Cisco Presentation Guide

Ethernet 

Petr Grygárek Gryg rek 

© 2005 Petr Grygarek, Advanced Computer Networks Technologies 1

Ethernet History Histor 

•Research Research background: AlohaNet 

•University University of Hawai, 1970: 1970: 

common (radio) channel 

sharing methods – basis for CSMA/CD 

•1980: 1980: DIX published Ethernet standard 

(Metcalfe) 

•1985: 1985: IEEE 802.3 802.3 

(MAC and LLC layers) 

•10Base5, 10Base5, 10Base2, 10BaseT 

•1995 1995 IEEE 802.3u (Fast Ethernet) 

•1998 1998 IEEE 802.3z (Gigabit Ethernet) 

•2002 2002 IEEE 802.3ae (10Gb Ethernet) 

•... ... 

© 2005 Petr Grygarek, Advanced Computer Networks Technologies 

2

Ethernet Naming Rules 

(IEEE Standard) 

Mbps [Base|Broad] [segment_length 

[segment_length_m 

_m | -medium] -medium 

-T T - Twisted Pair, -F F - Fiber optic, ... 

e.g. 10Base5, 10BaseT, 100BaseF 

Name of each particular Ethernet 

technology defined in individual 

supplements supplement of 802.3 standard 

•e.g e.g 802.3u, 802.3ab, 802.3z 


3

Half-duplex and Full-duplex 

Ethernet 

•Half Half duplex – colission envirnment 

(CSMA/CD) 

•Full Full duplex - colission-free 

(switched) environment 

In half-duplex mode we have to adhere CSMA/ 

CD timing that implies the maximum cable 

lengths 

For compatibility with half-duplex NICs, P2P 

links may also operate in half-duplex mode 

© 2009 Petr Grygárek, FEI VŠB-TU Ostrava, Computer Networks (Bc.) 

4

Historical Ethernet 

Implementations 


5

10Base5 

= Thick Ethernet = DIX Ethernet = 

ETHERNET II 


6

10Base5 Capabilities 

•Bus Bus (coax) „Yellow Cable“ 

•50ohm, 50ohm, diameter of 10 mm 

•Max Max segment length 500m, terminated 

•Max Max 5 segments interconnected by 4 repeaters, 

stations may be placed only on 3 segments (5-4-3 

rule) 

•Max Max 100 stations per segment, minimum distance 

of 2.5 m 

•Manchester Manchester encoding 

•Utilizes Utilizes external transceivers (AUI interface) 

•Attached Attached to bus by T-connector or wampire tap 


7

10Base2 

= Thin Ethernet = CheaperNet 

•bus, bus, coax RG58 

•50ohm, 50ohm, diameter of 5 mm) 

•Max Max segment length 185m, terminated 

•5-4-3 5-4-3 rule 

•Max Max 30 stations per segment, minimum 

distance 0.5m 

•Interconnection: Interconnection: BNC and T 

connectors 

•Transceiver Transceiver is integrated on the NIC 


8

10BaseT 

•Star Star (tree) topology 

•2 2 twisted pairs (UTP3) + RJ-45 connectors 

•May May operate in full-duplex mode when switches 

are applied 

•Stations Stations interconnected with hubs 

•5-4-(3) 5-4-(3) rule 

•max. ax. 512 stations in the whole tree 

•Max Max 100m between hub and NIC 

•min min 0.6m 

•Crossing Crossing of transmitter and receiver 

cable pairs 


9

Fast Ethernet (100Mbps) 

•IEEE IEEE 802.3u 

•Based Based on 10BaseT 

•the the same MAC address protocol and 

frame format 

•NICs NICs are obviously backward compatible with 

10BaseT 

•Speed Speed autonegotiation capability 

•different different line encoding 

•Uses Uses UTP5, 100m between network 

devices 


10

Physical Layer of Fast 

Ethernet 

•100BaseTX: 100BaseTX: UTP5, STP – UTP5, max 

100m, 4B5B + MLT3, 125 MHz 

•100BaseFX: 100BaseFX: FO, max. distance NICNIChub is 200m (because of CSMA/CD) 

