📄 go back nprotocol.htm
字号:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<!-- saved from url=(0068)http://www.macs.hw.ac.uk/~pjbk/nets/protocolsimulations/gobackn.html -->
<HTML><HEAD><TITLE>Go Back nProtocol</TITLE>
<META http-equiv=Content-Type content="text/html; charset=gb2312"><LINK rev=made
href="mailto:kjt@cs.stir.ac.uk">
<SCRIPT language=JavaScript>
<!--
var simulator;
var maxSeq;
var winSize;
function set () {
maxSeq = document.settings.MaxSeq.value.toString ();
winSize = document.settings.WinSize.value.toString ();
if (winSize > 0 || (false && winSize <= maxSeq)) {
simulator.setParameter ("maxSeq", maxSeq);
simulator.setParameter ("winSize", winSize);
simulator.restart ();
document.settings.btnSet.value = "Change Values";
}
else {
alert ("Window size must be in the range 1 to the maximum sequence number");
}
}
//-->
</SCRIPT>
<META content="MSHTML 6.00.2900.2963" name=GENERATOR></HEAD>
<BODY background="Go Back nProtocol.files/simulator.jpg"
onload=simulator=document.ProtocolSimulator>
<CENTER>
<H1>Go Back n Protocol</H1><IMG src="Go Back nProtocol.files/simulator.gif">
</CENTER>
<P>Go Back n is a connection oriented protocol in which the transmitter has a
window of sequence numbers that may be transmitted without acknowledgment. The
receiver will only accept the next sequence number it is expecting - other
sequence nubmers are silently ignored.
<P>The protocol simulation shows a time-sequence diagram with users A and B,
protocol entities A and B that support them, and a communications medium that
carries messages. Users request data transmissions with <I>DatReq(DATAn),</I>
and receive data transmissions as <I>DatInd(DATAn)</I>. Data messages are simply
numbered <I>DATA0</I>, <I>DATA1</I>, etc. without explicit content. The
transmitting protocol sends the protocol message <I>DT(n)</I> that gives only
the sequence number, not the data. Once sequence numbers reach a maximum number
(like 7), they wrap back round to 0. An acknowledgement <I>AK(n)</I> means that
the <I>DT</I> message numbered <I>n</I> is the next one expected (i.e. all
messages up to but not including this number have been received). Since sequence
numbers wrap round, an acknowledgement with sequence number 1 refers to messages
0, 1, 7, 6, etc. Note that if a <I>DT</I> message is received again due to
re-transmission, it is acknowledged but discarded.
<P>The protocol has a maximum number of messages that can be sent without
acknowledgement. If this window becomes full, the protocol is blocked until an
acknowledgement is received for the earliest outstanding message. At this point
the transmitter is clear to send more messages.
<P>The receiver delivers the protocol messages <I>DT(n)</I> to the user in
order. Any received out of order are ignored.
<H2>Protocol Parameters</H2>
<FORM name=settings>
<TABLE cellPadding=5>
<TBODY>
<TR>
<TD align=right>Maximum Sequence Number
<TD><INPUT size=2 value=7 name=MaxSeq>
<TD align=right>Window Size
<TD><INPUT size=2 value=3 name=WinSize>
<TD></TD>
<TD><INPUT onclick="set ()" type=button value="Change Values" name=btnSet>
</TD></TR></TBODY></TABLE></FORM>
<HR>
<APPLET height=600 archive=ProtocolSimulator.jar width=650
code=simulator.ProtocolSimulator.class name=ProtocolSimulator><PARAM NAME="protocol" VALUE="GoBackN"></APPLET>
<HR>
</BODY></HTML>
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -