencies.

The data is restored at the received by inverting scrambling function.

Power

Frequency

MLT-3

63 MHz

Power

Frequency

MLT-3

63 MHz

Effect of repetitionwithout scrambler with scrambler

100BT Transmission

4 bits (1/2 byte) processed at a time

4b/5b

byte

4 bits encoded to 5 bits≤3 bits changed in 5 bits

MLT-3 encoded (3 signal levels)

ScrambledBits randomised to disperse energy

125 Mbps

Scrambler

125 Mbps

MLT-3

31.2 MHz

100BT Transmission Power Spectrum

AMD


3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 241 2

1 1 1 0 0 1 1 1 0 1 0 0 1 0 1 0 0 1 1 1 1 01 1



NRZI Waveform

MLT-3 Waveform


18258A-4

10.0 dBm

0 dBm

-10 dBm

-20 dBm

-30 dBm

-40 dBm

-50 dBm

-60 dBm

-70 dBm10 25 40 55 70 85 100 115 130 145 160

Frequency – MHz




Log power plot v frequency using scrambler

1/100th powerof 10 MHz signal

§

4 bits (1/2 byte) processed at a time

4b/5b

byte

4 bits encoded to 5 bits

NRZ encoded (2 signal levels)

125 Mbps

NRZ

125 MHz

Bandwidth of the fibre is not a limiting function

Broadcast Domain

Collision Domains

10 Hub

10 Printer

10/100 Switch

10/100Switch

10/100 Switch

10 ES

10/100 ES

10/100 ES

Collision Domain

10 Mbps100 Mbps

Auto-negotiation

10BT 10BTuse 10

100BT 100BTuse 100

10BT 100BTuse 10

Most 100BT NICs also include an embedded 10BT NIC Auto- negotiation allows systems to find the lowest inter-operable physical layer (including whether to use CSMA/CD)

Fast Ethernet

100 HUB

10 HUB

10/100 Switch

10/100 Switch

10 Half Duplex100 Half Duplex100 Full Duplex

Automotive Ethernet (BroadR-Reach®)erreicht bis zu 100 Mbit/s bidirektional:Dank der Ethernet-Technologie lässt sichdie Datenrate gegenüber dem CAN-Buswesentlich steigern, ohne dass sich diephysikalische Verkabelung grundsätzlichändern müsste. Über eine im Auto verlegtezweiadrige Leitung (UTP: UnshieldedTwisted Pair) können Daten mit bis zu100 Mbit/s bidirektional übertragenwerden. Das klassische abgeschirmteEthernet-Kabel erlaubt sogar bis zu1 Gbit/s, ist für den Einsatz im Fahrzeugaber zu schwer und zu teuer. Ethernetermöglicht eine grundsätzlich andereTopologie der Netze. Mithilfe von Switcheskönnen kaskadenartige Strukturen reali-siert werden. Somit wird der Weg vom Buszum Netzwerk im Fahrzeug geebnet.

Die heutigen Bandbreitenanforderungen im Fahrzeug, insbesondere im Infotainment- undFahrerassistenzumfeld, bringen die klassischen Fahrzeugbusse an die Grenze der Möglich-keiten. Ethernet könnte hier Abhilfe schaffen. IAV betrachtet Automotive Ethernet als einkommendes Vernetzungssystem in Fahrzeugen und baut gezielt Kompetenz auf. Ziel ist es,OEMs und Tier-1-Zulieferer beim Einsatz von Ethernet zu beraten, Spezifikationen für OEMszu erstellen und den Test sowie die Evaluierung im Fahrzeug zu begleiten.

Im „Testhaus Automotive Ethernet@IAV“ werden daher gezielt Steuergeräte via Ethernetvernetzt und die Ausbreitung der Signale und mögliche Störungen untersucht. Neben dem„Physical Layer“ steht auch der „Link Layer“ im Fokus und damit die Möglichkeit, mit AVB undTTE echtzeitfähig zu werden. Auf dem „Application Layer“ wird geprüft, ob die Infotainment-systeme in Premiumfahrzeugen sinnvoll mit Ethernet verknüpft werden können, da sie zumBeispiel hochperformante Datenkanäle für den WLAN-Hotspot oder mehrere paralleleAudio-Video-Streams im Fahrzeug zur Verfügung stellen müssen. Interessant ist die Eignungvon Automotive Ethernet auch für Fahrerassistenzsysteme, wobei Bilder und Videostreams von vier und mehr Kameras – einschließlich deren Stromversorgung (Power over Ethernet) –über dieses Netzwerk geleitet werden können.

