computer repair in seattle
Call 206-335-5011 PC Repair ~ Upgrades ~ Systems ~ Network ~ Services & Rates ~ Contact Us
computer repair
computer repair in seattle

seattle

 

 
  

Local area networks page

General information

Typical networks today use two different addressing mechanisms on top of each other - and addressing is a necessity for data exchange between any two networked machines. The lowest level addressing is the MAC acess (aka ethernet addresses, hardware addresses). The MAC addresses are used for addressing within a single LAN. MAC addresses are programmed into the hardware (typically network adapters), Every Ethernet card has an unique MAC address (it is possible to change MAC on most adapters it's possible, but not advisable except in special circumstances).

The next address level are IP (Internet Protocol) addresses. These are in the form of "192.168.105.1" (four dot-separated numbers). An IP address is not programmed into hardware, but is set by software to either a fixed value for a machine, or can be queried from a server somewhere in the local LAN.

Also other addresses can be used if other protocols than IP are run on the LAN system. Some other protocols which are used sometimes in LANs are IPX, NetBIOS, DECnet, Banyan, etc.

  • Bridging and Switching Basics - Bridges and switches are data communications devices that operate principally at Layer 2 of the OSI reference model. As such, they are widely referred to as data link layer devices.
  • Connection Architectures (Client/Server, Host/Terminal, etc.)
  • Home networking overview by Microsoft
  • Home Networking Tutorial
  • How LAN Switches Work - This document covers the general concept of how LAN switches work and the most common features available on a LAN switch. It also covers the differences between bridging, switching, and routing.
  • Introduction to LAN Protocols - This document introduces the various media-access methods, transmission methods, topologies, and devices used in a local-area network (LAN). Topics addressed focus on the methods and devices used in Ethernet/IEEE 802.3, Token Ring/IEEE 802.5, and Fiber Distributed Data Interface (FDDI).
  • LAN Mail Protocols Summary
  • Logical Link Control IEEE 802.2 - The IEEE 802.2 standards for Logical Link Control define a programming interface between that part of the communications software that controls the network interface card (the Media Access Control and Physical Medium Dependent components) and the overlying protocol stack (IP, NetBIOS, NetWare, etc.). The connection between the network interface card and the rest of the communications system is through a structure called a Service Access Point. The SAP differentiates between communications protocols; there's a SAP for NetBIOS, another for SNA, another for NetWare, and so on. A programmer can select Type 2 Logical Link Control in which case the frames are given sequence numbers as they pass through the SAP and the 802.2 Logical Link Control layer at the receiver provides an acknowledgement for received frames. This creates a reliable data transfer mechanism at the Data Link Layer. Type 1 Logical Link Control simply provides the differentiation function, with no sequence and acknowledgement process.
  • Mixed-Media Bridging - Transparent bridges are found predominantly in Ethernet networks, and source-route bridges (SRBs) are found almost exclusively in Token Ring networks. Both transparent bridges and SRBs are popular, so it is reasonable to ask whether a method exists to directly bridge between them. Several solutions have evolved.
  • Source-Route Bridging (SRB) - means to bridge Token Ring LANs
  • Transparent Bridging - background, switching loops, spanning three algorithm

LAN cabling

Ethernet

Ethernet is a type of network cabling and signaling specifications (OSI Model layers 1 [physical] and 2 [data link]). Ethernet is alocal-area network (LAN) architecture developed by Xerox Corporation in cooperation with DEC and Intel in 1976. Ethernet uses a bus or star topology and supports data transfer rates of 10 Mbps. The Ethernet specification served as the basis for the IEEE 802.3 standard, which specifies the physical and lower software layers. Ethernet uses the CSMA/CD access method to handle simultaneous demands. It is one of the most widely implemented LAN standards. Ethernet uses the CSMA/CD access method to handle simultaneous demands. It is one of the most widely implemented LAN standards. A newer version of Ethernet, called 100Base-T (or Fast Ethernet), supports data transfer rates of 100 Mbps. And there are even newer ones for 1 Gbps and emergin one comign for 10 Gbps.

Ethernet has been a relatively inexpensive, reasonably fast, and very popular LAN technology for several decades. Two individuals at Xerox PARC -- Bob Metcalfe and D.R. Boggs -- developed Ethernet beginning in 1972 and specifications based on this work appeared in IEEE 802.3 in 1980. Ethernet specifications define low-level data transmission protocols and the technology needed to support them. In the OSI model, Ethernet technology exists at the physical and data link layers (layers 1 and 2).

From the time of the first Ethernet standard, the specifications and the rights to build Ethernet technology have been made easily available to anyone. This openness, combined with the ease of use and robustness of the Ethernet system, resulted in a large Ethernet market and is another reason Ethernet is so widely implemented in the computer industry. Most LANs must support a wide variety of computers purchased from different vendors, which requires a high degree of network interoperability of the sort that Ethernet provides.

Ethernet started as a 10 Mbit/s half-duplex networking technique which used a single coaxial cable as the communication medium. Ethernet has evolved from that to faster and more modern networking technique. Nowadays Ethernet most typically travels over twisted pair wiring or over fiber optic cabling. The typical physical Ethernet network structures are point-to-point links and star network with a HUB in the venter of the star. The speed of Ethernet has been updated from 10 Mbit/s to higher speeds like 100 Mbit/s, 1 Gbit/s and 10 Gbit/s.

Ethernet a "broadcast" network. This means that each device connected to the network listens for traffic on the network and then sends its "packets" when the line is quiet. Packets contain sequences of binary information and packet size is usually determined by the application that is running and the type of information that is being transmitted. Packet sizes can range from 64 to 1518 bytes. Typical packet sizes are 512 and 1024 bytes. In addition to the data being transmitted, each packet also contains source, destination, and parity (bit error detection) information. Errors occur when packets do not reach their destination or information is dropped from the data sequence.

Common types of errors that may be associated with full network utilization and/or noise disturbances in Ethenet network are:

  • Alignment: Packets do not end on an 8-bit boundary. This is typically caused by noise or broken equipment.
  • Collision: Two devices detect that the network is idle and try to send packets at exactly the same time. Collision errors are common in Ethernet systems and are expected as network utilization increases. Upon receipt of this error type, both devices hold, wait a "randomly" calculated amount of time (to avoid a second collision), and attempt to re-transmit. This is normal operation of (half duplex) Ethernet system.
  • Cyclic Redundancy Check (CRC): Packet size is correct, but the information contained in the frame check sequence (FCS) is corrupt.
  • Fragment: Packet is undersized and contains corrupt FCS.
  • Jabber: Packet is oversized and contains corrupt FCS.
  • Runt/Pygmy: Packets are less than 64 bytes in length.

Depending upon the severity of the error, the network may ignore packets, re-transmit packets or, the network may halt or 'crash’ because the error causes all devices to appear busy.

Ethernet has also evolved from half-duplex bus systems a switched full-duplex networking technique. Ethernet physical connectors provide circuits including the receive (RX), transmit (TX), and collision detection. When half duplex Ethernet is implemented, the TX circuit is always active at the transmitting station. When another station is transmitting, the station's RX circuit is always active. This is referred to as Shared Bandwidth. Standard Ethernet configuration efficiency is typically rated at 50-60 percent of the 10/100Mbps bandwidth.

Full duplex Ethernet Switching provides a transmit-circuit connection wired directly to the receiver circuit at the other end of the connection. This two station connected environment creates a collision free situation on the circuit. Recall half duplex Ethernet has to manage the conditions for multiple transmissions on the same physical wire as they cannot occur. Full-duplex operation is possible on networkign devices which use twisted pair or fiber wiring and support full-duplex operation. Full duplex Ethernet can operate at up to 100 percent efficiency in both directions. (100Mbps transmit, and 100Mbps receive.)

LAN switching is a technique that significantly improves Ethernet network performance without impacting the addressing structure within the network. Switching is defined as the ability to forward packets on the fly through a cross point matrix, a high speed bus, or shared memory arrangement. switch looks at the destination address of each incoming packet, and transmits the packet only on the port on which the destination node is located. Other ports on the switch can transmit or receive different packets at the same time. Beacially the idea of swiching has been in Ethernet world for a long time, but the availability of cheap switching devices has made it a mainstream technique (early two-port switches were known as "bridges").

The current Ethernet is standardized IEEE 802.3 standard. The current edition of IEEE Std. 802.3 is also published as ISO/IEC 8802-3:2000. All approved portions IEEE Std. 802.3 are approved and published at the international level.

