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:215px; 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:236px; left:129px' 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>The</b></i> <i><b>third</b></i> <i><b>instalment</b></i> <i><b>of</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:268px; left:576px' class="ft1"><pre><font face='Arial'>By Julian Moss</font></pre></span> <span name = "INTRA" style='top:329px; left:77px' class="ft0"><pre><font face='Arial'><b>I</b></font></pre></span> <span name = "INTRA" style='top:333px; left:96px' class="ft1"><pre><font face='Arial'>n the previous instalment of this</font></pre></span> <span name = "INTRA" style='top:333px; left:272px' class="ft1"><pre><font face='Arial'>pens many time servers do support</font></pre></span> <span name = "INTRA" style='top:333px; left:466px' class="ft1"><pre><font face='Arial'>communicate with each other. Com </font></pre></span> <span name = "INTRA" style='top:345px; left:96px' class="ft1"><pre><font face='Arial'>article [PCNA 88, File C04100] we</font></pre></span> <span name = "INTRA" style='top:345px; left:272px' class="ft1"><pre><font face='Arial'>connections using TCP as well. TCP's</font></pre></span> <span name = "INTRA" style='top:345px; left:466px' class="ft1"><pre><font face='Arial'>munication may be infrequent and</font></pre></span> <span name = "INTRA" style='top:357px; left:96px' class="ft1"><pre><font face='Arial'>looked at the transport layer pro </font></pre></span> <span name = "INTRA" style='top:357px; left:272px' class="ft1"><pre><font face='Arial'>built in reliability is of little use in this</font></pre></span> <span name = "INTRA" style='top:357px; left:466px' class="ft1"><pre><font face='Arial'>sporadic, and the amount of informa </font></pre></span> <span name = "INTRA" style='top:369px; left:77px' class="ft1"><pre><font face='Arial'>tocols of the TCP/IP suite: User Data </font></pre></span> <span name = "INTRA" style='top:369px; left:272px' class="ft1"><pre><font face='Arial'>application, because by the time the</font></pre></span> <span name = "INTRA" style='top:369px; left:466px' class="ft1"><pre><font face='Arial'>tion exchanged small. Usually a com </font></pre></span> <span name = "INTRA" style='top:381px; left:77px' class="ft1"><pre><font face='Arial'>gram Protocol (UDP) and Transmi </font></pre></span> <span name = "INTRA" style='top:381px; left:272px' class="ft1"><pre><font face='Arial'>protocol decides that the message may</font></pre></span> <span name = "INTRA" style='top:381px; left:466px' class="ft1"><pre><font face='Arial'>mand sent by the manager will</font></pre></span> <span name = "INTRA" style='top:393px; left:77px' class="ft1"><pre><font face='Arial'>ssion Control Protocol (TCP). We saw</font></pre></span> <span name = "INTRA" style='top:393px; left:272px' class="ft1"><pre><font face='Arial'>have been lost and re sends it, the in </font></pre></span> <span name = "INTRA" style='top:393px; left:466px' class="ft1"><pre><font face='Arial'>generate just a single response.</font></pre></span> <span name = "INTRA" style='top:405px; left:77px' class="ft1"><pre><font face='Arial'>that UDP is an unreliable, connection </font></pre></span> <span name = "INTRA" style='top:405px; left:272px' class="ft1"><pre><font face='Arial'>formation it contained will be out of</font></pre></span> <span name = "INTRA" style='top:405px; left:480px' class="ft1"><pre><font face='Arial'>SNMP uses UDP. This avoids the</font></pre></span> <span name = "INTRA" style='top:417px; left:77px' class="ft1"><pre><font face='Arial'>less protocol suitable for transferring</font></pre></span> <span name = "INTRA" style='top:417px; left:272px' class="ft1"><pre><font face='Arial'>date. UDP is the most suitable protocol</font></pre></span> <span name = "INTRA" style='top:417px; left:466px' class="ft1"><pre><font face='Arial'>overhead of having to maintain con </font></pre></span> <span name = "INTRA" style='top:429px; left:77px' class="ft1"><pre><font face='Arial'>small amounts of data and for broad </font></pre></span> <span name = "INTRA" style='top:429px; left:272px' class="ft1"><pre><font face='Arial'>for real time applications like this, and</font></pre></span> <span name = "INTRA" style='top:429px; left:466px' class="ft1"><pre><font face='Arial'>nections between the SNMP