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Black Box Explains…Media converters that also work as switches.

Media converters transparently convert the incoming electrical signal from one cable type and then transmit it over another type—thick coax to Thin, UTP to fiber, and so on. Traditionally, media... more/see it nowconverters were purely Layer 1 devices that only converted electrical signals and physical media and didn’t do anything to the data coming through the link.

Today’s media converters, however, are often more advanced Layer 2 Ethernet devices that, like traditional media converters, provide Layer 1 electrical and physical conversion. But, unlike traditional media converters, they also provide Layer 2 services and route Ethernet packets based on MAC address. These media converters are often called media converter switches, switching media converters, or Layer 2 media converters. They enable you to have multiple connections rather than just one simple in-and-out connection. And because they’re switches, they increase network efficiency.

Media converters are often used to connect newer 100-Mbps, Gigabit Ethernet, or ATM equipment to existing networks, which are generally 10BASE-T, 100BASE-T, or a mixture of both. They can also be used in pairs to insert a fiber segment into copper networks to increase cabling distances and enhance immunity to electromagnetic interference.

Rent an apartment…
Media converters are available in standalone models that convert between two different media types and in chassis-based models that house many media converters in a a single chassis.

Standalone models convert between two media. But, like a small apartment, they can be outgrown.

Consider your current and future applications before selecting a media converter. A good way to anticipate future network requirements is to choose media converters that work as standalone devices but can be rackmounted if needed later.

…or buy a house.
Chassis-based or modular media converter systems are normally rackmountable and have slots to house media converter modules. Like a well-planned house, the chassis gives you room to grow. These are used when many Ethernet segments of different media types need to be connected in a central location. Modules are available for the same conversions performed by the standalone converters, and they enable you to mix different media types such as 10BASE-T, 100BASE-TX, 100BASE-FX, ATM, and Gigabit modules. Although enterprise-level chassis-based systems generally have modules that can only be used in a chassis, many midrange systems feature modules that can be used individually or in a chassis. collapse


Black Box Explains...MIMO wireless.

Multiple-Input/Multiple-Output (MIMO) is a part of the new IEEE 802.11n wireless standard. It’s a technique that uses multiple signals to increase the speed, reliability, and coverage of wireless networks. It... more/see it nowtransmits multiple datastreams simultaneously, increasing wireless capacity to up to 100 or even 250 Mbps.

This wireless transmission method takes advantage of a radio transmission characteristic called multipath, which means that radio waves bouncing off surfaces such as walls and ceilings will arrive at the antenna at fractionally different times. This characteristic has long been considered to be a nuisance that impairs wireless transmission, but MIMO technology actually exploits it to enhance wireless performance.

MIMO sends a high-speed data stream across multiple antennas by breaking it into several lower-speed streams and sending them simultaneously. Each signal travels multiple routes for redundancy.

To pick up these multipath signals, MIMO uses multiple antennas and compares signals many times a second to select the best one. A MIMO receiver makes sense of these signals by using a mathematical algorithm to reconstruct the signals. Because it has multiple signals to choose from, MIMO achieves higher speeds at greater ranges than conventional wireless hardware does. collapse


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. collapse


Black Box Explains...Fiber.


Fiber versus copper.

When planning a new or upgraded cabling infrastructure, you have two basic choices: fiber or copper. Both offer superior data transmission. The decision on which one... more/see it nowto use may be difficult. It will often depend on your current network, your future networking needs, and your particular application, including bandwidth, distances, environment, cost, and more. In some cases, copper may be a better choice; in other situations, fiber offers advantages.


Although copper cable is currently more popular and much more predominant in structured cabling systems and networks, fiber is quickly gaining fans.


Fiber optic cable is becoming one of the fastest-growing transmission mediums for both new cabling installations and upgrades, including backbone, horizontal, and even desktop applications. Fiber optic cable is favored for applications that need high bandwidth, long distances, and complete immunity to electrical interference. It’s ideal for high data-rate systems such as Gigabit Ethernet, FDDI, multimedia, ATM, SONET, Fibre Channel, or any other network that requires the transfer of large, bandwidth-consuming data files, particularly over long distances. A common application for fiber optic cable is as a network backbone, where huge amounts of data are transmitted. To help you decide if fiber is right for your new network or if you want to migrate to fiber, take a look at the following:



The advantages of fiber.

