- Global Title
A Global Title (GT) is an
address used in the SCCP protocol for routing signaling messages ontelecommunications networks. In theory, a global title is a unique address which refers to only one destination, though in practice destinations can change over time.__TOC__
Overview
The "Global Title" is similar in purpose on the
PSTN to thehost name on theinternet . In design, however, global titles are quite different. The structure is usually hierarchical, the value can be of variable length, and is not necessarily a wholly numeric value -- though it often is for issues ofbackwards compatibility and association with regulartelephone number s.tructure of the global title value
The structure of a global title for
ITU-T applications is officially defined in [http://www.itu.int/rec/T-REC-Q.713/en/ ITU-T Recommendation Q.713] , and further extended in the supportingnumbering plan standards. Other national variants ofSignalling Connection Control Part (SCCP), such as theAmerican National Standards Institute variant specified in ANSI T1.112/2000, define their own format for the Global Title. The value of a global title is comprised of a sequence of attributes which modify the address value. To summarize:Global Title Format
A global title can be in a variety of formats, most of which are each defined in separate standards. The format parameter indicates which of the available formats are in use. Each format can include any of the subsequent parameters.
Numbering Plan Indicator
The
Numbering Plan Indicator (NPI) describes whichnumbering plan will be used for the global title. The numbering plan chosen will aid the routing system in determining the correct network system to direct the message.Type of Number
The
Type of Number (TON) or Nature of Address Indicator (NAI) parameter, which is of relevance toE.164 (regular telephone) numbers for example, indicates thescope of the address value, such as whether it is an international number (i.e. including the country code), a "national" or domestic number (i.e. without country code), and other formats such as "local" format (e.g. in the U.S., without anarea code ). (The latter two are equivalent to "site local" and "link local" type partial addresses inIPv6 .)Translation Type
The translation type (TT) parameter is used in a network to indicate the preferred method of "global title analysis" (see below). Normally in European networks, this parameter is set to 0 (the default) value. In
North America n mobile networks, different translation types are used for analysis of theIMSI and for messages between telephone systems. This parameter is valuable in complex routing problems, where the same number has to be routed differently depending on the circumstances, such as those introduced bynumber portability resolution.Global title translation
Global title translation is the
SS7 equivalent to IP routing. Translation examines the destination address (e.g. the number being called) and decides how to identify it over the telephone network. This process can include "global title analysis", which is the act of looking up the number and finding a result address, and "global title modification".It is possible for the result of Global Title Translation to be Route on SSN. This means that, instead of the Global Title routing, lower level MTP routing will be used for this message from this point on. Equivalently, in a system using
SS7 over IP (for example,SIGTRAN ), the result from Global Title Translation may be a to route to an IP server, though the exact details depend greatly on which variant ofSS7 over IP is being used.Fact|date=July 2008Global Title Analysis
Global Title Analysis together with Global Title Translation. The situation in this case is somewhat complicated by the additional parameters possible in the global title. Each set of parameter values (TT=0 NP=E.164, TON=INT) can be treated separately from each other one (TT=0 NP=E.214, TON=INT). This means that, instead of one single table, we potentially need a separate table for each possible set of values.
The variable length of the global title makes certain optimisations that can be used in IP routing are not so easy to use here. The number analysis of a Global Title is most often done in a tree structure. This allows reasonably efficient analysis to any depth which is chosen.
In the end, global title analysis gives some result. The exact possibilities vary from system to system, is sometimes called an "action" or is integrated into the analysis table.
