er Function Generator Circuit Analyzer Time/Div. DEMOT 100ms 0.5ms (wwwWMI 0.2ms 0.1ms 0.5us 0.2us 0.1us 1GS/s 0.2us 0.1us Single Running Volts/Div. Trigger AUTOSET PERSIST AUTOSET On/Off Source 0.15V 0.15V Coupling Coupling Position Position Level Figure 12.4 PC graphical user interface (GUI) of the Velleman PCS-500 digital oscilloscope. Tele-Measurement Services for m-Learning acquires an adjustable number of samples per transmitted frame (from 200 to 5000, the capacity of the buffer; default value is 1000) of the measured signal-real or internally simulated. The two main rates applied to data transmission are: the sampling rate (an adjustable value from 1250 to 50,000,000 samples/s) applied to the measured sig- nal, and the rate at which the buffer is read. These two values must be correlated; the reading of the buffer should not be done earlier than the next storage in the buffer-see formula (Equation 12.1) below. The actual signal measurement with the oscilloscope produces a 5000 sam- ples cluster ("frame" or "window") at once, that is, the effective buffer capacity of the I/O memory-1st location stores the Sampling Rate (SR) [samples/second], 2nd location the Full Scale (mV), 3rd location the Offset (mV), and the others, the 5000 acquired values (with 8 bits per scaled and centered sample). The Time to Wait (TTW) until the buffer is full and can be read again is given by the formula (12.1) 12.1.2.3 TCP/UDP Transport The difference between TCP and UDP consists in the acknowledgment of the received packets. TCP works on the basis of sending data as soon as the last sent data is positively acknowledged [18] by the receiving party (establishment of end- to-end operations). In UDP, the Datagrams are sent regardless of the successful receiving [19]. In case of TCP Round-Trip Time (RTT) is observed and studied. This is the time from the moment one IP packet is sent until the corresponding acknowledg- ment is received. This is the delay that could be perceived by an operator. In case of UDP the jitter is one parame