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# hw5 - appearing in the data stream During idle times the...

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(1) Consider a pure (un-slotted) ALOHA channel with the following characteristics: Capacity: 2 Mbps Packet length (fixed): 1000 bits Suppose that the probability that a station has a packet to transmit in one packet length is 0.02 and 50 stations are sharing the channel. (a) Compute the probability that an arriving packet can be transmitted successfully. (b) What is the average total number of packets that can be sent out successfully in one minute? (2) (a) Suppose we the following CRC generator is used for a network: x^4+x^3+x+1 (a) Compute the CRC field for the following message: 001110101100 (b) A network uses the following generator X^16 + x^12 + x^5 + 1 . Assume a packet has the following bits inverted during transmission: bit 45, 51, 58, 62. Bit 0 is sent first. Can this error pattern be detected? Explain. (3) PPP uses byte-stuffing to prevent its opening and ending flag 01111110 from
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Unformatted text preview: appearing in the data stream. During idle times, the sender will transmit continuously the same flag. (a) Under the worst case situation, how many more bytes will be added for a packet of 200 bytes? (b) The opening and ending flags are the same. What method can the receiver use to determine which one is the opening and which one is the ending flag? Explain. (4) Users of each cell in a cellular network uses a ALOHA channel for sending in requests for acquiring a signaling channel. Assume that each user only needs to send in one packet per call through this ALOHA channel and the packet length is 200 bits. The channel capacity is 4.8 Kbps. Assume on average a user will make one call in 10 minutes. Under the ALOHA is operating under the optimal condition. How many users can we support in a cell with this ALOHA channel?...
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