Ethernet Grundlagen - Hochschule für Technik Rapperswil

Ethernet Grundlagen - Hochschule für Technik Rapperswil

Computernetze 1 (CN1) 2 Ethernet Grundlagen Prof. Dr. Andreas Steffen Institute for Internet Technologies and Applications Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 1 Lesestoff im Ethernet Buch Kapitel 2 Ethernet, Seiten 31-83 2.1 2.2 2.3 2.4 2.6 2.7 2.8 2.9 Die Geschichte des Ethernet Der Physical Layer 10Base5 10Base2 10BaseT 10BaseF Das Manchester-Kodierungsverfahren Media Access Control (MAC)

Kapitel 6 Ethernet Internals, Seiten 208-214 6.2 Power over Ethernet Selbststudium Erarbeiten Sie als Vorbereitung fr die bung 2 selbststndig das Thema Media Access Control mit Hilfe von Kapitels 2.9 des Ethernet Buchs und des Kapitels 2.4 dieses Foliensatzes. Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 2 Wie es begann... 1972 stoss Robert Metcalfe auf ein Paper von Norman Abramson, welches das Aloha Random Access System der Universitt Hawaii beschrieb. Ausgehend von Aloha erfand er am Xerox Palo Alto Research Center (PARC) das robuste CSMA/CD* Protokoll, mit dem mehrere Teilnehmer fast kollisionsfrei auf ein shared-medium zugreifen knnen. 1976 stellte er sein Protokoll unter dem Namen Ethernet an einer Konferenz vor. 1979 grndete er die Firma 3Com.

Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 3 Computernetze 1 (CN1) 2.1 Ethernet Standards Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 4 Ethernet und das OSI Modell 802.2 802.3 Ethernet Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 5 IEEE 802 LAN standardization is done by the IEEE (Institute of Electrical and Electronical Engineers) The IEEE LAN/MAN standards committee 802 was founded in February 1980 OSI Data Link Layer (Layer 2) was originally designed for point-to-point line communication but LAN is multipoint line, shared media

Therefore OSI Layer 2 had to be split into two sublayers Logical Link Control (LLC) Media Access Control (MAC) Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 6 Aufgaben der Schicht 2 Logical Link Control (LLC) Verbindungsverwaltung Fehlererkennung und evtl. Korrektur Connect request, indication, response, confirm, etc. Synchronisation von gemeinsamen Zhlern, etc. Vorwrtsfehlerkorrektur Erkennen+Rckmelden+Wiederholung (ARQ), etc.

Flusssteuerung / Flow Control Erstellen von Rahmen / Frames Achtung: nur fr das nchste Segment Ethernet, Token Ring, FDDI, ATM etc. Media Layer 2 Addressierung dieser Frames Access Zugriffsverfahren Control Wie teile ich mir ein gemeinsames Medium mit anderen Kommunikationspartnern ? (MAC) Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 7 IEEE 802 Working Groups IEEE IEEE Standard StandardBoards Boards IEEE IEEE802 802 LAN/MAN LAN/MAN Standard

StandardCommittee Committee 802.24 802.24 Smart SmartGrid Grid Technical Technical Advisory AdvisoryGroup Group 802.1 802.1 Higher HigherLayer Layer LAN Protocols LAN Protocols Working WorkingGroup Group 802.3 802.3 Ethernet Ethernet Working WorkingGroup Group

802.11 802.11 Wireless WirelessLAN LAN Working Group Working Group P802.3bj P802.3bj P802.3bk P802.3bk P802.3bm P802.3bm P802.3bq P802.3bq 100 100 Gb/s Gb/s Backplane Backplane & & Copper Cable Copper Cable

Extended Extended Ethernet Ethernet Passive Optical Passive Optical Networks Networks (EPON) (EPON) 40 40 Gb/s Gb/s and and 100 100 Gb/s Gb/s Operation over Fiber Operation over Fiber Optic Optic Cables Cables 40GBASE-T 40GBASE-T Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 8 IEEE 802 Active Working Groups

