PM8610-BIAP PMC [PMC-Sierra, Inc], PM8610-BIAP Datasheet - Page 71

• Manufacturer Part Number: PM8610-BIAP
• Description: SBS Telecom Standard Product Data Sheet Preliminary
• Manufacturer: PMC [PMC-Sierra, Inc]

10.1.11
10.1.12
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-2000168, Issue 3
The Fractional Rate SBI mapping is intended for support of data services over fractional DS3 or
similar links. A fractional rate link is mapped into any SPE octet as defined in Table 1. Table 19
shows all the available information (I) octets useable for carrying a Fractional rate link mapped to
a single SPE. There are no V1 to V5 bytes nor frame alignment signals in a fractional rate link.
The Add bus and Drop bus payload signals, IPL and OPL, indicate when a fractional rate
information byte contains valid data or is empty. The fractional rate link Add bus can have the
timing master be either the PHY or the Link Layer device. When the PHY is the timing master the
JUST_REQ signal from the PHY communicates the transmit rate to the Link Layer device. The
JUST_REQ signal is asserted during any of the available fractional rate link octets to indicate that
the PHY can accept another byte of data. For every byte that is marked with the JUST_REQ
signal the Link Layer device should respond with a valid byte to the PHY within a short time. The
PHY accepts data from the Link Layer device whenever it sees valid data as indicated by the IPL
or OPL signal, whether it is timing master or slave.
Table 19 Fractional Rate Format
The 77.76 MHz SBI336 bus is exactly four interleaved 19.44 MHz SBI buses. There are some
slight differences between the two formats to accommodate the increased clock rate. The
differences are:
The JUST_REQ signal is referenced to the Drop bus C1FP alignment rather than the common
Add/Drop C1FP alignment of the SBI bus. This aids 77.76 MHz bus timing by allowing buffering
and retiming logic to be put between SBI336 devices. This change also aids construction of larger
SBI cross connect systems using smaller buffers between devices by controlling the C1 frame
alignment independently in each direction.
ROW
1
2
3
4
5
6
7
8
9
Fractional Rate Tributary Mapping
SBI336 Bus Format
SPE
COL #
SBI COL#
1,4,7,10,13
Unused
Unused
Unused
Unused
Unused
Unused
Unused
Unused
Unused
Fractional
1
16
I
I
I
I
I
I
I
I
I
Fractional
2-84
I
I
I
I
I
I
I
I
I
Fractional
Col 85
268
I
I
I
I
I
I
I
I
I
SBS Telecom Standard Product Data Sheet
Preliminary
71