LTE Accessibility KPIs

LTE ACCESSIBILITY KPIs

Evolved Radio Access Network (E-UTRAN) E-UTRAN represents the access network of LTEwhich is a network of eNodeBs. For normal user traffic there is no centralized controller in E-UTRAN, i.e. the EUTRAN architecture is considered to be flat. The Evolved eNodeB (eNodeBs 1) are normally inter-connected with each other by means of an interface known as X2 (see Fig.2). The NodeB also interfaces with the User Equipment (UE). T he eNB hosts the PHYsical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Control Protocol (PDCP) layers that include the functionality of user-plane header-compression and encryption. It also offers Radio Resource Control (RRC) functionality corresponding to the control plane. It performs many functions including radio resource management, admission control, scheduling, enforcement of negotiated UL QoS, cell information broadcast, ciphering/deciphering of user and control plane data, and compression/decompression of DL/UL user plane packet headers [1]. Mobility Management Entity (MME) The MME is the key control node for the LTE access network. It is responsible for idle mode UE tracking and paging procedure including retransmissions. It is involved in the bearer activation/deactivation pr ocess and it is also responsible for choosing the S-GW (Serving Gateway) for a UE at the initial attach and at time of intra-LTE handover involving Core Network (CN) node relocation. It is responsible for authenticating the user (by interacting with the HSS (Home Subscriber Server)). Serving Gateway (S - GW) The S-GW routes and forwards user data packets, while also acting as the mobility anchor for the user plane during inter-eNB handovers and as the anchor for mobility between LTE and other 3GPP technologies. Packet Data Network Gateway (P- GW) The P-GW provides connectivity to the UE to external packet data networks by being the point of exit and entry of traffic for the UE. An UE may have simultaneous connectivity with more than one P- GW for accessing multiple Packet Data Networks (PDNs). The P-GW performs policy enforcement, packet filtering for each user, charging support, lawful interception and packet screening. Another key role of the P-GW is to act as the anchor for mobility between 3GPP and non-3GPP technologies such as for instance WiMAX (Worl d Interoprability For Microwave Access) technology. Home Subscriber Server (HSS) The HSS contains users’ SAE subscription data such as EPS subscribed QoS profile and any access restrictions for roaming. It also holds information about PDNs to which user can connect.

Message flows for the initial call set up in LTE

RRC SETUP SUCCESS RATE RRC CONNECTION SUCC / RRC CONN REQUESTS ATTEMPTS

HUAWEI RRC Setup Success Rate = {100}* ([L.RRC.ConnReq.Succ.Emc] + [L.RRC.ConnReq.Succ.HighPri] + [L.RRC.ConnReq.Succ.Mt] + [L.RRC.ConnReq.Succ.MoData] + [L.RRC.ConnReq.Succ.MoSig]) / ([L.RRC.ConnReq.Att.Emc] + [L.RRC.ConnReq.Att.HighPri] + [L.RRC.ConnReq.Att.Mt] + [L.RRC.ConnReq.Att.MoData] + [L.RRC.ConnReq.Att.MoSig])

=L.RRC.ConnReq.Succ /L.RRC.ConnReq.Att

RRC Connection Setup Measurement (Cell) (RRC.Setup.Cell) An RRC connection is a Uu interface connection for carrying user signaling messages. The setup success rate of the RRC connection in a cell directly represents the capability of the cell to provide RRC connection setups for users. The RRC.Setup.Cell measurement unit measures the number of RRC connection setup requests, number of RRC connection setup attempts, and

number of successful RRC connection setups in a cell. The setup success rate of the RRC connection can be calculated on the basis of the reported counters. Figure 1 shows the measurement points of RRC connection setup. Figure 1

Counter The following table describes the counters contained in the "RRC Connection Setup Measurement (Cell) (RRC.Setup.Cell)" measurement unit:

Counter ID

Counter Name

Description

1526726657

L.RRC.ConnReq.Msg

Number of RRC Connection Request messages received from the UE in a cell, including the number of retransmitted messages

1526726658

L.RRC.ConnReq.Att

Number of RRC Connection Request messages received from the UE in a cell, excluding the number of retransmitted messages