802.1 Higher Layer LAN Protocols Working Group 802.3 Ethernet Working Group 802.11 Wireless LAN Working Group 802.15 Wireless Personal Area Network Working Group 802.16 Broadband Wireless Access Working Group (WiMAX) 802.18 Radio Regulatory Technical Advisory Group 802.19 Wireless Coexistence Working Group 802.21 Media Independent Handoff Working Group 802.22 Wireless Regional Area Networks Working Group 802.24 Smart Grid Technical Advisory Group Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 9 IEEE 802 Inactive and Disbanded Working Groups

802.2 Logical Link Control Working Group Inactive 802.4 Token Bus Working Group Disbanded 802.5 Token Ring Working Group Inactive 802.6 Metropolitan Area Network Working Group Disbanded 802.7 Broadband Technical Advisory Group Disbanded 802.8 Fiber Optic Technical Advisory Group Disbanded 802.9 Integrated Services LAN Working Group Disbanded 802.10 Security Working Group Disbanded 802.12 Demand Priority Working Group Inactive 802.14 Cable Modem Working Group Disbanded 802.17 Resilient Packet Ring Working Group Inactive Steffen/Stettler, 802.20 Mobile Broadband Wireless Access

WG 20.09.2013, 2-Ethernet.ppt 10 Computernetze 1 (CN1) 2.2 Ethernet Physical Layer (PHY) Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 11 Ethernet IEEE 802.3 Overview Fiber Twisted Pair Coax Rarely used 10GBase-T 802.3an-2006 40/100Gbps 802.3ba-2010 Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 12 Ethernet Technology Overview Logical Link Control LLC Data Link Layer MAC Control (optional) Media Access Control MAC PLS

Reconciliation Reconciliation Reconciliation MII MII GMII PLS PCS PCS AUI PMA PMA PMA (MAU) PMA PMD PMD MDI MDI MDI

MDI Medium Medium Medium Medium 100 Mbit/ s 1000 Mbit/ s AUI 1-10 Mbit/ s 10 Mbit/s PHY AUI...Attachment Unit Interface, PLS...Physical Line Signaling, MDI...Medium Dependent Interface, PCS...Physical Coding Sublayer, MII...Media Independent Interface, GMII...Gigabit Media Independent Interface, PMA...Physical Medium Attachment, MAU...Medium Attachment Unit, PMD...Physical Medium Dependent Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 13 PHY Sublayers

Physical Line Signaling (PLS) serves as an abstraction layer between MAC and PHY and provides Data encoding/decoding (Manchester) Signalling of media states (busy, free, collision occurred etc.) Attachment Unit Interface (AUI) to connect with PMA Several new coding techniques demand for a Media Independent Interface (MII) that serves as an interface between MAC and PHY hides coding issues from the MAC layer MII: often a mechanical connector for a wire; GMII is an interface specification between MAC-chip and PHY-chip upon a circuit board one independent specification for all physical media supports several data rates (10/100/1000 Mbits/s) 4 bit (GMII: 8 bit) parallel transmission channels to the physical layer Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 14

Today coding is done through a media-dependent Physical PHY Sublayers Physical Coding Sublayer (PCS) encapsulates MAC-frame between special PCS delimiters 4B/5B or 8B/10B encoding respectively appends idle symbols Physical Medium Attachment (PMA) interface between PCS and PMD (de) serializes data for PMD (PCS) Physical Medium Dependent (PMD) serial transmission of the codegroups specification of the various connectors (MDI) Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 15 10Base5

Introduced in 1980 as part of the original IEEE 802.3 standard. Transmits 10 Mbps over a single thick coaxial cable bus. The primary benefit of 10Base5 was its length: up to 500m without a repeater. 10Base5 uses Manchester encoding. The thick and sturdy cable was difficult to install and was therefore called Thick Net or due to its color Yellow Cable. Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 16 10Base2 I Introduced in 1985. Installation is easier then 10Base5 because of its lighter size and greater flexibility. Therefore it was called Thin Net or Cheaper Net. 10Base2 also uses Manchester encoding. Computers on the LAN are linked together by an uninterrupted chain of coaxial cable lengths.

