PM73121ꢀAAL1gator II
Data Sheet
PMC-Sierra, Inc.
PMC-980620
,VVXHꢀꢁ
AAL1 SAR Processor
2 SYSTEM FEATURES
The AAL1gator II provides DS1, E1, DS3, E3, or other high-speed line interface access to an
AAL1 CBR ATM network. It uses an external SRAM for temporary storage of data and statistical
data. The device provides a microprocessor interface for configuration, management, and statis-
tics gathering.
ATM technology can handle different types of traffic, including voice and video, within the same
network structure. Voice traffic and some kinds of video traffic are classified as CBR traffic.
AAL1 is defined for carrying CBR traffic.
2.1 Data Formats
The AAL1gator II supports the data formats described in Table 1.
Table 1. Data Formats and AAL1gator II Modes to Support Them
Corresponding
AAL1gator II
Mode
CAS
Signaling
Number of
Lines
Format
Channelization
Unstructured Data Format, Multiple Line
Unstructured Data Format, High-Speed
Structured Data Format, Multiframe-based
Structured Data Format, Frame-based
UDF-ML
UDF-HS
SDF-MF
SDF-FR
No
No
No
No
8
1
8
8
Yes
Yes
Yes
No
These modes are selectable on a per-line basis. In structured mode, each line can support either T1
or E1 interfaces. Line 0 can also support a high-speed UDF that is compatible with the specified
T3 or E3 framer.
UDFs are more appropriate for services that require no framing structure to transport data across
the network. Unframed point-to-point E1 and T1 and clear channel T1 and E1 are examples of
such services. The AAL1gator II uses simplified algorithms for unstructured data, placing data
into the appropriate line buffers without regard to frames. All byte locations are used. The Cell
Service Decision (CSD) credit assigning algorithm (refer to section 3.2 “Cell Service Decision
(CSD) Circuit” starting on page 33) is also simplified. Since there can be only eight queues, the
algorithm needs to identify only which line requires service. When UDF-HS is used for line 0,
only line 0 is monitored for activity.
Many installed networks, however, look for a framing structure and octet alignment to transport
data streams. Carriers have large installed bases of fractional T1 and Digital Data Service (DDS)
leased line services that must still be supported when the backbone is cut over to ATM. Many pri-
vate networks have the same support issue; the backbone is either ATM or circuit-switched, but
not both. If it is ATM, then all existing switched circuits must be migrated onto the ATM back-
bone through circuit emulation. Because of its extensive support of Digital Signal Level 0s
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PMC [ PMC-SIERRA, INC ]
