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E1-E2 (CFA)/SSTP Rev date: 25-03-11 Page: 1 For Internal Circulation Only BSNL, India Name of Course : E1-E2 CFA Chapter 8 Topic : SSTP Date of Creation : 25.03.2011
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Page 1: Name of Course : E1-E2 CFA Chapter 8 Topic : SSTP Date of …training.bsnl.co.in/DIGITAL_LIBRARY_SOURCE/upgradation/e1... · 2018-04-23 · BSNL, India For Internal Circulation Only

E1-E2 (CFA)/SSTP Rev date: 25-03-11

Page: 1 For Internal Circulation Only BSNL, India

Name of Course : E1-E2 CFA

Chapter 8

Topic : SSTP

Date of Creation : 25.03.2011

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SSTP

Common Channel Signaling Networks

Signaling System No. 7 (SS7) is a signaling protocol that has become a worldwide

standard for modern telecommunications networks. SS7 is a layered protocol following

the OSI reference model. It offers all of the same call setup advantages as CCS6, but also

enables network elements to share more than just basic call-control information through

the many services provided by the SS7 Integrated Services Digital Network-User Part

(ISUP), and the Transaction Capabilities Application Part (TCAP).

The functions of the TCAP and ISUP layers correspond to the Application Layer of the

OSI reference model, and allow for new services such as User-to-User signaling, Closed-

User Group, Calling Line Identification, various options on Call Forwarding, and the

rendering of services based on a centralized database (such as 800 and 910 service). All

of these services may be offered between any two network subscribers, not just to

subscribers served by the same telephone switch.

SS7 Link and Message Types

An SS7 Network consists of a flat non-hierarchical configuration enabling peer-to-peer

Communication. Figure 1: SS7 Common Channel Signaling Networks depicts the

makeup and connectivity of SS7 Common Channel Signaling networks currently

installed and in use.

Figure 1: SS7 Common Channel Signaling Networks

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Figure 1: SS7 Common Channel Signaling Networks shows the three principal network

elements of SS7 Common Channel Signaling networks, interconnected by the six

standard types of signaling links currently in use. Signaling links are data transmission

links that ordinarily operate on digital carrier facilities at 64,000 bits per second in most

regions of the world. High Speed Links (HSLs) at 2.048 Mbps are used.

Signaling links between any two signaling network elements are deployed in groups

called “link sets,” dimensioned to carry the estimated signaling traffic between two STPs.

Because STPs like the EAGLE 5 ISS are deployed in pairs, as shown in Figure 1: SS7

Common Channel Signaling Networks, an alternate route always exists between any two

STPs.

One combination of the link sets interconnecting an SSP or SCP with both members of

the STP pair is called a “combined link set.” The traffic carried between any two

signaling network elements is load-shared across links in a link set, rotating through all

links available according to the rules of the SS7 protocol.

Traffic destined for any network element through the STP pair is further load-shared over

the combined link set, unless restricted by network management rules also established by

the SS7 protocol.

Role of SSPs, STPs, and SCPs in SS7 Networks

Service Switching Points (SSPs)

In conventional telephone networks, Service Switching Points (SSPs) are usually

telephone central offices, also known as “End-Offices,” or “Access Tandems.” In the

cellular mobile or “wireless” communications environment, an SSP is frequently located

at the Mobile Switching Center (MSC).

In either case, the SSPs perform circuit-switching functions, and are capable of using the

SS7 protocol to signal other SSPs for call setup, or to query the centralized databases that

are stored in Service Control Points (SCPs).

Service Control Points (SCPs)

Service Control Points (SCPs) are network intelligence centers where databases of call

processing information are stored. The primary function of SCPs is to respond to queries

from other SCPs, by retrieving the requested information from the appropriate database

within the SCP node, and sending it back to the originator of the request.

SCPs currently serve as centralized databases to translate logical numbers (such as

1+N00 numbers) into network physical addresses, or to verify credit card data and status.

