Photonics' wireless networking uses infrared to link your computers
Howard Eglowstein
Wireless networks are attractive where running cable is inconvenient or impossible. Establishing a temporary workgroup with portable PCs in a meeting room is a good example. Or perhaps you're leasing your office space and don't have the flexibility of running wires. Many wireless network products, including the Photonics infrared LAN reviewed here, also let you connect wireless nodes to wired networks through wireless access-point devices.
If you decide to go wireless, which technology should you look at? Radio technology can reach through walls, allowing you to effectively bring walled offices into your network. Some can also reach across large open areas, such as factories, where cabling may be
inappropriate. The difficulty is that if someone in an office can see your data, perhaps someone outside your building can, too. Microwaves solve this security problem fairly well because they won't penetrate through most exterior walls, but mounting the transceivers in the right locations can be tricky.
Spread-spectrum radio LANs may also have problems with interference once such networks become common. While the currently developing wireless LAN standard (see ``Universal Wireless LANs'' in the May BYTE) provides avoidance mechanisms that let multiple networks coexist, sharing the same broadcast space reduces transmission speed.
IR (infrared) networking provides a reliable means of sharing data within a small space without opening up your network to the security problems you might have with radio systems. In short, your network traffic modulates an array of infrared LEDs, which bounce your data off the surfaces in the room. Receivers on other modules pick up the reflected energy and convert it
back to data. Because the IR signals don't leave the room, there are no security or interference problems.
Photonics has developed two product lines based on this technology. The Photonics Collaborative line is a series of PC-based products that connect through ISA cards, PCMCIA cards, or parallel ports to share data between PCs at rates up to 1 Mbps. The Cooperative line is based on the same transceiver technology, but as applied to Macintosh LocalTalk, and so is limited to 230 Kbps. Because Photonics was updating the PC line at the time of this review, I looked only at the Cooperative (Mac) product. (IBM also offers PC products using Photonics technology.)
A Cooperative Effort
Building a Cooperative network is extraordinarily simple. The $349 infrared transceiver is less than 3 inches square and weighs about 4 1/2 ounces. A thin, hinged plastic base lets you adjust the angle of the transceiver for best operation. With its 2-foot cable you attach the unit to the LocalTalk port of any Ma
cintosh computer, printer, or file server. To power the Cooperative, you connect a pass-through plug to the ADB (Apple Desktop Bus) port on your Mac and connect your keyboard or mouse to the back of the Cooperative plug.
By connecting a Cooperative transceiver to an optional Access/Power unit ($129), you create an access point that can connect a roomful of Macs-- wirelessly connected to each other--to conventionally wired Mac resources. The access point snaps onto the transceiver in place of the standard base. Besides holding three AA batteries, it provides an ADB connection (for powering the transceiver), LocalTalk connections for both the transceiver and a wired LocalTalk network, and a plug for a 5-V AC adapter.
If you are using a portable Mac that does not have an ADB port (e.g., the Macintosh Duo series) or would rather not increase the drain on your portable's battery, the optional access point can also serve as a power supply. It can power a transceiver for 24 hours with alkaline batterie
s or for about 12 hours with rechargeable batteries. One advantage of IR technology is that it draws less current than some of the radio-based solutions--typically less than 250 milliamperes.
To receive data, the IR receiver must be able to ``see'' the transmitter. Like conventional light, IR doesn't bend around objects to any significant degree. Photonics' products therefore rely on the walls and ceiling of the room to bounce the energy from one place to another. As with the light from a lamp, there will be few areas in a room that don't receive some illumination. Within reason, a Cooperative transmitter can flood a 30- by 30-foot room with enough energy to send its signal from one corner to another.
When you install the transceivers, you should place them as centrally in the room as possible, with the transmitter/receiver unit pointing up toward the ceiling. I tried installing my test pair of transceivers in a variety of rooms, and standard acoustic office ceiling tile worked quite well as an
IR-reflective surface. I encountered difficulties in only one room, where the ceiling was blocked by a decorative lattice of dark wood strips. In that case, I had to aim the transceivers directly at each other.
Performance
If you've just started working with Macs and have never experienced LocalTalk, or if you just don't remember how slow it is, it runs at a maximum data rate of 230 Kbps, or about 20 KBps. Ethernet on a bad day is at least four times that speed and often faster. To put it another way, a LocalTalk server shared among several active users may make you appreciate how fast floppy disks can be.
With that in mind, the IR section of Cooperative runs at a maximum data transfer rate of 1 Mbps--easily fast enough to handle LocalTalk (the PC versions are expected to run at the full 1-Mbps rate). According to Photonics, a Cooperative network will run as fast as that same network running over standard LocalTalk wiring. I had only two nodes, but I tried a number of tests to confirm Ph
otonics' performance claims.
