使用 Java 的位填充错误检测技术
原文:https://www . geesforgeks . org/bit-filling-检错-技术-使用-java/
先决条件: 1。Java 中的 Socket 编程 2。比特填充 3。数据链路层成帧
数据被封装在数据链路层的帧中，并通过网络发送。比特填充是一种错误检测技术。
使用的想法非常简单。每个帧以特殊的位模式“01111110”开始和结束，这是标志字节。每当发送方的数据链路层在数据中遇到五个连续的 1 时，它会自动在输出比特流中填充一个 0 位。位填充类似于字节填充，在字节填充中，转义字节被填充到数据中标志字节之前的正在进行的字符流中。
当接收器看到五个连续的 1 位，后跟一个 0 位时，它会自动删除 0 位。比特填充对于发送方和接收方计算机的网络层都是完全透明的。
利用比特填充，两个帧之间的边界可以由标志模式明确地识别。因此，如果接收器失去了对它所在位置的跟踪，它所要做的就是扫描输入中的标志序列。，因为它们只能出现在帧边界，而不能出现在数据中。
Illustrative Examples
*Sender Side(Client):*
User enters a binary data as input.
Enter data:
0000001
Data is stuffed and sent to the receiver for unstuffing.
Here server is the receiver.
Data stuffed in client: 01111110000000101111110
Sending to server for unstuffing
***Receiver Side(Server):***
Receiver receives the stuffed data.
Stuffed data from client: 01111110000000101111110
Receiver has to unstuff the input data from sender and get the original data which
was given as input by the user.
Unstuffed data:
0000001
下面给出了上述逻辑的代码实现。 发送方(客户端):
package bitstuffing;
import java.io.*;
import java.net.*;
import java.util.Scanner;
public class BitStuffingClient {
public static void main(String[] args) throws IOException
{
// Opens a socket for connection
Socket socket = new Socket("localhost", 6789);
DataInputStream dis = new DataInputStream(socket.getInputStream());
DataOutputStream dos = new DataOutputStream(socket.getOutputStream());
// Scanner class object to take input
Scanner sc = new Scanner(System.in);
// Takes input of unstuffed data from user
System.out.println("Enter data: ");
String data = sc.nextLine();
int cnt = 0;
String s = "";
for (int i = 0; i < data.length(); i++) {
char ch = data.charAt(i);
if (ch == '1') {
// count number of consecutive 1's
// in user's data
cnt++;
if (cnt < 5)
s += ch;
else {
// add one '0' after 5 consecutive 1's
s = s + ch + '0';
cnt = 0;
}
}
else {
s += ch;
cnt = 0;
}
}
// add flag byte in the beginning
// and end of stuffed data
s = "01111110" + s + "01111110";
System.out.println("Data stuffed in client: " + s);
System.out.println("Sending to server for unstuffing");
dos.writeUTF(s);
}
}
在接收端(服务器端):
package bitstuffing;
import java.io.*;
import java.net.*;
public class BitStuffingServer {
public static void main(String[] args) throws IOException
{
ServerSocket skt = new ServerSocket(6789);
// Used to block until a client connects to the server
Socket socket = skt.accept();
DataInputStream dis = new DataInputStream(socket.getInputStream());
DataOutputStream dos = new DataOutputStream(socket.getOutputStream());
// Receiving the string from the client which
// needs to be stuffed
String s = dis.readUTF();
System.out.println("Stuffed data from client: " + s);
System.out.println("Unstuffed data: ");
int cnt = 0;
// removal of stuffed bits:
// start from 9th bit because the first 8
// bits are of the special pattern.
for (int i = 8; i < s.length() - 8; i++) {
char ch = s.charAt(i);
if (ch == '1') {
cnt++;
System.out.print(ch);
// After 5 consecutive 1's one stuffed bit
//'0' is added. We need to remove that.
if (cnt == 5) {
i++;
cnt = 0;
}
}
else {
// print unstuffed data
System.out.print(ch);
// we only need to maintain count
// of consecutive 1's
cnt = 0;
}
}
System.out.println();
}
}
输入和输出如上所示。
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