Future plans call for expanding the centralized resource responsibilities of the SCP to

include greater interaction in call processing. This expansion of responsibilities will be

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attained through newly defined “call models” implemented in SSPs that may invoke

assistance from SCPs more than once for the same call.

The information managed by an SCP can be modified or updated without affecting any

other node in the SS7 network. This ease of data administration is a major appeal of SS7

implementation.

Applications of SCPs for 1+800 calls and credit card verifications could be implemented

by storing the respective databases at each network-switching node. This approach

creates an unmanageable task of administering multiple decentralized databases.

To appreciate the expediency and economy of centralized databases, consider adding a

new service to a 100-node network by updating 100 databases. The ease of administration

and greater control of new service offerings are obvious when one compares the two

alternatives.

SCP contains

Service Management Point (SMP)

- The SMP, which is a computer system, is the front-end to the SCP and provides

the user interface. It is sometimes referred to as the Service Management System

(SMS).

- It updates the SCP with new data and programs (service logic) and collects

statistics from it.

- The SMP also enables the service subscriber to control his own service

parameters via a remote terminal connected through dial-up connection or X.25

PSPDN.

This modification is filtered or validated by the network operator before

replicating it on the SCP. The SMP may contain the service creation environment

as well.

- In that case the new services are created and validated first on the SMP before

downloading to the SCP.

- One SMP may be used to manage more than one SCP's.

Service Logic Execution Environment (SLEE) & SEP

- The process that executes the Service Logic is called the Service Execution

Process (SEP).

- The name "service application copy" is only relevant in the context of a SS7

service, as this is the SEP using the SS7 protocol.

- The host that contains the SEP and the database is called a Service Logic

Execution Environment (SLEE).

- The SEPs for platform services are located in the SMFs whereas the SEPs for IN

services are located in the SLEEs.

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Service Data Point (SDP) The main reasons to use an SDF:

- When data must be shared by different services.

- The SDF acts as a centralized database. In case of dynamic data, an SDF is

always used. In case of static data, it is sometimes used.

- The SDF is a special service that interacts with other main services.

- In the SDF service, the three functional parts of a service are also present:

• A CORBA server

• The ORACLE service database

• The SDF service logic (script). This script has 2 main functions: ’get data’ and

‘update data’

Signaling Transfer Points (STPs)

STPs like the EAGLE 5 ISS are ultra-reliable, high-speed packet switches at the heart of

SS7 networks, which terminate all link types except “F” links. For reliability reasons,

they are nearly always deployed in mated pairs.

The primary functions of STPs are to provide access to SS7 networks and routing of

signaling messages. The SS7 protocol itself defines destination routing for both circuit-

related signaling (inter-SSP) and non-circuit-related database inquiries to Service Control

Points (SCPs). Many STPs contain additional routing information concerning the exact

location of specific databases stored at different SCPs, so that an SSP can request

information without knowing in which specific SCP it is stored.

STPs operate using the Message Transfer Part and Signaling Connection Control Part

(MTP and SCCP) of the SS7 protocol. MTP provides basic message handling and

network management procedures, and SCCP adds the capability to transmit database

queries and other non-circuit-related signaling messages across the network. SCCP also

provides a non-SS7-specific addressing interface (Global Title).

STP Functions

• SS7 Message routing

• Global Title Translation

• SS7 Network Management

• Network Interconnection

• Gateway Screening

STP Function – Message Routing

Message Routing: By using outgoing DPC contained in MTP’s routing label in a data-

gram environment (where a separate route may be chosen for each message packet)

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Routing tables which are prepared to allow message transport between any given pair of

STPs are stored and maintained within STPs. The STP’s SNM (signaling network

management) functions control message routing during periods of link congestion or

failure.

• Routing is performed using Destination Point Codes (DPCs) similar to street

address for the Postal Service. STPs have the ability to route messages to all types

of signaling points.

