Multicast video transmission vs. Unicast video transmission methods

describe the imageMulticast video transmissionWhen looking for the most effective way to manage video in a security system, there are two often-discussed video transmission methods: Multicast and Unicast. Both have their benefits, but which is best for security applications?

Multicast is a method of one-to-many transmissionwhich is often deployed in IP applications of streaming media. Multiple viewers can simultaneously tap into a single transmission from one source.

Television programming is a perfect analogy. When you want to watch HBO you tap into the HBO feed on the cable network, not to a dedicated signal of HBO. If your cable box is authorized, you get access to the existing stream of HBO on the cable network.

To benefit from Multicast, multiple simultaneous views of the same stream are required. For customers who have multiple operators viewing the same live cameras, Multicast may be a benefit.

However, in most security applications, Network Video Management Systems (NVMS) are used toview recorded video much more than live video, like reviewing video from a specific date and time, around an alarm event, or reviewing video as part of an investigation. Since all recorders, including the most advanced multicast-based recorders, are based on Unicast video streaming for playback, there really is no gain on operation performance by utilizing Multicast network.

To realize significant benefits from Multicast transmissions, a multicast-enabled network must be constructed to enable single stream replication on the IP network, making it available for every user looking to view it.

Multicast stream can only be used on the Local Area Network. Operators communicating over a wireless connection or over the corporate WAN will communicate using Unicast stream by default, and will not gain from the Multicast capability. In addition, IT departments are wary about enabling Multicast on their network due to security reasons, not to mention the cost associated with it.

Is Unicast a better option?

With Unicast transmission, every user in the network who would like to view video will receive adedicated video stream from the Video Management System (VMS). Compared to Multicast transmission, Unicast does utilize more bandwidth; however, these streams are only required between the source and the “viewer”, and do not affect the entire network (as a Multicast transmission would.)

With VMS implementation of advanced video compression technology and the ability to maintain symmetric bandwidth management of video, users can manage multiple high-quality video streams on a Unicast network without the deployment of Multicast transmission.

To summarize, Multicast transmissions do offer the benefit of lower bandwidth consumption, but comes with higher network construction cost.  Unicast provide cost-savings on the construction of Multicast-enabled networks while maintaining real-time, low latency, high-quality video with adequate bandwidth management for all users on the network.

At American Dynamics, we believe in empowering customers to invest in enhancing their security systems rather than investing in the construction of new IT equipment. VideoEdge is a Unicast-based network video recorder. Unlike Multicast-based digital video recorders that are dependent on the network to manage the video streaming (the Multicast network managing video transmission), VideoEdge utilizes advanced network management techniques that provide higher operational performance.

Note: Most recorders that are dependent on the multicast network to manage the streaming have different performance levels (e.g. 200 or 300Mbps write to disk, while operating on a multicast network compared to 100 or 150Mbps write to disk, while utilizing Unicast network.) The main reason is that these recorders are now tasked with the video management and are not capable of symmetric bandwidth management.

VideoEdge’s advanced networking architecture manages the video in real time. When a user requests video, live or instant playback, VideoEdge responds with no latency. This advanced architecture does not strain the system resources and, as a result, the rack-mount VideoEdge Network Video Recorder maintains full performance of 400Mbps write to disk, 400Mbps video streaming to client, with the Desktop maintainng 50/50Mbps, while providing metadata generation on all cameras. This is accomplished with no video quality degradation or frame-rate loss, all the time on all cameras.


Have any questions about Multicast or Unicast video transmissions; post them in the comments section below.

Technology for Safer Schools

safer schoolsViolence in American schools over the past two decades has resulted in the real need for an increase in security technology in the school setting. Federal government initiatives like Safe Schools, Healthy Students have been created to bring together school officials, law enforcement, and surrounding community leaders.

Along with federal grants, these initiatives have helped generate a national awareness for the increase of school security technologies to help keep our schools safe. Be sure to read Cheryl Shea’s blog post, “Technology for Safer Schools”, on the Tyco Security Products Blog to see what types of technologies are being deployed in the school setting and how manufacturers like Tyco Security Products are working to meet the specific requirements and limited budgets of this industry.

What are your areas of concern regarding school safety, let us know by leaving a comment.

IP Cameras at Low Light | What Has Changed and How to Choose

low lightWhether or not it’s deserved, IP cameras have developed a reputation for poor performance in low light. And because low-light conditions exist with nearly all camera installations, this perception has inhibited some organizations from adopting the technology, in spite of its many strategic and far-reaching benefits.

The challenges have had less to do with delivering the video over an IP network than with the CMOS sensors that most IP cameras use. Historically these sensors have been able to deliver higher megapixel resolution, but they weren’t able to match the CCD sensors often used in analog cameras for low-light performance. Because of this, some IP cameras generate grainy images at low light, resulting not only in decreased picture clarity but also in higher bandwidth usage and increased storage, since compression techniques interpreted the graininess as motion in the scene.

The past 12 months, however, have seen some advancements in technology propel the IP cameraforward as a more useful tool in low-light situations. Camera manufacturers have been able to leverage advances in sensors, encoding and processing power born from the automotive and other industries to resolve many of these issues. And High Profile H.264 compression helps to more effectively manage bandwidth usage, while more sensitive elements in the sensors provide higher-quality images.

Companies hoping to benefit from these advances should look for the following features in low-light IP cameras:

1) True day-night function, or an IR cut-filter. This means that when light drops below a certain level, only black and white is getting into the sensor, increasing its sensitivity.  This improves image clarity while decreasing noise or graininess in the image, which can be interpreted as motion in the encoder.  When the encoder compresses an image with a higher level of motion or noise, the bandwidth consumption can skyrocket.

2) An IR-corrected lens. Infrared light is invisible to the human eye, but it’s not invisible to camera sensors. It also travels at different wavelengths from visible light.  These differences result in the focal point that varies between the lights sources and means the sensor must actually move to achieve focus when lights sources produce varying amounts of IR light. If there is a lot of IR light in a scene that a camera has to adjust to, it can change the focal point of the camera. For instance, halogen light is very IR heavy when compared to fluorescent light, which has almost no IR light.  If you have a halogen light in an office and you turn that light off, the camera can go out of focus because it was focused for that light source. IR-corrected lenses resolve this problem.

Historically, “auto-back focus” was used to compensate for this type of change.  However, given that auto-back focus can hunt for a focal point for quite some time, often ending up at the wrong one, it is less effective in serving customers that expect 100% uptime in their security system.

3) A High Profile H.264 compression. There are multiple profiles of H.264 and users should be wary of which profile a manufacturer uses.  High profile is generally more processor intensive and is a bit harder for a manufacturer to deliver well.  But the result is worth the development effort.

Buyers should beware of the “base profile” H.264 implementations.  While the high profile is used for media such as Blu-ray, base profile is used for applications like teleconferencing.  The image quality standards between those two uses speak for themselves.

4) For applications at the very bottom of the low-light range, look for a camera that supplies its own IR illumination. Watch this quick video about the added benefits of IR illumination.

We encourage everyone who is concerned about low-light performance to enlist the help of their systems integrator in lining up their camera options where they’re intended to be used and test them out against each other.

Whenever possible, camera shoot-outs should be the norm for customers who care about image quality in any conditions, and this is especially true for low light applications.  At the end of the day, this is the best way to ensure that the best technology will be chosen for the application.


Leave a comment below and tell us what low-light feature you rely on the most and why.