Techniques for transmitting data between devices based on two-dimensional symbols are disclosed, where the devices are generally not equipped with the traditional networking capabilities, or at least these traditional networking capabilities are not used for the data communication. According to one aspect of the techniques, two devices communicate with each other by displaying one or more two-dimensional symbols. Data is encoded into one or more symbols that are displayed on one of the devices. Images of the symbols are taken by another one of the devices to receive the data. These images are sequentially processed and decoded so that the data is now received. To accommodate various environments, the system is configured to adjust parameters pertaining to the symbols to achieve an optimum transmission rate.