• All nodes in the network are identified by a unique point code. This point code is

used by CCSS #7 as the Origination Point Code (OPC) and the Destination Point

Code (DPC) in the routing label of all Message Signaling Units (MSUs).

STP Function – Global Title Translation

Global Title translation: By using SCCP to translate addresses (Global titles) from

signaling messages that do not contain explicit information allowing the MTP to route the

message. For (e.g. STP translates dialed 1+ 800 number into an SCP’s DPC for MTP

routing and gives sub system number SSN for delivery of the good data base application

at the SCP

When more information is needed to process a call, such as an 800 number, queries are

processed for SSPs. STPs contain a GTT table with routing information for the type of

1-1-1

2-2-2 4-4-4 254

℡℡℡℡

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query and address of SCP. In case of congestion or failures, the SCCP management at the

STP takes responsibility for rerouting signaling traffic, based on information received

through MTP concerning the point code routing status, and allowed or prohibited SSNs.

STP Function – Network Management

Acts as traffic cop to route traffic around failures in a network, and to control link

congestion.

TFP tells the connecting nodes not to send anything that is destined for the affected node.

TFR tells the connecting nodes – if all possible, not to send anything that is destined for

the affected node.

STP function – Gateway Screening by using MTP and SCCP to allow or deny access to

the “Home” SS7 network for transport of signaling messages from another network.

To establish and maintain trunk connections between two SSPs, and to notify both when

the connection is to be released, a pre-defined sequence of SS7 messages is exchanged

between the two SSPs. Except where “F" links have been installed between the

concerned SSPs, these messages are routed to one of a pair of STPs in the local (“Home”)

SS7 network over an “A" link” or to one of a pair of STPs in another SS7 network over

an “F" link. The following cases illustrate the STP function:

• For an ordinary customer-dialed call to a 7- or 10-digit domestic station address

(I±NPA+NXX+XXXX), the STP, after consulting its routing tables, will route its

received SS7 messages towards the designated SSP over the appropriate "A", "B",

or "D" link.

Note: A message will be rerouted through a "C" link only in cases of where the

uses of the other “B” or “D” link sets are restricted or unavailable

• For calls to be given special billing or routing treatment, as indicated by other

dialed prefix digits (such as I+NOO+..., IOXX +..., or 0+...), an intermediate step

requires the STP to retrieve routing information from a non-resident routing table

STP

STP

STP

SS

STP

SCP

TFR

TFR TFR

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or database. This retrieval process ordinarily involves translation of the signaling

address and a completely separate message transaction with an SCP.

Screening is the capability to examine Incoming and Outgoing packets and allow

those which are authorized. This is done by going through a series of Gateway screening

tables that must be configured by the service provider. For example out of the messages

which are coming via a link set only ISUP messages can be allowed whereas on another

link only SCCP messages can be allowed by utilizing two basic function allow and block.

• Software in STPs with inter-network connection is used to control who has access into

a Telco’s network.

As shown in Figure 1: SS7 Common Channel Signaling Networks, STPs are the hub of

the signaling network infrastructure. A less efficient, and more expensive, signaling

network might have each SSP connected to every other SSP by an “F” type signaling

link. This approach would be much more costly than the hubbed network shown in

Figure 1: SS7 Common Channel Signaling Networks, due to the total number of links

that would be required. For example, a fully connected, ten node network would require

45 “F" links, or 90 “F" links if each link was redundant. The alternative hubbed network

approach for ten SSPs utilizing STPs (deployed in pairs for increased availability)

requires only 20 links, one link to each member of the STP pair.

Why SSTP is required in BSNL

• When any mobile subscriber roams to other Service Area then the signaling traffic or

SMS are being handled by the signaling channel of BSNL taken by private operator

against POI. BSNL is not able to measure the traffic and kind of traffic. Now by

putting SSTP in system we can measure the traffic and bill to private operators.

• It will enable migration from TDM based network to IP based networks.

