The Ethernet Evolution The 180 Degree Turn (C) Herbert Haas 2005/03/11 1
“Use common sense in routing cable. Avoid wrapping coax around sources of strong electric or magnetic fields. Do not wrap the cable around flourescent light ballasts or cyclotrons, for example.” Ethernet Headstart Product, Information and Installation Guide, Bell Technologies, pg.
History: Initial Idea Shared media CSMA/CD as access algorithm COAX Cables Half duplex communication Low latency No networking nodes (except repeaters) One collision domain and also one broadcast domain 10 Mbit/s shared by 5 hosts 2 Mbit/s each !!! (C) Herbert Haas 2005/03/11 3 The initial idea of Ethernet was completely different than what is used today under the term "Ethernet".
History: Multiport Repeaters Demand for structured cabling (voice-grade twisted-pair) 10BaseT (Cat3, Cat4, ...) Multiport repeater ("Hub") created Still one collision domain ("CSMA/CD in a box") (C) Herbert Haas 2005/03/11 4 Later, Ethernet devices supporting structured cabling were created in order to reuse the voice-grade twisted-pair cables already installed in buildings. 10BaseT had been specified to support Cat3 cables (voice grade) or better, for example Cat4 (and today Cat5, Cat6, and Cat7).
History: Bridges Store and forwarding according destination MAC address Separated collision domains Improved network performance Still one broadcast domain Three collision domains in this example ! (C) Herbert Haas 2005/03/11 5 Bridges were invented for performance reasons. It seemed to be impractical that each additional station reduces the average per-station bandwidth by 1/n.
History: Switches Switch = Multiport Bridges with HW acceleration Full duplex Collision-free Ethernet No CSMA/CD necessary anymore Different data rates at the same time supported Autonegotiation VLAN splits LAN into several broadcast domains 1000 Mbit/s Collision-free plug & play scalable Ethernet ! 100 Mbit/s 100 Mbit/s 10 Mbit/s (C) Herbert Haas 2005/03/11 6 Several vendors built advanced bridges, which are partly or fully implemented in hardware.
Today No collisions no distance limitations ! Gigabit Ethernet becomes WAN technology ! Over 100 km link span already Combine several links to "Etherchannels" Acts as single link from the spanning-tree view • Cisco: Port Aggregation Protocol (PAgP) • IEEE 802.1ad: Link Aggregation Control Protocol (LACP) 1 Gbit/s or even 10 Gbit/s long reach connection !!! (C) Herbert Haas 2005/03/11 7 Today, Gigabit and even 10 Gigabit Ethernet is available.
What About Gigabit Hubs? Would limit network diameter to 2025 meters (Gigabit Ethernet) Solutions Frame Bursting Carrier Extension No GE-Hubs available on the market today forget it! No CSMA/CD defined for 10GE (!) (C) Herbert Haas 2005/03/11 8 Remember: Hubs simulate a half-duplex coaxial cable inside, hence limiting the total network diameter. For Gigabit Ethernet this limitation would be about 25 meters, which is rather impracticable for professional usage.
MAC Control Frames Additional functionality easily integrated Currently only Pause-Frame supported Always 64 bytes 8 bytes 6 preamble DA 6 SA 2 2 8808h MAC-ctrl opcode 44 MAC-ctrl parameters 4 FCS MAC-ctrl opcode ........... Defines function of control frame MAC-ctrl parameters ....
Auto Negotiation Enables each two Ethernet devices to exchange information about their capabilities Signal rate, CSMA/CD, half- or full-duplex Using Link-Integrity-Test-Pulse-Sequence Normal-Link-Pulse (NLP) technique is used in 10BaseT to check the link state (green LED) 10 Mbit/s LAN devices send every 16.
Fast Link Pulses Modern Ethernet NICs send bursts of Fast-Link-Pulses (FLP) consisting of 17-33 NLPs for Autonegotiation signalling Each representing a 16 bit word GE sends several "pages" (C) Herbert Haas 2005/03/11 11 A series of FLPs constitute an autonegotiation frame. The whole frame consists of 33 timeslots, where each odd numbered timeslot consists of a real NLP and each even timeslot is either a NLP or empty, representing 1 or 0. Thus, each FLP sequence consists of a 16 bit word.
100 Mbit Ethernet Overview IEEE 802.3u Signaling Schemes Fast Ethernet 100BaseX Signaling 100BaseFX 100BaseTX "100BaseT" (C) Herbert Haas 2005/03/11 IEEE 802.12 Demand Priority Fast Ethernet 100Base4T+ Signaling 100BaseT4 (half duplex) 100VG-AnyLAN HP and AT&T invention for real time applications 12 The diagram above gives an overview of 100 Mbit/s Ethernet technologies, which are differentiated into IEEE 802.3u and IEEE 802.12 standards. The IEEE 802.
