Vorlesung Kommunikationsnetze Ethernet and FDDI

Picture 15 13 Vorlesung Kommunikationsnetze Ethernet and FDDI Prof. Dr. H. P. Großmann mit B. Wiegel sowie A. Schmeiser und M. Rabel Sommersemester 2009 Institut für Organisation und Management von Informationssystemen

Ethernet and FDDI Ethernet History, Evolution, Overview OSI-Model Physical Layer: Coding Schemes MAC-Layer: CSMA/CD Ethernet Principles Versions and Parameters Topologies Communication Modes Collision Domain Framing Standards up to Gigabit Ethernet Gigabit Ethernet VLAN FDDI

History - Ethernet and DIX Consortium Creation of Ethernet DEC-Intel-Xerox (DIX) Consortium by Dr. Robert Metcalfe at Xerox Corporation in Palo Alto, California, 1973 operated at 2.94Mbps goal was to improve the connection speed between computers and printers developed the standard for 10Mbps Ethernet, 1980 thick multi-drop coaxial cable IEEE 802 standards, 1980 IEEE 802.3 for Ethernet IEEE 802.4 for Token Bus IEEE 802.5 for Token Ring

In the beginning 1976 R. Metcalfe presented Ethernet for the first time; he used this diagram

Evolution Ethernet 10Mb/s 1973 1980 Fast Ethernet 100Mb/s Gigabit Ethernet 1000Mb/s 10 Gigabit Ethernet 10000Mb/s 1995 1998 2002

IEEE Standards 802.2 Logical Link 802.10 Security 8 0 2.1 B r id g in g 802.1 Overview 802.3 Ethernet L A N 802.4 To k e n B u s 802.5 To k e n R i n g 802.7 802.6 D Q D B Broadband Ta g 8 0 2. 8 F i b e r O p t i c Ta g 802.9 Integrated Services 802.11 Wireless L A N

OSI Layers Application Presentation Session Transport Network LLC Data Link MAC Physical PHY PMD

Sub-Layers LLC MAC Logical Link Control LLC (de)multiplexing packets from the network layers MAC Media Access Control frame formats, addressing, sharing of the medium PHY physical medium independent layer encoding/decoding bits into pulses, synchronization of the transceiver clocks PMD Physical Medium Dependent Layer handling with electrical components PHY PMD

Inter-Layer Connections F ra m e s M A C P H Y P M D 1101 1 1 0 1 1 M A C S y m b o l s P H Y Pulses P M D

Physical Effects The basic problems of signal transmission are caused by Attenuation Dispersion EMI (Electro-Magnetic Interference) Power limitations Rise and fall times

Physical Layer - Summery of Coding Purposes optimizing signal for transmission prevent from the loss of the clock signal reduce the required bandwidth get line control signals

Pulse Coding - Schemes 0 c l o c k N R Z N R Z I M a n c h e s t e r 1 0 0 0 1 1

MLT-3 Coding Scheme 0 clock M L T - 3 1 0 1 1 1 1

NRZI-MLT-3 Bandwidth Gain 1 1 1 1 1 1 1 N R Z I 1 c y c le, 2 b its 100 MHz M L T - 3 1cycle, 4 bits 50 MHz

4B/5B Coding data code bits 11110 01001 10100 10101 01010 01011 01110 01111 10010 10011 10110 10111 11010 11011 11100 11101 symbol 0 1 2 3 4 5 6 7 8 9 A B C D E F original 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 control invalid code bits symbol 11000 J 10001 K 101 L 1101 T 111 R 11001 S code bits 1 10 11 110 1000 1100 10000 line state code bits symbol 0 Q 11111 I 100 H

Pulse Coding - Schemes 0 c l o c k N R Z N R Z I M a n c h e s t e r 1 0 0 0 1 1

MLT-3 Coding Scheme 0 clock M L T - 3 1 0 1 1 1 1

Bandwidth Sharing (Half Duplex Mode) For a bus or any other half duplex topology a method for bandwidth sharing is mandatory. In the development days of the Ethernet the following methods were tested: P u r e A lo h a Slotted Aloha C S M A C S M A / C D

