ifconfig and lmcconfig¶

The program lmcconfig(8) manipulates interface parameters beyond the scope of ifconfig(8). In normal operation only a few arguments are needed:

lmcconfig lmc0

displays interface configuration and status.

lmcconfig lmc0 -D

enables debugging output from the device driver only.

ifconfig lmc0 debug

enables debugging output from the device driver and from the line protocol module above it. 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¶

Activate a PPP link using SPPP and Netgraph with:

ngctl mkpeer lmc0: sppp rawdata downstream
ifconfig sppp0 10.0.0.1 10.0.0.2

Activate a PPP link using only SPPP with:

lmcconfig lmc0 -XYZ
ifconfig lmc0 10.0.0.1 10.0.0.2

Activate a Cisco-HDLC link using SPPP and Netgraph with:

ngctl mkpeer lmc0: sppp rawdata downstream
ifconfig sppp0 10.0.0.1 10.0.0.2 link2

Activate a Cisco-HDLC link using only SPPP with:

lmcconfig lmc0 -XYz
ifconfig lmc0 10.0.0.1 10.0.0.2

Activate a Cisco-HDLC link using only Netgraph with:

ngctl mkpeer lmc0: cisco rawdata downstream
ngctl mkpeer lmc0:rawdata iface inet inet
ifconfig ng0 10.0.0.1 10.0.0.2

Activate a Frame-Relay DTE link using SPPP with:

lmcconfig lmc0 -XYF
ifconfig lmc0 10.0.0.1 10.0.0.2

(SPPP implements the ANSI T1.617 annex D LMI.)

Activate a Frame-Relay DTE link using Netgraph with:

ngctl mkpeer  lmc0: frame_relay rawdata downstream
ngctl mkpeer  lmc0:rawdata lmi dlci0 auto0
ngctl connect lmc0:rawdata dlci0 dlci1023 auto1023
ngctl mkpeer  lmc0:rawdata rfc1490 dlci500 downstream
ngctl mkpeer  lmc0:rawdata.dlci500 iface inet inet
ifconfig ng0 10.0.0.1 10.0.0.2

Activate a RAWIP link using only the driver with:

lmcconfig lmc0 -x
ifconfig lmc0 10.0.0.1 10.0.0.2

Activate a RAWIP link using Netgraph with:

ngctl mkpeer lmc0: iface rawdata inet
ifconfig ng0 10.0.0.1 10.0.0.2

If the driver is unloaded and then loaded, reconnect hooks by:

Testing with Loopbacks¶

Testing with loopbacks requires only one 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 equipment, or at the far end of a circuit.

Activate the card with ifconfig(8):

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.

Loopback plugs test everything on the card.

HSSI

Loopback plugs can be ordered from SBE (and others). Transmit 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(8):

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(8):

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.

T3/HSSI

If you have a T3 modem with an HSSI interface (made by Digital Link, Larscom, Kentrox etc.) then use an HSSI card in one machine and a T3 card in the other machine. The T3 coax cables must use the null modem configuration (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 in one machine and a T1 card in the other machine. Use a T1 null modem cable (see below).

Testing with a Null Modem Cable¶

Testing with a null modem cable requires two cards of the same type.

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 normally 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(8):

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(8):

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 locking 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.

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.

This 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

SPPP enforces an MTU of (128..far-end-MRU) for PPP and 1500 bytes for Cisco-HDLC. RAWIP sets the default MTU to 4032 bytes, but it can be changed to anything.

BPF - Berkeley Packet Filter¶

This driver has hooks for bpf(4), the Berkeley Packet Filter. The line protocol header length reported to BPF is four bytes for SPPP and P2P line protocols and zero bytes for RawIP.

To include BPF support into your kernel, add the following line to conf/YOURKERNEL:

To test the BPF kernel interface, bring up a link between two machines, then run ping(8) and tcpdump(1):

and in a different window:

The output from tcpdump(1) 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 will appear among the ping(8) packets occasionally.

Device Polling¶

A T3 receiver can generate over 100K interrupts per second, this can cause a system to “live-lock”: spend all of its time servicing interrupts. FreeBSD has a polling mechanism to prevent live-lock.

FreeBSD's mechanism permanently disables interrupts from the card and instead the card's interrupt service routine is called each time the kernel is entered (syscall, timer interrupt, etc.) and from the kernel idle loop; this adds some latency. The driver is permitted to process a limited number of packets. The percentage of the CPU that can be consumed this way is settable.

See the polling(4) manpage for details on how to enable the polling mode.

SNMP: Simple Network Management Protocol¶

This 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 sufficient 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 Netgraph control messages or ioctl(2) system calls. User programs should poll sc->cfg.ticks which increments once per second after the SNMP state has been updated.

HSSI and SSI LEDs¶

The card should be operational if all three green LEDs are on (the upper-left one should be blinking) and the red LED is off. All four LEDs turn on at power-on and module unload.

T1E1 and T3 LEDs¶

The card 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! All four LEDs turn on at power-on and module unload.

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. Signalling 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 public 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 supported.

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.

T1 Raw Mode¶

Special gate array microcode exists for the T1/E1 card. Each T1 frame of 24 bytes is treated as a packet. A raw T1 byte stream can be delivered to main memory and transmitted from main memory. The T1 card adds or deletes framing bits but does not touch the data. ATM cells can be transmitted and received this way, with the software doing all the work. But that is not hard; after all it is only 1.5 Mb/s second!

T3 Circuit Emulation Mode¶

Special gate array microcode exists for the T3 card. Each T3 frame of 595 bytes is treated as a packet. A raw T3 signal can be packetized, transported through a packet network (using some protocol) and then reconstituted as a T3 signal at the far end. The output transmitter's bit rate can be controlled from software so that it can be frequency locked to the distant input signal.

HSSI and SSI Transmit Clocks¶

Synchronous interfaces use two transmit clocks to eliminate skew caused by speed-of-light delays in the modem cable. DCEs (modems) drive ST, Send Timing, the first transmit clock. DTEs (hosts) receive ST and use it to clock transmit data, TD, onto the modem cable. DTEs also drive a copy of ST back towards the DCE and call it TT, Transmit Timing, the second transmit clock. DCEs receive TT and TD and use TT to clock TD into a flip flop. TT experiences the same delay as (and has no skew relative to) TD. Thus, cable length does not affect data/clock timing.