1526728217

L.RRC.ConnReq.Att.Emc

Number of RRC Connection Request messages received from the UE for the emergency cause in a cell

1526728218

L.RRC.ConnReq.Att.HighPri

Number of RRC Connection Request messages received from the UE for the highPriorityAccess cause in a cell

1526728219

L.RRC.ConnReq.Att.Mt

Number of RRC Connection Request messages received from the UE for the mt-Access cause in a cell

1526728220

L.RRC.ConnReq.Att.MoSig

Number of RRC Connection Request messages received from the UE for the mo-Signalling cause in a cell

1526728221

L.RRC.ConnReq.Att.MoData

Number of RRC Connection Request messages received from the UE for the mo-Data cause in a cell

1526728216

L.RRC.ConnSetup

Number of RRC Connection Setup messages sent to the UE in a cell

1526726659

L.RRC.ConnReq.Succ

Number of RRC Connection Setup Complete messages received from the UE in a cell

1526728222

L.RRC.ConnReq.Succ.Emc

Number of RRC Connection Setup Complete messages received from the UE for the emergency cause in a cell

1526728223

L.RRC.ConnReq.Succ.HighPri

Number of RRC Connection Setup Complete messages received from the UE for the highPriorityAccess cause in a cell

1526728224

L.RRC.ConnReq.Succ.Mt

Number of RRC Connection Setup Complete messages received from the UE for the mtAccess cause in a cell

1526728225

L.RRC.ConnReq.Succ.MoSig

Number of RRC Connection Setup Complete messages received from the UE for the moSignalling cause in a cell

1526728226

L.RRC.ConnReq.Succ.MoData

Number of RRC Connection Setup Complete messages received from the UE for the moData cause in a cell

NSN RRC Setup Success Rate = 100*sum([SIGN_CONN_ESTAB_COMP]) /sum([SIGN_CONN_ESTAB_ATT_MO_S]+[SIGN_CONN_ESTAB_ATT_MT]+ [SIGN_CONN_ESTAB_ATT_MO_D]+ [SIGN_CONN_ESTAB_ATT_OTHERS]+[SIGN_CONN_ESTAB_ATT_EMG])

ERICSSON RRC Setup Success Rate = 100*pmRrcConnEstabSucc/(pmRrcConnEstabAtt-pmRrcConnEstabAttReatt)

pmRrcConnEstabAtt The total number of RRC Connection Request attempts. Condition: Stepped at reception of RRC message RRC Connection Request. pmRrcConnEstabAttReatt The total number of RRC Connection Request attempts that are considered as re-attempts. Condition: Stepped at reception of RRC message RRC Connection Request while an RRC Connection Setup is already ongoing for that S-TMSI.

pmRrcConnEstabSucc The total number of successful RRC Connection Establishments. Condition: Stepped at reception of RRC message RRC Connection Setup Complete.

S1 SETUP SUCCESS RATE S1 SETUP SUCC / S1 SETUP ATTEMPTS S1 - This is the interface between eNodeBs and MME and S-GW. The signalling protocol fo r S1 is called S1-AP.

HUAWEI S1 Setup Success Rate = L.S1Sig.ConnEst.Succ/ L.S1Sig.ConnEst.Att

The counters measure the number of UE-specific sig naling connection setups on the S1 interface, that is, number of INITIAL UE MESSAGE messages sent from the eNodeB to the MME and number of first S1 messages received from the MME. The eNodeB transmits the UE-specific NAS layer data configuration to the MME through the INITIAL UE MESSAGE. The MME sets up S1 signaling connections based on NAS information in the message. The first S1 interface message received from the MME may be the INITIAL CONTEXT SETUP REQUEST, DOWNLINK NAS TRANSPORT, or UE CONTEXT RELEASE COMMAND message. If t he message is received, an S1 signaling connection is set up successfully.