4B/5B Coding MII 0 4 x 25 Mbit/s 0 0 16 code groups 1 PCS 4B/5B Encoder/Decoder 0 125 MBaud (C) Herbert Haas 1 0 0 32 code groups 1 PMA 13 2005/03/11 The diagram above shows the basic principle of the 4B5B block coding principle, which is used by 802.3u and also by FDDI. The basic idea is to transform any arbitrary 4 bit word into a (relatively) balanced 5 bit word. This is done by a fast table lookup.
Gigabit Ethernet Media Access Control (MAC) Gigabit Media Independent Interface (GMII) 1000Base-X 8B/10B encoder/decoder 1000Base-LX LWL Fiber Optic 1000Base-SX SWL Fiber Optic 1000Base-T encoder/decoder 1000Base-CX Shielded Balanced Copper IEEE 802.3z physical layer (C) Herbert Haas 2005/03/11 1000Base-T UTP Cat 5e IEEE 802.3ab physical layer 14 Gigabit Ethernet has been defined in March 1996 by the working group IEEE 802.3z.
GE Signaling IEEE 802.3 Ethernet IEEE 802.3z Gigabit Ethernet ANSI X3T11 Fibre Channel 802.2 LLC IEEE 802.2 LLC FC-4 upper layer mapping CSMA/CD or full duplex MAC Reconciliation Sublayer FC-3 common services 802.3 CSMA/CD 802.
GE 8B/10B Coding GMII 1 256 code groups 1 1 1 1 1 1 Only used by 1000BaseX 1 8 x 125 Mbit/s PCS 1024 code groups 8B/10B Encoder/Decoder 125 million code groups per second 1 1250 Mbaud (C) Herbert Haas 1 1 1 1 1 1 1 1 1 PMA 2005/03/11 16 8B10B block coding is very similar to 4B5B block coding but allows fully balanced 10-bit codewords. Actually, there are not enough balanced 10-bit codewords available.
1000BaseX Two different wavelengths supported Full duplex only 1000Base-SX: short wave, 850 nm MMF 1000Base-LX: long wave, 1300 nm MMF or SMF 1000Base-CX: Twinax Cable (high quality 150 Ohm balanced shielded copper cable) About 25 m distance limit, DB-9 or the newer HSSDC connector (C) Herbert Haas 2005/03/11 17 Gigabit Ethernet can be transmitted over various types of fiber. Currently (at least) two types are specified, short and long wave transmissions, using 850 nm and 1300 nm respectively.
1000BaseT Defined by 802.3ab task force UTP Uses all 4 line pairs simultaneously for duplex transmission! (echo cancellation) 5 level PAM coding • 4 levels encode 2 bits + extra level used for Forward Error Correction (FEC) Signal rate: 4 x 125 Mbaud = 4 x 250Mbit/s data rate • Cat.
Several Physical Media Supported 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 PMD PMD MDI MDI MDI Medium Medium Medium 100 Mbit/s 1000 Mbit/s AUI PMA (MAU) MDI Medium 1-10 Mbit/s 10 Mbit/s PHY AUI Attachment Unit Interface, PLS Physical Layer Signaling, MDI Medium Dependent Interface PCS Physical Coding Sublayer, MII Media Independent Interface, G
10 Gigabit Ethernet / IEEE 802.3ae Only optical support 850nm (MM) / 1310nm /1550 nm (SM only) No copper PHY anymore ! Different implementations at the moment – standardization not finished! 8B/10B (IBM), SONET/SDH support, … XAUI ("Zowie") instead of GMII (C) Herbert Haas 2005/03/11 20 10 GE only supports optical links.
Note GE and 10GE use synchronous physical sublayer !!! Recommendation: Don't use GE over copper wires Radiation/EMI Grounding problems High BER Thick cable bundles (especially Cat-7) (C) Herbert Haas 2005/03/11 21 Both GE and 10GE are synchronous physical technologies on fiber. It not recommended to use GE over copper wires anymore although 802.3ab would specify it.
Summary Ethernet evolved in the opposite direction: Collision free WAN qualified Switched Several coding styles Complex PHY architecture Plug & play through autonegotiation Much simpler than ATM but no BISDN solution – might change! (C) Herbert Haas 2005/03/11 22 22
Quizz Why tends high-speed Ethernet to synchronous PHY? Can I attach a 100 Mbit/s port to a 1000 Mbit/s port via fiber? What is the idea of Etherchannels? (Maximum bit rate, difference to multiple parallel links) (C) Herbert Haas 2005/03/11 23 23
Hints Q1: On fiber its difficult to deal with asynchronous transmission, photons cannot be buffered easily, store and forward problems Q2: No, autonegotiation on fiber does not care for data rates Q3: "normal" parallel links would be disabled by STP, Etherchannel supports up to 8 links (C) Herbert Haas 2005/03/11 24 24