•Other Other sparsely used options 

•Developed Developed for compatibility with older 

cablings - 100BaseT2, 100BaseT4 


11

Fast Ethernet Topologies 

(half-duplex) 

•2 2 directly connected NICs 

•Star Star with Class I hub 

•Two Two Class II hubs interconnected by line 

of maximum 10 m in length 

Hub class I and II differ in 

•Maximum Maximum allowed signal delay 

•Capability Capability of encoding transformation, i.e. the 

ability of using different media in a single 

collision domain 

•e.g. e.g. transformaiton of 100BaseTX to 100BaseT4 


12

Ethernet Today 

•Ethernet Ethernet today is a whole family of 

networking technologies (100Mbps+) 

•LAN, LAN, MAN, WAN 

•Compatibility Compatibility still maintained 


13

Gigabit Ethernet (802.3z) 

•Developed Developed since 1995, originally supposed 

to require fiber optic or coax cable, 

standard later extended for twisted pair 

•802.3ab 802.3ab – compatible with existing wirings 

(Cat5e) 

•Makes Makes the standard Ethernet faster again 

• CSMA or switching, IEEE 802.3 frame, simple 

star topology 

•Problems Problems with minimum frame length in 

collision-mode when trying to keep the 

same maximum cable lengths as with 

10BaseT 

•Appends Appends a padding to 512B into a frame if 

necessary or applies packet bursting. 

• Most commonly used for backbone links 


14

Physical Layer of the Gigabit 

• 1000Base-T: UTP5e 

Ethernet 

• All 4 pairs used simultaneously in both directions 

(PAM5, echo cancellation), max. 100m 

• Problems with reflections connectors (the cabling 

system may start to resonate) 

• 1000Base-SX (short wavelength-850 nm) – used 

more often 

• 8B10B encoding 

• 62.5 um MMF 440m, 50 um MMF 550m 

• 1000Base-LX (long wavelength-1300 nm) 

• 8B10B encoding 

• SMF 3 km, 62.5 um MMF 440m, 50 um MMF 550m. 

• Usage of „offsets“ to limit transversal modes on MMF 

(decreases dispersion) 

• ANSI Fibre Channel 

• Supports bandwidths of 133Mpbs to 1Gbps on various 

cable types (MMF, STP, coax) 


15

1000BaseX (802.3z ( 802.3z): : Fiber Optics 

•extends extends the original LAN technology to 

distances that make Ethernet a WAN/MAN 

standard 

•1000BASE- 

1000BASE-SX SX 

•850nm 850nm laser/LED, laser/LED, 

MM fiber, SC – low cost 

•distances distances 220-550m (better better for 50/125 than 62.5/50 

fiber) fiber) 

•1000BASE- 

1000BASE- LX 

•1310nm 1310nm laser SM fiber (5km) or MM fiber (500m), (500m) , 

SC 

•8B10B+NRZ 8B10B+NRZ ("level-driven") encoding 

•Some Some bit combination have alternative 8B10B 

codewords 

•chosen chosen dynamically to reach balanced bit pattern 

•Because Because of high rate,1s rate, s and 0s 0 encoded with low and 

high power instead of presence/absence of light 


16

1000BaseT (802.3ab) 

• uses TP Category 5e or higher 

• cat5e at5e allows 125Mbps 

• all four pairs, 125 Mbd each 

• 4D-PAM5 line encoding 

• pulse amplitude modulation, 5 states 

•2bits/symbol 2bits/symbol + Forward Error Correction (8-state ( 8-state Trellis 

code) 

• control and data symbols 

•250 250 Mbps/pair if 125 Mbd used 

• 4x in parallel (for each pair) 

• See http://www.reed 

electronics.com/tmworld/article/CA287078.html 

• Full ull duplex: duplex: 

echo cancellation, cancellation, 

on all pairs 

• 9 voltage levels in idle periods, 17 during data 

transmission 

• need to synchronize clocks (clock master elected) 

• probl roblems ems with reflections (danger of resonance) 


17

Ethernet in Depth 


18

Ethernet Advantages 

•Simplicity 

Simplicity 

•lower lower learning and implementation cost 

•preferred preferred over (more sophisticated) FDDI, 

ATM etc. 