Short history: Ethernet was originally developed by Xerox in the late 1970. A very rarely used 2.94 Mbps version came out of Xerox's Palo Alto Research Center (PARC) in the early 70s. In 1980, Digital Equipment Corporation (DEC), Intel and Xerox published the DIX V1.0 standard which boosted the speed of Ethernet to 10 Mbps while maintaining Ethernet's thick trunk cabling scheme. In 1980, Digital Equipment Corp. (DEC), Intel and Xerox (the origin of the term DIX, as in DEC/Intel/Xerox) began joint promotion of this baseband, CSMA/CD computer communications network over coaxial cabling, and published the "Blue Book Standard" for Ethernet Version 1. This standard was later enhanced and 1982 the enhanced DIX V2.0 specification was released. In 1985 Ethernet II specification based on DIX V2.0 was released. Xerox then relinquished its trademark. At the time of the first DIX standard, the Institute of Electrical and Electronic Engineers (IEEE) was attempting to develop open network standards through the 802 committee. In 1985 the IEEE 802.3 committee published "IEEE 802.3 Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications." This technology is called 802.3 CSMA/CD and not Ethernet; however, it is frequently referred to as Ethernet even though the frame definition differs from DIX V2.0. Although 802.3 and DIX frames can coexist on the same cable, interoperability is not assured. Therefore, when discussing "Ethernet," it is necessary to clarify 802.3 frames or DIX V2.0 frames.

Ethernet history timeline (mostly based on information at http://www.techfest.com/networking/lan/ethernet1.htm):

  • 1979: Digital Equipment Corporation (DEC), Intel, and Xerox joined for the purpose of standardizing an Ethernet system that any company could use
  • 1980: In September 1980 the three companies released Version 1.0 of the first Ethernet specification called the "Ethernet Blue Book", or "DIX standard" (after the initials of the three companies). It defined the "thick" Ethernet system (10Base5), based on a 10 Mb/s CSMA/CD (Carrier Sense Multiple Access with Collision Detection) protocol
  • 1982: The first Ethernet controller boards based on the DIX standard became available.
  • 1983: Institute of Electrical and Electronic Engineers (IEEE) released the first IEEE standard for Ethernet technology. It was developed by the 802.3 Working Group of the IEEE 802 Committee. The formal title of the standard was IEEE 802.3 Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications. IEEE reworked some portions of the DIX standard, especially in the area of the frame format definition. However the 802.3 standard was defined in a manner that permitted hardware based on the two standards to interoperate on the same Ethernet LAN.
  • 1985: IEEE 802.3a defined a second version of Ethernet called "thin" Ethernet, "cheapernet", or 10Base2. It used a thinner, cheaper coaxial cable that simplified the cabling of the network. Also IEEE 802.3b 10Broad36 standard that defined transmission of 10 Mb/s Ethernet over a "broadband" cable system.
  • 1987: The IEEE 802.3d standard defined the Fiber Optic Inter-Repeater Link (FOIRL) that used two fiber optic cables to extend the maximum distance between 10 Mb/s Ethernet repeaters to 1000 meters. IEEE 802.3e defined a "1 Mb/s" Ethernet standard based on twisted pair wiring (this was never widely used).
  • 1990: Introduction of the IEEE 802.3i 10Base-T standard. It permitted 10 Mb/s Ethernet to operate over simple Category 3 Unshielded Twisted Pair (UTP) cable. This led to a vast expansion in the use of Ethernet.
  • 1993: IEEE 802.3j standard for 10Base-F (FP, FB, & FL) was released which permitted attachment over longer distances (2000 meters) via two fiber optic cables. This standard updated and expanded the earlier FOIRL standard.
  • 1995: IEEE improved the performance of Ethernet technology by a factor of 10 when it released the 100 Mb/s 802.3u 100Base-T standard (commonly known as "Fast Ethernet").
  • 1997: IEEE 802.3x standard became available which defined "full-duplex" Ethernet operation. Full-Duplex Ethernet bypasses the normal CSMA/CD protocol to allow two stations to communicate over a point to point link.
  • 1998: IEEE once again improved the performance of Ethernet technology by a factor of 10 when it released the 1 Gb/s 802.3z 1000Base-X standard. This version of Ethernet is commonly known as "Gigabit Ethernet".
  • 1999: 802.3ab 1000Base-T standard defined 1 Gb/s operation over four pairs of category 5 UTP cabling
  • 2002: IEEE 802.3ae standard introduced 10 Gigabit Ethernet.
  • 2003: IEEE802.3af Draft Standard has been Completed to standardize Power Over Ethernet technology.

What is an 802.3 network? That's IEEE-ism for Ethernet, but with a few small differences. The physical layer specifications are identical (though DIX Ethernet never specified standards for UTP and Fiber-Optic media) and the MAC sublayer are somewhat different.

What is the difference between an Ethernet frame and an IEEE802.3 frame? Why is there a difference? Ethernet was invented at Xerox Palo Alto Research Center and later became an international standard. IEEE handled making it a standard; and their specifications are slightly different from the original Xerox ones. Hence, two different types. 802.3 uses the 802.2 LLC to distinguish among multiple clients, and has a "LENGTH" field where Ethernet has a 2-byte "TYPE" field to distinguish among multiple client protocols. TCP/IP and DECnet (and others) use Ethernet_II framing, which is that which Xerox/PARC originated.

What is a MAC address? MAC address is the unique hexadecimal serial number assigned to each Ethernet network device to identify it on the network. With Ethernet devices (as with most other network types), this address is permanently set at the time of manufacturer, though it can usually be changed through software (though this is generally a Very Bad Thing to do). The MAC addresses are exactly 6 bytes in length, and are usually written in hexadecimal as 12:34:56:78:90:AB. Each manufacturer of Ethernet devices applies for a certain range of MAC addresses they can use. The first three bytes of the address determine the manufacturer. RFC-1700 (available via FTP) lists some of the manufacturer-assigned MAC addresses.

To further confuse issues, standard Ethernet sometimes means an attached protocol- mainly TCP/IP. Ethernet only defines the data link and physical layers of the Open Systems Interconnect (OSI) Reference Model whereas TCP/IP defines the transport and network layers respectively of the same model.

Generation of the data sent to the network and the reception of it is generally done in the combination of software (Ethernet card driver) and hardware (Ethernet card Ethernet controller chip). The Ethernet packet preamble is normally generated by the chipset. Software is responsible for the destination address, source address, type, and data. The chips normally will append the frame check sequence.

Ethernet card is highly loaded with traffic when things start slowing down to the point they are no longer acceptable. There is not set percentage point, but you usually start paying attention over 40-50%, or when things slow down.

Most typical Ethernet wiring system in use nowadays is one which uses twisted pair wiring. In this system maximum cable distance of 330 feet (100m) between devices. However, the signal can be repeated by either an Ethernet hub or repeater, and this can be done up to 3 times.

    General

    Ethernet information web pages

    • Charles Spurgeon's Ethernet Page - extensive collection of information about Ethernet
    • Dan Kegel's Fast Ethernet Page - collection of pointers to WWW and FTP documents
    • Ethernet Network Interfaces - General information, component placement, signal layout, EMI filtering
    • Ethernet Papers and Reports
    • Ethertype values - a list of Ethertype values as would be found in Version 2 Ethernet or in the Type field of a SNAP header in an 802.2-compliant protocol like 802.3 or 802.5
    • Site Networking Guide - information on building and wiring Ethernet network using UTP cable

      Cabling and connectors

      Technical specs

      10Base-T information

      The "T" in 10BASE-T stands for "twisted" in reference to the twisted-pair wire used for this variety of Ethernet. This is nowadays the most commonly used Ethernet variety (thanks to the popularity of structured cabling systems which are based on twisted pair wiring). The specifications for the twisted-pair media system were published in 1990. This system has since become the most widely used medium for connections to the desktop. The 10BASE-T system was the first popular twisted-pair Ethernet system. The invention of 10BASE-T in the early 1990s led to the widespread adoption of Ethernet for desktop computers.

      10BASE-T system is designed to work with unshielded twisted pair wiring with impedance of 100 ohms + or - 15%. The maximun link length is speified to be 100 meters when using data grade cable (category 3 or better). The 10BASE-T system is designed to support the transmission of 10 Mbps Ethernet signals over "voice-grade" Category 3 twisted-pair cables. However, the vast majority of twisted-pair cabling systems in use today are based on Category 5 twisted-pair cables. Category 5 cables have higher quality signal carrying characteristics and work very well with the 10BASE-T system.

      The 10BASE-T system operates over two pairs of wires, one pair used for receive data signals and the other pair used for transmit data signals. The two wires in each pair must be twisted together for the entire length of the segment, a standard technique used to improve the signal carrying characteristics of a wire pair. Output signal level of a typical 10Base-T ethernet device is 2.2V to 2.8V (leads to around 2Vpp on each of the wires in the pair). The input signal level in the receiver end should be from 350mV (minimum signal level) to 2.8V (maximum ethernet card signal level).

      Signaling in 10BASE-T Ethernet is performed using Manchester phase encoding. In a "phase encoded" signal, the logic state (0 or 1) is indicated by the phase of the carrier signal, rather than by a fixed voltage level as in standard logic circuits. In "Manchester phase encoding" the data bit rate is the same as the base frequency of the master clock oscillator (10 MHz for standard 10BASE-T Ethernet). A data bit 0 in the level encoded signal is represented in the phase encoded signal by a full cycle of the original clock, while a data bit 1 is represented by a full cycle of the inverted clock. This encoding technique has the advantage that regardless of the data being transmitted, the encoded data have regular transitions, with a maximum time of one clock period between transitions.

