Softswitch Report

8/14/2019 Softswitch Report

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Chapter 1

INTRODUCTION


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Introduction

In the 21st century, telephones and other communications devices are being

used in new and innovative ways. This represents a major historical shift for

the telecommunications industry. The telecommunications industry hasgrown dramatically over the past two decades. Worldwide connectivity and

inter operability has revolutionized trade across cultural and geographic

borders. Fax and data services have enhanced the versatility of telephone

devices and networks. The Internet has experienced dramatic growth with

millions of users worldwide. In the last five years, several factors have

driven the telecommunication industry to look at a new way to provide

services to any device, anytime, anywhere.

The traditional public switched telephone networks (PSTN) although werereliable and robust were built on hardware based circuit switching model

that leave the changeability and extensibility for service addition. The

coupling between the hardware and software was very tight making use of

COTS and services extremely difficult to add. A migration to the Internet

and IP (Internet Protocol) networks using the flexible packet switching

technology, in comparison to traditional telephone networks using circuit-

switching technology is a solution but that would have meant the existing

investments in PSTN networks would have been totally wasted. Hence the

need of the hour was to look for a hybrid PSTN/IP environment, which was

found in the form of soft switches. The emergence of softswitches signified

advancements in telecommunication switching architecture by having better

technology and better software architecture. This is limited to the

advancement in software architecture due to the introduction of softswitch.


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Chapter 2

DEFINITION

Definition of a Softswitch

Softswitch is the generic name for a new approach to telephony switching

that has the potential to address all the shortcomings of traditional local-

exchange switches. The softswitch is where all the service intelligence


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resides for the delivery of local telephone services. Softswitch technology

solutions can lower the cost of local-exchange switching, present the means

to create differentiated local telephony services, and ease the migration of

networks to support packet voice end-to-end. Packetized voice involves the

digitizing, compressing, and dividing of voice into packets. These packets

can then be sent from the sender, via various routes, to the receiver,

whereupon they are reassembled. Softswitch, media gateway controller, call

agent, gatekeeper are the varied nomenclatures that have been attached to

the products that perform the functions that are coming to be called

softswitches. Gatekeeper is the ancestor term, derived from VoIP systems in

which gateways converted the voice and signaling from analog PSTN and

SS7 to IP packets. The gatekeeper controlled one or more gateways, guiding

the setup and teardown of voice circuits between the two kinds of networks.

Media gateway controller is an elaboration of gatekeeper, growing out of the

first efforts to standardize the control of media gateways using a protocolcalled media gateway control protocol (MGCP). Call agent is a highly

generic term that attempts to describe all systems that handle call-control

functions.

softswitch

Softswitch (software switch) is a generic term for any openapplication program interface (API) software used to bridge a

public switched telephone network (PSTN) and Voice over Internet Protocol

(VoIP) by separating the call control functions of a phone call from the

media gateway (transport layer).


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Chapter 3

MOTIVATION OF SOFTSWITCH

Motivation for the Softswitch


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By far the most complex part of a local-exchange switch is the software that

controls call processing. This software has to make call-routing decisions

and implement the call processing logic for hundreds of custom calling

features. Todays local-exchange switches run this software on proprietary

processors that are integrated tightly with the physical circuit-switching

hardware itself. The inability of existing local-exchange switches to deal

directly with packet voice traffic, however, is a major barrier to packet voice

migration. In the future, delivery of local telephony will come over a purely

packet-based infrastructure. But for years to come, the migration path to

end-to-end packet voice will require working with a hybrid network

handling both packet and circuit voice.

Current Market trendsThe telecommunications landscape is changing dramatically due to

economic and technology changes. Service providers and vendors alike arerequired to respond to these changes in order to thrive. The points have been

borrowed largely from the reference

Worldwide deregulation of the telecommunications industry is

creating new market opportunities for traditional and innovative

services

Increased competition is emerging in every market - local, national

and worldwide - and geographic limits to competition are

disappearing

Evolution to a single voice/data network is moving rapidly, driven by

the inefficiencies and costs associated with maintaining two networks

(PSTN and IP).

Technology changes

Voice over packet is increasingly reliable and high-quality

'Always-on' solutions are now technically possible

Improved bandwidth and lower costs are available for all types of

communications

Higher-value packet-based services are more customizable, faster to

come to market and easier to deploy and manage, enabling providers

to differentiate their offers and capture high-value customers.


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One possible way to address all this is to create a hybrid device that can

switch voice in both packet and circuit formats, with all the necessary call

processing software integrated into this switch. While this approach may

help address the question of migration, it does not necessarily lower the cost

of local-exchange switching or improves the prospect for differentiated local

voice services.Separation of Functionality: Need of the Hour

The telecom industry appears to have reached broad consensus that the best

answer lies in separating the call processing function from the physical

switching function and connecting the two via a standard protocol. In

softswitch terminology, the physical switching function is performed by a

media gateway (MG), while the call processing logic resides in a media

gateway controller (MGC). There are a number of reasons why thisseparation of functionality is believed to be the best approach:

It opens the way for smaller and more agile players who specialize in

call processing software and in packet-switching hardware

respectively to make an impact in an industry that has been dominated

by large, vertically integrated vendors.

