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CHAPTER 4 ATM CELL PROCESSOR
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Preliminary User’s Manual S14767EJ1V0UM00
(a) GFC (General Flow Control) field: Used for flow control. At transmission, the value set in the packet
descriptor by the host is written into this field. At reception, this field is ignored, and its contents are not
reported to the host.
(b) VPI/VCI fields: VPI(Virtual Path Identifier), VCI(Virtual Channel Identifier) are routing fields which indicate
the routing path. ATM Cell Processor supports a total of 64 VPI/VCI combinations for transmission and
reception. For transmission, the 24-bit value set in the Tx VC table by the host is written into these fields.
For reception, only the VPIs/VCIs registered in the reception lookup table are allowed for reception.
(c) PTI(Payload Type Indication) field: 3-bit field indicating whether the cell payload is user data or
management data. It also contains congestion information.
PTI
usage
000
user data cell, no congestion, SDU type = 0
001
user data cell, no congestion, SDU type = 1
010
user data cell, congestion occurred, SDU type = 0
011
user data cell, congestion occurred, SDU type = 1
100
OAM F5 flow cell
101
OAM F5 flow cell
110
RM cell(for ABR service)
111
reserved for future use
Here,
SDU type = 0:
SDU type = 1:
all segment except last cell of AAL-PDU
last cell of AAL-PDU. In this segment, trailer is included.
However, setting SDU type = 1 by user is prohibited.
OAM F5 flow cell: The cells for Operation, Administration and Maintenance.
RM cell:
Resource management used in ABR service. Setting PTI=110 by user is prohibited.
(d) CLP(Cell Loss Priority) field: Indicates whether this cell is to be discarded preferentially if the network is
congested. A CLP value of 1 indicates that the cell is to be discarded preferentially. ATM Cell Processor
sets the appropriate value in this field according to the value that the host sets in the CLPM field of the
packet descriptor.
(e) HEC(Header Error Control) field: Used for cell delineation, header error detection and correction. This field
is processed in TC sublayer.