The difference between layer 2, 3, and 4 network switches

With the rapid development of computer networks over the last decade, high-end switching has become one of the most important functions of a network for moving data efficiently and quickly from one place to another.

Here’s how a network 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.

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 MAC- or IP-level. A MAC-level switch operates in Layer 2 of the OSI Model and can also operate in a combination of Layers 2 and 3. IP-level 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 the data link (MAC) layer addresses. 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 MAC addresses, but they do not look at the Layer 3 portion of the packet to learn anything more. Continue reading

5 common digital video errors, their causes, and how to fix them

Today’s new digital video formats like HDMI and DVI provide uncompressed digital audio and video with a sharp, crystal-clear image quality. No more flickering and blurry pictures. However, even the best inventions have their limitations. Digital video signals require a huge amount of bandwidth to be transmitted properly. Using low-quality cabling or distribution equipment may lead to problems. Here are the five most common:

Problem #1: Black screen (no picture at all).
Possible cause: A. Bad cable or one that’s too long, causing either the video signals or EDID/HDCP control signals not to be transmitted properly. Make sure that you use good-quality, high-speed HDMI® cables—they don’t even have to be expensive ones—or try an HDMI extender. B. HDCP is unsupported. Does the display support HDCP? DVI displays usually don’t.

Problem #2: “Sparkles” in the picture.
Usually caused by: Too long or inferior HDMI cable. Use a video extender or change to active cables with equalization.

Problem #3: RGB color tint.
Usually caused by: A color encoding issue, a common problem when using a DVI display with an HDMI source. If you’re using a splitter or an extender between your source and the link, make sure it handles EDID. If possible, force the source (for instance, a Blu-ray player) to output HDMI video with RGB color encoding instead of Component (YCbCr) video encoding.

Problem #4: White noise, or just “snow,” for a picture.
Usually caused by: An HDCP issue. This is actually what the encrypted video looks like. It happens when your display (or any active component, like an extender or a splitter, used in the transmission) doesn’t support HDCP. The display, in turn, isn’t able to decrypt the video stream. Be sure to use equipment that supports HDCP.

Problem #5: Flickering, unstable, or blinking image.
Can be caused by: Electromagnetic or radio frequency interference (EMI/RFI), bad cable, or cable that’s too long. These all can cause issues with HDCP or the video signal, resulting in flickering or the video randomly disappearing then reappearing after a second. The solution: Use certified high-speed HDMI cables instead of standard HDMI cables, or if you need to transmit longer distances, try an extender or change to active cables with equalization.

How to implement multicasting

While IP multicasting has many benefits, it also presents challenges. Multicasting delivers identical data to multiple receivers simultaneously, without transmitting multiple copies. So, when multicast data enter a subnet, the natural reaction of the switches is to send the multicast data to all their ports. This is referred to as multicast flooding and means that all the ports in that subnet (or at least their network interfaces) are required to process that multicast data even if they are not “seeing” this data. This can cause more data to travel across the network and slow or overrun the network infrastructure. IGMP (Internet Group Management Protocol) offers a solution to this issue.

Our MediaCento™ IPX extends HDMI video over any IP network to as many as 250 distant screens—or to video walls. You can run the MediaCento IPX in unicast (one transmitter to one receiver)MediaCento IPX or multicast (one transmitter to many receivers) mode applications. The unit can also support a video wall, using multicast mode to output a single source video to a matrix of screens, so that you can project your HD content on a larger scale with one image divided over multiple video screens.

For MediaCento IPX multicasting applications, it’s very important to choose the right Ethernet switch, one that can handle the requirements to multicast data in your network without flooding your IP infrastructure. Continue reading

How to choose the correct digital signage display

Shopping for digital signage displays is vastly different than shopping for flat-screen televisions for one’s home. When looking into purchasing displays for digital signage, the primary driver needs to be quality, not cost.

Consumer-grade displays
Consumer-grade LCDs are inexpensive and usually easily available. However, they do not come with extended warranties, usually only having warranty periods of a few months to a year. The screen performance and brightness are limited and do not last long in the scheme of things. Consumer-grade displays usually do not have a screen saver capability in case the video signal is lost, nor is an automatic on/off switch feature available.

displayCommercial-grade displays
In contrast, commercial-grade LCDs are designed specifically for the rigors of commercial digital signage applications and, as such, cost more. Digital signage usage differs significantly from consumer display usage, with displays needing to be on for longer hours. The hardware in commercial-grade displays enables more effective operation in commercial environments. Heat dissipation plates, cooling fans, and other electronics are components that enable these displays to be on for long hours with economical power consumption.

Other features in commercial grade LCDs may include video-wall processors, scheduling options, and lockable control panels. Commercial displays can be rotated, meaning they can be hung horizontally (landscape) or vertically (portrait). This flexibility enables businesses to use displays in a way that fits space requirements and desired look and feel of the environment. The bezel on commercial signage displays is uniform, unlike on consumer-grade TV screens, and usually much thinner than consumer-grade bezels. This enables creative layouts with more than one display.

Commercial displays also usually have warranties of several years. The industry standard warranty starts at three years, and some manufacturers are starting to offer standard five-year warranties. Continue reading

6 Things to remember when investing in digital signage

Digital signage can truly be an enigma. Today, it seems to be all around us in forms as diverse as interactive flat-panel displays, signs the size of buildings, and, most recently, on mobile devices we carry around with us.

Digital signage can be a very effective and surprisingly affordable communications medium for businesses and institutions of all types and sizes. But if you’re just getting started with a digital signage project — as well as designing the AV infrastructure behind the screens — you may be unsure of where exactly to begin and what all is needed to make it happen. Here are six things to remember when investing in digital signage.

1. Budget
A digital signage system is not a one-time purchase. The budget needs to include costs beyond the initial investment. Future purchases will likely include software upgrades, new hardware, tech support, and, possibly, training. A company may even seek outside design consultants occasionally to completely refresh its look. In general, a budget that accounts for up to 24 months is better than one that only considers the first outlay of cash for displays.

2. Scalability
Another factor in setting up digital signage systems that is often overlooked is scalability. An inflexible system seriously limits the ability to adjust, add, and change hardware and displays in the future. Content and functionality of the signage system will be in flux as well. Expanding signage configurations is par for the course when setting up a signage system. Other departments will want to deploy it once they see how effective it is. Companies get bigger and change locations, add offices, upgrade facilities. Signage needs to be able to scale with the organization.

3. Involve more than one person
Digital signage shouldn’t be software that goes onto one computer with only one person running the show. Many people in an organization should be involved in digital signage content and configurations. Licensing agreements or Web-based systems easily accommodate multiple users, and the effort that goes into creating content and maintaining the system won’t need to start at square one with each personnel change. Continue reading

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