Flowgen

Flowgen and flowparse are both implemented in C/C++ on FreeBSD-2.2.8. C++ was used solely for the Standard Template Library, which makes building and using dynamic arrays very easy.

Each flow is broken down into a series of bursts, which can be described by either a number of bytes per burst, or a number of packets per burst. Flowgen uses polling to send packets at the desired time. There is a continuous loop that checks each flow to see if a packet is ready to be sent. Every time a packet is sent, the next packet for that flow is computed. By default, if this next packet is part of a burst, it will be sent before checking other flows. In this way, flowgen can generate bursty traffic.

If the sender is unable to send a packet (out of buffer space, for example), flowgen will try sending it again the next time through the main loop. Every time a packet send time is computed, the next packet send time is also computed, so that if a packet cannot be sent before the sending time of the next packet, the current packet will be skipped. The next packet inherits the current packet's application-level sequence number, so that the skipped packet does not show up as a loss on the receiver end. Skipped packets are kept track of and the total number for each flow is reported at the end of an experiment.

By default, flowgen adds a 32-byte header to each packet sent. This header contains the packet size, flow id, sending time, sequence number, burst number, packet in burst, and burst size (in packets). This header is saved in the output file (if specified) on the receiver side.

No matter the packet size, flowgen will send packets as they are specified. When using TCP, large packets are at the mercy of TCP's Max Segment Size. Flowgen will pass packets to the operating system when they are ready to be sent, but makes no guarantees of their actual sending time.

Usage: flowgen -f config_file [-bcghnpq]
  -b bytes: set socket send/recv buffer size
  -c: force UDP sender to connect
  -g num: debugging level
     level 1 = lost & ooo packets
     level 2 = level 1 + out of buffer space warnings
     level 3 = level 2 + all packet headers
  -h: no app-level header
  -n: non-blocking sockets
  -p: packet-by-packet scheduling
  -q: quit when packets would be skipped

-b: To send high bit-rates of data, the socket send and recv buffer sizes should be sufficiently large. Use this option to increase the default socket buffer size.
-c: When connecting a UDP socket, if the receiver is not available, the sender will report an error and quit. By default, UDP senders do not connect to their remote hosts. If you would like to ensure that your receivers will see the entire run, use the -c option to force the UDP sender to connect.
-g: According to the level, debugging information will be displayed. For level 1, lost and out-of-order packet warnings when using UDP will be displayed by the receiver. For level 2, all level 1 messages, plus out of buffer space warnings will be displayed by the sender. For level 3, all level 2 messages, plus all packet headers will be displayed, by both the sender and receiver.
-h: Flowgen adds a 32-byte application-level header to each packet in order to collect loss and throughput statistics. If you wish to forfeit these statistics in order to have packet sizes less than 32 bytes, invoke flowgen with the -h option.
-n: Flowgen by default uses blocking send() calls. In some instances, non-blocking sockets would result in better perfomance.
-p: By default, flowgen will schedule a burst of packets to be sent at once. Using the -p option, flowgen will send one packet at a time from each available flow.
-q: As described in the implementation section, flowgen skips sending those packets that would have actually been sent more than one burst interval late. If using the -q option, when this occurs, flowgen will report an error and quit.

Legend

Grammar

Explanation of Terminals

Rules

• BURST_PACKETS must be accompanied by PACKET_SIZE
• PACKET_SIZE must NOT accompany BURST_BYTES

Notes

• Ranges
  • For any command in the configuration file that expects a number or expression, a range of values can be specified.
  • If there are multiple ranges used in one flow specification, all ranges must be of the same size.
  • Syntax: [min:step:max]
• Packet Sizes
  • Maximum unfragmented UDP packet -- 1472 bytes
  • Maximum unfragmented TCP packet -- 1440 bytes
  • Maximum TCP packet allowed -- 8191 bytes
• Available random distribution functions (and syntax)
  • gaussian (mu, sigma) or normal (mu, sigma)
  • exponential (mu)
  • uniform (a, b)
  • lognormal (zeta, sigma)
  • pareto (a, b)
  • weibull (mu, a)
  • poisson (mu)

