Method for switching cell site controllers

A radio frequency communication system includes a cell site (FIG. 1), the cell site including an on-line controller (100), an off-line controller (101) and one or more peripheral units (107, 108, 110, 112, 114) arranged to support the on-line controller. The cell site is arranged to switch from the on-line controller to the off-line controller based upon a failure of the on-line controller or a failure of any peripheral unit of the one or more peripheral units arranged to support the on-line controller.

FIELD OF THE INVENTION
 This application relates to radio frequency ("RF") communication system
 cell sites with redundant controllers including, but not limited to, a
 method for switching cell site controllers.
 BACKGROUND OF THE INVENTION
 Modern radio frequency ("RF") communication systems such as, for example,
 the "iDEN" system which is commerciallly available from Motorola, Inc. of
 Schaumburg, Ill., have one or more cells. As is known, each cell is served
 by a corresponding cell site, with each cell site being controlled by a
 controller unit. In high-performance systems, each cell site contains
 redundant controllers. With this arrangement, one controller is on-line
 (the "on-line controller"), while the other controller is off-line (the
 "off-line controller"). If the on-line controller fails, the off-line
 controller is arranged to take over control of the cell site.
 In the past, each of the multiple controllers was coupled to the RF system
 backbone by means of a dedicated link such as, for example, a T1 link.
 Obviously, for multiple controllers, this arrangement requires multiple
 links for each cell site. One problem with this arrangement, of course, is
 the cost of the multiple links.
 To remedy the problem of the multiple links, in the past a single link has
 been provided to the cell site, with the single link being split into two
 (2) parallel branches, each branch then being coupled to one of the two
 controllers. Further, as above, the controllers were programmed with a
 software algorithm so that, when the on-line controller failed, it would
 "pass off" control to the off-line controller. The off-line controller
 would then take over and operate the cell site.
 It is known that a cell site controller typically includes one or more
 peripheral units arranged to support the controller. Accordingly, the
 proper functioning of a cell site depends not only on the proper
 functioning of the cell site's on-line controller but also on the proper
 functioning of the one or more peripheral units arranged to support the
 cell site's on-line controller.
 One problem with the prior switching method was that it switched the cell
 site from the on-line controller to the off-line controller based solely
 on whether the on-line controller itself failed, and without regard to the
 status of any peripheral units arranged to support the on-line controller.
 This problem is illustrated below.
 One example of a peripheral unit that is typically arranged to support an
 on-line controller is a time frequency reference ("TFR") unit. It is known
 that an on-line controller can continue to operate for some time after the
 failure of its time frequency reference unit. As a result of the prior
 switching method, therefore, the on-line controller would continue to
 control the cell site even though its time frequency reference has failed.
 In this case, the cell site's timing ultimately will drift, then fail,
 probably within 30-40 minutes, thus bringing down the entire cell site.
 In the foregoing example it must be appreciated that whilst the on-line
 controller continues to operate with its failed time frequency reference,
 at all times there remain available for use the off-line controller with
 its corresponding good time frequency reference. However, since the prior
 switching method was based solely on the failure of the on-line controller
 itself and without regard to the status of the on-line controller's
 supporting peripheral units, the cell site was deprived of the opportunity
 to switch to the off-line controller in a timely manner.
 In summary, there is a need for an improved method for switching cell site
 controllers.

DESCRIPTION OF THE PREFERRED EMBODIMENT
 Briefly, in a cell site of a radio frequency communication system, the cell
 site including an on-line controller, an off-line controller, and
 including one or more peripheral units arranged to support the on-line
 controller, there is disclosed a method of switching from the on-line
 controller to the off-line controller, the method comprising the steps of,
 first, detecting a failure of the on-line controller or a failure of at
 least one peripheral unit of the one or more peripheral units arranged to
 support the on-line controller and, second, based on detecting the failure
 of the on-line controller or the failure of at least one peripheral unit
 of the one or more peripheral units arranged to support the on-line
 controller, switching to the off-line controller.
