LMC(4) BSD Kernel Interfaces Manual LMC(4)NAMElmc — device driver for LMC (and some SBE) wide-area network interface
cards
SYNOPSIS
This driver is built into the GENERIC kernel so it should "just work".
The driver can be built into a kernel by adding the following to
/sys/arch/ARCH/conf/YOURKERNEL:
lmc* at pci?
options ALTQ
options ALTQ_HFSC # for altq example
pseudo-device sppp
pseudo-device bpfilter
The driver can send and receive raw IP packets even if SPPP is not con‐
figured into the kernel.
DESCRIPTION
This is an open-source Unix device driver for PCI-bus wide-area network
interface cards. It sends and receives packets in HDLC frames over syn‐
chronous circuits. A computer plus UNIX plus some LMC cards makes an
open wide-area network router.
The lmc driver works with FreeBSD, NetBSD, OpenBSD, BSD/OS, and Linux
OSs. It has been tested on i386 (SMP 32-bit little-end), PowerPC (32-bit
big-end), Alpha (64-bit little-end), and Sparc (64-bit big-end) architec‐
tures.
The lmc driver works with the following cards:
LMC5200 HSSI—High Speed Serial Interface,
EIA612/613, 50-pin connector,
0 to 52 Mb/s, DTE only.
LMC5245 T3, 2xBNC conns, 75 ohm
C-Parity or M13 Framing,
DSX-3 up to 910 ft.
LMC1000 SSI—Synchronous Serial Interface,
V.35, X.21, EIA449, EIA530(A), EIA232,
0 to 10 Mb/s, DTE or DCE.
LMC1200 T1/E1, RJ45 conn, 100 or 120 ohms,
T1-B8ZS-ESF, T1-AMI-SF, E1-HDB3-many,
DSX-1 up to 1500 ft; CSU up to 6 Kft.
LMC cards contain a high-performance PCI interface, an HDLC function and
either integrated modems (T1, T3) or modem interfaces (HSSI and SSI).
PCI The PCI interface is a DEC 21140A Tulip Fast Ethernet chip.
This chip has an efficient PCI implementation with scat‐
ter/gather DMA, and can run at 100 Mb/s full duplex (twice
as fast as needed here).
HDLC The HDLC functions (ISO-3309: flags, bit-stuffing, CRC) are
implemented in a Field Programmable Gate Array (FPGA) which
talks to the Ethernet chip through a Media Independent
Interface (MII). The hardware in the FPGA translates
between Ethernet packets and HDLC frames on-the-fly; think
of it as a WAN PHY chip for Ethernet.
Modem The modem chips are the main differences between cards.
HSSI cards use ECL10K chips to implement the EIA-612/613
interface. T3 cards use a TranSwitch TXC-03401 framer chip.
SSI cards use Linear Technology LTC1343 modem interface
chips. T1 cards use a BrookTree/Conexant/Mindspeed Bt8370
framer and line interface chip.
Line protocol stacks exist above device drivers and below internet proto‐
col stacks. They typically encapsulate packets in HDLC frames and deal
with higher-level issues like protocol multiplexing and security. The
driver is compatible with several line protocol stacks:
SPPP sppp(4) implements Synchronous-PPP and Cisco-HDLC in
the kernel.
RawIP The null line protocol, built into the driver, sends
and receives raw IPv4 and IPv6 packets in HDLC frames
with no extra bytes of overhead and no state at the
end points.
EXAMPLES
ifconfig and lmcconfig
The program lmcconfig(8) manipulates interface parameters beyond the
scope of ifconfig(8). lmcconfig has many flags and options, but in nor‐
mal operation only a few are needed.
lmcconfig lmc0
displays interface configuration and status.
lmcconfig lmc0 -X 1
selects the built-in RawIP line protocol stack.
lmcconfig lmc0 -X 2 -x 2
selects the SPPP stack and the PPP protocol.
Some configuration options are available through ifconfig as well as
lmcconfig.
ifconfig -m lmc0
lists the available media options.
ifconfig lmc0 mediaopt loopback
loops the interface transmitter to the receiver for testing. This loop‐
back uses a path present in every card type. lmcconfig can select card-
specific loopbacks, such as outbound payload loopback.
ifconfig lmc0 debug
enables debugging output from the device driver and from the line proto‐
col stack above it.
lmcconfig lmc0 -D
enables debugging output from the device driver.
