Free Windows Help Tutorials sponsored by inkjet printer cartridges dot org /title> <META HTTP-EQUIV="imagetoolbar" CONTENT="no"> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; CHARSET=ISO 8859-1"> <META name="description" Content="Hundreds of downloadable Windows help tutorials, articles and how-to guides sponsored by inkjet printer cartridges dot org."><style type="text/css">  </style> </head> <body bgcolor=#999999 vlink=blue link=blue> <span name = "INTRA" class="pg" style="top:0px; left:5px; width:714px; height:1010px"></span> <span name = "INTRA" style='top:0px; left:5px; height:1010px; width:714px' class='img'> <img src="pg0001im.png" height = "1010 width = "714" border="0"> </span> <span class='nav' style='left: 10px; top: 10px'><pre></pre></span><span name = "INTRA" style='top:51px; left:568px' class="ft5"><pre><font face='Helvetica'>Connectivity:Overview</font></pre></span> <span name = "INTRA" style='top:107px; left:100px' class="ft4"><pre><font face='Arial'><b>Understanding</b> <b>TCP/IP</b></font></pre></span> <span name = "INTRA" style='top:205px; left:93px' class="ft2"><pre><font face='Arial'><i><b>TCP/IP,</b></i> <i><b>the</b></i> <i><b>ubiquitous</b></i> <i><b>network</b></i> <i><b>protocol,</b></i> <i><b>is</b></i> <i><b>actually</b></i> <i><b>a</b></i> <i><b>four layer</b></i> <i><b>suite</b></i> <i><b>of</b></i> <i><b>protocols</b></i> <i><b>and</b></i> <i><b>is</b></i> <i><b>well</b></i></font></pre></span> <span name = "INTRA" style='top:225px; left:93px' class="ft2"><pre><font face='Arial'><i><b>worth</b></i> <i><b>gaining</b></i> <i><b>an</b></i> <i><b>understanding</b></i> <i><b>of.</b></i> <i><b>This</b></i> <i><b>month</b></i> <i><b>we</b></i> <i><b>explain</b></i> <i><b>UDP</b></i> <i><b>and</b></i> <i><b>TCP,</b></i> <i><b>the</b></i> <i><b>two</b></i> <i><b>protocols</b></i></font></pre></span> <span name = "INTRA" style='top:246px; left:205px' class="ft2"><pre><font face='Arial'><i><b>used</b></i> <i><b>by</b></i> <i><b>applications.</b></i> <i><b>Continuing</b></i> <i><b>our</b></i> <i><b>four part</b></i> <i><b>article.</b></i></font></pre></span> <span name = "INTRA" style='top:278px; left:576px' class="ft1"><pre><font face='Arial'>By Julian Moss</font></pre></span> <span name = "INTRA" style='top:335px; left:77px' class="ft0"><pre><font face='Arial'><b>T</b></font></pre></span> <span name = "INTRA" style='top:339px; left:109px' class="ft1"><pre><font face='Arial'>he link layer and network layer</font></pre></span> <span name = "INTRA" style='top:339px; left:272px' class="ft1"><pre><font face='Arial'>other to some extent, though the pro </font></pre></span> <span name = "INTRA" style='top:339px; left:466px' class="ft1"><pre><font face='Arial'>address will not be passed by a router</font></pre></span> <span name = "INTRA" style='top:351px; left:109px' class="ft1"><pre><font face='Arial'>protocols of the TCP/IP suite,</font></pre></span> <span name = "INTRA" style='top:351px; left:272px' class="ft1"><pre><font face='Arial'>tocol field is not available to the higher </font></pre></span> <span name = "INTRA" style='top:351px; left:466px' class="ft1"><pre><font face='Arial'>on to the Internet.