SS7 Architecture and Network Protocols

SSTP Architecture and Network

• Signaling System No. 7 (SS7) is a global standard signaling protocol for modern telecommunications networks.
• SS7 is a layered protocol that adheres to the OSI reference model.
• It allows network elements to share information beyond basic call control.
• SS7 offers an Integrated Services Digital Network-User Part (ISUP) and a Transaction Capabilities Application Part (TCAP).
• Functions of the TCAP and ISUP layers correspond to the Application Layer of the OSI reference model.
• SS7 enables services such as user-to-user signaling, closed-user groups, calling line identification, call forwarding options, and centralized database services (e.g., 800 and 900 services).
• These services can be offered between any two network subscribers.

CCS Network Architecture

• The CCS Network has four major components: Service Switching Points (SSP), Signaling Transfer Points (STP), Service Control Points (SCP), and Data Signaling Links (SLK).
• An SS7 Network consists of a flat, non-hierarchical configuration, allowing peer-to-peer communication through SS7 Common Channel Signaling Networks.
• SS7 Common Channel Signaling Networks has three components interconnected by six signaling link types.
• Signaling links transmit data at 64,000 bits per second in most regions.
• High-Speed Links (HSLs) at 2.048 Mbps are also used.
• Signaling links between network elements are in groups called "link sets" sized to carry traffic between two STPs.
• STPs are deployed in pairs allowing an alternate route between any two STPs.
• A "combined link set" interconnects an SSP or SCP with both members of the STP pair.
• Traffic load is shared across links in a link set and STP pairs.

Service Switching Point (SSP)

• SSPs are the legacy switches of telecommunications networks, referred to as "End Office switch", "Central Officeswitch", “Toll Tandem switch".
• Central offices housing the SSP are identified by classes ranging from class 5 to class 1.
• The lowest class office in a network provides dial tone to subscribers.
• An SSP is typically in tandem or Class 5 offices and serves as the interface to networks outside of SS7.
• SSP can be a customer switch, end office, access tandem, or tandem.
• A switch is used to interface with premises, while the CO switch interfaces with the SS7 network through the SSP.
• SSP provides dial tone, routes calls between links and trunks, provides tones and announcements, and handles maintenance, revenue collection, and generation.
• It generates queries to signaling nodes or databases and carries out the connection function for handling calls upon receiving queried information.
• SSP establishes and maintains connections to Intelligent Peripherals (IPs) for Advanced Intelligent Network (AIN) services.

Service Control Point (SCP)

• SCPs and AIN SCPs are centralized databases giving real-time access to call completion and information services.
• These include Toll-Free Database Service, Alternate Billing Service (ABS), Custom Local Area Signaling Services (CLASS), Advanced Intelligent Network Services (AIN), Local Number Portability (LNP), Home Location Register (HLR), and Visitor Location Register (VLR).

Signaling Transfer Point (STP)

• STPs are routers placed within the core of CCS Networks.
• STPs are packet switches for common channel message routing and transport.
• They use stored programmed control switches using message information and memory to route messages to the destination signaling point.
• STPs are deployed in pairs with mirrored databases.
• If one of the STPs fails or signaling links are down, the other can process the traffic and geographically separated, which ensures protection for message routing during natural disasters.

STP Architectures

• In large CCS networks, STPs are in a hierarchical arrangement as Regional STPs and Local STPs.
• There is no functional difference between the two STP types, however
• LSTP handles call set-up and network management traffic, while
• RSTP handles query traffic needing access to SCP databases.
• STPs are categorized into two types: Integrated STP and Standalone STP.
• Integrated STP incorporates STP functionality along with a 'Service Switching Point' in a 'Service Switching Node', performing call switching and signaling functions.
• Standalone STP performs SS7 signaling transfer, enabling operators to manage network resources effectively and host more applications.

SSTP Functions

• SS7 Message routing
• Global Title Translation
• SS7 Network Management
• Network Interconnection
• Gateway Screening

SSTP Function - Message Routing

• Message Routing uses the outgoing Destination Point Code (DPC) in the MTP's routing label in a datagram environment.
• Routing tables, prepared to allow message transport between SSTP pairs, are stored and maintained within SSTPs.
• The SSTP's SNM (signaling network management) functions control message routing during link congestion or failure.
• Routing is performed using Destination Point Codes (DPCs), similar to street addresses for the Postal Service, allowing STPs to route messages to all signaling points.
• All nodes in the network have a unique point code to identify the Origination Point Code (OPC) and the Destination Point Code (DPC) in the routing label of all Message Signaling Units (MSUs).

SSTP Function – Global Title Translation

• Global Title translation uses SCCP to translate addresses (Global titles) from signaling messages lacking explicit routing information for the MTP.
• The SSTP translates dialed 1+800 numbers into an SCP's DPC for MTP routing and gives subsystem number SSN for delivery to the database application at the SCP.
• STPs contain a GTT table with details for the type of query and SCP address.

SSTP Function – Network Management

• SSTP function manages network traffic, routing it around failures and controlling link congestion.
• Transfer prohibited (TFP) tells connecting nodes not to send traffic destined for the affected node.
• Transfer restricted (TFR) tells connecting nodes, if possible, to not send anything destined for the affected node.

