Name in the cause table
Unknown PDU session type
Source: 3GPP TS 24.501 V20.1.0, clause 9.11.4.2, table 9.11.4.2.1. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: 24501-k10.zip in the 3GPP archive.
3GPP Scout / Reference / 5GSM causes / 5GSM cause #28
TS 24.5015GSM cause
5GSM cause #28: Unknown PDU session type
In plain words
The network sends this cause when the external DN rejects the requested service because the requested PDU session type is unrecognised or not allowed.
Our summary of the spec text quoted below.
What the spec says
When it is used
This 5GSM cause is used by the network to indicate that the requested service was rejected by the external DN because the requested PDU session type could not be recognised or is not allowed.
Source: 3GPP TS 24.501 V20.1.0, clause B.1. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: 24501-k10.zip in the 3GPP archive.
Same cause in EPS (TS 24.301)
TS 24.301 defines the corresponding cause for EPS. Its page quotes the EPS wording.
- ESM cause #28 (TS 24.301)
How this page was made
3GPP Scout built this page from TS 24.501 V20.1.0 as indexed on 2026-10-15. The quotes are copied from the spec, and code checks each one against the stored text and the 3GPP archive file before publishing. The plain-words line was written by an AI model (GPT-6 Sol) and checked against the quotes by a second AI model from another company (Claude Opus 5.5). The official 3GPP text governs.