It enables a common software solution for call processing to be

applied in a number of different kinds of networks, including

combinations of circuit-based networks and packet voice networks

using multiple different packet voice formats and physical transports. It allows standardized commodity computing platforms, operating

systems, and development environments to be leveraged, thereby

bringing considerable economies to the development, implementation,

and processing aspects of telephony software.

It allows a centralized intelligence in a service providers voice

network to remotely control switching devices located in customer

premises, a key requirement for the full exploitation of IP telephony in

the future.

Separation between Media Gateway and Media Gateway Controllerrequires a standardized protocol for communication between the two,

and an appropriate standard is now emerging.


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Chapter 4

ARCHITECTURAL DETAIL

Architectural Considerations:


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The key architectural consideration should include:

Interoperability with Telecom equipment and carriers

Services and protocols integration

Bandwidth and external connectivity required

Sizing requirements

Equipment required

Network operations interface(s) required

Operations management requirements

Scale as you grow criteria for services and volume

Service availability requirements


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Architecture of softswitch organization

Functional Planes

The architecture of the softswitch can be seen to be divided into the

following software planes. They represent the separation between the

functional entities in a Voice over IP (VoIP) network. There are four distinct

functional planes employed by the soft switch to describe the functioning of

an end-to-end VoIP network:

Transport

Call Control & Signaling

Service & Application

And Management.


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Transport Plane

The basic functionality served by the transport plane is to handle and

transport call signaling, call and media setup messages across the VOIPnetwork. Now the transport mechanism used could be based on any

technology conforming to the standards e.g. SS7 ANSI or ITU. This plane to

the external world is like an access form where they can enter to use the

services of call control. So often if we look at the implementations the

Transport Plane devices and functions are controlled by functions in the Call

Control & Signaling Plane. The transport plane gets sub-divided broadly into

three domains:

IP Transport Domain Interworking Domain

and Non-IP Access Domain. Let us look at each of them:

IP Transport DomainThe IP Transport Domain comprises of:

The transport backbone and routing/switching fabric

Devices like routers and switches domain.

Devices that provide Quality of Service (QoS) mechanisms and policies for

the transport also belong to this domain.

Interworking DomainThis domain comprises of:

The devices that are primarily responsible for the transformation of

signaling or media received from external networks into a form that can be

sent among the various entities in the VoIP network and vice versa.

It consists of devices like Signaling Gateways (signaling transport

conversion between different transport layers), Media Gateways (media

conversion between different transport networks and/or different media), and

Interworking Gateways (signaling Interworking on the same transport layerbut with different protocols).Non-IP Access DomainThe Non-IP Access Domain applies primarily to

Non-IP terminals and wireless radio networks that access the VoIP

network.


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Consists of Access Gateways or Residential Gateways for non-IP terminals

or phones, ISDN terminals, Integrated Access Devices (IADs) for DSL

networks, Cable Modem/Multimedia Terminal Adaptors (MTAs) for HFC

networks, and Media Gateways for a GSM/3G mobile radio access network

(RAN).

Call Control & Signaling Plane

The Call Control & Signaling Plane is like the centralized arbitrator

exercising control over the major elements of the VoIP network, especially

in the Transport Plane. This is the heart of the system and performs the basic

call processing and signaling. When we say call processing and signaling we

essentially means handles the subscriber requests for setting up and tearing

down the voice circuit, carries out call control based in signaling messages

received, controls components in Transport Plane, ensures digit translationand routing based on directory numbers, maintains trigger detection points

to access the intelligent database, keeps the finite state necessary for

maintaining the call context etc. Summarizing it controls what essentially is

switch has to do for setting up and releasing a call. The Call Control &

Signaling Plane consists of Devices like the Media Gateway Controller

(a.k.a. Call Agent or Call Controller), Gatekeepers and LDAP servers.

Service & Application Plane

The Service & Application Plane provides the controls the logic and

execution of feature servers and other applications like intelligent networks

which are mean to provide various services to the subscriber. The devices in

this plane control the flow of a call based on the service execution logic.

They achieve this by communication with devices in the Call Control &

Signaling Plane. The Service & Application Plane consists of devices like

Application Servers and Feature Servers. The Service & Application Plane

can also perform the control of specialized bearer components, such as

Media Servers, that perform functions like conferencing, IVR, toneprocessing etc.


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Management Plane

The Management Plane is responsible for providing functions such as

subscriber and service provisioning, operational support, billing and other

network management tasks. It can interact with any or all of the other three

planes through industry standard (e.g. SNMP) or proprietary protocols and

APIs. That is to say it forms the operation and maintenance zone. The

functional entities are the logical entities of a VoIP network. This plane

caters to the on the fly needs of the switch in expansion and modification of

networks and entities.


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Chapter 5

MAJOR COMPONENTS


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Major Components of a Softswitch:

A Softswitch can consist of one or more of these components. These

functions can reside in one system or span across several systems.