      When this manchester code is sent ot the cable there are few signal tricks used to minimize the EMI problems and guarantee that the signal goes nicely through the cable:

      • Pre-distorion which equalizes the signal so that around 50 meters of cable (acts as lowe pass filter) makes signal back to original, so the signal distortions are not too large in any part of cable (either some pre-distortion or some cable filtering)
      • Signal is send differentially to cable and is well balanced (good noise cancelling and rediced emissions)
      • The signal is sent to the cable through a balancing transformer (safety and good common mode rejection characteristics)
      • Common mode filters are used in the input and output wires (redices conducted emissions)

      Generally 10Base-T ethernet cards use RJ-45 connector to do the connection to the twisted pair wiring (some early card coud have had options for other connectors also). The transmitted data from the Ethernet card leaves at the wire pair which connects to RJ-45 connector pins 1 (Tx+) and 2 (Tx-). The received data comes to the Ethernet card through a twisted pair which connects to the RJ-45 connector pins 3 (Rx-) and 6 (Rc-). 10Base-T ethernet card can be directly wired to s structured cabling system wired according EIA/TIA 568A/568B and/or AT&T 258A.

      10BASE-T is point-to-point technique, which means that one wire can only connect two devices (two computer directly or computer to a HUB). This wire and devices on the end of it form one Ethernet segment. Multiple twisted-pair segments communicate by way of a multiport hub.

      10BASE-T MAUs continually monitor the receive data path for activity as a means of checking that the link is working correctly. When the network is idle, the MAUs (network cards or transceivers) also send a link test signal to one another to verify link integrity. Vendors can optionally provide a link light on the MAU; if the link lights on both MAUs are lit when you connect a segment, then you have an indication that the segment is wired correctly. 10BaseT NICs uses a single normal link pulse (NLP) to perform a link integrity test. Typically an indicator LED on the NIC showes the status of the link. NLP pulses are typically generated every 16 ms when the transmitter is idle.

      Link LEDs are very useful intetwork faulfinding, but they are not foolproof. Please note that link LEDs do not always guarantee that the wire link work for real traffic. Since the link test pulse operates more slowly than actual Ethernet signals, the link lights are not always a guarantee that Ethernet signals will work over the segment

      • 10BASE-T Crossover Wiring - When connecting two twisted-pair MAUs (two network cards) together over a segment, the transmit data pins of one eight-pin connector must be wired to the receive data pins of the other, and vice versa. For a single segment connecting only two computers you can provide the signal crossover by building a special crossover cable.
      • 10-Mbps Twisted-Pair, Type 10BASE-T Introduction

      Thick Coaxial Ethernet

      The thick coaxial media (10BASE-5) system was the first media system specified in the original Ethernet standard of 1980. Thick coaxial segments are still sometimes installed as a backbone segment for interconnecting Ethernet hubs, since thick coaxial media provides a low-cost cable with good electrical shielding that can carry signals relatively long distances between hubs. Thick coaxial cable is limited to carrying 10-Mbps signals only. Thick coaxial segments can only be connected in the bus cable form of physical topology. The maximum lenght of the cable segment is 500 meters. The cable impedance is 50 ohms.

      Coaxial cable for use in 10BASE-5 is double-shielded 0.4 inch diameter RG8 coaxial cable (about the size of a garden hose). The cable is not flexible, and difficult to work with. The cable has a characteristic impedance of 50 ohms.

      Thick Ethernet coaxial cable bus must be terminated. The standard termination is 50 +/-2 ohms. The end connector on the RG-8 cable is an "N" type connector. The cable is externally terminated with a resistor inside an N connector. Proper termination is essential for the proper operation of the network, because missing or wring termination causes signal reflections and causes that the signal collision detection does not work properly.

      The standard notes that the thick coax segment should be grounded at one point for electrical safety reasons. There must only be only one grounding point, to avoid disrupting the Ethernet signals carried by the cable. All other metal parts on the cable should be insulated or carefully routed and fastened in place with plastic cable ties to avoid accidentally touching an electrical ground.

      An Ethernet interface is attached to a thick Ethernet segment with an external MAU. The MAU provides an electrical connection to the thick Ethernet coax and transfers signals between the Ethernet interface and the network segment. The MAU physically and electrically attaches to the coaxial cable by a cable tap. The cable is pierced, and a connection is made (by a screw) to the center conductor.

      The specifications state that there may be a maximum of 100 MAUs attached to a segment, and that each MAU connection to the thick coax be placed on any one of the black bands marked on the coaxial cable.

      An AUI cable can be used to provide the connection between an external MAU and the Ethernet interface. The MAU is equipped with a male 15-pin connector with locking posts, and the Ethernet interface (DTE) is equipped with a female 15-pin connector that is typically provided with a sliding latch. The standard AUI cable is relatively thick (approx. 1cm or 0.4 inch diameter), and may be up to 50 meters (164 feet) long. The maximum allowable length between a station and a MAU for thinner "office grade" AUI cables is 12.5 meters (41 feet).

      Thin coaxial Ethernet

      The thin coaxial Ethernet system uses a flexible coaxial cable that makes it possible to connect the coaxial cable directly to the Ethernet interface in the computer. The cable used is typically RG-58 coaxial cable or similar. The cable is teriminated with BNC connecors. Thin coaxial cable is limited to carrying 10-Mbps signals only. Thin coaxial segments can only be connected in the bus cable form of physical topology. The maximum lenght of the cable segment is 185 meters. The cable impedance is 50 ohms. Up to 30 MAUs are allowed on each thin Ethernet segment. The standard requires that multiple segments of thin coaxial cable be linked with repeaters.

      Each end of a complete thin Ethernet segment must be equipped with a 50 ohm terminating resistance. It is essential that exactly two 50 ohm terminators be installed or enabled on a given segment, or the collision detection mechanism in the MAUs attached to the segment will not function correctly.

      The cable is connected to the Ethernet cable using BNC Tee that is connected directly to the female BNC on the interface. The standard notes that the length of the "stub" connection from the BNC MDI on the interface to the coaxial cable should be no longer than four centimeters (1.57 inches), to prevent the occurrence of signal reflections which can cause frame errors.

      The Ethernet standard notes that you may provide a thin coaxial segment with a grounding point for electrical safety. To avoid disrupting the Ethernet signals carried by the cable, there must only be one grounding point. All other metal parts on the cable should be insulated or carefully routed and fastened in place with plastic cable ties to avoid accidentally touching an electrical ground.

      The flexibility and low cost of the thin coaxial system continues to make it popular for networking clusters of workstations in an open lab setting, although twisted pair wiring s catching there quicly also.

      When making the wiring for 10Base-2 network, be sure your cable is the correct impedance. The correct cable impedance is 50 ohms. The right coaxial cable type to use is RG-58, although some other 50 ohm coaxial cable types can be also used (as long as they have similar characteristics as RG-58 and you have BNC connector that you can terminate that cable). Make sure that the connectors and terminators match the impedance of the cable. If you use wrong impedance cable for ethernet wiring, you'll get subtle and intermittant data errors that are tough to track down.

      When building the cables, buy and use a good crimping tool. Do not use those twist-on connectors. They loosen and bring more intermittant problems.

      Use "T" connectors to connect the PC to the cable segment. Connect the "T" directly to the PC. You aren't allowed to run a cable from the "T" to the PC. Remeber that you must have at least 4.5 feet (1.5 meters) of cable between PCs.

      One (and only one) end of the cable should be grounded. It's generally easy enough to do this by running a ground line from the terminator to some reliable grounding point (for example mains power ground). If you ground both ends or don't ground either end the result will be intermittant problems.

      The thin Ethernet standard is designed for 50 ohm coaxial cable and this is the cable type which should ne used. Some very old Ethernet cards (from 1980-1990) have also supported non-standard 75 ohm coaxial cable as a wiring option. This 75 ohm cable is very rarely used.

      10Broad36

      10BROAD36 is a seldom used Ethernet specification which uses a physical medium similar to cable television, with CATV-type cables, taps, connectors, and amplifiers. 10BROAD36 is the only 802.3 broadband media specisfication. It uses 75 ohm CATV coax as the medium. 10Broad36, which is part of the IEEE 802.3 specification, has a distance limit of 2.24 miles (3600 meters) per networkt. Single 10Broad36 segments can be as long as 1800 meters. All 10Broad36 networks are terminated by a "head end" device.

      Broadband cable systems like CATV support transmission of multiple services over a single cable by dividing the bandwidth into separate frequencies, with each frequency assigned to a different service. This capability can allow 10Broad36 share a single cable with other services such as video.

      Broadband is by nature analog, so analog encoding must be used. 10Broax36 uses PSK modulated radio frequency (RF). The transmission rate is 10 Mb/s. The broadband MAU uses a data band 14 MHz wide and an adjacent collision enforcement band 4 MHz

      Broadband transmission differs from baseband transmission in the direction of signal flow. The signal moves in only one direction along the cable. In order for signals to reach all the devices in the network, there must be two paths for data flow. This may be accomplished through either a "single cable" or "dual cable" configuration.