Greater bandwidth-Because fiber provides far greater bandwidth than copper and has proven performance at rates up to 10 Gbps, it gives network designers future-proofing capabilities as network speeds and requirements increase. Also, fiber optic cable can carry more information with greater fidelity than copper wire. That’s why the telephone networks use fiber, and many CATV companies are converting to fiber.


Low attenuation and greater distance-Because the fiber optic signal is made of light, very little signal loss occurs during transmission so data can move at higher speeds and greater distances. Fiber does not have the 100-meter (304.8-ft.) distance limitation of unshielded twisted-pair copper (without a booster). Fiber distances can range from 300 meters to 40 kilometers, depending on the style of cable, wavelength, and network. (Fiber distances are typically measured in metric units.) Because fiber signals need less boosting than copper ones do, the cable performs better.


Fiber networks also enable you to put all your electronics and hardware in one central location, instead of having wiring closets with equipment throughout the building.


Security-Your data is safe with fiber cable. It does not radiate signals and is extremely difficult to tap. If the cable is tapped, it’s very easy to monitor because the cable leaks light, causing the entire system to fail. If an attempt is made to break the security of your fiber system, you’ll know it.


Immunity and reliability-Fiber provides extremely reliable data transmission. It’s completely immune to many environmental factors that affect copper cable. The fiber is made of glass, which is an insulator, so no electric current can flow through. It is immune to electromagnetic interference and radio-frequency interference (EMI/RFI), crosstalk, impedance problems, and more. You can run fiber cable next to industrial equipment without worry. Fiber is also less susceptible to temperature fluctuations than copper is and can be submerged in water.


Design-Fiber is lightweight, thin, and more durable than copper cable. And, contrary to what you might think, fiber optic cable has pulling specifications that are up to ten times greater than copper cable’s. Its small size makes it easier to handle, and it takes up much less space in cabling ducts. Although fiber is still more difficult to terminate than copper is, advancements in connectors are making temination easier. In addition, fiber is actually easier to test than copper cable.


Migration-The proliferation and lower costs of media converters are making copper to fiber migration much easier. The converters provide seamless links and enable the use of existing hardware. Fiber can be incorporated into networks in planned upgrades.


Standards-New TIA/EIA standards are bringing fiber closer to the desktop. TIA/EIA-785, ratified in 2001, provides a cost-effective migration path from 10-Mbps Ethernet to 100-Mbps Fast Ethernet over fiber (100BASE-SX). A recent addendum to the standard eliminates limitations in transceiver designs. In addition, in June 2002, the IEEE approved a 10-Gigabit Ethernet standard.


Costs-The cost for fiber cable, components, and hardware is steadily decreasing. Installation costs for fiber are higher than copper because of the skill needed for terminations. Overall, fiber is more expensive than copper in the short run, but it may actually be less expensive in the long run. Fiber typically costs less to maintain, has much less downtime, and requires less networking hardware. And fiber eliminates the need to recable for higher network performance.


Multimode or single-mode, duplex or simplex?

Multimode-Multimode fiber optic cable can be used for most general fiber applications. Use multimode fiber for bringing fiber to the desktop, for adding segments to your existing network, or in smaller applications such as alarm systems. Multimode cable comes with two different core sizes: 50 micron or 62.5 micron.


Single-mode-Single-mode is used over distances longer than a few miles. Telcos use it for connections between switching offices. Single-mode cable features an 8.5-micron glass core.


Duplex-Use duplex multimode or single-mode fiber optic cable for applications that require simultaneous, bidirectional data transfer. Workstations, fiber switches and servers, fiber modems, and similar hardware require duplex cable. Duplex is available in single- and multimode.


Simplex-Because simplex fiber optic cable consists of only one fiber link, you should use it for applications that only require one-way data transfer. For instance, an interstate trucking scale that sends the weight of the truck to a monitoring station or an oil line monitor that sends data about oil flow to a central location. Simplex fiber comes in single- and multimode types.


