The format and sequence of messages exchanged between two or more communicating entities, and the actions taken to send and/or receive a message or other event
Packet Switching and Circuit Switching
packet switching
- End systems exchange messages with each other
- store-and-forward transmission: the entire packet must be received before the switch can begin transmitting the first bit of the packet to the output link
- Each router has a forwarding table (forwarding table), which is used to map the destination address (or part of the destination address) to the output link
circuit switching
- Create a dedicated end-to-end connection between two hosts
Latency in Packet Switched Networks
Nodal processing delay
queuing delay
- Waiting for transmission on the link
- The queue is full, the router discards the newly arrived packets, packet loss occurs
transmission delay
- The time it takes to push all the bits onto the link
- L bits, R Bps, transmission delay L/R
Propagation delay
- The time it takes to propagate from the start of the link to the router
- The distance between routers is d, the propagation speed is s, and the propagation delay is d/s
end-to-end delay
- Assuming that there are N-1 routers between the source host and the destination, the end-to-end delay is N(d(proc) + d(trans) + d(prop))
throughput in computer networks
- Its throughput can be approximated as the minimum transmission rate along the path between source and destination when there is no other interfering traffic
Layered architecture and its service model
As long as the layer provides the same services to the layers above it, and uses the same services from the layers below, when a layer's implementation changes, the rest of the system remains the same
application layer
- Where web applications and their application layer protocols reside
- HTTP,SMTP,FTP，DNS
- Information at the application layer is grouped into messages
transport layer
- Pass messages between application endpoints
- TCP, UDP
- The transport layer grouping is called a segment
network layer
- Move network layer packets from one host to another
- IP
- Network layer packets are called datagrams
link layer
- Serves the network layer when moving packets from one node to the next
- The link layer is grouped into frames (frame)
physical layer
- Move individual bits in a frame from one node to another
encapsulation
- At each layer, a packet has a header field and a payload field. The payload is usually a packet from the upper layer
Digression
In this first year of fast-growing technology, programming is like a ticket to a world of infinite possibilities for many people. In the star lineup of programming languages, Python is like the leading superstar. With its concise and easy-to-understand syntax and powerful functions, it stands out and becomes one of the most popular programming languages in the world.
The rapid rise of Python is extremely beneficial to the entire industry , but " 人红是非多" has caused it to add a lot of criticism, but it still cannot stop its hot development momentum.
Will Python remain relevant and intact for the rest of the next decade? Today, we're going to analyze the facts and dispel some misconceptions.
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