MT90500 Mitel Semiconductor, MT90500 Datasheet - Page 14

• Manufacturer Part Number: MT90500
• Description: Multi-Channel ATM AAL1 SAR
• Manufacturer: Mitel Semiconductor

MT90500
switch to occasionally repeat or delete data in order to handle buffer underflow or overflow. (In
telecommunications, this is known as a frame slip).
PHY - Physical Layer ; bottom layer of the ATM Reference Model; provides ATM cell transmission over the
physical interfaces that interconnect the various ATM devices.
PTI - Payload Type Identifier ; 3-bit field in the ATM cell header - MSB indicates if the cell contains OAM
information or user data; LSB indicates that a AAL5 cell is the final cell in a frame.
QoS - Quality of Service ; ATM performance parameters that characterize the transmission quality over a given
VC (e.g cell delay variation; cell transfer delay, cell loss ratio).
RTS - Residual Time Stamp ; see SRTS.
SAR - Segmentation and Reassembly ; method of partitioning, at the source, frames into ATM cells and
reassembling, at the destination, these cells back into information frames; lower sublayer of the AAL which
inserts data from the information frames into cells and then adds the required header, trailer, and/or padding
bytes to create 48-byte payloads to be transmitted to the ATM layer.
SDT - Structured Data Transfer ; format used within AAL1 for blocks consisting of N * 64 kbps channels; blocks
are segmented into cells for transfer and additional overhead bytes (pointers) are used to indicate structure
boundaries within cells (therefore aiding clock recovery).
SN - Sequence Number ; 4-bit field in the AAL1 header byte used as a sequence counter for detecting lost or
misinserted ATM cells.
SNP - Sequence Number Protection ; 4-bit field in the AAL1 header byte consisting of a CRC and a parity bit
which are designed to provide error-correction on the SN.
SRTS - Synchronous Residual Time Stamp; method for clock recovery in which difference signals between a
source clock and the network reference clock (time stamps) are transmitted to allow reconstruction of the
source clock. The destination reconstructs the source clock based on the time stamps and the network
reference clock. (Note that the same network reference clock is required at both ends.)
SSRAM - Synchronous Static RAM.
Synchronous - 1. The temporal property of being sourced from the same timing reference. Synchronous
signals have the same frequency, and a fixed (often implied to be zero) phase offset. 2. A mode of transmission
in which the sending and receiving terminal equipment are operating continually at the same rate and are
maintained in a desired phase relationship by an appropriate means.
UDT - Unstructured Data Transfer ; format used within AAL1 for transmission of user data without regard for
structure boundaries (e.g. circuit emulation); term used within ANSI standard - not explicitly stated in ITU.
UTOPIA - Universal Test and Operations Physical Interface for ATM; a PHY-level interface to provide
connectivity between ATM components.
VC - Virtual Channel; one of several logical connections defined within a virtual path (VP) between two ATM
devices; provides sequential, unidirectional transport of ATM cells. Also Virtual Circuit.
VCI - Virtual Channel Identifier; 16-bit value in the ATM cell header that provides a unique identifier for the
virtual channel (VC) within a virtual path (VP) that carries a particular cell.
VP - Virtual Path; a unidirectional logical connection between two ATM devices; consists of a set of virtual
channels (VC).
VPI - Virtual Path Identifier; 8-bit value in the ATM cell header that indicates the virtual path (VP) to which a cell
belongs.
VTOA - Voice and Telephony over ATM; intended to provide voice connectivity to the desktop, and to provide
interoperability with existing N-ISDN and PBX services.
Glossary References:
The ATM Glossary - ATM Year 97 - Version 2.1, March 1997
The ATM Forum Glossary - May 1997
ATM and Networking Glossary (http://www.techguide.com/comm/index.html)
Mitel Semiconductor Glossary of Telecommunications Terms - May 1995.
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