4. www.tandbergtv.com
Introduction
• We will discuss ASI versus IP for digital video
connectivity.
• For IP, we will really concentrate on Gigabit
Ethernet.
• We will discuss:
– Physical layer implementation
– Timing features
– Packet loss issues
– Routing of traffic
• And we will conclude that IP is a good
replacement for ASI!
5. www.tandbergtv.com
ASI Versus Gigabit Ethernet Physical
Parameter ASI Gigabit Ethernet
Line Bit Rate 270 Mb/s 1.25 Gb/s
Line Coding 8B/10B (based on
Fiber Channel)
8B/10B (based on
Fiber Channel)
Information Bit
Rate
216 Mb/s 1.0 Gb/s
Link Type Unidirectional
point-to-point
Dual-Unidirectional
point-to-point
When to transmit? Whenever I want Whenever I want
Byte
Synchronization
Sends sync pattern
when idle
Silence when idle,
8-byte sync before
packet
Frame check None (Reed-
Solomon optional)
CRC
6. www.tandbergtv.com
Physical Layer Notes
• Gigabit Ethernet is always switched
– No contention
– Always full-duplex
• ASI interfaces typically transmit at a constant bit
rate, hardware-metered
• ASI interfaces are unidirectional
• Gigabit Ethernet interfaces are always composed
of two unidirectional interfaces, one on each
direction
9. www.tandbergtv.com
Decoder Playback Process (Ethernet)
T=0, decoder
starts receiving data
Decoder starts playing
Buffer
Level
VBV
Time
I B B P B B P B B P B B P
Packet Reception Times
10. www.tandbergtv.com
Conclusions so far…
• From a physical layer point of view, ASI and
Ethernet are very similar
– Point-to-point packet transport mechanism
• Ethernet always has a CRC so bit errors can be
detected
– With ASI, even if configured for 204-byte mode (Reed-
Solomon), the great majority of the equipment does not
generate or check it – that is done by modulators and
demodulators.
• Differences in packet timing are very manageable
• But … what about packet loss???
11. www.tandbergtv.com
The Packet Loss “Issue”
• Let’s look first at a point-to-point connection with
a crossover cable.
• There is no contention, no buffering – it is almost
the same as having two ASI connections, one in
each direction.
• The only way a packet can be dropped is if the
receiver drops it – and that is not going to
happen (by design)!
12. www.tandbergtv.com
Ethernet Switches
• All modern switches are non-blocking and can
operate at line rate.
• Transmit and receive channels are independent.
• Switches also have a certain amount of buffering.
Ethernet
Port
Ethernet
Port
Non-Blocking
Switch
Fabric
Ethernet
Port
Ethernet
Port
13. www.tandbergtv.com
Where is the Packet Loss, then?
• Packet loss happens when a link is
oversubscribed – more traffic than its capacity.
• Switch will buffer instantaneous bursts, but
cannot buffer forever.
• Solution: don’t do it!!
Switch
Data
Source
Data
Source Link Capacity: 10 Mb/s
6 Mb/s
6 Mb/s
2 Mb/s Packet Loss
14. www.tandbergtv.com
Packet Loss Notes
• Packet loss happens when there is congestion in
the network.
• Short-term congestion introduces jitter (as
packets are buffered); long-term congestion
introduces packet loss.
• Congestion is avoided by properly designing the
network capacity for the traffic.
• Good news is that, unlike data, digital video
capacity requirements are well-known and easy
to design for.
• If you want to mix video and data in the same
network, high-end routers and switches can be
configured to give priority to video.
15. www.tandbergtv.com
Dealing with Occasional Packet Loss
• Occasional packet loss, for whatever reason, can
be handled by FEC.
– Slightly different from the traditional FEC – we rebuild
“lost” bits instead of “correcting” wrong bits.
• Standardized FEC options:
– RFC 2733: “Row” FEC.
– Pro-MPEG FEC: “Column” and “Row” FEC, can handle
burst losses.
• FEC is supported in most Tandberg equipment
and interoperates with equivalent
implementations from third-party vendors
– Interop demonstrated in VSF meeting in Orlando last
January.
16. www.tandbergtv.com
IP Advantages over ASI
• We have seen that, from a transport point of
view, IP and ASI are fairly equivalent, with a
small advantage in favor of IP (FEC).
