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+
+<head>
+<meta http-equiv="Content-Language" content="en-us">
+<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
+<title>Content</title>
+<base target="_self">
+</head>
+
+<body background="../../images/bg.gif" topmargin="0" leftmargin="0" marginheight="0" marginwidth="0" onLoad="window.focus();" link="#808080" vlink="#808080" alink="#808080">
+
+<table border="0" cellpadding="0" cellspacing="0" width="100%">
+ <tr>
+ <td bgcolor="#336666" width="18" valign="top">
+ <img border="0" src="../../images/content_lines.gif" width="16" height="25">
+ <img border="0" src="../../images/transdot.gif" width="2" height="1"></td>
+ <td bgcolor="#336666"><b><font face="Arial" size="2" color="#FFFFFF">5</font></b><font face="Arial" size="2" color="#FFFFFF"><b>.1</b></font></td>
+ <td bgcolor="#336666"><img border="0" src="../../images/transdot.gif" width="10" height="1"></td>
+ <td bgcolor="#336666" width="100%"><b style="mso-bidi-font-weight:normal"><span style="font-family:Arial;mso-bidi-font-family:"Times New Roman""><o:p>
+ <font size="2" color="#FFFFFF">Frame Relay Concepts</font>
+ </o:p>
+ </span></b></td>
+ <td width="9" bgcolor="#336666"> </td>
+ </tr>
+ <tr>
+ <td bgcolor="#669999" height="25" width="18"> </td>
+ <td bgcolor="#669999" height="25"><b>
+ <font face="Arial" size="2" color="#FFFFFF">5.1.6</font></b></td>
+ <td bgcolor="#669999"><img border="0" src="../../images/transdot.gif" width="10" height="1"></td>
+ <td bgcolor="#669999" height="25" width="100%"><strong>
+ <font face="Arial" size="2" color="#FFFFFF">Frame Relay LMI</font></strong></td>
+ <td bgcolor="#669999" height="25" width="9"> </td>
+ </tr></table>
+
+<table border="0" cellpadding="0" cellspacing="0" width="95%" bordercolor="#111111">
+ <tr>
+ <td width="15"></td>
+ <td>
+
+ <font FACE="Arial" SIZE="2">
+ Frame Relay was designed to provide packet-switched data transfer with
+ minimal end-to-end delays. Anything that might contribute to delays
+ was omitted. When vendors came to implement Frame Relay as a separate
+ technology rather than as one component of ISDN, they decided that
+ there was a need for DTEs to dynamically acquire information about the
+ status of the network. This feature was omitted in the original
+ design. The extensions for this status transfer are called the Local
+ Management Interface (LMI).</font><p>
+
+ <font FACE="Arial" SIZE="2">
+ The 10-bit DLCI field allows VC identifiers 0 through 1023. The LMI
+ extensions reserve some of these identifiers. This reduces the number of
+ permitted VCs. LMI messages are exchanged between the DTE and DCE
+ using these reserved DLCIs.
+ <img border="0" src="../../images/1.gif" align="absmiddle" width="12" height="12"></font></p>
+ <p>
+
+ <font FACE="Arial" SIZE="2">
+ The LMI extensions include the following:</font></p>
+ <ul>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ The heartbeat mechanism, which verifies that a VC is operational
+ </font>
+ </li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ The multicast mechanism</font></li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ The flow control</font></li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ The ability to give DLCIs global significance</font></li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ The VC status mechanism</font></li>
+ </ul>
+ <p>
+
+ <font FACE="Arial" SIZE="2">
+ There are several LMI types, each of which is incompatible with the
+ others. The LMI type
+ configured on the router must match the type used by the service
+ provider. Three types of LMIs are supported by Cisco
+ routers:
+ </font>
+ </p>
+ <ul>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ <b>Cisco</b> – The original LMI extensions
+ </font>
+ </li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ <b>Ansi</b> – Corresponding to the ANSI standard T1.617 Annex D</font></li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ <b>q933a</b> – Corresponding to the ITU standard Q933 Annex A</font></li>
+ </ul>
+ <p>
+
+ <font FACE="Arial" SIZE="2">
+ LMI messages are carried in a variant of LAPF frames. This variant
+ includes four extra fields in the header so that they will be
+ compatible with the LAPD frames used in ISDN. The address field
+ carries one of the reserved DLCIs. Following this are the control,
+ protocol discriminator, and call reference fields that do not
+ change. The fourth field indicates the LMI message type.
+ <img border="0" src="../../images/2.gif" align="absmiddle" width="12" height="12"></font></p>
+ <p>
+
+ <font FACE="Arial" SIZE="2">
+ There are one or more information elements (IE) that follow the header.
