Expand Configuration and Management Manual (G06.24+)

Subsystem Description
Expand Configuration and Management Manual—523347-008
18-42
Incoming Traffic Flow
When passthrough and $NCP traffic is queued to the outgoing list, it occupies buffer
space in the Expand line-handler process buffer pool.
$NCP formats $NCP messages into packets before sending them to the appropriate
Expand line-handler process for transmission. Passthrough traffic is already in the form
of packets; it is not reassembled into messages before being forwarded to the
destination node.
When they are transmitted, $NCP and passthrough packets are given precedence over
locally originated traffic and may be interleaved with packets from locally originated
messages.
After $NCP or passthrough packets have been sent, the Expand line-handler process
releases the buffer pool used by the packets.
Incoming Traffic Flow
Incoming traffic is data that is received from another system in the network. Incoming
traffic includes
•
Locally destined traffic (packets received from a remote node that are destined for
a process at the local node).
•
$NCP traffic (packets received from $NCP at a neighbor node that are destined for
$NCP at the local node).
•
Passthrough traffic (packets received from a remote node that are destined for
another remote node).
Figure 18-14
illustrates the paths of different types of incoming traffic.
As shown in Figure 18-14, the Expand line-handler process manages different types of
incoming packets differently. The following subsections describe each type of packet
and explain how each is processed by the Expand line-handler process.
Note. $NCP obtains packet size information from the value assigned to the network control
process FRAMESIZE modifier.
Note. The Expand line-handler process does not require an end-to-end (Layer 4)
acknowledgment for $NCP and passthrough packets before it releases buffer pool space. This
requirement is not necessary because $NCP and passthrough traffic do not use Layer 4
services.