Debugging messages that appear on the console are also written to file
/var/log/messages. Caution: when things go very wrong, a torrent of
debugging messages can swamp the console and bring a machine to its
knees.
Operation
Configure a PPP link using SPPP with
lmcconfig lmc0 -X 2 -x 2
ifconfig lmc0 10.0.0.1 10.0.0.2
Configure a Cisco-HDLC link using SPPP with
lmcconfig lmc0 -X 2 -x 3
ifconfig lmc0 10.0.0.1 10.0.0.2
Configure a RAWIP link with
lmcconfig lmc0 -X 1
ifconfig lmc0 10.0.0.1 10.0.0.2
TESTING
Testing with Loopbacks
Testing with loopbacks requires only one card and can test everything on
that card. Packets can be looped back at many points: in the PCI chip,
in the modem chips, through a loopback plug, in the local external equip‐
ment, or at the far end of a circuit.
All cards can be looped through the PCI chip. Cards with internal modems
can be looped through the modem framer and the modem line interface.
Cards for external modems can be looped through the driver/receiver
chips. See lmcconfig(8) for details.
Configure the card with
ifconfig lmc0 10.0.0.1 10.0.0.1
HSSI Loopback plugs can be ordered from SBE (and others). Trans‐
mit clock is normally supplied by the external modem. When
an HSSI card is operated with a loopback plug, the PCI bus
clock must be used as the transmit clock, typically 33 MHz.
When testing an HSSI card with a loopback plug, configure it
with
lmcconfig lmc0 -a 2
“-a 2” selects the PCI bus clock as the transmit clock.
T3 Connect the two BNC jacks with a short coax cable.
SSI Loopback plugs can be ordered from SBE (only). Transmit
clock is normally supplied by the external modem. When an
SSI card is operated with a loopback plug, the on-board
clock synthesizer must be used. When testing an SSI card
with a loopback plug, configure it with
lmcconfig lmc0 -E -f 10000000
“-E” puts the card in DCE mode to source a transmit clock.
“-f 10000000” sets the internal clock source to 10 Mb/s.
T1/E1 A loopback plug is a modular plug with two wires connecting
pin 1 to pin 4 and pin 2 to pin 5.
One can also test by connecting to a local modem (HSSI and SSI) or NI (T1
and T3) configured to loop back. Cards can generate signals to loopback
remote equipment so that complete circuits can be tested; see
lmcconfig(8) for details.
Testing with a Modem
Testing with a modem requires two cards of different types. The cards
can be in the same machine or different machines.
Configure the two cards with
ifconfig lmc0 10.0.0.1 10.0.0.2
ifconfig lmc1 10.0.0.2 10.0.0.1
T3/HSSI If you have a T3 modem with an HSSI interface (made by
Digital Link, Larscom, Kentrox etc.) then use an HSSI card
and a T3 card. The coax cables between the card and the
modem must “cross over” (see below).
T1/V.35 If you have a T1 (or E1) modem with a V.35, X.21 or EIA530
interface, then use an SSI card and a T1 card. Use a T1
null modem cable (see below) between the external modem
and the T1 card.
Testing with a Null Modem Cable
Testing with a null modem cable requires two cards of the same type. The
cards can be in the same machine or different machines.
Configure the two cards with
ifconfig lmc0 10.0.0.1 10.0.0.2
ifconfig lmc1 10.0.0.2 10.0.0.1
HSSI Three-meter HSSI null-modem cables can be ordered from SBE.
In a pinch, a 50-pin SCSI-II cable up to a few meters will
work as a straight HSSI cable (not a null modem cable).
Longer cables should be purpose-built HSSI cables because
the cable impedance is different. Transmit clock is nor‐
mally supplied by the external modem. When an HSSI card is
connected by a null modem cable, the PCI bus clock can be
used as the transmit clock, typically 33 MHz. When testing
an HSSI card with a null modem cable, configure it with
lmcconfig lmc0 -a 2
“-a 2” selects the PCI bus clock as the transmit clock.
T3 T3 null modem cables are just 75-ohm coax cables with BNC
connectors. TX OUT on one card should be connected to RX IN
on the other card. In a pinch, 50-ohm thin Ethernet cables
usually work up to a few meters, but they will not work for
longer runs—75-ohm coax is required.
SSI Three-meter SSI null modem cables can be ordered from SBE.
