In the CCS7 network each signalling node or entity is identified by an unique code called as Signalling Point Code (SPC in short).This is a unique value within a network.
In case of ITU-T SS7, the SPCs are 14 bit long, while in ANSI SS7, the Point Codes are 24 bit long. Thus, in case of ITU-T, the maximum number of unique SPCs within a “signalling network” are limited to 214 (16384), whereas in ANSI SS7 networks there can be upto 224 (16777216) unique SPCs.
There are different formats / styles in which the Point Codes are represented.
The ITU Point Codes are usually represented in simple decimal number format.
However the ANSI Point Codes are usually broken up into three parts and represented in the form of combination of the three parts. The three parts are A) the Network ID, B) the Cluster ID and C) the Member ID. All three parts are 8 bits long. The ANSI Point codes are represented as the equivalent decimal values of three parts separated by hyphen (e.g. 8-241-23 :: Network ID-Cluster ID-Member ID). This format is sometimes also called as the 8-8-8 format.
On the similar lines, the ITU Point Codes are also represented in Network – Cluster – Member ID format. The 14 bits of the ITU PC are divided in 3 bits of Network ID, 8 bits of Cluster ID and 3 bits of Member ID. Thus, this format is sometimes also called as 3-8-3 format.
In case of ANSI, the Network ID, by definition, is not permitted to be zero. In case of ITU, there is no such restriction. Hence the logical division among Network ID, Cluster ID and the Member ID may lead to a value of zero in Network ID portion of the ITU point code.
There are no standard mechanisms to convert ITU Point Codes into ANSI and vice versa. This is inherently because of the difference in the lengths of the PCs (14 bits in ITU v/s 24 bits in ANSI).
Usually, at the boundaries of two networks where one of the networks is in ITU domain while the other is in ANSI, the “Gateway” STPs are used. The Gateway STPs keep an internal mapping of ITU point codes represented by a dummy ANSI point code and vice versa.
A Route is a predetermined path in a signalling network, consisting of succession of different SEPs(Signalling End Point) / STPs for sending a signalling message from a “Originating Point Code (OPC)” to a particular Destination Point Code (DPC). For most of the practical purposes, a route corresponds to a LinkSet available at a particular Signalling Point to reach to a given DPC.
A RouteSet is a group of all possible Routes between two Signalling Points.
As an example consider following network diagram
There are 2 Signalling End Points (SEPs) A and B . And 2 STPs P and Q
As shown in the above figure, for SEP A , STP P as well as STP Q are the “adjacent Point Codes. The group links L0 to L3 between A & P form a Linkset (LS1). Similarly, the group links L0 to L3 between A & Q form another LinkSet (LS2).
When ‘A’ needs to send a signalling message to ‘B’, the message may traverse any of the following paths: A – P – B, A – P – Q – B and A – Q – B. However, from SEP A’s point of view, there are only two routes to choose from viz. A – P or A – Q.Similarly from STP P’s point of view, to reach the DPC B, there are only two routes: P – B or P – Q – B. Thus, from SEP A’s point of view the two LinkSets are the two possible Routes to reach the DPC B.
A Signalling Link is the physical time slot within an E1 or T1 – connected at both ends to “signalling terminals”. A signalling link is a bi-directional channel used for exchange of signalling information (see ITU-T Q.702 for more details).
LinkSet is signalling relation between two “adjacent” SPCs (Signalling Point Codes). A LinkSet is a group of Links between two adjacent SPCs. In ITU-T SS7 (ITU-T MTP layers), a LinkSet can have maximum of 16 links (due to 4 bit SLS field) whereas in ANSI SS7 (ANSI MTP layers) a LinkSet can have maximum of 32 links (due to 5 bit SLS field).
E.164 is an ITU-T recommendation which defines the international public telecommunication numbering plan used in the PSTN and some other data networks. It also defines the format of telephone numbers. E.164 numbers can have a maximum of fifteen digits. All mobile numbers that we use for calling are in this format.
For eg if you are India subscriber than CC will be 91, If in India you are Vodafone Delhi subscriber then NDC will be 9811 and SN can be any unique number under this CC NDC say 123456.
So you number will be CC+NDC+SN = 91 9811 123456
E.212
The IMSI conforms to the ITU E.212 numbering standard. An International Mobile Subscriber Identity or IMSI is a unique identification associated with all GSM and UMTS network mobile phone users. It is stored as a 64 bit field in the SIM inside the phone and is sent by the phone to the network for identification. IMSI help network identify susbcriber and hence provide all requried services. E212 number can have maximum 15 digits.
