Chapter Two: Getting Started | 3. Choose a connection protocol 22 |
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Only one PHONE port can be used when an MLPPP + BACP connection is active. However, since MLPPP + BACP may only be using one B-channel, either PHONE 1 or PHONE 2 may not be available. For example, if PHONE 2 was in use when the data connection was established, the data connection uses telephone number 1. Even though telephone number 2 becomes available when PHONE 2 hangs up, the data connection does not switch over. If you try to use PHONE 1, you will get a busy signal.
Multilink PPP + AO/DI
Always On/Dynamic ISDN uses the ISDN D-channel to maintain a permanent connection to your ISP or corporate network. This connection operates at 9.6 kbps using the X.25 protocol. It can be used to send and receive low-bandwidth data, such as e-mail or web-based push content.
AO/DI incorporates BACP, and uses it to monitor incoming and outgoing traffic. When traffic volume warrants, it enables one or two B-channels to meet the demand. For information on AO/DI, see “Configuring AO/DI” on page 63.
As with MLPPP, MLPPP + AO/DI reserves both B-channels for its exclusive use. This means that if your Internet connection uses MLPPP + AO/DI, you will not be able to make or receive other data calls.
MLPPP + AO/DI can drop both B-channels, allowing you to make or receive two analog calls. Since the data connection is still active on the D-channel, you can use both phone ports at any time. Note, however, that the speed of the D-channel (9.6 kbps) is much slower than a B-channel (64 kbps).
V.120
V.120 was designed to allow non-ISDN devices to communicate with the ISDN network. The DIVA LAN ISDN Modem provides support for V.120, so you can connect with such legacy systems. For example, in many countries around the world, Compuserve offers access to their network over ISDN, using the V.120 protocol.
V.120 operates on a single ISDN B-channel. Since two B-channels are available, the DIVA LAN ISDN Modem can support two V.120 connections at the same time. In general, you should use V.120 only when the site you are connecting to requires it. Once the V.120 connection is active, the DIVA LAN ISDN Modem automatically establishes a PPP connection on top of it. This is why you will see this option listed as PPP over V.120 on the configuration screens.
A V.120 connection will never be disconnected to allow an incoming or outgoing analog call. If two V.120 connections are active, no analog calls can be made.
Summary
The following summary will help you determine how ISDN channels are assigned by the various connection protocols. This summary assumes that call bumping is enabled.
•If a data connection using any MLPPP-related protocol is connected, it reserves both ISDN B-channels. This means that no other data call can be established.
•If a data connection using MLPPP is connected, only one PHONE port can be used at a time.
•If a data connection using MLPPP-BACP is connected, one PHONE port (in most cases PHONE 2), will not be available.
•If a data connection using MLPPP-AO/DI is connected on one or both ISDN B-channels, one or both B-channels will be dropped to allow an incoming or outgoing analog call to connect.
•Data connections using PPP or V.120 are established first on telephone number 1, then on telephone number 2. If two PPP or V.120 data connections are active, no PHONE ports are available.
•If both PHONE ports are in use, no data calls can be established. Unless you are using AO/DI, which can make use of the D-channel.
