V.92 Technology Summary

Quick Connect Theory of Operations

One of the main drawbacks of using the Internet over the public switched telephone network (PSTN) is the amount of time it takes to establish a connection to an Internet Service Provider (ISP). Unfortunately, the time it takes to establish a physical link between the two modems through the PSTN is time-consuming and little can be done to speed things up. Nevertheless, it is likely that we can save a second or so here by qualifying dial tone for a couple hundred milliseconds (instead of 700-800 ms) and shortening the DTMF digit duration and inter-digit delay. Not much else can be done in this area so we will concentrate on optimizing the final three stages of the PPP establishment.

We can drastically reduce the amount of time it takes to establish a PPP connection by saving time in two key areas. First, we recognize that the analog channel consists of the local loop from the client modem to its local central office. The analog channel characteristics (equalizer taps and echo canceller taps) are saved in non-volatile memory from a V.90 (standard train) connection. Similarly, the digital characteristics are saved in nonvolatile memory. On subsequent calls to a fast train-equipped server modem, the client modem examines the answer tone to verify that the line conditions are similar to its saved parameters. If the parameters match, a fast connection is attempted. If they do not match, a regular V.90 handshake commences.

Implications and Usage Models

In the simplest application, quick connect allows users to go from launch to activity in a much shorter time than was previously allowed with traditional standard training times. This improves the user model, and makes the connection more transparent than before. As quick connect is deployed more widely, primarily in central site modems, a different user model can be conceived. With quick connect, the IP connection between the ISP and the client can be maintained, while the physical connection between the POP and the client modem becomes dynamic. When the client requires more information or makes an IP request, the modem quick connects with the central site without having to log on again. This frees up a port when the client is idle, yet allows the user to remain online. This requires changes in the client ISP software and the ISP host software, but allows greater central site port utilization. It allows users to remain virtually online for extended periods of time while using a switched-circuit connection.

Modem-on-Hold/Call-Waiting Survival Background

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 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 modem-on-hold 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 modem-on-hold 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. Modem-on-hold request denied by remote: restart data connection
5. Modem-on-hold request denied by remote: clear down data connection

Figure 1-2 illustrates when a modem on hold 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. Figure 1-2.


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.

PCM Upstream Topology

PCM Upstream operates in a topology similar to that of V.90, where there must be only one analog loop, between the APCM and the central office.

PCM Upstream Implications and User Model

Unlike quick connect and modem-on-hold, PCM Upstream does not fundamentally change the modem's user model. It does provide some extra utility for services that require more symmetric data flow.

Summary

While much of the industry interest is in broadband DSL and Cable connection, for the next five years, the majority of connections to the Internet will still be via standard dial-up modems. As the next-generation modem standard, V.92 focuses not on speed, but on ease of use and better functionality. Increases in speed are indeed provided through PCM Upstream. Modem-on-hold and quick connect can approximate the always-on and simultaneous voice and data functions of broadband. These functions will be appearing throughout early 2001. Modems that have these features provide a better user experience when connecting to the Internet.