L.S1Sig.ConnEst.Att

Number of attempts to set up UE-specific signaling connections on the S1 interface

L.S1Sig.ConnEst.Succ

Number of successful UE-specific signaling connection setups on the S1 interface

NSN S1 Setup Success Rate = 100*sum([S1_SETUP_SUCC]) / sum([S1_SETUP_ATT])

S1 Setup Success Ratio KPI name

E-UTRAN S1 Setup Success Ratio

KPI ID

LTE_5014a

Description

The KPI shows the setup success ratio for the elementary procedur e "S1 Setup". When this procedure is finished, S1 interface is operational and other S1 messages can be exchanged.

Measurement

M8000: LTE S1AP

KPI logical formula

S1 SSR=(S1 setup successes / S1 setup attempts)*100%

KPI formula(with Counter IDs)

100*sum([M8000C7]) / sum([M8000C6])

KPI formula (with Counter names)

100*sum([S1_SETUP_SUCC]) / sum([S1_SETUP_ATT])

ERICSSON S1 Setup Success Rate = 1*(pmS1SigConnEstabSucc/pmS1SigConnEstabAtt)

pmS1SigConnEstabAtt This measurement provides the number of S1 Signalling connection establishment attempts for any establishment cause. pmS1SigConnEstabSucc The total number of successful S1 signalling connection establishments.

ERAB SETUP SUCCESS RATE ERAB SETUP SUCC / ERAB SETUP ATTEMPTS

E-RAB : radio and S1 bearers

HUAWEI ERAB_SSR (ALL)=(ERAB Setup Success/ERAB Setup Attempt)X100%

= L.E-RAB.SuccEst/ L.E-RAB.AttEst

E-RAB Setup Measurement (Cell) (E-RAB.Est.Cell) Description

An E-RAB is the access layer bearer for carrying service data of users. The E- RAB setup success rate in a cell directly represents the capability of the cell t o provide E-RAB connection setups for users. The E-RAB.Est.Cell measurement unit measures the number of E-RAB setup attempts and the number of successful E-RAB setups for each service with a different QoS Class Identifier (QCI) in a cell. The number of E -RABs is used as the unit. The setup of one E-RAB is measured as one time. Figure 1 shows the measurement points of an E-RAB setup procedure during a non-handover process. Figure 2 shows the measurement points of an E-RAB setup procedure during a handover. Figure 1

Figure 2

Counter

The following table describes the counters contained i n the "E-RAB Setup Measurement (Cell) (E-RAB.Est.Cell)" measurement unit:

Counter Name

Description

L.E-RAB.AttEst.QCI.1

Number of E-RAB setup attempts initiated by UEs for services with the QCI of 1 in a cell






Number of E-RAB setup attempts initiated by UEs fo r services with the QCI of 4 in a cell


Number of E-RAB setup attempts initiated by UEs fo r services with the QCI of 5 in a cell









L.E-RAB.SuccEst.QCI.1

Number of successful E-RAB setups initiated by UEs fo r services with the QCI of 1 in a cell

















L.E-RAB.InitAttEst

Total number of initial E-RAB setup attempts initiated by UEs in a cell

L.E-RAB.InitAttEst.QCI.1

Number of initial E-RAB setup attempts initiated by UEs for services with the QCI of 1 in a cell




Number of initial E-RAB setup attempts initiat ed by UEs for services with the QCI of 3 in a cell





Counter Name

Description









L.E-RAB.InitSuccEst

Total number of successful initial E- RAB setups initiated by UEs in a cell

L.E-RAB.InitSuccEst.QCI.1

Number of successful initial E-RAB setups initiated by UEs for services with the QCI of 1 in a cell

















L.E-RAB.SuccEst

Total number of successful E-RAB setups initiated by UEs

L.E-RAB.AttEst

Total number of attempts by UEs to initiate E-RAB setup procedures

L.E-RAB.AttEst.HOIn

Total number of E-RAB setup attempts for incoming handovers

L.E-RAB.SuccEst.HOIn

Total number of successful E-RAB setups for incomi ng handovers

L.S1Sig.ConnEst.Att

Number of attempts to set up UE-specific signaling connections on the S1 interface

L.S1Sig.ConnEst.Succ

Number of successful UE-specific signaling connection setups on the S1 interface

NSN ERAB_SSR =100*sum([EPS_BEARER_SETUP_COMPLETIONS]) / sum([EPS_BEARER_SETUP_ATTEMPTS])

