Accademia Navale Armi Navali LAUREA in INGEGNERIA DELLE TELECOMUNICAZIONI RETI DI TELECOMUNICAZIONI Stefano Giordano Lezione n.18n Ethernet Gruppo di Ricerca in Reti di Telecomunicazioni Dipartimento di Ingegneria della Informazione: Elettronica, Informatica, Telecomunicazioni 1
Ethernet dominant LAN technology: cheap $5 for 100Mbs! first widely used LAN technology Simpler, cheaper than token LANs and ATM-LANs Kept up with speed race: 10, 100, 1000, 10000 Mbps Metcalfe s Ethernet sketch Connection-less, best-effort, unreliable service 2
Ethernet and IEEE 802.3 1976: ethernet developed by Xerox Palo Alto Research Center, including Bob Metcalfe (who later founded 3Com) 1980: 10Mbps ethernet specification by DEC, Intel, and Xerox 1985: becomes IEEE 802.3 standard (already widely used before this time) 1995: 100Mbps Fast Ethernet standardized in IEEE 802.3u (already widely used before this time) 1998: 1Gbps Gigabit Ethernet IEEE standard issued 1999: 10Gbps ethernet under development 2002: 10Gbps products available
3Com ATM 0.5% 1979 Altro 0.2% Ethernet 99.3% 1973 3C107 Bob Metcalfe Bob Metcalfe inventa Ethernet nel 1973 Bob Metcalfe fonda 3Com il 4 Giugno 1979 4
Products timetable 1972 Bob Metcalfe inventa Ethernet 3Com fondata nel 1979 3Com Mar 94 Small Business Solution OC nel 1996 NBX introdotto 1999 Wireless Set 99 330.000.000 Ethernet connection shipped 400.000 Telefoni spediti 3Com Switch 7700 core enterprise Secure Switch 6200 launched 1972 1982 1992 1996 1999 2000 2002 2003 Ethernet patented #4063220 13 Dec 1977 1 st Tran sceiver 1982 3Com Introduce SuperStack line 1995 Stackable GbE Embedded Firewall Security launched Network Jack introduced Joint venture announced Con Router 5000 launched 1 mo Stackable Ethernet Hub 1992 Shipped 1.000.000 th 10/100 Managed Switch VCX for enterprise VoIP solutions announced 5
La più diffusa rete locale al mondo Più del 99 % delle reti aziendali utilizzano la tecnologia Ethernet Ogni anno vengono vendute >100 milioni di schede Ethernet 6
Ethernet Media Types Coaxial Cable - Thick and Thin Unshielded Twisted Pair Optical Fiber 7
10Base5 Thick Coax 10 Mbit/s Trasmissione in Banda Base 500 metri max per segmento tap: drill a small hole in cable and insert, cable doesn t need to be cut, but must use care to avoid a short transceiver: send/receive, collision detection, electronics isolation AUI: Attachment Unit Interface, a 5-pair cable up to 50 meters long use: backbone networks, long cable segments maximum segment length = 500m maximum number of stations per segment = 100 0.5-inch Coax vampire tap RG-8 or RG-213 transceiver Repeater AUI cable distance between stations must be a multiple of 2.5 m maximum network distance between two stations = 2.5km NIC Terminator: 50Ω
Covered by CRC Ethernet Overview CSMA/CD carrier sense multiple access collision detection Manchester Encoding Frame Format Ethernet V. 2.0 or Ethernet II Type: Demux Key IP 0800x CRC: checked at receiver, if error is detected, the frame is simply dropped In bits 64 48 48 16 46 L 1500 byte 32 Preamble Dest addr Src addr Type Body CRC 9
Manchester Encoding 10
IEEE 802.3 Frame Format Demux Key IP 06x LLC PDU 8 8 8 or 16 Dest SAP Src SAP Control Payload 0-42B PAD 56 48 48 16 32 Preamble SFD Dest addr Src addr IEEE 802.3 Length Body 46 L 1500 byte CRC Preamble: Covered by CRC 7 bytes with pattern 10101010 followed by one byte with pattern 10101011 used to synchronize receiver, sender clock rates 11
Ethernet and 802.3 Frame Format Hardware or Physical or MAC Addresses Bytes: 7 1 6 6 2 46 to 1500 4 01010101... SOH dest addr src addr length data FCS 7sync bytes Source and destination addresses Data, padded to at least 46 B 32-bit CRC In Ethernet: 01010101 In IEEE 802.3: 01010111 Type field in Ethernet (Type > 1500). Length of data in IEEE 802.3 (Length at most 1500). Organizationally Unique Identifiers; standards.ieee.org/ regauth/oui/oui.txt usually written: broadcast: 6 byte ethernet addr 3Bytes vendor 3Bytes card no. 00:02:4b:c6:90:f1 ff:ff:ff:ff:ff:ff 1st bit: 0 = unicast address 1 = multicast (group) addr 2nd bit: 0 = globally unique addr 1 = locally assigned addr 2 46 =7x 10 13 global addresses 12
