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...802.3ah.
802.3ah, also called Ethernet in the First Mile (EFM), is a new Ethernet standard designed to compete with standards such as DSL and cable modem in delivering broadband access to... more/see it nowhomes.
The 802.3ah specification covers point-to-point copper, point-to-point fiber, and point-to-multipoint fiber.
Ethernet in the First Mile over Copper (EFMC)
This point-to-point specification for copper wire takes advantage of DSL technology to send Ethernet over one pair of copper wires at 10 Mbps for 750 meters or 2 Mbps for 2700 meters.
Ethernet in the First Mile over Fiber (EFMF)
This point-to-point specification for single-mode, single-strand or single-mode, duplex fiber sends Ethernet at speeds of 100 Mbps or 1 Gbps up to 10 kilometers. It includes an optional extended temperature range from -40 to 185° F (-40 to 85° C) for outdoor use.
Ethernet in the First Mile over Passive Optical Networks (EPON)
This point-to-multipoint specification for fiber uses an optical splitter to divide the Ethernet signal into separate strands that go to individual subscribers. This enables an ISP to link many subscribers to a single uplink fiber without using active components in the field.
802.3ah includes the OAM specification, which provides utilities for monitoring and troubleshooting Ethernet links remotely, a capability vital for carrier-class deployment. OAM protocols address discovery, link monitoring, remote fault signaling, and remote loopback.
OAM is managed in-band but takes up very little bandwidth so network performance is not noticeably affected. OAM itself is not affected by VLANs or port-access restrictions.
Black Box Explains…Fiber Ethernet adapters vs. media converters.
When running fiber to the desktop, you have two choices for making the connection from the fiber to a PC: a fiber Ethernet adapter or a media converter like our... more/see it nowMicro Mini Media Converter.
Fiber Ethernet adapters:
Create no desktop clutter, but the PC must be opened.
Powered from the PC—require no separate power provision.
Require an open PCI or PCI-E slot in the PC.
Can create driver issues that must be resolved.
May be required in high-security installations that require a 100% fiber link to the desktop.
No need to open the PC but can create a cluttered look.
Powered from an AC outlet or a PC’s USB port.
Don’t require an open slot in the PC.
Plug-and-play installation—totally transparent to data, so there are no driver problems; install in seconds.
The short copper link from media converter to PC may be a security vulnerability. collapse
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...Designing your wireless network.
Setting up wireless devices that belong to the 802.11 family is relatively simple, but you do have to pay attention to a few simple factors.
Ad-hoc or infrastructure... more/see it nowmode?
The 802.11 wireless standards support two basic configurations: ad-hoc mode and infrastructure mode.
In ad-hoc mode, wireless user devices such as laptop computers and PDAs communicate directly with each other in a peer-to-peer manner without the benefit of access points.
Ad-hoc mode is generally used to form very small spontaneous networks. For instance, with ad-hoc mode, laptop users in a meeting can quickly establish a small network to share files.
Infrastructure mode uses wireless access points to enable wireless devices to communicate with each other and with your wired network. Most networks use infrastructure mode.
The basic components of infrastructure mode networks include:
One or many access points?
- The radios embedded or installed within the wireless devices themselves. Many notebook computers and other Wi-Fi-compliant mobile devices, such as PDAs, come with the transmitters built in. But for others, you need to install a card-type device to enable wireless communications. Desktop PCs may also need an ISA or a PCI bus adapter to enable the cards to work.
- The access point, which acts as a base station that relays signals between the 802.11 devices.
Access points are standalone hardware devices that provide a central point of communication for your wireless users. How many you need in your application depends on the number of users and the amount of bandwidth required by each user. Bandwidth is shared, so if your network has many users who routinely send data-heavy multimedia files, additional access points may be required to accommodate the demand.
A small-office network with fewer than 15 users may need just 1 access point. Larger networks require multiple points. If the hardware supports it, you can overlap coverage areas to allow users to roam between cells without any break in network coverage. A user’s wireless device picks up a signal beacon from the strongest access point to maintain seamless coverage.
