When HANA (High-Definition Audio-Video Network Alliance) chose IEEE-1394 as its recommended home network platform, it may have surprised some in the industry. Ethernet has won over the PC marketplace giving it a vast infrastructure base and economies of scale. In the consumer electronics world, HDMI already has taken a significant lead as the point-to-point connection of choice for moving video. With Ethernet's market dominance in PC networks, and HDMI's dominance in CE point-to-point connections, why didn't HANA select one of these technologies? So what compelling advantages does 1394 have that made it so appealing to HANA?
Bandwidth and quality of service
To transport a single, high-definition MPEG2 stream with audio typically requires anywhere between 20 to 30 Mbps of bandwidth, depending on the resolution for consumer applications. Although Ethernet, HDMI, and 1394 all have the bandwidth to transfer high-definition video content, each have their own pros and cons. Let's delve further into how each handles video.
In a perfect world, Ethernet at 100 Mbps would seem to be able to handle up to 5 HD streams. This assumes the minimum HD resolution, no overhead due to the protocol, each video stream has dedicated bandwidth, and there is no congestion with other devices on the network.
However, Ethernet IP networks provide only a best-effort packet delivery service, which means there is no guarantee that the network will not discard, duplicate, delay or mis-order the packets. This poses a major dilemma for clock reconstruction in MPEG2 transport streams, which is crucial for synchronizing video to audio (lipsync), multi-room audio and similar applications.
Due to the time sensitive nature of streaming video, you have two basic possibilities to improve the Quality of Service QoS in an IP system to prevent interruptions to the video: 1) reduce congestion by either increasing bandwidth or reducing the traffic on the network; and 2) add additional buffering to each display device.
In an attempt to improve QoS, the 802.1Q specification was created to offer a third alternative. Using a Tag Protocol ID (TPID), the 802.1Q spec creates a packet prioritization giving time sensitive data a greater chance of getting to the destination in time.
Although this frees the time-sensitive data from regular traffic, congestion may continue to be an issue as more and more time-sensitive products become integrated into our homes. HD video must compete with other HD streams, IPTV, VoIP, video conferencing, and gaming systems for packet priority.
NEXT: Advantages of 1394
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