Framing Start of Frame End of Frame Preamble Dest addr Src addr Type Body CRC Preamble Dest addr Src addr Type Body CRC 10101011 Or 10101010 96 bits silence 9.6µsec at 10 Mbit/s Absence of signal (current) 13
10Base2 Thin Coax or CheaperNet tap: splice cable and attach BNC connectors, use T-connector to attach NIC No drop (AUI) cable use: for connecting workstations cheaper and easier to use than thick coax, but more signal attenuation, accidental opens 10 Mbit/s Trasmissione in Banda Base 185 200 metri max per segmento 0.25-inch coax (RG58) BNC T-connector NIC maximum segment length = 185m maximum number of stations per segment = 30 STUB minimum distance between two stations =0.5m maximum network distance between two stations = 925 m
10BaseT Twisted Pair uses 4-pair twisted pair cable (Category-3, -4, or -5) a hub functions as a repeater fewer cable problems, easier to troubleshoot than coax cable length at most 100 meters due to high attenuation (with good Category-5 cable you can go longer) most commonly used cable today maximum segment length = 100m hub
Twisted Pair Cabling Contact Signal 1 TD+ 2 TD- 3 RD+ 4 not used 5 not used 6 RD- 7 not used 8 not used 1 2. 8 16
Cable Categories Categories 1 and 2 low grade voice/data not suitable for LAN applications Category 3 Data transmission up to 10 Mbps Category 4 Data transmission up to 16 Mbps Category 5 Data transmission up to 100 Mbps Category 5e Full-duplex four-pair Fast Ethernet Category 6 250 Mbps Category 7 600 1200 MHz 17
Ethernet Topology 50 ohm terminator 10Base5 -Thick Ethernet repeater 10Base2 -Thin Ethernet 10Base5 -Thick Ethernet repeater hub 10BaseT-Twisted pair server AUI cables bus and star segment topologies multiple segments can be joined together
Ethernet 5-4-3 Rule Any two nodes on the network may be separated by up to: 5 segments 4 repeaters 3 collision segments Restriction: two thick coax segments may not be joined by a thin coax segment hub repeater 10Base2 -Thin Ethernet 10Base5 -Thick Ethernet servers
Transmit Algorithm If line is idle send immediately upper bound message size of 1500 bytes must wait 9.6µs between back-to-back frames If line is busy wait until idle and transmit immediately called 1-persistent (special case of p- persistent) 20
Back-off Algorithm If collision jam for 32 bits, then stop transmitting frame minimum frame is 64 bytes (header + 46 bytes of data) delay and try again 1st time: 0 or 51.2µs (51.2 µs [0 1]) 2nd time: 0, 51.2, 102.4 or 153.6µs (51.2 µs [0 3]) 3rd time 0, 51.2, 102.4, 153.6,..., 358.4 µs (51.2 µs [0 7])... nth time: k x 51.2µs, for uniformly selected k=0..2 n -1 Increase k for the first 10 tries; give up after 16 tries trunkated exponential binary back-off algorithm 21
Collision Detection Rules 1.Stations must listen to the cable while transmitting in order to detect a collision. 2.A frame must be at least 64 bytes (512 bits, 51.2 µsec) long to ensure sender hears a collision before he finishes. (The transmission time must be more than the RTT.) 3. If a collision is detected, send a 32 bit jamming signal and then wait before retransmitting. Jamming signal Jamming signal
Collision Detection: Worst case A begins to transmit at t=0 A A A A detects collision at t= 2 t prop -δ B B B It takes 2 t prop to find out if channel has been captured B begins to transmit at t= t prop -δ; B detects collision at t= t prop 23
Worst Case Collision Timing 500 meters 2,500 meters Assume delay for repeater is 1 µsec; for transceiver 0.5 µsec. Component Propagation Time Microsecs Five 500 meter segments 2500m/0.77c 10.8 Four repeaters 4 x 1 µsec 4.0 Nine 50 meter AUI cables 450m/0.65c 2.3 Ten transceivers 10 x 0.5 µsec 5.0 Total one-way time 22.1 24
Worst Case Collision Timing 500 meters 44.2 microsecond RTT Under these assumptions, the round trip time would be 44.2 microseconds. Allowing some tolerance for equipment, IEEE chose 51.2 microseconds, equal to 512 bit-times, as the collision detection interval. This is why all frames must be at least 512 bits (64 bytes) long. 25