—Will your video router ever be an Ethernet switch? Today, the use of compressed
video (such as MPEG-2 or H.264) over IP is no longer unusual. Multichannel
service providers such as AT&T U-Verse TV and Verizon FiOS bring “IPTV”
to the home. Many traditional cable MSOs manage and groom their multichannel
offerings using IP-based systems before the final RF modulation of an MPEG-2
transport stream (TS) to the home. In the television broadcast plant, satellite
radios are beginning to not only have the traditional ASI interface for
carrying MPEG-2 TS over coaxial cable, but also gigabit Ethernet (GigE) for
their carriage over IP. Devices like Cisco’s Digital Media Player (DMP) can
provide affordable monitoring of these IP TS using consumer displays with HDMI
However it may soon be possible to send uncompressed video over IP as well.
High-definition video requires about 1.5 Gbps, so 10 Gbps Ethernet (10 GigE) is
needed to carry it. It is possible that up to six uncompressed HD streams could
be carried by a 10 GigE connection. But first standards must be developed so
that vendors can agree on interoperation of such systems.
In 2003, the Internet Engineering Task Force (IETF) issued RFC 3497, “RTP
Payload Format for Society of Motion Picture and Television Engineers (SMPTE)
292M Video,” which provided a specific mapping for SMPTE 292 over IP using the
Real Time Protocol (RTP). The IETF followed that up in 2005 with RFC 4175 “RTP
Payload Format for Uncompressed Video,” a more general mapping of SD and HD
uncompressed video to RTP (though the RFC only covers active video, not
blanking-interval or ancillary data). These RFCs were used for various
experiments involving IP carriage of uncompressed video over Internet2 and
other high-speed networks, however the standards did not meet the requirements
of the broadcast engineering industry, and were never widely adopted.
Links MD8000-VIF-OE bidirectional HD uncompressed video over Ethernet card
Enter the Video Services Forum. This organization recently founded the “High
Bit Rate Audio Video over IP” (HBRAV-IP) Committee, to create a more useful
standard for the broadcast engineering industry (see “A Lossless Season
, Nov. 18, 2009). Because of potential packet
loss in an IP system, it was felt that some level of Forward Error Correction
(FEC) might be required to allow for reliable video transmission. Most IP
networks have occasional packet loss, and the FEC can allow for the recreation
of lost data due to a dropped IP packet.
A draft uncompressed video
encapsulation document and a draft FEC document have been created, and these
were introduced for standardization in the SMPTE 32-NF “Video over IP” Ad Hoc
Group in November. The result of this process is expected to be a standard that
allows for the carriage of SMPTE 259, SMPTE 292 and SMPTE 424 video over IP
using RTP, including all embedded signals, ancillary data, and optional
Meanwhile, the IEEE has been working on mechanisms to make Ethernet more
reliable for high-speed data flows, possibly reducing the need for FEC within a
switched Ethernet network. This has been the job of the “Audio/Video Bridging
Task Group” of the IEEE 802.1 Working Group, colloquially known as “802.1 AVB”.
The set of AVB standards include:
- • 802.1AS, “Timing
and Synchronization for Time-Sensitive Applications in Bridged Local Area
Networks”, a timing standard over Ethernet based on the IEEE
1588 Precision Clock Synchronization Protocol standard. The goal of 802.1AS is
to provide synchronization accuracy of 1µ’s or better over seven
- • 802.1Qat, “Stream
Reservation Protocol”, that allows for the registration of a
stream of a certain bandwidth and reserves the resources required for that
stream throughout the entire end-to-end path of multiple Ethernet
- • 802.1Qav, “Forwarding
and Queuing for Time-Sensitive Streams”, that provides the rules
for Ethernet switches to properly deliver the streams reserved by
- • 802.1BA “Audio
Video Bridging Systems,” that ties all the AVB standards
together by defining the requirements of Ethernet switches and endpoints to
build networks that are capable of reliably synchronizing and transporting time
sensitive audio/video data streams. These systems will guarantee no more than 2
ms of latency through seven switch hops.
Although these standards define what is needed in Ethernet to carry high-speed
isochronous data streams, there also needs to be a description of how
higher-level protocols would be mapped onto the AVB-enabled Ethernet. To link
the standards of RTP carriage of uncompressed video to AVB Ethernet, IEEE 1733
describes the correlation of the RTP timestamp with the 802.1AS presentation
time through the use of the Real Time Control Protocol (RTCP), enabling
high-accuracy synchronization of video carried in RTP.
Standards, though, are useless without actual vendor support. It turns out that
a combination of network device companies, home entertainment component manufacturers,
and broadcast vendors have formed the “AVnu Alliance,” an industry forum
dedicated to promoting the adoption of the IEEE 802.1 AVB, IEEE 1722 (FireWire
payloads over AVB Ethernet) and IEEE 1733 standards. They expect to create
compliance test procedures and processes that ensure interoperability of
networked AVB audio/video devices. Alliance members include Avid, Barco, Cisco,
Intel, and Shure.
the 2009-2010 NFL season, CBS worked with Level 3 to test transport of
uncompressed HD-SDI video via fiber from Denver to New York
Some AVnu Alliance members have already announced AVB-capable products.
Broadcom has announced its “BroadSync HD” technology implementation of AVB for
its end-to-end Ethernet silicon portfolio that includes Ethernet switches,
end-point devices, physical layer devices (PHYs) and software.
Field-programmable gate array (FPGA) manufacturer Xilinx has announced
collaboration with Harman International Industries to provide “Ethernet AVB
LogiCORE” intellectual property core for the Xilinx Virtex-5 and Spartan-3A
series FPGAs. Harman has also announced an agreement between its BSS division
and NETGEAR, Inc. to introduce 16-port and 24-port co-branded Ethernet switches
featuring specialized AVB hardware and software.
It is likely that many early professional applications of AVB Ethernet will
involve audio systems. A 48 kHz sampled 24-bit PCM audio signal requires 1.152
Mbps of bandwidth. Eighty-six channels could be delivered in a single 100 Mbps
Ethernet cable, and 868 channels could be delivered in a single GigE cable,
potentially allowing dramatic simplification of audio distribution. Crown, a
unit of Harman, has introduced the PIP-USP4 programmable input processor module
for the CTs series 2-channel amplifiers, which has 100 Mbps Ethernet AVB input for
real-time digital audio.
The first uncompressed HD video over IP systems are just now becoming
available. For example, the Media Links MD8000-VIF-OE video module provides one
channel of HD-SDI input/output using Ethernet carriage as part of their MD8000
high capacity switching system. The MD8000 that has a backplane capacity of 180
Gbps, or 480 Gbps for the MD8000EX version.
But widespread use of uncompressed HD video over IP will probably have to wait
until the cost of 10 Gbps Ethernet ports drop. Brad Booth, chairman of the
board of the Ethernet Alliance, has been quoted in the press as saying 2012 is
when costs will be low enough for the market to see widespread adoption. But
the good news is that the work by the IEEE on AVB Ethernet, as well as the VSF
and SMPTE on HBRAV, will ensure that there are standards ready when the
Thomas Edwards is vice president of DTV Testing & Evaluation
for Fox Technology Group.