# US 4,398,063 A · Mobile telephone interoffice handoff limiting method and apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,398,063 A - Document ID: US4398063A - Status: Granted - Kind: A - Application number: 06/200,415 - Filed: 1980-10-24 - Granted: 1983-08-09 - Earliest claimed: 1980-10-24 - Inventors: Ronald J. Hass; Charles F. Hunnicutt - Web page: https://patentgrep.com/patent/US4398063A ## CPC - H04W 36/12: Reselecting a serving backbone network switching or routing node - H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72) ## Abstract Trunks (16-18) included among mobile telecommunication switching offices (MTSO.sub.1 -MTSO.sub.3) serving different mobile service areas (MSA1-MSA3), respectively, and included in a single call connection, are switched to drop from the connection any MTSO beyond a new handoff target MTSO that was already in the connection as a tandem MTSO. ## Claims ### Claim 1 A cellular mobile radiotelephone system including plural mobile telecommunication switching offices (MTSO.sub.1 -MTSO.sub.3), each controlling a different set of cell antenna sites (CS) provided for radio communication with at least one radiotelephone unit (11) that is movable amoung cells of the system, trunk paths (16-18) connected between different pairs of said MTSOs, and an extended call connection including an MTSO for serving said mobile unit through a cell site and including at least a tandem MTSO coupled through said serving MTSO to such mobile unit, the system being characterized in that each MTSO includes means (FIG. 5) for preventing an additional inclusion of one MTSO in said call connection in which that one MTSO is already included as a tandem MTSO. ### Claim 2 (depends on 1) The mobile radiotelephone system in accordance with claim 1 further characterized in that said preventing means includes means (28) for connecting said one MTSO and one of its cell sites to serve said mobile unit in said call connection, and means (23) for disconnecting from said call connection said serving MTSO and any other MTSOs theretofore in said call connection between said one MTSO and said serving MTSO. ### Claim 3 A cellular mobile radiotelephone system including plural mobile telecommunication switching offices (MTSO.sub.1 -MTSO.sub.3), each controlling a different set of cell antenna sites (CS) provided for radio communication with at least one mobile radiotelephone unit movable among cells of the system, trunk paths connected between different ones of said MTSO's, and means (23, 28) in each MTSO for interconnecting said paths to extend call connections, the system being characterized in that each MTSO serving a mobile unit engaged in a call connection includes means (27) for storing for such call connection a list identifying all MTSO's still included in that connection that have been serving MTSO's for the same mobile unit in that same call connection, and means (FIG. 5) for testing said list to detect whether or not a new handoff target MTSO for extending a call connection beyond a serving MTSO is already included in that connection. ### Claim 4 (depends on 3) The cellular mobile radiotelephone system in accordance with claim 3 which is characterized in that it further includes means (25), responsive to the detection of a identification of said target MTSO in said MTSO list, for producing an on-hook signal indication on an incoming trunk path for such call connection. ### Claim 5 (depends on 3) The cellular mobile radiotelephone system in accordance with claim 3 further characterized in that it includes means (23), responsive to the detection of an identification of said target MTSO in said MTSO list, for signalling said target MTSO and any additional MTSO's included in said call connection between said target MTSO and said serving MTSO to disconnect trunk circuits for said call connection. ### Claim 6 In a cellular mobile radiotelephone system including plural mobile telecommunication switching offices (MTSO), each controlling a different set of cell antenna sites (CS) provided for radio communication with mobile radiotelephone units (11) movable among cells of the system, a method (FIG. 5) for extending a call connection involving a mobile unit from one of said MTSOs (e.g. MTSO.sub.2 in FIG. 11) that is serving said mobile unit to a handoff target MTSO (e.g. MTSO.sub.3) without dual inclusion of any MTSO, the method including the steps of determining a suitable new handoff target MTSO (e.g. MTSO.sub.3) for said call connection, testing for the presence of said new handoff target MTSO among MTSOs already included in said call connection, and if said new handoff target MTSO (e.g. MTSO.sub.3) is already present in said call connection, disconnecting said serving MTSO (e.g. MTSO.sub.2) and any other ones (e.g. MTSO.sub.1) of said MTSOs theretofore in said call connection between a prior presence of said new handoff target MTSO (e.g. MTSO.sub.3) and said serving MTSO (e.g. MTSO.sub.2). ### Claim 7 (depends on 6) The call connection extending method in accordance with claim 6 and further including the step of limiting extension of said call connection from an initial serving MTSO to a total number of MTSO's predetermined to be capable of providing at least a predetermined minimum signal transmission quality. ### Claim 8 (depends on 7) The call connection extending method in accordance with claim 7 in which said limiting step includes the steps of maintaining a count of the number of different MTSO's in said call connection, and terminating call-connection extension with respect to any new handoff target MTSO which would, if included, raise said count beyond said predetermined number. ### Claim 9 A cellular mobile radiotelephone system including plural means for serving mobile radiotelephone units in predetermined geographical service areas, respectively, said serving means being interconnectable by trunks, and each one of said serving means including means for providing radio links for communications with selectable one of said mobile radio units, respectively, means for switchably interconnecting one of said units in a call connection through one of said links of said one serving means, as an initial serving means, to either another of said units or a different communication station, and means, responsive to movement of said one unit to a service area served by a different one of said serving means, for bypassing said one link and extending said call connection to said one unit through said interconnecting means of said initial serving means, at least one of said trunks, and at least said different serving means, and means, in at least one of said initial and different serving means, and responsive to movement of said one unit again to an area served by said initial serving means, for initiating drop-back by both (a) disconnecting from said call connection said different serving means and any other of said serving means between said initial serving means and said different serving means in said call connection, and (b) connecting said unit in said call connection through a radio link of said initial serving means.