S/UNI®-ATLAS-3200 Telecom Standard Product Data Sheet
Preliminary
Figure 10 VC Search Key Extraction
Routing Word
Cell Prepend + Postpend
Cell Header
Field A
Field B
HEC/UDF
VPI/VCI
START -L
START -L
B
m
START
START
64
35
31
0
A
A
B
A
B
Length <= 128
VC Search Key
PHY
ID
PHY
ID
Field A
Primary Key
Field B
VPI/VCI
Secondary Key
The ATLAS divides the VC Search Key into two search keys – the Primary Key and the
Secondary Key. The Primary Key is 17 bits long. It is constructed from two fields – the PHY ID
field and Field A. The PHY ID field and Field A can be programmed to be 0-6 bits and 0-17 bits
long, respectively; the Primary Key is LSB justified and padded on the left with zeroes to make it
17 bits long. The PHY ID field is the UTOPIA (or POS) address and must, therefore, include
sufficient bits to encode all the PHYs at the PHY Layer interface of the ATLAS. Field A starts at
location STARTA of the Routing Word, and has length LA. The number of bits in Field A plus the
number of bits in the PHY ID field must be less than or equal to 17. Field A and the PHYID are
always LSB justified within the 17-bit Primary Key (any unused MSBs are set to logic 0).
The Secondary Key is 46 bits long (although only 17 bits can be resolved at-speed in any given
search) and consists of three fields. The first field, Field B, is 0 to 12 bits long and may start
anywhere in the Routing Word. Field B parameters include starting position, STARTB and
length, LB. The second field is the 6-bit PHYID (zeroes are padded into the MSBs of the PHYID
if the PHYID is less than 6 bits). The third field is the 28-bit VPI/VCI taken from the cell header.
Field B and the VPI/VCI field are “right justified” within the Secondary Key.
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-1990553, Issue 4
74
PMC [ PMC-SIERRA, INC ]