50- vs. 62.5-micron cable.

Although 50-micron fiber cable features a smaller core, which is the light-carrying portion of the fiber, both 62.5- and 50-micron cable feature the same glass cladding diameter of 125 microns. You can use both in the same types of networks, although 50-micron cable is recommended for premise applications: backbone, horizontal, and intrabuilding connections, and should be considered especially for any new construction and installations. And both can use either LED or laser light sources.


The big difference between 50-micron and 62.5-micron cable is in bandwidth-50-micron cable features three times the bandwidth of standard 62.5-micron cable, particularly at 850 nm. The 850-nm wavelength is becoming more important as lasers are being used more frequently as a light source.


Other differences are distance and speed. 50-micron cable provides longer link lengths and/or higher speeds in the 850-nm wavelength. See the table below.




The ferrules: ceramic or composite?

As a general rule, use ceramic ferrules for critical network connections such as backbone cables or for connections that will be changed frequently, like those in wiring closets. Ceramic ferrules are more precisely molded and fit closer to the fiber, which gives the fiber optic cables a lower optical loss.


Use composite ferrules for connections that are less critical to the network’s overall operation and less frequently changed. Like their ceramic counterparts, composite ferrules are characterized by low loss, good quality, and a long life. However, they are not as precisely molded and slightly easier to damage, so they aren’t as well-suited for critical connections.


Testing and certifying fiber optic cable.

If you’re accustomed to certifying copper cable, you’ll be pleasantly surprised at how easy it is to certify fiber optic cable because it’s immune to electrical interference. You only need to check a few measurements.

Attenuation (or decibel loss)-Measured in decibels/kilometer (dB/km), this is the decrease of signal strength as it travels through the fiber cable. Generally, attenuation problems are more common on multimode fiber optic cables.

Return loss-This is the amount of light reflected from the far end of the cable back to the source. The lower the number, the better. For example, a reading of -60 decibels is better than -20 decibels. Like attenuation, return loss is usually greater with multimode cable.

Graded refractive index-This measures how the light is sent down the fiber. This is commonly measured at wavelengths of 850 and 1300 nanometers. Compared to other operating frequencies, these two ranges yield the lowest intrinsic power loss. (NOTE: This is valid for multimode fiber only.)

Propagation delay-This is the time it takes a signal to travel from one point to another over a transmission channel.

Optical time-domain reflectometry (OTDR)-This enables you to isolate cable faults by transmitting high-frequency pulses onto a cable and examining their reflections along the cable. With OTDR, you can also determine the length of a fiber optic cable because the OTDR value includes the distance the optic signal travels.


There are many fiber optic testers on the market today. Basic fiber optic testers function by shining a light down one end of the cable. At the other end, there’s a receiver calibrated to the strength of the light source. With this test, you can measure how much light is going to the other end of the cable. Generally, these testers give you the results in dB lost, which you then compare to the loss budget. If the measured loss is less than the number calculated by your loss budget, your installation is good.


Newer fiber optic testers have a broad range of capabilities. They can test both 850- and 1300-nanometer signals at the same time and can even check your cable for compliance with specific standards.


Fiber precautions.

A few properties particular to fiber optic cable can cause problems if you aren’t careful during installation.

Intrinsic power loss-As the optic signal travels through the fiber core, the signal inevitably loses some speed through absorption, reflection, and scattering. This problem is easy to manage by making sure your splices are good and your connections are clean.

Microbending-Microbends are minute deviations in fiber caused by excessive bends, pinches, and kinks. Using cable with reinforcing fibers and other special manufacturing techniques minimizes this problem.

Connector loss-Connector loss occurs when two fiber segments are misaligned. This problem is commonly caused by poor splicing. Scratches and dirt introduced during the splicing process can also cause connector loss.

Coupling loss-Similar to connector loss, coupling loss results in reduced signal power and is from poorly terminated connector couplings.


Remember to be careful and use common sense when installing fiber cable. Use clean components. Keep dirt and dust to a minimum. Don’t pull the cable excessively or bend it too sharply around any corners. That way, your fiber optic installation can serve you well for many years.

