1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
|
<html>
<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">2</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%"><strong>
<font face="Arial" size="2" color="#FFFFFF">WAN Technologies Overview</font></strong></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">2.1.2</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">WAN devices</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" COLOR="#000000">
WANs are groups of LANs connected together with communications links
from a service provider. Because the communications links cannot plug
directly into the LAN, it is necessary to identify the various pieces
of interfacing equipment.
<img border="0" src="../../images/1.gif" align="absmiddle" width="12" height="12"><p>
LAN-based computers with data to transmit send data to a router that
contains both LAN and WAN interfaces.
<img border="0" src="../../images/2.gif" align="absmiddle" width="12" height="12">
The router will use the Layer 3 address information to deliver the
data on the appropriate WAN interface. Routers are active and
intelligent network devices and therefore can participate in network
management. Routers manage networks by providing dynamic control over
resources and supporting the tasks and goals for networks. Some of
these goals are connectivity, reliable performance, management
control, and flexibility.</p>
<p>The communications link needs signals in an appropriate format. For
digital lines, a channel service unit (CSU) and a data service
unit (DSU) are required. The two are often combined into a single
piece of equipment, called the CSU/DSU. The CSU/DSU may also be built
into the interface card in the router.
<img border="0" src="../../images/3.gif" align="absmiddle" width="12" height="12"></p>
<p>A modem is needed if the local loop is analog rather than digital.
<img border="0" src="../../images/4.gif" align="absmiddle" width="12" height="12"> Modems
transmit data over voice-grade telephone lines by modulating and
demodulating the signal. The digital signals are superimposed on an
analog voice signal that is modulated for transmission. The modulated
signal can be heard as a series of whistles by turning on the internal
modem speaker. At the receiving end the analog signals are returned to
their digital form, or demodulated. </p>
<p>When ISDN is used as the communications link, all equipment
attached to the ISDN bus must be ISDN-compatible. Compatibility is
generally built into the computer interface for direct dial
connections, or the router interface for LAN to WAN connections.
Older equipment without an ISDN interface requires an ISDN
terminal adapter (TA) for ISDN compatibility.</p>
<p>
Communication servers concentrate dial-in user communication and remote access to a LAN. They may have a mixture of analog and
digital (ISDN) interfaces and support hundreds of simultaneous users.</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/ch02/activity_2_1_2.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/ch02/activity_2_1_2.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>Crossword Puzzle: WAN Devices and Interfaces</p>
<p>Upon completing this activity, the student
will be able to describe devices and interfaces associated with
WAN connections.</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>WAN<p>
<a target="_blank" href="http://www.cisco.com/en/US/tech/tk713/tech_topology_and_network_serv_and_protocol_suite_home.html">
http://www.cisco.com/en/US/tech/tk713/
tech_topology_and_network_ serv_and_protocol_suite_ home.html</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>
</font>
</TD>
</TR>
</TABLE>
</TD>
</TR>
</TABLE>
</font>
</td>
</tr>
</table>
</body>
</html>
|
