Making PPP/MLPPP Connections

PPP/MLPPP

Chapter 6: Point -t o-Point Communications: PPP/MLPPP

Bonding Using the &, I and + Characters

You can use the &, ! and + characters to bond two channels together when performing channel bonding (available only with the MLPPP protocol).

When you use the &, +, or! characters with the MLPPP protocol, the TA regards the number following that character as a second phone number. When used with MLPPP, the TA first dials the number given before the &, +, or! character. After establishing the LCP (Link Control Protocol) and authenticating (if requested), the TA dials the second number (the number after the &, +, or! character).

This is an alternative method to set up a MultiLink PPP call as opposed to using the &J1 command, which dials the given number twice rather than dialing two different numbers.

Example: ATD5551000&5553000 dials 5551000 first, sets up the LCP and authenticates, and then dials 5553000 and sets up the LCP and authenticates on the second B-channel (thus setting up an MLPPP call).

Note: Using these characters with any protocol other than the PPP/MLPPP protocol does not result in the use of two B-channels at this time.

Making a PPP or MLPPP connection is not as simple as using a terminal emulation program and dialing one or two phone numbers. Using the PPP data protocol provided by the TA (!Z=9) requires that the TA receives PPP-formatted data from the terminal. If the TA does not receive PPP-formatted data, the data is discarded by the TA and never sent to the peer. The TA can receive PPP-formatted data from the peer and send it to the terminal, but if it is sending the data to a terminal emulation program running on the terminal, the data appears as garbage.

The PPP data protocol requires PPP data to be sent from the terminal in order for the data to be sent to the other side. The MultiLink protocol requires the PPP protocol to establish itself on one B-channel before the second channel is dialed. The LCP can be established only if data is sent by the terminal to the TA. Negotiation actually occurs between the local terminal and the remote peer. The TA simply views the negotiation, so it knows how to negotiate on the second B-channel. When the second B-channel connects, the local terminal is unaware and doesn’t participate in the LCP negotiation. Therefore, the TA must mimic the negotiation that was witnessed on the first channel.

For example, sending ATDT5551000&5553000 from a terminal emulation program to the TA does NOT cause the TA to dial two channels and bring up the 128K LED. However, if that dial command was given by Windows Dial-Up Networking, for example, then there is a chance that the TA dials two channels and brings up the 128K LED if the user name and password are correct, if the IP address is okay, and if the peer allows a MultiLink connection. If MultiLink is not allowed, then the TA uses one channel for the PPP connection. If the user name or password are invalid or incorrect, the connection is terminated. If an IP address is in conflict, the connection is terminated as well.

Software Applications that can Format PPP Data

Software applications that can format PPP Data for Microsoft-compatible PCs include Windows Dial-Up Networking (DUN) and WinSock.

Software applications that can format PPP Data for Apple Macintoshes include OT/PPP, MacPPP, FreePPP, GearBox, and pppd via Internet Connect (Mac OS X).

Dynamic Bandwidth Allocation (DBA)

Dynamic Bandwidth Allocation (DBA) supports the addition and removal of data channels according to the level of throughput through the TA and according to analog POTS port use.

If throughput is above a given threshold, a second data channel is added to facilitate higher throughput.

If throughput drops below a given threshold, the second channel is removed to save the cost of having the second B-channel active but not fully used.