</font></pre></span> <span name = "INTRA" style='top:363px; left:109px' class="ft1"><pre><font face='Arial'>which are concerned with the</font></pre></span> <span name = "INTRA" style='top:363px; left:272px' class="ft1"><pre><font face='Arial'>level protocols. IP uses the protocol</font></pre></span> <span name = "INTRA" style='top:363px; left:480px' class="ft1"><pre><font face='Arial'>Broadcasts can be targeted at spe </font></pre></span> <span name = "INTRA" style='top:375px; left:77px' class="ft1"><pre><font face='Arial'>basic mechanics of transferring blocks</font></pre></span> <span name = "INTRA" style='top:375px; left:272px' class="ft1"><pre><font face='Arial'>field to determine whether data should</font></pre></span> <span name = "INTRA" style='top:375px; left:466px' class="ft1"><pre><font face='Arial'>cific networks. A UDP datagram with</font></pre></span> <span name = "INTRA" style='top:387px; left:77px' class="ft1"><pre><font face='Arial'>of data across and between networks,</font></pre></span> <span name = "INTRA" style='top:387px; left:272px' class="ft1"><pre><font face='Arial'>be passed to the UDP or TCP module.</font></pre></span> <span name = "INTRA" style='top:387px; left:466px' class="ft1"><pre><font face='Arial'>the host and subnet part of the IP ad </font></pre></span> <span name = "INTRA" style='top:399px; left:77px' class="ft1"><pre><font face='Arial'>are the foundations of TCP/IP. They</font></pre></span> <span name = "INTRA" style='top:399px; left:272px' class="ft1"><pre><font face='Arial'>UDP or TCP use the port number to</font></pre></span> <span name = "INTRA" style='top:399px; left:466px' class="ft1"><pre><font face='Arial'>dress set to all binary ones is broadcast</font></pre></span> <span name = "INTRA" style='top:411px; left:77px' class="ft1"><pre><font face='Arial'>are used by the protocol stack itself, but</font></pre></span> <span name = "INTRA" style='top:411px; left:272px' class="ft1"><pre><font face='Arial'>determine which application layer</font></pre></span> <span name = "INTRA" style='top:411px; left:466px' class="ft1"><pre><font face='Arial'>to all the hosts on all the subnets of the</font></pre></span> <span name = "INTRA" style='top:424px; left:77px' class="ft1"><pre><font face='Arial'>they are not used directly by applica </font></pre></span> <span name = "INTRA" style='top:424px; left:272px' class="ft1"><pre><font face='Arial'>protocol should receive the data.</font></pre></span> <span name = "INTRA" style='top:424px; left:466px' class="ft1"><pre><font face='Arial'>network which matches the net part of</font></pre></span> <span name = "INTRA" style='top:436px; left:77px' class="ft1"><pre><font face='Arial'>tions that run over TCP/IP.</font></pre></span> <span name = "INTRA" style='top:436px; left:286px' class="ft1"><pre><font face='Arial'>Although UDP isn't reliable, it is</font></pre></span> <span name = "INTRA" style='top:436px; left:466px' class="ft1"><pre><font face='Arial'>the IP address. If only the host part (in</font></pre></span> <span name = "INTRA" style='top:448px; left:91px' class="ft1"><pre><font face='Arial'>Now we'll look at the two protocols</font></pre></span> <span name = "INTRA" style='top:448px; left:272px' class="ft1"><pre><font face='Arial'>still an appropriate choice for many</font></pre></span> <span name = "INTRA" style='top:448px; left:466px' class="ft1"><pre><font face='Arial'>other words, all the bits that are zero in</font></pre></span> <span name = "INTRA" style='top:460px; left:77px' class="ft1"><pre><font face='Arial'>that are used by applications: User</font></pre></span> <span name = "INTRA" style='top:460px; left:272px' class="ft1"><pre><font face='Arial'>applications. It is used in real time ap </font></pre></span> <span name = "INTRA" style='top:460px; left:466px' class="ft1"><pre><font face='Arial'>the subnet mask) is set to binary ones,</font></pre></span> <span name = "INTRA" style='top:472px; left:77px' class="ft1"><pre><font face='Arial'>Datagram Protocol (UDP) and Trans </font></pre></span> <span name = "INTRA" style='top:472px; left:272px' class="ft1"><pre><font face='Arial'>plications like Net audio and video</font></pre></span> <span name = "INTRA" style='top:472px; left:466px' class="ft1"><pre><font face='Arial'>then the broadcast is restricted to all</font></pre></span> <span name = "INTRA" style='top:484px; left:77px' class="ft1"><pre><font face='Arial'>mission Control Protocol (TCP).