manager</font></pre></span> <span name = "INTRA" style='top:441px; left:77px' class="ft1"><pre><font face='Arial'>cast and multicast applications, and</font></pre></span> <span name = "INTRA" style='top:441px; left:272px' class="ft1"><pre><font face='Arial'>others like audio, video and network</font></pre></span> <span name = "INTRA" style='top:441px; left:466px' class="ft1"><pre><font face='Arial'>and each agent. Because the communi </font></pre></span> <span name = "INTRA" style='top:453px; left:77px' class="ft1"><pre><font face='Arial'>we saw that TCP implements reliabil </font></pre></span> <span name = "INTRA" style='top:453px; left:272px' class="ft1"><pre><font face='Arial'>gaming.</font></pre></span> <span name = "INTRA" style='top:453px; left:466px' class="ft1"><pre><font face='Arial'>cation protocol consists essentially of a</font></pre></span> <span name = "INTRA" style='top:465px; left:77px' class="ft1"><pre><font face='Arial'>ity mechanisms and requires clients to</font></pre></span> <span name = "INTRA" style='top:465px; left:466px' class="ft1"><pre><font face='Arial'>request for data and a reply containing</font></pre></span> <span name = "INTRA" style='top:477px; left:77px' class="ft1"><pre><font face='Arial'>establish a connection with a server</font></pre></span> <span name = "INTRA" style='top:479px; left:272px' class="ft2"><pre><font face='Arial'><i><b>SNMP</b></i></font></pre></span> <span name = "INTRA" style='top:477px; left:466px' class="ft1"><pre><font face='Arial'>the data requested, UDP's lack of reli </font></pre></span> <span name = "INTRA" style='top:489px; left:77px' class="ft1"><pre><font face='Arial'>before data can be transferred. This</font></pre></span> <span name = "INTRA" style='top:489px; left:466px' class="ft1"><pre><font face='Arial'>ability is not a problem. Reliability is</font></pre></span> <span name = "INTRA" style='top:502px; left:77px' class="ft1"><pre><font face='Arial'>month we will examine some of the</font></pre></span> <span name = "INTRA" style='top:502px; left:286px' class="ft1"><pre><font face='Arial'>A slightly more complex UDP ap </font></pre></span> <span name = "INTRA" style='top:502px; left:466px' class="ft1"><pre><font face='Arial'>easily implemented within the SNMP</font></pre></span> <span name = "INTRA" style='top:514px; left:77px' class="ft1"><pre><font face='Arial'>application layer protocols, how they</font></pre></span> <span name = "INTRA" style='top:514px; left:272px' class="ft1"><pre><font face='Arial'>plication is Simple Network Manage </font></pre></span> <span name = "INTRA" style='top:514px; left:466px' class="ft1"><pre><font face='Arial'>manager by re sending a request if no</font></pre></span> <span name = "INTRA" style='top:526px; left:77px' class="ft1"><pre><font face='Arial'>work, and how they exploit the char </font></pre></span> <span name = "INTRA" style='top:526px; left:272px' class="ft1"><pre><font face='Arial'>ment Protocol (SNMP). It allows</font></pre></span> <span name = "INTRA" style='top:526px; left:466px' class="ft1"><pre><font face='Arial'>response is received within a certain</font></pre></span> <span name = "INTRA" style='top:538px; left:77px' class="ft1"><pre><font face='Arial'>acteristics of UDP and TCP.</font></pre></span> <span name = "INTRA" style='top:538px; left:272px' class="ft1"><pre><font face='Arial'>applications to glean information</font></pre></span> <span name = "INTRA" style='top:538px; left:466px' class="ft1"><pre><font face='Arial'>period.</font></pre></span> <span name = "INTRA" style='top:550px; left:272px' class="ft1"><pre><font face='Arial'>about how various elements of the net </font></pre></span> <span name = "INTRA" style='top:550px; left:480px' class="ft1"><pre><font face='Arial'>The main function of SNMP is to al </font></pre></span> <span name = "INTRA" style='top:563px; left:77px' class="ft2"><pre><font face='Arial'><i><b>Time</b></i></font></pre></span> <span name = "INTRA" style='top:562px; left:272px' class="ft1"><pre><font face='Arial'>work are performing, and to control</font></pre></span> <span name = "INTRA" style='top:562px; left:466px' class="ft1"><pre><font face='Arial'>low the manager to get information from</font></pre></span> <span name = "INTRA" style='top:574px; left:272px' class="ft1"><pre><font face='Arial'>the network by means of commands</font></pre></span> <span