Ethernet Radovanovi Igor Thanks to B A Forouzan

Ethernet Radovanović Igor Thanks to B. A. Forouzan Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking /36

Reminder Application Transport Network Data link Physical 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 2/36

Reminder: IEEE standard 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 3/36

Ethernet protocol (LAN protocol) CSMA/CD 1 -persistant 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 4/36

Reminder: Data Link layer 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 5/36

Short history • Invented in the midst of 1970’s by Bob Metcalfe & David Bogs in Xerox Palo Alto Research Center – Norman Abramson developed an ALOHA network on Hawaii islands – Bob (a Harvard Ph. D student) worked on ARPAnet at MIT – 100 computers connected on a 1 km cable using CSMA/CD • • • Original Ethernet: 256 hosts running at 2. 94 Mbps Xerox, Digital & Intel established 10 Mbps Ethernet IEEE standardization (802. 3) 1979 Bob Metcalfe: 3 Com (left company in 1990) “Ethernet has been to LAN as Internet to global networking” 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 6/36

Why is Ethernet so popular? • First widely developed high-speed LAN – Network administrators reluctant to switch to other LAN techn. • Other technologies (Token Ring, FDDI) more complex & expensive • Ethernet evolved in speed • Ethernet hardware of low cost – CSMA/CD decentralized – simple design 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 7/36

Ethernet building blocks • Ethernet frame (packet) • Media Access Control protocol • Signaling components – Ethernet interface card, transceivers, repeaters • Physical medium 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 8/36

Traditional Ethernet frame -common to all Ethernet technologies • MAC frame • Preamble – 7 bytes of alternating 0 s and 1 s – receiver sync – Not necessary in high-speed Ethernet systems (Fast. Eth, Gig. E) • Start of Frame Delimiter – 10101011 – not unique sequence -> last chance to synchronize • Source Address, Destination Address – 48 bit unique address • Length/Type – Value up to 1518: length; value larger tan 1536 – type of PDU encaps • • • Data Frame Check Sequence (CRC); preamble and SFD excluded in calculat. Note: no ACK mechanism provided 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 9/36

MAC to PHY mapping • Unaltered transmission in all but preamble field • Start of Stream Delimiter and End of Stream Delimiter added 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 10/36

Min & Max Ethernet frame length • Minimum length - used for CSMA/CD – Every end station senses the frame within the correct time limits – Historical requirement derived for bus topology with a coax cable • Maximum length – to assure fair access – A station should not occupy the medium too long 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 11/36

Collision domain • “a single CSMA/CD network in which there will be a collision if two computers attached to the system both transmit at the same time” • “defined as all the Ethernet segments between a pair of bridges or other layer 2 devices” 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 12/36

Determining minimum frame length Repeaters every 500 m 10 Mbps L<1500 m Thick copper coaxial cable • In practice, minimum packet size = 512 bits – allows for extra time to detect collisions – allows for “repeaters” that can boost signal 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 13/36

Three generation of Ethernet 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 14/36

Physical layer implementation s. TYPE-t(l) s – speed in Mbps TYPE – broadband or baseband signaling l – cable distance in multiple of 100 m t – media type used 20/01/2022 10 Base-5: Original Ethernet: large thick coaxial cable 10 Base-2: Thin coaxial cable version 10 Base-T: Voice-grade unshielded twisted-pair Category-3 telephone cable 10 Base-F: Two optical fibers in a single cable Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 15/36

10 BASE-T twisted-pair wire • uses a physical star topology (logical bus) • end stations connected to a hub using external or internal transceiver • maximum distance 100 m using UTP cable • maximum number of hubs is 4 (total span 500 m) Q: How to increase the span? 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 16/36

Bridged Ethernet • Bridges: increase the bandwidth and separate collision domains – Attach more users and increase the distance between any 2 nodes Q: How to increase bandwidth further? 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 17/36

Switched Ethernet • Used to add bandwidth without replacing NICs • Each end station uses a separate path to the port in the switch (no sharing medium- no need for CSMA/CD) full-duplex Ethernet 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 18/36

Ethernet- Physical layer • If PLS to be connected to a different MAU – PLS the same • Medium Attachment Unit – Medium dependant • MDI – External: tap or a tee connector – Internal: jack 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 19/36

