MTA Bootfiles

An MTA (Multimedia Terminal Adapter) is the voice/telephony half of a cable voice gateway - a separate logical device from the DOCSIS cable modem it's usually bundled with in the same physical unit, provisioned under the PacketCable specification rather than plain DOCSIS. MTA bootfiles use a different encoding mode of the same tool covered on the Modem Bootfiles page.

How MTA encoding differs from modem encoding

The rlaager/docsis tool handles both with the same binary, but different flags and file structure:

# Modem config file - needs a key file for the CMTS MIC
./docsis -e modem.cfg key.txt modem.bin

# MTA config file - no key file
./docsis -p mta.cfg mta.bin

PacketCable MTA files don't carry the same CMTS MIC integrity check DOCSIS modem files do, so -p takes just the config file and output file - no key file argument.

MTA config file structure

MTA files use PacketCable-specific TLVs rather than the DOCSIS ones a modem config uses, and the encoder needs to be told it's building a PacketCable file rather than a plain DOCSIS one - typically via an MtaConfigDelimiter entry at the top of the file, which switches the encoder's parsing mode for everything that follows:

# mta.cfg
MtaConfigDelimiter 1

SnmpMibObject docsDevSwServer IPADDRESS 10.0.0.5
SnmpMibObject docsDevSwFilename STRING "mta-firmware-v3.bin"

Beyond the delimiter, the same SnmpMibObject mechanism used for modem files works here too - MTA firmware upgrades follow the same docsDevSwServer/docsDevSwFilename/docsDevSwAdminStatus pattern covered on the Modem Firmware Upgrades page, since that MIB isn't specific to the DOCSIS side of the device.

A note on comments

A documented quirk worth knowing before it costs you a debugging session: nested or malformed comments in an MTA config file don't always fail encoding the way you'd expect - in at least one reported case, the encoder accepted a file with a malformed comment structure without a clear error, silently producing an unintended result rather than refusing to encode. Keeping comments simple (one # per line, nothing nested) is the safest way to avoid this.

Where the two files end up

Both the DOCSIS modem bootfile and the MTA bootfile are typically served from the same TFTP server, but they're two separate files, referenced separately during provisioning - the CM side and the MTA side of a combined device each fetch and apply their own file independently, on their own schedule.