S/UNI®-ATLAS-3200 Telecom Standard Product Data Sheet
Preliminary
Figure 12 VC Search Key Construction
Field B
START , L
B
B
Location
Registers
Field B Size & Location
Field A
START , L
A
A
Location
Registers
Field A Size & Location
VPI/VCI
Field A
Primary
Secondary
Search Key
Search Key
PHY ID
Once the search keys are assembled, the Primary Search Key is first used to address an external
direct look-up table (this is the array of Primary Search Pointers in bits(16:0) of the external
search SRAM at SADDR(17) = 0). This table occupies 2n memory locations, where n = LPHY
LA, i.e. the length of the Primary Search Key. The result of this direct lookup is the address of a
root node of a search tree. From this root node, the Secondary Search Key is used by a patented
search algorithm to find the VC Table record address of the connection. The VC Table Record
address is used to access the VC Table Record in internal DRAM and to fetch the F4 Record
address if active and up to two PM Record addresses from the external linkage SRAM at
SADDR(17) = 1. These addresses are used to access the appropriate records (all of which are
stored on chip).
+
The validity of the record addresses fetched from the SRAM is checked by comparing the
secondary search key with the search key (VPI, VCI, and Field B) stored in first row of the VC
Table Record. Any unused bits within this stored search key word must be set to zero. The
Configuration field of the VC Table Record contains the NNI bit. This bit identifies if the virtual
connection belongs to a Network-Network Interface. If the NNI bit is set to zero, the connection
is part of a UNI, which means that the four MSBs of the VPI are excluded from the Secondary
Key verification. If the VCI field in the VC Table is set to all zeros, this signifies the connection
is a VPC, and the VCI field is to be ignored. If the search process does not lead to the successful
identification of the cell concerned (i.e. the search key stored in the VC Table does not match the
Secondary Search Key used for the search), the cell is declared to be invalid, and will not be
output. Optionally, the cell may be routed to the Microprocessor Cell Interface for error logging.
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-1990553, Issue 4
76
PMC [ PMC-SIERRA, INC ]
