Transaction Capabilities Application Part
TCAP enables the deployment of advanced intelligent network
services by supporting non-circuit related information exchange
between signaling points using the SCCP connectionless service. An
SSP uses TCAP to query an SCP to determine the routing number(s)
associated with a dialed 800, 888, or 900 number. The SCP uses TCAP
to return a response containing the routing number(s) (or an error
or reject component) back to the SSP. Calling card calls are also
validated using TCAP query and response messages. When a mobile
subscriber roams into a new mobile switching center (MSC)
area, the integrated visitor location register requests
service profile information from the subscriber's home location
register (HLR) using mobile application part (MAP)
information carried within TCAP messages.
TCAP messages are contained within the SCCP portion of an MSU. A
TCAP message is comprised of a transaction portion and a
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The transaction portion contains the package type
identifier. There are seven package types:
- Unidirectional: Transfers component(s) in one direction
only (no reply expected).
- Query with Permission: Initiates a TCAP transaction
(e.g., a 1-800 query). The destination node may end the
- Query without Permission: Initiates a TCAP transaction.
The destination node may not end the transaction.
- Response: Ends the TCAP transaction. A response to an
1-800 query with permission may contain the routing number(s)
associated with the 800 number.
- Conversation with Permission: Continues a TCAP
transaction. The destination node may end the transaction.
- Conversation without Permission: Continues a TCAP
transaction. The destination node may not end the
- Abort: Terminates a transaction due to an abnormal
The transaction portion also contains the Originating
Transaction ID and Responding Transaction ID fields which
associate the TCAP transaction with a specific application at the
originating and destination signaling points respectively.
The component portion contains components. There are six
kinds of components:
- Invoke (Last): Invokes an operation. For example, a
Query with Permission transaction may include an Invoke (Last)
component to request SCP translation of a dialed 800 number. The
component is the "last" component in the query.
- Invoke (Not Last): Similar to the Invoke (Last)
component except that the component is followed by one or more
- Return Result (Last): Returns the result of an invoked
operation. The component is the "last" component in the response.
- Return Result (Not Last): Similar to the Return Result
(Last) component except that the component is followed by one or
- Return Error: Reports the unsuccessful completion of an
- Reject: Indicates that an incorrect package type or
component was received.
Components include parameters which contain
application-specific data carried unexamined by TCAP.
SS7 over IPTelephone companies offload voice calls from
public switched telephone networks (PSTNs) to
voice-over-Internet Protocol (VoIP) networks because it is
cheaper to carry voice traffic over Internet Protocol (IP) networks
than over switched circuit networks. In the future, IP
telephony networks are expected to enable innovative new multimedia
services while working seamlessly with legacy telephone networks.
A VoIP network carries voice traffic cheaper than a switched
circuit telephone network because IP telephony networks make
better use of available bandwidth. In a public switched telephone
network, for example, a dedicated 64 kilobits per second (kbps)
end-to-end circuit is allocated for each call. In a VoIP network,
digitized voice data is highly compressed and carried in
packets over IP networks. Using the same bandwidth, a VoIP
network can carry many times the number of voice calls as a switched
circuit network with better voice quality. The savings realized in
using VoIP networks are often passed onto users in the form of lower
Learn more about reducing costs by routing SS7
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