Auch in der Vernetzungsarchitektur entstehen mit Ethernet als kaskadierbarem Netzwerkvöllig neue Möglichkeiten. Es geht um die optimale Topologie – also etwa um die Frage, wodie Gateways zum CAN-Bus und zu Flex Ray zu integrieren sind. Denn eines ist sicher: Selbstwenn Automotive Ethernet bald die Autos erobern sollte – die beiden anderen Bussystemewerden noch lange parallel dazu existieren.

Automotive Ethernet@IAVDer Fahrzeug-Bus gibt Gas

100Base-T1: Automotive Ethernet

100 MbpsPoint-to-Point: 15m reach4 inline connectors One electrical pair

3-level PAM Echo cancellation, DSP,PSD-shaping for automotive emissions

VLANs

VLAN Trunks

VLAN Tags

Enterprise Stage 3

Server Server

Switch

Switch

Switch

Server

Switch

Switches connect workgroups

Higher speed links connect to a switch

Servers connect to the switch

Enterprise Stage 4

Server Server

Switch

Switch

Server

Switch

Switch

Switches VLAN enabled

Separate virtual networks

Trunks connect switchesCould carry one VLAN (green trunk)Or many VLANs (red trunk)

Red trunk uses VLAN Tagging

VLANs

37

Chapter 5: Configuring the Switch through the Web UtilitySwitch Config

24-Port 10/100 + 2-Port Gigabit Switch with Webview and Power over Ethernet

Create VLAN

To create a VLAN, enter the VLAN ID and VLAN name, up to 32 characters long. Mark the Enable checkbox to activate the VLAN, and click Create VLAN.

To edit a VLAN, select a VLAN ID and click the Edit icon (which resembles a pen). Modify the VLAN name and status if required. Select the membership type by marking the appropriate radio button in the list of ports or lags. Click Submit.

Membership Type. Select VLAN membership for each interface by marking the appropriate radio button for a port or LAG:

• Tagged. Interface is a member of the VLAN. All packets transmitted by the port will be tagged, that is, carry a tag and therefore carry VLAN or CoS information.

• Untagged. Interface is a member of the VLAN. All packets transmitted by the port will be untagged, that is, not carry a tag and therefore not carry VLAN or CoS information. Note that an interface must be assigned to at least one group as an untagged port.

• None. Interface is not a member of the VLAN. Packets associated with this VLAN will not be transmitted by the interface.

Figure 5-16: Adding/Editing VLAN Screen!

Each port is in one of 3 modes:

None

VLAN cannot use this port

Tagged

All frames sent tagged

Untagged

Frames sent untagged

Tagged Ethernet Frames

Tagged Ethernet Frames

IEEE 802.1pQ Tag comprises:

Priority Field (3-bit)

CR

VLAN-ID

Gigabit Ethernet

1 Gigabit Ethernet

10 Gigabit Ethernet

Gigabit Ethernet Standardised by IEEE 802 Committee

Copper1 Gbps Fibre & UTP (100m CAT-5e)

1 Gbps Fibre - Distance 5km (short haul)70km (long haul)300 km (with optical repeaters)

Link layer allows sending bursts of frames with upto 8192 BBit time 0.001 µSSmall frames VERY inefficient64B frame => (64)/(512+12) = 12% efficiency

GBE Transmission

8 bits (1 byte) processed at a time

8b/10b

byte

8 bits encoded to 10 bits (constant disparity)Each value contains 5 ones or 5 zeros

Transmitted using the PHY (e.g. over Fibre)

Bit

ScrambledBits randomised to disperse energy

Scrambler PHY

Manchester signal

PAM5 signal

MLT3 signal

Line signal

0

+1

+2

-1

-2

Groups 2 bits & maps to PAM-5 signal (4 level + FEC)Uses all four pairs to reach 125 MHz limit of CAT-5e 4D mapping of data to levels is complex,designed to optimise immunity to noise across all pairs

1000BT PAM-5 Transmission

PAM-5

125 MHz

4 streams at ~250 M pulse/sec

2 streams at ~500 Mbps

Scrambler

PAM-5

125 MHz

Gigabit Ethernet Spectrum

MHz

CAT 5e Channel

Slot Time in GBE10 Mbps Traditional Ethernet

Bit time 0.1 µS Minimum frame size (512 bits), Slot time 9.6 µS

100 Mbps Fast EthernetBit time 0.01 µSKept the same minimum frame size (512 bits) slot-time 5.12 µS5-4-3 rule had to be abandoned (but Hubs seldom used)

1000 Mbps GBEBit time 0.001 µS (1 nS)IFG 12B (0.096 µS)

For 1500B payload, n=1526 (incl overhead) = 12.304 µS Small frames VERY inefficient64B frame => (64)/(512+12) = 12% efficiency