To begin with, I connected one node to a Mac PowerBook 170 (which had a 25-MHz 68030 processor) and the other node to a Mac SE/30 (with a 16-MHz 68030).
I enabled file sharing on both of these machines under System 7 and then copied files in each direction. The IR nodes managed a data transfer speed of approximately 16 KBps. When I replaced the IR nodes with two Farallon PhoneNet connectors wired together, the same file transfer test yielded the same 16 KBps.
I then reattached the PowerBook to the IR node and attached the other Photonics node through its access point to the BYTE building's LocalTalk wiring. The building has an extensive network of interconnected wiring that includes two active LocalTalk hubs (Farallon StarControllers). Through the StarController, a Mac can find the BYTE network's Cayman GatorBox, which then provides access to any of the AppleShare or NetWare for Macintosh servers. To complete the connection, I attached the Mac SE/30 to a thin
Ethernet connection.
To get data from the PowerBook to the Mac SE/30, the traffic now had to brave BYTE's bustling building-wide network. In that environment, the effective data transfer rate dropped to between 10 and 11 KBps. I disconnected the IR node and attached the PowerBook directly to the LocalTalk wiring, and the transfer rate jumped back to 16 KBps.
What happened? According to Photonics, the access point gives a higher priority to traffic coming from the IR node than to traffic from the wired LocalTalk port. The company suggested that I should have put a LocalTalk-to-LocalTalk bridge between the access point and the wired network. This is an added expense, but it's not an uncommon performance fix even for wired LocalTalk networks.
I was also curious about the effective range of the transmitter. We have one large conference room that's a tad over 50 feet long. One wall is packed with windows, the ceiling is acoustic tile with a dark-wood decorative lattice mounted to it (mentioned
previously), and the other walls are dark paneling. I thought the Cooperative wouldn't have a chance. To my delight, I was able to set the two machines at either end of the room and, by pointing the transceivers toward each other, get excellent communications from 50 feet. Even when I walked back and forth between the machines, the transfer didn't slow down. Photonics' 30-foot range claim is quite reasonable.
Warming Up to IR
While I started out unsure that these tiny transceivers could perform as well as the company said they would, working with them has made me a believer. They're not perfect, however. For the transceivers to work well, you need a fairly small, somewhat confined area with reflective walls and ceiling. Photonics recommends a practical maximum of 40 or so units per network. Although I tested with only two, I spoke with folks at a test site that is currently running 30-plus nodes in a room simultaneously. While they wish that the technology were faster, they're happy with the so
lution.
In addition to these limitations, the Photonics system has trouble with bright light sources blinding or confusing the receivers. The transceivers don't work outdoors and may have difficulty in a bright, sunny conference room.
At $349 per machine (plus an additional $129 for transceivers used as access points), the Photonics system is not an inexpensive solution. A LocalTalk network node runs about $25 in any computer store, and wiring a temporary network using LocalTalk is assuredly less expensive than the Photonics solution. But considering how easily these units connect and how well they work, the Photonics Cooperative network could be the right answer for some sticky networking problems. It offers adequate performance (as good as LocalTalk ever gets) and connections that are secure from eavesdropping, and it works reliably.
For situations in which radio solutions are inappropriate, IR might be just the answer. Photonics' Cooperative is a shining example of a technology with a
bright future.
The Facts
Cooperative
LocalTalk transceiver $349
Access/Power unit $129
Photonics Corp.
2940 North First St.
San Jose, CA 95134
(800) 628-3033
(408) 955-7930
fax: (408) 955-7950
Infrared Vs. Radio
A comparison of some of the advantages and disadvantages of these two types of wireless LANs.
INFRARED RADIO
Transmission speed Photonics limited to 230 Kbps Many spread-spectrum
on the Mac, 1 Mbps on PCs LANs support 2 Mbps;
some other radio LANs,
more than 10 Mbps
Range 30- by 30-foot room alone; 100 feet to 1000 feet
unlimited with access points alone; unlimited with
access points
Interference
Interference from bright Electromagnetic inter-
sunlight limits use to ference from other
indoors electronic devices or
neighboring radio LANs
can reduce transmission
speed
Security Transmitted information Can be monitored with
stays in room modified receiver;
tight security requires
encryption
Access through walls Limited to use in one room or Many radio LAN products
enclosed space unless work through walls
rooms are connected
by wired backbone
Power requirements L
ow Moderate
Cost per node $349 $500 to $800
Cost per access point $478 $1500 to $5000
Photograph: Two Cooperative transceivers. Each cord provides both LocalTalk and pass-through ADB (for power) connections. The optional Access/Power unit (base of left transceiver) can serve as an access point to a wired LocalTalk network.
Howard Eglowstein is a developer with Penmanship, Inc. (Incline Village, NV), and works with handwriting and embedded systems for education. You can reach him on the Internet or BIX at
heglowstein@bix.com
.
Networking on a Beam of Light