+ Each IE consists of the following:</font></p>
+ <ul>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ A one byte IE identifier
+ </font>
+ </li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ An IE length field
+ </font>
+ </li>
+ <li>
+
+ <font FACE="Arial" SIZE="2">
+ One or more bytes containing actual data that typically includes
+ the status of a DLCI</font></li>
+ </ul>
+ <p>
+
+ <font FACE="Arial" SIZE="2">
+ Status messages help verify the integrity of logical and physical
+ links. This information is critical in a routing environment because
+ routing protocols make decisions based on link integrity.</font></p>
+ <TABLE bgcolor="#B0AFAF" width="95%" border="0" cellspacing="0" cellpadding="0">
+ <TR>
+ <TD valign="top">
+ <TABLE bgcolor="#669999" width="100%" cellspacing="0" cellpadding="0" border="0">
+ <TR>
+ <TD width="5">
+ <img border="0" src="../../images/lab_toplft.gif" width="116" height="23"></TD>
+ <TD><IMG alt="" height="1" width="3" src="../../images/s.gif"></TD><TD align="right" valign="top">
+ <IMG alt="" src="../../images/corner_ur_7.gif" width="7" height="7"></TD>
+ </TR>
+ </TABLE>
+
+ <TABLE bgcolor="#B0AFAF" width="100%" cellspacing="0" cellpadding="0" border="0">
+ <TR>
+ <TD>
+ <TABLE width="100%" cellpadding="2" cellspacing="0" border="0" bordercolor="#111111">
+ <TR>
+ <TD bgcolor="#ffffff" width="15"> </TD>
+ <TD bgcolor="#ffffff"><font FACE="Arial" SIZE="2" COLOR="#000000">
+ <p><font color="#808080">
+ <a href="javascript:void(0)" onClick="window.open('../../activities/ch05/activity_5_1_6.html','Interactivity','width=740,height=390,toolbar=0,resizable=yes,scrollbars=0,screenX=26,screenY=38,left=26,top=38');">
+ <img border="0" src="../../images/media_icon.gif" width="25" height="25"></a> <b>
+ <a onClick="window.open('../../activities/ch05/activity_5_1_6.html','Interactivity','width=740,height=390,toolbar=0,resizable=yes,scrollbars=0,screenX=26,screenY=38,left=26,top=38');" href="javascript:void(0)">Interactive Media Activity</a></b></font></p>
+ </font><font FACE="Arial" SIZE="2" COLOR="#808080">
+ <p>Drag and Drop: LMI Message Format</p>
+ <p>When the student has completed this activity, the student
+ will be able to correctly order the fields in a LMI message
+ frame.</p>
+ </font><font FACE="Arial" SIZE="2" COLOR="#000000">
+ <p><IMG alt="" height="2" width="1" src="../../images/s.gif"></p></TD>
+ </TR>
+ </TABLE>
+ </TD>
+ </TR>
+ </TABLE>
+ </TD>
+ </TR>
+ </TABLE>
+
+
+
+
+ <TABLE bgcolor="#B0AFAF" width="95%" border="0" cellspacing="0" cellpadding="0">
+ <TR>
+ <TD valign="top">
+ <TABLE bgcolor="#669999" width="100%" cellspacing="0" cellpadding="0" border="0">
+ <TR>
+ <TD width="5">
+ <img border="0" src="../../images/lab_toplft.gif" width="116" height="23"></TD>
+ <TD><IMG alt="" height="1" width="3" src="../../images/s.gif"></TD><TD align="right" valign="top">
+ <IMG alt="" src="../../images/corner_ur_7.gif" width="7" height="7"></TD>
+ </TR>
+ </TABLE>
+
+ <TABLE bgcolor="#B0AFAF" width="100%" cellspacing="0" cellpadding="0" border="0">
+ <TR>
+ <TD>
+ <TABLE width="100%" cellpadding="2" cellspacing="0" border="0" bordercolor="#111111">
+ <TR>
+ <TD bgcolor="#ffffff" width="15"> </TD>
+ <TD bgcolor="#ffffff"><font FACE="Arial" SIZE="2" COLOR="#000000">
+ <p><font color="#808080">
+ <img border="0" src="../../images/links_icon.gif" width="25" height="25">
+ <b>Web Links</b></font></p>
+ </font><font FACE="Arial" SIZE="2" COLOR="#808080">
+
+ <p>Frame Relay<p>
+ <a target="_blank" href="http://www.tele.sunyit.edu/internetworking/55149.htm">
+ http://www.tele.sunyit.edu/
+ internetworking/ 55149.htm</a></font></p>
+
+ <p>
+ <IMG alt="" height="2" width="1" src="../../images/s.gif"></p>
+ </TD>
+ </TR>
+ </TABLE>
+ </TD>
+ </TR>
+ </TABLE>
+ </TD>
+ </TR>
+ </TABLE><p>
+
+ <font face="Arial" size="2"> </font>
+ </td>
+ </tr>
+ </table>
+
+</body>
+
+</html>
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