3Com SuperStack 3 NBX Administrator's Manual page 309

Figure 128 ISDN PRI Span List Dialog Box
5 From the CO Switch Protocol pull-down list, select AT&T Custom - 4ESS.
6 Click OK to enable the 4ESS protocol and exit from the dialog box.
Otherwise click Apply to enable 4ESS, stay in the Modify Span dialog box,
and configure Call-By-Call Service. See "Configuring Call-By-Call Service"
in the next section.
Configuring Call-By-Call Service
You order the optional Call-By-Call Service from your long-distance
carrier, only if you order the 4ESS protocol. 3Com does not support
Call-By-Call Service with any other protocol.
To configure Call-By-Call Service:
1 In the Modify Span dialog box, click the Enable Call-By-Call Service check
box.
2 In the Carrier Identification Code text box, type the identification code for
your long-distance carrier.
Your long-distance carrier can supply this code at the time that you order
PRI services, or you can ask the carrier for their code number. Another
way to obtain the code is to access the web site for the North American
Number Plan Administration (http://www.nanpa.com). In the menu in the
left frame, expand Number Assignments, and click Carrier Identification
Codes. Follow the instructions to download and unzip the two files
Configuring and Managing T1 Digital Line Cards 309