Translation

English
`DLE STX` **1** **2** **3** **DLE** `DLE` **STX** `4` `DLE ETX`
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`z` : `1111010` b
`@` : `1000000` b
`space` : `0100000` b
In addition, the :term:`ASCII` table also defines several non-printable or control characters. These characters were designed to allow an application to control a printer or a terminal. These control characters include `CR` and `LF`, that are used to terminate a line, and the `BEL` character which causes the terminal to emit a sound.
`NUL`: `0000000` b
`BEL`: `0000111` b
`CR` : `0001101` b
`LF` : `0001010` b
`DLE`: `0010000` b
`STX`: `0000010` b
`ETX`: `0000011` b
Some characters are used as markers to delineate the frame boundaries. Many `character stuffing` techniques use the `DLE`, `STX` and `ETX` characters of the ASCII character set. `DLE STX` (resp. `DLE ETX`) is used to mark the beginning (end) of a frame. When transmitting a frame, the sender adds a `DLE` character after each transmitted `DLE` character. This ensures that none of the markers can appear inside the transmitted frame. The receiver detects the frame boundaries and removes the second `DLE` when it receives two consecutive `DLE` characters. For example, to transmit frame `1 2 3 DLE STX 4`, a sender will first send `DLE STX` as a marker, followed by `1 2 3 DLE`. Then, the sender transmits an additional `DLE` character followed by `STX 4` and the `DLE ETX` marker.
**1** **2** **3** **4**
`DLE STX` **1** **2** **3** **4** `DLE ETX`
**1** **2** **3** **DLE** **STX** **4**
`DLE STX` **1** **2** **3** **DLE** `DLE` **STX** `4` `DLE ETX`
**DLE STX DLE ETX**
`DLE STX` **DLE** `DLE` **STX** **DLE** `DLE` ETX** `DLE ETX`
Recovering from transmission errors
In this section, we develop a reliable datalink protocol running above the physical layer service. To design this protocol, we first assume that the physical layer provides a perfect service. We will then develop solutions to recover from the transmission errors.
The datalink layer is designed to send and receive frames on behalf of a user. We model these interactions by using the `DATA.req` and `DATA.ind` primitives. However, to simplify the presentation and to avoid confusion between a `DATA.req` primitive issued by the user of the datalink layer entity, and a `DATA.req` issued by the datalink layer entity itself, we will use the following terminology :
the interactions between the user and the datalink layer entity are represented by using the classical `DATA.req` and the `DATA.ind` primitives
the interactions between the datalink layer entity and the framing sub-layer are represented by using `send` instead of `DATA.req` and `recvd` instead of `DATA.ind`
To solve this problem, a reliable protocol must include a feedback mechanism that allows the receiver to inform the sender that it has processed a frame and that another one can be sent. This feedback is required even though there are no transmission errors. To include such a feedback, our reliable protocol must process two types of frames :
data frames carrying a SDU

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Glossary

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String information

Source string location
../../principles/reliability.rst:261
String age
4 years ago
Source string age
4 years ago
Translation file
locale/fr/LC_MESSAGES/principles/reliability.po, string 81