How many access points to use also depends on your operating environment and the required range. Radio propagation can be affected by walls and electrical interference that can cause signal reflection and fading. If you’re linking mobile users indoors-where walls and other obstructions impede the radiated signal-the typical maximum range is 150 feet. Outdoors, you can get greater WLAN range-up to 2000 feet (depending on your antenna type) where there’s a clear line of sight!
For optimal speed and range, install your wireless access point several feet above the floor or ground and away from metal equipment or large appliances that may emit interference.
Battle of the bands.
In addition to sharing bandwidth, users also share a band. Most IEEE 802.11 or 802.11b devices function in the 2.4-2.4835-GHz band. But these frequencies are often congested, so you may want to use devices that take advantage of the IEEE 802.11a 5.725-5.825-GHz band.
No matter what frequency you use, you’ll want to isolate your users from outsiders using the same frequency. To do this, assign your users a network identifier, such as an Extended Service Set Identifier (ESSID), as well as distinct channels.
Web and wired network links.
The access point links your wireless network to your wired network, enabling your wireless users to access shared data resources and devices across your LAN enterprise. Some access points even feature capabilities for routing traffic in one or both directions between a wired and wireless network.
For Internet access, connect a broadband router with an access point to an Internet connection over a broadband service such as DSL, cable modem, or satellite.
For connecting network printers, you can dedicate a computer to act as a print server or add a wireless print server device; this enables those on your wireless network to share printers.
When to use external antennas.
If you plan to install access points, you can boost your signal considerably by adding external antennas. Various mounting configurations and high- and low-gain options are available.
You can also use add-on antennas to connect nodes where the topology doesn’t allow for a clear signal between access points. Or use them to link multiple LANs located far apart.
Additional external antennas are also useful to help overcome the effects of multipath propagation in which a signal takes different paths and confuses the receiver. It’s also helpful to deploy antennas that propagate the signal in a way that fits the environment. For instance, for a long, narrow corridor, use an antenna that focuses the RF pattern in one direction instead of one that radiates the signal in all directions.
Plan ahead with a site survey.
A site survey done ahead of time to plot where the signal is the strongest can help you identify problem areas and avoid dead spots where coverage isn’t up to par or is unreliable. For this, building blueprints are helpful in revealing potential obstructions that you might not see in your physical site walkthrough.
To field test for a clear signal path, attach an antenna to an access point or laptop acting as the transmitter at one end. Attach another antenna to a wireless device acting as a receiver at the other end. Then check for interference using RF test equipment (such as a wireless spectrum analyzer) and determine whether vertical or horizontal polarization will work best.
Need help doing this? Call us. We even offer a Site Survey Kit that has a variety of antennas included. Great for installers, the kit enables you to test a variety of antennas in the field before placing a larger antenna order. collapse
Black Box Explains...PoE phantom power.
10BASE-T and 100BASE-TX Ethernet use only two pairs of wire in 4-pair CAT5/CAT5e/CAT6 cable, leaving the other two pairs free to transmit power for Power over Ethernet (PoE) applications. However,... more/see it nowGigabit Ethernet or 1000BASE-T uses all four pairs of wires, leaving no pairs free for power. So how can PoE work over Gigabit Ethernet?
The answer is through the use of phantom power—power sent over the same wire pairs used for data. 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.
10- and 100-Mbps PoE may also use phantom power. The 802.3af PoE standard for use with 10BASE-T and 100BASE-TX defines two methods of power transmission. In one method, called Alternative A, power and data are sent over the same pair. In the other method, called Alternative B, two wire pairs are used to transmit data, and the remaining two pairs are used for power. That there are two different PoE power-transmission schemes isn’t obvious to the casual user because PoE Powered Devices (PDs) are made to accept power in either format.
Black Box Explains...Why media converters need SNMP.
The number of Ethernet switches and fiber optic segments being added to Ethernet networks keeps increasing. And as long as most Ethernet switches are only available with 10BASE-T and 100BASE-TX... more/see it nowinterfaces, media converters will remain in demand.
Until now, a failure on the network could go unnoticed. Once a failure was detected, it could take a long time to isolate it, especially if a technician had to be sent to the site. But media converters with SNMP eliminate some of the guesswork.
With SNMP, the IS manager can detect a failure, isolate it to a specific port, and determine what hardware is required to repair it. A technician can then be sent directly to the right place to fix faulty hardware or repair a broken cable.