name = "INTRA" style='top:574px; left:466px' class="ft1"><pre><font face='Arial'>tables maintained by the agents. The ta </font></pre></span> <span name = "INTRA" style='top:586px; left:91px' class="ft1"><pre><font face='Arial'>A network time service is one of the</font></pre></span> <span name = "INTRA" style='top:586px; left:272px' class="ft1"><pre><font face='Arial'>sent over it rather than by physical</font></pre></span> <span name = "INTRA" style='top:586px; left:466px' class="ft1"><pre><font face='Arial'>bles are known as the Management In </font></pre></span> <span name = "INTRA" style='top:598px; left:77px' class="ft1"><pre><font face='Arial'>simplest possible Internet applica </font></pre></span> <span name = "INTRA" style='top:598px; left:272px' class="ft1"><pre><font face='Arial'>configuration of equipment.</font></pre></span> <span name = "INTRA" style='top:598px; left:466px' class="ft1"><pre><font face='Arial'>formation Base (MIB). The MIB is</font></pre></span> <span name = "INTRA" style='top:610px; left:77px' class="ft1"><pre><font face='Arial'>tions. It tells you the time as a 32 bit</font></pre></span> <span name = "INTRA" style='top:610px; left:286px' class="ft1"><pre><font face='Arial'>In SNMP there are two distinct com </font></pre></span> <span name = "INTRA" style='top:610px; left:466px' class="ft1"><pre><font face='Arial'>divided into groups, each containing in </font></pre></span> <span name = "INTRA" style='top:622px; left:77px' class="ft1"><pre><font face='Arial'>value, giving the number of seconds</font></pre></span> <span name = "INTRA" style='top:622px; left:272px' class="ft1"><pre><font face='Arial'>ponents, the SNMP manager and</font></pre></span> <span name = "INTRA" style='top:622px; left:466px' class="ft1"><pre><font face='Arial'>formation about a different aspect of the</font></pre></span> <span name = "INTRA" style='top:634px; left:77px' class="ft1"><pre><font face='Arial'>that have elapsed since midnight on</font></pre></span> <span name = "INTRA" style='top:634px; left:272px' class="ft1"><pre><font face='Arial'>SNMP agents. A manager can commu </font></pre></span> <span name = "INTRA" style='top:634px; left:466px' class="ft1"><pre><font face='Arial'>network. Examples of the information</font></pre></span> <span name = "INTRA" style='top:646px; left:77px' class="ft1"><pre><font face='Arial'>1st January 1900.</font></pre></span> <span name = "INTRA" style='top:646px; left:272px' class="ft1"><pre><font face='Arial'>nicate with many agents. Typically, the</font></pre></span> <span name = "INTRA" style='top:646px; left:466px' class="ft1"><pre><font face='Arial'>that the MIB may contain include the</font></pre></span> <span name = "INTRA" style='top:658px; left:91px' class="ft1"><pre><font face='Arial'>Time servers use the well known</font></pre></span> <span name = "INTRA" style='top:658px; left:272px' class="ft1"><pre><font face='Arial'>SNMP manager would be an applica </font></pre></span> <span name = "INTRA" style='top:658px; left:466px' class="ft1"><pre><font face='Arial'>name, type and speed of a network in </font></pre></span> <span name = "INTRA" style='top:670px; left:77px' class="ft1"><pre><font face='Arial'>port number 37. When your time client</font></pre></span> <span name = "INTRA" style='top:670px; left:272px' class="ft1"><pre><font face='Arial'>tion running on the network man </font></pre></span> <span name = "INTRA" style='top:670px; left:466px' class="ft1"><pre><font face='Arial'>terface, a component's physical location</font></pre></span> <span name = "INTRA" style='top:682px; left:77px' class="ft1"><pre><font face='Arial'>opens UDP port 37 on the server, the</font></pre></span> <span name = "INTRA" style='top:682px; left:272px' class="ft1"><pre><font face='Arial'>ager's console, and agents will run on</font></pre></span> <span name = "INTRA" style='top:682px; left:466px' class="ft1"><pre><font face='Arial'>and the contact person for it, and statis </font></pre></span> <span name = "INTRA" style='top:694px; left:77px' class="ft1"><pre><font face='Arial'>server responds by sending the four</font></pre></span> <span name = "INTRA" style='top:694px; left:272px' class="ft1"><pre><font face='Arial'>user workstations, in hubs, routers and</font></pre></span> <span name = "INTRA" style='top:694px; left:466px' class="ft1"><pre><font face='Arial'>tics such as the number of packets sent</font></pre></span> <span name = "INTRA" style='top:706px; left:77px' class="ft1"><pre><font face='Arial'>bytes of time information.