TELECOMMUNICATION SYSTEMS

Transcription

1 TELECOMMUNICATION SYSTEMS By Syed Bakhtawar Shah Abid Lecturer in Computer Science 1

2 SS7 Network Architecture SS7 can employ different types of signaling network structures. The worldwide signaling network has two functionally independent levels: National International This structure makes possible a clear division of Responsibility for signaling network management Numbering plans of SS7 nodes belonging to the international and national networks. 2

3 SS7 Network Architecture SS7 network nodes are called signaling points (SPs). Each SP is addressed by an integer called a point code (PC). The international network uses a 14-bit PC. The national networks also use a 14-bit PC except North America and China, which use an incompatible 24-bit PC, and Japan, which uses a 16-bit PC. The national PC is unique only within a particular operator's national network. International PCs are unique only within the international network. Other operator networks (if they exist) within a country also could have the same PC and also might share the same PC as that used on the international network. 3

4 Signaling Links and Linksets 4 SPs are connected to each other by signaling links over which signaling takes place. The bandwidth of a signaling link is normally 64 or 56 kbps. High-speed links have been introduced that use an entire Mbps T1 carrier for signaling. Links are typically engineered to carry only 25 to 40 percent of their capacity so that in case of a failure, one link can carry the load of two. To provide more bandwidth and/or for redundancy, up to 16 links between two SPs can be used. Links between two SPs are logically grouped for administrative and load-sharing reasons.

5 Signaling Links and Linksets A logical group of links between two SP is called a linkset. 5 A number of linksets that may be used to reach a particular destination can be grouped logically to form a combined linkset. A group of links within a linkset that have the same characteristics (data rate, terrestrial/satellite, and so on) are called a link group. Normally the links in a linkset have the same characteristics, so the term link group can be synonymous with linkset.

6 Routes and Routesets SS7 routes are statically provisioned at each SP. There are no mechanisms for route discovery. A route is defined as a preprovisioned path between source and destination for a particular relation. The following figure shows a route from SP A to SP C. 6

7 Routes and Routesets All the preprovisioned routes to a particular SP destination are called the routeset. The following Figure shows a routeset for SSP C consisting of two routes. 7

8 SS7 Node Types There are three different types of SPs The following figure graphically represents these nodes 8

9 Signal Switching Point SSPs are voice switches which exists in the embedded telephone switch circuit, that have SS7 software and terminating signaling links. An SSP can originate and terminate messages An SSP voice switch have the ability to send messages using ISDN User Part (ISUP) (call setup and teardown) & TCAP (database lookup) SS7 protocols. The Transaction Capabilities Application Part (TCAP) of the SS7 protocol allows services at network nodes to communicate with each other using an agreed-upon set of data elements. SSPs create packets (signal units) and send those messages to other SSPs, as well as queries to remote shared databases to find out how to route calls. 9

10 Signal Transfer Point STPs are packet switches, and act like routers in the SS7 network. Routes each incoming message to an outgoing signaling link, based on routing information contained in the SS7 message and a pre-defined route table. Messages are not usually originated by an STP. Does not offer termination services 10

11 Levels of STP There are three levels of STPs. National STP National STP exists within the national network It can transfer messages that use the same national standards of protocol. Protocol converters often interconnect a National and an International STP by converting from ANSI to ITU-TS. International STP An International STP functions within an international network. It provides for SS7 interconnection of all countries, using the ITU-TS protocol. 11

12 Levels of STP Gateway STP A Gateway STP converts signaling data from one protocol to another. Gateway STPs are often used as an access point to the international network Gateway STP also serves as an interface into another network's databases Example When International STP & National STP calling to each others, if International STP is in US and National STP is in Europe, for protocol translation, the STP used is called Gateway STP. 12

13 Signal Control Point 13 An SCP is usually a computer used as a front end to a database system. A Service Control Point (SCP) acts as an interface between telecommunications databases and the SS7 network. or It is an interface to Telco databases and other applicationspecific databases. Call management DB call processing, routing, 800, 900 Home / Visitor location register cell phones Line information billing Local number portability A popular example is freephone calling (known as toll-free). The SCP provides the routing number (translates the tollfree number to a routable number) to the SSP to allow the call to be completed.

14 Databases Accessible via SCP HLR LNP Home Location Register Local Number Portability Used in cellular networks to store subscriber information. Allows people to change service providers but keep their same telephone number OSS Operation Support System Associated with remote maintenance center for monitoring and managing SS7 and voice networks. VLR Visitor Location Register Used when a cell phone is not recognized by the mobile switching center (MSC). 14

15 SS7 Signaling Architecture SCP control SCP SS7 link typical speed 56K or 64K SSP Switching STP transfer STP SSP STP STP 15

16 SS7 Links An SS7 link is the physical transmission line (serial 56/64 Kbps or DS0 channel) that connects the individual nodes in an SS7 network. SS7 Link Types Access links (A links) Crossover links (C links) Bridge links (B links) Diagonal links (D links) Extended links (E links) Fully associated links (F links) 16

17 A-Links Access links (A links) provide access to the network. They connect "outer" SPs (SSPs or SCPs) to the STP backbone. Always two A links, one to each of the home STP pairs A links connect SSPs and SCPs to their serving STP or STP mated pair. Maximum of 16 A links into one STP 17

18 B-Links Bridge links (B links) are used to connect mated pairs of STPs to each other across different regions within a network at the same hierarchical level. These links help form the backbone of the SS7 network. The following figure shows two sets of mated pairs of B links. 18

19 D-Links Diagonal links (D links) are the same as B links in that they connect mated STP pairs. The difference is that they connect mated STP pairs that belong to different hierarchical levels or to different networks altogether. For example, they may connect an interexchange carrier (IXC) STP pair to a local exchange carrier (LEC) STP pair or a cellular regional STP pair to a cellular metro STP pair. Max. of 8 D links between mated STP pairs 19

20 C-Links Cross links (C links) are used to connect two STPs to form a mated pair that is, a pair linked such that if one fails, the other takes the load of both. Under normal conditions, they are used only to carry network management messages. Not used for routing, up to 8 C links between paired STPs 20

21 E & F-Links 21 Extended links (E-links) connect an SSP to an alternate STP to provide backup connectivity to the network if the SSP's "home" STP cannot be reached on its A-link E links connect to a non-home STP pair Fully associated links (F-links) directly connect two signaling end points (SSPs and/or SCPs). These links are not usually used in networks with STPs because they allow associated signaling only.

22 SS7 Network Segments 22

23 SS7 Network Segments 23

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25 Thank You 25