MT90220

The MT90220 device is targeted to systems implementing the ATM FORUM UNI specifications for T1/E1 rates or Inverse Multiplexing for ATM (IMA). In the MT90220 architecture, up to 8 physical and independent T1/E1 streams can be terminated through the utilization of off-the-shelf, traditional T1/ E1 framers and LIUs. This allows ATM designers to leverage previous T1/E1 design experience, hardware and software implementation, and to select the best T1/E1 framer for the required application.

The MT90220 device provides ATM system designers with a flexible architecture when implementing ATM access over existing and deployed trunk interfaces, allowing a migration towards ATM service technology. In addition to allowing for the design of ATM UNI specifications for T1/E1 rates, the MT90220 device is compliant with the ATM FORUM IMA specifications for controlling IMA groups of up to 8 trunks in a single chip. The MT90220 can be configured to operate in different modes to facilitate the implementation of the IMA function at both CPE and Central Office sites. For systems targeting ATM over T1/E1 with IMA and UNI operating simultaneously, the MT90220 device provides the ideal architecture and capabilities.

The device provides up to 4 internal IMA circuits and allows for bandwidth scaleability through the use of the UTOPIA MPHY, Level 2 specification at 25Mhz.

The implementation of the IMA as per AF-PHY- 0086.001 Inverse Multiplexing for ATM (IMA) Specification Version 1.1 is divided into hardware and software functions. Hardware functions are implemented in the MT90220 device and software functions are implemented by the user. Additional hardware functions are included to assist in the collection of statistical information to support MIB implementation.

Hardware functions that are implemented in the MT90220 device are:

• Utopia Level 2 PHY Interface
• Incoming HEC verification and correction (optional),
• Generation of a new HEC byte
• Format outgoing bytes into multi-vendor PCM formats
• Retrieve ATM Cells from the incoming multivendor PCM format
• Perform cell delineation
• Provide various counters to assist in performance monitoring

Hardware functions that are implemented by the IMA processor in the MT90220 device are:

• Transmit scheduler (one per IMA group)
• Generation of the TX IMA Data Cell Rate
• Generation and insertion of ICP cells, Filler Cells and Stuff Cells in IMA mode and Idle Cells in UNI (non-IMA) mode; the ICP cells are programmed by the user and the Filler and Idle cells are pre-defined
• Retrieve and process ICP cells in IMA Mode
• Perform IMA Frame synchronization
• Management of RX links to be part of the internal re-sequencer when active
• Extraction of RX IMA Data Cell Rate
• Verification of delays between links
• Perform re-sequencing of ATM cells using external asynchronous Static RAM
• Can accommodate more than 400 msec of link differential delay depending on the amount of external memory
• Provide structured Interrupt scheme to report various events.