Computer network notes] Overview 2

Computer Network Performance

rate

1. I.e., the rate of data rate (data rate), or said data transmission rate or bit rate (bit rate)
2. The amount of information transmitted per unit of time
3. The most important performance indicators of a computer network
4. b / s (bps), kb / s, Mb / s, Gb / s
   NOTE: \ (K = 10. 3 ^ \) , \ (M = 10. 6 ^ \) , \ (G = 10. 9 ^ \)
5. Often it refers to the rate of nominal rate or nominal rate

bandwidth

Bandwidth refers to the original bandwidth signal having a frequency bandwidth, i.e., the difference between the highest frequency and the lowest frequency, hertz Hz
bandwidth of the network is typically a digital channel can be transmitted "maximum data rate", Unit: b / s (bps)

Delay / latency (delay / latency)

Q: Why is packet switching packet loss and delay
A: In the router packet queue cache

1. Four kinds of packet delay
   (1) the node processing delay error detection, determining an output link, typically <ms (often negligible)
   (2) queuing delays waiting for output link is available, depending on the degree of congestion router
   (3) propagation delay (transmission delay ) packet length, link bandwidth (bps)
   (. 4) propagation delay (propagation delay) the length of the physical link, the signal propagation velocity ( \ (2 * 10 ^ 8M / S \) )
   \ [Nodal D_ {proc} = D_ { } + d_ {queue} + d_ {trans} + d_ {prop} \]

Distinguish between propagation delay and propagation delay: Analogue team toll booths

Queuing delay:
R & lt: link bandwidth
L: Packet length
a: average packet arrival rate

Traffic intensity (Traffic intensity) estimated La / R

Delay-bandwidth product

1. = Propagation delay bandwidth product delay bandwidth of X = \ (D_ {} prop XR (bits) \)
2. How many bits on the forward link can accommodate. (Also known as link length in bits) of

Packet loss (loss)

1. Queue buffer capacity is limited, packet arrival queue is full will be dropped, the packet may be discarded by the node or the source to the preamble retransmission (retransmission may not)
2. \ (Packet loss rate = \ frac {} {the number of packet loss total number of packets sent} \)

Throughput / throughput (Throughput)

1. Throughput: indicates the data transfer rate between the transmitting and receiving ends
2. Instant Throughput
3. Average throughput
4. Bottleneck link: the end path, limits the throughput of a link end