Operation
The IrDA-SIR specification takes a standard asynchronous serial character stream from the UART—where a frame is defined as a start bit, 8 data bits, no parity bit, and a stop bit—and encodes the output such that 0 is represented by a pulse and 1 is represented by no pulse. A pulse is further defined as occupying a minimum of 1.6 microseconds to a maximum of 3/16th of a bit period, the length of which is inversely proportional to the bit rate of the data (i.e., the slower the data rate, the longer the pulse). This pulse stream forms the input to the driver for the IR emitter that converts the electrical pulses to IR energy.
IrDA-standard infrared links are half-duplex with the maximum data rate of 115.2 Kbps. There are IrDA high-speed extensions for 1.15 Mbps and 4 Mbps transmission. The hardware consists of an infrared transmit encoder/receiver decoder and the IR transducer, which consists of the output driver and infrared emitter for transmitting and the receiver/detector. The encoder/decoder interfaces to the UART, which is already available in most computers.
IrLAP provides two roles for participating stations, one of which is the Primary (commanding) station and the other is the Secondary (responding) station(s). The primary station has responsibility for the data link. All transmissions over a data link go to, or from, the primary station. IrLAP communication links can be point-to-point or point-to-multipoint. There is always one and only one primary station; all other stations must be secondary stations. Any station that is capable can contend to play the primary station role. The role of primary is determined dynamically when the link connection is established and continues until the connection is closed. The exception is that there is a method provided for a primary and secondary on a point-to-point link to exchange roles without closing the connection.
IrLAP uses most of the standard types of frame defined by the HDLC standards. The frames are classified by function as follows: unnumbered or U frames, supervisory or S frames, and information or I frames.
U frames are used for such functions as establishing and removing connections and discovery of other station device addresses. I frames are used to transfer information from one station to another. S frames are used to assist in the transfer of information and may be used to specifically acknowledge receipt of I frames (I frames can implicitly acknowledge other I frames also) and to convey ready and busy conditions.
IrLAP also describes procedures that support link initialization, device address discovery, connection startup (including link data rate negotiation), information exchange, disconnection, link shutdown, and device address conflict resolution. While each of these procedures is adapted to the IrDA serial infrared environment the link initialization and shutdown, connection startup, disconnection, and information transfer procedures all resemble similar operations in HDLC protocols. However, the discovery and address conflict resolution procedures are unique to IrLAP.
A link operates essentially as follows. A device will want to connect to another device (either by automatic detection via the discovery and sniffing capability of IrLAP, or via direct user request). After obeying the media access rules, the initiator will send connection request information at 9.6 Kbps to the other device, which includes such things as its address and data rate. The responding device will assume the secondary role and, after obeying the media access rules, return information that contains its address and capabilities. The primary and secondary stations will then change the data rate and other link parameters to the common set defined by the capabilities described in the information transfer. The primary station will then send data to the secondary station confirming the link data rate and capabilities. The two devices are now connected and the data is transferred between them under the complete control of the primary station. Rules are defined which ensure that the secondary and primary stations are both able to efficiently transfer data.
Infrared is a communications medium that makes it easy to establish connections between devices. In such a situation, the configuration of devices is not a static configuration, but is highly dynamic. It is determined by the services and protocols offered by the devices within range and the applications the user wishes to use. Three additional elements are necessary for an IrDA IR enabled device: discovery, link control, and multiplexing.
Discovery occurs when two devices first encounter each other. Each service and each protocol on a device will have registered with the link management (i.e., IrLMP). The information registered includes both standard and protocol specific information. An application can query the capabilities of devices within range.
Once an application on one device has determined which service or protocol it wishes to use, it requests the link control to use the protocol. The link management framework allows multiplexing of application or transport protocols on the same link connection at the same time.
Flow control is provided via IrTTP using a credit-based flow control scheme. Not only does IrTTP provide per-transport-connection flow control, but segmentation and reassembly of arbitrary sized packet data units (PDUs) as well.
Niche applications
Infrared systems address a niche market because they impose more restrictive distance limitations that other wireless LAN technologies such as spread spectrum. On the other hand, the infrared systems do offer high levels of throughput. Infrared's primary impact will take the form of benefits for mobile professional users. It enables simple, point-and-shoot connectivity to standard networks, which streamlines users' workflow and allows them to reap more of the productivity gains promised by portable computing. Infrared also confers substantial benefits to network administrators. Infrared is easy to install and configure, requires no maintenance, and imposes no remote-access tracking hassles. It does not disrupt other network operations and it provides data security. And because it makes connectivity so easy, it encourages the use of high-productivity network and groupware applications on portables, thus helping administrators amortize the costs of these packages across a larger base of users.
IrDA-standard infrared ports promise to become pervasive as a low-cost, low-power, dependable two-way data exchange technology on a wide range of products that are increasingly digital and intelligent as the industries of computers, telecommunications, and consumer electronics converge.
Joining the notebooks are other "beaming" products such as mobile printers, mobile digital phones, digital pagers, handheld PCs, PDAs, organizers, modems, PC card adapters, plus a number of flexible printer and computer IrDA adapters. New handheld PCs and organizers from numerous vendors already feature onboard IrDA ports, enabling cordless file exchange and printing functions. Models of cellular phones and pagers from firms such as Nokia Mobile Phones and NEC also have IrDA ports. Sharp and Sony have even announced digital cameras featuring direct IrDA beaming of images to another camera, a computer, or a printer. Future platforms expected to be equipped with IrDA ports include public phones, business phones, USB adapters, watches, and devices for a variety of vertical market applications in the distribution, warehouse, field service, utility, medical, and automotive markets.
Emerging technology
Japanese researchers at NEC have developed infrared wireless network technology that uses the IEEE 1394 high-speed serial bus—also known as Fire Wire—an emerging standard for data transmission in electronics consumer and PC products. The new technology, aimed at the home- and small-office markets, supports multimedia speeds of up to 125 Mbps.
Fire Wire can transmit data from between 100 Mbps and 400 Mbps. Although there are many emerging bus standards, Fire Wire is now appearing in digital camcorders, digital satellite receivers, and digital video recorders. The technology also has the advantages of attracting plug-and-play add-ons and applications. The technology is expected to reach the marketplace in late 1998.
Of note is that NEC researchers have found a way to use ordinary infrared transmission diodes—typically used in remote controllers for consumer products such as TVs—to transfer data at high speeds. Data is converted into an infrared signal that can be transmitted between two transceivers up to 10 meters apart. For distances greater than 10 meters, NEC has developed Fire Wire-based wall sockets to which devices can be physically wired using relatively inexpensive plastic fiber optic cable. By comparison, networks using copper cabling are limited to 4.5 meters, after which they need a repeater to boost the signal.
Because the system used standard parts and diodes, it would be relatively inexpensive to implement in homes and small offices, compared with network systems such as Ethernet. Because infrared is used, there is no concern about electromagnetic interference, which is a growing problem in both home and office environments. The system also meets industry health standards regarding eye protection.
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