Driven by cellular phone and PDA applications, Personal Area Network (PAN) solutions such as Bluetooth emphasize the minimization of cost and power consumption. Corporate wireless LANs (WLANs) focus on standards compliance, range, data throughput and roaming capability as found in the IEEE 802.11 specifications. Home and small office-home office (SoHo) WLAN solutions require balancing range and data throughput against cost and ease of use. To date, HomeRF and HomeCast Open Protocol (HOP) solutions are the only ones to specifically target the home-SoHo WLAN category.
The fact that these categories exist does not prevent many vendors from touting network products in each category as home network solutions. However, what truly are low-cost and low-power networks for small offices and home offices becomes apparent when the competitive aspects of each are evaluated, based solely on whether they meet or exceed realistic end-user requirements. In most cases, what the industry indicates will fulfill the needs of home and small-office users falls on the side of overkill.
Wireless home-network end users are driven by the fact that, although they require inexpensive connectivity, an increasing number of devices must access existing central resources. Most often, users do not have the experience, capacity or interest to configure or maintain a network as complex as those found in the corporate enterprise. Simple and robust solutions are mandatory for sharing data within a family home or a small home office and have the potential to meet a household's ever-growing needs.
A closer look at available wireless network solutions reveals a clear separation by end user and cost within each. For example, the Bluetooth standard targets the connectivity of portable devices rather than concentrating on home networking. Driven by cellular phone and PDA manufacturers, Bluetooth combines voice and data, is a point-to-multipoint solution and communicates with up to seven slaves simultaneously at 1-Mbit/second data rates. Operating in the 2.4-GHz industrial-scientific-medical (ISM) band, it requires an integrated digital signal processor. Viable Bluetooth devices should become commercially available by the middle of next year.
IEEE 802.11 is a high-end corporate network solution that will drive higher bandwidth. Current 802.11 solutions also operate in the 2.4-GHz ISM band with throughputs between 1 and 11 Mbits/s, but at a substantially higher cost. Future implementations will move to the 5.8-GHz band, with throughputs from 11 to 50 Mbits/s. These 802.11-based solutions may eventually find their way into the home if the cost of networks drops far enough. At that point, they will still be high-end solutions.
HomeRF targets true home-SoHo applications. Utilizing features of both the IEEE 802.11 and the Digital European Cordless Telephony (DECT) standards, it integrates both voice and data channels, so it could be more expensive than other home wireless networks. The first products will be available next year.
Also for true home network applications, HOP, invented by Alation Systems Inc. (Mountain View, Calif.), is a proven low-cost, high-performance wireless Internet Protocol (IP) transport system. It is specified as an industry-standard protocol with a focus on consumer and productivity applications, especially the efficient and reliable transmission of TCP/IP packets throughout the home. HOP is the basis of a 1-Mbit/s home WLAN solution jointly developed by National Semiconductor Inc. and Alation Systems. The HOP protocol simply appends a HOP-specific header to an 802.3 "packet," and hands the data to the radio section, where it is fragmented and reassembled dynamically in response to channel quality. All packets are received by all HOP nodes simultaneously and all nodes communicate with all other logically connected nodes. Connections are bidirectional and every node is simultaneously connected to all other nodes in the network-a HOP network resembles a star bus network topology. HOP provides a logically shared interconnect, since all connected devices share available channel bandwidth. The protocol allows for a highly dynamic single-cell network in which devices may come and go at will.
Using a 2.4-GHz Frequency Hopping Spread Spectrum (FHSS) radio to deliver data over the air, HOP technology makes possible the industry's first sub-$100 wireless home network for data networking. The radio is a simple yet robust design that is inexpensive and easily manufactured. HOP allows up to 16 devices to communicate on a peer-to-peer network with a line-of-sight range of 50 to 100 meters, depending on wall and ceiling barriers. While cost effective, it provides full connectivity between devices.
A HOP reference design, co-developed by National Semiconductor and Alation, features a complete software/hardware networking solution component kit, consisting of an RF front end combined with a DP83600 baseband controller and a software-based media access controller (MAC). FCC certification is guaranteed.
The software-based MAC is unique to HOP. The MAC is based on the industry-standard NE2000 Ethernet driver, integrating all required MAC functionality in software. The software MAC takes up a negligible portion of CPU cycles and is transparent to the user, allowing transmission and receipt of standard IEEE 802.3 Ethernet packets, while the baseband controller enables it to do so wirelessly. The physical layer that is accessed is wireless rather than cable. Because of its implementation over a wireless transmission medium, HOP uses several techniques to transmit data in an efficient manner, including clear channel assessment, collision avoidance and random back-off. The MAC has current Windows 95 and 98 support, allowing flexibility for future designs. Using a software MAC also reduces chip count and therefore system cost, but makes the transmission medium transparent to upper layers in the protocol stack. The protocol is optimized to account for multipath propagation and adaptively adjusts data packet lengths to optimize throughput with minimal CPU overhead on the host.
The HOP-based DP83600 baseband controller is one that, when used with a 2.4-GHz radio, contains most of the functionality needed to implement a wireless LAN controller. The controller is designed specifically for networking and interfaces directly to a PCMCIA bus with minimal cost and board space. It is also compatible with third-party bridge chips, allowing it to be used in PCI and USB implementations.
The HOP network is designed to be scalable, with no hard limits on its extendability. Network capacity is affected by its use and by the amount of bandwidth consumed by each node-for example, video transmission uses up more network bandwidth than the transmission of control signals. Performance is implementation-dependent. The bit rate of 1 Mbit/s is equivalent to one data octet per 8 microseconds. The data transmission rate can sustain 450 kbits/s during file copy under Microsoft Windows. There also are implementations that demonstrate over 600 kbits/s of sustained throughput.
Once entry-vehicle network products take hold, products are expected to take two possible paths: multiprotocol devices and higher-bandwidth ones. As competing standards mature, products will need to remain responsive to the rapidly changing wireless landscape.
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