The "destination" would typically be given as a signalling point code in an MTP network, but could also be an IP system if we are using
SS7 over IP .Fact|date=July 2008Routing Structure
The most commonly used numbering plans for global title routing are
E.164 andE.214 (although E.212 is also common in America). These simply look like telephone numbers. That is to say, in the most common, international, variant there is acountry code at the start of the number and aNetwork Code immediately following the "country code". Beyond that is the "subscriber number" or "mobile subscriber identity" number, though even that may be divided into sections. This structure allows for the use of hierarchical routing.* international SCCP gateways know which systems handle each of the other countries
* the international SCCP gateway belonging to each country knows which SCCP gateways handle each network
* the SCCP gateway of each network knows the networks own internal structureIn America, the limitations of the
North American Number Plan mean that the destination country is not immediately obvious from the called party address. However, the fact that there is unified administration means that this can be overcome by having complete analysis at every point where it is needed.Global Title Modification
In Global Title Translation it is quite normal that at some point the Global Title will have to be changed. This happens, for example, as GSM mobility management messages enter and leave networks in America. In America, typically most routing of mobility management messages for all
mobile network s is done using theE.212 (IMSI) number. In international networks,E.214 is always used.At the boundary incoming toward America (this can mean the
Signaling Transfer Point at the edge of the American operator's network), numbers routed from European networks are converted from E.214 numbers into E.212 numbers. In the outgoing direction, from America toward the rest of the world, are converted from E.212 numbers into E.214 numbers.Global Title Routing in Mobile Networks
In mobile networks, there are database queries such as "how can I tell if this subscriber is really who he says he is" (MAP_Send_Authentication_Info) which have to be routed back to the database which holds the subscriber's information (the HLR, or in this case, the AUC).gg
Unfortunately, at the time the subscriber first arrives, we don't know which HLR is the subscriber's HLR. For this reason, the queries have to be routed on the subscriber's identity (
IMSI ) is used to generate the called party address in the message. How this is done depends whether we are in world area 1 (North America) or somewhere else.Mainly there are three type of GT in use in mobile networks known as E.164 (MSISDN), E.212(IMSI) and E.214(MGT).Fact|date=June 2008
* E.164(MSISDN) = CC+NDC+SN, e.g. 91-98-71405178
* E.212(IMSI) = MCC+MNC+MSIN, e.g. 404-69-6600620186 (MTNL Mumbai)
* E.214(MGT) = combination of E.212 and E.164Mobile Global Title Routing (Except North America)
Everywhere in the world, except North America, the subscriber's IMSI is converted to a Mobile Global Title (MGT)
E.214 number. See the entry about theIMSI for more details. The E.214 number has a structure which is similar to the E.164 number, and, except in a mobile network it can be routed identically. This means that the same routing tables can be used for both and means considerably reduced administrative overhead in maintaining the tables.Once a signalling message with an E.214 number enters a mobile network in its own country, the routing is dependent on the operator of that mobile network. In networks without
number portability , it is normal that theMSIN has a structure and that, by analysing the first few digits we can further route the message to the right element.IMSI Routing (North America)
In World Area 1 (corresponding to North America) ANSI
SCCP is in use. In this case, due to North American standards, the routing of mobility related messages must be done with the E.212 number directly. This has the advantage that in it is easier to identify to which country messages should be routed based on the mobile country code. The design of theNorth American Number Plan means that there is not a separate country code for each country inNorth America . Working with E.214 numbers would not be an insurmountable challenge, as can be seen from the fact that routing of phone calls using E.164 numbers is normal, but it would mean adding full E.164 routing tables to signalling transfer points where it has never been needed before.That is the simplest way to search the destination.
Routing of mobility messages on the ANSI / ITU Boundary
Where a signalling message travels from North America to the rest of the world or from the rest of the world to North America, there must be a conversion done from
E.212 based global title toE.214 based global title. This conversion is reasonably simple, well defined and fully reversible. The conversion is not totally simple since each individual network must be listed.Recommendation E.214 has been interpreted as suggesting that the analysis of the Mobile Country Code (MCC) and Mobile Network Code (MNC) should be done separately. The relationship between the MNC and the Network Code (NC), however, varies from country to country as does the length of the MNC (two or three digits). This means that the analysis of the MNC is dependent on the analysis of the MCC, or alternatively that the analysis must be done for all five or six digits at once (which is how it is done in practise across at least five separate switch vendors).
Examples
Outbound from America:
*NPI=E.212: 24801 xxxxxxxxxx (248 =Bulgaria MCC + 01 =MobilTel MNC) ->
*NPI=E.214: 359888 xxxxxxxxx (359 =Bulgaria country code )Please note the truncation of the number by one digit since E.214 numbers, as with E.164 numbers have a maximum length of 15 digits.
Inbound toward America:
*NPI=E.214: 14054 xxxxxxxxx (1 = U.S.country code ) ->
*NPI=E.212: 310150 xxxxxxxxx (310 = U.S. MCC + 150 =Cingular MNC)
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