Format of E.212 Address is as following
MCC(mobile country code) + MNC(mobile network code) + MSIN( mobile station identification number)
For eg if you are India subscriber than MCC will be 404, If in India you are Vodafone Delhi subscriber then MNC will be 10 and SN can be any unique number under this CC NDC say 1234567890.
So you number will be MCC+MNC+MSIN = 404101234567890
E.214
E.214 is a numbering plan used for delivering mobility management related messages in GSM networks. The E.214 number is derived from the IMSI E.212 numbers are composed of two parts. The first, the E.164 part, is made up of a country code followed by the network code. The second part of the number is made from the MSIN part of the IMSI which identifies an individual subscriber.
For eg if IMSI is 404101234567890 , then corresponding E214 address will be formedby replacing MCC(404) by CC(91) and replacing MNC(10) with NDC(9811) and keeping MSIN as is (as long as it is less than equal to 15 digits).
40410 1234567890 becomes 91 9811 123456789
So basically number format of E.214 is similar to E164 , just that E214 is generated from IMSI and is not actual GT but a virtual GT.
E.214 numbers are routed separately from E.164 numbers since they are marked with a different Numbering Plan Indicator, however, it is possible to reuse the Global Title analysis tables used E.164 numbers everywhere except for the final destination network of the message. This saves considerable administrative work.
2G (or 2-G) is short for second-generation wireless telephone technology. Second generation 2G cellular telecom networks were commercially launched on the GSM standard in Finland by Radiolinja[1] (now part of Elisa Oyj) in 1991. Three primary benefits of 2G networks over their predecessors were that phone conversations were digitally encrypted; 2G systems were significantly more efficient on the spectrum allowing for far greater mobile phone penetration levels; and 2G introduced data services for mobile, starting with SMS text messages.
After 2G was launched, the previous mobile telephone systems were retrospectively dubbed 1G. While radio signals on 1G networks are analog, and on 2G networks are digital, both systems use digital signaling to connect the radio towers (which listen to the handsets) to the rest of the telephone system.
2G has been superseded by newer technologies such as 2.5G, 2.75G, 3G, and 4G; however, 2G networks are still used in many parts of the world.
2G technologies
2G technologies can be divided into TDMA-based and CDMA-based standards depending on the type of multiplexing used. The main 2G standards are:
GSM (TDMA-based), originally from Europe but used in almost all countries on all six inhabited continents. Today accounts for over 80% of all subscribers around the world. Over 60 GSM operators are also using CDMA2000 in the 450 MHz frequency band (CDMA450).[2]
IS-95 aka cdmaOne (CDMA-based, commonly referred as simply CDMA in the US), used in the Americas and parts of Asia. Today accounts for about 17% of all subscribers globally. Over a dozen CDMA operators have migrated to GSM including operators in Mexico, India, Australia and South Korea.
PDC (TDMA-based), used exclusively in Japan
iDEN (TDMA-based), proprietary network used by Nextel in the United States and Telus Mobility in Canada
IS-136 aka D-AMPS (TDMA-based, commonly referred as simply 'TDMA' in the US), was once prevalent in the Americas but most have migrated to GSM.
2G services are frequently referred as Personal Communications Service, or PCS, in the United States.
Evolution
2G networks were built mainly for voice services and slow data transmission.
Some protocols, such as EDGE for GSM and 1x-RTT for CDMA2000, are defined as "3G" services (because they are defined in IMT-2000 specification documents), but are considered by the general public to be 2.5G services (or 2.75G which sounds even more sophisticated) because they are several times slower than present-day 3G services.
2.5G (GPRS)
2.5G is a stepping stone between 2G and 3G cellular wireless technologies. The term "second and a half generation" is used to describe 2G-systems that have implemented a packet switched domain in addition to the circuit switched domain. It does not necessarily provide faster services because bundling of timeslots is used for circuit switched data services (HSCSD) as well.
The first major step in the evolution of GSM networks to 3G occurred with the introduction of General Packet Radio Service (GPRS). CDMA2000 networks similarly evolved through the introduction of 1xRTT. The combination of these capabilities came to be known as 2.5G.
