Expand Configuration and Management Manual (G06.24+)

Subsystem Description
Expand Configuration and Management Manual—523347-008
18-44
Incoming Traffic Flow
Request Packets
An incoming request packet, or an LRQ, is a fragment of a request message destined
for a process at the local node. The first LRQ includes the length of the total message,
in bytes. The Expand line-handler process reserves memory from its buffer pool for the
total message based on the length information contained in the first packet.
As the Expand line-handler process receives each packet of the request message, it
places the packet in the reserved buffer pool space. If the first packet is received out of
sequence, the Expand line-handler process places packets in the OOS buffer.
When the Expand line-handler process has received all the packets of the request
message and has reassembled the message in the reserved buffer pool space, it
decompresses the message (if the message was compressed by the sending Expand
line-handler process) and performs a message-level checksum. If packets are received
out of sequence, the Expand line-handler process retrieves them from the OOS buffer.
If the message’s security bit is set, the Expand line-handler process also checks
security.
Security-checking involves acquiring the remote password from the USERID file and
comparing it to the remote password that is attached to the incoming request message.
If the passwords do not match, an error is returned to the sender of the LRQ (the
requester). If the Safeguard product is being used, the request message is also
checked by Safeguard, and Safeguard’s response is incorporated into the message.
Once the request message is successfully processed, the message system routes the
request to the appropriate process, and the Expand line-handler process releases the
buffer pool used by the request message.
Reply Packets
An incoming reply packet, or an LCMP, is a fragment of a reply message that is a reply
to a request previously generated by a process (the requester) at the local node.
The Expand line-handler process matches the reply to the request and places the
incoming reply packets into the buffer pool occupied by the matching request. If
packets are received out of sequence, the Expand line-handler process retrieves them
from the OOS buffer and moves them to the buffer pool space for the reply.
When the Expand line-handler process has received all the packets of the reply
message and has reassembled it, it decompresses the reply message (if the reply
message was compressed by the sending Expand line-handler process) and performs
a message-level checksum. No security-checking is performed on reply messages; all
security-checking is done on request messages.
Note. LRQs are also described in Protocol Packet Types on page 18-13.
Note. LCMPs are also described in Protocol Packet Types
on page 18-13.