</font></pre></span> <span name = "INTRA" style='top:484px; left:272px' class="ft1"><pre><font face='Arial'>where, if data is lost, it's better to do</font></pre></span> <span name = "INTRA" style='top:484px; left:466px' class="ft1"><pre><font face='Arial'>the hosts on the subnet that matches</font></pre></span> <span name = "INTRA" style='top:496px; left:272px' class="ft1"><pre><font face='Arial'>without it than send it again out of</font></pre></span> <span name = "INTRA" style='top:496px; left:466px' class="ft1"><pre><font face='Arial'>the rest of the address.</font></pre></span> <span name = "INTRA" style='top:509px; left:77px' class="ft2"><pre><font face='Arial'><i><b>User</b></i> <i><b>Datagram</b></i> <i><b>Protocol</b></i></font></pre></span> <span name = "INTRA" style='top:508px; left:272px' class="ft1"><pre><font face='Arial'>sequence. It is also used by protocols</font></pre></span> <span name = "INTRA" style='top:508px; left:480px' class="ft1"><pre><font face='Arial'>Multicasting is used to send data to</font></pre></span> <span name = "INTRA" style='top:520px; left:272px' class="ft1"><pre><font face='Arial'>like the Simple Network Management</font></pre></span> <span name = "INTRA" style='top:520px; left:466px' class="ft1"><pre><font face='Arial'>a group of hosts that choose to receive</font></pre></span> <span name = "INTRA" style='top:532px; left:91px' class="ft1"><pre><font face='Arial'>The User Datagram Protocol is a</font></pre></span> <span name = "INTRA" style='top:532px; left:272px' class="ft1"><pre><font face='Arial'>Protocol (SNMP).</font></pre></span> <span name = "INTRA" style='top:532px; left:466px' class="ft1"><pre><font face='Arial'>it. A multicast UDP datagram has a</font></pre></span> <span name = "INTRA" style='top:544px; left:77px' class="ft1"><pre><font face='Arial'>very simple protocol. It adds little to</font></pre></span> <span name = "INTRA" style='top:544px; left:466px' class="ft1"><pre><font face='Arial'>destination IP address in which the</font></pre></span> <span name = "INTRA" style='top:556px; left:77px' class="ft1"><pre><font face='Arial'>the basic functionality of IP. Like IP, it</font></pre></span> <span name = "INTRA" style='top:557px; left:272px' class="ft2"><pre><font face='Arial'><i><b>Broadcasting</b></i></font></pre></span> <span name = "INTRA" style='top:556px; left:466px' class="ft1"><pre><font face='Arial'>first four bits are 1110, giving ad </font></pre></span> <span name = "INTRA" style='top:568px; left:77px' class="ft1"><pre><font face='Arial'>is an unreliable, connectionless proto </font></pre></span> <span name = "INTRA" style='top:568px; left:466px' class="ft1"><pre><font face='Arial'>dresses in the range 224.x.x.x to</font></pre></span> <span name = "INTRA" style='top:580px; left:77px' class="ft1"><pre><font face='Arial'>col. You do not need to establish a</font></pre></span> <span name = "INTRA" style='top:580px; left:286px' class="ft1"><pre><font face='Arial'>UDP is suitable for broadcasting in </font></pre></span> <span name = "INTRA" style='top:580px; left:466px' class="ft1"><pre><font face='Arial'>239.x.x.x. The