Zap time

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The zap time is the total duration of time from which the viewer changes the channel using a remote control to the point that the picture of the new channel is displayed. This includes the corresponding audio. These delays exist in all television systems, but they are more pronounced in digital television and systems that use the internet such as IPTV. Human interaction with the system is completely ignored in these measurements, so zap time is not the same as channel surfing.

Remote control system or device used to control other device remotely (or wirelessly)

In electronics, a remote control is a component of an electronic device used to operate the device from a distance, usually wirelessly. For example, in consumer electronics, a remote control can be used to operate devices such as a television set, DVD player, or other home appliance, from a short distance. A remote control is primarily a convenience feature for the user, and can allow operation of devices that are out of convenient reach for direct operation of controls. In some cases, remote controls allow a person to operate a device that they otherwise would not be able to reach, as when a garage door opener is triggered from outside or when a Digital Light Processing projector that is mounted on a high ceiling is controlled by a person from the floor level.

Television telecommunication medium for transmitting and receiving moving images

Television (TV), sometimes shortened to tele or telly, is a telecommunication medium used for transmitting moving images in monochrome, or in colour, and in two or three dimensions and sound. The term can refer to a television set, a television program, or the medium of television transmission. Television is a mass medium for advertising, entertainment and news.

Digital television (DTV) is the transmission of television signals, including the sound channel, using digital encoding, in contrast to the earlier television technology, analog television, in which the video and audio are carried by analog signals. It is an innovative advance that represents the first significant evolution in television technology since color television in the 1950s. Digital TV transmits in a new image format called HDTV, with greater resolution than analog TV, in a wide screen aspect ratio similar to recent movies in contrast to the narrower screen of analog TV. It makes more economical use of scarce radio spectrum space; it can transmit multiple channels, up to 7, in the same bandwidth occupied by a single channel of analog television, and provides many new features that analog television cannot. A transition from analog to digital broadcasting began around 2006 in some countries, and many industrial countries have now completed the changeover, while other countries are in various stages of adaptation. Different digital television broadcasting standards have been adopted in different parts of the world; below are the more widely used standards:

Contents

Zap time can be very disturbing for some viewers and for this reason it is considered an issue that must be addressed in IPTV systems. [1]

Factors

The delays when changing the channel can be caused by several different factors. These factors can be classified according to the systems that cause them. Consequently, there are network factors, MPEG acquisition factors, and set top box buffering/decode factors. [2]

A television network is a telecommunications network for distribution of television program content, whereby a central operation provides programming to many television stations or pay television providers. Until the mid-1980s, television programming in most countries of the world was dominated by a small number of terrestrial networks. Many early television networks evolved from earlier radio networks.

Network Factors

An access network is a type of telecommunications network which connects subscribers to their immediate service provider. It is contrasted with the core network, which connects local providers to one another. The access network may be further divided between feeder plant or distribution network, and drop plant or edge network.

  1. STB – IGMP Leave channel X, Join Y
  2. DSLAM – Stop X, Start Y
  3. DSL FEC/Interleave
  4. IGMP features used (version, fast leave, snooping, etc.)
  5. Availability of the channel (channel replication point)
  1. Multicast routing mechanisms used
  2. Availability of the channel (channel replication point)

Network factors tend to make up only a small portion of the overall delay, between 50 and 200ms of the overall zap time. Network quality of service (QoS) can reduce these time to minimize jitter, latency, and packet drop.

Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a telephony or computer network or a cloud computing service, particularly the performance seen by the users of the network. To quantitatively measure quality of service, several related aspects of the network service are often considered, such as packet loss, bit rate, throughput, transmission delay, availability, jitter, etc.

In electronics and telecommunications, jitter is the deviation from true periodicity of a presumably periodic signal, often in relation to a reference clock signal. In clock recovery applications it is called timing jitter. Jitter is a significant, and usually undesired, factor in the design of almost all communications links.

MPEG Acquisition Factors

Program-specific information (PSI) is metadata about a program (channel) and part of an MPEG transport stream.

