Can Ethernet AV help unify the home network?
Although in the current consumer electronics industry, there is still a clear technology winner to solve the distribution of digital home media, but some people predict that after 2009, Ethernet will become the best choice for home networks.
Rick Kreifeldt, vice president of Harman Professional System Development and Integration Group, said that the IEEE 802 working group is perfecting the Ethernet AV standard, which is a set of work to modify the existing Ethernet standard to make the protocol for transmission Audio streaming and video streaming are more "sturdy" without any "click or pop".
Today, the general IT-oriented Ethernet network uses the best protocol. These protocols can promise that no errors will occur during the transmission of data through the network, but there is no guarantee that they will arrive in time.
In contrast, the emerging Ethernet audio / video bridging (AVB) standards-including 802.1AS, 802.Qas, and 802.1Qav-can guarantee the following conditions: a maximum of 2 ms delay is guaranteed through 7 Ethernet bridges; corresponding bandwidth is guaranteed , Precise timing and synchronization services are used for the coordination of time stamps and media.
Tony Jeffree, chairman of the IEEE802.1 working group, said, "There are two forces driving the development of Ethernet AVB."
One group, represented by Harman and BMW, hopes to establish a reliable, standards-based method to provide audio and video for professional studios, concert scenes, and automotive applications. Another group is manufacturers of Ethernet and WiFi routers, who want to provide low-latency, synchronized audio and video content for home networks and take advantage of the price advantage of current Ethernet technology.
For example, Harman ’s Kreifeldt pointed out that the company is committed to launching Ethernet AVB compatible products, including Harman / Becker Automotive Systems, Harman Professional Group and Harman Consumer Electronics Group.
Chip manufacturers such as Broadcom, Marvell and Xilinx are also said to be eager to implement Ethernet AVB in their new Ethernet hardware products.
Of course, the IEEE AVB working group's efforts are not the first attempt to solve the lack of real-time support of existing Ethernet in this industry.
DiffServ is a concept once created to add traffic priority. Similarly, the industry has developed real-time protocol (RTP), which is a standardized method for transmitting audio and video over the Internet based on IP.
However, neither of these technologies can meet the AVB performance of Ethernet. DiffServ cannot guarantee the transmission of end-to-end data streams. RTP was originally defined as an application software, which was difficult to implement on chip. In addition, RTP requires a larger stack protocol, which makes lower latency applications difficult to implement.
Michael Johas Teener, Head of Pipeline Architecture / Technology at Broadcom and Chairman of the IEEE 802.1 AVB Working Group, emphasized, “There is no interoperable method to guarantee bandwidth and latency, or to ensure that Ethernet and 802 LAN The synchronization problem within the microsecond between the endpoints in the bridge network. The AVB protocol can do this, and we believe that the complexity of the implementation does not increase much. "
In addition, Teener said that the working group developed Ethernet AVB to be "not only compatible with Ethernet, but also compatible with many other things that are not Ethernet."
The second layer technology is unknown
Calling Ethernet AVB "the second layer technology is unknown", he believes that "this is not all about Ethernet. We developed this to ensure time-sensitive services regardless of which layer 2 technology is used, as long as The second layer follows the AVB interface. "
All in all, the Ethernet AVB project team hopes to be able to use ordinary traffic shaping and reservation protocol functions for wifi (such as 802.11e) and non-802.11 devices that are expected to be used in multiple standard home networks (such as coaxial cable multimedia alliance- MoCA, and ITU-T G9960).
When asked how the achievements of Ethernet AVB are comparable to the UPnP AV standard, Teener is slightly blunt. He said: "These (UPnP) ideas about QoS are Byzantine. They assume that the lower layers are awkward and then try to coordinate. This will not have much impact."
On the contrary, the advantage of Ethernet AVB is that it is designed to "do not require complicated network preliminary design or classify all traffic applications in advance." Kreifeldt said.
