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Black Box Explains...SFP, SFP+, and XFP transceivers.

SFP, SFP+, and XFP are all terms for a type of transceiver that plugs into a special port on a switch or other network device to convert the port to... more/see it nowa copper or fiber interface. These compact transceivers replace the older, bulkier GBIC interface. Although these devices are available in copper, their most common use is to add fiber ports. Fiber options include multimode and single-mode fiber in a variety of wavelengths covering distances of up to 120 kilometers (about 75 miles), as well as WDM fiber, which uses two separate wavelengths to both send and receive data on a single fiber strand.

SFPs support speeds up to 4.25 Gbps and are generally used for Fast Ethernet or Gigabit Ethernet applications. The expanded SFP standard, SFP+, supports speeds of 10 Gbps or higher over fiber. XFP is a separate standard that also supports 10-Gbps speeds. The primary difference between SFP+ and the slightly older XFP standard is that SFP+ moves the chip for clock and data recovery into a line card on the host device. This makes an SFP+ smaller than an XFP, enabling greater port density.

Because all these compact transcievers are hot-swappable, there’s no need to shut down a switch to swap out a module—it’s easy to change interfaces on the fly for upgrades and maintenance.

Another characteristic shared by this group of transcievers is that they’re OSI Layer 1 devices—they’re transparent to data and do not examine or alter data in any way. Although they’re primarily used with Ethernet, they’re also compatible with uncommon or legacy standards such as Fibre Channel, ATM, SONET, or Token Ring.

Formats for SFP, SFP+, and XFP transceivers have been standardized by multisource agreements (MSAs) between manufacturers, so physical dimensions, connectors, and signaling are consistent and interchangeable. Be aware though that some major manufacturers, notably Cisco, sell network devices with slots that lock out transceivers from other vendors. collapse

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Product Data Sheets (pdf)...PoE PD Switches


Black Box Explains…Energy-Efficient Ethernet.

The IEEE 802.3az Ethernet standard, ratified in 2010, provides a standardized way for some Ethernet devices to reduce power consumption. Energy-Efficient Ethernet devices have a low-power idle (LPI) mode that... more/see it nowcan cut power use by 50% or more during periods of low data activity. Because energy-efficient Ethernet devices scale down power consumption when the load is lower, they save both the energy used to power processors and the energy used to cool them.

These energy savings are currently available for 100BASE-TX, 1000BASE-T, and 10GBASE-T Ethernet as well as some backplane Ethernet. 802.3az can be found on most types of network equipment, including NICs, switches, routers, and media converters. Because these devices are totally backwards compatible with other Ethernet devices, all you need to do to reap energy savings is to swap out devices. collapse

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  • Value Console Managed Switch User Manual
    User Manual for the LB9316A and LB9324A (Version 2)
 

Black Box Explains...Ethernet hubs vs. Ethernet switches.

Although hubs and switches look very similar and are connected to the network in much the same way, there is a significant difference in the way they function.

What is a... more/see it nowhub?
An Ethernet hub is the basic building block of a twisted-pair (10BASE-T or 100BASE-TX) Ethernet network. Hubs do little more than act as a physical connection. They link PCs and peripherals and enable them to communicate over a network. All data coming into the hub travels to all stations connected to the hub. Because a hub doesn’t use management or addressing, it simply divides the 10- or 100-Mbps bandwidth among users. If two stations are transferring high volumes of data between them, the network performance of all stations on that hub will suffer. Hubs are good choices for small- or home-office networks, particularly if bandwidth concerns are minimal.

What is a switch?
An Ethernet switch, on the other hand, provides a central connection in an Ethernet network in which each connected device has its own dedicated link with full bandwidth. Switches divide LAN data into smaller, easier-to-manage segments and send data only to the PCs it needs to reach. They allot a full 10 or 100 Mbps to each user with addressing and management features. As a result, every port on the switch represents a dedicated 10- or 100-Mbps pathway. Because users connected to a switch do not have to share bandwidth, a switch offers relief from the network congestion a shared hub can cause.

What to consider when selecting an Ethernet hub:
• Stackability. Select a stackable hub connected with a special cable so you can start with one hub and add others as you need more ports. The entire stack functions as one device.
• Manageability. Choose an SNMP-manageable hub if you have a large, managed network.

What to consider when selecting an Ethernet switch:
• Manageability. Ethernet switches intended for large managed networks feature built-in management, usually SNMP.
• OSI Layer operation. Most Ethernet switches operate at “Layer 2,” which is for the physical network addresses (MAC addresses). Layer 3 switches use network addresses, and incorporate routing functions to actively calculate the best way to send a packet to its destination. Very advanced Ethernet switches, often known as routing switches, operate on OSI Layer 4 and route network traffic according to the application.
• Modular construction. A modular switch enables you to populate a chassis with modules of different speeds and media types. Because you can easily change modules, the modular switch is an adaptable solution for large, growing networks.
• Stackability. Some Ethernet switches can be connected to form a stack of two or more switches that functions as a single network device. This enables you to start with fewer ports and add them as your network grows. collapse


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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  • Gigabit Ethernet Managed Switch User Manual
    User Manual for the LGB5028A and LGB5052A (Version 1)
 
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