Provided by: udpcast_20120424-2build1_amd64 
NAME
udp-sender - broadcast file on a LAN
SYNOPSIS
udp-sender [--file file] [--full-duplex] [--half-duplex] [--pipe pipe] [--portbase portbase] [--blocksize
size] [--interface net-interface] [--mcast-data-address data-mcast-address] [--mcast-rdv-address mcast-
rdv-address] [--max-bitrate bitrate] [--pointopoint] [--async] [--log file] [--min-slice-size min]
[--max-slice-size max] [--slice-size] [--ttl time-to-live] [--fec stripesxredundancy/stripesize]
[--print-seed] [--rexmit-hello-interval interval] [--autostart autostart] [--broadcast] [--min-receivers
receivers] [--min-wait sec] [--max-wait sec] [--nokbd] [--retries-until-drop n] [--bw-period n]
[--rate-governor module.so:key1=value1,key2=value2] [--stat-period n] [--print-uncompressed-position
flag]
DESCRIPTION
"Udp-sender" is used to broadcast a file (for instance a disk image) to multiple "udp-receivers" on the
local LAN. In order to do this, it uses Ethernet multicast or broadcast, so that all receivers profit
from the same physical datastream. Thus, sending to 10 destinations does not take more time than it would
take to send just 2.
OPTIONS
Basic options
--file file
Reads data to be transmitted from file. If this parameter is not supplied, data to be transmitted is
read from stdin instead.
--pipe command
Sends data through pipe before transmitting it. This is useful for compressing/decompressing it, or
for stripping out unused blocks. The command gets a direct handle on the input file or device, and
thus may seek inside it, if needed. "Udpcast" itself also keeps a handle on the file, which is used
for an informal progress display. The command's stdout is a pipe to udpcast.
--autostart n
Starts transmission after n retransmissions of hello packet, without waiting for a key stroke. Useful
for unattended operation, where udp-sender is started from a cron-job for a broadcast/multicast at a
scheduled time.
Networking options
The following networking options should be supplied both on the sender and the receivers:
--portbase portbase
Default ports to use for udpcast. Two ports are used: portbase and portbase+1 . Thus, Portbase must
be even. Default is 9000. The same portbase must be specified for both "udp-sender" and
"udp-receiver".
--interface interface
Network interface used to send out the data. Default is "eth0"
--ttl time to live
Sets the time-to-live parameter for the multicast packets. Should theoretically allow to use UDPCast
beyond the local network, but not tested for lack of a multicast router.
--mcast-rdv-address address
Uses a non-standard multicast address for the control (rendez-vous) connection. This address is used
by the sender and receivers to "find" each other. This is not the address that is used to transfer
the actual data.
By default "mcast-rdv-address" is the Ethernet broadcast address if "ttl" is 1, and 224.0.0.1
otherwise. This setting should not be used except in very special situations, such as when 224.0.0.1
cannot be used for policy reasons.
The following networking options should be supplied only on the sender:
--mcast-data-address address
Uses the given address for multicasting the data. If not specified, the program will automatically
derive a multicast address from its own IP (by keeping the last 27 bits of the IP and then prepending
232).
--pointopoint
Point-to-point mode. Only a single receiver is allowed, but the data will be directly send to this
receiver (in unicast mode), rather than multicast/broadcast all over the place. If no async mode is
chosen, and there happens to be only one receiver, point-to-point is activated automatically.
--nopointopoint
Don't use point-to-point, even if there is only one single receiver.
--full-duplex
Use this option if you use a full-duplex network. T-base-10 or 100 is full duplex if equipped with a
switch. Hub based networks, or T-base-2 networks (coaxial cable) are only half-duplex and you should
not use this option with these networks, or else you may experience a 10% performance hit.
N.B. On high-latency WAN links, the full-duplex option can lead to substantial performance
improvements, because it allows udp-sender to send more data while it is still waiting for the
previous batch to get acknowledged.
--half-duplex
Use half duplex mode (needed for Hub based or T-base-2 networks). This is the default behavior in
this version of udpcast.
--broadcast
Use Ethernet broadcast, rather than multicast. Useful if you have Ethernet cards which don't support
multicast.
By default, "udpcast" uses multicast. This allows sending the data only to those receivers that
requested it. Ethernet cards of machines which don't participate in the transmission automatically
block out the packets at the hardware level. Moreover, network switches are able to selectively
transmit the packets only to those network ports to which receivers are connected. Both features thus
allow a much more efficient operation than broadcast. This option should only be supplied on the
sender.
-b blocksize
Choses the packet size. Default (and also maximum) is 1456.