Traditional Mesh Network Analysis

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Advantages:

• Cost effective at start-up

• Signaling is added as bearer capacity added

• STP function not mandatory

Disadvantages

• Difficult to “grow”

• Traffic capacity not optimized

– Fixed relationship between sites

– Fixed relationship between bearer channels and signaling links (30:1)

• No STP functionality

• Verification on signaling traffic not possible

• Difficult to add network-level services, features

Integrated STP Network Analysis

SSPSSPSSPSSP MSCMSCMSCMSC

SSPSSPSSPSSP

MSCMSCMSCMSC

MSCMSCMSCMSC

MSCMSCMSCMSC

SS7 associated / mesh SS7 associated / mesh SS7 associated / mesh SS7 associated / mesh signalingsignalingsignalingsignaling

HLRHLRHLRHLR HLRHLRHLRHLR

HLHLHLHLRRRR HLRHLRHLRHLR

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• Advantages: – Cost effective at start-up

– Uses SSP processor, call control

• Disadvantages: – Difficult to “grow”

– Trade-off between SSP functions and STP functions

– Upgrades driven by SSP, not STP

– Traffic capacity not optimized

– Difficult to add network-level services, features

Stand-alone STP Network Analysis

SSPSSPSSPSSP SSPSSPSSPSSP

SSPSSPSSPSSP

SSPSSPSSPSSP

SSPSSPSSPSSP

SSPSSPSSPSSP

SSP SSP SSP SSP SSP

MSC MSC MSC

MSC HLR VMS SMSC

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Advantages

• Dedicated signaling processors, resources

• Upgrade path divorced from MSC / SSP functions, growth

• Most effective method to manage network level resources, features

• Frees up processing capacity from the switches

• Can host most of the applications, centrally • Full mated pair redundancy

• 0.4 Erlang normal load

Disadvantages:

• Requires additional investment (However compensated by freeing up extra resources

of the switches)

• Requires traffic study, SS7 management.

EAGLE 5 Integrated Signaling System (ISS)

The EAGLE 5 ISS is a large-capacity, multi-functional, fully scalable Signaling Transfer

Point (STP). High capacity and scalability allow this system to grow from a single-shelf,

80-link STP to a multi-frame, 2000-link STP. The EAGLE 5 ISS can handle increasing

voice and data traffic loads and all of the signaling routing within a core network for

signaling applications and services. The EAGLE 5 ISS performs key functions such as

signal transfer, signaling gateway, and number portability. Integrated applications,

dramatic database size, signaling capacity, and transaction speed coupled with next-

generation IP connectivity provide the transition to the converged network model.

EAGLE 5 ISS-based products are NEBS-compliant (GR-63-CORE, Network Equipment-

Building Systems). These products are configured in standard equipment frames to

provide services to SS7 telephony networks.

Because of the distributed processor design, the EAGLE 5 ISS does not have a separate

central processing unit to bottleneck traffic throughput. Application and interface cards

provide plug-and-play functions that facilitate future growth. These cards generally do

not have specific shelf or frame limitations, and allow full customization and definition of

STP configuration. The EAGLE 5 ISS supports a variety of interface cards to support

connectivity to a wide range of network elements. EAGLE 5 ISS provides connectivity

interfaces for IP, ATM, DS0A, V.35, OCU, T1, and E1 protocols.

Features

• Exceptional Capacity: The system supports up to 2,000 links, one million global title

translation (GTT) table entries and 384 million subscriber records.

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• High Performance: Transaction speeds of up to 640,000 message signaling units

(MSUs) per second.

• Flexible Interconnection: Supports multiple link interface types, including: 100 Base-

T, DS0A, V.35, OCU, E1/T1 ATM HSL, channelized E1 and T1, and synchronous E1

HSL (SE-HSL).

• Network Security: Because signaling connectivity to other service providers is

centralized at the EAGLE 5 ISS, gateway screening is centralized and not required at

multiple switches.

