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  • Manual... 
  • Pure Networking II 10/100 Ethernet Switch User Manual
    User Manual for LB016A (version 1)
 

Black Box Explains...Ethernet.



If you have an existing network, there’s a 90% chance it’s Ethernet. If you’re installing a new network, there’s a 98% chance it’s Ethernet—the Ethernet standard is... more/see it nowthe overwhelming favorite network standard today.


Ethernet was developed by Xerox®, DEC®, and Intel® in the mid-1970s as a 10-Mbps (Megabits per second) networking protocol—very fast for its day—operating over a heavy coax cable (Standard Ethernet).


Today, although many networks have migrated to Fast Ethernet (100 Mbps) or even Gigabit Ethernet (1000 Mbps), 10-Mbps Ethernet is still in widespread use and forms the basis of most networks.


Ethernet is defined by international standards, specifically IEEE 802.3. It enables the connection of up to 1024 nodes over coax, twisted-pair, or fiber optic cable. Most new installations today use economical, lightweight cables such as Category 5 unshielded twisted-pair cable and fiber optic cable.


How Ethernet Works

Ethernet signals are transmitted from a station serially, one bit at a time, to every other station on the network.


Ethernet uses a broadcast access method called Carrier Sense Multiple Access/Collision Detection (CSMA/CD) in which every computer on the network “hears” every transmission, but each computer “listens” only to transmissions intended for it.


Each computer can send a message anytime it likes without having to wait for network permission. The signal it sends travels to every computer on the network. Every computer hears the message, but only the computer for which the message is intended recognizes it. This computer recognizes the message because the message contains its address. The message also contains the address of the sending computer so the message can be acknowledged.


If two computers send messages at the same moment, a “collision” occurs, interfering with the signals. A computer can tell if a collision has occurred when it doesn’t hear its own message within a given amount of time. When a collision occurs, each of the colliding computers waits a random amount of time before resending the message.


The process of collision detection and retransmission is handled by the Ethernet adapter itself and doesn’t involve the computer. The process of collision resolution takes only a fraction of a second under most circumstances. Collisions are normal and expected events on an Ethernet network. As more computers are added to the network and the traffic level increases, more collisions occur as part of normal operation. However, if the network gets too crowded, collisions increase to the point where they slow down the network considerably.


Standard (Thick) Ethernet (10BASE5)


  • Uses “thick” coax cable with N-type connectors for a backbone and a transceiver cable with 9-pin connectors from the transceiver to the NIC.
  • Both ends of each segment should be terminated with a 50-ohm resistor.
  • Maximum segment length is 500 meters.
  • Maximum total length is 2500 meters.
  • Maximum length of transceiver cable is 50 meters.
  • Minimum distance between transceivers is 2.5 meters.
  • No more than 100 transceiver connections per segment are allowed.
Thin Ethernet (ThinNet) (10BASE2)


  • Uses "Thin" coax cable.
  • The maximum length of one segment is 185 meters.
  • The maximum number of segments is five.
  • The maximum total length of all segments is 925 meters.
  • The minimum distance between T-connectors is 0.5 meters.
  • No more than 30 connections per segment are allowed.
  • T-connectors must be plugged directly into each device.
Twisted-Pair Ethernet (10BASE-T)


  • Uses 22 to 26 AWG unshielded twisted-pair cable (for best results, use Category 4 or 5 unshielded twisted pair).
  • The maximum length of one segment is 100 meters.
  • Devices are connected to a 10BASE-T hub in a star configuration.
  • Devices with standard AUI connectors may be attached via a 10BASE-T transceiver.
Fiber Optic Ethernet (10BASE-FL, FOIRL)


  • Uses 50-, 62.5-, or 100-micron duplex multimode fiber optic cable (62.5 micron is recommended).
  • The maximum length of one 10BASE-FL (the new standard for fiber optic connections) segment is 2 kilometers.
  • The maximum length of one FOIRL (the standard that preceded the new 10BASE-FL) segment is 1 kilometer.
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  • Application Note... 
  • Ethernet Switches and ServSwitch Agility KVM-over-IP Extension
    The important interoperability considerations when choosing Ethernet switches for use with Agility systems. (Version 1)
 
  • Quick Start Guide... 
  • Hardened Managed Ethernet Switch Quick Start Guide
    Quick Start Guide for the LEH1100 Series (Version 1)
 

Black Box Explains...LAN switches.



