The 5G System, as the 4G before it, is a Packet-Switched connectivity network. The Circuit Switched option – simply because of the cost it implies – is no longer a viable solution for the mass-market usages of the mobile systems. What follows, the more recent mobile networks basically offer transportation of information between a UE and some data network, with the service definitions of the application residing in some Application Server (AS).

Application Servers in the 2G/3G/4G systems

On the one hand, GPRS and HSPA offered connectivity towards ASs that were either in the public internet realm, or to some private ASs, i.e. ran within a certain organisation’s private network, providing therefore both internet and intranet access options. In these use-case scenarios the ASs are external from the perspective of a mobile operator. On the other hand, the SMS service requires the deployment of an SMS AS with its store-and-forward capacity being the main service enabler. The SMS AS is an internal entity, ran by the mobile operators’ themselves.

This type of service connectivity was then continued in the LTE case – internet connectivity, intranet access and SMS support – since the initial days of the 4G Systems. Over time, though, the LTE networks got an overhaul in order to add the PS-based voice service (in the form of Voice over LTE, VoLTE) to the already supported mobile broadband and SMS services. The addition of VoLTE required the mobile operators to deploy new ASs for the control of that particular service – a TAS (Telephony AS), an SCC AS (Session and Service Continuity AS) or the MRFC (Media Resource Function Controller) were defined to handle Supplementary Services, session mobility and conference calls, respectively. All of these were deployed within the operators’ networks, being therefore internal ASs.

Application Servers in 5G

In the 5G System internet/intranet connectivity are of course also supported, granting a transport path from a 5G UE to an external AS. Also, operators of 5G networks will run their own internal ASs in order to offer services like SMS or Voice over IP. But on top of that a need for a new transport path has recently emerged: various low-latency services require ASs that are physically placed close to the UE in order to minimise the transfer delay. We therefore expect that in the 5G environment there will be quite a number of AS deployed at, or very close to, the gNB sites.

UE AS Transport Options

Locally placed ASs can utilise the ETSI-defined concept of MEC, Multi-Access Edge Computing, and that in turn can be the tool to realize Local Area Data Networks, LADN, as defined by the 3GPP.

More information about the 5G System

For more information on the 5G System and what services it can carry, please have a look at one of our 5G courses.

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