Section: A.36 Monitor of E-RAB release
Content: E-RAB is the key and limited resource for E-UTRAN to deliver services. The release of the E-RAB needs to be monitored as: - an abnormal release of the E-RAB will cause the call(/session) drop, which directly impacts the QoS delivered by the networks, and the satisfaction degree of the end user; - a successfully released E-RAB can be used to setup other requested calls(/sessions). The E-RAB failed to be released will still occupy the limited resource and hence it can not be used to admit other requested calls(/sessions). From a retainability measurement aspect, E-RABs do not need to be released because they are inactive, they can be kept to give fast access when new data arrives. To define (from an E-RAB release measurement point of view) if an E-RAB is considered active or not, the E-RABs can be divided into two groups: a) Continuous flow, E-RABs that are always considered active, i.e. independent of if there is ongoing traffic or not at the moment. Examples: VoIP sessions, Real-time sessions, Live streaming sessions. b) Bursty flow, E-RABs that are only considered active when there is data in UL/DL buffer. Example: Web sessions. How to decide for a particular QCI if the E-RAB is of type bursty flow or continuous flow is outside the scope of this document. The specific reason causing the abnormal and failed release of the E-RAB is required in order to find out the problem and ascertain the solutions. And due to different priority and tolerance for different service type with different OoS level in the networks, the monitor needs to be opened on each service type with OoS level. The E-RAB can be released by E-RAB Release procedure (See 3GPP TS 36.413[ Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP) ] [9]) , UE Context Release procedure (See 3GPP TS 36.413[ Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP) ] [9] and 3GPP TS 36.423[ Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 Application Protocol (X2AP) ] [10]) procedure, Reset procedure(See 3GPP TS 36.413[ Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP) ] [9]) either initiated by eNodeB or MM, Path Switch procedure (See 3GPP TS 36.413[ Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP) ] [9]) and Intra-eNB HO procedure (See 3GPP TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ] [8])E. So performance measurements related to E-RAB Release (See 3GPP TS 36.413[ Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP) ] [9]) and UE Context Release (See 3GPP TS 36.413[ Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP) ] [9]) procedure for each service type with QoS level are necessary to support the monitor of E-RAB release. From quality point of view the E-RAB or UE Context drop ratio of the same values in two different cells may be perceived differently by the end user especially for VoIP services, depending on the duration of the dropped call in comparison to intended call duration when call would not be dropped. For example, having the E-RAB drop ratio of 90% in two cells may be perceived differently by the end user, where in the first cell there was a dropped call which lasted for 99% of intended call duration and in the other cell it lasted only 40%. In the first case, the end user with high probability may not follow up with an additional call request, while in the second it may be the opposite as the main goal of the conversation has not been achieved yet. Therefore, as an extended monitoring especially for VoIP sessions observation of the "Distribution of Normally Released Call (QCI1 E-RAB) Duration" and "Distribution of Abnormally Released Call (QCI1 E-RAB) Duration" is recommended.