 Referring now to FIG. 1, there is shown a typical radio frequency
 communication system cell site 1 suitable for demonstrating the present
 invention. As shown, the cell site 1 is linked to the rest of the fixed
 network equipment 301 by means of a T1 link 201. Through switching by the
 fixed network equipment 301, the cell site 1 is connected to the
 operations and maintenance center 300 by means of an X.25 link 302. The
 cell site may comprise, for example, an iDEN system cell site. As
 discussed below, the cell site includes an on-line controller, an off-line
 controller, and includes one or more peripheral units arranged to support
 the on-line controller.
 As shown, the cell site 1 includes two redundant cell site controllers,
 also known as "access controller gateway units," with the first access
 controller gateway unit designated "ACG-A," reference number 100, and the
 second access controller gateway unit designated "ACG-B," reference number
 101. Also, these two redundant cell site controllers 100 and 101 are
 interconnected to a plurality of base radios 106A, 106B and 106C by means
 of an Ethernet link 200.
 Still referring to FIG. 1, the first controller 100 is coupled to a first
 dedicated network transition module designated "NTM-A," reference number
 102, by means of a first link 202. Likewise, the second controller 101 is
 coupled to a second dedicated network transition module designated
 "NTM-B," reference number 103, by means of a second link 203. In turn, the
 two network transition modules 102 and 103 couple the controller units 100
 and 101 to the channel service unit ("CSU") 104 by means of a third link
 212 and a fourth link 213. In turn, the channel service unit 104 is
 coupled to the fixed network equipment 301 by means of the T1 link 201.
 The modules 102 and 103 also negotiate control of the T1 link 201 by means
 of a shared synchronization link 211.
 A first group of one or more peripheral units, collectively designated "A"
 in FIG. 1, is arranged to support the first controller 100. This first
 group of peripheral units includes a first time frequency reference unit
 designated "TFR-A," reference number 108, a base monitor radio designated
 "BMR," reference number 107, and an environmental alarm system designated
 "EAS," reference number 110. Since the present invention is applicable in
 situations where still further peripheral units are arranged to support
 the first controller 100, the first group of peripheral units is depicted
 as including other peripheral units designated "X," reference number 112,
 and "Z," reference number 114. It will be appreciated that peripheral
 units X and Z may comprise peripheral units now existing or created in the
 future. With respect to the first group of peripheral units, note the
 first time frequency reference unit 108 and the peripheral unit X are
 arranged to support the first controller 100 exclusively, while the base
 monitor radio 107, the environmental alarm system 110 and the peripheral
 unit Z are arranged to support both cell site controllers 100 and 101.
 Also, a second group of one or more peripheral units, collectively
 designated "B" in FIG. 1, is arranged to support the second controller
 101. This second group of peripheral units includes a second time
 frequency reference unit designated "TFR-B," reference number 109, and the
 base monitor radio 107 and the environmental alarm system 110. Since the
 present invention is applicable in situations where still further
 peripheral units are arranged to support the second controller 101, the
 second group of peripheral units is depicted as including the unit Z and a
 further peripheral unit designated "Y," reference number 113. It will be
 appreciated that peripheral unit designated Y may comprise any peripheral
 unit now existing or created in the future. With respect to the second
 group of peripheral units, note the second time frequency reference unit
 109 and the peripheral unit Y are arranged to support the second
 controller 101 exclusively, while the base monitor radio 107, the
 environmental alarm system 110 and the peripheral unit Z are arranged to
 support both cell site controllers 100 and 101.
 Referring now to FIG. 2, there is shown a flow diagram for a method of
 switching between the two redundant cell site controllers 100 and 101,
 that is, a method of switching from the on-line controller to the off-line
 controller. With momentary reference to FIG. 1, it will be appreciated
 that this method is performed by whichever controller--that is, either the
 first controller 100 or the second controller 101--is presently
 functioning as the cell site's on-line controller. In what follows, it
 will be assumed that the first controller 100 is functioning as the
 on-line cell site controller and that the second controller 101 is
 functioning as the off-line cell site controller.
 The process starts, step 501, and then goes to step 503, where it
 determines when the on-line controller has failed. (Here the on-line cell
 site controller is assumed to be the first controller 100, and the
 off-line cell site controller is assumed to be the second controller 101.)
 When step 503 determines that the on-line controller has failed, the
 result is positive and the process goes to step 510. In step 510, the
 process switches the cell site to the off-line controller, here assumed to
 be the second controller 101.
