[OpenSTA-devel] Addition of Bandwidth Limiting Functionality

[Kamal, S. \(Cognizant\) <Swa...@co...>]

Hi All,

  We have identified and implemented a Bandwidth Limiting Functionality for=
 OpenSTA,the details of which are listed below.
Also we are interested in contributing this back to the OpenSTA project.=
 Kindly let us know the procedures for the same.


Details of the new Functionality:
*********************************

OpenSTA Bandwidth Limiting
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D

Functionality:
--------------
 The new functionality here is to Add "Bandwidth Limiting" feature to=
 OpenSTA. The OpenSTA commander will have additional provision to enable=
 bandwidth limiting and set the bandwidth to be simulated during testing.=
 Bandwidth limiting is the ability to simulate a lower bandwidth network=
 link over a higher bandwidth link.=0D

Bandwidth Limiting Algorithm:
----------------------------
 The Bandwidth Limiting algorithm used is a modified version of bandwidth=
 limiting algorithm used in "Trickle". More information about trickle and=
 the source code is available at <http://monkey.org/~marius/pages/?page=
=3Dtrickle>.
   The basic idea behind limiting bandwidth is the to limit the amount of=
 data read and written during each operation and introducing delays.

The Steps followed are as follows:
        1.If the total amount of data to be read or written is less than=
 the bandwidth to simulate, the read/write operation proceeds without any=
 change.
        2.If the length of data to be sent, or the length of data requested=
 in the read is greater than the bandwidth to be simulated, a delay is=
 calculated as
        delay =3D (length of data / simulated rate)*1000 (where delay is in=
 milliseconds)
        The corresponding length of data would be equal to simulated rate.=
 Thereby
        adjusted_length =3D simulated_rate
        3.If data is sent/received after each delay in this manner, the=
 traffic would become bursty. This burstiness may even result in over=
 shaping as network conditions are changing, and the scheduler could=
 allocate more I/O to the stream in question. In order to avoid burstiness,=
 a smoothing factor is introduced for the sleep time and transfer length.=
 If the calculated delay is greater than the time smoothing factor, the=
 delay is set equal to the time smoothing factor and the adjusted length is=
 calculated as
        delay =3D time_smoothing_factor
        adjusted length  =3D simulated rate * time_smoothing_factor /1000
        4.If the new adjusted length is too small i.e., almost equal to=
 zero then we set the adjusted length as the length smoothing factor and=
 calculate the new delay as
        adjusted length =3D lsmooth (where lsmooth is the length smoothing=
 factor)
        delay =3D adjusted length /rate

Implementing Bandwidth Limiting Algorithm in OpenSTA:
----------------------------------------------------
 As opposed to trickle, which uses synchronous sockets OpenSTA uses=
 Asynchronous sockets for running the tests. Hence the algorithm used in=
 trickle is modified to simulate Bandwidth Limiting for the Asynchronous=
 read and write in OpenSTA. For write the restricted length and delay time=
 is calculated using the algorithm and data, which is equivalent to the=
 adjusted length, is sent after each sleep (sleep time is equivalent to the=
 delay time calculated) till the whole data is sent.

For read, since the sockets are asynchronous, limiting can't happen by=
 simply performing a read after a sleep. So the restricted length is=
 calculated, and a read is scheduled as per the restricted length. After=
 completion of each read when a call back is received from the client we=
 introduce a sleep. The sleep time is proportional to the data received and=
 is calculated as:=0D
sleep_msec =3D (length)/simulated_rate*1000
(where, sleep_msec is the sleep time and simulated_rate is the restricted=
 read rate.)
But if the sleep time calculated, is too small then the sleep would not=
 make any effect. Such small sleep times accumulated for each socket. Once=
 the accumulated time is greater than 100 milliseconds, a sleep is=
 initiated.

Changes for the GUI:=0D
--------------------
An additional checkbox has been added to the openSTA commander, using which=
 a user can choose whether bandwidth limiting is enabled. On selecting this=
 checkbox the user is allowed to edit the "receive rate"(in kilo bits) and =
 "send rate"(in kilo bits) for Bandwidth limiting.=0D
      Once the user input is captured the data has to be passed from the=
 Test Manager to Test Executer. Since these are two independent exe(s)=
 there has to be a mechanism to pass parameters between the two. OpenSTA=
 uses CORBA for this. This mechanism in OpenSTA is used to pass the=
 bandwidth limiting parameters. Also the entire bandwidth limiting=
 functionality is captured in the singleton class CBwtThrottle.


Thanks,
Swathy

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