Information about Q.931
ITU-T Recommendation Q.931 is ISDN's connection control protocol, roughly comparable to TCP in the Internet Protocol stack. Q.931 doesn't provide flow control or perform retransmission, since the underlying layers are assumed to be reliable and the circuit-oriented nature of ISDN allocates bandwidth in fixed increments of 64 kbit/s. Q.931 does manage connection setup and breakdown. Like TCP, Q.931 documents both the protocol itself and a protocol state machine. Q.931 has more recently been used as part of the VoIP H.323 protocol stack (see H.225.0) and in some mobile phone transmission systems.
Q.931 is a layer 3 protocol, mainly used used for the ISDN call establishment, maintenance, and release of network connections between two DTEs on the D channel. A Q.931 frame contains the following elements:
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Q.931 is a layer 3 protocol, mainly used used for the ISDN call establishment, maintenance, and release of network connections between two DTEs on the D channel. A Q.931 frame contains the following elements:
- Protocol discriminator (PD) - Specifies which signaling protocol is used for the connection (e.g. PD=8 for DSS1)
- Call reference value (CR) - Addresses different connections which can exist simultaneously. The value is valid only during the actual time period of the connection
- Message type (MT) - Specifies the type of a layer 3 message out of the Q.931-defined Message type set for call control (e.g. SETUP). There are messages defined for the call set up, the call release and the control of call features.
- Information elements (IE) - Specify further information which is associated to the actual message. An IE contains of the IE name (e.g. bearer capability), their length and a variable field of contents.
Message examples
- SETUP (indicating the establishment of a connection)
- CALL PROCEEDING (indicating that the call is being processed by the destination terminal)
- ALERTING (tells the calling party that the destination terminal is ringing)
- CONNECT (sent back to the calling party indicating that the intended destination has answered the call)
- RELEASE (sent by either the source or the destination indicating that the call is to be terminated).
The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU) and is based in Geneva, Switzerland.
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Integrated Services Digital Network (ISDN) is a circuit-switched telephone network system, designed to allow digital transmission of voice and data over ordinary telephone copper wires, resulting in better quality and higher data speeds than are available with analog.
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computing protocols, see Protocol (computing). For protocols on two-way voice communications, see Voice procedure. For other meanings of the word protocol, see Protocol.
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The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. TCP provides reliable, in-order delivery of a stream of bytes, making it suitable for applications like file transfer and e-mail.
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Internet is a worldwide, publicly accessible series of interconnected computer networks that transmit data by packet switching using the standard Internet Protocol (IP). It is a "network of networks" that consists of millions of smaller domestic, academic, business, and government
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Not to be confused with control flow.
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Open Systems Interconnection Basic Reference Model (OSI Reference Model or OSI Model for short) is a layered, abstract description for communications and computer network protocol design, developed as part of the Open Systems Interconnection (OSI) initiative.
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A telecommunication circuit is defined as follows:
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- The complete path between two terminals over which one-way or two-way communications may be provided. See communications protocol.
- An electronic path between two or more points, capable of providing a number of channels.
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Bandwidth is the difference between the upper and lower cutoff frequencies of, for example, a filter, a communication channel, or a signal spectrum, and is typically measured in hertz.
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kilobit per second (kbit/s or kb/s or kbps) is a unit of data transfer rate equal to 1,000 bits per second. It is sometimes mistakenly thought to mean 1,024 bits per second, using the binary meaning of the kilo- prefix, though this is incorrect.
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finite state machine (FSM) or finite state automaton (plural: automata) or simply a state machine is a model of behavior composed of a finite number of states, transitions between those states, and actions.
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H.323 is an umbrella recommendation from the ITU Telecommunication Standardization Sector (ITU-T) that defines the protocols to provide audio-visual communication sessions on any packet network.
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H.225.0 is a member of the H.323 family of protocols.
The main objective of H.225.0 is the definition of messages:
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The main objective of H.225.0 is the definition of messages:
- Call Signaling: establish, control and end an H.323 call. The call signaling of H.225.
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mobile phone or cell phone is a long-range, portable electronic device used for mobile communication. In addition to the standard voice function of a telephone, current mobile phones can support many additional services such as SMS for text messaging, email, packet switching
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