Example Sender Configuration File

# sender.cfg
#
OUTPUT /tmp/sender.flg           # output file
#
OUTFLOW                          # this is a new outgoing flow
SENDER tyagi                     # sender's address
RECEIVER thurston                # receiver's address
PORT [7003:1:7005]               # receiver's port to send to
                                   # (The range specification says to create
                                   # three flows with port numbers
                                   # 7003, 7004, 7005, respectively.)
PROTOCOL UDP                     # use UDP
PACKET_SIZE 3000                 # constant packet size
BURST_PACKETS 5                  # constant burst size
BURST_INTERVAL poisson ([0.500:.5:1.5]) # burst interval -- poisson distributed
                                   # mu = 0.5, 1.0, 1.5, respectively
START_TIME 0                     # start as soon as flowgen starts
END_TIME 60.75                   # end 60.75 seconds after start
SEED 123456                      # use this specific seed
#
OUTFLOW                          # this is a new outgoing flow
RECEIVER thurston                # receiver's address
PORT 7004                        # receiver's port
PROTOCOL TCP                     # use TCP
BURST_BYTES normal (2900, 100)   # bytes per burst -- normal distributed
                                   # mu = 2900, sigma = 100
BURST_INTERVAL 0.500             # constant burst interval 
START_TIME 15                    # start 15 seconds after flowgen starts
END_TIME 90                      # end 90 seconds after flowgen starts

Example Receiver Configuration File

# recvr.cfg
#
OUTPUT /tmp/recv.flg             # output file
#
INFLOW                           # this is a new incoming flow
RECEIVER thurston                # listen at this address
PORT [7003:1:7005]               # listen on this port
                                   # (3 flows on ports 7003, 7004, 7005)
PROTOCOL UDP                     # listen for UDP
END_TIME 65                      # quit 65 seconds after start
#
INFLOW                           # this is a new incoming flow
PORT 7004                        # listen on port 
PROTOCOL TCP                     # listen for TCP

Usage

flowparse -f flowgen_file [-ciprs]
  -c flow: print config info for flow      [0 = all]
  -i     : print info on all flows         [default]
  -p flow: print packet headers for flow   [0 = all]
  -r flow: print receiver's stats for flow [0 = all]
  -s flow: print sender's stats for flow   [0 = all]

Examples

Run on thurston at Thu Nov 2 10:42:15 1999
[flow   1] {sender} --> thurston:7003  UDP
[flow   2] {sender} --> thurston:7004  UDP
[flow   3] {sender} --> thurston:7005  UDP
[flow   4] {sender} --> thurston:7004  TCP

Run on thurston at Tue Nov  2 10:42:15 1999
# recvr.cfg
#
OUTPUT /tmp/recv.flg             # output file
#
INFLOW                           # this is a new incoming flow
RECEIVER thurston                # listen at this address
PORT [7003:1:7005]               # listen on port
                                   # (3 flows on ports 7003, 7004, 7005)
PROTOCOL UDP                     # listen for UDP
END_TIME 65                      # quit 65 seconds after start
#
INFLOW                           # this is a new incoming flow
PORT 7004                        # listen on port 
PROTOCOL TCP                     # listen for TCP

INFLOW                           # this is a new incoming flow
RECEIVER thurston                # listen at this address
PORT 7003                        # listen on port
PROTOCOL UDP                     # listen for UDP
END_TIME 65                      # quit 65 seconds after start

flow #  sender     received       lost       % lost    duration     tput
[   1] (   1)     408 pckts      157 lost   27.788 %    58.59 s    0.167 Mbps
[   2] (   2)     260 pckts       40 lost   13.333 %    58.49 s    0.107 Mbps
[   3] (   3)     168 pckts        2 lost    1.176 %    59.49 s    0.068 Mbps
[   4] (   4)     150 pckts        0 lost    0.000 %    74.30 s    0.047 Mbps

recv_flow sender_flow recv_time size seq_num send_time burst packet_in_burst burst_size
1 1 944766578.121739 3000 1 944766577.573220 1 1 5
1 1 944766578.228574 3000 2 944766577.573426 1 2 5
1 1 944766578.228711 3000 3 944766577.573574 1 3 5
1 1 944766578.228827 3000 4 944766577.573727 1 4 5
1 1 944766578.228937 3000 5 944766577.573872 1 5 5
1 1 944766579.594936 3000 6 944766579.570934 2 1 5
1 1 944766579.595006 3000 7 944766579.571103 2 2 5
1 1 944766579.595058 3000 8 944766579.571244 2 3 5
1 1 944766579.595110 3000 9 944766579.571385 2 4 5
...

flow #         sent    skipped         sent       duration     tput
[   1]      565 pckts  (     0)      113 bursts    60.75 s    0.223 Mbps
[   2]      300 pckts  (     0)       60 bursts    60.75 s    0.119 Mbps
[   3]      170 pckts  (     0)       34 bursts    60.75 s    0.067 Mbps
[   4]      150 pckts  (     0)      150 bursts    75.00 s    0.046 Mbps