Modem-on-hold (MOH)
A large call and trouble generator for modems stems from users who do not disable call-waiting when online. A call-waiting signal looks to a modem-like a line disconnect, and depending on how the modem is configured, can often result in the modem hanging up. In some cases, users prefer this behavior, because they want to receive the call coming in. Unfortunately, the feature that is enabled for those who want the call is trouble for those who do not.

Call-waiting survival has been identified as another feature required in a next-generation modem standard. Communication between the server and client that enables a rational call-waiting survival allows the client to put the server on hold, or vice versa. The notable application for a Modem-On-Hold™ (MOH) allows the client modem (after seeing call-waiting and optionally processing the call-waiting caller ID), to put the server modem on hold for a short time (e.g., 4 minutes). This allows two callers to have a rational and unhurried conversation. Competitive solutions now allow only seven seconds. This is not enough time to answer, identify the caller, get a phone number, and politely terminate the call. The MOH method allows the server and client modem to negotiate a mutually agreeable time period in which the other remains on hold.

Modem-on-Hold/Call-Waiting Survival Theory of Operations

There are several different scenarios covered by the MOH capability:

1. Incoming Call accepted by local: modem is placed on hold
2. Incoming Call denied by local: continue with data
3. Incoming Call accepted by local: clear down data connection
4. MOH request denied by remote: restart data connection
5. MOH request denied by remote: clear down data connection

Case 1
In the case of call-waiting on the APCM (Client modem) accepted by the DPCM (Server modem). The APCM is interrupted by the call-waiting tone. The client issues a DTMF “D” in order to receive the call-waiting caller ID. From this, the APCM user decides that he wants to accept the call. The APCM and DPCM then negotiate the maximum time that the server will allow before hanging up. The APCM flashes the line, the user is connected to the voice call, and the DPCM is on hold. When coming back, another flash hook connects the APCM and DPCM, at which time they renegotiate the connection using quick connect.

Case 2
When a MOH request is denied. The two modems negotiate, and the server denies the hold; then the two modems reconnect. This is the call-waiting survival mode.

Modem-on-Hold/Call-Waiting Survival Implications and User Model
This model provides the broadband-like service of data and voice service on the same line. The service does not allow for simultaneous voice and data, as broadband does. However, it does allow a single phone line to serve as voice and data; the data call is returned without resetting the user’s context. Additionally, the model allows ISPs and OSPs to determine the maximum amount of on-hold time. ISPs and OSPs can potentially charge for this service, and provide a level of service (number of minutes on hold) based on the assessed amount.

Many households use the same phone line for both voice calls and data (Internet), so when the user is browsing the Internet, an incoming call cannot get through. MOH allows you to receive an incoming call and stay connected to the Internet (Call-Waiting service from your phone company is all that is required). It also works in reverse; you can initiate a voice call while connected and keep the modem connection.

Your ISP defines the “hold” time. The V.92 specification allows for hold times to be anywhere from 10 seconds to infinite. When you hang up the phone you can resume browsing. Initiating calls is easy with MOH. First, a MOH application is executed. This program suspends the data connection between your modem and the ISP so you can pick up your phone and make an outgoing call in the usual way. The application puts the modem "on-hold", flashes the hook, and a dial tone appears on the extension handset so you can make a call. When your call is complete, the modem will detect an extension on hook, flash the hook twice, and return to the data (Internet) connection.

There are different types of CallerID available from the telephone companies. These services may be called by a different name in other countries. First and foremost, you must have Call Waiting in order to take advantage of MOH. CallerID (CID) is not required. There are 2 types of CID, type 1 and type 2.

Type 1 CID is a service that allows a telephone subscriber to receive information on the incoming call BEFORE the user (or modem) takes the call by going off-hook. Sometimes called on-hook CID, it does not require Call Waiting, but it does require hardware support on the modem board if you want to use this feature via the modem. This is because without specific hardware support, there is no data path from the telephone line to our modem device when the modem is in the on-hook condition.

Type 2 CID (also referred to as CID on Call Waiting) does not require hardware support on the modem board. Type 2 CID is not required for MOH to work. However without type 2 CID support from the Telco, the user will not be able to receive details (telephone number) of the incoming third-party call. For the purposes of a MOH discussion, we will only refer to Type 2 CID.

For MOH functionality, the user must have Call Waiting service from their telephone company at a minimum. Optionally, for CID on CW, the user must have CID on Call Waiting (not just CID) service from the Telco. Most international Telcos support Call Waiting, however it is up to the modem to support the various CW tones in the driver. Please check with your modem manufacturer. Not every international Telco offers CID on Call Waiting as a commercial package, even if it is supported in the Telco equipment. First, check with your telephone company to see if Call Waiting CID is offered as a service. Second, check with your modem manufacturer for a list of countries supported.

Most modem manufacturers will supply a MOH applet with the modem driver. Check with your modem manufacturer for details.

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