IP Connectivity

The EAGLE 5 ISS provides connectivity between SS7 and IP networks, enabling

messages to pass between the SS7 network domain and the IP network domain. It

receives and sends Switched Circuit Network (SCN) native signaling at the edge of the IP

network. This signaling gateway function can relay, translate, or terminate SS7 signaling

in an SS7-Internet gateway. The signaling gateway function can also be co-resident with

the media gateway function to process SCN signaling associated with line or trunk

terminations controlled by the media gateway.

LNP

Local Number Portability (LNP) functions allow a subscriber to change location, service

provider, or service while keeping the same directory number. LNP ensures that

subscribers receive the same freedom of choice for local service as they do with long-

distance service providers. LNP requires the Local Service Management System (LSMS),

which provides the interface between the Number Portability Administration Center

(NPAC) service management system and the EAGLE 5 ISS. LSMS is composed of

hardware and software components that interact to create a secure and reliable LNP

system.

The EAGLE 5 ISS with LNP solution provides fully scalable transaction rates from 1,700

to 40,800 TPS. Tekelec simplifies number portability by integrating advanced database

management and signaling functions directly into the EAGLE 5 ISS platform. Using a

memory-based approach, LNP functions are combined with EAGLE 5 ISS capabilities in

a single network node.

Theory of Operation

The EAGLE 5 ISS implements SS7 MTP function, level 2 and level 3, through software

contained entirely within the Link Interface Modules (LIMs). No separate central

processing unit exists within the EAGLE 5 ISS. All message processing logic, including

the links, link sets, and routes associated with each origination point code and destination

point codes in the signaling network are included within the MTP Routing feature

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module. The STP offers full point code routing. (For rapid recovery from processor

faults, copies of this software are also stored on the hard disk.) The LIMs can handle a

100% traffic load on each link, assuming a small MSU size.

The EAGLE 5 ISS consists of the following subsystems:

• Maintenance and Administration Subsystem (MAS)

• Communication Subsystem (Gigabit backbone)

• Application Subsystem

There are five types of EAGLE frames:

• Control Frames

• Extension Frames

• Miscellaneous Frames

• General Purpose Frames

• OAP Frame (not shown)

Control Frame (CF)

o Principal frame for system.

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o Control shelf contains all components of Maintenance Administration Subsystem

(MAS)

o Control shelf with up to ten application modules.

o Up to two extension shelves, each with up to 16 application modules.

Extension Frames (EF)

o Provisioned when more than two extension shelves are needed.

o Up to five per system (EF-00 to EF-04)

o Up to three extension shelves mounted in each frame (EF-04 has one extension shelf)

General Purpose Frame (GPF) can be used for:

o Integrated Sentinel- Sentinel Processor Frame ( SPF)

o Extended Services Platform (ESP)

o Sentinel Processor Frame (SPF)

o Multi – Purpose Server.

o These frames are numbered GPF – 00 through GFP- xx

Miscellaneous Frame (MF)

o Optional frame

o May be equipped with a Fuse Alarm Panel (FAP)

o Equipment accommodated holdover clock: test equipment: jack panels: spare card

shelf; printer; terminal; etc

Alarm Side Panel

o Provides -48VDC lamps for critical, major, and minor alarms (bulb part number: 525-

0036-02)

o Connects to row alarm connector (row ALM) on control shelf.

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Questions:

1.Define the role of SCP in CCS7 network ?

2. What are the functions performed by SCP ?

3.What are the functions done by STP ?

4. Explain Gateway screening ?

5.What are the different subsystems in EAGLE 5 ISS ?

6. Describe about the control frame of EAGLE SSTP ?

7. Describe about the extension frame of EAGLE SSTP ?

8. Describe the different features of EAGLE SSTP ?

9. Describe about the general purpose frame of EAGLE SSTP ?

10. Explain LNP ?

xxxx

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