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Question of the Day
If you were to design a network to potentially be shared by many users, how would you control access to it?
Assigned Reading
N/A
Physical Local Area Networks
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The data unit on a LAN is referred to as a frame (not a packet). When a frame is transmitted, it propagates over the entire physical medium. How a frame is forwarded depends on the LAN topology used. There are two popular LAN topologies:
- Bus
- Ring
Bus Topology
Each end host on a bus has a transceiver that transmits and passively monitors the bus for passing transmissions. Synchronization is performed on frame headers, which contain control information. In a bus topology, every end host connected to the bus receives the header of all transmissions on the bus. If an end host receives a frame header addressed to a different end host, the rest of the frame will be ignored.
Ring Topology
In a ring topology, each end host has a transceiver that breaks the circuit of the ring. Unlike a bus topology where each end host passively listens to the bus, each end host actively participates in the ring regardless of a frame’s destination. If an end host receives a frame with header addressed to itself, the end host will copy the frame from the ring; otherwise, the end host will forward the frame towards the next end host on the ring. In a ring topology, frames typically flow in a single predetermined direction.
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Let the number of arrivals through time t be denoted A(t), where A(t) takes on integer values.
The time between the (i – 1)th and ith arrival is referred to as the interarrival time and is denoted τi. If we model each interarrival time τi as a RV, then A(t) is a random process (RP), and the arrival rate of the source is given as:
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Suppose s = 1:
For example, s = 1, t = 1:
Suppose s = 2:
For example, s = 2, t = 1:
As indicated by the examples, the interarrival times depend on s. Thus, the source is not memoryless.
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Suppose s and t are >= 0:
For example, s = 1, t = 1:
For example, s = 2, t = 1:
As indicated by the examples, the interarrival times do not depend on s. Thus, the source is memoryless.
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A memoryless data source with arrival rate λ starts at time 0. At t = 0, what is the density function of possible times for the first arrival?
At t = t1, if no arrivals have occurred, what is the density of possible times for the first arrival?
Example 3
Suppose a memoryless source has an arrival rate of two per second. What is the probability that zero arrivals occur in the interval [t1, t2]?
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