•Scalability 

Scalability 

•maintains maintains the same frame format at all 

transfer rates 

•Compatibility 

Compatibility 

•frame frame format (including MAC address format) 

•CSMA/CD CSMA/CD (until ( until 1000Base-T) 

1000Base T) 

•Modularity 

Modularity 

•Only Only physical layers differs 


19

Legacy Ethernet: 

Common Characteristics 

•10Base5-1980, 10Base5-1980, 10Base2-1985, 

10BaseT-1990 

•Timing Timing parameters (100ns bit timeslot, 

51.2us slot time) 

•Frame Frame format 

•Transmission Transmission processes 

•Manchester Manchester encoding 

•CSMA/CD CSMA/CD (half duplex) 

•full full duplex defined later for 10BaseT (1997) 

•Basic Basic design rule (5-4-3) 

•No No more than four repeaters can be used in 

series between any two stations. There can 

also be no more than three populated 

segments between any two stations. 


20

Ethernet Frame 

•Preamble: Preamble: 7x 10101010, 1x 10101011 (SFD) 

•necessary necessary only for (asynchronous) 10Mbps Ethernet 

•Type Type

802.1q Frame Header 

•extra extra 2+2 bytes (priority, VLAN ID) 

•Inserted Inserted behind TYPE field 

•Indicated Indicated by TYPE=8100h 

•Original Original TYPE repeated just behind 

802.1q header 


22

Timing 

•Propagation Propagation delay (UTP): (UTP) : 20.3 cm/ns, 

•100m 100m UTP = 5 bit times (10Mbps) 

•Slot Slot time = minimum mi um frame duration 

•512bit 512bit times (64B ( 64B) ) for 10 and 100 Mbps bps 

Ethernet 

•4096 4096 bit time time 

slots (512 B) for 1000 Mbps Mbps 

•calcula calculated ed assuming maximum maximu cable lengths 

(and repeater delay) 

•max max delay defined as 51,2 micro mi roseconds seconds 

•32bit 32bit “jam jam” signal 

•Interframe Interframe spacing 96 bit timeslots timeslots 

•time time that allows receiver(s) to process frame 

and prepare for another frame reception 


23

Timing Considerations 

for Mixed-media Network Design 

•Cable Cable length 

•Velocity Velocity of signal propagation 

•Transceiver Transceiver delay 

•Repeater Repeater delay 

•Interframe Interframe gap shrinkage due to 

repeaters 

•repeater repeater is expected to regenerate all 64 bits 

of preamble, despite the potential loss of some 

of the strarting preamble bits because of slow 

synchronization 

•this his forced reintroduction of timing bits 

reduces original interframe gap 

•Processing Processing delay in station NIC’s CPU 


24

Collisions 

•When hen a transmitting station detects a 

collision, it stops sending it's frame and 

sends 32bit Jam sequence to announce 

collision to other stations 

•jam jam signal may be composed of any binary 

data that do not form the proper checksum for 

the portion of the frame already transmitted 

•most most commonly 101010… 

•The The majority of collisions occurs occur very 

early in the frame, often before the SFD 

•Collision Collision fragments = frames

Collision Detection 

•Coax: Coax: amplitude of the signal on the 

network media increases 

•Manchester Manchester characteristics: 

number of High level intervals =number 

of Low level intervals, average should 

be 0 

•If If two Manchester waveform mix, 

average level moves 

•waveform waveform can be smoothed and level 

measured on capacitor 

•UTP: UTP: signal on RX pair while 

transmitting on TX pair 


26

•Local Local collision 

Collision Types 

•simultaneous simultaneous transmission of multiple stations 

on the same coaxial segment, detected as 

amplitude increase (signal “sums up” on 

terminators) 

•Remote Remote collision 

•collision collision behind repeater 

•cannot cannot be detected by amplitude increase 

(repeater will not pass it) or by simultaneous 

signal on RX and TX pair 

•identified identified by presence of collision fragment 

(short frame with wrong CRC) 


