PM73121ꢀAAL1gator II
Data Sheet
PMC-Sierra, Inc.
PMC-980620
,VVXHꢀꢁ
AAL1 SAR Processor
8.5 External SRTS-Based Clock Recovery Application
While the AAL1gator II has built-in SRTS, to remain backward compatible with previous
versions of the device, external based SRTS is still supported. External SRTS-based clock
recovery can be accomplished with the circuitry shown in Figure 90 on page 173. The circuit
produces a clock around the nominal T1 or E1 frequency derived from the network clock. This
clock frequency is then increased or decreased based on the SRTS difference produced by the
AAL1gator II.
The following requirements apply to the 38.88 MHz clock:
•
If SRTS is being used, the clock generation logic and AAL1gator II must use the same 38.88 MHz clock.
The SRTS information passes from the AAL1gator II to the clock generator logic across a synchronous
boundary.
•
•
If a nominal frequency clock is generated and the generated clock needs to be locked to a network clock, the
clock generation logic must use a network-derived 38.88 MHz clock only.
If a locally generated 38.88 MHz clock is used, the clock must be within the tolerance of the network clock
requirements. For E1, this is 50 ppm (G.703) and for T1, it is 130 ppm (T1.403). Other specifications exist
for different modes of operation. Refer to Appendix B, “References”, on page 203 for a list of references.
PMC-Sierra, Inc. has secured an agreement with Bellcore which allows PMC-Sierra to freely
market and sell components that contain the SRTS function, such as the AAL1gator II product.
However, the Bellcore-PMC-Sierra agreement does not provide any patent infringement
protection to any users (that is, equipment manufacturers) of AAL1gator II products. Any
equipment manufacturer which makes use of the SRTS function (by using an AAL1gator II
product or via some other implementation) needs to determine if it may be necessary to establish
a separate licensing agreement with Bellcore.
NOTE: As PMC-Sierra understands it, Bellcore will not license the SRTS patent to silicon
manufacturers. Instead, it is Bellcore’s desire to license the SRTS patent under a roy-
alty arrangement only to equipment manufacturers. The ATM Forum states that
Bellcore must make this patent available under fair and equitable conditions.
Bellcore believes they are satisfying this requirement by offering the license to the
equipment manufacturers rather than to the silicon manufacturers.
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PMC [ PMC-SIERRA, INC ]