SSTP Function – Gateway Screening

• Screening is the capability to examine incoming and outgoing packets and allow only authorized packets through gateway screening tables configured by the service provider.
• Only ISUP messages over one link set can be allowed, while only SCCP messages can be allowed over another link using allow and block functions.
• SSTP software with inter-network connection manages access into a Telco's network.
• Main objectives of SSTP's:
• Regulate, measure, and account for inter-network traffic, including SMS messages from GSM and CDMA mobile networks.
• Flexibility and transparency in signaling for BSNL's wired and wireless networks.
• Optimal expansion of GSM & CDMA networks of BSNL.
• Introduction of new services.
• Offer CCS7 & IP Signaling Services to other Wire line & Wireless Network Operators.

Stand-Alone STP Network in BSNL

• Advantages of stand-alone STP network includes
• Dedicated signaling processors, resources
• Upgrade path divorced from MSC / SSP functions, growth
• Effective method to manage network level resources, features
• Frees up processing capacity from the switches
• Hosts most of the applications, centrally

Stand-Alone STP Network in BSNL: Pt 2

• Full mated pair redundancy.
• Disadvantages:
• Requires additional investment (compensated by freeing up extra resources of the switches).
• Requires traffic study, SS7 management.
• BSNLCO issued PO no. SE/PO/005/2016-17/SSTP/New/UTStarcom dtd.01.03.2017 for Supply, Installation, Commissioning and Migration.
• The PO will replace the SSTP network of M/s.Tekelec (now M/s. Oracle) with a new SSTP network to M/s.UTStarcom India Telecom Private Ltd.
• There are total 18 SSTP nodes with EMS NOC at Bangalore & DR EMS NOC at Mumbai with equipment supplied, installed, and ATed at all nodes.

ISG6400

• UTSTARCOM SSTP iSG6400 implements translation, adaptation, and distribution for SIGTRAN and SS7 signaling messages, along with translation, adaptation and distribution for M3UA-based SIGTRAN, M2UA-based SIGTRAN, SIP and Diameter signaling.
• Flexible Hardware and Software Platforms
• Carrier-Class High Availability
• Powerful System Functions
• MTP Message Screening
• Number Portability
• Diameter Signaling Controller
• Graphical and Convenient Network Management
• BSNL's SSTP network includes 16 SSTP nodes with mated pair configuration. SSTPs at Delhi, Chennai, Pune, and Ernakulum have International Signaling Gateway functionality.
• Each of the TAXs/IP TAXS & MSCs in BSNL Network is connected to at least two SSTPs through IP and/or E1 link for load balancing and failover.
• MSCs in the Indian Telecom Network connected to TAXs/IP TAXs of BSNL Network are routed through one of the sixteen SSTPs installed as part of this tender.
• SSTPs are connected with the BSNL's IP MPLS network via two L3 LAN switches with at least two GE interfaces in high availability mode (Active-Active).
• SSTPs are interconnected with mated SSTP nodes with FE/HSL links through the SDH network of BSNL for redundancy, in addition to interconnecting the SSTPs themselves and to the EMS locations on the IP MPLS networks.
• Network elements are also connected with HSL/FE links at NOC/ DR NOC at Bangalore and Mumbai.
• The chassis accommodate function boards in six categories:
• MPU Card (MPU1A): system main control board, managing hardware resources and functioning as a communication agent for the SNMS.
• Line Card (PEM-S8): supports TDM-based MTP2 protocol and IP-based M2PA protocol, implementing reliable signaling link transmission and translation between SS7 common channel signaling and MTP3 messages.
• CLOCK I/O board (PCU1A): Provides the synchronization clock signal for E1/T1 trunks.
• SPU (Signaling Processing Unit): signal processing for SIGTRAN and SS7 signaling messages translation and distribution, supporting MTP3, SCCP, and M3UA protocols.
• Hardware Platform: X86 based Server
• ISG6400 Chassis is active and active load sharing mode, failure of any hardware module in one chassis has no effect, the LSL and HSL links from SSP are duplicated and connected to E1 ports on both chassis, LAN SW Pair works in Active-Active mode.
• SPU (Signaling Processing Unit): software application based on IBM servers, signal processing supports SIGTRAN and SS7 signaling messages translation and distribution, and also supports MTP3, SCCP, and M3UA protocols, two SPUs run on active – Active load sharing mode.

Unique features of UTSTARCOM SSTP:

• MNP capacity is 250M NP entries, with expansion potential.
• UT SSTP uses Oracle DB for eMS and NP DB, with centralized data management.
• The network includes distributed SSTP nodes and Centralized eMS/NP SRV/DB SRV.
• Centralized DB means low CAPEX and OPEX.
• Veritas synchronizes the Oracle DB between different NOC/DR-NOC for DB Geographic Redundancy.
• Centralized eMS manages SSTP nodes deployed around PAN India.
• eMS is GUI based.
• Supports SS7 and SIGTRAN.
• Supports the emerging DIAMETER and SIP protocol.

Conclusion

• SS7's efficiency enables fast connection setup in PSTN, "short message service," and "location update" messages in GSM.
• The Standalone Signal Transfer Point (SSTP) introduction addressed complexity by converting mesh networks into star networks.
• SSTPs handle non-call related messages efficiently and support new signaling technologies like SIP and diameter, along with existing SS7/SIGTRAN, catering to the signaling needs of the BSNL network.