Transcript IPTV Technology

IPTV Technology
Team 3 – Christopher Monclova,
Rafael Leefoon, Nick Adasi, Robb
Zucker & Oscar Ucedo
IPTV Transmission
IPTV supports two kinds of services:
• 1. Multicast IPTV, which consists of an emitter
which sends the same content to multiple
receivers the same time.
• Unicast IPTV, which also consists of an emitter
which sends TV content to multiple receivers.
In contrast to multicast IPTV every receiver
receives different content. This kind of service
can be used to send personalized TV content,
e.g. video on demand.
Mpeg Transport Stream
Codecs are used to encode video and audio information
into a compressed data stream.
Several Codecs combine to create a transport stream for
the media being transmitted.
Real-time transport Streaming
Protocol
• The Real-time Transport Streaming Protocol (RTSP)
enables a client to control a media server by
• issuing commands. Necessary for Unicast .
• RTSP reuses many design principle from HTTP:
–
–
–
–
URL identifies resources;
requests contain a method name and various parameters;
replies contain a status code and parameters;
messages are text based.
• RTSP is a stateful protocol. The server maintains state
of the client.
• With RTSP, every message contains a session identifier,
enabling the server to link received commands to a given
multimedia session.
.
Typical Video setup message
Multicast
• Multicast IPTV enables a TV content provider to send TV content to
many subscribers at the same
• time.
• IP multicast saves considerable bandwidth, since only one stream is
transmitted over the network
• When a server multicasts data to several clients, it sends this data to
the corresponding
router only once.
• Similarly to regular TV, multicast IPTV supports multiple channels
and sends them at the same time.
• IPTV does not broadcast to a user all channels at the same time.
– IPTV divides channels into groups and sends to each user the group
that contains the requested channel.
– The user can switch between channels at any time.
Multicast Service
Unicast
• Unicast IPTV sends a given TV content to a
given user. Video on Demand is a typical service
of
IPTV, which enables a user to request a specific
movie and to receive it on his TV set.
• Contrary to multicast IPTV, unicast IPTV does
not save bandwidth, since the server must send
the content once for each user.
• Unicasting can be extremely demanding on the
server if multiple streams must be generated by
the media server and transmitted over the
network.
Unicast Service
QoE – Quality of Experience
• QoE is reliant upon error free delivery of
packet data without retransmission.
• Very similar to packet voice where packets
are not acknowledged
• Customers are much less accepting of
poor video quality
Error Free Transmission
• Pixelation due to poor transmission
Components of a typical IPTV
System
• A National head-end - Origination point of network
Broadcasts for transmission over the IP network.
• Core networks - Usually an IP/MPLS network
transporting traffic to the access network
• Access networks - Distributes the IPTV streams to
the DSLAMs
• Regional head-end – Origination point for local
content
• Customer premises - Where the IPTV stream is
terminated and viewed using a Set Top Box or
Computer.
Typical IPTV Network Design
Datastream Delivery
• Broadcast information coming from the national head-end is typically
distributed using MPEG-2 encoding to the video service nodes.
• Competing compression algorithms are growing in popularity such
as H.264 (MPEG-4 Part 10) or the Society of Motion Picture and
Television Engineers (SMPTE) 421M (also known as VC-1)
• The channel content can be of standard or high definition.
• Distribution over the access network is done though digital
subscriber line access multiplexers (DSLAM) and fiber-to-the-home
(FTTH) services.
• The subscriber’s set top box (STB) acts as the terminating interface
for the network providing output to the television.
• For IPTV, each channel is distributed using a multicast IP address.
Factors Affecting Service
•
Encoding and Compression – The quality of a transmission can be affected from the source
depending on the encoding technique and level of compression. Generally speaking increased
compression leads to a poorer video quality but a smaller data stream. There is a tradeoff
between bandwidth and compression level.
•
Jitter in IPTV transmission is defined as a short-term variation in the packet arrival time. Jitter is
typically caused by network or server congestion. To help combat jitter, STB’s use buffers to
smooth out the arrival times of the data packets. I the buffer overflows or underflows, at the STB,
there is often a degradation of the video output.
•
Limited Bandwidth – Bandwidth availability is often an issue that affects the access network or
the customers home network. When traffic utilizes the entire bandwidth, packets are dropped,
leading to video quality degradation.
•
Packet Loss Loss of IP packets may occur for multiple reasons:
–
–
–
–
–
bandwidth limitations
network congestion
failed links
transmission errors
Packet loss usually presents a bursty behavior, commonly related to periods of network congestion.
Mpeg-2 Compression
•Frame Types
•I frames- least compressed reconstructed independently
•P frames use data from previous frames leading to greater compression
•B frames use data from previous as well as following video frames leading to
even greater compression.
•Affect of err’d packets is greatest on I frames.
Key QoE Metrics
• IPTV is evolving and is not well defined for
testing.
• The most popular parameters for testing delivery
of IPTV packets are the media delivery index
(MDI) and PCR jitter for MPEG-2 TS.
• Other parameters are also used in the IPTV
network, but require intense packet inspection to
determine transmission problems.
Media Deliver Index (MDI)
• MDI is a standards based video quality
metric (RFC-4445)
• MDI measures two factors:
– Delay Factor
– Media Loss Rate
• Factors lead to a QoS measure that
directly relates to the customers QoE
Benefits of Using MDI
•
•
•
•
•
•
MDI does not perform any type of stream decoding to achieve its
metrics and therefore does not require significant real-time processing
power.
MDI can be used with encrypted media payloads.
MDI is not dependent on any one type of video-encoding technique, so
it can easily be scaled to monitor video quality on hundreds of
simultaneous channels.
MDI is typically sampled at multiple points throughout the stream path
with the measurements serving as indicators of problems in the
network that can be proactively addressed before they become
service-affecting issues.
Since MDI relies on transport-layer metrics (DF and MLR), it can be
used to set network margins and it directly correlates to impending
network problems with respect to video quality.
Since MDI uses packet-level metrics, it helps validate the performance
of network equipment such as switches and routers that play a key
role in determining whether a packet is delayed or dropped.
MDI Values increase through
network.
References
• IPTV related standardization activities – from international
Telecommunication Union Website
http://www.docstoc.com/docs/10154710/IPTV-PresentationsPresentation%5B641%5D
• EXFO Test Equipment Manufacturer Website http://www.exfo.com/en/applications/IPTV-Overview.aspx
• Video Compression picture types form Wikipedia
http://en.wikipedia.org/wiki/Video_compression_picture_types
• Definition and Specifications of IPTV and VoIP
Services from Adamantium Web Site
http://www.ictadamantium.eu/documents/deliverables/ADAMANTIUM_D2.3.pdf