3G Codecs and IPTV
Mar 17, 2007 8:00 AM
IPTV is the delivery of television over a closed broadband IP distribution network to consumers. And no matter how you look at it, lower bit rates save bandwidth, which increases channel offerings and maximizes the bottom line. Because of this, 3G video codecs are a perfect match for IP-based digital TV.
With compressed data rates half that of MPEG-2, third generation (3G) video codecs make IPTV possible. VDSL and ADSL2+ broadband networks stream content at upward of 25Mb/s.
The last-mile access network requires fiber-optic system upgrades. One of two methods is typically used. FTTP (fiber-to-the-premises) runs fiber-optic cable to the customer's equipment. FTTN (fiber-to-the-node), in lieu of upgrading every connection to a customer, uses optical cable to the distribution point (pole or box) and then uses copper wire to reach the customer's home.
Regardless of which method is used, end-to-end IPTV service solutions with encoding, encapsulation, third-party middleware, scrambling/descrambling, satellite receivers, conditional access, set-top boxes (STBs), service management and integration services require a large financial investment. Aggregation and distribution of content is heavily dependent on satellite networks; therefore, large players dominate the field and are joining together to deliver turnkey infrastructures.
IPTV networks
An IPTV network essentially consists of three fundamental components: a content aggregation segment, a content distribution segment and a consumption device.
Aggregation takes place at a super headend where programming is collected from multiple sources: off air, fiber networks and satellite feeds. This content is encoded and multiplexed into an MPEG transport stream, IP encapsulated, L-band modulated and then uplinked to a satellite.
AVC or VC-1 codecs maximize transponder bandwidth efficiency. This can also eliminate transcoding farther downstream. AVC/VC-1 compressed video is IP encapsulated and multiplexed in an MPEG transport stream. Using this methodology, content can be delivered to the customer's premise and decoded by the STB or PC.
IPTV system operators build regional headends where additional content is received. This content can arrive from a satellite, off air or over landlines. In the IPTV network operations center, EPG information is generated, content is encrypted and conditional access and DRM control is implemented by middleware. Customer service and billing systems are integrated into the content management system layer.
Delivery to the customer continues over telco or cable broadband systems to a local DSLAM (Digital Subscriber Line-Access Multiplexer), and then the last mile to an IPTV STB or media PC that completes the system. The MPEG-IP packets are transported as UDP (User Datagram Protocol) packets using RTSP (Real-Time Streaming Protocol.)
IP as a routing protocol
Live TV is sent as an MPEG-2 transport stream delivered via IP Multicast, using IGMP (Internet group management protocol) for connecting to a multicast stream, i.e. a TV channel, and for changing from one multicast stream to another.
The MPEG transport stream is divided into UDP packets, also known as datagrams. These UDP packets may include a check sum for identifying bad packets, but the actual transmission of UDP packets is on a "best effort" basis. In other words, packets are sent only once, regardless of errors.
IP Multicast is a technique where a single datagram is sent to a multicast address. Routers distribute copies of the datagram to "interested" receivers — in this case, an IPTV subscriber.
Receivers declare their "interest" by joining a multicast group, and membership is managed by using IGMP. All members of the group have the same IP address. Membership is dynamic and changes as viewers drop in and out. IGMPv2 facilitates rapid group membership updates to router tables, which explains its use in high-bandwidth DTV-over-IP networks.
As a point of comparison, IP Unicast is often used for VoD-over-IPTV distribution networks. ICMP (Internet control message protocol) is used for internetwork datagram transfers.
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