Copyright (c) 1997, Jim Binkley All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation an...
NAMEwl - T1 speed ISA/radio lan card
SYNOPSISdevice wl0 at isa? port 0x300 irq 5
DESCRIPTIONThe sysctl Cm net.inet.tcp.syncookies driver controls a radio lan card system made originally by NCR, then ATT, now Lucent. The system is spread-spectrum radio at around 915 MHz (or 2.4 GHz). With the supplied omni-directional antennae, about 400 feet (indoors, more outdoors) can be covered in circumference. This card can talk to the companion (wlp0) pccard. Speeds vary from 1 megabit to theoretically 2 megabits (roughly T1 in speed).
The card has three fundamental hardware units, a so-called PSA or programmable storage area, a radio modem, and a Ethernet lan controller. The latter component is the ancient (and not very honorable) Intel 82586 Ethernet chip. Fundamentally it appears to the operating system as an Ethernet system, and speaks IEEE MAC addresses. The radio modem simply translates Ethernet packets to/from radio packets, that are either at 2.4 GHz or 915 MHz depending on the radio modem. It supports a collision avoidance scheme. The lan controller supports promiscuous mode, broadcast, and multicasting (although there is a glitch in the latter). "It thinks it is Ethernet".
How it is used depends on the kind of antennae deployed with it. Point to point applications are possible as are Ethernet-like lan use. The vendor ships an omni-directional antennae that works in the vicinity of 400 feet (indoors). Point to point antennae can be purchased that will go miles.
SETUPThe card can either be initialized with the vendor supplied DOS setup software. Typically minimally an IRQ, port, and Network ID must be supplied. Michael Smith's wlconfig(8) utility can now be used to do this work from the UNIX side. The card is "not" plug and play. The network id controls whether one set of cards can hear another. If different, cards will read physical packets, but they will be discarded by the radio modem.
CONTROLIn addition to the config utility, there are several sysctl switches that can be used to modify runtime parameters. The sysctl(8) variables are as follows:
- "machdep.wl_xmit_delay <useconds>"
- This variable will cause the driver to insert a delay on transmit. 250 is the default. The delay should probably be a bit longer on faster cpus and less on slower cpus. It exists because the 82586 was not designed to work with Pentium-speed cpu systems and if overdriven will have copious xmit side errors.
- machdep.wl_ignore_nwid <0 | 1>
- This switch defaults to 0; i.e., the nwid is not ignored. It can be set to 1 to cause the nwid to not be used. This may be useful when the device is in promiscuous mode as one can watch for all packets and ignore nwid differences.
- machdep.wl_xmit_watch <milliseconds>
- This switch is not currently useful.
- machdep.wl_gather_snr <milliseconds>
This switch is not currently useful.
There is also a signal strength cache in the driver. It may be interrogated with wlconfig(8). Incoming packets are checked for certain hardware radio-modem values including signal strength, silence, and quality, which range fro 0..63, 0..63, and 0..15 respectively. Thus one can read out signal strenth values to see how close/far peer nodes are. The signal strength cache is indexed by sender MAC address. There are two sysctls that change how it filters packets. Both are on by default.
- machdep.wl_wlcache_mcastonly <0 | 1>
- By default this switch is on. It forces the cache to filter out unicast packets. Only broadcast or multicast packets are accepted.
- machdep.wl_wlcache_iponly <0 | 1>
- By default this switch is on. It forces the driver to discard non-IP packets and also stores the IP src address. ARP packets are ignored, as are any other network protocol barring IPv4 packets.