Rush hour-all day, every day.

Applications such as document imaging, video/multimedia production, and intranetworking are very demanding. They generate huge data files that often must be transferred... more/see it nowbetween stations based on strict timing requirements. If such traffic is not transmitted efficiently, you end up with jerky video, on-screen graphics that take forever to load, or other irritating, debilitating problems.


These problems arise because in traditional LANs, only one network node transmits data at a time while all other stations listen. This works in conventional, server-based LANs where multiple workstations share files or applications housed on a central server. But if a network has several servers, or if it supports high-bandwidth, peer-to-peer applications such as videoconferencing, the one-station-at-a-time model just doesn’t work.


Ideally, each LAN workstation should be configured with its own dedicated LAN cable segment. But that’s neither practical nor affordable. A far more reasonable solution is a network designed to provide clear paths from each workstation to its destination on demand, whether that destination is another workstation or server.


These vehicles clear the lanes.

Unlike bridges and routers, which process data packets on an individual, first-come, first-served basis, switches maintain multiple, simultaneous data conversions among attached LAN segments.


From the perspective of an end-user workstation, a switched circuit appears to be a dedicated connection-a direct, full-speed LAN link to an attached server or other remote LAN node. Although this technique is somewhat different from what a LAN bridge or router does, switching hubs are based on similar technologies.




Which route will you choose?

Switching hubs that use bridging technologies are called Layer 2 switches-a reference to Layer 2 or the Data-Link Layer of the OSI Model. These switches operate using the MAC addresses in Layer 2 and are transparent to network protocols. Switches that use routing technologies are known as Layer 3 switches, referring to Layer 3—the Network Layer—of the OSI Model. These switches, like routers, represent the next higher level of intelligence in the hardware hierarchy. Rather than passing packets based on MAC addresses, these switches look into the data structure and route it based on the network addresses found in Layer 3. They are also dependent on the network protocol.


Layer 2 switches connect different parts of the same network as determined by the network number contained with the data packet. Layer 3 switches connect LANs or LAN segments with different network numbers.


If you’re subdividing an existing LAN, obviously you’re dealing with only one network and one network number, so you can install a Layer 2 switch wherever it will segment network traffic the best, and you don’t have to reconfigure the LAN. However, if you use a Layer 3 switch, you’ll have to reconfigure the segments to ensure that each has a different network number.


Similarly, if you’re connecting existing networks, you have to examine the currently configured network numbers before adding a switch. If the network numbers are the same, you need to use a Layer 2 switch. If they’re different, you must use a Layer 3 switch.


When dealing with multiple existing networks, you’ll find they usually use different network numbers. In this case, it’s preferable to use a Layer 3 switch (or possibly even a full-featured router) to avoid reconfiguring the network.


But what if you’re designing a network from scratch and can choose either type of switch? Your decision should be based on the expected complexity of your LAN. Layer 3 routing technology is well suited for complex networks. Layer 2 switches are recommended for smaller, less complex networks.

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  • Manual... 
  • Hardened Managed Ethernet Switch User Manual
    User Manual for the LEH900 Series, LEH1000 Series, LEH1100, & LEH1200 Series (Version 3)
 
  • Quick Start Guide... 
  • PoE+ Fast Ethernet Unmanaged Switch (8-Port) QSG
    Quick Start Guide for the LPB308A (Version 1)
 
  • Quick Start Guide... 
  • Gigabit Ethernet Managed Switch Installation & Getting Started Guide
    Installation & Getting Started Guide for the LGB5028A and LGB5052A (Version 1)
 
  • Manual... 
  • 100 Mbps Economy Crossover Media Converters
    Installation and User Guide (Feb-02)
 

Black Box Explains... GBICs

A Gigabit Interface Converter (GBIC) is a transceiver that converts digital electrical currents to optical signals and back again. GBICs support speeds of 1 Gbps or more and are typically... more/see it nowused as an interface between a high-speed Ethernet or ATM switch and a fiber backbone. GBICs are hot-swappable, so switches don’t need to be powered down for their installation. collapse

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