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Tag Archives: Video over Ethernet
Here is a great discussion on network traffic and video over IP.
By Phil Hippensteel On November 28, 2012
Dear Professor Phil,
At lunch several of us were discussing our new videoconferencing deployment. A debate developed. Some of the group said UDP traffic such as VoIP would be the most likely to interfere with the videoconferencing traffic because it gets high priority, just like the video. Others argued that traffic from TCP data applications would be more of a problem because of their socalled “bursty” nature. Who is correct? Terrance, Canton, OH
Both will cause problems but for very different reasons. The group arguing that VoIP will cause problems is assuming some things. First, to interfere with the video, the voice traffic must be on the same VLAN as the video traffic. Often it is not. Second, if the VoIP and video traffic are on the same physical LAN and have the same priority settings, the VoIP must be using enough of the bandwidth that it constrains the bandwidth available to the video conferencing devices. With good design, this should never happen. So, to summarize this side of the argument, VoIP can interfere with videoconferencing, but only if the network design is inadequate.
On the other hand, TCP traffic such as database applications and web traffic can have unpredictable effects on video conferencing traffic. The burstiness of TCP applications is virtually uncontrollable. It’s the way that TCP protocol works. So, when TCP traffic and video share a physical network, TCP has a tendency to grab all of the bandwidth it can. In addition, the TCP algorithm groups the packets in blocks of packets that can vary in size which is dependent on network conditions and application design. The resulting bursty nature of the traffic increases variation in delivery relative to time, or jitter. If the jitter becomes excessive, the jitter buffers can’t compensate and packets are dropped. This means that it is important to separate video conferencing traffic from data applications using VLANs or completely separate networks.
In addition to all of these facts, my experience has taught me that the group arguing that TCP traffic is more of a problem is indeed correct.
Phil Hippensteel, Ph.D., has spent more than forty years in higher education and now teaches for Penn State Harrisburg.
By Phil Hippensteel
We’re using IPTV at our school and have discovered a situation that we don’t understand. The video is delivered over a group of Ethernet switches. When we investigate the individual links, we find some links carry large amounts of traffic, while others transport no traffic at all. Can you offer a possible explanation?
Barry, Alexandria, VA
Barry, Alexandria, VA
A very likely explanation is that the switches have a loop circuit within them and the spanning tree process has automatically disabled a link. That’s not bad. In fact, it is a very necessary requirement.
The spanning tree algorithm is used with Ethernet switches to routinely remove loop circuits. If these loops weren’t removed, a single IP packet carrying video could loop endlessly while consuming valuable bandwidth. To understand essentially how spanning tree works, look at the diagram of a hypothetical network of switches. The simple hexagon with a diagonal has three loops in it: A-D-E-F-A, A-D-C-B-A, and A-B-C-D-E-F-A.
The spanning tree algorithm picks a switch, say B, to be the root of a tree that will be formed. A series of spanning tree messages is sent over the links starting from the root switch, B. These messages allow the switches to discover that a loop exists. For example, in our drawing, switch E received messages from both F and D. Therefore, E disables the link to one of them, say the one to D. In the same manner, C chooses to disable its link to D. After these two operations, the loops are eliminated and the entire structure forms a tree. Now every switch is connected to every other switch through exactly one path. Occasionally, technicians disable the spanning tree operation to reduce traffic, but that is almost always a bad idea.
Phil Hippensteel, Ph.D., has spent more than forty years in higher education and now teaches at Penn State Harrisburg.
The House of Lords, the UK’s second legislative chamber, has called for a wholesale switch from digital terrestrial to IPTV.
Original Story from Broadcast Engineering – http://broadcastengineering.com/news/uk-s-lords-calls-iptv
Aug. 13, 2012 11:19am
The UK’s House of Lords has put its weight behind a wholesale switch from digital terrestrial to broadband for public service broadcast delivery, even though this might in the short term threaten universal access provision.
