Review: Agere ORiNOCO AS-2000, part 1 - Page 3

 By Lisa Phifer
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Wi-Fi is a broadcast medium. To join in, a wireless NIC must be within range of the access point or peer station. This brings us to the other function of the ORiNOCO Client Manager: monitoring and testing. (Click on image to enlarge.)

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A Card Check panel verifies hardware/firmware compatibility and integrity. A Link Test panel evaluates quality of communication between this NIC and a test partner. Other NICs broadcasting with the same network name are automatically discoveredpotential test partners are identified by computer name and MAC. A Site Monitor panel displays base station availability. All results are presented graphically and can be logged on-demand or intervals.

When problems are detected, the Client Manager offers advice. In many cases, advice is specific and helpful.For example, configure matching keys, reduce transmit rate. In other situations, advice amounts to a virtual shrug of the shoulderscheck IRQ, move NIC, add range extender antenna.

Earlier this year, we had a disappointing experience with another vendor's residential gateway, where communication was poor just one wall and ten feet away from the base. With ORiNOCO, we had much better luck. According to specs, 11 Mbps should be possible up to 525 feet in an open office or 80 feet in a closed office. 1 Mbps ranges are 1750 and 165 feet, respectively. So, how did we fare?

On a green-yellow-red scale, quality was green 50 feet and two floors away, dropping to yellow when shielded by enclosed desk, steel beam, or air duct. Strength, measured on a five bar scale, dropped from 5 to 3 at that distance. Because rates were adjusted automatically and Internet bandwidth was our constraint, signal degradation was not that noticeable to the user.

Of course, we only had a handful of NICs competing for attention from our base station. According to specs, the AS-2000 can handle 250 clients per AS radio card. That is, 500 clients when both AS-2000 slots are filled. In the field, Agere technical support typically sees 30-40 clients per AS radio card.

Adding PPP
Installing ORiNOCO cards, drivers, and Client Manager software creates your WLAN. The WLAN is then bridged to a wired network to route traffic to the public Internet. The AS-2000 does this by layering PPP on top of Wi-Fi, communicating with an AS Client.

Click on image to enlarge

AS Client software essentially binds Windows dial-up networking or RRAS to the ORiNOCO NIC. The AS Client associates with an AS-2000, creating an unauthenticated cleartext channel. (ORiNOCO uses null "Open System" authentication at the link level.) To initiate PPP-over-802.11b, the user launches the AS Client, entering his username and password. (Click on image to enlarge.)

The AS Client uses the cleartext channel to send a PPP connection request. The AS-2000 responds, and the two parties use Diffie-Hellman to generate session keys. The AS Client uses this now-encrypted channel to send a PPP LCP configure request, eliciting a CHAP challenge from the AS-2000.

The AS-2000 wraps the AS Client challenge response inside a RADIUS Access Request message and relays it to a RADIUS server on the wired network. The RADIUS server accepts or rejects access by this client, based on the supplied username and password. The AS-2000 relays the outcome to the AS Client, completing CHAP authentication. If successful, the AS Client gains authenticated, encrypted access to the wired network.

RADIUS servers record session accounting information and can enforce concurrency limits or session timeouts. By integrating RADIUS, the AS-2000 gives a wireless ISP a familiar infrastructure to meter and charge for service. One might configure prepaid accountsfor example, a hotel guest purchases a 5-hour login, and uses it to access the Internet during his stay. Universities might create student accounts for use in dorms or classrooms. Private enterprise network access can also be supported by the AS-2000, using RADIUS accounting for chargeback or audit.

This article was originally published on Aug 23, 2001
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