CSMA/CD Carrier Sense Multiple Access with Collision Detection wait until medium is available medium must be idle for the Interframe Gap (IFG) time before sending start transmission if a collision is detected while transmitting, transmit a jam signal wait for a random time and retry (up to 16 times) collision detection is done by comparing transmitted and received signals

CSMA/CD

Ethernet Versions Two incompatible versions: Ethernet II (DIX - consortium of the companies DEC, Intel and Xerox) Ethernet 802.3 (standard of IEEE) PMD, PHY, and MAC layers are covered in the standard IEEE 802.3 LLC - covered in the standard IEEE 802.2 (general standard, not only for Ethernet)

Ethernet II Principles fixed 10Mbps Manchester coded signals CSMA/CD used for bandwidth sharing frame size range 64 to1518 bytes truncated binary back-off algorithm used for retransmission little-endian bit-order 64 bit preamble at front and 9.6μs delay between frames bus topology Ethernet is a passive network, only transmitting stations can be detected

Example for a Bus Topology (obsolete) 1 0 M b /s

Example for a Star/Tree Topology 100Mb/s 100Mb/s 100Mb/s 1 0 M b / s 1 0 M b / s 100Mb/s 1 0 0 M b /s 100Mb/s 1 0 M b / s 100Mb/s 100Mb/s

Example for a Star Topology

Half-duplex Mode Stations share a single Ethernet channel by using a medium access control protocol (see CSMA/CD) Only one station can send data over the channel at any given time Disadvantage: segment length is limited by timing requirement caused by requirements of collision detection mechanism

Full-duplex Mode Point-to-point links over twisted pair or fiber optic media Both devices may send data at any time Disable the carrier sense function Disable collision detect Disable the looping back of transmitted data onto the receiver input Advantages: Segment length is limited by the signal-carrying capabilities of the segment media The multiple access algorithm (CSMA/CD) is unnecessary Standard IEEE 802.3x

Physical Extension Ethernet cards detect collisions only while transmitting. A collision that occurs at the far end of the medium must reach the sender before it stops transmitting.

Collision Domain Repeater R e p e a te r

Separate Collision Domains Switch R e p e a te r Repeater Repeater

Framing Layer 2 encapsulation Breaking the stream into fields Start and stop indicator fields Naming or addressing fields Data fields Quality control fields

IEEE MAC Address I/G 1 Bit U / L 1 Bit O U I 22 Bits 24 Bits by OUI assigned Owner I/G Individual/Group U/L Universal/Local OUI Organizationally Unique Identifier specifies the manufacturer of the Ethernet card

Ethernet II Frame F ra m e H e a d e r Pream ble (8 Byte) Destination Address S o u r c e Address (6 Byte) (6 Byte) T y p e D a t a F C S (2 Byte) (46-1500 Byte) (4 B y te ) Preamble for synchronization of the stations Type specifies Layer 3 Protocol FCS Frame Check Sequence

Ethernet 802.3 Frame F ra m e H e a d e r P r e a m b l e S F D (7 Byte) ( 1 B ) Destination A d d r e s s (6 Byte) S o u r c e A d d r e s s (6 D S A P S S A P D e s tin a tio n S A P (1 Byte) Source SAP (1 Byte) 802.2 LLC L e n g t h / Type Byte) (2 Byte) Control Field (1-2 Byte) D a t a (46-1500 Byte) F C S (4 Byte) D a t a (42-1497 Byte) Header Length/Type SFD Length of data or Type Start Frame Delimiter shows the start of a Frame LLC Header: SAP Control Field Service Access Point for the Layer 3 Protocol determination for the indication of supervisory, information, unnumbered frames

802.2 SNAP Header Destination Address Source Address (6 Byte) Length Data FCS (6 Byte) (2 Byte) (46-1500 Byte) (4 Byte) DSAP SSAP Destination SAP (1 Byte) Source SAP (1 Byte) Control Field (1 Byte) SNAP Data (5 Byte) (<= 1492 Byte) OUI Protocol Type (3 Byte) (2 Byte)