GPRS could provide data rates from 56 kbit/s up to 115 kbit/s. It can be used for services such as Wireless Application Protocol (WAP) access, Multimedia Messaging Service (MMS), and for Internet communication services such as email and World Wide Web access. GPRS data transfer is typically charged per megabyte of traffic transferred, while data communication via traditional circuit switching is billed per minute of connection time, independent of whether the user actually is utilizing the capacity or is in an idle state.
1xRTT supports bi-directional (up and downlink) peak data rates up to 153.6 kbit/s, delivering an average user data throughput of 80-100 kbit/s in commercial networks[3]. It can also be used for WAP, SMS & MMS services, as well as Internet access.
2.75G (EDGE)
GPRS networks evolved to EDGE networks with the introduction of 8PSK encoding. Enhanced Data rates for GSM Evolution (EDGE), Enhanced GPRS (EGPRS), or IMT Single Carrier (IMT-SC) is a backward-compatible digital mobile phone technology that allows improved data transmission rates, as an extension on top of standard GSM. EDGE was deployed on GSM networks beginning in 2003--initially by Cingular (now AT&T) in the United States.
EDGE is standardized by 3GPP as part of the GSM familylike the sopranos and the Corleone families, and it is an upgrade that provides a potential three-fold increase in capacity of GSM/GPRS networks. The specification achieves higher data-rates (up to 236.8 kbit/s) by switching to more sophisticated methods of coding (8PSK), within existing GSM timeslots.
3G
International Mobile Telecommunications-2000 (IMT — 2000), better known as 3G or 3rd Generation, is a generation of standards for mobile phones and mobile telecommunications services fulfilling specifications by the International Telecommunication Union.Application services include wide-area wireless voice telephone, mobile Internet access, video calls and mobile TV, all in a mobile environment. Compared to the older 2G and 2.5G standards, a 3G system must allow simultaneous use of speech and data services, and provide peak data rates of at least 200 kbit/s according to the IMT-2000 specification. Recent 3G releases, often denoted 3.5G and 3.75G, also provide mobile broadband access of several Mbit/s to laptop computers and smartphones.
A Serving GPRS Support Node (SGSN) is responsible for the delivery of data packets from and to the mobile stations within its geographical service area. Its tasks include packet routing and transfer, mobility management (attach/detach and location management), logical link management, and authentication and charging functions. The location register of the SGSN stores location information (e.g., current cell, current VLR) and user profiles (e.g., IMSI, address(es) used in the packet data network) of all GPRS users registered with this SGSN.
A Short Message Service Center (SMSC) is a network element in the mobile telephone network which delivers SMS messages.
All SMS sent by a mobile subscriber are first submitted to SMSC of his mobile network. After submission SMSC find the location of destination mobile subscriber and deliver the SMSC to that subscriber. SMSC works on store and forward mechanism. If for some reasons SMSC is unable to deliver SMS to destination subscriber, SMSC can store this SMS for longer durations and keep retrying to deliver this SMS at regular interval.
The Mobile Switching Center or MSC is the primary service delivery node for GSM, responsible for handling voice calls and SMS as well as other services (such as conference calls, FAX and circuit switched data). The MSC sets up and releases the end-to-end connection, handles mobility and hand-over requirements during the call and takes care of charging and real time pre-paid account monitoring.
In the GSM mobile phone system, in contrast with earlier analogue services, fax and data information is sent directly digitally encoded to the MSC. Only at the MSC is this re-coded into an "analogue" signal (although actually this will almost certainly mean sound encoded digitally as PCM signal in a 64-kbit/s timeslot, known as a DS0 in America).
There are various different names for MSCs in different contexts which reflects their complex role in the network, all of these terms though could refer to the same MSC, but doing different things at different times.
A Gateway MSC is the MSC that determines which visited MSC the subscriber who is being called is currently located. It also interfaces with the Public Switched Telephone Network. All mobile to mobile calls and PSTN to mobile calls are routed through a GMSC. The term is only valid in the context of one call since any MSC may provide both the gateway function and the Visited MSC function, however, some manufacturers design dedicated high capacity MSCs which do not have any BSSes connected to them. These MSCs will then be the Gateway MSC for many of the calls they handle.
The Visited MSC is the MSC where a customer is currently located. The VLR associated with this MSC will have the subscriber's data in it.
The Anchor MSC is the MSC from which a handover has been initiated. The Target MSC is the MSC toward which a Handover should take place. An MSC Server is a part of the redesigned MSC concept starting from 3GPP Release 5.
