Travel Time and Data Frames

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Travel Time and Data Frames

Please reference this figure for the question:

7. A host computer is one of the sources in Figure 1. The computer is part of a network that has a transport layer header of 1000 bits and information field capacity of 9000 bits. The network layer header has 500 bits and an information field capacity of 4,500 bits. The datalink layer has a 40-bit header and 5-bit trailer. The data field can hold up to 2500 bits. A 16-kilobyte file is sent over the interface. Assume that the multiplexer is not used and the modem is providing a data rate capacity of 64 kbps. The media is copper and the distance is 15,000 km.

a. Assuming no errors during the transmission, how many data link frames are required to send
the file?

b. Assuming no errors, what is the time required to send the file?

c. Assuming that probability of error is 10-5, what is the time required to send the file? (Assume a "Go-Back N" protocol with a window size of 127 for error correction.)

High Rate Data Link Frame Format
The sources of the data to be transmitted on the High Rate link are the AMS data acquisition (DAQ) and housekeeping (MCC) systems. The data which corresponds to one event (if you don't understand this correspondence, don't worry, we do), known as event data, is delivered in blocks to a particular one of six level-3 computers (JL3's), called a DATA FRAMER, which has been selected for this task. These blocks are then collated and stored into a partially filled Frame Body. The corresponding Frame Header was constructed as needed beforehand (the Status defined, the Major ID and Minor ID assigned, etc). As required, the Event Link is filled in. When the Frame Body is filled up, the Status word is updated as needed and the Header and then the Body are input to the Error Detection/Correction (ED/C) symbols calculation, the results of which are appended. Two ED/C possible calculations are forseen, Reed-Solomon Encoding (R-S) or Cyclic Redundancy Check (CRC). This now complete Frame is then stored in the DATA BUFFER, 3GByte of memory (JBU). The DATA FRAMER is thus active only when it is receiving, processing and storing event data.
A different process, called the DATA EMITTER, probably running on another of the six JL3 boards, is always active. It controls the emission of frames on the high rate link. After system initialization, and until otherwise directed via (time-delayed) telecommands it constructs a sequence of fill frames. These fill frames are constructed on the fly, using the appropriate Status, and Major and Minor IDs which are local to the DATA FRAMER. The first long word of the Frame body is set to zero, redundantly indicating the frame contains only fill data, and the remainder of the body filled with a TBD fill sequence. The appropriate ED/C is calculated and appended.
Under telecommand direction, that is in step with Ku band transmission windows, the DATA EMITTER pauses in the generation of fill frames and iteratively tries to retrieve data frames from the buffer. Alternatively, it may look for a series of data frames for which retransmission has been requested. If no data frames are available, it continues the generation of fill frames. In all cases, a frame is available for subsequent processing.
The DATA EMITTER passes the available frame through a TBD bit ``scrambler'' or ``equalizer'', also known as a pseudo-random modulator, the output of which has the same 4080 byte length (for each bit input, a bit is output). This scrambulator exists to comply with the Ku-band requirements on the number of bit transitions (no more than 64 successive bits without a transition and at least 128 transitions in every 512 bits). The counter in the ASM is incremented and prepended to this frame and the combination forwarded to the F/O TRANSMITTER (JFO).

The JFO double buffers the delivered ASM+Frame and the data is smoothly clocked through a chain of Taxi transmitter, LED driver and LED, emerging on to the fiber optic as an even, metered flow of data bytes.
Downstream, this flow is converted into a constant 2 Mbit/sec, NRZ-L PCM signal to the Ku band Signal Processor (KUSP), multiplexed with other traffic bound for the Ku band antenna, broadcast to a Tracking and Data Relay Satellite (TDRS), rebroadcast to White Sands, and linked over to JSC, in which it is subsequently delivered, after demux'ing, to the Customer Interface Panel (CIP) in NRZ-L PCM RS-422 (data & clock) form. On the AMS side of the CIP this bit stream is received by AMS FSE, which is described elsewhere.
Before the signal reaches the KUSP it is teed off to the PGSE Digital Data ...