These lengths are attached by BNC connectors to a Tshaped connector on the NIC. Each 10Base2 segment may be up to 185 meters long and may accommodate up to 30 stations. Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 17 10Base2 II 1. 2. 3. 4. 5. Termination of each end of the coax should be 50 Ohms. Minimum distance between taps is 0.5 meters. Each station must be connected within four centimeters of the thin coaxial cable. Maximum segment length is 185 meters. Link segments between repeaters should have a total of only two attachments, the repeaters themselves. Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 18 10Base-T I

Introduced in 1990. 10base-T uses cheap and easy to install Cat 3 Unshielded Twisted Pair (UTP) copper cable rather than coaxial cable. The UTP cable is plugged into a central connection device that contains the shared bus => Hub. Preferred Topologies: Star and Extended Star. Originally 10Base-T was a half-duplex protocol, but fullduplex features were added later. 10Base-T also uses Manchester encoding. Due to their high attenuation 10Base-T links can have unrepeated lengths of up to 100 m. Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 19 10Base-T II UTP cable uses RJ-45 connectors with eight pins. All four pairs of wires are used either with the straightthrough T568-A or the cross-over T568-B cable pinout Pin Signal arrangement. Cat 3 cable is adequate for use in 10Base-T networks, although Cat 5e or better is strongly recommended for any new cable installations.

1 TD+ (Transmit Data) 2 TD- (Transmit Data) 3 RD+ (Receive Data) 4 6 (reserved for POTS) b (reserved for POTS) RD- (Receive Data) 7 unused 8 unused 5

a Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 20 Power-over-Ethernet (IEEE 802.3af PoE) 1 Alternative A Alternative B 1 2 48 V DC 3 1 Pair 3 2 350 mA PSE Pair 3 2

2 4 4 Pair 1 5 5 350 mA 3 48 V DC 7 6 PSE 8 8 3 3 13.0 [email protected] Pair 2 6 1

PSE Power Sourcing Equipment PD Powered Device PD 13.0 [email protected] 7 Pair 4 PD Pair 2 6 6 Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 21 Power-over-Ethernet (IEEE 802.3at PoE+) 1 Alternative A Alternative B 1 2 53 V DC 3

1 Pair 3 2 600 mA PSE Pair 3 2 2 4 4 Pair 1 5 5 600 mA 3 53 V DC 7 6 PSE 8

8 3 3 25.5 [email protected] Pair 2 6 1 PSE Power Sourcing Equipment PD Powered Device PD 25.5 [email protected] 7 Pair 4 PD Pair 2 6 6 Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 22

Power-over-Ethernet (IEEE 802.3at PoE+) 1 Alternative A Alternative B 1 2 53 V DC 3 1 Pair 3 2 600 mA PSE Pair 3 2 2 4 4 Pair

1 5 5 600 mA 3 53 V DC 7 6 PSE 8 8 3 3 25.5 [email protected] Pair 2 6 1 PSE Power Sourcing Equipment PD Powered Device

PD 25.5 [email protected] 7 Pair 4 PD Pair 2 6 6 Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 23 Energy-Efficient-Ethernet (IEEE 802.3az EEE) In 2005 all Network Interface Controllers (NICs) in the US used 5.3 TWh (600 MW) EEE introduces a Low Power Idle (LPI) sleep signal Transmitter sends LPI in place of Idle for a period Ts to indicate that the link can go to sleep and then stops signaling. Periodically, the transmitter sends a refresh signal for a time Tw so that the link does not remain quiescent for too long.