An SSI null modem cable reports a cable type of V.36/EIA449.
Transmit clock is normally supplied by the external modem.
When an SSI card is connected by a null modem cable, an on-
board clock synthesizer is used. When testing an SSI card
with a null modem cable, configure it with
lmcconfig lmc0 -E -f 10000000
“-E” puts the card in DCE mode to source a transmit clock.
“-f 10000000” sets the internal clock source to 10 Mb/s.
T1/E1 A T1 null modem cable has two twisted pairs that connect
pins 1 and 2 on one plug to pins 4 and 5 on the other plug.
Looking into the cable entry hole of a plug, with the lock‐
ing tab oriented down, pin 1 is on the left. A twisted pair
Ethernet cable makes an excellent straight T1 cable. Alas,
Ethernet cross-over cables do not work as T1 null modem
cables.
OPERATING NOTES
LEDs
HSSI and SSI cards should be operational if all three green LEDs are on
(the upper-left one should be blinking) and the red LED is off.
RED upper-right No Transmit clock
GREEN upper-left Device driver is alive if blinking
GREEN lower-right Modem signals are good
GREEN lower-left Cable is plugged in (SSI only)
T1/E1 and T3 cards should be operational if the upper-left green LED is
blinking and all other LEDs are off. For the T3 card, if other LEDs are
on or blinking, try swapping the coax cables!
RED upper-right Received signal is wrong
GREEN upper-left Device driver is alive if blinking
BLUE lower-right Alarm Information Signal (AIS)
YELLOW lower-left Remote Alarm Indication (RAI)
RED blinks if an outward loopback is active.
GREEN blinks if the device driver is alive.
BLUE blinks if sending AIS, on solid if receiving AIS.
YELLOW blinks if sending RAI, on solid if receiving RAI.
Packet Lengths
Maximum transmit and receive packet length is unlimited.
Minimum transmit and receive packet length is one byte.
Cleaning up after one packet and setting up for the next packet involves
making several DMA references. This can take longer than the duration of
a short packet, causing the adapter to fall behind. For typical PCI bus
traffic levels and memory system latencies, back-to-back packets longer
than about 20 bytes will always work (53 byte cells work), but a burst of
several hundred back-to-back packets shorter than 20 bytes will cause
packets to be dropped. This usually is not a problem since an IPv4
packet header is at least 20 bytes long.
The device driver imposes no constraints on packet size. Most operating
systems set the default Maximum Transmission Unit (MTU) to 1500 bytes;
the legal range is usually (72..65535). This can be changed with
ifconfig lmc0 mtu 2000
SPPP enforces an MTU of 1500 bytes for PPP and Cisco-HDLC. RAWIP sets
the default MTU to 4032 bytes, but allows it to be changed to anything.
ALTQ: Alternate Output Queue Disciplines
The driver has hooks for altq(9), the Alternate Queueing package. To see
ALTQ in action, use your favorite traffic generation program to generate
three flows sending down one T3 circuit. Without ALTQ, the speeds of the
three connections will vary chaotically. Enable ALTQ and two of the con‐
nections will run at about 20 Mb/s and the third will run at about 2
Mb/s.
Enable altqd(8) and add the following lines to /etc/altq.conf:
interface lmc0 bandwidth 44M hfsc
class hfsc lmc0 a root pshare 48
filter lmc0 a 10.0.0.2 12345 10.0.0.1 0 6
filter lmc0 a 10.0.0.1 0 10.0.0.2 12345 6
class hfsc lmc0 b root pshare 48
filter lmc0 b 10.0.0.2 12346 10.0.0.1 0 6
filter lmc0 b 10.0.0.1 0 10.0.0.2 12346 6
class hfsc lmc0 c root pshare 4 default
filter lmc0 c 10.0.0.2 12347 10.0.0.1 0 6
filter lmc0 c 10.0.0.1 0 10.0.0.2 12347 6
The example above requires the altq(4) Hierarchical Fair Service Curve
queue discipline to be configured in conf/YOURKERNEL:
options ALTQ
options ALTQ_HFSC.
BPF: Berkeley Packet Filter
The driver has hooks for bpf(4), the Berkeley Packet Filter, a protocol-
independent raw interface to data link layers.
