Computer Networks Fundamentals

For a full-duplex cross-point switch with n lines and no self-connections, the number of cross-points is n(n-1)/2. For n=10, this is 10*9/2 = 45.

Bit stuffing (often called bit stuffing, not snuffing) is the process of inserting a bit (usually a 0) into a data stream to prevent a sequence of bits from being misinterpreted as a control flag.

Cyclic Redundancy Check (CRC) is the standard error detection method at the data link layer. Option B says 'cycle redundancy codes' which is a typo for 'cyclic', but refers to CRC.

In the X.121 standard for Network User Addresses (NUA), the Data Network Identification Code (DNIC) occupies the first 4 digits, while the area code or network-specific digits typically follow in the 5-7 range.

ARPANET was the first network to implement dynamic routing, allowing packets to find paths based on current network conditions rather than fixed tables.

Under the X.121 standard, the final digits of the Network User Address are reserved for the user-defined sub-address, which corresponds to positions 13-14.

In the X.121 NUA structure, the terminal number digits are located in the 8-12 range, following the DNIC and area code.

The Data Network Identification Code (DNIC) in the X.121 standard consists of the first 4 digits of the Network User Address.

Manchester encoding is a polar line coding scheme where the signal level transitions in the middle of each bit period, representing binary data as positive and negative voltages.

The constellation points (0, 1) and (0, 2) have the same phase (90 degrees) but different amplitudes (1 and 2). Therefore, the modulation is Amplitude Shift Keying (ASK).

The transport layer is responsible for end-to-end communication and reliability between hosts, while the network layer handles hop-to-hop routing.

Cyclic Redundancy Check (CRC) is the standard method for error detection at the data link layer.

The total incoming rate must be less than or equal to the outgoing rate: (6 * 1200) + (n * 300) <= 9600. 7200 + 300n <= 9600. 300n <= 2400. n <= 8.

Resilience in the context of the transport layer refers to the ability of the connection to remain stable and the probability of it not terminating spontaneously due to internal errors.

For a noiseless channel, the Nyquist theorem states the maximum data rate is 2 * bandwidth * log2(V), where V is the number of signal levels. For a binary channel, V=2, so rate = 2 * 3000 * 1 = 6000 bps.

In a sliding window protocol with n bits for sequence numbering, the maximum window size is 2^n - 1. For 4 bits, 2^4 - 1 = 16 - 1 = 15.

Bit stuffing inserts a 0 after five consecutive 1s to prevent data from being mistaken for the flag 01111110. The string 01111110 appears twice in the input; stuffing results in 011111010.

Shannon's capacity theorem is C = B * log2(1 + SNR). SNR in dB = 30, so 10 * log10(SNR_linear) = 30, SNR_linear = 1000. C = 3000 * log2(1 + 1000) = 3000 * log2(1001) approx 3000 * 9.96 = 29880 bps. 30,000 bps is the closest approximation.