Interfacing Serial Encrypters to Fiber Links

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HSSI and EIA530 serial encryption devices have a limitation with their line driving capability. The maximum drive distance of HSSI is 15 metres, and the maximum drive distance of EIA530 comes down dramatically the faster the data rate. There is an installed base of fiber optic modems and fiber optic links in use today within Government networks.

Metrodata provide two different solutions for interfacing serial encrytper to fibre:

  • FIMO-2000, a flexible fibre modem supporting EIA530, X.21, RS449, V.36 and V.35 up to 8.192Mbps, and RS232 up to 256kbps
  • AP3000, a flexible access concentrator supporting EIA530, X.21, RS449 and V.36 up to 20Mbps, and HSSI, ECL up to 100Mbps

The FIMO-2000 is a flexible fibre modem, with some specialist features for backhauling asymmetric data from a satellite modem, or radio relay system. The main FIMO-2000 operating modes are as follows:

  • Operating between two DTE devices, e.g. routers, the FIMO-2000 can generate clocking on an Nx64kbps basis up to 8.192Mbps asymmetrically (i.e. different data rates in each direction)
  • Operating between two DCE devices, the FIMO-2000 can accept clocks from the devices at either end, transporting the incoming data over fibre, and buffering the received data to deal with any clock phasing issues. These clocks can be asymmetric and up to 8.192Mbps in each direction.
  • Operating between a DCE and a DTE, e.g. an encrypter and a satellite modem, the FIMO-2000 operates asymmetrically in a data agile manner to transport data at the rates specified by the modem. These clocks can be asymmetric and up to 8.192Mbps in each direction.

The Metrodata AP3000 Access Processor is a chassis based system that allows you to aggregate single or multiple serial encrypter devices over fiber:

  • EIA530, X.21, RS449 or V.36 devices supported at up to 20Mbps with 1bps granularity and asymmetric operation, or slaved to associated equipment, e.g. a satellite modem
  • HSSI or ECL devices supported at up to 100Mbps with 1bps granularity and asymmetric operation, or slaved to associated equipment, e.g. a satellite modem
  • 1+1 resilience available on the fibre interface
  • AP3000 Access Processor: 3 module chassis, converges 1-2 serial encrypters over a fibre
  • AP4000 Access Processor: 4-5 module chassis, converges 3-4 serial encrypters over a fibre
  • AP8000 Access Processor: 8-9 module chassis, converges 7-8 serial encrypters over a fibre

An example of EIA530 serial over fibre conversion using the AP3000 Access Processor is shown in the diagram below. The OC-3 Fibre" reference on the diagram relates to the AP fibre interface module that is used, and not a requirement that this is an OC-3 link.

Optical Fibre Link

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