Editing Signalling System No. 7 (section)

==SS7 protocol suite==
{{SS7 stack}}
The SS7 [[protocol stack]] may be partially mapped to the [[OSI Model]] of a packetized digital protocol stack. OSI layers 1 to 3 are provided by the [[Message Transfer Part]] (MTP) and the [[Signaling Connection Control Part]] (SCCP) of the SS7 protocol (together referred to as the Network Service Part (NSP)); for circuit related signaling, such as the [[Interconnect User Part|BT IUP]], [[Telephone User Part (TUP)]], or the [[ISDN User Part]] (ISUP), the User Part provides layer 7. Currently there are no protocol components that provide OSI layers 4 through 6.<ref name="q700"/> The [[Transaction Capabilities Application Part]] (TCAP) is the primary SCCP User in the Core Network, using SCCP in connectionless mode. SCCP in connection oriented mode provides transport layer for air interface protocols such as BSSAP and [[RANAP]]. TCAP provides transaction capabilities to its Users (TC-Users), such as the [[Mobile Application Part]], the [[INAP|Intelligent Network Application Part]] and the [[Camel Application Part|CAMEL Application Part]].{{citation needed|date=December 2014}}

The Message Transfer Part (MTP) covers a portion of the functions of the OSI network layer including: network interface, information transfer, message handling and routing to the higher levels. Signaling Connection Control Part (SCCP) is at functional Level 4. Together with MTP Level 3 it is called the Network Service Part (NSP). SCCP completes the functions of the OSI network layer: end-to-end addressing and routing, connectionless messages (UDTs), and management services for users of the Network Service Part (NSP).<ref>{{cite web|url=https://www.itu.int/rec/T-REC-Q.711-200103-I/en/|title=ITU-T Recommendation Q.711, section 1|page=1-2}}</ref> Telephone User Part (TUP) is a link-by-link signaling system used to connect calls. ISUP is the key user part, providing a circuit-based protocol to establish, maintain, and end the connections for calls. Transaction Capabilities Application Part (TCAP) is used to create database queries and invoke advanced network functionality, or links to Intelligent Network Application Part (INAP) for intelligent networks, or Mobile Application Part (MAP) for mobile services.

===BSSAP===
'''BSS Application Part''' ('''BSSAP''') is a protocol in SS7 used by the [[Network switching subsystem#Mobile switching center (MSC)|Mobile Switching Center]] (MSC) and the [[Base station subsystem]] (BSS) to communicate with each other using signaling messages supported by the [[Message_Transfer_Part|MTP]] and [[Connection-oriented communication|connection-oriented services]] of the [[Signaling_Connection_Control_Part|SCCP]]. For each active [[Mobile station|mobile equipment]] one signaling connection is used by BSSAP having at least one active transactions for the transfer of messages.<ref>{{cite web|url=https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=2759|title=3GPP TS 48.008, Mobile Switching Centre - Base Station System (MSC-BSS) interface; Layer 3 specification}}</ref> 

BSSAP provides two kinds of functions:

* The BSS Mobile Application Part (BSSMAP) supports procedures to facilitate communication between the MSC and the BSS pertaining to resource management and [[handover]] control.
* The Direct Transfer Application Part (DTAP) is used for transfer of those messages which need to travel directly to mobile equipment from MSC bypassing any interpretation by BSS. These messages are generally pertaining to [[mobility management]] (MM) or [[call management]] (CM).