04-23-2010
Most apps that are worried about that use some sort of short packet header kind of ack-back system example:
One system I just coded used packet header format:
nnnnnnnnXXmmmmmmmmmm
where nnnnnnnnn= zero-filled len of whole packet
XX == type of packet: DT == data AK == acknowledge
mmmmmm==unique packet identifier, rolling
An AK packet is 00000020AK0000001234, with only 20 bytes is sent back to acknowledge a datapacket named 00000576DT0000001234
The system expects an AK packet back in 1 minute or less, AK
packets are stored in a queue with a timestamp. I can check for receipt success or resend status. There are also keepalive packets of the same short format sent every 30seconds, for low traffic times.
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PK(4) Kernel Interfaces Manual PK(4)
NAME
pk - packet driver
DESCRIPTION
The packet driver implements a full-duplex end-to-end flow control strategy for machine-to-machine communication. Packet driver protocol
is established by calling pkon(2) with a character device file descriptor and a desired packet size in bytes. The packet size must be a
power of 2, 32<=size<=4096. The file descriptor must represent an 8-bit data path. This is normally obtained by setting the device in
raw mode (see ioctl(2)).
The actual packet size, which may be smaller than the desired packet size, is arrived at by negotiation with the packet driver at the
remote end of the data link.
The packet driver maintains two data areas for incoming and outgoing packets. The output area is needed to implement retransmission on
errors, and arriving packets are queued in the input area. Data arriving for a file not open for reading is discarded. Initially the size
of both areas is set to two packets.
It is not necessary that reads and writes be multiples of the packet size although there is less system overhead if they are. Read opera-
tions return the maximum amount of data available from the input area up to the number of bytes specified in the system call. The buffer
sizes in write operations are not normally transmitted across the link. However, writes of zero length are treated specially and are
reflected at the remote end as a zero-length read. This facilitates marking the serial byte stream, usually for delimiting files.
When one side of a packet driver link is shut down by close(2)or pkoff (see pkon(2)), read(2) on the other side will return 0, and write on
the other side will raise a SIGPIPE signal.
SEE ALSO
pkon(2), pkopen(3)
local PK(4)