Three generation of Ethernet 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 20/36

Ethernet NIC with MII connector Network Interface Card with the MII connector Physical Layer Device attached to the NIC with the MII connector Optical MII transceiver - Physical Layer Device 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 21/36

Fast Ethernet • Keep MAC layer untouched • Increase the speed 10 times while keeping the compatibility with the Ethernet • Quick deployment • Autonegotiation – negotiate the mode (full- or half-duplex) or data rate of operation (10 Mbps, 100 Mbps) • Different encoding technique to transfer the high data rate signal – Q: What is the data rate of the transmitted signal if the Manchester encoding is used? 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 22/36

Fast Ethernet implementations 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 23/36

100 BASE-TX • • uses two pairs of twisted-pair cable (Cat 5 UTP or STP) in the physical star topology Maximum number of repeaters is 2 (Class II repeaters). Maximum cable length to a repeater is 100 m. Maximum distance between repeaters is 5 m. encoding 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 24/36

MLT-3 • Uses 3 levels of signals (+1, 0, -1) • Transition at the beginning of bit 1 • Used to decrease transmission frequency – Q: Why? 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 25/36

100 BASE-FX • Two pairs of fiber-optic cables in a physical star topology • Can support larger distances (unrepeated) – up to 2 km full-duplex; 412 m half-duplex – single-mode fiber • Long-wavelength lasers in NICs • Problem: not compatible with previous fiber standards 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 26/36

100 BASE-FX - encoding 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 27/36

100 BASE-SX • Not an IEEE standard • Only Physical layer changed • Based on short-wavelength lasers (850 nm) – Q: Why is this important? A: – backwards compatibility – lower cost of the NIC? • Shortcoming: – shorter fiber span (300 m) 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 28/36

Comparing different standards 20/01/2022 Description 100 BASE-TX 100 BASE-FX 100 BASE-SX Max. unrepeated segment length [m] 100 412 2000 300 Cabling type UTP Multimode fiber Single-mode fiber Multimode fiber Connection type Point-to-point NIC cost Low High Low upgrade Medium Reliability Low Medium Max. numb. of PCs per coll. segment High Compatibility with previous networks Yes No Yes Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 29/36

Three generation of Ethernet 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 30/36

Gigabit Ethernet • Once more, 10 times faster Ethernet – what was the motivation for developing this standard? • wanted to keep MAC layer unaltered; did this happen? • 802. 3 z (z indicates the end of the road) • Design goals: – backwards compatibility – offer unacknowledged datagram services – same 48 bit address scheme • • All configurations are point-to-point Defined for both half- & full-duplex Half-duplex supports CSMA/CD All implementations today are full-duplex 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 31/36

Gigabit Ethernet (cnt’d) • Requirement: To implement CSMA/CD – signal propagation time (~ to Slot Time) must stay the same – keeping the Slot Time the same requires decreasing the span (10 times) • this would limit the span to 25 m only! • possible remedy: – increase the minimum size packet • Q: What was the minimum size of the packet in Ethernet? – by doing this we loose backwards compatibility – introduce Carrier extension 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 32/36

Gigabit Ethernet (cnt’d) • Carrier extension is very inefficient for the short packets – for example for 64 byte packet we have 448 bytes of padding • low throughput • Solution: introduce Frame bursting • Q: What is the maximum burst size? 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 33/36

Gig. Eth implementations based on optical fiber short wavelengths 260 m -> MM fiber 550 m -> SM fiber 20/01/2022 based on STP; never implemented long wavelengths 550 m -> MM fiber 3 km -> SM fiber 25 m Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking Cat 5 e UTP 100 m 34/36

10 G Ethernet (IEEE 803. 2 ae) • Only full-duplex (no CSMA/CD) • Based on optical fibers • Standard specified for both LANs and WANs 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 35/36

Ethernet Retrospective • Been around for 20 years • Few technologies made it that long (OS, architectures etc) • Pros: – simple, popular, flexible • Cons – non-deterministic, unreliable, no priorities, min frame size – Q: Why are these important? 20/01/2022 Igor Radovanović, i. radovanovic@tue. nl TU/e Computer Science, System Architecture and Networking 36/36