      On a dual-cable system the transmit and receive carrier frequencies are identical and the MAU connects to the medium via two taps, one on the receive cable and the other on the transmit cable.

      CATV-type broadband cable installation is typically a single bidirectional cable with bandsplit amplifiers and filters. In single cable system te physical tap is a passive directional device such that the MAU transmission is directed toward the headend location (reverse direction). On a single-cable system the transmission from the MAU is at a carrier frequency f1. A frequency translator (or remodulator) located at the headend up-converts to a carrier frequency f2, which is sent in the forward direction to the taps (receiver inputs). A single cable midsplit con.guration with a frequency offset of 156.25 MHz or 192.25 MHz between forward and reverse channels is recommended.

      The collision detection in 10Broad36 is quite special: A transmitting MAU logically compares the beginning of the received data with the data transmitted. Any difference between them, which may be due to errors caused by colliding transmissions, or reception of an earlier transmission from another MAU, or a bit error on the channel, is interpreted as a collision. When a collision is recognized, the MAU stops transmission in the data band and begins transmission of an RF collision enforcement (CE) signal in a separate CE band adjacent to the data band. The CE signal is detected by all MAUs and informs them that a collision has occurred. All MAUs signal to their attached Medium Access Controllers (MACs) the presence of the collision. The transmitting MACs then begin the collision handling process. Collision enforcement is necessary because RF data signals from different MAUs on the broadband cable system may be received at different power levels.

      When introduced, 10Broad36 offered the advantage of supporting much longer segment lengths than 10Base5 and 10Base2. But this advantage was diminished with introduction of the fiber based FOIRL and 10Base-F standards. 10Broad36 is not capable of supporting the full-duplex mode of operation.

      Metropolitan Access Ethernet

      Ethernet technology is designed originally or LAN, but it's usage has expended to campus networks and metropolitan area networks. Outside of enterprise networks, Ethernet is beginning to catch on as a means of Internet access and for connecting metropolitan LANs. But Ethernet has stalled there because it lacks some of the features, particularly in quality-of-service, needed to provide private-line services. Several technologies are coming together to make Ethernet compelling for metro access. Sonet and Ethernet, two of the networking industry's most popular standards, are uniting in a way that might be inevitable given recession-era carrier trends. The idea of using Ethernet throughout the network - replacing Sonet entirely - appears to have vanished, but equipment vendors are still keen on selling the technology as a means of creating services at the network edge.

      Many metropolitan networks nowadays are based on Sonet/SHD technologues. Carriers built the metro using mature Sonet technologies, which, while optimal for voice or other jitter- and delay-sensitive applications, lack fast circuit-provisioning capabilities, scalability and bandwidth efficiency. This makes the MAN inefficient for the cost-effective transport of data. To leverage Ethernet in the metro it is often necessary to understand the existing Sonet/SDH infrastructure and how it can be adopted to take Ethernet traffic efficiently. With recent innovations in Sonet/SDH and metro Ethernet, the perfect storm of technologies has been brewed to offer Ethernet essentially over any distance. Switched Ethernet over Sonet is emerging as a viable way to migrate to packet-switched nets while preserving the current infrastructure.

      The advent of generic framing procedure (GFP) and related standards promise the ability to merge the worlds of Ethernet and Sonet more efficiently. One of the most interesting technologies is the combination of virtual concatenation (VCAT) and generic framing procedure (GFP) in the Sonet/SDH segment, along with the enhancements to Ethernet that make it "carrier-worthy."

      VCAT comes in two varieties: High-order VCAT and Low-order VCAT. For high-order VCAT, two STS-1 data paths could be grouped to yield a 100-Mbit point-to-point Ethernet network that spans any distance. For low-order, seven VT1.5 tributaries could be grouped to create a cost-effective 10-Mbit Ethernet point-to-point network. VCAT can be incorporated into an existing Sonet/SDH network by adding technology at the end points.

      Another technology crucial to offering metro Ethernet services is the generic framing procedure. GFP is standardized by the ITU as G.7041 and describes the encapsulation and data-rate adaptation techniques for transporting various protocols over Sonet/SDH networks.

      GFP offers two categories of service: framed and transparent. Framed GFP packages a complete Ethernet (or other) frame into a GFP header. It is important to realize that the frame is carried in its entirety; thus, to the end user, it appears that the Ethernet network is expanded and can be managed like a large enterprise network. Transparent GFP creates a data pipe that moves 8B/10B encoded data from end to end in a streaming fashion. Streams of 8B/10B traffic are encoded into 64B/65B superblocks for transport over the Sonet/SDH network. Rate adaptation is achieved by inserting and removing idle characters.

      Today, framed GFP is standardized for Gigabit Ethernet. Other protocols, including Fibre Channel and lower-speed Ethernets, will be standardized in the future. Today it is possible to transport Gigabit Ethernet, 1- and 2-Gbit Fibre Channel, Ficon, Escon/Sbcon and DVB-ASI over transparent GFP.

      In a typical scenario a service provider offers 10/100 Ethernet virtual private network (VPN) services by aggregating the 10/100 Ethernet traffic over a Gigabit Ethernet connection. Aggregated Ethernet flows can be distinguished by inspecting parts of the Ethernet frame. By examining the outer-most virtual LAN (VLAN) tag, multiprotocol label switching (MPLS) label, Internet Protocol (IP) type-of-service byte, DiffServ code point or Ether-net source address (or combinations of these), we can use a simple table lookup to determine the Sonet/SDH VCAT group into which the flow should be encapsulated. If the incoming traffic already has labels that can collide with the ones used by the operator, there is sometimes needs to switch or stack labels. Ethernet VLANs can be stacked using the relatively new "Q in Q" label-stacking scheme, so named for VLAN standard IEEE 802.1Q. MPLS labels have had stacking capabilities from the start.

      One challenge that will be encountered in moving Ethernet to the metro is the need for lossless flow control. Ethernet comes equipped with the ability to send pause frames once a watermark is tripped. To preserve a loss-free environment in metro applications, there needs to be enough buffering to hold up to three jumbo frames (9,600 bytes) per interface to accommodate a span of 10 km.

      Ethernet has become so economical that using a link to less than its throughput capacity has a very minor impact on the total cost of the solution. The bulk of the cost is still in the Sonet/SDH part of the network. So the operatotr might offer service like 10-Mbit Ethernet connection that is policed down to 3 Mbits/s. Provisioning is always provided by, at a minimum, specification of a committed information rate (CIR). Traffic that complies with its CIR is always delivered. Provisioning can also be offered using a burst information rate (BIR). Here, traffic that exceeds the CIR parameter but is less than the BIR parameter is delivered on a "best effort" basis.

      Power over Ethernet

      Power over Ethernet (PoE) is a technology for wired Ethernet LANs (local area networks) that allows the electrical current, necessary for the operation of ach device, to be carried by the data cables rather than by power cords. The idea for supplying power and data shared lines are not new - they were also shared in the days of the telegraph and are shared in normal telephone lines (PSTN) for very many decades. Sharing the same wires on the LAN environment is much newer technology. Traditionally the LAN cabling has provided thew data connectivity and all the computer devices connected to it have received the power from nearby mains wall outlet. The history of the idea of using LAN cabling to supply also power to devices connected to it seems to be around 15 years or so (Patent US4733389 shows the PoE concept for Ethernet). PoE has gained the lage interrest only on last several years with introduction of a large variaety of WLAN products. There are now components that allow power to be sent over Ethernet data cables. Those allow some low power devices like IP phones and wireless access points to be powered through LAN cabling.

      The use of same wires for power and data minimizes the number of wires that must be strung in order to install the network. Power over Ethernet allows for example next generation IP telephones, wireless LAN and Bluetooth access points to share power and data over the same cable so that they do not require additional AC wiring or external power transformers. When power-over-Ethernet technology becomes widespread, corporations and businesses will see at least one set of wiring hassles disappear or reduced considerably.

      For PoE to work, the electrical current must go into the data cable at the power-supply end, and come out at the device end, in such a way that the current is kept separate from the data signal so neither interferes with the other. The current enters the cable by means of a component called an injector or PoE power feeding HUB. If the device at the other end of the cable is PoE compatible, then that device will function properly without modification. If the device is not PoE compatible, then a component called a picker or tap must be installed to remove the current from the cable. This 'picked-off' current is routed to the power jack.

      To minimize the possibility of damage to equipment in the event of a malfunction, the more sophisticated PoE systems employ fault protection. This feature shuts off the power supply if excessive current or a short circuit is detected. Many modern intelligent PoE devices are also designed so that they will supply the power to the line only if there is a PoE capable device connected to line (there is a low-power OpE device detecting scheme). In this way the devices that are not PoE capable will not get the power and there is no changes of any equipment damage. The IEEE 802.3af standard committee has selected a resistor method of detection.