M8006C0 / EPS Bearer setup attempts Counter ID: M8006C0

Network element name: EPS Bearer setup attempts

Version: 4.1

NetAct name: EPS_BEARER_SETUP_ATTEMPTS

Description: The number of EPS bearer setup attempts. Each bearer of the "SAE Bearer to Be Setup List" IE is counted. Updated: The receipt of an S1AP:Initial Context Setup Request or an S1AP:E-RAB SETUP REQUEST message sent by the MME to eNB. M8006C1 / EPS Bearer setup completions Counter ID: M8006C1 Network element name: EPS Bearer setup completions Version: 4.1

NetAct name: EPS_BEARER_SETUP_COMPLETIONS

Description: The number of EPS bearer setup completions. Each bearer of the "SAE Bearer Setup List" IE is counted. Updated: The transmission of an S1AP:Initial Context Setup Response or an S1AP:S1AP:E-RAB SETUP RESPONSE message sent by the eNB to MME.

ERICSSON ERAB_SSR = 100*(pmErabEstabSuccInit)+(pmErabEstabSuccAdded)/(pmErabEstabAttInit)+[pmErabEstabAttAdded)

pmErabEstabAttAdded The total number of added E-RAB Establishment attempts. Added E-RABs are all E-RABs present in S1 message E-RAB Setup Request. pmErabEstabSuccAdded The total number of successfully added E-RABs. Added E-RABs are all E-RABs present in S1 message E-RAB Setup Request.

pmErabEstabAttInit The total number of initial E-RAB Establishment attempts. Initial E-RABs are all E-RABs present in t he S1 message Initial Context Setup Request. pmErabEstabSuccInit The total number of successful initial E-RAB Establishments. Initial E-RABs are all E-RABs present in t he S1 message Initial Context Setup Request.

The three KPIs multiplied would result in the Call Setup Success Rate formula.

Call Setup Success Rate (%)

CSSR_ALL = RRC Setup Success Rate x S1 Setup Success rate x ERAB Setup Success Rate

BEARERS IN LTE EPS uses the concept of EPS bearers to route IP traffic from a gateway in the PDN to the UE. A bearer is an IP packet flow with a defined Quality of Service (QoS). The E-UTRAN and EPC together set up a nd release bearers as required by applications.

Two types of Bearer exist – Dedicated bearer and Default bearer. Default bearer is established when a UE is initially attached to LTE network while dedicated bearer is always established when there is n eed to provide QoS to specic service (like VoIP, video etc).

Default Bearer in LTE When LTE UE attaches to the network for the first time, it will be a ssigned default bearer which remains as long as UE i s attached. Default bearer is best effort service. Each default bearer comes with an IP address. UE can have additional default bearers as well. Each default bearer will have a separate IP address. QCI 5 to 9 (Non- GBR) can be assigned to default bearer.

Dedicated Bearer To put it simple, dedicated bearers provides dedicated tunnel to one or more specific traffi c (i.e. VoIP, video etc). Dedicated bearer acts as an additional bearer on t op of default bearer. It does not re quire separate IP address due to the fact that only additional default bearer needs an IP address and therefore dedicated bearer is always linked to o ne of the default bearer established previously. Dedicated bearer can be GBR or non-GBR (whereas default bearer can only be non-GBR). For services like VoLTE we need to provide better user experience and this is where dedicated bearer would co me handy. Dedicated bearer uses Traffic flow templates (TFT) to give special treatment to specific services

Example Usually LTE networks with VoLTE implementations has two default and one dedicated bearer Default bearer 1: Used for signaling messages (sip signaling) related to IMS network. It uses qci 5 Dedicated bearer: Used for VoLTE VoIP traffic. It uses qci 1 and is linked to default bearer 1 Default bearer 2: Used for all other smartphone traffic (video, chat, email, browser etc)