  1. Wait for and parse PAT (Program Association Table)
  2. Wait for and parse PMT (Program Map Table)
  1. I-frame (MPEG 2) or IDR frame (H.264)
  2. One Index frame per group of pictures (GOP) – 12 to 30 (IBP) frames
  3. Typical frequency of I-frame – 500ms.
  4. Long GOP structure (2–4 seconds) saves bandwidth, but can cause significant channel change latency

Set Top Box Buffering/Decode Factors

Zap Time Examples

The various factors that affect zap time do not do so in the same way. The table below is an example of zap time in IPTV DSL:

Channel Change Latency Factor Device/Location Typical Latency Cumulative Latency
1 Send IGMP Leave for channel X STB < 10 ms
2 Send IGMP Join for channel Y STB < 10 ms
3 DSLAM receives Leave for channel X DSLAM/Network < 10 ms
4 DSLAM receives Join for channel Y DSLAM/Network < 10 ms ~ 20 - 40 ms
5 DSLAM stops channel X, and sends Channel Y DSLAM/Network ~ 30 – 50 ms ~ 50 – 90 ms
6 DSL Latency (FEC/Interleave) DSLAM/Network ~ 10 ms ~ 60 - 100 ms
7 Core/Agg Network Latency Router/Network ~ 20 – 60ms ~ 80 – 160ms
8 De-jitter buffer STB ~ 300 ms ~ 380 - 460 ms
9 Wait for PAT/PMT STB MPEG buffer ~ 125 ms ~ 500 - 580 ms
10 Wait for ECM/CA STB MPEG buffer ~ 125 ms ~ 620 - 700 ms
11 Wait for I-frame STB MPEG buffer ~ 250 ms to 2s ~ 870 ms – 2.7s
12 MPEG buffer STB MPEG buffer ~ 1s to 2s ~ 1.8s – 4.7s
13 Decode STB ~ 50ms ~ 1.9s – 4.8s

Zap time delays are greater in IPTV television than in other technologies. For example:

Related Research Articles

MPEG-1 is a standard for lossy compression of video and audio. It is designed to compress VHS-quality raw digital video and CD audio down to 1.5 Mbit/s without excessive quality loss, making video CDs, digital cable/satellite TV and digital audio broadcasting (DAB) possible.

MPEG-2 standard for the generic coding of moving pictures

MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods, which permit storage and transmission of movies using currently available storage media and transmission bandwidth. While MPEG-2 is not as efficient as newer standards such as H.264/AVC and H.265/HEVC, backwards compatibility with existing hardware and software means it is still widely used, for example in over-the-air digital television broadcasting and in the DVD-Video standard.

The Internet Group Management Protocol (IGMP) is a communications protocol used by hosts and adjacent routers on IPv4 networks to establish multicast group memberships. IGMP is an integral part of IP multicast.

H.264 or MPEG-4 Part 10, Advanced Video Coding is a block-oriented motion-compensation-based video compression standard. As of 2014, it is one of the most commonly used formats for the recording, compression, and distribution of video content. It supports resolutions up to 8192×4320, including 8K UHD.

Protocol Independent Multicast Internet protocol

Protocol-Independent Multicast (PIM) is a family of multicast routing protocols for Internet Protocol (IP) networks that provide one-to-many and many-to-many distribution of data over a LAN, WAN or the Internet. It is termed protocol-independent because PIM does not include its own topology discovery mechanism, but instead uses routing information supplied by other routing protocols. PIM is not dependent on a specific unicast routing protocol; it can make use of any unicast routing protocol in use on the network. PIM does not build its own routing tables. PIM uses the unicast routing table for reverse path forwarding.

Internet Protocol television (IPTV) is the delivery of television content over Internet Protocol (IP) networks. This is in contrast to delivery through traditional terrestrial, satellite, and cable television formats. Unlike downloaded media, IPTV offers the ability to stream the source media continuously. As a result, a client media player can begin playing the content almost immediately. This is known as streaming media.

In computer networking and telecommunications, TDM over IP (TDMoIP) is the emulation of time-division multiplexing (TDM) over a packet switched network (PSN). TDM refers to a T1, E1, T3 or E3 signal, while the PSN is based either on IP or MPLS or on raw Ethernet. A related technology is circuit emulation, which enables transport of TDM traffic over cell-based (ATM) networks.