Unidirectional mode (without return channel)
The options described below are useful in situations where no "return channel" is available, or where
such a channel is impractical due to high latency. In an unidirectional setup (i.e. without return
channel), the sender only sends data but doesn't expect any reply from the receiver.
Unidirectional options must be used together, or else the transfer will not work correctly. You may for
example use the following command line:
"udp-sender --async --max-bitrate 10m --fec 8x8"
--async
Asynchronous mode. Do not request confirmations from the receiver. Best used together with forward
error correction and bandwidth limitation, or else the receiver will abort the reception as soon as
it misses a packet. When the receiver aborts the reception in such a way, it will print a list of
packets lost in the slice causing the problem. You can use this list to tune the forward error
correction parameters.
--max-bitrate bitrate
Limits bandwidth used by udpcast. Useful in asynchronous mode, or else the sender may send too fast
for the switch and/or receiver to keep up. Bitrate may be expressed in bits per second (--bitrate
5000000), kilobits per second ("--bitrate 5000k") or megabits per second ("--bitrate 5m"). This is
the raw bitrate, including packet headers, forward error correction, retransmissions, etc. Actual
payload bitrate will be lower.
--fec interleave"x"redundancy"/"stripesize
Enables forward error correction. The goal of forward error correction is to transmit redundant data,
in order to make up for packets lost in transit. Indeed, in unidirectional mode, the receivers have
no way of requesting retransmission of lost packets, thus the only way to address packet loss is to
include redundant information to begin with. The algorithm is designed in such a way that if r
redundant packets are transmitted, that those can be used to compensate for the loss of any r packets
in the same FEC group (stripe).
In order to increase robustness of the FEC algorithm against burst packet losses, each slice is
divided in interleave stripes. Each stripe has stripesize blocks (if not specified, stripesize is
calculated by diving slice-size by interleave). For each stripe, redundancy FEC packets are added.
Stripes are organized in such a fashion that consecutive packets belong to different stripes. This
way, we ensure that burst losses affect different stripes, rather than using all FEC packets of a
single stripe. Example: "--fec 8x8/128"
--rate-governor module.so:key1=value1,key2=value2
Applies a dynamically loadable rate governor. module.so is the name of the preloadable module, which
is followed by a number of property assignments (key1=value1). The rate governor controls the
transmission rate according to various criteria, such as congestion information received from a
routing or encapsulating device. See comments in "/usr/include/udpcast/rateGovernor.h" and example in
"examples/rateGovernor" for more details
--rexmit-hello-interval timeout
If set, rebroadcasts the HELLO packet used for initiating the casting each timeout milliseconds.
This option is useful together with asyc mode, because with async mode the receiver won't send a
connection request to the sender (and hence won't get a connection reply). In async mode, the
receivers get all needed information from the hello packet instead, and are thus particularly
dependent on the reception of this packet, making retransmission useful.
This option is also useful on networks where packet loss is so high that even with connection
requests, sender and receiver would not find each other otherwise.
--retries-until-drop retries
How many time to send a REQACK until dropping a receiver. Lower retrycounts make "udp-sender" faster
to react to crashed receivers, but they also increase the probability of false alerts (dropping
receivers that are not actually crashed, but merely slow to respond for whatever reason)
--streaming
Allows receivers to join an ongoing transmission mid through
Keyboardless mode
The options below help to run a sender in unattended mode.
--min-receivers n
Automatically start as soon as a minimal number of receivers have connected.
--min-wait t
Even when the necessary amount of receivers do have connected, still wait until t seconds since first
receiver connection have passed.
--max-wait t
When not enough receivers have connected (but at least one), start anyways when t seconds since first
receiver connection have passed.
--nokbd
Do not read start signal from keyboard, and do not display any message telling the user to press any
key to start.
--start-timeout sec
sender aborts at start if it doesn't see a receiver within this many seconds. Furthermore,
transmission of data needs to start within this delay. Once transmission is started, the timeout no
longer applies.
--daemon-mode
Do not exit when done, but instead wait for the next batch of receivers. If this option is given
twice, udp-sender puts itself into the background, closes its standard file descriptors, and acts as
a real daemon.
--pid-file file
Allow to specify a pid file. If given together with "--daemon-mode", udp-sender will write its pid
into this file. If given together with "--kill", the process with the given pid will be killed.
--kill
Shuts down the udp-sender identified by the pid file (which also must be specified). Kill does not
interrupt an ongoing transmission, but instead waits until it is finished.
