Ethernet Standard. Campus Network Design. Ethernet address. OSI Model. Thana Hongsuwan

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1 Campus etwork Design Thana Hongsuwan Ethernet Standard 2003, Cisco Systems, Inc. All rights reserved , Cisco Systems, Inc. All rights reserved. BCMS v OSI Model Ethernet address Six bytes = 48 bits Flat address not hierarchical Burned into the IC ROM First three bytes from left specify the vendor. Cisco C, 3Com C and the last 24 bit should be created uniquely by the company Destination Address can be: Unicast: second digit from left is even (one recipient) Multicast: Second digit from left is odd (group of stations to receive the frame conferencing applications) Broadcast (ALL ones) (all stations receive the frame) Source address is always Unicast 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v

2 Ethernet address Ethernet address 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v Example Show how the address 47:20:1B:2E:08:EE is sent out on line. Solution The address is sent left-to-right, byte by byte; for each byte, it is sent right-to-left, bit by bit, as shown below: 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v

3 Example Ethernet Frame Format Define the type of the following destination addresses: a. 4A:30:10:21:10:1A b. 47:20:1B:2E:08:EE c. FF:FF:FF:FF:FF:FF Solution To find the type of the address, we need to look at the second hexadecimal digit from the left. If it is even, the address is unicast. If it is odd, the address is multicast. If all digits are F s, the address is broadcast. Therefore, we have the following: a. This is a unicast address because A in binary is b. This is a multicast address because 7 in binary is c. This is a broadcast address because all digits are F s. 2003, Cisco Systems, Inc. All rights reserved. BCMS v PA SFD DA SA LE LLC PDU Pad calculation of the FCS bytes PA : Preamble s for synchronization SFD : Start of Frame delimiter to start frame DA: Destination Address -- MAC address SA: Source Address -- MAC address LE: Length -- umber of data bytes Type: identify the higher -level protocol (> 0x0800 ; IPv4 = 0x0800) LLC PDU+pad -- minimum 46 bytes, maximum 1500 FCS : Frame Check Sequence -- CRC-32 Obligatory 9.6 ms interval between the emitted frame and the new one. To enable other stations wishing to transmit to take over at this time. IEEE PA DA SA Type Data Pad FCS Ethernet 2003, Cisco Systems, Inc. All rights reserved. BCMS v FCS Unreliable, connectionless service Ethernet CSMA/CD Connectionless: o handshaking between sending and receiving adapter. Unreliable: receiving adapter doesn t send acks or nacks to sending adapter stream of datagrams passed to network layer can have gaps gaps will be filled if app is using TCP otherwise, app will see the gaps 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v

4 Sending and receiving Ethernet frames on a bus nnnn Abbreviated MAC Addresses Sending and receiving Ethernet frames on a bus ope Hey, that s me! ope nnnn Abbreviated MAC Addresses When an Ethernet frame is sent out on the bus all devices on the bus receive it. What do they do with it? Each IC card compares its own MAC address with the Destination MAC Address. If it matches, it copies in the rest of the frame. If it does OT match, it ignores the rest of the frame. Unless you are running a Sniffer program 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v Sending and receiving Ethernet frames on a bus Sending and receiving Ethernet frames on a bus nnnn Abbreviated MAC Addresses nnnn Abbreviated MAC Addresses X So, what happens when multiple computers try to transmit at the same time? Collision! 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v

5 Carrier Sense Multiple Access Collision Carrier sense: station listens to media before transmitting Multiple access: multiple stations may access at same time Media idle? Media idle? ES Transmit immediately O -- wait Listen until the media is idle, then transmit More than one station may send a frame during overlapping times. How does a station know that a collision occurred? What does the station do after a collision? 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v Collision Detect Frame transmission Assemble frame carrier sense signal O? Wait interframe gap time Start trnasmission collision detected? transmission done? tranmit OK send jam sequence Increment attempt. attempt limited? Discard frame Compute backoff and wait backoff time 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v

6 Frame reception Binary Backoff delay= 2 start receiving send frame done receiving? Matched DA FCS and frame size OK? Discard frame 1 st wait 0 or 1 slot time 2 nd wait 0,1,2 or 3 slot time 3 rd wait 0,1,2,..7 slot time k th wait k slot time transmission done? tranmit OK collision detected? >16 attempts Discard frame random wait between 0 and delay-1 double delay Pass frame to next layer after 10th collisions the interval is frozen at 1023 slots after 16th collisions, frame is discarded and report failure back to the upper layer limited delay<1024 max delay is limited at 1023*51.2 µs=52.4 ms 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v Ethernet uses CSMA/CD Minimum frame size o slots adapter doesn t transmit if it senses that some other adapter is transmitting, that is, carrier sense transmitting adapter aborts when it senses that another adapter is transmitting, that is, collision detection Before attempting a retransmission, adapter waits a random time, that is, random access A and B locates at the far end of the cable A A (1) packet starts at time 0 (3) B send packet; collision occurs at t B B (2) packet almost at B at t (4) jam signal gets back to A at 2t A frame must take more than 2t to send to prevent the situation that the sender incorrect conclude that the frame was successfully sent. A A B B 5: DataLink Layer 5-23 v , Cisco Systems, Inc. All rights reserved. BCMS 2003, Cisco Systems, Inc. All rights reserved. BCMS v