 Otherwise, when step 503 does not determine that the on-line controller has
 failed, the result is negative and the process goes to step 505.
 In step 505, the process determines when a peripheral unit of the one or
 more peripheral units arranged to support the on-line controller has
 failed. As the on-line controller is the first controller 100, step 505
 thus determines when a peripheral unit of the corresponding first group of
 peripheral units has failed, the first group of peripheral units
 comprising the first time frequency reference unit 108, the base monitor
 radio 107, the environmental alarm system 110, and the units X (112) and Z
 (114).
 When step 505 determines that a peripheral unit of the one or more
 peripheral units arranged to support the on-line controller has failed,
 the result is positive and the process goes to step 510. In step 510, the
 process switches the cell site to the off-line controller, here assumed to
 be the second controller 101.
 Otherwise, when step 505 does not determine that a peripheral unit of the
 one or more peripheral units arranged to support the on-line controller
 has failed, the result is negative and the process goes to step 507. In
 step 507, the process returns to start.
 Accordingly, in a radio frequency communication system cell site 1 that
 includes an on-line controller 100, an off-line controller 101, and one or
 more peripheral units 107, 108, 110, 112 and 114 arranged to support the
 on-line controller, there has been disclosed a method of switching from
 the on-line controller to the off-line controller, the method comprising
 the steps of:
 (a) determining (in step 503) when the on-line controller fails;
 (b) when the on-line controller fails, switching (in step 510) to the
 off-line controller;
 (c) determining (in step 505) when a peripheral unit of the one or more
 peripheral units fails; and,
 (d) when a peripheral unit of the one or more peripheral units fails,
 switching (in step 510) to the off-line controller.
 Moreover, in the radio frequency communication system cell site 1, there
 has also been disclosed a method of switching from the on-line controller
 100 to the off-line controller 101, the method comprising the steps of:
 (a) detecting (in step 503) the failure of the on-line controller or (in
 step 505) the failure of at least one peripheral unit; and,
 (b) based on detecting the failure of the on-line controller or the failure
 of at least one peripheral unit, switching (in step 510) to the off-line
 controller.
 The functional and/or structural differences between the present invention
 and previous methods are discussed below.
 One unique aspect of the present invention is the swap of network manager
 and agent functions between the access controller gateway units when a
 redundancy switch occurs. In this invention the on-line controller
 performs the network manager function for the off-line controller and all
 other components of the cell site. Management messages between the
 off-line controller's agent and the system network manager are directed
 through the on-line controller. In contrast, prior controller-switching
 schemes support redundant controllers that act as peers.
 Moreover, previous access controller gateway redundancy methods involved an
 automated version of simple redundancy in which the backup controller was
 able to take control of the system without manual intervention. No
 information regarding the system capabilities of the standby unit were
 involved. In contrast, the present invention uses state information from
 both the primary and the standby units to determine the viability of the
 two controllers in the system. In this manner, the system can operate in a
 degraded fashion, while still performing most of its operations.
 Some results achieved by the present invention are discussed as follows.
 The present invention provides a cost-effective, controller redundancy
 solution for cell sites for which line costs are an issue.
 Some advantages of the present invention over the prior method are
 discussed as follows. In the prior method, no system state or
 configuration information was saved during the control changeover.
 Further, this prior method was not in complete compliance with the site
 restart time required for our customers. It must be appreciated that loss
 of certain parts of the system does not necessarily imply that the system
 will not operate. In the previous method, this was not taken into account.
 In contrast, in the present invention, a degraded mode of operation is
 possible while still processing calls in the site until repairs can be
 made. Accordingly, system reliability and down time are both improved by
 the present invention.
 While the foregoing example depicts a cell site (reference number 1 in FIG.
 1) whose on-line controller (reference number 100 in FIG. 1) includes a
 plurality of peripheral units arranged to support the on-line controller,
 it will be understood that the present invention is equally applicable for
 a cell site having only one (1) peripheral unit arranged to support the
 cell site's on-line controller.
 While various embodiments of a method for switching cell site controllers,
 in accordance with the present invention, have been described hereinabove,
 the scope of the invention is defined by the following claims.