remaining bits of the ad </font></pre></span> <span name = "INTRA" style='top:592px; left:77px' class="ft1"><pre><font face='Arial'>connection with a host before exchang </font></pre></span> <span name = "INTRA" style='top:592px; left:272px' class="ft1"><pre><font face='Arial'>formation, since it doesn't require a</font></pre></span> <span name = "INTRA" style='top:592px; left:466px' class="ft1"><pre><font face='Arial'>dress are used to designate a multicast</font></pre></span> <span name = "INTRA" style='top:604px; left:77px' class="ft1"><pre><font face='Arial'>ing data with it using UDP, and there</font></pre></span> <span name = "INTRA" style='top:604px; left:272px' class="ft1"><pre><font face='Arial'>connection to be open before commu </font></pre></span> <span name = "INTRA" style='top:604px; left:466px' class="ft1"><pre><font face='Arial'>group. This is rather like a radio or</font></pre></span> <span name = "INTRA" style='top:616px; left:77px' class="ft1"><pre><font face='Arial'>is no mechanism for ensuring that data</font></pre></span> <span name = "INTRA" style='top:616px; left:272px' class="ft1"><pre><font face='Arial'>nication can take place. On a network,</font></pre></span> <span name = "INTRA" style='top:616px; left:466px' class="ft1"><pre><font face='Arial'>television</font></pre></span> <span name = "INTRA" style='top:616px; left:524px' class="ft1"><pre><font face='Arial'>channel.</font></pre></span> <span name = "INTRA" style='top:616px; left:576px' class="ft1"><pre><font face='Arial'>For</font></pre></span> <span name = "INTRA" style='top:616px; left:604px' class="ft1"><pre><font face='Arial'>example,</font></pre></span> <span name = "INTRA" style='top:628px; left:77px' class="ft1"><pre><font face='Arial'>sent is received.</font></pre></span> <span name = "INTRA" style='top:628px; left:272px' class="ft1"><pre><font face='Arial'>receiving a broadcast is something</font></pre></span> <span name = "INTRA" style='top:628px; left:466px' class="ft1"><pre><font face='Arial'>224.0.1.1 is used for the Network Time</font></pre></span> <span name = "INTRA" style='top:640px; left:91px' class="ft1"><pre><font face='Arial'>A unit of data sent using UDP is</font></pre></span> <span name = "INTRA" style='top:640px; left:272px' class="ft1"><pre><font face='Arial'>over which you have no choice. The</font></pre></span> <span name = "INTRA" style='top:640px; left:466px' class="ft1"><pre><font face='Arial'>Protocol. If a TCP/IP application</font></pre></span> <span name = "INTRA" style='top:652px; left:77px' class="ft1"><pre><font face='Arial'>called a datagram. UDP adds four 16 </font></pre></span> <span name = "INTRA" style='top:652px; left:272px' class="ft1"><pre><font face='Arial'>targets of a broadcast message are de </font></pre></span> <span name = "INTRA" style='top:652px; left:466px' class="ft1"><pre><font face='Arial'>wants to receive multicast messages, it</font></pre></span> <span name = "INTRA" style='top:664px; left:77px' class="ft1"><pre><font face='Arial'>bit header fields (8 bytes) to whatever</font></pre></span> <span name = "INTRA" style='top:664px; left:272px' class="ft1"><pre><font face='Arial'>termined by the sender, and specified</font></pre></span> <span name = "INTRA" style='top:664px; left:466px' class="ft1"><pre><font face='Arial'>must join the appropriate multicast</font></pre></span> <span name = "INTRA" style='top:676px; left:77px' class="ft1"><pre><font face='Arial'>data is sent. These fields are: a length</font></pre></span> <span name = "INTRA" style='top:676px; left:272px' class="ft1"><pre><font