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TLEM(1) General Commands Manual TLEM(1) NAME tlem -- high speed, netmap based link emulator (similar to dummynet) SYNOPSIS tlem [-i port] [-B bandwidth] [-D delay] [-L loss] [-R reordering] [-Q queue-size] [-C cpu-placement] [-G gateway] [-b batch-size] [-w wait-link] [-s session-name] [-a] [-v] [-q] [-r] [-M max-bw,max-delay,max-hold] DESCRIPTION tlem implements a high speed bidirectional link emulator between netmap ports, capable of supporting rates up to 20 Mpps / 40 Gbit in each di- rection. tlem use two threads per direction to achieve high speed while maintaining packet ordering, and can enforce queue size and rate limitation, introduce deterministic or random delays and packet losses, in a way similar to the popular dummynet(4) emulator. tlem differs from dummynet in the following ways: • tlem only connects netmap ports, whereas dummynet sits between the IP layer and the network interface; • tlem does not provide packet filtering, whereas dummynet selects traffic using the ipfw firewall; • tlem is 20-40 times faster than the in-kernel dummynet; • tlem runs entirely in userspace, hence it is much easier to modify and extend. Command line options are listed below. The -B, -D, -L, -Q options can omitted (in which case default values are used), specified once (in which case they affect both directions), or twice (once per direction). -i port Name of the netmap port. It must be supplied exactly twice to identify the two ports that must be interconnected. Any netmap port type (physical interface, VALE switch, pipe, monitor port...) can be used. -B bps | constant,bps | ether,bps Desired bandwidth, default to 0 (which means infinite) if not specified. bps is a floating point number optionally follow by a character (k, K, m, M, g, G) that multiplies the value by 10^3, 10^6 and 10^9 respectively. constant (can be omitted) means that the bandwidth will be computed with reference to the actual packet size (excluding CRC and framing). ether indi- cates that the ethernet framing (160 bits) and CRC (32 bits) will be included in the computation of the packet size. -D dt | constant,dt | uniform,dmin,dmax | exp,dmin,davg Additional delay in transmission, with constant, uniform or ex- ponential distribution, defaults to 0. dt, dmin, dmax, avg are times expressed as floating point numbers optionally followed by a character (s, m, u, n) to indicate seconds, milliseconds, microseconds, nanoseconds. The delay is adjusted so that there is never packet reordering. -L x | plr,x | ber,x Optional packet or bit error rate, defaults to 0. Simulates packet or bit errors, causing offending packets to be dropped. x is a floating point number indicating the packet or bit error rate. -R const,p,t Optional packet reordering, defaults to none. With probability p incoming packets are hold for the given t amount of time. The probability and time are expressed as in the loss and delay ar- guments. -Q size Queue size, size is a number optionally followed by k, K, m, M, g, G to specify the queue size in bytes, Kilobytes, Megabytes, Gigabytes. The queue is used to buffer incoming packets before bandwidth limitations are applied. -C a[,b[,c,d]] Indicates the cores on which the four threads should be placed. One, two or four values can be specified. -G ipv4-address Indicates the optional default gateways to be used in route- mode. -w wait-link indicates the number of seconds to wait before transmitting. It defaults to 2, and may be useful when talking to physical ports to let link negotiation complete before starting trans- mission. -s session-file Enables client/server mode. The first instance of tlem that successfully creates and/or locks the session-file becomes the server. Other tlem instances that use the same session-file do not start new emulations, but rather send their parameters to the server. This feature can be used to dynamically change the emulation parameters of a running emulation. Please note that the internal buffers are not re-allocated, and therefore the dynamic emulated delay and bandwidth can never exceed the val- ues used initially by the server. Alternatively, the -M option can be used when starting the server to set the maximum band- width, delay and hold-time that can be accepted in client re- quests. -a Only useful in client/server mode. Ask the server to shutdown and wait until it terminates. -v Increase verbosity. -q Decrease verbosity. -b batch-size Maximum batch size to use during transmissions. tlem normally transmits packets one at a time, but it may use larger batches, up to the value specified with this option, when running at high rates. -r Enable route-mode. -M max-bw,max-delay,max-hold Set the maximum bandwidth, delay and packet-reordering hold- time. The parameters are only meaningful for the server process when operating in client/server mode (see the -s option). OPERATION tlem creates two threads per direction, binds them to specific cores, and uses them to read and write to the netmap ports. A fifth thread is used to periodically display the amount of traffic flowing in each of the two directions. The input thread reads from a netmap port, and for each packet computes the time when it should exit the transmit queue according to the emu- lated bandwidth; drops the packet if the queue is full; further applies random drops according to the loss probability specified; and finally computes the transmit time applying the additional delay. Packets an- notated with their transmit time are copied in a large in-memory buffer. The output thread spins on the buffer, doing short sleeps, un- til packets reach their transmit time. ROUTE-MODE In route-mode tlem operates as an IPv4 router between the two subnets at its ends, replying to and sending the necessary ARP messages and up- dating the destination MAC addresses. The IP addresses and subnets are obtained from the ports, so this mode cannot be used with software-only netmap ports like ephemeral VALE ports and pipes. There are some limitations: unresolved destinations are sent as broad- casts until resolution; packets destined to the same subnet as their incoming port are dropped; TTL is not decremented. Each subnet may also optionally have a default gateway: for each direction, incoming packets not destined to either of the two known subnets are sent to the default gateway of the output port, if specified, and dropped other- wise. PERFORMANCE We have measured speeds in excess of 20 Mpps and 40 Gbit/s per direc- tion on a modern i7 CPU with 4 cores. The accuracy in delays is in the order of 30-50us provided that C states higher than C1 are disabled, and the CPU clock is set to the maximum speed. Performance depends heavily on memory speed and suitable NICs with native netmap drivers. See the paper below for more details. SEE ALSO http://info.iet.unipi.it/~luigi/netmap/ Luigi Rizzo, Giuseppe Lettieri, TLEM, very high speed link emulation, AsiaBSDCon 2016, Tokyo, March 2016 http://info.iet.unipi.it/~luigi/re- search.html AUTHORS tlem has been written by Luigi Rizzo at the Universita` di Pisa, Italy. Route mode and client/server operation has been added by Giuseppe Let- tieri at the Univerista` di Pisa, Italy. This work has received funding from the European Union's Horizon 2020 research and innovation programme 2014-2018 under grant agreement No. 644866, and from East Cost Datacom Inc., Rockledge, FL, USA. FreeBSD ports 15.quarterly February 13, 2020 TLEM(1)
NAME | SYNOPSIS | DESCRIPTION | OPERATION | ROUTE-MODE | PERFORMANCE | SEE ALSO | AUTHORS
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