Red SS7 Conceptos claves

Nortel Networks Confidential 1

SS7 Networks and Key Concepts


SS7 Defined• Common Channel Signaling System No. 7 (i.e., SS7 or C7) is a global

standard for telecommunications defined by the International Telecommunication Union (ITU) Telecommunication Standardization Sector (ITU-T).

• The standard defines the procedures and protocol by which network elements in the public switched telephone network (PSTN) exchange information over a digital signaling network to effect wireless (cellular) and wireline call setup, routing and control.

• The ITU definition of SS7 allows for national variants such as the American National Standards Institute (ANSI) and Bell Communications Research (Bellcore) standards used in North America and the European Telecommunications Standards Institute (ETSI) standard used in Europe.


What is SS7 used for?

The SS7 network and protocol are used for: • basic call setup, management, and tear down• wireless services such as personal communications services

(PCS), wireless roaming, and mobile subscriber authentication

• local number portability (LNP) • toll-free (800/888) and toll (900) wireline services • enhanced call features such as call forwarding, calling party

name/number display, and three-way calling • efficient and secure worldwide telecommunications


Signaling Links

SS7 messages are exchanged between network elements over 56 or 64 kilobit per second (kbps) bidirectional channels called signaling links. Signaling occurs out-of-band on dedicated channels rather than in-band on voice channels. Compared to in-band signaling, out-of-band signaling provides:

• faster call setup times (compared to in-band signaling using multifrequency (MF) signaling tones)

• more efficient use of voice circuits • support for Intelligent Network (IN) services which require signaling to

network elements without voice trunks (e.g., database systems) • improved control over fraudulent network usage


Signaling PointsEach signaling point in the SS7 network is uniquely identified by a numeric point code. Point codes are carried in signaling messages exchanged between signaling points to identify the source and destination of each message. Each signaling point uses a routing table to select the appropriate signaling path for each message. There are three kinds of signaling points in the SS7 network: SSP (Service Switching Point) STP (Signal Transfer Point) SCP (Service Control Point)

• SSP’s are switches that originate, terminate or tandem calls• STP’s route network traffice between signaling points (ie acts like a network hub)• Centralize database which determines how to route a call (ie 1-800/888 services)


Signaling Interconnection

E Links

A Links B-LinkQuad

D Links

C Links

RSTP

SSP

SSP

SCP

LSTP LSTP

LSTP LSTP

• Link Types:- Access (A-Links): Connects STPs with SSPs, SCPs or MSC (Message Switching Center)- Bridge (B-Links): Connects STPs - Cross (C-Links): Connects mated STPs- Diagonal (D-Links): Connects regional/local STPs to primary STPs- Extended Links (E-Links): Connects SSPs , SCPs or MSC to alternate STPs- Fully-Associated (F-Links): Connects SSPs


Linksets• Linksets:

- Group of links between two nodes in the network- Links are deployed in numbers to the power of 2 (1, 2, 4, 8)- Traffic is loadshared over all link in the linksets- Linkset size is limited by the protocol being used- Combined linksets between STP pairs allow for loadsharing over both

nodes to increase redundancy.

Linkset 1

Linkset 2

Linkset 3

Combined Linksets


Point Codes• Point Codes:

- Each signaling point in a SS7 network is assigned a unique point code- Point code structure:

• ITU - 14 bit Point code• ANSI - 24 bit Point code• China - 24 bit Point code • Japan - 16 bit Point code

- ITU Point Code:• Basic: 14• International: 3 (Zone) - 8 (Area Network) - 3 (Signaling Point)• Austria: 5 (Zone) - 4 (Region) - 5 (Signaling Point)• China: 4 (Zone) - 7 (Exchange) - 3 (Signaling Point)• Germany: 4 (Num Area) - 3 (HVST) - 4 (KVST) - 3 (Signaling Point)

- Node Identifiers:• Origination Point Code (OPC) • Destination Point Code (DPC)

0-1-0

1-1-0

3-3-3


Routesets• Routesets

- Routes are defined between paths to a specific DPC- A collection of Routes are defined as a Routeset- Multiple Routes in a Routeset ensure that redundancy is

build into the product.- Routes are costed (Less expensive routing)

0-1-0

1-1-0

3-3-3

0-1-0

1-1-0

3-3-3


Subsystems Numbers/GTT• Subsystem Number (SSN)

- Uniquely identifies an application residing on a destination point; typically an SCP database.

