Plain Old Telephone System From Comfort to Numbering RIPE 46 VoIP and ENUM 1. September 2003 Richard STASTNY ÖFEG/TELEKOM AUSTRIA, Postbox 147, 1103-Vienna enum:+43 664 420 4100 E-Mail: [email protected] [email protected] Today's Roadmap on Numbering 1. POTS – from Comfort to Numbering ¾ Why are the numbers in the PSTN in the way they are? ¾ A historical "Tour de Force" 2. ENUM and VoIP – Numbering and Dialing Plans ¾ ENUM Mapping of E.164 Numbers to Internet Names and Addresses ¾ E.164 Numbers for VoIP and Routing on the PSTN ¾ Why Numbering and Dialing Plans for VoIP? ¾ An Overview and a Proposal 3. VoIP and CLI – Trusted Identification ¾ Calling Line Identification on VoIP ¾ A Proposal Richard Stastny 2 More then 100 Years of Telephony ¾ What has changed since 1900? ¾ Not very much, same as railways ... ¾ same speed, but reduced prices and reduced comfort Richard Stastny 3 From POTS to VoIP The technology was already established after 20 years (more then VoIP today) Functions then now Alerting, Ringing D D Off hook – on hook D D Call set up, dialing Voice, Dial Keys, MFC Receiver and transmitter D D Battery central local Richard Stastny 4 C.B. Steam Phone Circuits ¾ A subscriber line with DC power from a Central Battery ¾ A hook-switch ¾ if on-hook ¾ an AC circuit with a bell and a capacitor for Ringing (high resistance) ¾ if off-hook ¾ a DC circuit with a microphone (low resistance for off-hook detection in C.O.) ¾ an induction coil for separation of the transmitter (to block the DC current) Richard Stastny 5 The Switchboard in the Central Office ¾ You picked up the transmitter (off-hook) ¾ a flap signals this at the switchboard in the central office ¾ the operator answers ¾ you tell her: "Give me the Undertaker" ¾ and she establishes the connection - this was very comfortable Richard Stastny 6 Almon Brown Strowger ¾ This system was nearly perfect, but ... ¾ A.B. Strowger was an undertaker in Kansas City ¾ and the operator was the wife of another undertaker ¾ and connected the calls for undertakers to her husband ¾ Strowger did not like this at all ¾ so he invented the automatic telephone exchange Richard Stastny 7 The Strowger Selector ¾ The strowger selector is controlled by the dial pulses directly ¾ A final selector is able to connect to 100 lines with two digits ¾ the first digit is stepping up vertically ¾ the second digit is turning horizontally bell-head counting ¾ and the digit '0' is ten steps! Richard Stastny 8 A complete automatic switch ¾ Three basic types of selectors: ¾ Uniselector to find a free first selector and attach dial tone ¾ eventually 1 or more group selectors (first, second, ...) ¾ the group selector uses up 1 digit and searches for the next free selector ¾ The final selector uses up 2 digits. ¾ So a local switch uses 2 or more digits ¾ and a number was really an address Richard Stastny 9 The Dial ¾ To control the strowger selectors, a device was needed in the phone to generate the necessary pulses ¾ The idea was, that the caller is controlling the phone system manually with a dial (so "automatic" is questionable) ¾ The dial is able to generate digits transmitted as pulses by "breaking" the DC circuit (you may also dial with the hook switch) ¾ The dial is providing a standardized length of "make" and "break" ¾ Dialing is signaling Richard Stastny 10 Dials – Number Rings and Finger Plates Vienna 1928 Richard Stastny 11 Dialing at central office Richard Stastny 12 Selector Richard Stastny 13 A Strowger automatic exchange Richard Stastny 14 Basic Signals Then ¾ Before we continue, we should recapitulate the basic signals in step–by- step systems, transmitted in-band with DC signals, AC signals or audible tones: ¾ Off-hook (DC) ¾ dialtone (tone) ¾ dialing (DC) ¾ call proceeding (clacker, tucker, hackety-hack, … ;-) ¾ trunk busy (tone) ¾ subscriber busy (tone) ¾ number unavailable (tone) ¾ ringtone (tone) ¾ ringing (AC) ¾ Answer ¾ on-hook or release from far end (DC and tone) ¾ These are still the main signals we have now. Richard Stastny 15 Basic Signals Now Network A-sub B-sub Off-hook Dial tone Call Set-up Dialing Ringing Ring tone Signalling traffic Answer Answer Ind. User traffic Release Release Ind Release Release Quelle: Siegmund, Intelligente Netze Richard Stastny 16 A phone network ¾ All phone or subscriber lines where connected to the local office ¾ but people sometimes people also wanted to call long distance ¾ so even in switchboard times a central office was connected via "trunk" lines to other central offices Richard Stastny 17 Trunking ¾ Even if local calls could be made automatically in the first half of the last century, long distance calls still required operators. ¾ The connections between the local offices (the trunks) where still only accessible from switchboard operators. ¾ In many cases the digit '0' of the first selector was used to route the call to a switchboard and the operator established