S/UNI®-ATLAS-3200 Telecom Standard Product Data Sheet
Preliminary
Figure 9 ATM Cell Format
Note: optional words encased in [].
Bits 31 -24
Bits 23 -16
Bits 15 - 8
Bits 7- 0
[Pre1
[Pre5
Pre2
Pre6
Pre3
Pre7
Pre4]
Pre8]
Header 1
[UDF1/HEC
Payload 1
:
Header 2
UDF 2
Payload 2
:
Header 3
UDF 3
Payload 3
:
Header 4
UDF 4]
Payload 4
:
Payload 45
[Post1
[Post5
Payload 46
Post2
Post6
Payload 47
Post3
Post7
Payload 48
Post4]
Post8]
The prepended/postpended bytes and HEC/UDF will be translated, added, or subtracted as needed
based on the translation settings, the input cell format, and the output cell format.
10.2 Connection Identification
The ATLAS makes use of a flexible approach to identify incoming cells and to determine the
record in the VC Table with which they are associated. The ATLAS identifies the VC record of
each connection by traversing a search tree in SRAM using selected portions of the cell header,
prepend, postpend and the PHY address. To do this, the ATLAS creates an internal Routing Word,
which is the concatenation of the cell prepend, cell postpend, and cell header. The ATLAS is
programmed to select portions of the Routing Word plus the PHY address to create a VC Search
Key. The VC Search Key, therefore, consists of portions of the cell’s header, prepend, postpend
and PHY address.
The figure below illustrates the Routing Word and VC Search Key construction. This figure is
not intended to imply any restrictions on the positioning of Field A and Field B. These fields may
occur anywhere within the appended octets or the ATM header. The Primary Key and Secondary
Key may also intersect.
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-1990553, Issue 4
73
PMC [ PMC-SIERRA, INC ]