Visitor Location Register (VLR) is a database - part of the GSM mobile phone system - which stores information about all the mobiles that are currently under the jurisdiction of the MSC (Mobile Switching Center) which it serves. Of all the information it stores about each MS (Mobile Station), the most important is the current LAI (Location Area Identity). LAI identifies under which BSC (Base Station Controller) the MS is currently present. This information is vital in the call setup process.
Whenever an MSC detects a new MS in its network, in addition to creating a new record in the VLR, it also updates the HLR of the mobile subscriber, apprising it of the new location of that MS.
The Home Location Register or HLR is a central database that contains details of each mobile phone subscriber that is authorized to use the GSM core network. There is one logical HLR per PLMN, although there may be multiple physical platforms.
The HLR stores details of every SIM card issued by the mobile phone operator. Each SIM has a unique identifier called an IMSI which is the primary key to each HLR record.
The next important items of data associated with the SIM are the MSISDNs, which are the telephone numbers used by mobile phones to make and receive calls. The primary MSISDN is the number used for making and receiving voice calls and SMS. Each MSISDN is also a primary key to the HLR record.
Examples of other data stored in the HLR against an IMSI record is:
GSM services that the subscriber has requested or been given, like can he make call, can he receive call , can he make sms, can he roam etc
GPRS settings to allow the subscriber to access packet services
Current Location of subscriber (VLR and SGSN), i.e where is this subscriber currently.
Call divert settings applicable for each associated MSISDN.
Signaling System #7 (SS7) is a set of telephony signaling protocols which are used to set up most of the world's public switched telephone network telephone calls. The main purpose is to set up and tear down telephone calls.
Other uses include number translation, prepaid billing mechanisms, short message service (SMS), and a variety of other mass market services.It is usually abbreviated to SS7 though in North America it is often referred to as CCSS7, an acronym for "Common Channel Signaling System 7".
In some European countries, specifically the United Kingdom, it is sometimes called C7 (CCITT number 7) and is also known as number 7 and CCIS7. (ITU-T was formerly known as CCITT.)There is only one international SS7 protocol defined by ITU-T in its Q.700-series recommendations.
There are however, many national variants of the SS7 protocols. Most national variants are based on two widely deployed national variants as standardized by ANSI and ETSI, which are in turn based on the international protocol defined by ITU-T. Each national variant has its own unique characteristics. Some national variants with rather striking characteristics are the China (PRC) and Japan (TTC) national variants.
The Internet Engineering Task Force (IETF) has also defined level 2, 3, and 4 protocols that are compatible with SS7 MTP2 (M2UA and M2PA) MTP3 (M3UA) and SCCP (SUA), but use an SCTP transport mechanism. This suite of protocols is called SIGTRAN.
History :
Common Channel Signaling protocols have been developed by AT&T, BT and the ITU-T since 1975 and the first international Common Channel Signaling protocol was defined by the ITU-T as Signalling System No. 6 in 1977. Signalling System No. 7 was defined as an international standard by ITU-T in its 1980 (Yellow Book) Q.7XX-series recommendations. SS7 was designed to replace Signalling System No. 6, which had a restricted 28-bit signal unit that was both limited in function and not amenable to digital systems.SS7 has substantially replaced SS6, SS5, R1 and R2, with the exception that R1 and R2 variants are still used in numerous nations.
SS5 and earlier used in-band signaling, where the call-setup information was sent by playing special multi-frequency tones into the telephone lines (known as bearer channels in the parlance of the telecom industry). This led to security problems with blue boxes. Modern designs of telephone equipment that implement out-of-band signaling protocols explicitly keep the end-user's audio path—the so-called speech path—separate from the signaling phase to eliminate the possibility that end users may introduce tones that would be mistaken for those used for signaling.
SS6 and SS7 moved to a system in which the signaling information was out-of-band, carried in a separate signaling channel. This avoided the security problems earlier systems had, as the end user had no connection to these channels. SS6 and SS7 are referred to as so-called Common Channel Interoffice Signalling Systems (CCIS) or Common Channel Signaling (CCS) due to their hard separation of signaling and bearer channels. This required a separate channel dedicated solely to signaling, but the greater speed of signaling decreased the holding time of the bearer channels, and the number of available channels was rapidly increasing anyway at the time SS7 was implemented.
The common channel signaling paradigm was translated to IP via the SIGTRAN protocols as defined by the IETF. While running on a transport based upon IP, the SIGTRAN protocols are not an SS7 variant, but simply transport existing national and international variants of SS7.