the "trunk" call ('0' was selected because it was used rarely) ¾ Subscriber Trunk Dialing (STD) on large scale was introduced in the 50s ¾ International Subscriber Dialing (ISD) was introduced ¾ in the 60s continental and ¾ in the 70s inter-continental. Richard Stastny 18 Trunk Auto ¾ In the beginning, the caller dialed directly into the trunk network like into the local network ¾ but the problem was that the numbers (trunk codes) to dial for a given destination were different for each origination ¾ To unify all trunk codes in a country, additional equipment was necessary between local network and the trunk network ¾ the access equipment (e.g. 2-to-4 wire conversion, tariff pulses) ¾ the register (storing and out pulsing of digits, tariff selection) ¾ and the translator (digit translation) – a preliminary IN-service ;-) ¾ access equipment was needed throughout the call, registers only during call set-up and translators only during translation Richard Stastny 19 Access to Trunk Auto Richard Stastny 20 Register and Translator ¾ Since at this time registers and translators where electromechanical, they had to be simple ¾ Most translation was done by simply deleting and/or adding digits ¾ How could this be achieved? ¾ By creating a tree structured hierarchy of central offices (switching centers) Richard Stastny 21 Austrian Trunk Network ¾ The Austrian Hierarchy - EA, VBA, NGA, HBA, (AVSt) ¾ The Austrian Trunk Code is normally 4 digits: K1 K2 K3 K4 ¾ The Registers are located at the incoming VBA trunks and are adding '0's to go up the hierarchy and/or deleting digits ¾ Step-by-Step System using an Open Numbering Plan (variable digit length) AVSt - Auslandsvermittlungsstelle Register Richard Stastny 22 The translation by the register (RV) – introduced 1951 – The user always dials '0 K1 K2 K3 K4' – The RV dials: To other local office in own "Verbundgruppe" – 'K3 K4' – To other local office in own "Netzgruppe" – '0 K3 K4' – All other: '0 0 K1 K2 K3 K4' II.NGW I.NGW VbGW I. Group Selector, I.GW Richard Stastny 23 North American Trunk Network ¾ The NANP Hierarchy ¾ Class 1 Regional Center ¾ Class 2 Sectional Center ¾ Class 3 Primary Center ¾ Class 4 Toll Centre ¾ Class 5 End Office ¾ Crossbar system using a Closed Numbering System originally in the format X0/1N XXN NNNN; since 1974 in the format XXN XXN NNNN; where X= 2-9 and N=1 to 0; ¾ In addition to the Numbering and Routing Plan also a Transmission Plan and a Tariff Plan was necessary Richard Stastny 24 Dialling Plans ¾ Dialing Plans have a clear hierarchy ¾ for local calls, the local number (subscriber) is dialed directly ¾ for national (trunk) calls ¾ the national trunk network is accessed with a prefix (e.g. '0'), ¾ then the trunk code is dialed to reach the distant local office ¾ and then the local number in the distant local office is dialed ¾ for international (trunk) calls ¾ the national trunk network is accessed with a prefix (e.g. '0') ¾ then the international trunk network is accessed with another prefix (e.g. '0') ¾ then the country code to reach the national network of the foreign country ¾ then the trunk code to reach the distant local office ¾ and then the local number in the distant local office is dialed ¾ e.g. '0 0 CountryCode TrunkCode SubscriberNumber' ¾ This will be discussed in more detail in Part II Richard Stastny 25 International Subscriber Dialing ¾ ISD was introduced in 1960 ¾ Many concerns where raised: ¾ Who needs it? ¾International traffic in Germany 1960 was 0.6% ¾ My Grandma (= normal subscribers) cannot use it! ¾She will not be able to dial 11 to 14 digits in one rush without making a mistake. ¾ All dials need to be unified (remember slide 11) ¾Who will pay for this? (CCITT Redbook 1960 Unified Dials, no letters – Keypad 1964) ¾ Automatic Tariffing (time and distance proportional) required ¾ In many countries it was considered problematic that a citizen is able to call any other foreign citizen in the world without asking anybody for permission. Richard Stastny 26 History of ITU and E.164 ¾ ITU was founded in 1865 (International Telegraph Union) ¾ CCIR(1927), CCIF(1924) and CCIT(1925) merged 1956 to form CCITT ¾ 1932 ITU changed name to International Telecommunication Union ¾ 1956 CCIF(1924) and CCIT(1925) merged to form CCITT ¾ 1989 Sectors ITU-T, ITU-R and ITU-D ¾ History of county codes ¾ 1960 CCITT Red Book featured a list of 2 digit country codes for Europe (some of them are still in force) ¾ 1964 CCITT Blue Book E.29: basis for existing international numbering plan ¾ 1968 CCITT White Book E.161/Q.11 ¾ 1972 CCITT Green Book E.161/Q.11 ¾ 1976 CCITT Orange Book E.163 ¾ 1980 CCITT Yellow Book E.163 ¾ 1984 CCITT Red Book E.163, E.164 for ISDN ¾ 1988 CCITT Blue Book E.163, E.164 for IDSN ¾ 1992 onwards ITU-T White Book E.164, E.164.1, E.164.3, E.164.3 Richard Stastny 27 Fast Forward: Switching Matrix ¾ The next step where electromechanical register systems (e.g.