7 Worst Case Collision Timing Worst Case Collision Timing (cont.) 500 meters 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 ine 50 meter AUI cables 450m/0.65c 2.3 ine transceivers 9 x 0.5 µsec 4.5 Total one-way time microsecond RTT Under these assumptions, the round trip time would be 43.2 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. 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v Collision Detection Rules Late Collision 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 brief jamming signal and then wait before retransmitting. Late collisions are collisions which occur after the first 64 bytes have been transmitted on to the network Primary causes: excessive cable lengths and repeaters Jamming signal Jamming signal More than two station may send a frame at overlapping times. How does a station know that a collision has occurred? What next? 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v

8 Faster Ethernet and Collision Detection Fast Ethernet and Collision Detection 100 Mbps v = 2 x 10 8 m/sec Max etwork Size How does the ethernet collision detection rule limit network size for 100Mbps and 1Gbps ethernet? The collision detection rule states that a sender must detect a collision before he finishes transmission. Using the ethernet minimum frame size of 512 bits, a signal propagation speed 2 x 10 8 m/sec (the speed in fiber or UTP), and assuming no hubs or repeaters (which would add a delay), what is the maximum network size? For Fast Ethernet, without any repeater delay: TransmissionTime = 512 bit /10 9 bps = 5.12 x 10-6 sec Max Round Trip = TransmissionTime x PropagationSpeed = (5.12 x 10-6 sec) x (2 x 10 8 m/sec) = 1024 m Max etwork Diameter = 0.5 x Max Round Trip = 512 m Clearly, the 10 Mbps ethernet diameter (2.5 km) must be reduced for collision detection on fast ethernet! 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v Gigabit Ethernet and Collision Detection Ethernet Speed and Collision Detection 1000 Mbps For Gigabit Ethernet: v = 2 x 10 8 m/sec TransmissionTime = 512 bit /10 10 bps = x 10-6 sec Max Round Trip = TransmissionTime x PropagationSpeed = (0.512 x 10-6 sec) x (2 x 10 8 m/sec) = m Max etwork Diameter = 0.5 x Max Round Trip = 51.2 m Who would buy a network that can only span 51 meters? Max etwork Size So, without any delay due to repeaters or network interfaces, the largest network size in a shared media configuration is: Ethernet Minimum Min Frame Upper Bound Speed Frame Size TX Time on etwork Size 10 Mbps 64 byte 51.2 µsec 5,120 m 100 Mbps 64 byte 5.12 µsec 512 m 1 Gbps 64 byte µsec 51 m ext we will see how the fast and gigabit ethernet standards address these limits. 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v

9 100Mbps Introduction 100BaseTX (UTP) Fast Ethernet IEEE 802.3u Formal Spec July Mbps over Cat 5 UTP/STP/Fiber. Cat 5 UTP = Category 5 Unshielded twisted pair. Up to 125MHz signaling. Star wired using Switches & Hubs. 100Base-TX Unchanged Frame/MAC Protocols. 100 meters hub 5 meters 100 meter maximum cable length using Category-5 UTP or STP up to 2 class A hubs, with a maximum 5 m. between hubs, or one class B hub maximum network diameter is 205 meters a standard for Category-3 UTP using all 4-pairs called 100BaseT4 also exists, but is rarely used Hubs: may support autosensing of 10 Mbps or 100 Mbps links using fast link pulses, and autonegotiation of speed hub 100 meters 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v BaseFX (Fiber Optic) 1,000Mbps Introduction. host or switch uses 62.5/125 multimode fiber and an 850 nm LED source Two configurations: hub 400 meters 300 meters 400 meter maximum direct station-to-station connection; a station can be a host or a switch 300 meter maximum network diameter with 1 hub ote: more complicated configurations are possible using switches with either UTP or fiber optic cable host or switch Gigabit Ethernet IEEE 802.3z. Formal Spec June ,000 Over Cat 5e (802.3ab) /Fiber Only. Star wired using Switches & Hubs. 1000Base-T Unchanged Frame/MAC Protocols. 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v

