A method for upgrading a plurality of application processor groups (110, 112) in a communication network while maintaining data synchronization, the method comprising: upgrading an application software on an application processor group, selected from the plurality of application processor groups (110, 112), to obtain an upgraded application processor group; characterized in that said method further comprises: comparing at least one data segment on the upgraded application processor group with a corresponding data segment on another application processor group not yet upgraded to determine whether the at least one data segment on the upgraded application processor group has been modified in response to the upgrading; identifying at least one modified data region in the at least one data segment on the upgraded application processor group, based in part on the comparing; preserving session data relating to active sessions handled by the another application processor group from a data region on the another application processor group to a temporary memory space within the upgraded application processor group, wherein the data region on the another application processor group corresponds to the modified data region on the upgraded application processor group; and copying the session data from the temporary memory space to a pre-defined memory space within the upgraded application processor group, wherein the pre-defined memory space is allocated to the modified data region. upgrading an application software on an application processor group, selected from the plurality of application processor groups (110, 112), to obtain an upgraded application processor group; characterized in that said method further comprises: comparing at least one data segment on the upgraded application processor group with a corresponding data segment on another application processor group not yet upgraded to determine whether the at least one data segment on the upgraded application processor group has been modified in response to the upgrading; identifying at least one modified data region in the at least one data segment on the upgraded application processor group, based in part on the comparing; preserving session data relating to active sessions handled by the another application processor group from a data region on the another application processor group to a temporary memory space within the upgraded application processor group, wherein the data region on the another application processor group corresponds to the modified data region on the upgraded application processor group; and copying the session data from the temporary memory space to a pre-defined memory space within the upgraded application processor group, wherein the pre-defined memory space is allocated to the modified data region. comparing at least one data segment on the upgraded application processor group with a corresponding data segment on another application processor group not yet upgraded to determine whether the at least one data segment on the upgraded application processor group has been modified in response to the upgrading; identifying at least one modified data region in the at least one data segment on the upgraded application processor group, based in part on the comparing; preserving session data relating to active sessions handled by the another application processor group from a data region on the another application processor group to a temporary memory space within the upgraded application processor group, wherein the data region on the another application processor group corresponds to the modified data region on the upgraded application processor group; and copying the session data from the temporary memory space to a pre-defined memory space within the upgraded application processor group, wherein the pre-defined memory space is allocated to the modified data region.