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Encyclopedia > T.38

T.38 is an ITU recommendation for sending fax messages over IP networks in real time by encapsulating a standard T.30 fax data stream. T.38 is also used to describe the actual data and is a registered MIME sub-type in RFC 3362 Image File history File links Merge-arrows. ... // The T.38 fax relay standard was devised in 1998 as a way to permit faxes to be transported across IP networks between existing G3 fax terminals. ... This article is about the location. ... A Samsung fax machine Fax (short for facsimile, from Latin fac simile, make similar, i. ... The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ... A Samsung fax machine. ... Look up mime in Wiktionary, the free dictionary. ... In internetworking and computer network engineering, Request for Comments (RFC) documents are a series of memoranda encompassing new research, innovations, and methodologies applicable to Internet technologies. ...

Fax over IP alternatives to T.38

  • T.37 is a store and forward mechanism of sending faxes over IP using email as transport (SMTP and TIFF attachments).
  • G.711 pass through - this is where the T.30 fax call is carried in a VOIP call encoded as audio. This is sensitive to network packet loss, jitter and clock synchronization.

T.37 is an ITU standard which deals with sending fax messages using email. ... Simple Mail Transfer Protocol (SMTP) is the de facto standard for email transmission across the Internet. ... This article is about TIFF, the computer image format. ... G.711 is an ITU-T standard for audio companding. ... This page meets Wikipedias criteria for speedy deletion. ... In telecommunication, jitter is an abrupt and unwanted variation of one or more signal characteristics, such as the interval between successive pulses, the amplitude of successive cycles, or the frequency or phase of successive cycles. ...


In practical scenarios, a T.38 fax call has at least part of the call being carried over PSTN, although this is not required by the T.38 definition, and two T.38 devices can send faxes to each other.

The typical scenario where T.38 is used is - T.38 Fax relay - where a T.30 fax device sends a fax over PSTN to a T.38 Fax gateway which converts or encapsulates the T.30 protocol into T.38 data stream. This is then sent either to a T.38 enabled end point such as fax machine or fax server or another T.38 Gateway that converts it back to PSTN and terminates the fax on a T.30 device.

The T.38 recommendation defines the use of both TCP and UDP to transport T.38 packets. Implementations tend to use UDP, due to TCPs requirement for acknowledgement packets and resulting retransmission during packet loss, which introduces delays. When using UDP, T.38 copes with packet loss by using redundant data packets. The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. ... User Datagram Protocol (UDP) is one of the core protocols of the Internet protocol suite. ...

T.38 is not a call setup protocol, and the T.38 devices need to be using the same call setup protocols to negotiate the T.38 call. eg H.323, SIP & MGCP H.323 is an umbrella recommendation from the ITU-T, that defines the protocols to provide audio-visual communication sessions on any packet network. ... The Session Initiation Protocol (SIP) is an application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants. ... In computing, Media Gateway Control Protocol (MGCP) is a protocol used within a Voice over IP system. ...

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