GBE allowed several frames to be sent as a burstBurst size up to 8192 bytes

10 Gbps over fibre

Single ModeMultimodeOM3 Multimode

Two sets of versionsLAN & WAN versions share a common “transceiver”Various fibre physical “sublayers” have been defined

64b/66b encoding (10GBASE-X uses 8b/10b)

Work in 2017 on 10km optical pays for 50, 200 and 400 Gbps

UTP Cable

Telephony/ADSL/10BT

FE

• Cat 6e10BASE-GT500 MHz

400 MHz

300 MHz

100 MHz

200 MHz

30 MHz

GBE

CAT-6a

CAT-6

CAT-5eCAT-5

CAT-4

Time

Cable Bandwidth 10 Gbps over copper

10G BASE-T

UTP over shorter distancesCAT6 cable <~ 55 m*Symbol rate 3,200 000 000 Symbols/secEach pair operating at 10 Gbps (128 DSQ coded with LDPC)**Screened CAT6a cable <100m

Available from 2014

* This shorter distance targets the needs of data centre applications, rather than home/enterprise applications.** Transceiver significantly more complex - approx 10M gates, 10W

Category 6/6a Cabling

Thicker wires that are much more tightly twistedCross-shaped former in centreBetter cable insulation

CAT-6250 MHz bandwidthMaximum length: 100m (Max 90m solid wire)10BASE-GT limits length to 55m

CAT-6a500 MHz bandwidthMaximum length 100m (Max 90m solid wire)10BASE-GT limits length to 100m

Results in a much thicker cable

Current cost x2 for CAT-5e

40 Gbps over copper

40G BASE-T

IEEE 802.3bq over CAT7a copper UTP (March 2013)4 Pairs up to 30 m*Each pair operating at 10 Gbps (128 DSQ coded with LDPC)Signal bandwidth 1600 MHz (SFTP) **

* Shorter distance targets data centre applications, rather than home/enterprise applications.** Current spec at Dec 2014, suggests a cable bandwidth of ~2 GHz, more than CAT 7a.

100 Gbps over Fibre

Ciena 5170

Ciena 5170

Ciena 5170

100G core 40 x 1G/10G access to Universities & Colleges

40 x 1G/10G access to Universities & Colleges

40 x 1G/10G access to Universities & Colleges

Evolution of the Ethernet Specification

10Mbps 100Mbps 1 Gbps 10 Gbps 40 Gbps 100 Gbps

CableFibreUTPCoax

FibreUTP

(CAT-5)

FibreUTP

(CAT5e)

FibreUTP

(CAT6)

FibreUTP

(CAT7)

Fibre

Encoding Manc (4b/5b) (8b/10b) (64b/66b) (64b/66b) (64b/66b)

Format 2 level 3 levels 5 level 16 levels 16 levels

Pairs 2 2 4 4 4 4

Bandwidth(MHz)

20 31 125 413 >1000

Mode HDXHDX/FDX FDX FDX FDX FDX

Hubs 4 (1 or 2 in std 0 0 0 0

Summary of GBENew Physical Layer technology

Bandwidth limit for CAT-5 UTPFast Ethernet : 4b/5b+MLT-3 (over CAT-5/CAT-5e/Fibre)GBE: 8b/10b+PAM-5 (over CAT-5 /CAT-5e/Fibre)10GBE: 64/66b (over CAT-6/Fibre/CX-4)1 GHz CAT-7 Screened cable

•

Ethernet continues to evolve

Switches & HubsPacket rate becomes major challengeNew rules for fast Ethernet Hubs, but rarely usedHubs rarely supported in FE and GB Ethernet

Next steps...40 Gbps... was standardised 2010 (over Fibre)First 100 Gbps Philadelphia, 2008.100 Gbps... variant of above (over Fibre)Many variants being designed/built1 Tb/s in research labs

Data Centres

Four computers (W,X,Y,Z) are connected by 3 Ethernet segments (A,B,C)

Simple DC designOne switch at the top of each rackConnecting switches together poses a problemstandard switches have one or two “uplink ports”

Priority-Based Flow Control FramesA lot of packets can arrive in a very short timeSend a pause frame upstream when input buffer fills to a threshold If next upstream switch congests, also send PAUSE on this upstream

IEEE 802.1Qbb

Advanced DC designGoogle Juniper Data Centre SwitchAll switches meshed together - effectively creates one 10,000 port switch

google jupiter DC switch

Performance

Two key performance measures:ThroughputUtilisation

Ethernet FramesTransmission

An 1000 byte frame takes 8000/(10 000 0000) at 10 Mbps= 800 µS

An 1000 byte frame takes 8000/(1000 000 0000) at 1 Gbps= 8 µS

Actually takes slightly longer because there must be anInterframe Gap between frames of 96 bit periods.

