HP Survivable Branch Communication zl Module powered by Microsoft Lync Planning and Design Guide 2011-02

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SBM Overview
SBM PSTN Capabilities
In regions that use T1, you might encounter several different ISDN standards.
The SBM T1 interfaces support these types:
■ National ISDN-2 (NI2)—Based on National ISDN-1, this standard was
intended to outline a common set of options that ISDN manufacturers and
public carriers must provide.
■ Class 5 Electric Switching System (5ESS)—Alcatel-Lucent sells
switches that use this standard. Many telcos have such switches, including
AT&T.
■ Class 4 Electric Switching System (4ESS)—Another ISDN standard
used by AT&T, 4ESS is less commonly encountered today. However, some
4ESS switches remain in operation.
■ Digital Multiplex System (DMS) 100—Many telcos also use DMS 100
switches, which are manufactured by Nortel.
Analog with FXO and FXS
The SBM also supports FXO and FXS Telephony Cards, which provide analog
voice connections.
Each analog voice line features an FXO interface that connects to an FXS
interface and receives the signal from it. Traditionally, you found the FXO on
a phone and the FXS interface in the wall jack provided by the PSTN carrier.
On the SBM you still connect FXO interfaces to the wall jack. The FXO
interface, however, receives the signal on behalf of clients behind the PSTN
gateway. In other words, you use the FXO interfaces to provide voice channels
to your branch. Each FXO interface provides one channel in contrast to T1’s
24 and E1’s 30; however, the analog lines are more cost effective.
The SBM’s FXS interfaces deliver an analog signal to a device that is incapable
of receiving digital signals, such as a fax machine. To receive the signal itself,
of course, the SBM must have one or more T1/E1 or FXO interfaces.
For more information about selecting E1/T1, FXO, or FXS interfaces, see
“Considerations for Local PSTN Calls and Planning Your Telephony Cards” on
page 2-5 in Chapter 2: “Design Considerations.”