MT90220
MT90220 interface, such as cell errors, excessive
delay between-links, etc.; or, from the T1 or E1
framer, such as Loss Of Signal (LOS), Loss Of
Frame (LOF), Remote Alarm Indication (RAI) etc.
1.0 Device Architecture
The MT90220, supported by software, implements
the
ATM
Forum
Inverse
Multiplexing
for
Asynchronous Transfer Mode (IMA) Specification.
This approach minimizes the impact of any changes
that might occur in the specification. Actions are
implemented by the MT90220 and decisions by the
software.
On-chip registers are used to generate the ICP cells
that communicate the LSM states to the Far End
(FE).
1.1.2 IMA Group State Machines
The IMA GSMs and Group Traffic State Machines
(GTSM) must be implemented in software. One of
each state machine should be implemented for each
IMA Group.
The MT90220 supports following two major modes of
operation:
•
the IMA mode (as defined by the ATM Forum
IMA Specification)
•
the User Network Interface (UNI) mode
On-chip registers are used to generate the ICP cells
that communicate the various states to the FE.
Up to four IMA Groups can be implemented. Any of
the eight PCM Interfaces can be assigned
dynamically to any of these IMA Groups. A different
UTOPIA PHY address is assigned to each of the IMA
Groups.
1.1.3 Link Addition, Removal or Restoration
The addition, removal or restoration of a link is
controlled by software using the various control
registers in the MT90220 and in the T1 or E1
framers. Decisions are based on the MT90220 and
T1 or E1 framers status registers.
The UNI mode is used to transfer the cells from the
UTOPIA Interface to a PCM port without any
overhead. Up to 8 UTOPIA PHY addresses can be
supported in UNI mode.
1.1.4 Interrupt
The MT90220 also supports a mixed mode where
the PCM Interfaces not assigned to an IMA Group
can be used in UNI mode.
The MT90220 provides numerous registers and
counters to implement a polling and/or interrupt
mechanism for tracking link and IMA Group status.
This traffic in and out information is used by the
Management Information Base (MIB) for each IMA
Group.
The IMA implementation is divided into hardware
and software functions. The MT90220 implements
the hardware functions. The software functions are
implemented by the user. The hardware and
software functions are described below. Notice that a
number of MT90220 functions are included to assist
in the collection of statistical information. This
information supports the MIB implementation.
1.1.5 Signaling and Rate Adjustment
The microprocessor controls the operation of the T1
or E1 link by providing handshaking between the FE
and Near Ends (NE) including such functions as
signaling and loopback controls. Rate adjustment is
controlled by:
1.1 Software Functions
•
•
adding or removing one or more T1 or E1 links
For the MT90220 to comply with the IMA
specification, the following functions must be
implemented by software:
providing feedback to the ATM network for adjust-
ing the ATM traffic.
•
the transmit and receive Link State Machines
(LSM)
1.1.6 Performance Monitoring
Software implements most of the performance
•
•
•
the IMA Group State Machines (GSM)
monitoring.
The
MT90220
provides
status
the IMA Group Traffic State Machines (GTSM)
information for:
the Operations and Maintenance (OAM)
functions
•
the Cell Delineation Block and IMA Frame State
Machine
•
•
•
the number of ICP violations
the total number of cells
1.1.1 Link State Machines
The software implemented transmit and receive
LSMs are independent (i.e., each link has its own
LSM). LSMs rely on various events from the
the number of idle or discarded cells.
8
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