      There has been several prorietary technologues for PoE in use by many equipment manufacturers, but stadardization on this field is coming fast. The IEEE 802.3af specification defines how to transport the pover through Ethernet wiring. The idea on Power-over-Ethernet (PoE) is to feed the power using the same set of wires that carry the data. The power can be carried over the normally unused wires in 4-pair on CAT5 wiring (normally only two pairs are in use, two pairs not used in 10/100 Mbit/s Ethernet). Power can be also fed through the same wires as the data. In-Band-Powering is when the Power over Ethernet power is supplied on the same wires as the Data Pairs of the Ethernet cable (on pins 1&2, 3&6 on 10Base-T and 100Base-TX systems, Gigabit Ethernet uses all four pairs). Out-of-Band-Powering is when the Power over Ethernet power is supplied on the Spare wires of the Ethernet cable (on pins 4&5, 7&8 that are spare pairs on 10Base-T and 100Base-TX systems).

      Power-Over-LAN or Power-Via-MDI (Media Dependent Interface) or Power-over-Ethernet (PoE) is a network infrastructure to deliver 48V power over the existing network Category 5 (CAT-5) data cable. Power-Over-LAN provides signals as well as power to the connected power devices (PDs) such as IP Phones and Wireless Access Nodes, eliminating the need for local power sources. The power that is fed to the devices is typically norminally 48V (The IEEE802.3af standard has set a maximum limit of 57V) and maximum available power to the device is around 13W (Hub cutoff current limit is typically around 350mA). The voltage used for PoE according IEEE 802.3af standard is within Safety Extra Low Voltage (SELV) limits. SELV is a protected secondary circuit designed to work under normal operating conditions and single fault conditions, such that its voltages do not exceed a safe value (60V max). The power can be fed to the cable from the power supplying special hub/switch or it can be fed with a separate power supply in the mid-span between the hub/switch and the power consuming device. Powered Device (PD) is a Terminal Device, which has been designed to receive power on the same cable as the data. Only one input connector is required. PD is the term defined by the IEEE 802.3af committee. Powered Sourcing Equipment (PSE) is an equipment supplying power over ordinary CAT5 cables. Power can be supplied on the spare or the data wires of the Ethernet LAN transmission cable. PSE is the term defined by the IEEE 802.3af committee.

      The devices are compatible with existing Ethernet or Fast Ethernet switches and enable a unified supply of data and power through a single connection by sending power over standard Category 5 twisted pair cable. The compatibility is done in such way that the power supplying device supplies the power only to devices that can handle this power (there is a standardized detection scheme for this). Some devices that are not originally designed for PoE Ethernet operation can be converted for PoE operation using a device called power splitter. Splitter is used to separate the power from the communication lines. This device is used when equipment has not been designed to receive the data and power input on the same cable. The Splitter splits the two components into two cables, one providing Ethernet data communication and the other providing power.

      As a result, enterprises can deploy IP telephony and other devices without the time and cost required to install separate power cabling to existing infrastructure. In addition, the Power Sorcing Equipment can be connected to a uninterruptable power supply (or 48V battery!) to ensure peripherals are powered inthe case of mains power failures. in this way Power over LAN provides continuous service during power outages by utilizing the same centralized UPS system that backs up the network. This architecture enhances a customer's investment in both Category 5 infrastructure and in Ethernet switch equipment.

      • 802.3af Specification Makes a Lot of Sense - Power over ethernet, the 802.3af specification, is an impressive standard that will affect everything from IP telephony to wireless LANs. The 802.3af specification was finalized late this summer and is moving toward final adoption at year's end (end of 2002). The 802.11af Power over Ethernet standard means that wireless access points will no longer need to rely on proprietary products to provide energy when the access point is tacked up on a wall with no outlet nearby.
      • 802.3af Specification Makes a Lot of Sense - Power over ethernet, the 802.3af specification, is an impressive standard that will affect everything from IP telephony to wireless LANs.
      • BAWUG Power over Ethernet - A number of Access Point manufacturers are now offering Power over Ethernet add-on's for their Access Points. A PoE module insert a DC voltage into the unused wires in a standard ethernet cable (pairs 7-8 and 4-5). The idea is to supply the AP's power and UTP ethernet connectivity requirements via a single ethernet cable. This works great in areas where you may not have power and/or ethernet easily accessible, like a roof. There are currently two types of PoE adapters: a module jack or hub-like device for multiple access points. The hack described in the document creates a simple PoE module pair.
      • Choosing a Power-Over-Ethernet Approach - When planning the layout of a wireless LAN, you must take into consideration power sources for access points. PoE technology enables an access point to receive electrical power and data over the same cable.
      • Don't overlook cable and connector imbalances in POE applications - Using network wiring to supply power to networked devices makes installing the devices much easier. Whereas POE (power-over-Ethernet) designs aren't rocket science, designers still have to know what they're doing.
      • Hyperlink Technologies Power-over-Ethernet (PoE) Products - Power over ethernet product manufacturer page
      • IEEE P802.3af DTE Power via MDI Task Force - This is the standardizing group that works to standardize power over Ethernet technology.
      • LTC4255: Quad 48V Hot Swap Controller Protects IEEE 802.3af Powered Ethernet Applications
      • LTC4257 IEEE 802.3af PD Power-Over-Ethernet Interface Controller - The LTC®4257 provides complete signature and power interface functions for a device operating in an IEEE 802.3af Power Over Ethernet system. The LTC4257 simplifies Powered Device (PD) design by incorporating the 25k signature resistor, the classification current source, inrush current limit, undervoltage lockout, thermal current limit and power good signalling, all in a single 8-pin package.
      • PoE (Power Over Ethernet) Step By Step Hack Howto: power over your ethernet cable to an access point - A number of WLAN Access Point manufacturers (Lucent, Symbol) are now offering Power over Ethernet add-on's for their Access Points. A PoE module inserts DC voltage into the unused wires in a standard ethernet cable (pairs 7-8 and 4-5). The idea is to supply the AP's power and UTP ethernet connectivity requirements via a single ethernet. This document shows how this is done.
      • PowerDsine Contribution to the IEEE 802.3af
      • PowerDSine Power over LAN - power over Ethernet product manufacturer page
      • PowerOverEthernet.com - This website is devoted to the IEEE802.3af Power Over Ethernet technology.
      • Power Over Ethernet in a 5 1/4 inch bay - This is a simple plan to add RJ45 connector pins 4,5,7,8 are to carry the 12V power to WLAN access point (4&5 run to negative and pins 7&8 run to positive). This modification can be fit inside a 5 1/4 inch bay on the PC.
      • Power over LAN Glossary and Abbreviations
      • Power over LAN White Papers
      • Power Supplies for IEEE802.3af Compliant Power Devices - Three practical transformer-coupled circuits are detailed for providing isolated load power from power-over-LAN or power-via-MDI systems. All circuits employ a hot-swap switch to allow hot plug-in operation and a current-mode-switching controller to provide three possible load requirements. The first is a 6W flyback supply offering 4.25W output. The second is a forward converter with synchronous rectification to provide 3.3V or 5V at 2.5A. The third is a forward converter with synchronous rectification to provide a triple output at 14.2W. All are transformer coupled to provide and 1500Vrms isolation. Complete design information is given including circuits, component values, important waveforms, and efficiency data.
      • Why you should be thinking about Power over Ethernet - If you haven't done so already, perhaps now is a good time to start looking into migrating your existing network infrastructure to one that supports the IEEE 802.3af draft standard, which makes possible the distribution of Power over Ethernet (PoE) cabling.

      Ethernet testing

      How Ethernet is depends on what level you want to test it. . The most basic test (a.k.a., "the fire test") is to connect a pair of devices to the network and see if they can communicate with each other. If you want to test the electrical integrity of the wiring (i.e., will it carry a signal properly), you need to use a suitable cable tester and/or TDR device for it. If you need to test the performance or troubleshoot protocol transmission problems, you will need special and usually very expensive software, usually coupled with custom hardware, to capture, optionally filter, and analyze the network packets.

      • 10Base-T Repeater Test Suite
      • Ethernet Test Suites
      • Measuring Ethernet Tap Capacitance - when a node is added to an Ethernet network which uses coaxial cabling, its nodal capacitance changes the impedance of the cable at the point of connection to the cable and impedance change causes a reflection of the Ethernet waveform, IEEE802.3 standard specifies a maximum value of capacitance that a node may add to the network, as well as a minimum node to node distance spacing

      Special wirings

      Special techniques

      • Can I change the MAC address of a NIC? - Some NICs have the ability to change the MAC (Media Access Control) address through software. If you NIC and driver support this, Windows 2000 can change it using the tips shown in this article.
      • Designing for EMC in Datacom Systems - Electromagnetic compliance is not an area of "black magic," but rather another aspect of engineering where systematic design procedures, along with a little educated debugging, can provide quality solutions and shorten the design cycle. By following simple design rules, a two-layer, 10-Mbps Ethernet PCB can be created with minimal effort in debug time.
      • Magic Packet - Technology Application in Hardware and Software - Magic Packet technology is used to remotely wake up a sleeping or powered off PC on a network. This is accomplished by sending a specific packet of information, called a Magic Packet frame, to a node on the network. This application note addresses the use of the Magic Packet technology in conjunction with green PC hardware and system-level software. Its objective is to assist individuals in using this new technology in their own environments.

