Information about 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
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.
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
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.
Overview
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.
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
External links
Itu is a municipality in the state of São Paulo in Brazil. The population in 2004 is 149,758 and the area is 641.68 km². The elevation is 583 m. This place name comes from the Tupi language.
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Fax (short for facsimile, from Latin fac simile, "make similar", i.e. "make a copy") is a telecommunications technology used to transfer copies (facsimiles) of documents, especially using affordable devices operating over the telephone network.
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Internet protocol may refer to:
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- The Internet Protocol, a data-oriented protocol used for communicating data across a packet-switched internetwork
- The Internet protocol suite, a set of communications protocols that implement the protocol stack on which the Internet runs
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Fax (short for facsimile, from Latin fac simile, "make similar", i.e. "make a copy") is a telecommunications technology used to transfer copies (facsimiles) of documents, especially using affordable devices operating over the telephone network.
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Mime or pantomime is a theatrical medium or performance art, involving the acting out of a story by a mime artist through body motions, without use of speech.
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History
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Request for Comments (RFC) documents are a series of memoranda encompassing new research, innovations, and methodologies applicable to Internet technologies.
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T.37 is an ITU standard which deals with sending fax messages using email. It is also referred to as "iFax", "Internet Fax", or "Store-forward-fax".
A fax machine supporting T.
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A fax machine supporting T.
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Simple Mail Transfer Protocol (SMTP) is the de facto standard for e-mail transmissions across the Internet. Formally SMTP is defined in RFC 821 (STD 10) as amended by RFC 1123 (STD 3) chapter 5. The protocol used today is also known as ESMTP and defined in RFC 2821.
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Tagged Image File Format
File extension:
MIME type:
Type code: TIFF
Uniform Type Identifier: public.
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File extension:
.tiff, .tifMIME type:
image/tiff, image/tiff-fxType code: TIFF
Uniform Type Identifier: public.
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G.711 is an ITU-T standard for audio companding. It is primarily used in telephony. The standard was released for usage in 1972.
G.711 represents logarithmic pulse-code modulation (PCM) samples for signals of voice frequencies, sampled at the rate of 8000 samples/second.
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G.711 represents logarithmic pulse-code modulation (PCM) samples for signals of voice frequencies, sampled at the rate of 8000 samples/second.
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Packet loss occurs when one or more packets of data traveling across a computer network fail to reach their destination.
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Causes
Packet loss can be caused by a number of factors, including signal degradation over the network medium, oversaturated network links, corrupted..... Click the link for more information.
Jitter is an unwanted variation of one or more signal characteristics in electronics and telecommunications. Jitter may be seen in characteristics such as the interval between successive pulses, or the amplitude, frequency, or phase of successive cycles.
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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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User Datagram Protocol (UDP) is one of the core protocols of the Internet protocol suite. Using UDP, programs on networked computers can send short messages sometimes known as datagrams (using Datagram Sockets) to one another.
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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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