articles for telecom engineers

IPTV is known as broadcasting TV signals over the Internet protocol and the displaying the broadcast media on devices such as tele· visions or computer screens. IPTV service is also named as TelcoTV, in the sense that these service providers are not standard sa­tellite or cable tv operators, but telecom ope­rators. Although IPTV concept has been around for quite a long time, due to its difficult to achi­eve technical requirements, it hasn’t been implemen­ted in wide scale so far.

The major complication is the requirement of high bandwidth capacity for video streams, which couldn’t be provided by broadband Internet access mechanisms available such as ADSL or cable. However, new technological improvements in video compression techniques as well as the incre­ased bandwidth for broadband access, provides an opportunity for IPTV for consumer use. According to the lates market research, number of IPTV users is expected to reach up to 3,3 Million until the end of 2007 and to 16,7 Million in 2010, for Europe.
IPTV is usually perceived as watching TV over the Internet, however instead of a wide area network lik Internet, TV broadcast service is actually provi­ded inside an lP-based closed-circuit network that is managed by a telecom operator. The telecom opera­tor broadcasts to its subscribers using IPTV headend devices on its own network. IP packages that carry video signals, are not transmitted over the Internet, the broadcast content can only be seen by the opera­·tor’s own subscribers. This way, IPTV packages don’t generate traffic on the network, but only on “last mile” of the subscriber lines between the tele­corn operator POP and the end user.
Today, Intemet access speed has increased consi­derably. With ADSL2+ technology, download spe­eds up to 24Mbps is achievable. Although the theore­tical speed is 24Mbps that can be only be reached within short distance, the actual throughput is about 8-10 Mbps that can be aItained up to 3 km distances. The bandwitdh required for video depends on the compression algorithm used and the expected image quality. MPEG2 is a standard compression technique for DVD and digital TV technologies. Video signals, that are compressed with MPEG2, require around 5­6Mbps bandwidth for acceptable video quality on standard TVs. However, today’s most advanced compression standard, MPEG4 and its TV-broadcast­adapted version H.264, standardized by ITU (Inter­national Telecommunication Union) decreased the bandwidth requirement to only 1.5 Mbps. Users of MPEG2 technology can display I or at short distan­ces 2 channels simultaneously on ADSL2+ service, while H.264 users can display 4 or 5 TV channels at the same time in their homes.
With the information above, one can conclude that the optimal solution for an IPTV service opera­tor would be to establish ADSL2+ infrastructure and integrate H.264 compression algorithm. However, in the recent IPTV applications worldwide, MPEG2 is still the most commonly used compression algorithm, through which broadcast can be realized up to 1-2km. The main reason for usage of MPEG2 instead of the more advanced technology, H.264, is the requirement of much higher processing power needed for H.264. These processors are not commonly available or very expensive. Also, while ADSL2+ subscribers can atta­in 10 Mbps speeds up to 3 km, this speed decreases and package loss is experienced as the number of ADSL subscribers increase within the same district. This results in diminishing quaility in IPTV service over time. Telecom operators that aim to reach a stan­dard service quality, do not prefer to offer the IPTV service over ADSL2+ lines within 3km distances. Instead they install fiber optic cables to each neighborhood and install ADSL2+ or VDSL2 at each ne­ighborhood. ADSL2+ or VDSL2 service runs on te­lephone lines that goes to subscribers homes. This structure enables high speed ADSL and low packet loss by the help of high bandwidth over fiber lines and short cable distances for ADSL2+ or VDSL2 li­nes.
It looks like with the broadband technology and
the video compression techniques available today, ‘ providing IPTV service is quite easy to do. However, recently emerging HDTV (High definition TV) bro­adcast has increased the bandwidth requirement. As a . result of increasing demand for plazma and LCD te­levisions at homes, IPTV service now needs to sup-
port HDTV broadcast as well. Even with H.264 ‘
compression technology, bandwidth requirement for HDTV service is between 6 to 8Mbps, which is app­roximately 4 to 6 times of a standard definition TV’s bandwidth requirement. HDTV broadcast is obvi­ously impossible through ADSL2+. Instead, fiber cables are needed up to end users’ homes or buil­dings.
As seen in the personal computer technologies, the execution speed of computer software do not do­uble while processor speeds and memory capacities almost double every year. This is because the compu­ter software includes more features and gets more complex with time and that increases the requirement for high processor speed and more memory. The sa­me process is seen in increasing broadband access speed. Although the internet access speed available increase continuously, new services like IPTV, Vo· lP, Videophone require more bandwidth than ever.
I expect the advancements for providing higher speed broadband access and investments for new bro­adband equipment will continue in coming years.

source:

telekomdunyasi (mag.)

number:55 page:86