Example:
"udp-sender -f zozo --min-receivers 5 --min-wait 20 --max-wait 80"
• If one receiver connects at 18h00.00, and 4 more within the next 5 minutes, start at 18h00.20. (5
receivers connected, but min-wait not yet passed)
• If one receiver connects at 18h00.00, and 3 more within the next 5 minutes, then a last one at
18h00.25, start right after.
• If one receiver connects at 18h00.00, then 3 more within the next 15 minutes, then no one, start at
18h01.20. (not enough receivers, but we start anyways after max-wait).
Logging and statistics options
The options instruct "udp-sender" to log some additional statistics to a file:
--stat-period seconds
Every so much milliseconds, print some statistics to stderr: how much bytes sent so far log, position
in uncompressed file (if applicable), retransmit count... By default, this is printed every half
second.
--print-uncompressed-position flag
By default, udp-sender only prints the position in uncompressed file if the 2 following conditions
are met:
• Input is piped via a compressor ("-p " option).
• The primary input is seekable (file or device)
With the "--print-uncompressed-position", options, you can change this behavior:
• If flag is 0, uncompressed position will never be printed, even if above conditions are met
• If flag is 1, uncompressed position will always be printed, even if above conditions are not met
--log file
Logs some stuff into file.
--no-progress
Do not display progress statistics.
--bw-period seconds
Every so much seconds, log instantenous bandwidth seen during that period. Note: this is different
from the bandwidth displayed to stderr of the receiver, which is the average since start of
transmission.
Tuning options (sender)
The following tuning options are all about slice size. Udpcast groups its data in slices, which are a
series of blocks (UDP packets). These groups are relevant for
• data retransmission: after each slice, the server asks the receivers whether they have received all
blocks, and if needed retransmits what has been missing
• forward error correction: each slice has its set of data blocks, and matching FEC blocks.
--min-slice-size size
minimum slice size (expressed in blocks). Default is 16. When dynamically adjusting slice size (only
in non-duplex mode), never use smaller slices than this. Ignored in duplex mode (default).
--max-slice-size size
maximum slice size (expressed in blocks). Default is 1024. When dynamically adjusting slice size
(only in non-duplex mode), never use larger slices than this. Ignored in duplex mode (default).
--default-slice-size size
Slice size used (starting slice size in half-duplex mode).
--rehello-offset offs
in streaming mode, how many packets before end of slice the hello packet will be transferred (default
50). Chose larger values if you notice that receivers are excessively slow to pick up running
transmission
Tuning the forward error correction
There are three parameters on which to act:
redundancy
This influences how much extra packets are included per stripe. The higher this is, the more
redundancy there is, which means that the transmission becomes more robust against loss. However, CPU
time necessary is also proportional to redundancy (a factor to consider on slow PC's), and of course,
a higher redundancy augments the amount of data to be transmitted.
interleave
This influences among how many stripes the data is divided. Higher interleave improves robustness
against burst loss (for example, 64 packets in a row...). It doesn't increase robustness against
randomly spread packet loss. Note: interleave bigger than 8 will force a smaller stripesize, due to
the fact that slicesize is limited to 1024.
stripesize
How many data blocks there are in a stripe. Due to the algorithm used, this cannot be more than 128.
Reducing stripe size is an indirect way of augmenting (relative) redundancy, without incurring the
CPU penalty of larger (absolute) redundancy. However, a larger absolute redundancy is still
preferable over a smaller stripesize, because it improves robustness against clustered losses. For
instance, if 8/128 is preferable over 4/64, because with 8/128 the 8 FEC packets can be used to
compensate for the loss of any of the 128 data packets, whereas with 4/64, each group of 4 FEC
packets can only be used against its own set of 64 data packets. If for instance the first 8 packets
were lost, they would be recoverable with 8/128, but not with 4/64.
Considering these, change parameters as follows:
• If you observe long stretches of lost packets, increase interleave
• If you observe that transfer is slowed down by CPU saturation, decrease redundancy and stripesize
proportionnally.
• If you observe big variations in packet loss rate, increase redundancy and stripesize
proportionnally.
• If you just observe high loss, but not necessarily clustered in any special way, increase redundancy
or decrease stripesize
• Be aware that network equipment or the receiver may be dropping packets because of a bandwidth which
is too high. Try limiting it using "max-bitrate"
• The receiver may also be dropping packets because it cannot write the data to disk fast enough. Use
hdparm to optimize disk access on the receiver. Try playing with the settings in
"/proc/sys/net/core/rmem_default" and "/proc/sys/net/core/rmem_max", i.e. setting them to a higher
value.
SEE ALSO
udp-receiver
AUTHOR
Alain Knaff
current February 17, 2024 UDP-SENDER(1)