A 1000 B frame takes 809.6 µS at 10 Mbps

IFG IFG

Example 1 Calculate the maximum frame rate of a node on a 10 Mbps Ethernet LAN.

Frame Part Minimum Size Frame

Inter Frame Gap (9.6µs)

MAC Preamble (+ SFD)

MAC Destination Address

MAC Source Address

MAC Type (or Length)

Payload (Network PDU)

Check Sequence (CRC)

Total Frame Physical Size

Example 1

Calculate the maximum frame rate of a node on an Ethernet LAN.





MAC Source Address





Throughput

Defined as “the number of bits transferred per second from a given layer to the upper layer as a result of a conversation between two users of the layer”Considers only data forwarded (i.e. not overhead)Expressed in bits per second

Throughput

Defined as “the number of bits transferred per second from a given layer to the layer above as a result of a conversation between two users of the layer”Considers only data forwarded (i.e. not overhead)Expressed in bits per second

A source sends 1470 byte Ethernet frames at 10 frame/sec what is the throughput across the network?

Size of 1 frame = (1470-26)x8 bitsThroughput = 115.5 kbps

Calculation of Throughput

1) A source sends 1526 byte Ethernet frames at 50 frame/sec What is the throughput across the network?

2) An application sends 25 PDUs per second with a size of 100 bytes- what is the total network capacity consumed in bits per second?

3) Given that Ethernet also requires an Inter Frame Gap (IFG) of 9.6 µS before each frame, how long does it take at 10 Mbps to transmit a frame that carries 46 bytes of PDU?

Example 2Calculate maximum throughput of link service provided by 10 Mbps Ethernet

Frame Part Maximum Size Frame




MAC Source Address





Utilisation

Defined as “the total number of bits transferred at the physical layer to communicate a certain amount of data divided by the time taken to communicate the data.”

Unused capacity

Transmission rate (e.g. 10, 100, ... Mbps)

Utilised capacity

Includes all bits in all types of frame irrespective of whether they are corrupted or correctly received.

Expressed as a percentage of transmission rate.

Measures link capacity used

Example 3One node transmits 100 B frames at 10 frames per second, another transmits 1000 B frames at 2 frames per second, calculate the utilisation of a 10 Mbps Ethernet LAN.





MAC Source Address





Over to you....

• Spend one session reviewing material on web.

• Answers to examples are at:

• ./lan-pages/enet-calc.html

• Finally, do the revision questions....

• ./questions/intro/index.html

Secure configurationApply security patches and ensure the secure configuration of all systems is maintained. Create a system inventory and define a baseline build for all devices.

Managing user privilegesEstablish effective management processes and limit the number of privileged accounts. Limit user privileges and monitor user activity. Control access to activity and audit logs.

Network SecurityProtect your networks from attack. Defend the network perimeter, filter out unauthorised access and malicious content. Monitor and test security controls.

Incident managementEstablish an incident response and disaster recovery capability. Test your incident management plans. Provide specialist training. Report criminal incidents to law enforcement.

Set up your Risk Management Regime

Assess the risks to your organisation’s information and systems with the same vigour you would for legal,

regulatory, financial or operational risks. To achieve this, embed a Risk Management Regime across

your organisation, supported by the Board and senior managers.

User education and awarenessProduce user security policies covering acceptable and secure use of your systems. Include in staff training. Maintain awareness of cyber risks.

MonitoringEstablish a monitoring strategy and produce supporting policies. Continuously monitor all systems and networks. Analyse logs for unusual activity that could indicate an attack.

Malware preventionProduce relevant policies and establish anti-malware defences across your organisation.

Home and mobile workingDevelop a mobile working policy and train staff to adhere to it. Apply the secure baseline and build to all devices. Protect data both in transit and at rest.

Removable media controlsProduce a policy to control all access to removable media. Limit media types and use. Scan all media for malware before importing onto the corporate system.

10 Steps to Cyber Security

Defining and communicating your Board’s Information Risk Regime is central to your organisation’s overall cyber security strategy. The National Cyber Security Centre recommends you review this regime – together with the nine associated security areas described below, in order to protect your business against the majority of cyber attacks.

Produce supporting risk managem

ent policies

Mak

e cy

ber r

isk

a pr

iorit

y for y

our Board

Determine your risk appetite

www.ncsc.gov.uk @ncscFor more information go to

es/eg 4546 a local area network is simple low cost local ...es/eg 4546 the ethernet local area...

Documents