Efficiency, Switching & Multiplexing Flashcards
Q: What is multiplexing in networking?
A: Technique to combine multiple signals into one transmission medium
Q: What is Time Division Multiplexing (TDM)?
A: Multiple signals share the same medium by taking turns in time slots
Q: What is Frequency Division Multiplexing (FDM)?
A: Each signal is assigned a different frequency band within the medium
Q: What is Wavelength Division Multiplexing (WDM) used for?
A: Optical fiber multiplexing using multiple light wavelengths
Q: What is the main limitation of TDM?
A: Inefficient when a channel is idle — time slots are wasted
Q: What is the efficiency formula for Stop-and-Wait protocol?
A: η = L / (L + 2TₚR)
Q: What is the efficiency formula for Go-Back-N ARQ?
A: η = W / (1 + 2a), where a = Tₚ / T𝒻
Q: What does a high a = Tₚ / T𝒻 ratio indicate about protocol efficiency?
A: Greater delays and lower protocol efficiency
Q: What is a circuit-switched network?
A: A dedicated communication path is established between sender and receiver for the duration of the call
Q: What is the main disadvantage of circuit switching?
A: Inefficient use of bandwidth — resources reserved even when no data is sent
Q: What is a packet-switched network?
A: Data is broken into packets and routed individually over shared links
Q: What is statistical multiplexing?
A: Dynamic allocation of time slots based on demand — improves efficiency over fixed TDM
Q: What are virtual tributaries (VTs) in SONET?
A: Logical subchannels within an STS signal, used to carry lower-rate signals
Q: Formula for number of crosspoints in an n×n crossbar switch?
A: N = n²
Q: What is a multistage switch and why is it used?
A: A switch built from smaller switches in stages; reduces complexity and cost compared to a full crossbar
Q: What is head-of-line (HOL) blocking in switching?
A: A queued packet at the front blocks others even if their paths are free — reduces switch throughput
Q: What is store-and-forward switching?
A: Switch stores the entire packet before forwarding — introduces delay but enables error checking
Q: What is cut-through switching?
A: Switch forwards the packet as soon as destination address is read — lower delay, but no error check
Q: What is switching fabric?
A: The internal path and hardware in a switch that moves packets from input to output
Q: What is the difference between ingress and egress in a switch?
A: Ingress is where packets enter; egress is where they exit toward the destination
