PAM Programming Manual

Link-Level Interfaces
PAM Programming Manual—142482
3-5
Delivery Mode
applications for LLC1 and Ethernet type ports. LLC2 type frames received from token-
ring adapters are aggregated and forwarded to the host.
Ports can be stopped, started, or aborted independently of other objects in PAM. All port
attributes can be altered in the stopped state; however, only the DFT and DFC
parameters can be altered while a port is in the started state by using a SETMODE file-
system call.
Delivery Mode
The delivery mode attribute for an Ethernet port determines whether READ requests
from applications are queued in series for all openers or in parallel for each opener. If
the Ethernet port is configured for serial delivery of data (ZPAM^Val^Deliv^Mode^Srl),
the inbound aggregate SDU satisfies the first READ on the single first-in-first-out
(FIFO) READ queue that can handle it. This has the effect of delivering aggregate SDUs
in a round-robin manner between the Ethernet port’s openers, and makes it possible to
have multiple applications sharing work associated with a particular L2 address.
If an Ethernet port is configured for parallel delivery (ZPAM^Val^Deliv^Mode^Pllel),
there are separate READ queues for each opener. The inbound aggregate SDU is used to
satisfy the first READ on each of the openers’ FIFO READ queues that can handle it.
This has the effect of fanning out each inbound aggregate SDU to all openers of an
Ethernet port.
The delivery mode attribute for a port is set through the SCF ADD PORT command or
programmatically through SPI. (Refer to the PAM Configuration and Management
Manual and PAM Management Programming Manual for more details about SCF
commands and the SPI interface.
Data Forward Time (DFT) and Data Forward Count (DFC)
The DFT attribute for a port determines the maximum amount of time that an inbound
aggregate SDU message should wait before it is delivered. The default value is infinity,
which means that an inbound message will wait until the DFC (MAX^REQ^SIZE) is
reached before it is delivered or until a TEST/XID frame is received.
The DFC attribute for a port determines the maximum number of inbound SDU
messages that can be queued before they are delivered. The delivery of inbound
aggregate SDU messages is triggered when the number of messages present in the
receive queue equals this value.
There are two copies of the DFT and DFC attributes: the default values and the current
values. The current values control data forwarding events. The current values are set to
the default values when the port object is added or stopped, when the port’s attributes
are altered, or when SETMODE #28 is activated.
The DFT and DFC attributes for a port are set through the SCF ADD PORT command,
programmatically through SPI, or through file-system SETMODE calls. (Refer to the
PAM Configuration and Management Manual and PAM Management Programming
Manual for more details about SCF command and the SPI interface.)