How to Identify Network Slices in NG RAN

About 5G

In my last post I described how NG RAN resources can be divided into network slices. 

Now I would like to show how these network slices and the traffic they carry can be identified. 

The key to this is a parameter from the NG Application Protocol (NGAP) called the Single Network Slice Selection Assistance Information (S-NSSAI). When configuring virtual network functions in NG RAN there are lists of S-NSSAI exchanged, e.g. between gNB-CU CP and AMF during NGAP Setup procedure, to negotiate which network slices have to be supported in general. 

When it comes to connection establishment starting with NGAP Initial Context Setup for each PDU session that is established its individual S-NSSAI is signaled. 

The S-NSSAI – as show in the figure below – consists of two parameters, the Slice/Service Type (SST – 8 bit) and the optional Slice Differentiator (SD – 24 bit). The exact format and numbering ranges are defined in 3GPP 23.003.

3GPP 23.501 defines a set of default values for SST as listed in the following table:

Slice/Service type

SST value

Characteristics

eMBB

 

1

Slice suitable for the handling of 5G enhanced Mobile Broadband.

URLLC

2

Slice suitable for the handling of ultra- reliable low latency communications.

MIoT

3

Slice suitable for the handling of massive IoT.

V2X

4

Slice suitable for the handling of V2X services.

So when looking back at the figure it emerges that for each subscriber represented by an IMSI the SST allows to identify which services are running. 

On the other hand allows to see if in which virtual network the subscriber is active. In my example I have defined that the resources are shared among a Public MNO that I consider the owner of the network hardware and two different private (campus) networks. While IMSI 1 and IMSI 2 are not allowed to use any other network slice the IMSI 3 is allowed to “roam” betweent the public slice and the two private network slices. This explains why a slice-specific authentication functionality as defined in Rel. 16 is necessary.   

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