Some of the Standards for 10Mbit/s StandardTopology Medium first released 10Base5 DIX-1980 802.3-1983 10Base2 802.3a-1985 Bus 10Base-T 802.3i-1990 Star 10Base-F 802.3j-1993 Star 10 stands for 10Mbit/s Base stands for Baseband Bus single 50 Ohm coaxial cable (10mm thick) - thicknet single 50 Ohm RG 58 coaxial cable (5mm thick) - thinnet two pairs of 100 Ohm Cat3 or better UTP cable two optical fibres Max Cable Segment [m] halfduplex full-duplex 500 not supported 185 not supported 100 100 2000 > 2000

Standards for 100Mbit/s StandardTop. first released 100Base-TX 802.3u-1995 Star 100Base-FX 802.3u-1995 Star 100Base-T4 802.3u-1995 Star 100Base-T2 802.3y-1997 Star Medium Max Cable Segment [m] halfduplex full-duplex two pairs of 100 Ohm Cat5 UTP cable two optical fibres 100 100 412 2000 four pairs of 100 Ohm Cat3 or better UTP cable two pairs of 100 Ohm Cat3 or better UTP cable 100 not supported 100 100

Standards for 1Gbit/s Standard Top. Medium -first released 1000Base-LX 802.3z1998 Star 1000Base-SX 802.3z1998 Star 1000Base-CX 802.3z1998 Star 1000Base-T 802.3ab- Star 1999 long wavelength laser: - 62.5μm multi-mode fiber - 50μm multi-mode fiber - 10μm single-mode fiber short wavelength laser: - 62.5μm multi-mode fiber - 50μm multi-mode fiber specialty shielded balanced copper jumper cable assemblies ( twinax ) four pairs of 100 Ohm Cat5 or better cable Max Cable Segment [m] halfduplex fullduplex 316 316 316 550 550 5000 275 316 275 550 25 25 100 100

Encoding of the IEEE Standards Ethernet Manchester coding Fast Ethernet 100Base-FX NRZI and 4B/5B encoding 100Base-TX MLT-3 (or NRZI-3) and 4B/ 5B encoding 100Base-T4 8B/6T encoding 1000Base-LX 8B/10B encoding Gigabit Ethernet 1000Base-SX 8B/10B encoding 1000Base-CX 8B/10B encoding 1000Base-T PAM5

Parameters 10MBit/s 100MBit/s 1GBit/s nominal Bit Time 0,1 μs 0,01 μs 0,001 μs Slot Time [Bit Times] 512 512 4096 Interframe Gap 9,6 μs 0,96 μs 0,096 μs Max Frame Size 1518 Byte 1518 Byte 1518 Byte Min Frame Size 64 Byte 64 Byte 64 Byte Extended Size 0 Bit 0 Bit Burst Limit no no Slot-TimeMinFrameSize 65536 Bit

Gigabit Ethernet Standards Media Access Control(MAC) full duplex / half duplex Gigabit Media Independent Interface (GMII) optional 8B/10B encoding/decoding 1000BASE-LX LWL Fiber Optic 1000BASE-SX SWL Fiber Optic 1000BASE-CX Shielded Balanced Copper 802.3z physical layer 1000BASE-T encoder/decoder 1000BASE-T UTP Category 5 802.3ab physical layer

Migration to Gigabit Ethernet Gigabit Ethernet looks identical to Ethernet from data link layer upwards Changes are made to physical interface Gigabit Ethernet Physical Media Attachment (PMA) is identical to Fiber Channel PMA Standard takes advantage of High speed physical interface of fiber channel IEEE 802.3 Ethernet frame format Full or half duplex CSMA/CD

IEEE 802.3z Gigabit Ethernet Upper Layers Logical Link Control (LLC) MAC Reconciliation MII GMII: Gigabit Media Independent Interface PMA: Physical Media Attachment PMD: Physical Media Dependent Reconciliation: Mapping between: Physical layer signaling primitives & Signals on GMII Reconciliation GMII PCS PCS PMA PMA PMD PMD Medium Medium 100Mbps 1000Mbps

Frame Formats IEEE 802.3 frame format 7 octets 7 octets Preamble 1 octet Start-of-Frame Delimiter 6 octets Destination Address Source Address 2 octets Length/Type Start-of-Frame Delimiter Destination Address 6 octets Source Address 2 octets Length/Type 46-1500 octets 4 octets Data... Frame Check Sequence Preamble......... 4 octets Data 1 octet 6 octets 6 octets 46-1500 octets Gigabit Ethernet frame format Data Link Layer Encapsulation Page 48 Frame Check Sequence 1 octet.. Extension.. 0-448 octets