SNMP enables you to set up alarms or traps when a link is down. You can turn features on and off from a central terminal, so theres no need to leave your desk. You can also monitor power supplies and replace them without interrupting service. SNMP management reduces the time and money it takes to get your network up and running again. The users on your network will notice—and appreciate—the improved service and reliability. collapse
Black Box Explains...T1 and E1.
If you manage a heavy-traffic data network and demand high bandwidth for high speeds, you need digital super-fast T1 or E1.
Both T1 and E1 are foundations of global communications. Developed... more/see it nowmore than 35 years ago and commercially available since 1983, T1 and E1 go virtually anywhere phone lines go, but theyre much faster. T1, used primarily in the U.S., sends data up to 1.544 Mbps; E1, used primarily in Europe, supports speeds to 2.048 Mbps. No matter where you need to connectNorth, South, or Central America, Europe, or the Pacific RimT1 and E1 can get your data there fast!
T1 and E1 are versatile, too. Drive a private, point-to-point line; provide corporate access to the Internet; enable inbound access to your Web Servereven support a voice/data/fax/video WAN that extends halfway around the world! T1 and E1 are typically used for:
• Accessing public Frame Relay networks or Public Switched Telephone Networks (PSTNs) for voice or fax.
• Merging voice and data traffic. A single T1 or E1 line can support voice and data simultaneously.
• Making super-fast LAN connections. Todays faster Ethernet speeds require the very high throughput provided by one or more T1 or E1 lines.
• Sending bandwidth-intensive data such as CAD/CAM, MRI, CAT-scan images, and other large files.
Basic T1 service supplies a bandwidth of 1.536 Mbps. However, many of todays applications demand much more bandwidth. Or perhaps you only need a portion of the 1.536 Mbps that T1 supplies. One of T1s best features is that it can be scaled up or down to provide just the right amount of bandwidth for any application.
A T1 channel consists of 24 64-kbps DS0 (Digital Signal [Zero]) subchannels that combine to provide 1.536 Mbps throughput. Because they enable you to combine T1 lines or to use only part of a T1, DS0s make T1 a very flexible standard.
If you dont need 1.536 Mbps, your T1 service provider can rent you a portion of a T1 line, called Fractional T1. For instance, you can contract for half a T1 line768 kbpsand get the use of DS0s 112. The service provider is then free to sell DS0s 1324 to another customer.
If you require more than 1.536 Mbps, two or more T1 lines can be combined to provide very-high-speed throughput. The next step up from T1 is T1C; it offers two T1 lines multiplexed together for a total throughput of 3.152 on 48 DS0s. Or consider T2 and get 6.312 Mbps over 96 DS0s by multiplexing four T1 lines together to form one high-speed connection.
Moving up the scale of high-speed T1 services is T3. T3 is 28 T1 lines multiplexed together for a blazing throughput of 44.736 Mbps, consisting of 672 DS0s, each of which supports 64 kbps.
Finally theres T4. It consists of 4032 64-kbps DS0 subchannels for a whopping 274.176 Mbps of bandwidththats 168 times the size of a single T1 line!
These various levels of T1 service can by implemented simulta-neously within a large enterprise network. Of course, this has the potential to become somewhat overwhelming from a management standpoint. But as long as you keep track of DS0s, you always know exactly how much bandwidth you have at your disposal.
T1s cousin, E1, can also have multiple lines merged to provide greater throughput. collapse
Black Box Explains...vDSL.
VDSL (Very High Bit-Rate Digital Subscriber Line or Very High-Speed Digital Subscriber Line) is a “last-mile” broadband solution for both businesses and homes, providing economical, high-speed connections to fiber optic... more/see it nowbackbones.
VDSL enables the simultaneous transmission of voice, data, and video on existing voice-grade copper wires. Depending on the intended applications, you can set VDSL to run symmetrically or asymmetrically. VDSL’s high bandwidth allows for applications such as high-definition television, video-on-demand (VOD), high-quality videoconferencing, medical imaging, fast Internet access, and regular voice telephone services—all over a single voice-grade twisted pair. The actual VDSL distances you achieve vary based on line rate, gauge and type of wire, and noise/crosstalk environment.