Components of Ethernet AVB construction
Jeffree pointed out that the basic parts of the construction of Ethernet AVB probably include 802.1Qat (stream reservation protocol), 802.1Qav (forward and queue), 802.1AS (timing and synchronization of time-sensitive applications in bridged LAN), and 802.1BA (type ).
802.1Qat is the foundation. It should ensure that the network link resources between the source and destination in the link are available.
802.1Qav is used to coordinate data traffic and provide a reliable mechanism to support time-sensitive data flows. At the same time, it must also ensure that AV communication does not occupy the entire bandwidth of data communication. This will allow the upstream traffic limit of any link to not exceed 75% of the bandwidth.
802.1AS is used to generate clocks and repair network audio and video systems. Because time compressed packets leave and arrive at the physical layer (PHY) in the form of whole packets, all delays during time transmission can be measured and repaired. At the same time, it can also provide a synchronization mechanism for different paths in the network, because it is difficult to synchronize the audio and video data streams from different paths at the receiving end, so it is difficult to prevent problems in synchronization.
The full name of 802.1 BA is an audio and video bridging system. It is about training in molding. It provides a second-layer toolkit to support AV communication in different situations, Jeffree said.
It defines the configuration file selection function, options, configuration, default values, protocols, and the process of bridging and locating the local area network. These all determine the network's ability to transmit audio and / or video data streams.
Jeffree explained that the work of 802.1BA has just begun, mainly including the following aspects, such as internal AV installation, professional production room, automotive (distribute AVS standard to seats) and applications on Boeing aircraft.
Each of these standards is in a different draft or voting stage, some of which will be voted by the working group and sponsors from the middle of the year to the end of 2009.
MAC chip implementation
Now more and more consumers have the opportunity to choose to use network media devices. Including watching online content or shared content, for example, not only watching movies on the computer, but also watching movies on the TV.
Kreifeldt of Harman said, "But now, you need a good network to accurately transfer the content from the computer to the TV."
In the domestic network environment, if you want to receive them correctly and achieve traffic shaping, you need to use a reservation protocol in the audio and video data stream. "You need a chip solution," Kreifeldt said, "no longer need so much Configuration, "Kreifeldt added later." The cost will also be lower. "
To be precise, in order to be able to adapt to the new Ethernet AVB protocol, what special changes does a chip supplier need to make to the Ethernet MAC chip?
Broader's Teener said, "The biggest change to the Ethernet MAC is the ability to measure time-the start frame (SOF) of the special event frame is really * transmitted or received on the physical layer medium (cable) * "He pointed out," This accuracy is already very high (± 20ns), such accuracy can not be achieved by software. "
Event frames are defined in 802.1AS and can be easily decoded, so this is not a challenge, Teener said. In the design of the AVB Ethernet network interface card, there are still many functions that have not been solved. An example is multi-transmission queues to support multiple transmission types, as well as things that make highly interrupt-delayed operating systems simpler, such as Linux operating systems, Windows operating systems, and BSD, to support traffic shaping specified by 802.1Qav.
When asked how long Broadcom will prepare these MAC chips, Teener added, "We have already demonstrated the 802.1AS protocol on the 5395 exchange reference platform at the ISPCS '07 conference in Vienna."
Does the family use multiple HD format data streams?
Another question about the results achieved by the AVB working group is how they plan to solve the problem of supporting multiple uncompressed high-definition video data streams when using Wifi and Ethernet.
He said that all current plans for home use support compressed video formats. "The wireless HD group wants to support an uncompressed HD data stream, as well as HDMI for cables."
Teener admits that, in fact, "gigabit-level Ethernet is required to achieve uncompressed HD streaming, and even gigabit-level switches are useless," but this does not mean that it is impossible.
He mentioned an article he wrote several years ago, in which he described how to use 10G (above) Ethernet in a professional media studio environment.
In fact, the bigger misconception about this industry is that any type of home networking technology is considered a luxury by consumers who are struggling.
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