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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LANCE(3) Library Functions Manual LANCE(3)
NAME
lance - LANCE Ethernet device
SYNOPSIS
bind -a #l /net
/net/ether/clone
/net/ether/[0-7]
/net/ether/[0-7]/data
/net/ether/[0-7]/ctl
/net/ether/[0-7]/stats
/net/ether/[0-7]/type
DESCRIPTION
The LANCE Ethernet interface is a directory containing 9 stream directories: one for each of 8 Ethernet packet types and a clone file.
Each stream directory contains files to control the stream, receive and send data, and supply statistics. Incoming Ethernet packets are
demultiplexed by packet type and passed up the corresponding open stream. Reading from the data file reads packets at the head of the
stream. A read will terminate at packet boundaries. Each write to the data file causes a packet to be sent. The Ethernet address of the
interface is inserted into the packet header as the source address.
A stream is assigned a packet type by opening its ctl file and writing connect n where n is a decimal integer constant identifying the Eth-
ernet packet type. A value of -1 stands for all types. If multiple streams are assigned to a given packet type a copy of the packet is
passed up each stream.
Reading the type file returns the decimal value of the assigned Ethernet packet type. Reading the stats file returns status information
and the Ethernet address of the interface.
An interface normally receives only packets whose destination address is that of the interface or is the broadcast address,
ff:ff:ff:ff:ff:ff. The interface can be made to receive all packets on the network by writing the string promiscuous to the ctl file. The
interface remains promiscuous until the control file is closed. The extra packets are passed up only streams of type -1.
SOURCE
/sys/src/9/port/devlance.c
LANCE(3)