2. Overview
• Network Entry Success Rate (NESR) is one of the
KPI’s dealing with Network accessibility
• NESR determines what percentage of network
entry attempts are successful and results in
access to the network
• It is very important to understand what
constitutes the formulation of the KPI
3. NESR - Breakdown
• Network Entry can be broadly divided into the following categories:
1. System Acquisition and Network Selection
2. Establishing RF link
3. Authentication and Key Generation
4. Registration
5. Setup of Pre-Provisioned Service Flows
6. IP Assignment
7. Data Exchange
• The user’s equipment goes though each of these steps before it can
access the network
• Network Entry failure can occur at any of the aforementioned step
5. System Acquisition and
Network Selection
• On power up the SS scans for the preamble. From this the SS learns the
basic frame timing of the target base station
• Once preamble is acquired it can start to decode the broadcast
configuration messages
• The SS needs to read the different broadcast information of a cell,
specifically the DCD, UCD, DL-MAP and UL-MAP-messages
• The first stage is to read the Frame Control Header (FCH). This provides
information to decode the DL-MAP, which specifies the location of the DCD
and UCD
• The SS reads the Operator ID from either DL-MAP or DCD, and checks
whether the operator is part of its preferred list. If so, it is selected and SS
is DL synchronized
• SS reads the UL-MAP, which carries information defining the availability of
the ranging channels and the UCD, which has the definition of the ranging
code values
7. Establishing RF link
• Once network selection is completed, the SS is now ready
to start establishing the RF link with the site.
• Naturally, this link is made with the best server and the
steps that follow are divided into three broad categories.
1. Ranging
2. Capability Negotiation
3. Power Control (switching to open loop power control)
8. Ranging:
• At this point, the SS is “DL Synchronized” and is to obtain “UL Synchronization”.
• Initial ranging consists randomly selecting from common ranging resources.
• The resources are available to all users and the process is contention based
which may result in collisions.
• Initial Ranng giprocess includes steps to mitigate the effects of such collisions.
• SS will identify itself to the network using its 48–bit MAC address.
• It will be allocated its Basic and Primary Management CIDs.
• These CID’s are used to exchange MAC signaling messages to complete the
network entry procedure.
• The ranging process achieves three important objectives:
– The SS achieves time-alignment with the BS in the uplink.
– SS transmit power is adjusted to take into account the distance of the SS from the BS
– The transmit frequency of the SS is “fine tuned” to best match with the BS.
Continued
10. Capability Negotiation:
• It is essential that the capabilities of that SS are known to the network.
• On completion of ranging, it will immediately notify the BS of its basic
capability set, including various Physical and MAC layer parameters to
complete Authentication and Registration.
• The BS will determine the capabilities that are supported by both, SS and
the BS, and sends a list of the common capabilities back to the SS
Continued
11. Authentication and Key
Generation
• Before the SS can initiate services, it must authenticate itself to the
network.
• As part of the authentication procedures, security keys are generated
independently at the AAA server and the SS and these are used to create
the security keys used on the air interface and for IP sessions.
• The most popular authentication method currently in use with EAP is
Transport Layer Security (TLS).
• EAP-TLS is based upon using Digital Certificates as the credentials for
authentication and Public Key Infrastructure (PKI) for the secure exchange
of authentication information.
12. Registration
• After authentication, the SS registers with the network so that SS
informs how it wishes to interact with the network, and the
network provides network-specific mobility parameters for the SS
to use.
• This message will carry the SS supported capabilities (such as CS
capabilities, Mobility parameters and Handover support, etc.).
14. Setup of Pre-Provisioned
Service Flows
• After registration is completed, the mobile must obtain an IP address. To
do this, the SS must first have a service flow to use for the IP session
traffic and to carry the IP management messages.
• AT this point, the network will initiate the Initial Service Flows and
optionally, a number of pre-provisioned services flows (to carry data)
based on the subscribers profile.
• The indicated procedure is always initiated by the BS or rather the ASN-
GW based on the user profile which is downloaded from the AAA-server of
that SS during network entry
16. IP assignment
• The ISF or other pre-provisioned service flows and related CIDs
will be used for IP messages to obtain a dynamic IP address for
the SS, from the CSN.
• Prior to initiating any data transfer services, the SS must be
allocated an IP address. It is possible for the SS to hold a static IP
address, but it is more likely that an address will be allocated
dynamically by the CSN.
• If the SS operates in Simple IP mode, it uses DHCP to obtain its
IP Address. This is done by exchanging DHCP messages with the
DHCP Server located in the CSN. These messages are IP based,
and usethe ISF created during the Pre-provisioned Service Flow
creation described in the previous section.
18. Data Exchange
• The data is transferred to the SS almost
instantaneously because the SS continuously
listens to the DL-MAP-messages in normal
operation mode.
• The SS just listens to the downlink broadcast
messages, namely the DL-MAP messages in the
consecutive frames.
• Eventually, the BS receives DL-data for that SS.