face='Arial'>in the destination IP address. A UDP</font></pre></span> <span name = "INTRA" style='top:676px; left:466px' class="ft1"><pre><font face='Arial'>group, which it does by passing the</font></pre></span> <span name = "INTRA" style='top:688px; left:77px' class="ft1"><pre><font face='Arial'>field, a checksum field, and source and</font></pre></span> <span name = "INTRA" style='top:688px; left:272px' class="ft1"><pre><font face='Arial'>datagram with a destination IP ad </font></pre></span> <span name = "INTRA" style='top:688px; left:466px' class="ft1"><pre><font face='Arial'>address of the group to the protocol</font></pre></span> <span name = "INTRA" style='top:700px; left:77px' class="ft1"><pre><font face='Arial'>destination</font></pre></span> <span name = "INTRA" style='top:700px; left:143px' class="ft1"><pre><font face='Arial'>port</font></pre></span> <span name = "INTRA" style='top:700px; left:175px' class="ft1"><pre><font face='Arial'>numbers.</font></pre></span> <span name = "INTRA" style='top:700px; left:233px' class="ft1"><pre><font face='Arial'> Port</font></pre></span> <span name = "INTRA" style='top:700px; left:272px' class="ft1"><pre><font face='Arial'>dress</font></pre></span> <span name = "INTRA" style='top:700px; left:317px' class="ft1"><pre><font face='Arial'>of</font></pre></span> <span name = "INTRA" style='top:700px; left:347px' class="ft1"><pre><font face='Arial'>all</font></pre></span> <span name = "INTRA" style='top:700px; left:379px' class="ft1"><pre><font face='Arial'>binary</font></pre></span> <span name = "INTRA" style='top:700px; left:431px' class="ft1"><pre><font face='Arial'>ones</font></pre></span> <span name = "INTRA" style='top:700px; left:466px' class="ft1"><pre><font face='Arial'>stack.</font></pre></span> <span name = "INTRA" style='top:712px; left:77px' class="ft1"><pre><font face='Arial'>number , in this context, represents a</font></pre></span> <span name = "INTRA" style='top:712px; left:272px' class="ft1"><pre><font face='Arial'>(255.255.255.255) will be received by</font></pre></span> <span name = "INTRA" style='top:712px; left:480px' class="ft1"><pre><font face='Arial'>Multicasts are, in effect, filtered</font></pre></span> <span name = "INTRA" style='top:724px; left:77px' class="ft1"><pre><font face='Arial'>software port, not a hardware port.</font></pre></span> <span name = "INTRA" style='top:724px; left:272px' class="ft1"><pre><font face='Arial'>every host on the local network. Note</font></pre></span> <span name = "INTRA" style='top:724px; left:466px' class="ft1"><pre><font face='Arial'>broadcasts. The multicaster does not</font></pre></span> <span name = "INTRA" style='top:736px; left:91px' class="ft1"><pre><font face='Arial'>The concept of port numbers is</font></pre></span> <span name = "INTRA" style='top:736px; left:272px' class="ft1"><pre><font face='Arial'>the word local: a datagram with this</font></pre></span> <span name = "INTRA" style='top:736px; left:466px' class="ft1"><pre><font face='Arial'>address individual messages to each</font></pre></span> <span name = "INTRA" style='top:748px; left:77px' class="ft1"><pre><font face='Arial'>common to both UDP and TCP. The</font></pre></span> <span name = "INTRA" style='top:760px; left:77px' class="ft1"><pre><font face='Arial'>port numbers identify which protocol</font></pre></span> <span name = "INTRA" style='top:772px; left:77px' class="ft1"><pre><font face='Arial'>module sent (or is to receive) the data.