The House of Lords is the UK’s second legislative chamber whose main function is to revise primary legislation emerging from the House of Commons comprising elected members of parliament (MPs). The House of Lords’ Communications committee has now proposed that broadcasting be moved away from terrestrial delivery towards IPTV and OTT over the Internet as the primary means of distribution. This recommendation is made in the report “Broadband for all,” which sets out an alternative vision to that of the government. The government wants to retain digital terrestrial as the base medium for delivery of services from the country’s Free To Air broadcasters including the BBC and ITV.
Part of this government strategy is to roll out superfast broadband across the country to provide the basis for future multichannel HD services. But surprisingly, the House of Lords questions this, suggesting the nation’s interests might be better served by first ensuring universal access. The problem with this is that such universal access would be at speeds of 2Mb/s at best given current technology, without substantial fiber deployment in remote areas at great cost.
Therefore, the country will probably be better served for universal access in the short term by continuing with digital terrestrial, and in the long term by pursuing superfast broadband. Because of this, the House of Lords report seems to fall between two stools.
VidOvation is an authorized Value-added reseller for Visionary Solutions Inc. VSI provides encoding products for edge acquisition and distribution applications using IP technology. Anywhere that content originates — and anywhere content goes — Visionary Solutions is there to help you leverage the convenience and flexibility of IP whether for acquisition, backhaul, or distribution.
Our solutions are deployed worldwide powering all types of applications:
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…and many more. Continue reading
Original content from Transition to Digital Newsletter, November 6, 2011, Ned Soseman – http://broadcastengineering.com/infrastructure/mpeg-2-basic-training-part-2
Is MPEG compression your friend? Of course, the answer to this question is that MPEG compression is your friend, unless it’s not working properly. When that happens, it’s our job to make it friendly again. This “Transition to Digital” tutorial continues the discussion from the preceding mid-October “Transition to Digital” tutorial about monitoring and evaluating MPEG-2 streams.
Streams are made of packets with headers and are filled with metadata, compressed video or compressed audio. To reconstruct a program from a stream, all of its video, audio and table components, and the corresponding PID assignments, must be correct. Also, there must be consistency between PSI table contents and the associated video and audio streams. This is a good place to look for trouble in a suspicious MPEG-2 stream.
Program Specific Information
Program Specific Information (PSI) is part of the Transport Stream (TS). PSI is a set of tables needed to demultiplex and sort out PIDs that are tagged to programs. A Program Map Table (PMT) must be decoded to find the audio and video PIDs that identify the content of a particular program. Each program requires its own PMT with a unique PID value.
The master PSI table is the Program Association Table (PAT). If the PAT can’t be found and decoded in the transport stream, no programs can be found, decompressed or viewed.
PSI tables must be sent periodically and with a fast repetition rate so channel-surfers don’t feel that program selection takes too long. A critical aspect of MPEG testing is to check and verify the PSI tables for correct syntax and repetition rate.
Another PSI testing scenario is to determine the accuracy and consistency of PSI contents. As programs change or multiplexer provisioning is modified, errors may appear. One is an “Unreferenced PID,” where packets with a PID value are present in the TS that are not referred to in any table. Another would be a “Missing PID,” where no packets exist with the PID value referenced in the transport stream PSI table.
Good broadcast engineers never forget common sense. Just because there aren’t any unreferenced or missing PIDs doesn’t guarantee the viewer is necessarily receiving the correct program. There could be a mismatch of the audio content from one program being delivered with the video content from another.
Because MPEG-2 allows for multiple audio and video channels, a real-world “air check” is the most common-sense test to ensure that viewers are receiving the correct language and video. It’s possible to use a set-top box with a TV set to do the air check, but it’s preferable to use dedicated MPEG test gear that allows PSI table checks. It’s also handy if the test set includes a built-in decoder with picture and audio displays.
So, all the bits and bytes appear to be organized and in place. How do you evaluate the quality of an MPEG-2 stream? Most use the concept of QoE. Some engineers call QoE Perceived Quality of Service (PQoS), because QoE is the quality of service as it is actually perceived by the viewer. In this tutorial, we’ll call the measurement of viewer satisfaction QoE.
QoE methodology for the evaluation of audio and video content provides broadcasters with a variety of choices, covering low, medium or high levels of quality. The QoE evaluation allows operators to pre-determine a specific level of viewer satisfaction and then use it to minimize storage and network resources by allocating only the resources necessary to maintain that particular QoE level.
The most basic recognized method to measure video content QoE is known as referenceless analysis. Essentially, referenceless analysis is what everyone does subconsciously when they watch TV. Using this method of analysis, QoE is not measured by comparing the original video to what is delivered. Instead, the images are visually inspected for artifacts such as blockiness, blurred or jerky video, frame-by-frame if possible. The referenceless analysis approach is based on the theory that viewers don’t know the quality of the original content.
These days, I wouldn’t be so certain. Bigger, brighter, undistorted plasma, LCD and LED screens make artifacts more difficult for even the most casual viewers to ignore. Funny thing about the new non-CRT screens: They don’t “Lie like a Trinitron.” That’s the good news and the bad news for engineers and others in the production and delivery chain.
More scientific evaluations of QoE consist of objective and subjective evaluation procedures, each one taking place after encoding. More subjective quality evaluation processes require more eyeballs, making the process more time-consuming with each viewer’s opinion.
Objective evaluation methods are based on and make use of multiple scientific metrics. Objective QoE evaluation methodology can provide results quicker, but it requires some physical resources and dedicated test gear.
One objective method of monitoring QoE is to use devices such as the one shown in our image. This device is an Ethernet video quality and service assurance monitoring and troubleshooting probe. Some products such as this provide analysis to the PID level, and may contain a hard drive for offline verification and inspection. Products like this are designed to monitor, analyze and possibly debug IP and MPEG transport quality issues at a problem viewer’s location, the receiving end of an STL, your home, your station’s maintenance shop or anywhere typically described as the video edge. It sure beats investigating problem locations with a portable TV and a 10ft mast.
Quality of Service is the ability to provide different priorities to different applications, users or data streams, or to guarantee a certain level of performance to a specific data stream. QoS may guarantee a required bit rate, delay, jitter, packet dropping probability and bit error rate. Quality of service guarantees are important if the network capacity has little headroom, especially for real-time MPEG-2 streaming, because it often requires a fixed bit rate and is delay-sensitive.
A network that supports QoS may agree on a traffic contract with the application software and reserve capacity in the network nodes, often during a session establishment phase. In computer networking and other packet-switched telecommunication networks, the term “traffic engineering” refers to resource reservation controls, not the achieved service quality.
During a session, QoS may monitor the achieved level of performance, such as the data rate and delay, and dynamically control scheduling priorities in the network nodes.
QoS is sometimes used as a quality measure, with many alternative definitions, rather than referring to the ability to reserve resources. Quality of service sometimes refers to a guaranteed level of quality of service. High QoS is often confused with a high level of performance or achieved service quality, such as a high bit rate, low latency and low bit error probability. A high level of performance is, in fact, a QoE factor.
Best-Effort non QoS
A so-called Best-Effort network or service does not fully support quality of service. It is also not all that unusual in broadcast facilities. Why? Because the technical foundations of most broadcast facilities are built on best-effort overprovisioning and redundancy. Many new devices such as routers and switches support QoS. Many older devices do not. As older devices are replaced within a station’s system, it will ultimately be capable of QoS monitoring and measurements.
A generously overprovisioned best-effort system shouldn’t need to rely on QoS, just as a well designed Master Control shouldn’t need a “Technical Difficulties” graphic. At least that’s the way some IT-centric people I’ve met seem to think. We broadcast engineers know it can’t hurt to have both readily available, just in case.
In the meantime, “Best Effort” can be a good substitute for complicated QoS control mechanisms. Your goal is to provide high-quality program content over a best-effort network by over-provisioning its capacity so that it has more than sufficient headroom for expected peak traffic loads. The resulting absence of network congestion eliminates the need for QoS mechanisms.
What is most interesting about MPEG-2 monitoring and evaluation is that there are more recognized methods worthy of discussion than space allows for now. The next “Transition to Digital” tutorial will address these methods to help you ensure your station’s MPEG streams meet viewer expectations.
The author would like to thank Les Zoltan at DVEO Pro Broadcast Division for his help in the preparation of this tutorial.