Network Slice Selection Function NSSF

M-CORD Based

Introduction

A Network Slice Selection Function is in charge of making the selection of an appropriate Network Slice in base of some parameters that a UE will send when it wants to attach to a Network. In the next sections the level of functionality achieved and the steps that are required for running this module will be described

Description

The NSSF is part of the 3gpp solution for having E2E slicing in a Mobile Network. According to documentation of the 5G Architecture, the NSSF sits beside Access and Mobility Function AMF. As we are working with 4G open source components we have replaced the AMF interaction by using the MME According to 3gpp documentation during Session Establishment the NSSF will be involved in Reselection of a Network Slice only if, the Network Configuration changed. Because of this is not part of the scope of our project, Slice reselection is not included in the functionality.

The current functionality present in the code is:

• Assign a Network Slice during Network Attach procedure
• Erase UE slice assignation during the Network Detach procedure In progress

It is important to make clear, the NSSF is not in charge of doing the Attach/Reattach procedure, it only passes the information received from MME, and once the UE is allowed to have connection will assign the Network Slice based on the Type of Service that the UE requires.

Functionality during UE Attach/Reattach procedure

The following Flow chart, shows the Attach/Reattach procedure of the NSSF

The process for slice selection is the following:

1. The UE sends the connection message to the vMME by means of the eNodeB emulator (OAISIM). This information includes: PLMN, IMSI, MNC, MCC.

2. The vMME forwards the UE information to the vHSS for checking if it is allowed to attach and register to network.

3. Once the vHSS approves the UE, the vMME will forward the IMSI of the UE to the NSSF during session request.

4. The NSSF will verify the IMSI and see if there is a specific vSPGW that can serve the connection.

   • a) If the vSPGW exists, the NSSF will reply the vMME with the Id (Ip address) of the vSPGW that will be used to serve.
   • b) If it does not exist, it will use a default vSPGW for session establishment.

Functionality During Detach

When the Detach procedure is triggered, the NSSF will do Two tasks:

1. It will update the Network Slice Database, removing the UEId that was assigned to the Network Slice. This way we clean the Slices that are being served.
2. It will erase all the UE related information from the Local Connection Database. Effectively disconnecting the device from the network.

Code

The present GitHub repository has 1 directories for running the module:

• src It is where the actual code of the NSSF reside

Steps on how to run the Code and the requirements that are needed for having a Deployment Environment are in the User Guide that you can access inside the src folder or in this here

Impact of the NSSF in our Mobile Network scenario

Because the NSSF has a very specific role, the existence of this Function is mandatory if we want to have E2E slicing inside a Mobile Network, or any kind of Network that requires slicing. The functionality of NSSF really comes into place, when the number of Slices that are created in a Network is High and there is a mechanism to provide Dynamic Network Slice Creation M-CORD.

Acknowledgment

This research was supported by the MSIP (Ministry of Science, ICT and Future Planning), Korea, under the ITRC (Information Technology Research Center) support program (IITP-2017 2017-0-01633) supervised by the IITP (Institute for Information & communications Technology Promotion.

Glossary

• 3gpp The 3rd Generation Partnership Project
• E2E End to End slicing
• MME Mobile Management Entity
• AMF Access and Mobility Function
• NSSF Network Slice Selection Function