X2 Application Protocol (X2AP)


The X2AP protocol is used to handle the UE mobility within E-UTRAN and provides the following functions:
·         Mobility Management
·         Load Management
·         Reporting of General Error Situations
·         Resetting the X2
·         Setting up the X2
·         eNB Configuration Update
Protocol specification
3GPP TS 36.423 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 Application Protocol (X2AP)


X2 layer 1


 The main functions of X2 interface layer 1 are as following:
·         Interface to physical medium;
·         Frame delineation;
·         Line clock extraction capability;
·         Layer 1 alarms extraction and generation;
·         Transmission quality control.
Protocol specification
3GPP TS 36.421 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 layer 1


S1 Signalling Transport

S1 signalling bearer provides the following functions:
·         Provision of reliable transfer of S1-AP message over S1-MME interface.
·         Provision of networking and routeing function
·         Provision of redundancy in the signalling network
·         Support for flow control and congestion control
L2 - Data link layer
Support of any suitable data link layer protocol, e.g. PPP, Ethernet
IP layer
·         The eNB and MME support IPv6 and/or IPv4
·         The IP layer of S1-MME only supports point-to-point transmission for delivering S1-AP message.
·         The eNB and MME support the Diffserv Code Point marking
Transport layer
SCTP is supported as the transport layer of S1-MME signalling bearer.
·         SCTP refers to the Stream Control Transmission Protocol developed by the Sigtran working group of the IETF for the purpose of transporting various signalling protocols over IP network.
·         There is only one SCTP association established between one MME and eNB pair.
·         The eNB establishes the SCTP association. The SCTP Destination Port number value assigned by IANA to be used for S1AP is 36412.
Protocol specification
3GPP TS 36.410 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1 general aspects and principles               
3GPP TS 36.411 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1
3GPP TS 36.412 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 signalling transport
IETF RFC 2460: "Internet Protocol, Version 6 (IPv6) Specification"
IETF RFC 791 (September,1981): "Internet Protocol"
IETF RFC 2474 (December 1998): "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers"


S1 layer 1


the main functions of S1 interface layer 1 are as following:
·         Interface to physical medium;
·         Frame delineation;
·         Line clock extraction capability;
·         Layer 1 alarms extraction and generation;
·         Transmission quality control.
Protocol specification
3GPP TS 36.411 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1


Reason for SDCCH DROP in GSM Network



·         Low Rx level DL& UL, Bad Qual (Interference ) DL & UL, and High TA
·         Drop on LAC boundary.
·         SW congestion
·         Due to TCH Congestion.
·         Hardware issue, Timeslot Faulty, High VSWR, Alarm or Antenna Faulty, mismatch combining.
·         Interference or error on E1.
·         Drop due to radio failure.
·          SD drop due to MS faulty.
·         SD drop due to mismatch Rxlev_access_min value & RACH busy threshold

·         SD drop due to mismatch BA2 list, due to drop occur during HO.

Reason for TCH DROP in GSM Network


·         The parameters SACCH Multi-Frames and Radio Link Timeout are set to too small values.
·         The parameter RXLEV_ACCESS_MIN is set to a too small value.
·         The parameter RACH Min.Access Level is set to a too small value.
·         The parameters Min DL Power on HO Candidate Cell and Min Access Level Offset are inappropriately set.
·         The length of timer T3103 (this timer is set to wait for a Handover Complete message) is set to a too small value.
·         The length of timer T3109 (this timer is set to wait for a Release Indication message) is set to a too small value.
·         The length of timer T3111 (this timer specifies the connection release delay) is set to a too small value.
·         The length of timer T305/T308 is set to an invalid or too great value.
·         The parameter TCH Traffic Busy Threshold is set to a too small value.
·         The parameter Call Reestablishment Forbidden is set to Yes.
·         The parameters related to edge handover are inappropriately set.
·         The parameters related to BQ handover are inappropriately set.
·         The parameters related to interference handover are inappropriately set.
·         The parameters related to concentric cell handover are inappropriately set.
·         The parameters related to power control are inappropriately set.
·         T200 and N200 are set to too small values.
·         Some neighboring cell relations are not configured.
·         The parameter MAIO is inappropriately set.
·         The parameter Disconnect Handover Protect Timer is set to a too small value.
·         The parameter TR1N is set to a too small value.
·         The parameters Software Parameter 13 and MAX TA are set to too small values.
·         If a repeater is used, the parameter Directly Magnifier Site Flag is set GSM BSS Network KPI (TCH Call Drop Rate) Optimization Manual INTERNAL to No
·         Drop due to hardware issue (Faulty, VSWR, ICM, Mismatch combining & Alarm)
·         Drop due abis link error or high abis link UTL.
·         Drop due to Co-Channel interference or due to poor Qual UL & DL.
·         Drop due to poor level UL & DL or due to High TA.
·         Drop due to HO Delay.
·         Drop due to Poor Antenna installation.

·         Drop due to poor path Imbalance ( UL & DL)