      Ethernet circuits

      Today it does not mych pay the touble of trying to build mass market Ethernet products, like hubs or network cards. At the current time, you can buy an ethernet card or hub for much less than the price of the parts needed to build one. The reson is that the manufacturers of those buy the components much more cheply than you will ever get those (unless you are readdy to buy millions of them).

      For some special applications builfing might be reasonable. FOr example for connecting two computers to each other it is possible to create a 'null hub', which is a simple crossover cable to allow the Ethernet cards in those two computers to be linked.

Fast Ethernet (100 megabit/s)

Fast Ethernet standard defines the 100-Mbps Fast Ethernet system which operates over twisted-pair and fiber optic media. The Fast Ethernet specifications include mechanisms for Auto-Negotiation of the media speed. This makes it possible for vendors to provide dual-speed Ethernet interfaces that can be installed and run at either 10-Mbps or 100-Mbps automatically. There are three media varieties that have been specified for transmitting 100-Mbps Ethernet signals.

  • The "T4" segment type is a twisted-pair segment that uses four pairs of telephone-grade twisted-pair wire. This is not much used.
  • The "TX" segment type is a twisted-pair segment that uses two pairs of wires and is based on the data grade (Category 5) twisted-pair physical medium. This is the most widely used version. The 100BASE-TX system operates over two pairs of wires (unshielded or shielded), one pair for receive data signals and the other pair for transmit data signals. The most popular wiring used today is Category 5 unshielded twisted-pair cable.
  • The "FX" segment type is a fiber optic link segment based on the fiber optic physical medium standard developed by ANSI and that uses two strands of fiber cable.
The TX and FX medium standards are collectively known as 100BASE-X.

The 100BASE-TX Ethernet segments are defined as link segments in the Ethernet specifications. A link segment is formally defined as a point-to-point medium that connects two and only two devices. A typical installation uses multiport repeater hubs, or packet switching hubs, to provide a connection between a larger number of link segments. You connect the Ethernet interface in your computer to one end of the link segment, and the other end of the link segment is connected to the hub. That way you can attach as many link segments with their associated computers as you have hub ports, and the computers all communicate via the hub. This means that the physical topology supported by twisted-pair link segments is the star. In this topology a set of link segments are connected to a hub, radiating out from the hub to the computers like the rays from a star.

The 100BASE-TX specifications allow a segment of up to 100 meters. Two 100 meter 100BASE-TX segments can be connected together through a single Class I or Class II repeater. This provides a system with a total diameter of 200 meters between two communicating devices. If longer distances are needed, an Ethernet switch is needed in between (this breaks the network to two part with their own 200 meter limits).

In 100BASE-T, the signal is encoded using a 125 MHz clock. 100BASE-T standard adopts a 3-level from of data encoding called MLT-3. Here, the output (encoded) signal is selected from a repeating 4-state pattern of {1, 0, -1, 0}. If the next data bit is a 1, the output transitions to the next state in the pattern. If the next data bit is a 0, the output remains constant. This method of data encoding has the advantage that the highest frequency in the encoded signal occurs when transmitting a long sequence of data bit 1's, in which case the encoded signal repeats the {1, 0, -1, 0} pattern, which has a cycle length of 1/4 of the basic clock rate. Thus, in this worst case the primary energy component would be at 32.5 MHz when using a 125 MHz clock. For other data bit patterns, the energy would be distributed at lower frequencies. The data is 100Mbit/s Ethernet data is encoded using 4B-5B encoding before passing it to MLT-3 coder (this gives the 125 Mbit/s coding rate).

    General

    Fast Ethernet pages

    Technical information

    With 100BaseT technology came the ability to perform auto-negotiation between each end of a 100BaseT connection. When the connection is established (plugging both ends of the UTP cable into their respective ports), a series of fast link pulses (FLP) are exchanged between the ports. The 33 pulses contain 17 clock pulses and 16 data pulses. The 16 data pulses form a 16-bit code indicating the capabilities of the port, such as Communication mode (half duplex or full duplex) and speed (10, 100, 10/100).

    Fast Ethernet contains specifications for two types of repeaters, Class I and Class II. Class I repeaters are slower (140 bit times for its round-trip delay) than Class II repeaters (92 bits times or less), but provide functions such as translation between the many different 100BaseT technologies. Class II repeaters, although faster, support only a single technology.

    Standard topologies for 100BaseT networks are one Class I repeater, which provides a network diameter of 200 m using copper cable and stations that may be 100 m from the repeater, and two Class II repeaters. The latter are connected via a 5-m cable that provides a diameter of 205 m and stations that may be 100 m from each repeater.

    The 100BASE-TX and 100BASE-FX media standards used in Fast Ethernet are both adopted from physical media standards first developed by ANSI, the American National Standards Institute. The ANSI physical media standards were originally developed for the Fiber Distributed Data Interface (FDDI) LAN standard (ANSI standard X3T9.5), and are widely used in FDDI LANs.

    Design articles

    Full duplex Ethernet flow control

    Flow control is a mechanism created to manage the flow of data between two full-duplex Ethernet devices. Through flow control, a device that is oversubscribed - either macroscopically from a system resource perspective or microscopically on a port-by-port basis - sends a pause message to its link partner to temporarily reduce the amount of data it's transmitting. Otherwise, buffer overflow occurs, data is lost and retransmission is required.

Gigabit Ethernet

Gigiabit Ethernetnet links are mostly built using fiber optic cabling.

Gigiablit Ethernet can also be run over a good quality (good CAT5 or better) twisted pair wiring. It uses all four pairs of wires to both send and recieve! Gigabit was designed to work with existing CAT5 cable installations. You need to buy CAT5 cable or better. The better means CAT5E or CAT6. This means that cat 5 cabling is suitable, though 5E or 6 may be better. It's speculated, by some, that 90% or more of properly installed and certified Category 5 installations will be able to handle Gigabit Ethernet without problems.

Gigabit NICs are different from lower speeds in that, instead of using one pair for transmit and another for receive, they use all four pairs for both send and receive, that is, each pair is bidirectional. The NIC is smart enough to figure out how to spit and recombine the data over the 4 pairs, no matter what's at the other end. This means that "direct cable" can be used to connect PC to Gigabit Ethernet Switch or to connect two PCs together.

Twisted pair signaling techniques for GbE were originally developed for the 100BASE-T2, -T4, and -TX standards have been adopted and extended for Gigabit Ethernet. Signal encoding on a 1000BASE-T link is based on a complex block encoding scheme called 4D-PAM5.

10 Gigabit Ethernet

10GBE is a new 10 gigabit version of Ethernet. Standardization got ready at the end of year 2002. 10GBE is so fast that it works only on fiber optic links. 10GBE is designed to give more bandwidth in metro, access, and transport systems.

In order to service two broad network applications, the IEEE is defined a 10 Gigabit Ethernet WAN physical (PHY) layer and 10 Gigabit Ethernet LAN PHY. The LAN PHY is intended to maximize the data rate to 10 Gbps cheaply for short distances, while the WAN PHY is rate compatible with the existing OC-192 (9.95328 Gbps) WAN infrastructure. The data rate and frame structure for the WAN PHY were specifically engineered to match current SONET/SDH WAN and optical networking data rates. This was done so that 10 Gigabit Ethernet traffic could be format-and rate-compatible with existing SONET/SDH and optical transport infrastructure. Rate matching is required to accommodate a rate of 10 Gbps at the media access control (MAC) and the WAN PHY running at 9.953-Gbps line rate (MAC adds extra spaces between frames in LAN implementation to match WAN speed).

The LAN PHY data rate is chosen to operate at 10 Gbps to optimize for throughput. In order to facilitate longer reach applications, additional fiber management capability has been added. The line rate of the LAN PHY depends on the coding scheme employed. The serial LAN PHY uses 64B/66B coding, while in applications using 4-l optics, 8B/10B is used.

The WAN PHY employs a basic SONET frame and scrambling to transport Ethernet data. The 64B/66B code characters generated from the same coding scheme used by the LAN PHY are encapsulated in SONET frames rather than being directly fed to the optics. Frame delineation within the received SONET payload is accomplished by recognizing valid 64B/66B data blocks.