27

Late Collision 

•Collision Collision out of the timeslot (after 

first 64B) 64B 

•NIC NIC will not repeat the transmitted 

frame 


28

Bit Synchronization 

•10Mbps: 10Mbps: synchronizes before every 

frame independently using preamble 

(“asynchronous Ethernet”) 

•faster faster versions: synchronization 

always maintained 

•using using reserved “idle” symbols 


29

100BaseTX, 100BaseFX 

•100BaseTX 

100BaseTX (UTP5 ( UTP5) 

•4B5B 4B5B 

(1995) 

•reserved reserved symbols for frame delimitation and idle link 

indication 

•125 125 Mbaud 

•Scrambl Scrambling ing 

•MLT3 MLT3 - MuLTilevel encoding 

•3-level 3-level code, cycles in sine-like style, 

change represents 1, same level represents 0 

•100BaseFX 100BaseFX (FO) 

•4B5B 4B5B 

•NRZI NRZI 

•change change in the middle of bit time represents 1, 

change absence represents 0 


30

100BaseT2, 100BaseT4 (1) 

•Proposed Proposed technologies for UTP3 

•Did Did not reached a widespread usage 

•US US UTP Cat 3 installations only 

•Helped Helped to develop technologies applicable in 

Gigabit Ethernet 

•multilevel multilevel encoding, echo cancellation 


31

100BaseT2, 100BaseT4 (2) 

•100Base-T4 

100Base-T4 

•1 1 pair -> 1 pair

Ethernet Capability 

Autonegotiation 


33

Autonegotiation of 

Capabilities 

•10BaseT: 10BaseT: Normal Link Pulse (NLP) 

every 16.8 ms– ms– 

used for link integrity 

test only 

•pulses pulses present when a station has 

nothing to send 

•Fast Fast Ethernet & later: Fast Link 

Pulses (FLP) 

•FLP FLP burst - sent in NLP intervals for 

compatibility reasons 


34

FLP Bursts 

•data data pulses interleaved with clock 

pulses and carry 16 bit Link Code 

Word (LCW) 

•LCW LCW consists of 17 to 33 NLPs and 

takes 2ms in total 

•LCW LCW announces device’s capabilities 

to it’s link partner 


35

Link Code Word (LCW) 

Selector implies how to interpret 

Technology Ability Field 

• selector value 00001 assigned to IEEE 

802.3 

• For details, see http://www.scyld 

http://www. scyld.com com/ 

NWay.html 

NWay html 


36

Negotiated capabilities 

•speed speed (+modulation/pair usage) 

•duplex duplex 

•clock clock master (Gigabit Ethernet) 

•… 


37

Capability Negotiation Process (1) 

• After both link partners have interpreted other side’s 

LCWs, they start to use “highest” capabilities 

supported by both of them 

• Capability priorities: 

• 1000Base-T FD 

• 1000Base-T HD 

• 100Base-TX FD 

• 100BASE-T4 

• 100BASE-TX HD 

• 10BASE-T FD 

• 10BASE-T HD 


38

Capability negotiation 

process (2) 

•Station Station attempt attempts 

to detect and use 

100BaseTX signalling before 

autonegotiation 

•If f link partner does’n does offer FLPs FLP but 

offers NLPs, NLP , 10BaseT is assumed 

•If If the link is lost, link partners first 

attempt to connect at the last negotiated 

speed. If that fails, or link was down for 

long, long, 

autonegotiation autonegotiation 

starts again. 


39

802.3x Flow Control 

•Link Link layer 

•PAUSE PAUSE frame 

(full duplex) 

•EtherType EtherType 8808h 

•Reserved Reserved destination MAC address 

•not not forwarded by switch 

•Similar Similar to Xon/Xoff, but with timeout for 

Xoff 

•Parameter Parameter specifies number of units to wait 

•0 0 cancels PAUSE request 

unit corresponds to 1 time slot (512ns) 

•unit © 2005 Petr corresponds Grygarek, Advanced Computer Networks to 1 Technologies time slot (512ns) 

40

Modern Ethernet 

Technologies 


41

10Gbps Ethernet 

•Bit Bit time 0.1 ns (=100ps (!)), IFG 96 bits 

•Full Full duplex only 

•no no more collision timing calculation 

•Much Much more WAN/MAN WAN MAN or data center 

technology 

•but but still interoparable with Ethernet LAN‘s 

frame format (!) 

