WikiSysop: 1 revision

2009-01-28T07:32:16Z

1 revision

← Older revision		Revision as of 07:32, 28 January 2009
(No difference)

Dank at 11:02, 30 September 2008

2008-09-30T11:02:06Z

New page

==History==
* 1942 - [http://en.wikipedia.org/wiki/SIGSALY SIGSALY] system is used for secure voice communications, introducing PCM and spectrum spreading
* 1972 - [http://www.itu.int/rec/recommendation.asp?type=folders&lang=e&parent=T-REC-G.711 ITU-T G.711] audio companding standard
* 1977 - [http://tools.ietf.org/html/rfc741 RFC 741], the Network Voice Protocol
* 1990 - [http://www.ietf.org/rfc/rfc1183.txt RFC 1183] introduces the [[VoIP#ISDN record|ISDN record]]

==Content==
===Voice===
====Encodings====
* [http://en.wikipedia.org/wiki/Linear_predictive_coding Linear Predictive (LPC)]
* [http://en.wikipedia.org/wiki/Continuously_variable_slope_delta_modulation Continuously Variable Slope Data Modulation (CVSDM)]
* [http://en.wikipedia.org/wiki/Pulse-code_modulation Pulse Code Modulation (PCM)] (used in [http://en.wikipedia.org/wiki/G.711 G.711] and many others)
* [http://en.wikipedia.org/wiki/Companding Companding] mitigates the detrimental effects of a channel with limited dynamic range
===Modem/Digital FAX===
* [http://en.wikipedia.org/wiki/ITU-T_V-Series_Recommendations ITU-T V-Series] recommendations
* Group 3 FAX -- ITU-T T.4 + ITU-T T.30 (interoperable with Group 2)
* Group 4 FAX -- ISDN-oriented, ITU-T T.6, T.563, T.503, T.521, T.6, T.62, T.70, T.72, T.411 to T.41

===Analog FAX===
* Group 1 -- ITU-T T.2
* Group 2 -- ITU-T T.3 + ITU-T T.30 (interoperable with Group 3)

==POTS==
Plain ol' Telephone Service. At the user level, analog telephones connect to telco Network Interfaces (NIs) and thus the [http://en.wikipedia.org/wiki/Telephone_exchange telephone exchanges] making up the [http://en.wikipedia.org/wiki/PSTN Public Switched Telephone Network], most commonly via [http://en.wikipedia.org/wiki/Twisted_pair twisted pair] cable, this most commonly terminated via [http://en.wikipedia.org/wiki/RJ11,_RJ14,_RJ25 Registered Jacks 11, 14 and 25] (handsets and the like use [http://en.wikipedia.org/wiki/4P4C 4P4C] terminators, with no Registered Jack identifier). Connection of an analog telephone to a digital network is performed via an Analog Telephony Adapter (ATA), implementing one or more Foreign Exchange Stations (FXS). Devices on the PSTN use [http://en.wikipedia.org/wiki/E.164 E.163/E.164] addresses, also known as '+1 telephone numbers'; these can further reduce to, for instance, [[http://en.wikipedia.org/wiki/North_American_Numbering_Plan#Current_system NANP Numbers]] (3-3-4-style North American numbers). Unification of the E.163/E.164 and IPv4/IPv6 address spaces is attempted via [http://en.wikipedia.org/wiki/ENUM tElephone NUmber Mapping (ENUM)] and NAPTR records.

The PSTN is implemented atop [http://en.wikipedia.org/wiki/Carrier_system carrier systems] such as [http://en.wikipedia.org/wiki/T-carrier T-Carrier] (North America, Japan, Korea) and [http://en.wikipedia.org/wiki/E-carrier E-Carrier] (most everywhere else). These carrier systems specify the digital transmission hierarchy in terms of circuits and the multiplexing strategies used to aggregate and disaggregate circuits.

Between the customer and the telco lies the [http://en.wikipedia.org/wiki/Demarcation_point Point of Demarcation] (aka MPOE, Minimum Point Of Entry). The customer owns wiring and appliances behind the MPOE; telcos (ILECs) and common carriers (CLECs) own everything above (switches/NIs are housed in CO (when a CLEC rents space from the ILEC, this is a POP)). In the United States, demarcation points are wiring junctions produced under the regulating auspices of [http://www.part68.org/ FCC 47 C.F.R. Part 68]. The customer may freely implement either or both of:
* Extension telephones -- multiple phones wired to the same physical circuit and numbers
* Telephone extensions -- internal lines using a PBX or key system
===PBXs===
* Circuits to the telco are "trunk lines", internal circuits are "extension lines"
* Require a Direct Dial Central Office (DDCO) prefix to select an external line
===Key Systems===

A "line" is the combination of physical circuitry and a number by which equipment might be addressed and billed.

