MT90520AG ZARLINK [Zarlink Semiconductor Inc], MT90520AG Datasheet - Page 176

• Manufacturer Part Number: MT90520AG
• Description: 8-Port Primary Rate Circuit Emulation AAL1 SAR
• Manufacturer: ZARLINK [Zarlink Semiconductor Inc]

MT90520
Data Sheet
10.0
Glossary
AAL - ATM Adaptation Layer; standardized protocols used to translate higher layer services from multiple
applications into the size and format of an ATM cell.
AAL1 - ATM Adaptation Layer 1, used for the transport of constant bit rate, time-dependent traffic (e.g., voice,
video); requires transfer of timing information between source and destination; maximum of 47-bytes of user data
permitted in payload as an additional header byte is required to provide sequencing information.
Asynchronous - 1. Not synchronous; not periodic. 2. The temporal property of being sourced from independent
timing references. Asynchronous signals have different frequencies, and no fixed phase relationship. 3. In telecom,
data which is not synchronized to the public network clock. 4. The condition or state when an entity is unable to
determine, prior to its occurrence, exactly when an event will transpire.
ATM - Asynchronous Transfer Mode; a method in which information to be transferred is organized into fixed-length
cells; asynchronous in the sense that the recurrence of cells containing information from an individual user is not
necessarily periodic. (While ATM cells are transmitted synchronously to maintain clock between sender and
receiver, the sender transmits data cells when it has something to send and transmits empty cells when idle, and is
not limited to transmitting data every Nth cell.)
CBR - Constant Bit Rate; an ATM service category supporting a constant or guaranteed rate, with timing control
and strict performance parameters. Used for services such as voice, video, or circuit emulation.
CDV - Cell Delay Variation; a QoS parameter that measures the peak-to-peak cell delay through the network;
results from buffering and cell scheduling.
Cell - fixed-size information package consisting of 53 bytes (octets) of data; of these, 5 bytes represent the cell
header and 48 bytes carry the user payload and required overhead. Note: If a 16-bit UTOPIA interface is used,
each cell is 54 bytes long, composed of 6 bytes of cell header and 48 bytes carrying user payload and required
overhead.
CES - Circuit Emulation Service; ATM Forum service providing a virtual circuit which emulates the characteristics of
a constant bit rate, dedicated-bandwidth circuit (e.g., DS1).
CLP - Cell Loss Priority; a 1-bit field in the ATM cell header that corresponds to the loss priority of a cell; cells with
CLP = 1 can be discarded in a congestion situation.
CSI - Convergence Sublayer Indication bit in the AAL1 header byte; when present in an even-numbered cell using
SDT, indicates the presence of a pointer byte; used to transport RTS values in odd-numbered cells using SRTS
clock recovery.
GFC - Generic Flow Control; 4-bit field in the ATM header used for local functions (not carried end-to-end); when
cells are configured for NNI formatting, this value forms the four MSBs of the VPI field.
HEC - Header Error Control; using the fifth octet in the ATM cell header, ATM equipment (usually the PHY) may
check for an error and correct the contents of the header; CRC algorithm allows for single-error correction and
multiple-error detection.
Isochronous - The temporal property of an event or signal recurring at known periodic time intervals (e.g., 125 µs).
Isochronous signals are dependent on some uniform timing, or carry their own timing information embedded as part
of the signal. Examples are DS1, E1 and TDM in general. From the root words, “iso” meaning equal, and
“chronous” meaning time.
OAM - Operations, Administration and Maintenance; MSB within the PTI field of the ATM cell header which
indicates if the ATM cell carries management information such as fault indications.
PHY - Physical Layer; bottom layer of the ATM Reference Model; provides ATM cell transmission over the physical
interfaces that interconnect the various ATM devices.
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