•Physical Physical layer: 

• Fiber 

• Copper (Cat6a) 

• Twinax (similar to 2x coax) 

• WAN PHY 


42

10GE on Fiber (10GBase-R) 

802.3ae 

• 10GBASE-SR (short reach) 

•MMF, MMF, 850nm laser, 64B/66B 

•26 26-82m -82m 

• 10GBASE-LR (long reach) 

•SMF, SMF, 1310nm laser, 64B/66B 

•10 10 km and 40 km over SMF 

• 10GBASE-ER (extended reach) 

•SMF, SMF, 1550nm laser, 64B/66B 

•40 40 km over SMF 

• 10GBASE-LX4 

•coarse coarse WDM (4x 1300nm laser) 

•MMF, MMF, 240-300m 


43

10GE on Copper (10GBase-T) 

802.3ab 

•10GBASE-CX4 10GBASE-CX4 – special cable 

•10GBASE-T 10GBASE-T – STP/UTP 

•45m 45m on Cat5e, 55m on Cat6 

•100m 100m on Cat6a (partitioned) 

•PAM16+complicated PAM16+complicated encoding 


44

Ethernet WAN PHYs 

(10GBASE-W) 

10GBASE-W) 

• 10GBASE-SW, 10GBASE-LW, 10GBASE-EW, and 

10GBASE-Z 

•Correspond Correspond to 10GBASE-SR, 10GBASE-LR, 

10GBASE-ER and 10GBASE-ZR 

• Use OC-192/STM-64 SDH/SONET (9.953 Gbit/s) 


45

Emerging Ethernet 

Technologies 

echnologies 

• 40 GB using DWDM 

•4x 4x 10Gbps carriers 

• Upcoming standards: 

•40/100 40/100 GbE - IEEE P802.3ba 

•under under development 

•single single light source 

•various various PHY types 

•maximum maximum compatibility with 803.3 framing 


46

Additional Information 


47

Ethernet Statistics Statistics 

Terminology (1) 

• Collision - simultaneous imultaneous transmission occurring 

before slot time (64/512B) has elapsed 

• Late collision - simultaneous imultaneous transmission 

occurring after slot time has elapsed 

• NIC does not retransmit the frame (!) 

• Jabber, abber, long frame, frame, 

range errors - excessively xcessively or 

illegally long transmission 

• Short hort frame, collision fragment, fragment, 

runt - illegally llegally 

short transmission 

• collision fragment - partial frames < 64B 64B 

with invalid 

CRC 

•typically typically result of remote collision 

• if signal it does not exhibit the local collision symptoms 

symptom 

• runt =

Ethernet statistics terminology (2) 

•Alignment Alignment error - Insufficient or excessive 

number of bits transmitted 

•Out Out of range error - illegal Length value (too 

large) 

•Range Range error - actual ctual and reported (Length 

field) number of octets in frame do not match 

•too too small Length value or Length does not match 

the actual number of octets received 

•Ghost Ghost or jabber - Unusually long Preamble or 

Jam signal 

•Ghost: Ghost: noise >72B, without valid SFD 

•Jabber: Jabber: >20000 bit times 


49

Signal Quality Error (SQE) 

signal of AUI transceivers 

• sent by a transceiver back to the controller to let 

the controller know whether the collision 

circuitry is functional. 

• designed to fix the problem in earlier versions of 

Ethernet where a host does not know if a 

transceiver is connected. 

• SQE is active: 

• Within 4 to 8 microseconds after a normal transmission 

to indicate that the outbound frame was successfully 

transmitted 

• Whenever there is a collision on the medium 

• Whenever there is an improper signal on the medium 

(jabber, cable short) 

• Whenever a transmission has been interrupted 


50

Useful Ethernet 

information 

•http://www.ieee.org 

http://www.ieee.org 

•http://www. 

http://www.ethermanage 

ethermanage.com com/ 

ethernet 


51

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