ADTRAN L128T user manual Ordering ISDN, Interoperability, Connecting to the Internet

Chapter 1: Understanding ISDN and the Express L128/L128T

Ordering ISDN

When ordering ISDN from the telephone company, request EZ-ISDN 1 (Ca- pability Package U) to ensure it is set up properly. EZ-ISDN 1 is recommend- ed by the industry for most home office/small business applications. If this is not available from your service provider or you would like more information regarding ordering ISDN, see the ADTRAN document Ordering ISDN Service User Guide part number 60000.015-8 or contact your telephone company for al- ternative line configurations. The Ordering ISDN Service User Guide is avail- able on the ADTRAN home page at http://www.adtran.com or by calling

ADTRAN.

Interoperability

The Express L128/L128T is standards based and uses PPP developed by Inter- net Engineering Task Force (IETF). PPP provides a standard method of trans- porting multiprotocol datagrams over point-to-point links. PPP is widely accepted by many ISDN bridge/router manufacturers. The Express L128/ L128T will negotiate Multilink PPP when connecting both B-channels. The Bandwidth Allocation Protocol (BAP) may also negotiate, which enhances the management of adding and removing a B-channel. Data compression is also supported using LZS® technology from hi/fn™.

Connecting to the Internet

Internet Service Providers (ISPs) assign an IP address to use when connected to their service using PPP negotiation. This assignment is based on the as- sumption that the user has an ISDN terminal adapter running PPP async-to- sync conversion or another rate adaption where the PPP negotiation is termi- nated inside the PC’s IP stack. However, if an ISDN-Ethernet gateway device is used, the ISP must preassign the customer a subnet which uses multiple IP addresses. This may result in a much higher cost to the user.

The Express L128/L128T permits the user to assign any IP addresses to the unit and computers. Operations on the network can occur normally. In fact, one B-channel can connect to the ISP using NAT while the other B-channel connects to another “private” or “fake” network. All packets transmitted or re- ceived over the ISP connection are translated. The Express L128/L128T keeps track of the computers that request services over the Internet. A web server ad- dress can be assigned under the Configuration/IP/NAT menu that allows

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