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
The difference between unmanaged, managed, and Web-smart switches
With regard to management options, the three primary classes of switches are unmanaged, managed, and Web smart. Which you choose depends largely on the size of your network and how... more/see it nowmuch control you need over that network.
Unmanaged switches are basic plug-and-play switches with no remote configuration, management, or monitoring options, although many can be locally monitored and configured via LED indicators and DIP switches. These inexpensive switches are typically used in small networks or to add temporary workgroups to larger networks.
Managed switches support Simple Network Management Protocol (SNMP) via embedded agents and have a command line interface (CLI) that can be accessed via serial console, Telnet, and Secure Shell. These switches can often be configured and managed as groups. More recent managed switches may also support a Web interface for management through a Web browser.
These high-end switches enable network managers to remotely access a wide range of capabilities including:
Enabling and disabling individual ports or port Auto MDI/MDI-X.
Port bandwidth and duplex control.
IP address management.
MAC address filtering.
Port mirroring to monitor network traffic.
Prioritization of ports for quality of service (QoS).
802.1X network access control.
Link aggregation or trunking.
Managed switches, with their extensive management capabilities, are at home in large enterprise networks where network administrators need to monitor and control a large number of network devices. Managed switches support redundancy protocols for increased network availability.
Web-smart switches—sometimes called smart switches or Web-managed switches—have become a popular option for mid-sized networks that require management. They offer access to switch management features such as port monitoring, link aggregation, and VPN through a simple Web interface via an embedded Web browser. What these switches generally do not have is SNMP management capabilities or a CLI. Web-smart switches must usually be managed individually rather than in groups.
Although the management features found in a Web-smart switch are less extensive than those found in a fully managed switch, these switches are becoming smarter with many now offering many of the features of a fully managed switch. Like managed switches, they also support redundancy protocols for increased network availability.
Black Box Explains...Media converters that are really switches.
A media converter is a device that converts from one media type to another, for instance, from twisted pair to fiber to take advantage of fiber’s greater range. A traditional... more/see it nowmedia converter is a two-port Layer 1 device that performs a simple conversion of only the physical interface. It’s transparent to data and doesn't “see” or manipulate data in any way.
An Ethernet switch can also convert one media type to another, but it also creates a separate collision domain for each switch port, so that each packet is routed only to the destination device, rather than around to multiple devices on a network segment. Because switches are “smarter” than traditional media converters, they enable additional features such as multiple ports and copper ports that autosense for speed and duplex.
Switches are beginning to replace traditional 2-port media converters, leading to some fuzziness in terminology. Small 4- or 6-port Ethernet switches are very commonly called media converters. In fact, anytime you see a “Layer 2” media converter or a media converter with more than two ports, it’s really a small Ethernet switch.
Black Box Explains...DIN rails.
A DIN rail is an industry-standard metal rail, usually installed inside an electrical enclosure, which serves as a mount for small electrical devices specially designed for use with DIN rails.... more/see it nowThese devices snap right onto the rails, sometimes requiring a set screw, and are then wired together.
Many different devices are available for mounting on DIN rails: terminal blocks, interface converters, media converter switches, repeaters, surge protectors, PLCs, fuses, or power supplies, just to name a few.
DIN rails are a space-saving way to accommodate components. And because DIN rail devices are so easy to install, replace, maintain, and inspect, this is an exceptionally convenient system that has become very popular in recent years.
A standard DIN rail is 35-mm wide with raised-lip edges, its dimensions outlined by the Deutsche Institut für Normung, a German standardization body. Rails are generally available in aluminum or steel and may be cut for installation. Depending on the requirements of the mounted components, the rail may need to be grounded. collapse
Black Box Explains...Power over Ethernet (PoE).
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.
Converters and Scalers Selector
IEEE 802.3 af
|PoE IEEE 802.3 at
|Power available at powered device
|Maximum power delivered
|Voltage range at powred source
|Voltage range at powred device
|Maximum cable resistance
The ANSI/ISA Standard and Hazardous Locations
Fires and explosions are a major safety concern in industrial plants. Electrical equipment that must be installed in these locations should be specifically designed and tested to operate under extreme... more/see it nowconditions. The hazardous location classification system was designed to promote the safe use of electrical equipment in those areas “where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable fibers of flyings.”
The NEC and CSA define hazardous locations by three classes:
Class 1: Gas or vapor hazards
Class 2: Dust hazards
Class 3: Fibers and flyings
Division 1: An environment where ignitable gases, liquids, vapors or dusts can exist
Division 2: Locations where ignitables are not likely to exist
Hazardous classes are further defined by groups A, B, C, D, E, F, and G:
C. Ethlene, carbon monoxide
D. Hydrocarbons, fuels, solvents
F. Carbonaceous dusts including coal, carbon black, coke
G. Flour, starch, grain, combustible plastic or chemical dust
Our line of Industrial Ethernet Switches (LEH1208A, LEH1208A-2GMMSC, LEH1216A and LEH1216A-2GMMSC) is fully compliant with ANSI/ISA 12.12.01, a construction standard for Nonincendive Electrical Equipment for Use in Class I and II, Division 2 and Class III, Divisions 1 and 2 Hazardous (Classified) Locations. ANSI/ISA 12.12.01-2000 is similar to UL1604, but is more stringent (for a full list of changes, see Compliance Today). UL1604 was withdrawn in 2012 and replaced with ISA 12.12.01.