MPEG transport stream is a standard digital container format for transmission and storage of audio, video, and Program and System Information Protocol (PSIP) data. It is used in broadcast systems such as DVB, ATSC and IPTV.

IP multicast is a method of sending Internet Protocol (IP) datagrams to a group of interested receivers in a single transmission. It is the IP-specific form of multicast and is used for streaming media and other network applications. It uses specially reserved multicast address blocks in IPv4 and IPv6.

The Media Delivery Index (MDI) is a set of measures that can be used to monitor both the quality of a delivered video stream as well as to show system margin for IPTV systems by providing an accurate measurement of jitter and delay at network level, which are the main causes for quality loss. Identifying and quantizing such problems in this kind of networks is key to maintaining high quality video delivery and providing indications that warn system operators with enough advance notice to allow corrective action.

Latency refers to a short period of delay between when an audio signal enters and when it emerges from a system. Potential contributors to latency in an audio system include analog-to-digital conversion, buffering, digital signal processing, transmission time, digital-to-analog conversion and the speed of sound in the transmission medium.

IGMP snooping

IGMP snooping is the process of listening to Internet Group Management Protocol (IGMP) network traffic to control delivery of IP multicasts. Network switches with IGMP snooping listen in on the IGMP conversation between hosts and routers and maintain a map of which links need which IP multicast transmission. Multicasts may be filtered from the links which do not need them conserving bandwidth on those links.

In computer networking, packet delay variation (PDV) is the difference in end-to-end one-way delay between selected packets in a flow with any lost packets being ignored. The effect is sometimes referred to as packet jitter, although the definition is an imprecise fit.

I-Frame Delay (IFD) is a scheduling technique for adaptive streaming of MPEG video. The idea behind it is that streaming scheduler drops video frames when the transmission buffer is full because of insufficient bandwidth, to reduce the transmitted bit-rate. The characteristics of the algorithm.:

  1. number of frames currently in the buffer is indicating buffer fullness,
  2. less important frames (B-frame) from the buffer are dropped before the more important frames,
  3. the transmission of I-frames is delayed when conditions are bad, even if they are out-of-date w.r.t. the display time.

G.718 is an ITU-T recommendation embedded scalable speech and audio codec providing high quality narrowband speech over the lower bit rates and high quality wideband speech over the complete range of bit rates. In addition, G.718 is designed to be highly robust to frame erasures, thereby enhancing the speech quality when used in internet protocol (IP) transport applications on fixed, wireless and mobile networks. Despite its embedded nature, the codec also performs well with both narrowband and wideband generic audio signals. The codec has an embedded scalable structure, enabling maximum flexibility in the transport of voice packets through IP networks of today and in future media-aware networks. In addition, the embedded structure of G.718 will easily allow the codec to be extended to provide a superwideband and stereo capability through additional layers which are currently under development in ITU-T Study Group 16. The bitstream may be truncated at the decoder side or by any component of the communication system to instantaneously adjust the bit rate to the desired value without the need for out-of-band signalling. The encoder produces an embedded bitstream structured in five layers corresponding to the five available bit rates: 8, 12, 16, 24 & 32 kbit/s.

ITU-T Y.156sam Ethernet Service Activation Test Methodology is a draft recommendation under study by the ITU-T describing a new testing methodology adapted to the multiservice reality of packet-based networks.

ITU-T Y.1564 is an Ethernet service activation test methodology, which is the new ITU-T standard for turning up, installing and troubleshooting Ethernet-based services. It is the only standard test methodology that allows for complete validation of Ethernet service-level agreements (SLAs) in a single test.

Unreal Media Server is a streaming server software created by Unreal Streaming Technologies.

References

  1. ↑ IPTV over DSL systems. "IPTV testing over DSL Archived January 26, 2007, at the Wayback Machine ."
  2. ↑ IPTV challenges and metrics. "IPTV Challenges Archived July 10, 2011, at the Wayback Machine ."
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