Quality of Service and EPS Bearers In a typical case, multiple applications may be running in a UE at the same time, each one having different QoS requirements. For example, a UE can be engaged in a VoIP call while at the same time browsing a web page or downloading an FTP file. VoIP has more stringent requirements for QoS in terms of delay and delay jitter than web browsing and FTP, while the latter requires a much lower packet loss rate. In order to support multiple QoS requirements, different bearers are set up within EPS, each being associated with a QoS. Broadly, bearers can be classified into two categories based on the nature of the QoS they provide: • Minimum Guaranteed Bit Rate (GBR) bearers which can be used for applications such as VoIP. These have an associated GBR value for which dedicated transmission resources are permanently allocated (e.g. by an admission control function in the eNodeB) at bearer establishment/modification. Bit rates higher than the GBR may be allowed for a GBR bearer if re sources are available. In such cases, a Maximum Bit Rate (MBR) parameter, which can also be associated with a GBR bearer, sets an upper limit on the bit rate which can be expected from a GBR bearer. • Non-GBR bearers which do not guarantee any particular bit rate. These can be used for applications such as web browsing or FTP transfer. For these bearers, no ba ndwidth resources are allocated permanently to the bearer.

In the access network, it is the eNodeB’s responsibility to ensure that the necessary QoS for a bearer over the radio interface is met. Each bearer has an associated Class Identifier (QCI), and an Allocation and Retention Priority (ARP). Each QCI is characterized by priority, packet delay budget and acceptable packet loss rate. The QCI label for a bearer determines the way it is handled in the eNodeB. Only a dozen such QCIs have been standardized so that vendors can all have the same understanding of the underlying service characteristics and thus provide the corresponding treatment, including queue management, conditioning and policing strategy. This ensures that an LTE operator can expect uniform traffic handling behaviour throughout the network regardless of the manufacturers of the eNodeB equipment. The set of standardized QCIs and their characteristics (from which the PCRF in an EPS can select) is provided in Table 2.

An EPS bearer has to cross multiple interfaces as shown in Figure 2.7 – the S5/S8 interface from the P-GW to the S-GW, the S1 interface from the S-GW to the eNodeB, and the radio interface (also known as the LTE-Uu interface) from the eNodeB to the UE. Across each interface, the EPS bearer is mapped onto a lower layer bearer, each with its own bearer identity. Each node must keep track of the binding between the bearer IDs across its different interfaces. An S5/S8 bearer transports the packets of an EPS bearer between a P-GW and an S-GW. The S-GW stores a one-to-one mapping between an S1 bearer and an S5/S8 bearer. The bearer is identifie d by the GTP tunnel ID across both interfaces. An S1 bearer transports the packets of an EPS bearer between an S-GW and an eNodeB. A radio bearer [6] transports the packets of an EPS bearer between a UE and an eNodeB. An E-UTRAN Radio Access Bearer (E-RAB ) refers to the concatenation of an S1 bearer and the corresponding radio bearer. An eNodeB stores a one-to-one mapping between a radio bearer ID and an S1 bearer to create the mapping between the two. The overall EPS bearer service arch itecture is shown in Figure 2.8.

As part of the procedure by which a UE attaches to the network, the UE is assigned an IP address by the P-GW and at least one bearer is established, called the default bearer, and it remains established throughout the lifetime of the PDN connection in order to provide the UE with always-on IP connectivity to that PDN. The initial bearer-level QoS parameter values of the default bearer are assigned by the MME, based on subscription data retrieved from the HSS. The PCEF may change these values in interaction with the PCRF or according to local configuration. Additional bearers called dedicated bearers can also be established at any time during or after completion of the attach procedure. A dedicated bearer can be either GBR or non-GBR (the default bearer always has to be a non-GBR bearer since it is permanently established). The distinction between default and dedicated bearers should be transparent to the acc ess network (e.g. E-UTRAN). Each bearer has an associated QoS, and if more than one bearer is established for a given UE, then each bearer must also be associated with appropriate TFTs. These dedicated bearers could be established by the network, based for example on a trigger from the IMS domain, or they could be requested by the UE. The dedicated bearers for a UE may be provided by one or more P-GWs. The bearer-level QoS parameter values for dedicated bearers are received by the P-GW from the PCRF and forwarded to the S-GW. The MME only transparently forwards those values received from the S-GW over the S11 reference point to the E-UTRAN.

LTE Accessibility KPIs

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