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)
Thin Ethernet (ThinNet) (10BASE2)
- 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.
Twisted-Pair Ethernet (10BASE-T)
- 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.
Fiber Optic Ethernet (10BASE-FL, FOIRL)
- 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.
- 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.
Product Data Sheets (pdf)...Back Office Switches
Unmanaged Gigabit Switch
Gigabit Unmanaged Switch, with SFP Uplinks, User Manual
User Manual for the LGB516A & LGB524A (Version 1)
Gigabit PSE Web Smart Switch Manual
Manual for the LPBG716A, and LPBG724A (Version 1)
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 doesnt 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...Power over Ethernet (PoE).
Product Data Sheets (pdf)...Gigabit Unmanaged Switches with SFP Uplinks
What is PoE?
The seemingly universal network connection, twisted-pair Ethernet cable, has another role to play, providing electrical power to low-wattage electrical devices. Power over Ethernet (PoE) was ratified by the... more/see it nowInstitute of Electrical and Electronic Engineers (IEEE) in June 2000 as the 802.3af-2003 standard. It defines the specifications for low-level power delivery—roughly 13 watts at 48 VDC—over twisted-pair Ethernet cable to PoE-enabled devices such as IP telephones, wireless access points, Web cameras, and audio speakers.
Recently, the basic 802.3af standard was joined by the IEEE 802.3at PoE standard (also called PoE+ or PoE plus), ratified on September 11, 2009, which supplies up to 25 watts to larger, more power-hungry devices. 802.3at is backwards compatible with 802.3af.
How does PoE work?
The way it works is simple. Ethernet cable that meets CAT5 (or better) standards consists of four twisted pairs of cable, and PoE sends power over these pairs to PoE-enabled devices. In one method, two wire pairs are used to transmit data, and the remaining two pairs are used for power. In the other method, power and data are sent over the same pair.
When the same pair is used for both power and data, the power and data transmissions don’t interfere with each other. Because electricity and data function at opposite ends of the frequency spectrum, they can travel over the same cable. Electricity has a low frequency of 60 Hz or less, and data transmissions have frequencies that can range from 10 million to 100 million Hz.
There are two types of devices involved in PoE configurations: Power Sourcing Equipment (PSE) and Powered Devices (PD).
PSEs, which include end-span and mid-span devices, provide power to PDs over the Ethernet cable. An end-span device is often a PoE-enabled network switch that’s designed to supply power directly to the cable from each port. The setup would look something like this:
End-span device → Ethernet with power
A mid-span device is inserted between a non-PoE device and the network, and it supplies power from that juncture. Here is a rough schematic of that setup:
Non-PoE switch → Ethernet without PoE → Mid-span device → Ethernet with power
Power injectors, a third type of PSE, supply power to a specific point on the network while the other network segments remain without power.
PDs are pieces of equipment like surveillance cameras, sensors, wireless access points, and any other devices that operate on PoE.
PoE applications and benefits.
• Use one set of twisted-pair wires for both data and low-wattage appliances.
• In addition to the applications noted above, PoE also works well for video surveillance, building management, retail video kiosks, smart signs, vending machines, and retail point-of-information systems.
• Save money by eliminating the need to run electrical wiring.
• Easily move an appliance with minimal disruption.
• If your LAN is protected from power failure by a UPS, the PoE devices connected to your LAN are also protected from power failure.
10/100 PSE Web Smart Switch User Manual
User Manual for 10/100 PSE Web Smart Switch (2)
Black Box Explains...Layer 2, 3, and 4 switching.
The Open Systems Interconnection (OSI) Reference Model provides a layered network design framework that establishes a standard so that devices from different vendors work together.
Layer 2 (The Data-Link Layer)
Layer 2... more/see it nowswitches operate using physical network addresses. Physical addresses, also known as link-layer, hardware, or MAC-layer addresses, identify individual devices. Most hardware devices are permanently assigned this number during the manufacturing process.
Switches operating at Layer 2 are very fast because they’re just sorting physical addresses, but they usually arent very smart.
Layer 3 (The Network Layer)
Layer 3 switches use network or IP addresses that identify locations on the network. Physical addresses identify devices; network addresses identify locations. A location can be a LAN workstation, a location in a computer’s memory, or even a packet of data traveling through a network.
Network addresses are hierarchical. The more details included, the more specific the address becomes and the easier it is to find.
Switches operating at Layer 3 are smarter than Layer 2 devices and incorporate routing functions to actively calculate the best way to send a packet to its destination. However, because Layer 3 Switches take the extra time to read more details of a network address, they are sometimes much slower than Layer 2 Switches.
Layer 4 (The Transport Layer)
Layer 4 of the OSI Model coordinates communications between systems. Layer 4 identifies which application protocols (HTTP, SNTP, FTP, etc.) are included with each packet and uses this information to hand off the packet to the appropriate higher-layer software. Layer 4 switches make packet forwarding decisions based not only on the MAC address and IP address, but also on the application a packet belongs to.
Because Layer 4 devices enable you to establish priorities for network traffic based on application, you can assign a high priority to packets belonging to vital in-house applications, such as Peoplesoft®, with different forwarding rules for low-priority packets, such as generic HTTP-based Internet traffic.
Layer 4 switches also provide an effective wire-speed security shield for your network. collapse