The MDR-3670 is part of a family of data transcoders for converting between the commonly used MPEG2 Transport Stream formats in the broadcast industry for video distribution.
The MDR-3670 operates with either an E3 (34.368 Mb/s) or DS3 (44.736 Mb/s) G.703 rates.
There are several industry modes of encoding that can be decoded by the MDR-3670. They are loosely classified as follows :

Standard: IRT MDT-3570, DDC-3480
Upstream: Similar to above
Downstream: Packet stuffed
Compatible: Legacy framing

This range covers most other manufacturer's equipment.

Front panel switches allow Reed Solomon correction and/or the removal of interleaving and scrambling (energy dispersal). On board switches allow 204 to 188 conversion, after decoding, and the output ASI packet structure to be set to either "Distributed" or "Contiguous" mode.
The MDR-3670 is fabricated in IRT's standard Eurocard format and may be housed in a variety of IRT's frames.

The MMM-4230 and MMX-4230 are part of a family of data transcoders for converting between the commonly used MPEG2 Transport Stream formats for video distribution in the broadcast industry.
With the MMM-4230 up to four ASI and one RS422 data signals can be multiplexed together and converted into an framed or unframed DS3 signal for transmission down a single 45 Mb/s G.703 line.
The MMX-4230 converts and demultiplexes the 45 Mb/s G.703 signal back into the original four ASI signals (at their original rates) and the RS422 data signal.
An on board switch on the MMM-4230 sets the maximum data rates for each ASI input allowing the efficient use of the available bandwidth and for protection against overuse of the bandwidth by the other channels. Total maximum data rate up to 43.5 Mb/s is allowed. Temporary packet stuffing is used to automatically bring the rate up to 45 Mb/s.

The MMM-4681 and MMX-4681 are part of a family of data transcoders for converting between the commonly used MPEG2 Transport Stream formats for video distribution in the broadcast industry.
With the MMM-4681 up to four ASI and one RS232 data signal can be combined together and converted into a 155Mb/s G.703 (STM‑1) electrical CMI signal, or NRZ standard (NRZ for optically interfacing to an STM-1 optical fibre network using IRT's DDT-4210/DDR-4211 fibre link set to match corresponding rate for transmission),
The sum of the ASI input payload rates can be anything up to 148 Mb/s. Inputs may be 188 or 204 byte packet length, burst or continuous, and may have energy dispersal scrambling, interleaving and/or Reed Solomon bytes included.
The MMX-4681 separates the 155 Mb/s G.703 signal back into the original four ASI signals (at their original rates) and the RS232 data signal. The ASI outputs are suitable for Single Frequency Network use, in that there is no data rate conversion or PCR restamping of the ASI streams.

Inputs are automatically equalised for lengths of up to 250m of Belden 8281 or equivalent cable.
RS232 uni-directional data may also be sent on the same link. It can pass rates up to 19.2 kb/s with any combination of start/stop & parity bits. The data rate does not affect the payload available for the ASI streams.

Front panel indication and relay alarm on the MMM‑4681 transmitter shows if there is an input data rate violation. Corresponding alarm on the MMX‑4681 receiver shows a loss of STM-1 input.

Optional SNMP (Simple Network Management Protocol) version is available for monitoring and control when used in an IRT frame fitted with SNMP capability.

The MMM-4681 and MMX-4681 are designed to fit IRT’s standard Eurocard frames and may be used alongside any other of IRT’s analogue or digital Eurocards.

¹ When used in conjunction with IRT's DDT-4210/DDR-4211 fibre link set to match corresponding rate.