Frame delimitation means 10

Question 10: In descriptions of how the data link layer works, two different terms are often seen – "lost" and "discarded". Are they different?

A: There are some differences.

"Lost" is usually used in situations where A sends a dataframe to B, but B doesn't receive it at all. As for why B didn't receive it, we're not interested, because we're not going to do it right now, or we don't want to figure out where exactly this data frame was lost.

Here we care just "b did not receive this dataframe". So, let's say, this data frame is missing. Obviously, the "loss" here is not "we deliberately threw this frame away".

"Drop" is typically used in cases where A sends a dataframe to B, and upon receipt by B, the data link layer protocol uses a CRC verifier (hardware) to check for errors. We found an error, so we said that the CRC inspector automatically discarded the data frame.

As a result, "discarding" tends to make it clear "who threw the data frame" and "actively threw it away". In this case, it is the CRC verifier that actively discards the wrong frame (why does it actively discard this wrong frame?). Because the wrong frame is useless.

If you don't throw it away and continue to move it forward** and deliver it all the way to the destination host, then eventually the error frame will still be discarded. However, this wastes a lot of network resources. In other words, the loss of discarding the wrong frame is smaller, and the loss of discarding the wrong frame at the end is greater).

However, such a "drop" has the same effect as "B did not receive this frame", and B will not send any reply message at this time. For this reason, people often use the term "discard silently" to describe this discarding of erroneous frames. In this case, we can also say it in another way:

A sends a data frame to B, but B doesn't receive it, and the frame is lost. "Saying that shows that we don't want to go after the cause of the frame loss. In short, a "dropped" frame is also a "lost" frame, but "dropped" has the meaning of "actively discarded" or "intentionally discarded".

But there is also another way to "discard". The data frame sent by A was transmitted to B error-free and successfully passed the error check of the CRC. This frame was transmitted without errors.

However, when B's link-layer protocol examines the frame further, it finds that the frame has the wrong sequence number (e.g., it is a duplicate frame). As a result, the data link layer protocol drops the duplicate frame. But at the same time, the protocol stipulates that B also sends an acknowledgment frame to A, that is, the last acknowledgment frame that was originally sent.

Such a "discard" is obviously somewhat different from a "loss". Because the frame was originally teleported to B, B took it first, but later found out that it was a duplicate frame, so he discarded it again. In terms of effect, there are similarities between "discard" and "loss".

But "discarding" often involves the reason for discarding the frame.

Asynchronous communication can also be sent in frames. The receiver must be ready to receive frames at all times. This is why the first part of the frame must have some special bit combinations that allow the receiver to find the beginning of a frame.

This is also known as frame demarcation. Frame delimitation also involves determining where the frame ends. There are two ways to do this.

One is to have some special combination of bits at the end of the frame to mark the end of the frame. Or you can have a field with the frame length in the frame header. It should be noted that when sending frames asynchronously, it does not mean that the sender must add a start and stop bits to each character in the frame before sending it, but that the sender can send a frame at any time, and the time interval between frames can also be arbitrary.

All bits in a frame are sent consecutively. The sender does not need to coordinate with the receiver before sending a frame (no bit synchronization is required).

The time at which each character starts sending can be any t0

0 start bit, end bit t, each frame start to send time, can be arbitrary, sent in characters, sent in frames, start frame, end frame.

One frame: It is a static picture, and successive frames form an animation, such as a TV image.

The recording is made up of a game, and each one is called a frame. Frames per second is actually the number of frames shown per second of animation or **. Frames refer to "screens", and frames per second refer to "frames per second".

There are also metaphors for the past of love with each frame, for example, "every frame is love" refers to love all the time, and a frame is a very short period of time, so it represents all the time, and love all the time is still relatively difficult to do. Every frame is love Chong Zheng more often appears in the title of **, every frame is love, in a short life, we have to go.

Classification of "frames".

1. Frames are divided into key frames and transition frames. There can be no transition frames in the middle of the two keyframes (such as frame-by-frame animation), but there must be keyframes before and after the transition frames, because the transition frames are attached to the keyframes; Keyframes can modify the content of the frame, but transition frames cannot modify the content of the Scattering Frame, so there is a strict distinction between the two.

2. Keyframes can contain shapes, clips, groups and other types of elements or many elements, but objects in transition frames can only be clips (movie clips, graphic clips, buttons) or independent shapes. The film is composed of successive **, each ** is a frame, 25 frames per second in the PAL system, and 30 frames per second in the NTSC system.

A frame is a still picture.

Frame - is the smallest unit in image animation.

A single image is equivalent to each frame of the lens on the motion picture film. A frame is a static picture, and successive frames form an animation, such as a television image.

We usually say frame count.

To put it simply, it is the number of frames transmitted in 1 second, which can also be understood as the graphics processor.

It can be refreshed several times per second, usually expressed as frames per second (fps). Each frame is a static image, and the rapid succession of frames creates the illusion of motion. High frame rate.

You can get smoother, more realistic animations. The more frames per second (fps), the smoother the action will be.

Classification

Frames are divided into keyframes.

and transition frames. There can be no transition frames in the middle of the two keyframes (such as frame-by-frame animation), but there must be keyframes before and after the transition frames, because the transition frames are attached to the keyframes;

Keyframes can modify the contents of that frame, but transition frames cannot modify the contents of that frame.

Keyframes can contain shapes, clips, groups, and other elements or many other elements, but objects in transition frames can only be clips (movie clips, graphic clips, buttons) or stand-alone shapes.

The film is composed of successive **, each ** is a frame, PAL format.

25 frames per second and 30 frames per second in NTSC mode.

The above content refers to Encyclopedia - One Frame.