  • 10 Gigabit Ethernet Alliance
  • 10 Gigabit Ethernet - Convergence of LAN and WAN - This is a a silide set from BICSI 2000 Fall Conference, Nashville, TN.
  • 10-Gigabit Ethernet takes on SONET - The 10-Gigabit Ethernet specification promises not only to eventually enable delivery of Gigabit Ethernet to the desktop but also to bridge the gap between datacomm and telecomm.
  • 10 Gbit Rates Shake Up Backplane Design - At multi-Gbit data rates attenuation and signal integrity problems rise to new levels. Solutions such as pre-emphasis keep the situation under control.
  • Ethernet Adds WAN to its Sphere of Influence - With a 10 Gigabit Ethernet standard now ratified, LANs, MANs and WANs can now unite under Ethernet as a transport layer technology.
  • Manning Up for 10 Gigabit Ethernet - Emerging Ethernet technology promises more bandwidth in metro, access, and transport systems.
  • Son of Gigabit Ethernet - 10-Gigabit Ethernet is coming soon to a LAN (and MAN) near you
  • The Once and Future Ethernet - The inevitable move to 10-Gb speeds will make Ethernet the architecture of choice for large-scale networks.
  • XAUI Interface - Among the many technical innovations of the 10 Gigabit Ethernet Task Force is an interface called the XAUI. The XAUI is designed as an interface extender, and the interface, which it extends, is the XGMII, the 10 Gigabit Media Independent Interface. Though transparent to end-users of 10 Gigabit Ethernet, XAUI is an important compatibility interface for 10 Gigabit Ethernet component and system implementers. It provides the low pin-count and long PC board trace lengths that system vendors need to drive down port costs. XAUI supports 10 Gb/s using four transmit and four receive lanes.

HomePNA

HomePNA is a phoneline networking standard which allows using normal telephone line wiring for LAN wiring inside home. The Home Phoneline Networking Alliance (HomePNA) is an association of leading companies working together to help ensure adoption of a single, unified phoneline networking industry standard and rapidly bringing to market a range of interoperable home networking solutions.

Currently actively used standard versions are HomePNA 1.0 and HomePNA 1.1. Those are also sometimes marketed with name HPNA. They provide 1 Mbit/s networking over ordinary home telephone wiring up to 150 meters. The card products for this look very much like Ethernet cards (just cost somewhat more). For getting cood compatilibitly with differnet manufacturers there is "Home Phoneline Network Certified" marking on many products which are are known to nicely interwork with other products marked with that mark. This HomePNA versions 1.0 and 1.1 can coexist on the same line with technologies like analogue telephone (PSTN) and ADSL.

There has been some standardization work on HomePNA technology ITU also apprroved 2001 a set of standards for Home Phone-line Networking transceivers, ITU-T Recommendation G.989.1. This will allow home-networking devices (e.g. computer peripherals) to operate over existing telephone wiring.

The brand news HomePNA 2.0 promises higher data speeds (10 Mbit/s or more) and transmission distances up to 320 meters. HomePNA 2.0 specification claims a line rate of 32 Mbps; however, when accounting for things like overhead and retransmission, the rate is closer to 20 Mbps. Due higher data rate, HomePNA 2.0 is more sensitive to telephone line crosstalk than earlier versions.

HomePNA has completed version 3.0 of its spec in early June 2003. The technology offers a top data rate of 128 Mbits/sec and has deterministic QoS features. HomePNA 3.0 is reported to achieve data rates of more than 100 Mbits/sec in about 50 percent of the scenarios and more than 40 Mbits/sec in "just about all" the others, The first ICs for this specification are expected to be available at the end of year 2003.

Token Ring

Token Ring is a network architechture which uses token passing technology and ring type network structure. Token Ring is standardized in IEEE 802.5 standard. Token Ring was widely used competitior of Ethernet, but nowadays it's use has quite much faded to only those organizations which have already large Token Ring infrastructure.

Wireless LANs

Wireless local area networks (WLAN) are very much talked about technology. It is a very fas growing technology. 802.11x based WLAN chipset shipments are set to hit 23 to 25 million units at year 2003. It is a strong growth up from 7.9 million in 2001. Wlan growth is driven by strong growth in the SOHO/retail market segment and broader global demand.

WLAN allows wireless networking and is very suitable for pretty fast data communications for laptops and other portable appliances. The most commonly used WLAN standard nowadays is IEEE 802.11b standard which uses frequency range of 2.4 - 2.4835 GHz and gives operation speed of 1-11 Mbps per second depending on traffic conditions (nominal speed of old cards was 2 Mbps and for newer cards it is 11 Mbps). The typical operating range indoors is 35-100 meters and for outdoor conditions 100-300 meters. Right now, current WLAN devices (802.11b) achieve a maximum data rate of 11 Mbps. However, once overhead and other factors are included, these systems achieve a real throughput around 4.5 to 6.4 Mbps.

WLAN technology is a promising technology for providing wireless high speed access. This provides both opportunities and threads to the wireless telecommunication operators, because cheap WLAN technology can compete with some other technologies in some applications (threatens to compete with 3G on some hot-spots).

A quick overview of wireless LANs and related technologies: 

Technology     Characteristics   Data rate      Standards body   Frequency 
 
IEEE 802.11a   Broadband LAN     54 Mbit/s      IEEE             5 GHz (5.150 to 5.350 GHz)
HiperLAN/2     Broadband LAN     54 Mbit/s      ETSI BRAN        5 GHz
IEEE 802.11b   Broadband LAN     11 Mbit/s      IEEE             2.4 GHz (ISM)
DECT           Voice and Data    1.152 Mbit/s   ETSI DECT        1.9 GHz
HomeRF (SWAP)  Voice and Data    2 Mbit/s       HomeRF WG        2.4 GHz (ISM)
Bluetooth      serial data PAN   1 Mbit/s       Bluetooth SIG    2.4 GHz (ISM)

Today, most wireless connections use a technology called Wi-Fi, the 802.11b wireless standard, which offers speeds of up to 11Mbps, although you can usually pull in speeds closer to 4Mbps to 8Mbps. WiFi, 802.11 or IEEE 802.11 is a type of radio technology used for wireless local area networks, based on a standard developed by the IEEE for local and wire networks within the 802.11 section. WiFi 802.11 is composed of several standards operating in different frequencies.

During the past few years, wireless connectivity has come down in price and become much easier to install and configure. Typical 802.11b WLAN cards have +15 dBm (32mW) of output power (regulations generally limit maximum output below 100 mW). WLAN cards usually specify a -83 dBm RX sensitivity (minimum RX signal level required for 11Mbps reception).

Wireless LANs can be an important part of future communications networks. Internet idealists hope for a future of ubiquitous free wireless networks. Instead of relying on slow and expensive cellular service, laptop users would simply connect to the nearest Wireless LAN (WLAN) and borrow its Internet connection. In the central business districts of most major cities, this is already a reality.

    General information

    • About HiperLAN2 - HiperLAN2 (for High Performance Radio Local Area Network Type 2) is a new high-performance 5GHz radio networking technology, specifically suited for operating in LAN environments. HiperLAN2 is being developed by the European Telecommunications Standardisation Institute (ETSI) Broadband Radio Access Networks (BRAN) project. This document is a very short introduction to this technology.
    • Adding Wireless to Your Home Network - Why add wireless capabilities to your home network? If you have a laptop, wireless connectivity is a no-brainer; this type of connection lets you use your laptop to its fullest and move freely around the house.
    • Are cabled networks facing a wireless rival?
    • Bluetooth vendors bite the bullet - After a year of indecision over interoperability issues, manufacturers bravely line up to test the market with a flood of new Bluetooth products.
    • dMystifying the dB - The basic unit of measurement used in Wi-Fi radio signals is the decibel or dB for short. Understanding decibels and their use in Wi-Fi radio systems is not rocket science.
    • Efficient Computing & Wireless Internet
    • HiperLAN Introduction - HiperLAN is a set of wireless local area network (WLAN) communication standards developed in European countries. There are two specifications: HiperLAN/1 and HiperLAN/2. Both have been adopted by the European Telecommunications Standards Institute (ETSI). HiperLAN operates at 5-GHz RF band.
    • Hotspot WLAN is not broadband nirvana - Sonera Corporation is one the most advanced providers of public wireless local area networks, WLANS. Public WLANs are usually set up in hotspots, airports, conference centers, hotels and such. WLANs have been considered by some consultants "3G killers" since they seem to able to everything that 3G networks can do but much faster. Unfortuantely WLAN can't solve all the needs. Sonera has about 60 WLANs in Finland. All the 25 largest Finnish airports are covered under the agreement with Finnish Aviation Administration. All Sonera hotspots share centralized customer handling and roaming.
    • Learn how to deploy safe wireless LANs - Wireless local area networks (WLANs) can provide high convenience for users at the cost of significant disruption to the IS organization. Deploying WLANs without carefully building in security will provide lucrative entry points for hackers and cybercriminals.
    • No more wires? - WLAN connectivity provides remarkably convenient, but it carries with it a number of implications. What indeed are the implications of all this? One is very positive. Installation of home wiring has long been a headache for the cable business. Wireless networking gives rise to the possibility that our cable modem, and eventually, our video digital terminal as well, can be located near the cable entry to the customer's home. TVs and PCs would be accessed within the home through wireless connections. There is another implication to all this which is more disturbing. My wireless connection works just fine from my neighbor's apartment, and there is no technical reason that I could not share my cable modem connection with him. This would be invisible to the cable company.
    • Reaching the 20 Mbps WLAN Plateau - Wireless developers are being pushed to support more functionality in their WLAN architecture. Through the use of the PBCC modulation technique and by improving packet overhead, designers can easily reach this plateau.
    • Recent Developments in Short-Range Wireless Communications - 8 page technical publication in pdf format
    • Roadblocks for War Drivers: Stop Wi-Fi from Making Private Networks Public - Internet idealists hope for a future of ubiquitous free wireless networks. Few are left open out of generosity: Even when an enterprise doesn't mind sharing its bandwidth with the outside world, it rarely wants to share its confidential data too. Despite frequent warnings about the poor security in the IEEE 802.11b (Wi-Fi) standard, more private networks are broadcasting to the public than ever. The maps of open access points compiled by war drivers-people who travel around a city and pick up signals from thousands of networks a day, armed only with a Wi-Fi card and an antenna made from a Pringles can-have gone from isolated dots to large conglomerations that can blot out entire downtown areas.
    • The Wireless Office: Understanding the Technology Options - The wireless office is becoming an increasingly affordable reality, however users are faced with a bewildering array of products and technologies. In this article John Burns, of radio spectrum management specialists Ægis Systems Ltd, reviews the technologies currently available and how these fit with the needs cost constraints of potential users.
    • Useful radio terms: A tutorial - This is a tutorial to decibels and other radio terms you might encounter in WLAN installation.
    • What Is a WLAN? - A wireless LAN (WLAN) is basically just what it sounds like--a network without wires. Like their wired counterparts, WLANs use a transmission media. WLANs use radio frequencies as their transmission media, sending network traffic sailing over the air.
    • Why 802.11b Should Stay Indoors - While the development of the 802.11b standards has received much attention and has gone a long way towards increasing the visibility of unlicensed wireless technology, it is very clear that products designed for this standard are best suited to indoor applications. This white paper has an explanation of problems surrounding the use of 802.11b compliant radio products for outdoor point-to-multipoint communications and metropolitan area networks.
    • Wireless Access - article which covers use of cellular networks, cordless acess and fixed wirelss access
    • Wireless LANs Explode With A Kaleidoscope Of Options - there are options from IEEE standards, to HomeRF, to personal-area networks like Bluetooth, users will be untethered like never before
    • Wireless LAN Standards - general overview
    • Wireless LAN: technology update - The advent of new wireless technologies will impact greatly on portable embedded systems. There is a choice between infrared and radio, as physical media, and within each, there are different frequencies and protocols to consider. Above all, will the technology only link point to point or can it support networking/internetworking. Then of course there is the bandwidth.
    • WLAN Antenna Terminology - The purpose of this page is to provide definitions of WLAN/fixed-wireless antennas and their characteristics. The definitions in quotation marks are taken from IEEE Standard Definitions of Terms for Antennas, IEEE Std 145-1983.
    • WLAN Foorumi - WLAN information and discussion in Finnish.
    • Wlan keeps beating expectations