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Black Box Explains... Video extenders with built-in skew compensation.

To ensure the best video resolution, it’s important to match your video extension device with a compatible grade of cable. Some multimedia extenders are not designed to transmit video across... more/see it nowcable that’s higher than CAT5. In fact, with these extenders, the higher-grade cable may actually degrade video.

The problem is with the cable twists of CAT5e and CAT6 cables. To reduce signaling crosstalk, these higher-grade cables have tighter twists—and more of them—than CAT5 cable does. For this reason, the wire distance that an electrical signal has to travel is different for each pair. This doesn’t normally cause a problem with data, but if you’re sending higher-resolution analog video signals across long cables, you may see color separation caused by the video signals arriving at different times.

To avoid this, you could use only the lower-grade cable with the extenders. But what if you already have CAT5e or higher cable installed in your building, or you simply want the latest and greatest copper wiring? Order an extender receiver that features built-in skew compensation so it can work properly with higher cable grades at longer distances. 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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Black Box Explains...Coax connectors.

The BNC (Bayonet-Neill-Concelman) connector is the most commonly used coax connector. This large ”bayonet“ connector features a slotted outer conductor and an inner plastic dielectric, and it offers easy connection... more/see it nowand disconnection. After insertion, the plug is turned, tightening the pins in the socket. It is widely used in video and Radio Frequency (RF) applications up to 2.4 GHz. It is also common in 10BASE2 Ethernet networks, on cable interconnections, network cards, and test equipment.

The TNC connector is a threaded version of the BNC connector. It works in frequencies up to 12 GHz. It‘s commonly used in cellular telephone RF/antenna applications.

The N connector is a larger, threaded connector that was designed in the 1940s for military systems operating at less than 5 GHz. In the 1960s, improvements raised performance to 12 GHz. The connector features an internal gasket and is hand tightened. It is common on 2.4-GHz antennas.

The UHF connector looks like a coarse-threaded, big center-conductor version of the N connector. It was developed in the 1930s. It is suitable for use up to 200–300 MHz and generally offers nonconstant impedance.

The F connector is most often used in cable and satellite TV and antenna applications; and it performs well at high frequencies. The connector has a 3/8–32 coupling thread. Some F connectors are also available in a screw-on style.

The SMA (Subminiature A) connector is one of the most common RF/microwave connectors. This small, threaded connector is used on small cables that won’t be connected and disconnected often. It’s designed for use to 12.4 GHz, but works well at 18, and sometimes even up to 24 GHz. This connector is often used in avionics, radar, and microwave communications.

The SMC (Subminiature C) connector is a small, screw-on version of the SMA. It uses a 10–32 threaded interface and can be used in frequencies up to 10 GHz. This connector is used primarily in microwave environments.

The SMB (Subminiature B) connector is a small version of the SMC connector. It was developed in the 1960s and features a snap-on coupling for fast connections. It features a self-centering outer spring and overlapping dielectric. It is rated from 2–4 GHZ, but can possibly work up to 10 GHz.

The MCX (Micro Coax) connector is a coax RF connector developed in the 1980s. It has a snap-on interface and uses the same inner contact and insulator as the SMB connector but is 30% smaller. It can be used in broadband applications up to 6 GHz. collapse


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:

  • 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.
One or many access points?

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.

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Black Box Explains…VoIP

Voice over Internet Protocol (VoIP) is a recently developed, cost-saving alternative to traditional telephone service that enables voice data to be transported over IP networks, like the Internet, instead of... more/see it nowthe public switched telephone network (PSTN) or a cellular network.

VoIP, which operates strictly over IP networks, can connect to other VoIP nodes or traditional phone lines. The IP network used may be the Internet or a private network.

In either instance, the actual data-transport portion of this network can still be made up of the full gamut of network services: high-speed leased lines, Frame Relay, ATM, DSL, copper, fiber, wireless, satellite, and microwave signals. VoIP simply digitizes voice data and adds it to other information traveling along the same network.