10 Gigabit Ethernet Collision Detection on Gigabit Ethernet same frame format, media access, and collision detection rules as previous ethernet generations same 64 byte minimum frame and 96 bit interframe gap can combine 10 Mbps, 100 Mbps, and gigabit ethernet on same network (but not on same cable) using a switch 200 meter network diameter (using UTP) requires a minimum transmission time of 512 bytes on shared media several media types: UTP, shielded copper short-wave fiber optics long-wave fiber optics Round Trip 200 meters Hub How long must a frame be for the sender to detect a worst case collision before he finishes transmission? Gigabit Ethernet allows a 200 meter network diameter over UTP. Assuming a 0.5 µsec delay in the hub, the signal RTT is RTT = 400m/0.65c + 2 x 0.5 µsec = 3.05 µsec So the transmission length must be at least 1 Gbps x 3.05 µsec = 3050 bits How can we maintain collision detection and 64 byte frame standard? 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v Carrier Extension and Frame Bursting Standards Frame Frame Frame Frame pad Frame bursting Minimum 4096 bits Carrier extension Gigabit ethernet transmissions must be at least 4096 bit-times long for collision detection, but minimum frame length is still only 64 bytes. On a shared access segment, sender must pad short frames with a special signal to 4096 bits, called carrier extension. Frame bursting: if sender has several short frames, he can send them back-to-back (no interframe gap) to minimize carrier extension. On a dedicated segment (host connected to a switch), carrier extension and frame bursting are not required. Why? IEEE 802.3z standard 1000 BASE-LX 1000 BASE-SX 1000 BASE-CX 1000 BASE-T Two standards of MMF or SMF fiber 1000 Mbps CSMS/ CD MAC Optional GMII Layer Two standards of MMF Two pairs of twinax IEEE 802.3ab standard Four pairs of cat 5 UTP or better 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v

11 Gigabit Ethernet Media Types 1000Mbps And beyond 1000baseLX 1300 nm laser 9 micron single mode fiber 50 or 62.5 micron multimode fiber MHz modal bandwidth 550 m 5 km 10GBps is already issued. IEEE 802.3ae 1000baseSX 850 nm LED 1000baseT 1000baseCX 50 micron multimode 500 MHz modal bandwidth 50 micron multimode 400 MHz modal bandwidth 62.5 micron multimode 200 MHz modal bandwidth 62.5 micron multimode 160 MHz modal bandwidth 4 pair Cat-5 UTP Copper STP 25 m 100 m 220 m 275 m 500 m 550 m 40 KM length. WA Enabled Protocol: FDX only, CSMA/CD off Distance 100m, 300m over MMF 2Km, 10Km, 40Km over SMF 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v Standard IEEE 802.1D Series IEEE 802: Overview and Architecture IEEE 802.1B Management IEEE 802.1D MAC Bridges IEEE 802.1E System Load Protocol IEEE 802.1F Common Definition for Management IEEE 802.1G Remote MAC Bridging IEEE 802.1H Bridging of Ethernet IEEE 802.1Q Virtual Bridged LAs IEEE 802.1X Port Based etwork Access Control 802.1D-1990 MAC Bridges Superseded by 802.1D i-1995 FDDI bridging (see ASI X3T9.5) Superseded 802.1j-1996 Managed objects for MAC Bridges Superseded by 802.1D P802.1p Traffic Class Expediting and Dynamic Merged into 802.1D-1998 Multicast Filtering 802.1D-1998 P802.1r MAC Bridges (rollup of 802.1D-1990, 802.1j, 802.6k, P802.12e and P802.1p) GARP Proprietary Attribute Registration Protocol (GPRP) Superseded by 802.1D Withdrawn 802.1t-2001 Technical and Editorial corrections for Incorporated into 802.1D D w-2001 Rapid Reconfiguration of Spanning Incorporated into 802.1D- Tree 2004 P802.1y Maintenance to 802.1D-1998 Merged into 802.1D , Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v

12 802.3 Standard Encapsulation Ethernet Standard Date Description Experimental Ethernet Mbit/s (367 kb/s) over coaxial cable (coax) bus 10 Mbit/s (1.25 MB/s) over thick coax. Frames have a Type field. This frame format is Ethernet II 1982 used on all forms of Ethernet by protocols in the Internet protocol suite. IEEE standard BASE5 10 Mbit/s (1.25 MB/s) over thick coax. Same as Ethernet II (above) except Type field is replaced by Length, 802.3a BASE2 10 Mbit/s (1.25 MB/s) over thin Coax (a.k.a. thinnet or cheapernet) 802.3e BASE5 or StarLA 802.3i BASE-T 10 Mbit/s (1.25 MB/s) over twisted pair 802.3j BASE-F 10 Mbit/s (1.25 MB/s) over Fiber-Optic 802.3u BASE-TX, 100BASE-T4, 100BASE-FX Fast Ethernet at 100 Mbit/s (12.5 MB/s) w/autonegotiation 802.3z BASE-X Gbit/s Ethernet over Fiber-Optic at 1 Gbit/s (125 MB/s) 802.3ab BASE-T Gbit/s Ethernet over twisted pair at 1 Gbit/s (125 MB/s) 802.3ad 2000 Link aggregation for parallel links, since moved to IEEE 802.1AX 802.3ae Gigabit Ethernet over fiber; 10GBASE-SR, 10GBASE-LR, 10GBASE-ER, 10GBASE- SW, 10GBASE-LW, 10GBASE-EW 802.3af 2003 Power over Ethernet (15.4 W) 802.3an GBASE-T 10 Gbit/s (1,250 MB/s) Ethernet over unshielded twisted pair (UTP) 802.3aq GBASE-LRM 10 Gbit/s (1,250 MB/s) Ethernet over multimode fiber 2003, Cisco Systems, Inc. All rights reserved. BCMS v , Cisco Systems, Inc. All rights reserved. BCMS v Encapsulation 2003, Cisco Systems, Inc. All rights reserved. BCMS v