NAME
strip —
Metricom Ricochet packet radio wireless
network device
SYNOPSIS
pseudo-device strip
DESCRIPTION
The strip driver takes outbound network
packets, encapsulates them using the Metricom "star mode" framing,
and sends the packets out an RS-232 interface to a Metricom
Ricochet packet radio. Packets arriving from the packet
radio via the serial link are decapsulated and then passed up to the local
host's networking stack.
strip is an acronym for
STarmode
Radio
IP.
The strip interfaces can be created by
using the ifconfig(8) create command. Each
strip interface is a pseudo-device driver for the
Metricom Ricochet packet radio, operating in peer-to-peer
packet mode.
In many ways, the strip driver is very
much like the sl(4) SLIP pseudo-device driver. A strip
device is attached to a tty line with
slattach(8). Once attached, the interface is configured via
ifconfig(8). The major difference between the
sl(4)
SLIP pseudo-device driver and the strip driver is
that SLIP works only between two hosts over a dedicated point-to-point
connection.
In contrast, strip sends packets to a
frequency-hopping packet radio, which can address packets to any peer
Metricom Ricochet packet radio, rather than just to a
single host at the other end of a point-to-point line. Thus, one
strip pseudo-device is usually sufficient for any
kernel.
In other respects, a strip interface is
rather like an Ethernet interface. Packets are individually addressed, and
subsequent packets can be sent independently to different MAC addresses.
However, the "star mode" framing and MAC addressing are not in any
way compatible with Ethernet. Broadcast or multicast to more than one packet
radio is not possible, due to the independent frequency-hopping operation of
the packet radios. The interface flags
IFF_POINTOPOINT and
IFF_BROADCAST are not supported on the
strip interface.
In other words, strip implements a
multiple-access, non-broadcast device, accessed via an RS-232 serial line,
using a proprietary packet framing scheme.
This version of the strip driver maps IP
addresses to Metricom Ricochet packet radio addresses
using statically configured entries in the normal routing table. These
entries map IP addresses of peer packet radios to the MAC-level addresses.
The exact syntax of this mapping and an example are discussed below. The
Internet Assigned Numbers Authority (IANA) has allocated an ARP type code
for use with STRIP. A future version of this driver will support
arp(4) to obtain the IP address of reachable peer packet radios
dynamically.
ADDRESS CONFIGURATION
This version of the STRIP driver requires static pre-configuration of the mapping from IP addresses to packet radio MAC addresses. The route(8) command should be used to bind a peer STRIP host's packet radio IP address to the peer's link-level packet radio address.
Radio addresses are encoded using the hex equivalent of the packet radio's decimal ASCII address. For example, the following route command will configure a routing entry to a packet radio with a MAC address of 1234-5678, and an IP address 10.11.12.13, reachable via the strip0 interface:
route add -host 10.11.12.13 -link strip0:1:2:3:4:5:6:7:8Generalising from this example to other IP addresses and to other 8-digit MAC addresses should be clear.
RADIO CONFIGURATION
The Metricom Ricochet packet radios can
auto-baud at speeds up to 38.4K baud. At higher speeds -- 57600 or 115200 --
the packet radio cannot autobaud. When running at high speeds, the packet
radio's serial port should be manually configured to permanently run at the
desired speed. Use a terminal emulator and the Hayes command
ATS304=115200 to set the serial baudrate to the
specified number (or 0 for autobaud). The command
AT&W will then save the current packet radio
state in non-volatile memory.
Metricom Ricochet packet radios can operate in
either “modem-emulation” mode or in packet mode (i.e.
"star mode"). The strip driver
automatically detects if the packet radio has fallen out of "star
mode", and resets it back into "star mode", if the baud rate
was set correctly by
slattach(8).
SEE ALSO
HISTORY
strip was originally developed for the
Linux kernel by Stuart Cheshire of Stanford's Operating Systems and
Networking group, as part of Mary Baker's MosquitoNet project.
This strip driver was ported to
NetBSD by Jonathan Stone at Stanford's Distributed
Systems Group and first distributed with NetBSD
1.2.
BUGS
Currently, strip is IP-only.
Encapsulations for AppleTalk and ARP have been defined, but are not yet
implemented in this driver.
strip has not been widely tested on a
variety of lower-level serial drivers.
The detection and resetting of packet radios that crash out of
"star mode" does not always work in this version of the driver.
One workaround is to kill the
slattach(8) process,
ifconfig(8) the strip interface down, and
then start a new slattach and rerun ifconfig to enable the interface
again.