</font></pre></span> <span name = "INTRA" style='top:784px; left:77px' class="ft1"><pre><font face='Arial'>Most protocols have standard ports</font></pre></span> <span name = "INTRA" style='top:775px; left:304px' class="ft3"><pre><font face='Arial'><i> Once</i> <i>a</i> <i>connection</i> <i>has</i> <i>been</i> <i>made,</i></font></pre></span> <span name = "INTRA" style='top:796px; left:77px' class="ft1"><pre><font face='Arial'>that are generally used for this. For</font></pre></span> <span name = "INTRA" style='top:808px; left:77px' class="ft1"><pre><font face='Arial'>example, the Telnet protocol generally</font></pre></span> <span name = "INTRA" style='top:799px; left:277px' class="ft3"><pre><font face='Arial'><i>data</i> <i>can</i> <i>be</i> <i>sent.</i> <i>TCP</i> <i>is</i> <i>a</i> <i>sliding</i> <i>window</i></font></pre></span> <span name = "INTRA" style='top:820px; left:77px' class="ft1"><pre><font face='Arial'>uses port 23. The Simple Mail Transfer</font></pre></span> <span name = "INTRA" style='top:832px; left:77px' class="ft1"><pre><font face='Arial'>Protocol (SMTP) uses port 25. The use</font></pre></span> <span name = "INTRA" style='top:823px; left:292px' class="ft3"><pre><font face='Arial'><i>protocol,</i> <i>so</i> <i>there</i> <i>is</i> <i>no</i> <i>need</i> <i>to</i> <i>wait</i> <i>for</i></font></pre></span> <span name = "INTRA" style='top:844px; left:77px' class="ft1"><pre><font face='Arial'>of standard port numbers makes it</font></pre></span> <span name = "INTRA" style='top:856px; left:77px' class="ft1"><pre><font face='Arial'>possible for clients to communicate</font></pre></span> <span name = "INTRA" style='top:847px; left:292px' class="ft3"><pre><font face='Arial'><i>one</i> <i>segment</i> <i>to</i> <i>be</i> <i>acknowledged</i> <i>before</i></font></pre></span> <span name = "INTRA" style='top:868px; left:77px' class="ft1"><pre><font face='Arial'>with a server without first having to</font></pre></span> <span name = "INTRA" style='top:880px; left:77px' class="ft1"><pre><font face='Arial'>establish which port to use.</font></pre></span> <span name = "INTRA" style='top:871px; left:368px' class="ft3"><pre><font face='Arial'><i>another</i> <i>can</i> <i>be</i> <i>sent. </i></font></pre></span> <span name = "INTRA" style='top:892px; left:91px' class="ft1"><pre><font face='Arial'>The port number and the protocol</font></pre></span> <span name = "INTRA" style='top:904px; left:77px' class="ft1"><pre><font face='Arial'>field in the IP header duplicate each</font></pre></span> <span name = "INTRA" style='top:946px; left:52px' class="ft1"><pre><font face='Arial'>Issue 88 (October 1997) page 13</font></pre></span> <span name = "INTRA" style='top:946px; left:610px' class="ft1"><pre><font face='Arial'>File: C04100.5</font></pre></span> <span name = "INTRA" style='top:944px; left:261px' class="ft3"><pre><font face='Arial'><i>PC</i> <i>Network</i> <i>Advisor</i></font></pre></span> <span name = "INTRA" class='nav' style='left: 357px; top: 1010px'><pre>Next page <a href='page0002.htm'>></a></pre></span> <span name = "INTRA" style='top:1050px; left:50px' class="ft4"><pre><b><font color="#FF0000" size="3" face="Arial">New!</font><font color="#FF0000" size="3" face="Arial Narrow"> </font><font size="2" face="Arial">The best sites for quality <a href="http://www.inkjet-printer-cartridges.org">inkjet printer cartridges</a> and the best sites for <a href="http://www.cheap-inkjet-cartridges.com">cheap inkjet cartridges</a></font></b></pre></span></body> <span name = "INTRA" style='top:1100px; left:300px' class="ft4"><pre><b><font color="#FF0000" size="3" face="Arial"><a href="../index.html">Windows Help Desk Home</a> </font></b></pre></span></body></html>