In order to perform realistic network simulations, one needs a traffic generator that is capable of generating realistic synthetic traffic that ``looks like'' traffic found on an actual network. Tmix takes as input a packet header trace taken from a network link of interest. The trace is ``reverse compiled'' into a source-level characterization, called a connection vector, of each TCP connection present in the trace. This set of connection vectors is what drives the Tmix traffic generation in ns-2.
Connection vectors are represented through a pattern of application data units (ADUs) which are based on the a-b-t model . Modeling TCP connections as a pattern of ADU transmissions provides a unified view of connections that does not depend on the specific applications driving each TCP connection. The first step in the modeling process is to acquire a trace of TCP/IP headers and process the trace to produce a set of connection vectors; one vector for each TCP connection in the trace.
The Tmix module in ns-2 takes a set of connection vectors and emulates the socket-level behavior of the source application that created the corresponding connection in the trace. This emulation faithfully reproduces the essential pattern of socket reads and writes that the original application performed without knowledge of what the original application actually was. When combined with Tmix_DelayBox (Section 44.4), the resulting traffic generated in the simulation is statistically representative of the traffic measured on the real link. All a user needs to replay traffic from a certain link is the file of a-b-t style connection vectors obtained from a trace of that link and this Tmix generator. This approach to synthetic traffic generation allows one to automatically reproduce in ns-2 the full range of TCP connections found on an arbitrary link.
Tmix supports both Full-TCP and one-way TCP agents (see the set-agent-type command).
The remainder of this chapter describes the implementation and use of Tmix in ns-2. For more details on the a-b-t model and validation of the Tmix generator, see .
Citation Request: If you use Tmix traffic generation in your work, please cite  (M.C. Weigle, P. Adurthi, F. Hernandez-Campos, K. Jeffay, and F.D. Smith, ``Tmix: A Tool for Generating Realistic Application Workloads in ns-2'', ACM SIGCOMM Computer Communication Review, July 2006, Vol 36, No 3, pp. 67-76.).
Note: For more information on Tmix and to obtain Tmix tools and connection vectors, see http://netlab.cs.unc.edu/Tmix or http://www.cs.odu.edu/inets/Tmix.