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
|
<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">4</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">ISDN Concepts</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">4.1.2</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">ISDN standards and access
methods</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">Work on standards for ISDN began in the
late 1960s. A comprehensive set of ISDN recommendations was published
in 1984 and is continuously updated by the International
Telecommunication Union Telecommunication Standardization Sector (ITU-T),
formerly known as the Consultative Committee for International
Telegraph and Telephone (CCITT). The ISDN standards are a set of
protocols that encompass digital telephony and data communications.
The ITU-T groups and organizes the ISDN protocols according to the
following general topic areas:
<img border="0" src="../../images/1.gif" align="absmiddle" width="12" height="12"></font><ul>
<li><font face="Arial" size="2"><b>E Protocols</b> � Recommend
telephone network standards for ISDN. For example, the E.164
protocol describes international addressing for ISDN.</font></li>
<li><font face="Arial" size="2"><b>I Protocols</b> � Deal with
concepts, terminology, and general methods. The I.100 series
includes general ISDN concepts and the structure of other I-series
recommendations. I.200 deals with service aspects of ISDN. I.300
describes network aspects. I.400 describes how the UNI is provided.</font></li>
<li><font face="Arial" size="2"><b>Q Protocols</b> � Cover how
switching and signaling should operate. The term signaling in this
context means the process of establishing an ISDN call.</font></li>
</ul>
<p><font face="Arial" size="2">ISDN standards define two main channel
types, each with a different transmission rate. The bearer channel, or
B channel, is defined as a clear digital path of 64 kbps. It is said to
be clear because it can be used to transmit any type of digitized data
in full-duplex mode. For example, a digitized voice call can be
transmitted on a single B channel. The second channel type is called a
delta channel, or D channel. There can either be 16 kbps for the Basic
Rate Interface (BRI) or 64 kbps for the Primary Rate Interface (PRI).
<img border="0" src="../../images/2.gif" align="absmiddle" width="12" height="12"> The D
channel is used to carry control information for the B channel. </font>
</p>
<p><font face="Arial" size="2">When a TCP connection is established,
there is an exchange of information called the connection setup. This
information is exchanged over the path on which the data will
eventually be transmitted. Both the control information and the data
share the same pathway. This is called in-band signaling. ISDN
however, uses a separate channel for control information, the D
channel. This is called out-of-band signaling.</font></p>
<p><font face="Arial" size="2">ISDN specifies two standard access
methods, BRI and PRI.
A single BRI or PRI interface provides a multiplexed bundle of B and D
channels.</font></p>
<p><font face="Arial" size="2">BRI uses two 64 kbps B channels plus
one 16kbps D channel. BRI operates with many
Cisco routers. Because it uses two B channels and one D channel, BRI
is sometimes referred to as 2B+D.</font></p>
<p><font face="Arial" size="2">The B channels can be used for
digitized speech transmission. In this case, specialized methods are
used for the voice encoding. Also, the B channels can be used for
relatively high-speed data transport. In this mode, the information is
carried in frame format, using either high-level data link control (HDLC) or PPP as the Layer 2
protocol. PPP is more robust than HDLC because it provides a mechanism
for authentication and negotiation of compatible link and protocol
configuration.</font></p>
<p><font face="Arial" size="2">ISDN is considered a circuit-switched
connection. The B channel is the elemental circuit-switching unit.</font></p>
<p><font face="Arial" size="2">The D channel carries signaling
messages, such as call setup and teardown, to control calls on B
channels. Traffic over the D channel employs the Link Access Procedure
on the D Channel (LAPD) protocol. LAPD is a data link layer protocol based on HDLC.</font></p>
<p><font face="Arial" size="2">In North America and Japan, PRI offers
twenty-three 64 kbps B channels and one 64 kbps D channel. A PRI offers the same service as a T1 or DS1
connection. In Europe and much of the rest of the world, PRI offers 30
B channels and one D channel in order to offer the same level of
service as an E1 circuit. PRI uses a Data Service Unit/Channel Service
Unit (DSU/CSU) for T1/E1 connections.</font></p>
<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">
<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>Integrated Services Digital Network (ISDN)<p>
<a target="_blank" href="http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/isdn.htm">
http://www.cisco.com/univercd/cc/
td/doc/ cisintwk/ito_doc/ isdn.htm</a>s</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>
|
