A method, operable at or by a packet data network gateway, comprising acquiring a trustworthiness indication of an access network with respect to a core network together with an access technology type of the access network by receiving a signaling message from the access network, said signaling message being a message according to a proxy mobile internet protocol or a message according to a general packet radio service tunneling protocol, detecting a trusted or untrusted property of the access network of the access technology type based on the acquired trustworthiness indication and access technology type, and operating according to the detected trusted or untrusted property of the access network, wherein the trustworthiness indication and the access technology type are acquired from an access technology type parameter, one value of the access technology type parameter indicating a trusted property of the access network of the access technology type and another value of the access technology type parameter indicating an untrusted property of the access network of the access technology type, or the access technology type is acquired from an access technology type parameter and the trustworthiness indication is acquired from a trustworthiness parameter indicating a trusted or untrusted property of the access network of the access technology type indicated in the access technology type parameter, wherein the access technology type parameter comprises an access technology type option field in case said signaling message is a message according to a proxy mobile internet protocol or a radio access technology type element in case said signaling message is a message according to a general packet radio service tunneling protocol, and the trustworthiness parameter comprises a trustworthiness-related option field in case said signaling message is a message according to a proxy mobile internet protocol or a trustworthiness-related element in case said signaling message is a message according to a general packet radio service tunneling protocol. acquiring a trustworthiness indication of an access network with respect to a core network together with an access technology type of the access network by receiving a signaling message from the access network, said signaling message being a message according to a proxy mobile internet protocol or a message according to a general packet radio service tunneling protocol, detecting a trusted or untrusted property of the access network of the access technology type based on the acquired trustworthiness indication and access technology type, and operating according to the detected trusted or untrusted property of the access network, wherein the trustworthiness indication and the access technology type are acquired from an access technology type parameter, one value of the access technology type parameter indicating a trusted property of the access network of the access technology type and another value of the access technology type parameter indicating an untrusted property of the access network of the access technology type, or the access technology type is acquired from an access technology type parameter and the trustworthiness indication is acquired from a trustworthiness parameter indicating a trusted or untrusted property of the access network of the access technology type indicated in the access technology type parameter, wherein the access technology type parameter comprises an access technology type option field in case said signaling message is a message according to a proxy mobile internet protocol or a radio access technology type element in case said signaling message is a message according to a general packet radio service tunneling protocol, and the trustworthiness parameter comprises a trustworthiness-related option field in case said signaling message is a message according to a proxy mobile internet protocol or a trustworthiness-related element in case said signaling message is a message according to a general packet radio service tunneling protocol.