With this flexible technology, a phone call can be placed between two PCs, between a PC and a standard telephone, between a PC and an IP phone, between an IP phone and a standard telephone, or between two IP phones. It will take a long time for the PSTN to support this technology seamlessly, but this seems to be the direction in which phone systems are headed.

Benefits of VoIP
Because VoIP is inexpensive, has a worldwide reach, and operates on a few simple principles, it’s exploded in popularity in recent years—especially among both small and large businesses that incur significant long-distance telephone expenses.

Savings
Without question, the primary benefit of a VoIP system is decreasing or eliminating long-distance telephone charges. Organizations with a high volume of long-distance voice traffic stand to save quite a lot of money by implementing a VoIP system. However, this factor alone may not warrant a full commitment to VoIP for some companies.

Setup fees for VoIP are usually quite low so your organization can generally start saving money after only a month or two of service. And with the wide variety of VoIP products and services on the market, it’s easier than ever to set up a VoIP phone system over your network.

Convenience
VoIP can be set up in a way that enables you to use phone numbers in exactly the same way as you did before VoIP. Most of the services you get with traditional phone service—Voice Mail, Call Waiting, and Call Routing, for instance—are also available with VoIP.

VoIP doesn’t interfere with other network services either, so you can surf the Web while making a VoIP call.

Portability
VoIP doesn’t tie you to one phone or to a single location. Anywhere you find high-speed reliable Internet access, you can use VoIP. Your phone number stays the same wherever you are—office, home, hotel, or even traveling overseas.

Standards
Although the ITU standards for VoIP have evolved significantly in the last few years, VoIP is still suffering from a lack of generally accepted interoperability standards.

H.323, a standard for real-time audio, video, and data communications across IP-based networks (including the Internet), is almost universally accepted as the primary standard for VoIP call setup and signaling. It’s actually a collection of standards that works together for sending multimedia and data over networks that don’t provide guaranteed Quality of Service (QoS).

The H.323 standard includes:
- Real-Time Transport Protocol (RTP) specifies end-to-end network transport functions for applications transmitting real-time data such as video. RTP provides services like payload type identification, sequence numbering, time stamping, and delivery monitoring to real-time applications. Plus, it works with RTCP.
- Real-time Transport Control Protocol (RTCP) works with RTP to provide a feedback mechanism, providing QoS status and control information to the streaming server.
- Registration, Admission, Status (RAS) is a gateway protocol that manages functions such as signaling, registration, admissions, bandwidth changes, status, and disengage procedures.
- Q.931 manages call setup and termination.
- H.245 negotiates channel usage and capabilities.
- H.235 provides security and authentication.

As VoIP product manufacturers began conducting interoperability tests for more complex operations, they recognized that they needed a simpler and more adaptable standard for call handling and signaling protocol.

To this end, the IETF developed the Session Initiation Protocol (SIP). SIP is built with less computer code than H.323 is, so it’s less cumbersome. Because SIP is similar in nature to HTML—it uses ASCII text for configuration—users can adapt it more easily for specific VoIP systems. In contrast, modifying H.323 for VoIP applications requires a knowledgeable computer programmer.

Both H.323 and SIP are considered “thick clients,” where intelligence is maintained in the end devices such as IP telephones. In this respect, H.323 has a head start, although most VoIP systems today support both H.323 and SIP.

Providers
Despite the fact that VoIP standards are still developing, providers are already flooding the market with products and services while forming partnerships and matching expertise to strengthen their position in this new market. The biggest of these players and alliances—the ones who have the size and experience to grasp technical issues and quickly build infrastructures over which to offer VoIP services—are able to keep up with (and often influence) the continual changes in this market and keep rolling out new services.

Components
A VoIP system depends on devices that connect your traditional phone or phone system to an IP network. Components that you’ll see in a VoIP system include:
- End-user devices
- Gateways or gatekeepers
- IPBXs
- IP Networks

End-user devices are usually VoIP telephones or PCs running VoIP software. End-user devices have their own IP address and make a direct connection to the IP network.

A gateway is a device that converts circuit-switched analog voice calls from a traditional PBX into VoIP packets and transmits them over an IP network either to another gateway or directly to an end-user device.

