| Number | Date | Country | Kind |
|---|---|---|---|
| 63-240981 | Sep 1988 | JPX |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3916177 | Greenwald | Oct 1975 | |
| 4390953 | Johnstone | Jun 1983 | |
| 4520233 | Smith | May 1985 | |
| 4695946 | Andreasen | Sep 1987 | |
| 4766548 | Cedrone | Aug 1988 | |
| 4823290 | Fasack | Apr 1989 | |
| 4823343 | Takahashi | Apr 1989 | |
| 4829560 | Evanyk | May 1989 | |
| 4893248 | Pitts | Jan 1990 | |
| 4962449 | Schlesinger | Oct 1990 | |
| 4974255 | Defay | Nov 1990 |
| Number | Date | Country |
|---|---|---|
| 61-6426 | Feb 1986 | JPX |
| 61-250715 | Nov 1986 | JPX |
| 62-95621 | May 1987 | JPX |
| 62-134750 | Jun 1987 | JPX |
| 1140260 | Jun 1989 | JPX |
| Entry |
|---|
| Telecommunications, Apr. 1986, "ITT Security Modem", p. 101, vol. 20, No. 4. |
| Electronics, Mar. 1984, "Call-Back Schemes Ward off Unwanted Access by Telephone", pp. 131-135. |
| IBM Program Announcement, Jun. 16, 1987, Information Systems Group, North-Central Marketing Division, South-West Marketing Division, pp. 287-235 through 287-237. |