Figure 1.9: Quality of Service(Qos) Congestion and Latency(拥塞和延迟) Congestion because traffic chronically or momentarily exceeds capacity Latency delay measured in milliseconds(ms Especially bad for some services such as voice communication or highly interactive applications
11 Figure 1.9: Quality of Service (QoS) • Congestion and Latency（拥塞和延迟） – Congestion because traffic chronically or momentarily exceeds capacity – Latency delay measured in milliseconds (ms) – Especially bad for some services such as voice communication or highly interactive applications
Figure 1.9: Quality of Service(Qos) Re| abilit!y可靠性 Availability可用性 Percent of time the network is available to users for transmission and reception Want 24x7x365 availabilit Telephone network: Five 9s(99.999% Error rate错误率 Percent of lost or damaged messages or bits 12
12 Figure 1.9: Quality of Service (QoS) • Reliability 可靠性 – Availability 可用性 • Percent of time the network is available to users for transmission and reception • Want 24x7x365 availability • Telephone network: Five 9s (99.999%) – Error Rate 错误率 • Percent of lost or damaged messages or bits
I Figure 1.9: Quality of Service(Qos) Service Level Agreements (SLAS) Quantitative guarantees for various service parameters Example: Better than 99% availability and a packet loss error rate of less 0.5% measured over each day, latency not exceeding 45 ms 99% of the time Network provider pays performance penalties if guarantees are not met 13
13 Figure 1.9: Quality of Service (QoS) • Service Level Agreements (SLAs) – Quantitative guarantees for various service parameters – Example: Better than 99% availability and a packet loss error rate of less 0.5% measured over each day; latency not exceeding 45 ms 99% of the time. – Network provider pays performance penalties if guarantees are not met
Chp 2 Topics Covered
Chp 2 Topics Covered
I Topics Covered Standards govern the semantics and syntax of messages Http: Text request and response messages Data field. header and trailer Header and trailer subdivided into fields Reliability In TCP receiver sends ACKs Senders retransmit non -acknowledged segments 15
15 Topics Covered • Standards govern the semantics and syntax of messages – HTTP: Text request and response messages – Data field, header, and trailer – Header and trailer subdivided into fields • Reliability – In TCP, receiver sends ACKs – Senders retransmit non-acknowledged segments