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IperfProtocolSpecification
This is an initial version, and may have mistakes or omissions and probably both...
In Iperf terminology the client is the process which sends the data, e.g. the source. The server is the process that receives the data, e.g. the sink. A stream is a single traffic flow from the client to the server. A test is a collection of one or more streams.
The Iperf protocol is the very simple protocol that Iperf uses on the wire. it has three very specific goals:
- stream and test initiation and termination
- results exchange
- collision prevention
There are many additional features that could be put into the Iperf protocol but ultimately such things will overly complicate and muddy the intent of Iperf and are best left in other packages. For example, scheduling, authentication, authorization and centralized result reporting are already implemented by BWCTL which uses Iperf as one of several possible testing tools.
This provides an explicit method for indicating the end of a stream and a test. TCP has explicit semantics for determining when a stream has been closed, but UDP does not. In order to provide a uniform and simple mechanism for determining the end of a stream we use the stream termination mechanism for both UDP and TCP.
IPERF_STREAM_BEGIN <cookie>
A stream will terminate when it receives a packet with exactly the following contents:
IPERF_STREAM_END <cookie>
IPERF_TEST_BEGIN <cookie>
IPERF_TEST_END <cookie>
This provides a mechanism for provide transferring results information from the server back to the client.
The client sends IPERF_RESULTS_REQUEST <cookie>.
The server responds with IPERF_RESULTS_RESPONSE <cookie> <result data>.
All results exchange messages must be sent over a TCP connection to avoid the need to packetize the results. One connection per request. The server does not perform per interval results collection so although an IPERF_RESULTS_REQUEST can be made during an active test the data may not be of much use.
This prevents multiple tests from colliding with each other.
The collision prevention mechanism is very simple. The client generates 32 bytes of random data. This is the cookie. Every time the client opens a new connection to the server the first 32 bytes must be the cookie. If the server is not presently servicing a client it will not have a cookie defined and will accept the connection and store the cookie. If the cookie for a new connection does not match the cookie the server holds the new connection will be rejected. Once a test is complete This allows a long lived Iperf server to handle one client session at a time.
The collision prevention mechanism does not provide any kind of security and can be easily circumvented. It's meant to protect innocent people from innocent mistakes.
C>S IPERF TEST BEGIN $cookie
C>S IPERF STREAM BEGIN $cookie # one per stream
C>S [DATA TRANSFER]
C>S IPERF STREAM END $cookie # one per stream
C>S IPERF RESULTS REQUEST $cookie
S>C IPERF RESULTS RESPONSE $cookie $data
C>S IPERF TEST END