Embedded Systems November 2000 Vol13_12

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IEEE 1394 (also known as Firewlre) seems destined to be a major player in the consumer electronics and multimedia spaces. FIGURE' ~etSend protocol stack Device Specific Code Negotiation and Data Conversion UTP up to 100 meters. This will allow 1394 to be used as the home network backbone, assuming, of course, that the home has Category 5 cabling installed. IEEE 1394, shown in Figure 7, is a bus that provides physical layer, link layer, transaction layer, and discovery capabilities. Up to 64 devices can be connected on a single bus, and up to 1,024 individual buses can be connect- ed. The network provides automatic address assignment and peer-to-peer communications. Refer to Reference 1 for detailed information on IEEE 1394. Many upper layer protocols can Network D Device Code ยท ~ JetSend Protocols - Direct Non-JetSend Protocols run on top of the 1394 stack. This is both a blessing and a curse. It is a blessing because it means that the entire industry recognizes the poten- tial of the bus; the cur e is that too many protocols can become very con- fusing to both designers and end users alike. The leading contenders to ride on top of 1394 in a home networking scenario are TCP / IP and the Home Audio/ Video Interoperability (HAVi) specification. likely be relegated to devices that are truly encwnbered by cables, such as cell phones, digital still cameras, and personal organizers. Twisted pair All other things being equal, run- ning 10/ 100 Base-T Ethernet over Category 5 Untwisted pair (UTP) is an attractive solution. Standard Ethernet chipsets can be had for under $10 in volume. In addition, many off-the-shelf protocol stacks are available and TCP / IP is well understood. Unfortunately, all things are not equal. Existing homes do not have the cabling infrastruc- ture and it is quite expensive to install thi after the fact. In addition, Ethernet may still suffer from QoS issues when loaded with several mul- timedia channels. Most eve ryone is familiar with the Etherne t protocol, including the ubiquitous IEEE 802.3 twisted pair incarnation also known as 10Base-T and 100Base-T. It should be noted that 10/ 100 Base-T only specifies up through the link layer, with the net- work layers defined elsewhere. One drawback from a multimedia stand- point is the lack of isochronous capability in a 10/ 100 Base-T physi- cal layer. Guaranteed bandwidth is preferable for audio and video applications. IEEE 1394 (also known as Firewire) seems destined to be a major player in the consumer elec- tronics and multimedia spaces. The current implementation and next generation provide up to 400Mbps asynchronous and isochronous data transfer. In addition, work is well underway in defining the standard for sending IP packets over 1394. From a home networking perspec- tive, the current tandard has one major drawback-a 5m cable length limitation. This situation will be resolved when 1394B is completed. 1394B will allow data transfers over 74 NOVEMBER 2000 Embedded Systems Programming Power line Powerline carrier systems provide the most convenient wired access, requir- ing no new wiring and multiple ports in every room. Powerline carrier sys- tems must deal with the harsh environ- ment mentioned earlier and getting fast reliable throughput requires a tremendous amount of sophistication. Technical challenges aside, systems are currently available with 1Mbps throughput. Products and compo- nents supporting 10Mbps are sup- posed to be available this year. The biggest issue with the power- line systems has been that they all involve proprietary protocols and fair- ly large amounts of protective circuit- ry. The proprietary issue is being addressed by the recently formed HomePlug Alliance. The alliance has adopted the Intellon COFDM tech- nique for version 1.0 of the standard. However, even 10Mbps may not be adequate for some of the more

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