</font></pre></span> <span name = "INTRA" style='top:706px; left:272px' class="ft1"><pre><font face='Arial'>other pieces of network hardware.</font></pre></span> <span name = "INTRA" style='top:706px; left:466px' class="ft1"><pre><font face='Arial'>and the number that wereundeliverable.</font></pre></span> <span name = "INTRA" style='top:718px; left:91px' class="ft1"><pre><font face='Arial'>For such a simple transaction UDP</font></pre></span> <span name = "INTRA" style='top:718px; left:286px' class="ft1"><pre><font face='Arial'>All communication is between the</font></pre></span> <span name = "INTRA" style='top:730px; left:77px' class="ft1"><pre><font face='Arial'>is perfectly adequate, though as it hap </font></pre></span> <span name = "INTRA" style='top:730px; left:272px' class="ft1"><pre><font face='Arial'>manager and an agent. Agents don't</font></pre></span> <span name = "INTRA" style='top:732px; left:466px' class="ft2"><pre><font face='Arial'><i><b>Object</b></i> <i><b>IDs</b></i></font></pre></span> <span name = "INTRA" style='top:754px; left:480px' class="ft1"><pre><font face='Arial'>Data is addressed using object IDs.</font></pre></span> <span name = "INTRA" style='top:766px; left:466px' class="ft1"><pre><font face='Arial'>These are written as sequences of num </font></pre></span> <span name = "INTRA" style='top:778px; left:466px' class="ft1"><pre><font face='Arial'>bers separated by periods, rather like</font></pre></span> <span name = "INTRA" style='top:773px; left:103px' class="ft3"><pre><font face='Arial'><i> A</i> <i>network</i> <i>time</i> <i>service</i> <i>is</i> <i>one</i> <i>of</i> <i>the</i></font></pre></span> <span name = "INTRA" style='top:790px; left:466px' class="ft1"><pre><font face='Arial'>long IP addresses. Each number going</font></pre></span> <span name = "INTRA" style='top:802px; left:466px' class="ft1"><pre><font face='Arial'>from left to right represents a node in</font></pre></span> <span name = "INTRA" style='top:797px; left:87px' class="ft3"><pre><font face='Arial'><i>simplest</i> <i>possible</i> <i>Internet</i> <i>applications.</i> <i>It</i></font></pre></span> <span name = "INTRA" style='top:814px; left:466px' class="ft1"><pre><font face='Arial'>a tree structure, with related informa </font></pre></span> <span name = "INTRA" style='top:826px; left:466px' class="ft1"><pre><font face='Arial'>tion being grouped in one branch of the</font></pre></span> <span name = "INTRA" style='top:821px; left:83px' class="ft3"><pre><font face='Arial'><i>tells</i> <i>you</i> <i>the</i> <i>time</i> <i>as</i> <i>a</i> <i>32 bit</i> <i>value,</i> <i>giving</i></font></pre></span> <span name = "INTRA" style='top:838px; left:466px' class="ft1"><pre><font face='Arial'>tree. There are standardised object IDs</font></pre></span> <span name = "INTRA" style='top:850px; left:466px' class="ft1"><pre><font face='Arial'>for commonly used items of informa </font></pre></span> <span name = "INTRA" style='top:845px; left:93px' class="ft3"><pre><font face='Arial'><i>the</i> <i>number</i> <i>of</i> <i>seconds</i> <i>that</i> <i>have</i> <i>elapsed</i></font></pre></span> <span name = "INTRA" style='top:862px; left:466px' class="ft1"><pre><font face='Arial'>tion, and also a section for vendor spe </font></pre></span> <span name = "INTRA" style='top:874px; left:466px' class="ft1"><pre><font face='Arial'>cific information. The assignment of</font></pre></span> <span name = "INTRA" style='top:869px; left:101px' class="ft3"><pre><font face='Arial'><i>since</i> <i>midnight</i> <i>on</i> <i>1st</i> <i>January</i> <i>1900. </i></font></pre></span> <span name = "INTRA" style='top:886px; left:466px' class="ft1"><pre><font face='Arial'>object IDs is controlled by the Internet</font></pre></span> <span name = "INTRA" style='top:898px; left:466px' class="ft1"><pre><font face='Arial'>Assigned Numbers Authority (IANA).</font></pre></span> <span name = "INTRA" style='top:946px; left:52px' class="ft1"><pre><font face='Arial'>Issue 91 (January 1998) page 13</font></pre></span> <span name = "INTRA" style='top:946px; left:610px' class="ft1"><pre><font face='Arial'>File: C04100.9</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>