• As a system interconnect solution, IP has two
major advantages over ASI:
– IP has a network layer: IP packets contain routing
information, indicating where they should go. That
includes IP multicast – one-to-many delivery.
– IP equipment is universal, and there are many vendors
to choose from – high volume items, very cost-
effective.
20. www.tandbergtv.com
Ingress: Encoders
• All Tandberg Encoders either have IP output built
in (iPlex, Mediaplex) or offered as an option (EN
series)
EN Series iPlex Mediaplex
21. www.tandbergtv.com
Encoders at a Glance
• EN Series (single channel) SDTV/HDTV – MPEG2/MPEG4
– EN5710/5720: MPEG-2 Standard Definition
– EN5770/5775: MPEG-2 Standard Definition Dual-Pass
– EN5780/5782: MPEG-2 High Definition
– EN5920: Windows Media/VC-1 Standard Definition
– EN5930: H.264 Standard Definition
– EN5980: Windows Media/VC-1 High Definition
– EN5990: H.264 High Definition
– EN8030: Second Generation H.264 Standard Definition
– EN8090: Second Generation H.264 High Definition
• Mediaplex, iPlex (multiple channel)
– MPEG-2 Standard Definition Submodule (up to 48 in the
Mediaplex, up to 8 in the iPlex)
– H.264 Standard Definition (up to 48 in the Mediaplex, up to 8
in the iPlex)
– H.264 Second Generation Standard Definition (up to 4 in the
iPlex, Mediaplex support planned).
– H.264 High Definition (up to 4 in the iPlex, Mediaplex support
planned)
22. www.tandbergtv.com
Network Interfaces and Protocols
• Interfaces:
– EN Series:
• Dual copper Gigabit Ethernet Interfaces
– iPlex:
• Dual Gigabit Ethernet (SFP – fiber and copper available)
– Mediaplex
• Four Gigabit Ethernet Interfaces (multimode fiber)
– Mediaplex/iPlex also support optional ATM OC-3, DS-3
and E-3 interfaces.
• Protocols:
– UDP
– RTP
– Forward Error Correction
23. www.tandbergtv.com
Receivers at a Glance
• All Tandberg Receivers include a Professional Decoder
• Receivers have a variety of available input front-ends
(including IP), optional descrambler, and an ASI output
• The TT1222 includes an IP output option.
TT1222: MPEG-2 SD 4:2:0 TT1260: MPEG-2 SD 4:2:2
TT1280/2: MPEG-2 HD RX1290: Everything
24. www.tandbergtv.com
Process: Multiplexers and Demultiplexers
• Capable of multiplexing
and demultiplexing IP
flows.
• Extensive set of (P)SI
table generation options
• Functions also available
on ASI.
Mediaplex iPlex MX8400
• High-end
multiplexer, GE
inputs and outputs
• Scrambling also
available
25. www.tandbergtv.com
Process: Rate Shaping
• Rate Shaping: Converting a service
from one bit rate to another
– To fit in a bandwidth-limited channel
– Convert to CBR for video servers
• Function provided by the Media
Processor submodule in
iPlex/Mediaplex
– Mediaplex: support for approximately
144 services.
– iPlex: support for approximately 36
services.
– Actual number depends on bit rate
• Inputs and outputs can be IP
streams
Mediaplex
iPlex
26. www.tandbergtv.com
Process: MPEG-2 to H.264 Conversion
• Most existing content from
broadcasters comes in as MPEG-2.
• In some installations, it may be
desirable to convert it to H.264.
• The Media Processor submodule in
the iPlex/Mediaplex can provide this
function.
• Capacity:
– Mediaplex: 48 services
– iPlex: 8 services
• Inputs and outputs can be IP
streams.
Mediaplex
iPlex
27. www.tandbergtv.com
Conclusions
• There are devices available for the entire digital
video processing chain that can use an IP
network as the interconnection method.
• This IP interconnect can be restricted to the
head-end or can extend all the way to the
consumer set-top box.
• IP interconnects can be used in traditional digital
video architectures (digital cable, satellite) inside
the head-end, while maintaining the same egress
method.
• Tandberg Television has all the “bits and pieces”
required to make this work!