===Signaling===
Signaling within the PSTN is accomplished via the use of tones. Within the [http://en.wikipedia.org/wiki/NANP North American Numbering Plan (NANP)], these are specified by the [http://en.wikipedia.org/wiki/Precise_Tone_Plan Precise Tone Plan]:
* dial tone, a continuous tone having frequencies of 350 and 440Hz at a level of −13dBm
* ringback tone, frequencies of 440 and 480Hz at a level of −19dBm and a cadence of 2 seconds ON and 4 seconds OFF
* busy tone, frequencies of 480 and 620Hz at a level of −24dBm and a cadence of half a second ON and half a second OFF
* reorder tone (also called "fast busy tone"), a busy tone with a cadence of 0.25 of a second ON and 0.25 of a second OFF

==Address Resolution==
===ISDN record===
* [http://www.ietf.org/rfc/rfc1183.txt RFC 1183], "New DNS RR Definitions", defines the ISDN record:
<pre>3.2. The ISDN RR

The ISDN RR is defined with mnemonic ISDN and type code 20 (decimal).

An ISDN (Integrated Service Digital Network) number is simply a
telephone number. The intent of the members of the CCITT is to
upgrade all telephone and data network service to a common service.

The numbering plan (E.163/E.164) is the same as the familiar
international plan for POTS (an un-official acronym, meaning Plain
Old Telephone Service). In E.166, CCITT says "An E.163/E.164
telephony subscriber may become an ISDN subscriber without a number
change."

ISDN has the following format:

<owner> <ttl> <class> ISDN <ISDN-address> <sa>

The <ISDN-address> field is required; <sa> is optional.

<ISDN-address> identifies the ISDN number of <owner> and DDI (Direct
Dial In) if any, as defined by E.164 [8] and E.163 [7], the ISDN and
PSTN (Public Switched Telephone Network) numbering plan. E.163
defines the country codes, and E.164 the form of the addresses. Its
format in master files is a <character-string> syntactically
identical to that used in TXT and HINFO.

<sa> specifies the subaddress (SA). The format of <sa> in master
files is a <character-string> syntactically identical to that used in
TXT and HINFO.

The format of ISDN is class insensitive. ISDN RRs cause no
additional section processing.

The <ISDN-address> is a string of characters, normally decimal
digits, beginning with the E.163 country code and ending with the DDI
if any. Note that ISDN, in Q.931, permits any IA5 character in the

general case.

The <sa> is a string of hexadecimal digits. For digits 0-9, the
concrete encoding in the Q.931 call setup information element is
identical to BCD.

For example:

Relay.Prime.COM. IN ISDN 150862028003217
sh.Prime.COM. IN ISDN 150862028003217 004

(Note: "1" is the country code for the North American Integrated
Numbering Area, i.e., the system of "area codes" familiar to people
in those countries.)

The RR data is the ASCII representation of the digits. It is encoded
as one or two <character-string>s, i.e., count followed by
characters.

CCITT recommendation E.166 [9] defines prefix escape codes for the
representation of ISDN (E.163/E.164) addresses in X.121, and PSDN
(X.121) addresses in E.164. It specifies that the exact codes are a
"national matter", i.e., different on different networks. A host
connected to the ISDN may be able to use both the X25 and ISDN
addresses, with the local prefix added.</pre>

==Synonyms==
* Station == Phone
* Switch == Exchange
* Network Interface == Terminal Attachment == MPOE
* Local Loop == Subscriber Line == Last Mile (wrt PSTN)

==See also==
* [http://www.itu.int/rec/T-REC-E.164/en E.164 specifications] at the International Telecommunications Union (ITU), aka "Numbering Plan for the ISDN Era"
* [http://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm Federal Standard 1037C] Telecommunications: Glossary of Telecommunication Terms (superseded by 2001's ANSI T1.523-2001)
* A good glossary of [http://www.arcelect.com/RJ_Jack_Glossary.htm Registered Jacks 11 through 48]
* [http://www.tech-faq.com/telephone-tone-frequencies.shtml Tone Frequencies] from tech-faq.com
* [http://www.nanpa.com/ NANPA], the North American Numbering Plan Administration
* [http://www.voip-info.org/ VoIP-info.org]

VoIP - revision history

WikiSysop: 1 revision

Dank at 11:02, 30 September 2008