The standard provides the requirements for the design, construction, and marking of electrical equipment or parts of such equipment used in Class I and Class II, Division 2 and Class III, Divisions 1 and 2 hazardous (classified) locations. This type of equipment, in normal operation, is not capable of causing ignition.
The standard establishes uniformity in test methods for determining the suitability of equipment as related to their potential to ignite to a specific flammable gas or vapor-in-air mixture, combustible dust, easily ignitable fibers, or flyings under the following ambient conditions:
a) an ambient temperature of -25°C to 40°C.
b) an oxygen concentration of not greater than 21 percent by volume.
c) a pressure of 80 kPa (0.8 bar) to 110 kPa (1.1 bar).
The standard is available for purchase at www.webstore.ansi.org. To learn more about ANSI/ISA 12.12.01 and hazardous location types, visit https://www.osha.gov/doc/outreachtraining/htmlfiles/hazloc.html.
Black Box Explains…SFP compatibility.
Standards for SFP fiber optic media are published in the SFP Multi-Source Agreement, which specifies size, connectors, and signaling for SFPs, with the idea that all SFPs are compatible with... more/see it nowdevices that have appropriate SFP slots. These standards, which also extend to SFP+ and XFP transceivers, enable users to mix and match components from different vendors to meet their own particular requirements.
However, some major manufacturers, notably Cisco®, HP®, and 3Com®, sell network devices with SFP slots that lock out transceivers from other vendors. Because the price of SFPs—especially Gigabit SFPs and 10GBASE SFP+ and XFP transceivers—can add significantly to the price of a switch, this lock-out scheme raises hardware costs and limits transceiver choices.
Many vendors don’t advertise that SFP slots on their devices don’t accept standard SFPs from other vendors. This can lead to unpleasant surprises when a device simply refuses to communicate with an SFP.
Another game that some vendors play is to build devices that accept open-standard SFPs, but refuse to support those devices when SFPs from another vendor are used with them.
The only way around this “lock-in” practice is to only buy network devices that accept standard SFPs from all vendors and to buy from vendors that support their devices no matter whose SFPs are used with them. Questions? Call our FREE Tech Support at 724-746-5500.
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.
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 dont need to be powered down for their installation. collapse
Black Box Explains...Layer 2, 3, and 4 switches.
... more/see it now
E-Mail, Diagnostics, Word Processing, Database
Shells and Gateway Workstation Software
TR=Token Ring; A=ARCNET®; P=PhoneNET®
With the rapid development of computer networks over the last decade, high-end switching has become one of the most important functions on a network for moving data efficiently and quickly from one place to another.
Here’s how a switch works: As data passes through the switch, it examines addressing information attached to each data packet. From this information, the switch determines the packet’s destination on the network. It then creates a virtual link to the destination and sends the packet there.
The efficiency and speed of a switch depends on its algorithms, its switching fabric, and its processor. Its complexity is determined by the layer at which the switch operates in the OSI (Open Systems Interconnection) Reference Model (see above).
OSI is a layered network design framework that establishes a standard so that devices from different vendors work together. Network addresses are based on this OSI Model and are hierarchical. The more details that are included, the more specific the address becomes and the easier it is to find.
The Layer at which the switch operates is determined by how much addressing detail the switch reads as data passes through.
Switches can also be considered low end or high end. A low-end switch operates in Layer 2 of the OSI Model and can also operate in a combination of Layers 2 and 3. High-end switches operate in Layer 3, Layer 4, or a combination of the two.
Layer 2 Switches (The Data-Link Layer)
Layer 2 switches 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 aren’t very smart—that is, they don’t look at the data packet very closely to learn anything more about where it’s headed.
Layer 3 Switches (The Network Layer)
Layer 3 switches use network or IP addresses that identify locations on the network. They read network addresses more closely than Layer 2 switches—they identify network locations as well as the physical device. A location can be a LAN workstation, a location in a computer’s memory, or even a different packet of data traveling through a network.
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. But although they’re smarter, they may not be as fast if their algorithms, fabric, and processor don’t support high speeds.
Layer 4 Switches (The Transport Layer)
Layer 4 of the OSI Model coordinates communications between systems. Layer 4 switches are capable of identifying which application protocols (HTTP, SNTP, FTP, and so forth) are included with each packet, and they use 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 to which a packet belongs.
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 because any company- or industry-specific protocols can be confined to only authorized switched ports or users. This security feature is often reinforced with traffic filtering and forwarding features. collapse