• Global Title Translation (GTT)- Global Title Translation(GTT) provide specific

information with regards to the Destination Point Code of the location of the application.


SS7 Protocol Layers


SS7 Protocol Stack

The hardware and software functions of the SS7 protocol are divided into functional abstractions called "levels". These levels map loosely to the Open Systems Interconnect (OSI) 7-layer model defined by the International Standards Organization (ISO).


SS7 Protocol• SS7 Protocol Layer

- Message Transfer Part (MTP) Level 1- Message Transfer Part (MTP) Level 2- Message Transfer Part (MTP) Level 3- Signal Connection Control Part (SCCP)- Transaction Capabilities Part (TCAP)

• Key Protocol Specifications- ITU Specifications: White Book (1992) Q701-Q709 (MTP),

Q710-Q716 (SCCP), Q75x (Measurements)- ETSI Specifications: 300 008 (MTP), 300 009 (SCCP)- ANSI Specifications: GR-82, GR-246


Message Transfer Point (MTP): Level 1 to 2

MTP Level 1 • The lowest level, MTP Level 1, is equivalent to the OSI Physical Layer. MTP Level 1

defines the physical, electrical, and functional characteristics of the digital signaling link.

• Physical interfaces defined include E-1 (2048 kb/s; 32 64 kb/s channels), DS-1 (1544 kb/s; 24 64 kp/s channels), V.35 (64 kb/s), DS-0 (64 kb/s), and

MTP Level 2• Data link layer “handshaking”• Ensure message are transmitted accurately end to end, in sequence• error control, flow control between two nodes


Message Types

FISU

MSU

LSSU


Message Transfer Point (MTP):Level 3

• MTP Level 3- Network level- Message routing and network management- Most effective message route between two signaling points - Rerouting traffic away from failure- Notification to all network to ensure minimal impact during

failure modes (congestion control).


SCCP Layer

- Provides connectionless and connection-oriented network services. Where MTP route messages to a signaling point, SCCP will determine an application at that point.

- Determines network address and relay the information to MTP layer

- SCCP also provides the means by which an STP can perform global title translation (GTT), a procedure by which the destination signaling point and subsystem number (SSN) is determined from digits (i.e., the global title) present in the signaling message.


Application Layer

• Application Layer- ISUP (ETSI, ANSI), xTUP

• Call control part of the protocol• The ISDN User Part (ISUP) defines the protocol and procedures

used to set-up, manage, and release trunk circuits that carry voice and data calls over the public switched telephone network (PSTN). ISUP is used for both ISDN and non-ISDN calls.

- TCAP• Transfer non-circuit related information • Supports database queries and responses between SSPs and SCPs• TCAP enables the deployment of advanced intelligent network

services by supporting non-circuit related information exchange between signaling points using the SCCP connectionless service.


Example ITU ISUP Message


Signaling Solution Group Products

•DMS-STP: First Generation, DMS-100 architecture STP Product Field proven, Global Product solution with - ITU Capability

•BroadBand-STP: Third Generation product based on Signaling Server Platform Technology • Cost effective, Low Power/Real estate requirements• SCP/Boundary Gateway solutions - LNP, Mediation, etc.

•DMS-SSP: DMS switch architecture SSP product SS7 access switch for all Nortel PSTN switching products

•Universal NP Master: Third generation number portability solution based on the Signaling Server Platform Technology• Scalable, flexible implementation, proven LSMS• Wireless and wireline solutions


Signaling Solution Group Products

•Universal Signaling Point - SS7/IP Gateway application: Third Generation application based on Signaling Server Platform Technology - Part of Succession CS2K, CS3K and e-mobility solution

•Universal Mediation Platform - Adds ability to control requests from another operator’s networks. Guards against inappropriate and/or illegal use of host network and services. Screens ISUP and TCAP messages and their content.

Red SS7 Conceptos claves

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