DCN | Semi-Markovian system

M/G/1 queuing systemG means general distribution / more general situation. In this case, service time of the server has a general distribution with mean $X=E[x ]=1/\mu$ and standard deviation $\sigma_x$, where $mu$ is the mean service rate (services per second, etc.)Mean waiting time for a service request can be described by P-K formula: $$W=\frac{\lambda E[x^2]}{2(1-\rho)} $$ Using Little's Law, we can obtain the mean number of service requests in the buffer: $$N_Q=\lambda W=\frac{\lambda^2 E[x

Data communication networks · 2024-11-05

DCN | Queuing models in data link networks

Ergodic process:As nothing is neither generated or lost in the queuing system, the arrival rate of packages equals to the departure rate.Little's LawStochastic processes and Markov chainsGiven appropriate state space and time variable, a stochastic process can be properly described. If the time variable is discrete, the process is called discrete-time process; otherwise, it's called continuous-time process.$\mu$ is the number of customers that can be served at one time (serving rate) $\lambda$

Data communication networks · 2024-10-25

DCN | Data link layer: Framing & error detection

Data link layer is responsible for delivering data from one node to another node, which means that the duty scope of data link layer is only node-to-node. A packet at the data link layer is called a frame. Any mistakes made in physical layer is supposed to be solved in data link layer.Types of data link layer:Point to point link: it consists of a single sender at one end of the link and a single receiver at the other end.Broadcast link: it can have multiple sending and receiving nodes all connec

Data communication networks · 2024-10-08

DCN | Switching in data networks

Circuit switchingCircuit switching approaches are used in traditional telephone networksFrequency-Division Multiplexing (FDM)Time-Division Multiplexing (TDM)Three phases are needed for communication in a circuit-switched network:Setup: dial the phone numberData transfer: communicationTeardownDelay in circuit-switched networks is the sum of times needed to setup the connection (connection delay, propagation delay), transfer the data and disconnect the circuitPacket-switched networksDefinition: No

Data communication networks · 2024-09-29