udp-sender

UDP-SENDER(1) Udpcast UDP-SENDER(1)

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 July 29, 2019 UDP-SENDER(1)