Problems with Gigabit Ethernet In half-duplex mode, the physical extension would - without further measures - be less than 20 meters reason: dependence between minimum sized frames, speed and physical extension The minimum CSMA/CD carrier time and the Ethernet slot time have been extended to 512 bytes. Packets 512 bytes are not modified Packets < 512 bytes have a carrier extension field following the CRC field

Frame with Extension Field Packets smaller than 512 Byte will be extended with an additional field: Destination A d d r e s s (6 Byte) S o u r c e A d d r e s s (6 Byte) T y p e / L e n g t h (2 D a t a F C S (4 B y te ) Byte) 512 Byte E x te n s io n

Packet Bursting Mechanism to improve the performance of the small sized packets: Packet Bursting the devices are allowed to send some small packets together but a burst limit is defined too: one transmission of a station must not be longer than 65,536 bit times Frame Inter-Frame-Gaps 1 Extension 5 1 2 B y te Frame 2 Frame 3 Frame n

VLANs (Virtual Local Area Network) R o u te r Switch H Switch H H H Switch H H H H H H: H H H VLAN A VLAN B VLAN C Host

Benefits of VLANs facilitating network administration allowing formation of work groups enhancing network security providing a means of limiting broadcast domains

VLAN Standards IEEE 802.3ac (1998) defines frame format extensions to support Virtual Local Area Network (VLAN) Tagging on Ethernet networks. IEEE 802.1Q defines the general VLAN protocol.

VLAN Tag The VLAN protocol permits the insertion of an identifier, or "tag", into the Ethernet frame format to identify the VLAN to which the frame belongs. It allows frames from stations to be assigned to logical groups. Destination A d d r e s s (6 Byte) S o u r c e A d d r e s s (6 Byte) Length/ T y p e 8 0 2. 1 Q Ta g Type (2 Byte) 0x8100 Ta g Control Information (2 Byte) Length/ T y p e (2 Byte) D a t a F C S (46-1500 Byte) (4 B y te )

FDDI (Fiber Distributed Data Interface) 100Mbps bandwidth up to 500 stations in one network up to 60km between two stations total length 200km guaranteed waiting time Redundancy in topology

FDDI Summary fixed 125Mbps 4b/5b coded signals timed token rotation used for bandwidth sharing frame size 3...4500 bytes topology: dual ring of trees big-endian bit order offers synchronous and asynchronous transmissions stations have station-management duties

FDDI Topology tre e D u a l R in g Ring with Trees

FDDI Stations D A S D A S p r im a r y r in g B r in g A da ry B A se co n Page 61 A B M M D A C S S A S S S A S DAS: DAC: SAS: A: B: M: S: Dual Attachment Station Dual Attachment Concentrator Single Attachment Station Primary Port Secondary Port Master Port Slave Port

Wrapped Ring primary ring secondary ring Dual Ring Wrapped Ring

FDDI Frame S ta r tin g Delimiter F r a m e Control ( 2 s y m b o ls ) (2 symbols) C L F F Destination Address (12 Z Type symbols) Z of Frame Length of Address 0=16bits, 1=48bits Class of Service 0=asynchronous, Z 1=synchronous Source Address (12 Z symbols) Information (<= 8956) Ending Delimiter F r a m e Status (1 symbol) (3 symbols) Error Detected Address Recognized F r a m e Copied (1 symbol) (1 symbol) (1 symbol)

Access Method

FDDI Access Method There are 2 types of transfers: synchronous and asynchronous Synchronous transfers can be done whenever the station gets the token; was never really used Asynchronous traffic can be started whenever the station gets a token that is not late The last frame is always allowed to complete The token is immediately released after transmission The transmitting station removes its own data

Token Release Methods S F r a m e To k e n S To k e n Wasted Immediate Release Time Delayed Release F r a m e

FDDI Error Detection a station suspects a fault in the ring it starts sending beacon frames every station that receives a beacon frame stops sending beacons if a station receives its own beacon everything is OK else the ring is broken right before the station the SMT takes action

FDDI Ring Wrapping and Hold A B C F E D wrapping results in partitions A B C F E D global hold maintains primary ring