23.1103GPPRelease 17Services and functionsTSUniversal Mobile Telecommunications System (UMTS) access stratum
4.1 Boundaries of the Access Stratum
The Access Stratum (AS) is defined in TS 23.101 . It consists of a functional grouping which includes all the layers embedded in the URAN; and part of the layers in the User Equipment (UE) and the infrastructure (IF); i.e. the edge-node. Its boundary is the frontier between the layers which are independent of the access technique and the ones which are dependent on it. This frontier is located in the UE (mobile boundary) and in an edge-node (fixed boundary). There is a direct or "transparent" dialogue (i.e. not interpreted by the AS) between the UE and the edge-node for the Non-Access Stratum layers.
4.2 Main design guidelines
1) The Access Stratum contains all access specific functionality, e.g. all mode specific functionality in case of the UTRAN.
2) Reconfiguration of the AN, or changes in the AN domain functionality shall have minimal impact on Core Network functions, and vice-versa.
3) A given Access Network (e.g., the UTRAN) may provide access to different type of Core Networks via the Iu reference point.
4) The services, access signalling, mobility and subscriber management specific to each Core Network are completely outside the Access Stratum, and are transferred transparently by the Access Stratum.
5) The Access Stratum provides flexible radio access bearers characterised by parameters describing the type of information and QoS transported over the radio interface (i.e. not the actual radio resources). Some radio access bearers may be asymmetric, i.e., have different parameters on uplink and downlink.
6) There are radio access bearers for both connection oriented packet-switched services, connectionless (store-and-forward) services, and circuit-switched traffic.
7) Parameters for connection-oriented radio access bearers may change during connection (bandwidth on demand, quality management).
8) Whether a terminal can be registered and have connections to several Core Networks simultaneously (i.e., over different instances of Iu) is FFS.
9) The Access Stratum can provide several parallel and independent radio access bearers to one user equipment each with its own characteristics.
10) Multimedia is handled outside the Access Stratum by multiplexing several streams onto one radio access bearer or by requesting several parallel radio access bearers. In the latter case, the possibly needed synchronisation is handled outside the Access Stratum.
11) Connection of a user equipment to several URAN at a time has to be studied.
12) Handover and if applied macrodiversity within one Access Network is handled within the Access Stratum.
13) Handover between two Access Networks (e.g., two UTRANs, or between UTRAN and GSM BSS) may use support from the Core Network.
14) The Access Stratum should hide all access -specific parameters, e.g., location data provided to the Core Networks should be independent from the actual configuration of the Access Network.
15) The user equipment can be connected to different AN/CN points via a single Access Network. The Access Stratum should be able to provide a flexible routing to the appropriate AN/CN point.