To resume the transmitter sends normal Idle Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 24 signals. After a time Tw the link is active. Computernetze 1 (CN1) 2.3 Ethernet Frame Synchronisation Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 25 10Mb/s-Ethernet: Manchester Code 0 1 0 1 1 1 0 0 1 0

"0" = fallende Flanke in Bitmitte (H->L) "1" = ansteigende Flanke in Bitmitte (L->H) 1 1 0 0 T=Bitdauer Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 26 10Mb/s-Ethernet: Frame-Synchronisation 1 0 1 0 1 0 1

0 1 0 1 0 Bitmitt e Prambel bestehend aus einer 1-0-1-0- Sequenz ermglicht die Synchronisation auf die Bitmitte. Das erste Auftreten von 1-1 kndigt den Start der Nutzdaten an. 1 1 Frame Start Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 27 IEEE 802.3 Ethernet Frame Prambel 1010101010101010101010101010101010101010101010101010101010101011 7 Bytes

1 Byte Pramb el SFD SFD Start-of-Frame Delimiter Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 28 Computernetze 1 (CN1) 2.4 Ethernet Media Access Control (MAC) Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 29 Half-Duplex Transmission Historically Ethernet was a half-duplex technology. Using half-duplex, a host could either transmit or receive at one time, but not both. Host checks the network to see whether data is being transmitted before it transmits data.

If the network is already in use, the transmission is delayed. Only ONE host can transmit at a time. Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 30 Carrier Sense Multiple Access / Collision Detection 1. Listen to the medium 2. Sending if medium is free, else waiting for a random time and try again 3. The amplitude of the signal increases because a collision occurs. 4. The nodes stop transmitting for a random period of time, which is different for each device. Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 31 CSMA/CD Ablaufdiagramm Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 32 CSMA/CD Collision Handling

Abortion of current transmission by all stations involved Emission of a Jam-signal (32 bit) to make sure that every station can recognize the collision collision is spread to a minimum length Generation of a random backoff timeout value truncated binary exponential backoff algorithm (the more often a collision occurs the larger is the range for the random number) After expiration of the timeout a retransmission is attempted Number of retransmission trials is limited to 16 after 16 collisions in a sequence a error is signaled to the higher layer Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 33 Truncated Binary Exponential Backoff Algorithm

Runde 0: 0 Runde 1: 0 Runde 2: pcollision = 1 (3 hosts) t pcollision = 1 (3 hosts) t 1 0 1 2 3 pt collision = (2 hosts) slot tim

e Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 34 Signalausbreitung auf Koaxialkabel A B C Lmax, v = 0.2 m/ns Raum T1 Collision T1 = Lmax/v T1 Late Collision Zeit Tmax = 2T1 = 2Lmax / v Lmax = vTmax / 2 Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 35 Collision Window und Kollisionsdomne

Worst-Case Betrachtung Um eine Kollision zuverlssig detektieren zu knnen, muss die minimale Dauer eines Ethernet Frames grsser als die doppelte einfache Signallaufzeit, d.h. dem Round Trip Delay (RTD) sein. Diese maximale Zeit Tmax nennt man Collision Window. 10 Mbit/s und 100 Mbit/s Ethernet definieren eine minimale Frame-Grsse von 512 Datenbits (64 Bytes). Maximale Ausdehnung einer Kollisionsdomne 10 BASE: Tmax = 512100 ns = 51.2 s s Lmax 2000 m 100 BASE: Tmax = 51210 ns = 5.12 us Lmax 200 m Werden diese Lngen berschritten, knnen Late Collisions auftreten. Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 36 Full-Duplex Transmission Allows transmission of a packet and the reception of a different packet at the same time.

Host can transmit immediately without checking the network first. The connection is considered point-to-point and is collision free. Full-duplex Ethernet offers 100% of the bandwidth in both directions. Requires a dedicated connection to a switched port. X X Steffen/Stettler, 20.09.2013, 2-Ethernet.ppt 37

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