To test the BPF kernel interface, bring up a link between two machines,
then run ping(8) and tcpdump(8):
ping 10.0.0.1
and in a different window:
tcpdump -i lmc0
The output from tcpdump should look like this:
03:54:35.979965 10.0.0.2 > 10.0.0.1: icmp: echo request
03:54:35.981423 10.0.0.1 > 10.0.0.2: icmp: echo reply
Line protocol control packets may appear among the ping packets occasion‐
ally.
The kernel must be configured with
options bpfilter
SNMP: Simple Network Management Protocol
The driver is aware of what is required to be a Network Interface Object
managed by an Agent of the Simple Network Management Protocol. The
driver exports SNMP-formatted configuration and status information suffi‐
cient for an SNMP Agent to create MIBs for:
RFC-2233 Interfaces group
RFC-2496 DS3 interfaces
RFC-2495 DS1/E1 interfaces
RFC-1659 RS232-like interfaces
An SNMP Agent is a user program, not a kernel function. Agents can
retrieve configuration and status information by using ioctl(2) system
calls. User programs should poll sc->cfg.ticks which increments once per
second after the SNMP state has been updated.
E1 Framing
Phone companies usually insist that customers put a Frame Alignment
Signal (FAS) in time slot 0. A Cyclic Redundancy Checksum (CRC) can also
ride in time slot 0. Channel Associated Signalling (CAS) uses Time Slot
16. In telco-speak signalling is on/off hook, ringing, busy, etc. Sig‐
nalling is not needed here and consumes 64 Kb/s. Only use E1-CAS formats
if the other end insists on it! Use E1-FAS+CRC framing format on a pub‐
lic circuit. Depending on the equipment installed in a private circuit,
it may be possible to use all 32 time slots for data (E1-NONE).
T3 Framing
M13 is a technique for multiplexing 28 T1s into a T3. Muxes use the C-
bits for speed-matching the tributaries. Muxing is not needed here and
usurps the FEBE and FEAC bits. Only use T3-M13 format if the other end
insists on it! Use T3-CParity framing format if possible. Loop Timing,
Fractional T3, and HDLC packets in the Facility Data Link are not sup‐
ported.
T1 & T3 Frame Overhead Functions
Performance Report Messages (PRMs) are enabled in T1-ESF.
Bit Oriented Protocol (BOP) messages are enabled in T1-ESF.
In-band loopback control (framed or not) is enabled in T1-SF.
Far End Alarm and Control (FEAC) msgs are enabled in T3-CPar.
Far End Block Error (FEBE) reports are enabled in T3-CPar.
Remote Alarm Indication (RAI) is enabled in T3-Any.
Loopbacks initiated remotely time out after 300 seconds.
T1/E1 'Fractional' 64 kb/s Time Slots
T1 uses time slots 24..1; E1 uses time slots 31..0. E1 uses TS0 for FAS
overhead and TS16 for CAS overhead. E1-NONE has no overhead, so all 32
TSs are available for data. Enable/disable time slots by setting 32
1s/0s in a config param. Enabling an E1 overhead time slot, or enabling
TS0 or TS25-TS31 for T1, is ignored by the driver, which knows better.
The default TS param, 0xFFFFFFFF, enables the maximum number of time
slots for whatever frame format is selected. 56 Kb/s time slots are not
supported.
SEE ALSOioctl(2), bpf(4), de(4), sppp(4), altq.conf(5), altqd(8), ifconfig(8),
init(8), lmcconfig(8), modload(8), ping(8), tcpdump(8), altq(9), ifnet(9)
http://www.sbei.net/
HISTORY
Ron Crane had the idea to use a Fast Ethernet chip as a PCI interface and
add an Ethernet-to-HDLC gate array to make a WAN card. David Boggs
designed the Ethernet-to-HDLC gate array and PC cards. We did this at
our company, LAN Media Corporation (LMC). SBE Corporation acquired LMC
and continues to make the cards.
Since the cards use Tulip Ethernet chips, we started with Matt Thomas'
ubiquitous de(4) driver. Michael Graff stripped out the Ethernet stuff
and added HSSI stuff. Basil Gunn ported it to Solaris (lost) and Rob
Braun ported it to Linux. Andrew Stanley-Jones added support for three
more cards. David Boggs rewrote everything and now feels responsible for
it.
AUTHORS
David Boggs ⟨boggs@boggs.palo-alto.ca.us⟩
BSD April 11, 2006 BSD