    Tutorials and white papers

    Other articles

    • 50-Mbps wireless LANs: not yet a done deal - At 11 Mbps, Ethernet-based IEEE 802.11b is the clear leader. Another 802.11-series standard, 802.11a, promises to quintuple 11b's data rate. But challenges from competing standards and the 5-GHz carrier frequency suggest a less-than-smooth journey to widespread deployment.
    • 802.11 multivendor interoperability -- What's the real story? - These pages serve to record actual operational experience with 802.11 multivendor interoperability, related to card vs base-station compatibility, roaming, antennas, and various other issues.
    • Antenna Considerations in the Deployment of Wireless Broadband Networks - Antenna selection for wireless broadband networks is critical, due to the technology's inherent line-of-sight limitations.
    • Antennas Enhance WLAN Security - Antennas are most often used to increase the range of WLAN (wireless LAN) systems, but proper antenna selection can also enhance the security of your WLAN. A properly chosen and positioned antenna can reduce the signal leaking out of your workspace, and make interception extremely difficult. This article analyzes analyze the signal of different antenna designs, and how the positioning of the user's antenna makes a difference in signal reception.
    • Can Bluetooth And 802.11b Co-Exist? - Both the WLAN and Bluetooth devices occupy the same 2.4-to-2.483-GHz unlicensed frequency range--the same band, by the way, that is also occupied by a number of other devices such as microwave ovens and cellular phones. Does anyone see a problem here?
    • FCC Regulations on External radio frequency power amplifiers and antenna modifications
    • Have WLANs Come Of Age? - Uncovering the truths and misconceptions surrounding the 5-GHz WLAN indoor-coverage range.
    • Improving WLAN Performance in the Office Environment - WLANs are making inroads into the office environment, but this also presents challenges to radio chip designers as the indoor environment severely limits the performance. In addition, the new IEEE 802.11a standard for high rate systems in the 5GHz band also calls for new requirements.
    • Interference Immunity of 2.4 HJz Wireless LANs
    • Introduction to PRISM Chip Sets - PRISM® is a widely used chip set solution for 2.4GHz Direct Sequence Spread Spectrum (DSSS) applications like IEEE 802.11b WLAN.
    • Low Cost Wireless Network How-To - A paper on designing and building a high performance, independent, secure, wireless network using easily obtainable hardware. This paper covers all technical aspects of wireless networking, including documenting little known facts, and illustrating the actual network setup and installation. Also covered will be instructions for using MMDS antennas in 2.4 GHz wireless networks and several modifications for Proxim Symphony wireless network cards. Adaptation to wireless network cards other than the Symphony should be (is) trivial.
    • Troubleshooting WLAN Radio Designs - Optimizing 802.11b radio architectures can be a challenging task for today's system designers. This two-part series diagnose/correct problems in the transmit and receive portions of a radio design.
    • Troubleshooting WLAN Radio Designs: Part 2 - Optimizing 802.11b radio architectures can be a challenging task for today's system designers. This two-part series diagnose/correct problems in the transmit and receive portions of a radio design.
    • Valid comparisons of wireless-LAN-radio performance rely on multipath test conditions - Accurate comparative data is critical to choosing a WLAN chip set. The test methodology for comparison purposes must correctly simulate the real-world, multipath, indoor operating environment.
    • WLAN Technology Promises Real Mobile Internet - 5 GHz band gives new speed to Internet access. Article is in pdf format.

    Organizations

    News

    Resource pages

    Tools

    Antenna building projects

    Card / base station modifications and circuit information

    • Adding an antenna to the D-Link DWL-650 - A short guide to voiding your WLAN card warranty and getting external antenna connection cheaply.
    • Airport Base Station Extreme Revealed and Extended! - This article shows what is inside Apple Airport Base Station Extreme.
    • Airport Extreme Dissected! - This article shows what can be found at Apple Airport model AEBS WLAN base station.
    • Block Diagram for 2.4GHz IEEE802.11b DSSS WLAN Transceiver Application - Existing 2.4GHz DSSS WLAN chipsets incorporate almost all the functions of a typical superheterodyne transceiver, including RF and IF PLLs and I/Q modulator/demodulators. Incorporating the power amplifier (PA) and voltage-controlled oscillators (VCOs) on-chip remains a design challenge for many IC manufacturers.
    • Evolution of the ABS - Apple revolutionized high-speed wireless networking in 1999 with the introduction of the Airport system. This short article is meant to show the differences as the ABS design evolved through the generations. It also attempts to answer the questions that I received from some readers regarding whether they should upgrade to Airport "Extreme".
    • Raylink WLAN Card Modification - The Raylink wlan cards are actually very simple to modify to use external antenna.

    Amplifiers

    In some countries you can use an amplifier to amplify WLAN signals to get more transmissiong range. In most countries this kind of amplifiers are not legal.

    Othet building projects information

    • 802.11 Wireless LAN Cards Circuit Diagrams
    • Apple Airport Modification - Instructions how to add an external antenna to Apple Airport WLAN access point.
    • BAWUG Power over Ethernet - A number of Access Point manufacturers are now offering Power over Ethernet add-on's for their Access Points. A PoE module insert a DC voltage into the unused wires in a standard ethernet cable (pairs 7-8 and 4-5). The idea is to supply the AP's power and UTP ethernet connectivity requirements via a single ethernet cable. This works great in areas where you may not have power and/or ethernet easily accessible, like a roof. There are currently two types of PoE adapters: a module jack or hub-like device for multiple access points. The hack described in the document creates a simple PoE module pair.
    • Hacking The Original 915 MHz WaveLAN (NCR 915 MHz WaveLAN 2 Mbps DSSS) - amplifier circuit, datasheets, antenna designs, etc.
    • PoE (Power Over Ethernet) Step By Step Hack Howto: power over your ethernet cable to an access point - A number of WLAN Access Point manufacturers (Lucent, Symbol) are now offering Power over Ethernet add-on's for their Access Points. A PoE module inserts DC voltage into the unused wires in a standard ethernet cable (pairs 7-8 and 4-5). The idea is to supply the AP's power and UTP ethernet connectivity requirements via a single ethernet. This document shows how this is done.
    • Simple Home Built Indoor / Outdoor Enclosure for Access Points Howto - Construct an enclosure for your access point out of a $4 Plastic Food Container. Useful for roof mounting access points, or in less then perfect indoor environments. This is a step by step instruction on how to make an Indoor / Outdoor enclosure for your access point.

Wireless communication circuits