Polytope of Correct (Linear Programming) Decoding and Low-Weight Pseudo-Codewords

We analyze Linear Programming (LP) decoding of graphical binary codes operating over soft-output, symmetric and log-concave channels. We show that the error-surface, separating domain of the correct decoding from domain of the erroneous decoding, is a polytope. We formulate the problem of finding the lowest-weight pseudo-codeword as a non-convex optimization (maximization of a convex function) over a polytope, with the cost function defined by the channel and the polytope defined by the structure of the code. This formulation suggests new provably convergent heuristics for finding the lowest weight pseudo-codewords improving in quality upon previously discussed. The algorithm performance is tested on the example of the Tanner [155, 64, 20] code over the Additive White Gaussian Noise (AWGN) channel.Comment: 6 pages, 2 figures, accepted for IEEE ISIT 201

Modeling of OpenFlow-Based SDN Node with Taking into Account the Differences of Serving TCP and UDP Trafic Streams

OpenFlow is one of the widely used protocols controller to switch communications in software-defined networking (SDN). The queueing model that capture the communication between single switch and controller is constructed. In the model two types of traffic flows are used to take into account the differences of serving TCP and UDP traffic streams. The first flow represents the process of coming and serving TCP-packets. The corresponding flow is described by Poisson model. The second flow represents the process of coming and serving UDP-packets. The corresponding flow is also described by Poisson model. It is supposed that switch and controller have finite buffers and maximum allowed time for packets to be in the buffers is restricted. In the model it is assumed that UDP-packets have priority in occupying the switch. It means that when the process of packet servicing is about to complete in the switch, and if there are TCP and UDP packets in the buffer of the switch, the priority will be given to the UDP packets over TCP for servicing. All random variables used in the model have exponential distribution with corresponding mean values. Using the model the main performance measures of interest are given with help of values of probabilities of model's stationary states. The model and derived algorithms of characteristics calculation can be used for estimation of performance characteristics of controller to switch communications and size of buffers