A gateway can have additional features such as voice compression, echo cancellation, and packet prioritization.

Because VoIP-enabled end-user devices can communicate directly with each other over an IP network, a gateway is not a required component of a VoIP system as long as the VoIP devices are connected directly to the IP network.

An IPBX is a PBX with a built-in gateway. IPBX systems are equipped for hundreds of telephone ports, with WAN support for trunk connections to the PSTN, and with high-speed IP WAN links. In addition to VoIP features, these systems usually include other features typical of traditional PBX systems such as music on hold, auto-attendant, and call management. Often, they include Ethernet ports to support VoIP telephones.

VoIP can be set up with or without a connection to standard PSTN phone service. You can, of course, place calls over the Internet directly from your PC or IP phone to another VoIP-enabled device. But what makes VoIP so versatile is that, through the use of a gateway service, it can also be used to call the numbers of phones connected to standard land-line or cellular phone services. They can also receive calls from standard telephones.

Not all fun and free calls
There are still things to consider when you’re deciding whether or not to invest in VoIP.

Regulation vagaries
Much of the government regulation of VoIP is still being worked out. The U.S. government hasn’t decided whether VoIP is going to be regulated as phone service or whether to tax it. VoIP isn’t available worldwide because some governments fear the loss of tax revenue or control.

Compatibility
Although older VoIP equipment may still have some compatibility issues, current VoIP products from different vendors generally work together.

Cost
For all the popular talk about VoIP being free, it isn’t truly free. Any VoIP system has costs associated with its implementation—equipment, high-speed Internet access, and gateway service. So, although it’s inexpensive, it’s a long way from being free. For organizations with a high volume of long-distance calls, especially to international locations, VoIP almost always pays for itself quickly. However, private users or organizations with a low volume of long-distance calls primarily within the U.S., may find that a standard service is actually more economical in the short- to mid-term.

QoS
VoIP depends on having a fast, reliable network to operate. A fast network connection with guaranteed bandwidth is not a problem in a corporate intranet where you have complete control over the network. However, if you’re using the Internet for VoIP, you’re using a public network that may be subject to slowdowns that cause drop-outs and distortion. You may find that your high-speed Internet connection is faster than the actual Internet and that the quality of your connection is generally unacceptable or is unacceptable at times when Internet usage is high.

There are four common network issues that can cause problems with a VoIP system:
- Latency is a delay in data transmission. With VoIP, this usually results in people speaking over one another because neither can tell when the other is finished talking.
- Loss. Losing a small percentage of voice transmission doesn’t affect VoIP, but too much (more than 1%) compromises the quality of the call.
- Jitter—is common to congested networks with bursty traffic. Jitter can be managed to some degree with software buffers.
- Sequence errors—or changes in the order of packets when they’re recompiled at the receiving station, degrades sound quality.

Emergency services
If you subscribe to a VoIP gateway service that enables you to use your VoIP phone like a regular phone, be aware that you may not be able to call 911 for emergencies. If 911 service is important to you because you don’t have an alternative way to call 911, shop for a VoIP provider who does provide this service.

Consider, too, that VoIP needs both working Internet access and power to work. If you lose your Internet service, your phone goes, too. And, unlike regular phone service that can keep basic telephones working when the power goes out, VoIP needs power—if you lose power, you lose your phone.

Moving forward
Before VoIP technology becomes truly universal, the current worldwide PSTN will have to migrate to a packet-based IP equivalent. Industry inertia alone dictates this will not occur instantly. The current worldwide PSTN system has grown to what it is over a period of 125 years. Given the sheer complexity of the existing PSTN, the migration to an IP packet network will probably occur during several decades.

As migration from the PSTN to IP-based networks proceeds, businesses and home users will gradually discover reasons of their own to implement VoIP. It won’t happen right away, but we predict that VoIP will become a big part of telecommunications in the not-so-distant future.

Although it’s not quite as convenient as conventional phone service, VoIP can offer serious savings—particularly if you now regularly pay for multiple overseas phone calls. Keep in mind though, VoIP isn’t a one-size-fits-all solution. But with a little planning, VoIP could spell savings for you! collapse


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