Steering of Roaming

Steering of roaming (SoR) is the set of techniques a home operator uses to make its roaming subscribers register on preferred partner networks instead of any network that happens to be available. Operators steer toward partners with better commercial terms, quality or technology support — and away from networks they would rather their roamers did not use.

Steering methods

GSMA IR.73 describes the main approaches:

Method	How it works	Trade-offs
SIM-based (OTA)	The home operator updates the operator-controlled PLMN list on the SIM over the air	Clean, but the device acts on the list only during network selection
Signaling-based	The home network rejects registration attempts on non-preferred networks, so the device tries another	Takes effect immediately, but adds delay and load on the visited network
5G control plane	The home network sends a steering list to the device in NAS signaling during registration, with integrity protection (3GPP TS 23.122, Annex C)	Requires 5G; the visited network must relay it transparently

What signaling-based steering looks like

When the home network rejects a registration on a non-preferred network, the device sees what looks like a failure, often with a generic reject cause. The device then retries before moving on: IR.73 describes four location update attempts (five for packet-domain procedures) with 15 seconds between them, adding roughly 60 to 75 seconds per steered network. After that, the device tries the next network on its list.

If no preferred network is available, a well-behaved steering platform eventually lets the device register on the non-preferred one — for example when it sees the same device return repeatedly — so steering does not leave a subscriber without service.

Why it matters for testing

Steering changes which network a device ends up on and how long it takes to get there, and devices react to steering rejects differently. IoT devices in particular can back off for long periods or, depending on the reject cause used, add a network to their forbidden list (see attach reject cause). Roaming tests that ignore steering produce misleading attach times and network choices. SimCheck.ai’s signaling view shows each registration attempt and the network’s reject cause — see roaming testing.