background knowledge
| Message switching |
Packet switching |
|
|
example
M = 7.5Mbits, L = 1500bits, there are M = 5000L, R = 1.5Mbps. Through the following ways, seeking packet switching and packet switching their required delivery time (sec). (Not consider splitting and recombination time; addition time without regard to the packet header.)
Message switching
M / R = 7.5Mbits / 1.5Mbps = 5sec; At this time a message arrives at the first router.
Thus the packet from the source host to the destination host needs a total of 3 × 5sec = 15sec
Thoughts: The router requires at least how much cache?
A: At least 7.5Mbits, that is, at least this time the packet size.
Packet switching
L / R = 1500bits / 1.5Mbps = 1ms; In this case the first packet to reach the first router.
Since M = 5000L, i.e., the message is divided into packets 5000; and when the first packet arrives at the router, the remaining packet is transmitted one by one.
So when the first time 5000ms, 5000 of packets from the source host to begin transmitting; the first 5002ms, the first packet to the destination host 5000, the packet transmission is completed.
Message delivery time = 5002ms = 5.002sec
Thoughts: The router requires at least how much cache?
A: At least 1500bits, that is, requires at least one packet size. In contrast, packet switching than packet switching more space-saving.
Summary - packet switching, packet delivery time
Entire packet transmission delay time + one intermediate router in the packet transfer delay
Message: M bits
Data transfer rate = link bandwidth: R & lt bps
Packet size = length: L bits
Number of hops: H
Number of routers: n-=. 1 H-
Source examples
Chinese University computer network mooc Harbin Institute of Technology Liquan Long, Nie Lanshun
Tips
Export mooc Courseware: Andrews clients do not click on the download button to download courseware (if download, delete), click open courseware, find the cache file Chinese University mooc folder in the file manager, locate and open the corresponding time and no file format to begin with "PDF_", rename the file to expand named pdf, to open.