1. The Gateway Controller is one of the key functional units of theSoftswitch. The Gateway Controller holds the call processing rules, but uses

the Media Gateway and Signaling Gateway to perform the job. There are

many types of protocol media managers that need to be controlled those that

access the softswitch through Transport plane. It is the responsibility of the

Signaling Gateway to perform call set-up and teardown and media gateway

basically controls and coordinates the operations. An example could be

sending data related to call set up to signaling media manager and receiving

finite state messages in response. The gateway controller here is like an

arbitrator for the signaling interface and the corresponding stack utilizing itsservice. In addition, it interfaces to the OSS and BSS systems. Often this

unit is referred as Call Agent or Media Gateway Controller interchangeably.

Sometimes the Call Agent by itself is referred as a Softswitch. This

component communicates within other parts of the Softswitch and also the

external networks using different protocols.

2. The Signaling Gateway serves as the gateway between the SS7Signaling network and the nodes managed by the Softswitch in the IP

network. A Signaling Gateway requires physical connectivity to the SS7network and must be aware of the required protocol suites. There is a

standardized implementation of SS7 signaling protocol both ANSI and ITU-

T which is managed by the gateway. The services of the stack are given to

external world via the gateway which takes care of API formation and

retrieval for incoming and outgoing messages and presenting the extracted

data to the external world which may not need to worry of the stack PI

3. The Media Gateway handles the voice media data payload (the

digitized samples of speech during conversation). In the future, video datawill also need to be supported. In the current model, the Media Gateway

must support connectivity to a TDM bus carrying voice media data to the

Telco switch side. Applicable voice data encoding, decoding and

compression are also performed by the Media Gateway. It also supports

legacy telephony (PSTN) interfaces and protocols such as CAS and ISDN.


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4. The Media Server performs peripheral functions, to enrich theSoftswitch with media capabilities. If required, it supports digital signal

processing (DSP) resources. If IVR functionality is needed (eg: to prompt

voice responses), those tasks would be performed by the Media Server. AMedia Server when applicable would also serve video Media.

5.The Feature Server provides all the revenue generating features andservices such as billing, multi-party conferencing, etc. The Feature Server

uses the resources and related services located on other components of the

Softswitch. It may also support certain services to meet certain

implementation necessity e.g.: Gatekeeper


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Figure 1 Figure 2


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Chapter 6

BENIFITS


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Benefits of the Softswitch:

The distribution of functionality will enable the benefits of improved feature

development and delivery as well as lower costs. Distributing functionality

means that switches will be simpler, more efficient, and cheaper. Switcheswill be able to focus on switching, allowing other components to provide

network control and service logic. Distributed service logic means that

application development will not be constrained to centralized creation,

control, and delivery of services. Instead, services can be created and

deployed at various places through an extended network.

The benefits of the Softswitch approach will include: New revenue stream

for service providers and operators

Flexibility, which supports the development of highly programmable

telephony equipment

Several types of e-business, accessible using newer devices

Unified messaging

Enhanced customer services that it reduces time to market

Easy integration of dissimilar networks and network components

Lower cost of development, deployment and ownership.


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Highly Flexible Architecture

A soft-switch-based system provides network design engineers with a highly

flexible, fully distributed, open standards-based network architecture. A

well-architected softswitch separates call-control intelligence and services

software from media hardware with open, standards-based interfaces between the different layers. Typically, call-control and signaling

intelligence resides within the softswitch, while services intelligence is

distributed among the softswitch and application servers that reside at an

upper layer. The interface between the softswitch and different types of

media hardware is provided by open protocols, such as Media Gateway

Control Protocol (MGCP), H.248/Megaco and Session Initiation Protocol

(SIP). The interfaces between the softswitch and application servers are also

open and standards-based, and use protocols such as SIP and H.323, and

tools like Extensible Markup Language (XML) and Java in advancedintelligent networks. This gives network designers the flexibility to choose

best-of-breed components from multiple vendors for their media hardware

and software needs. The fully distributed architecture allows network

topologies with media devices located throughout the network, while the

softswitch provides centralized call control and services. Such a network can

be quickly scaled without the need to deploy expensive circuit switches in

each new market. Furthermore, by enabling voice transport and services

over packet-switched networks while seamlessly inter-working with the

public-switched telephone network (PSTN), softswitches play a critical role

in enabling the design of a common packet network for converged voice anddata services.

Qualities Imparted:

Loose Coupling

Better Extensibility

Higher Changeability

Ability to Interoperate with COTS

Better Scalability

Open architecture

The most important characteristic of the next-generation network is an open

architecture. A softswitch utilizing an open architecture provides best-of-

breed vendor selection, a platform for third party development of new

services and service provider empowerment. Service providers are able to


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select best-of-breed products that allow them to harness innovation

regardless of vendor. The softswitch is the engine powering the next

generation network, controlling edge devices such as media gateways and

broadband Integrated Access Devices (IADs) and interfacing to third party

feature servers and back office systems, including billing. Rapid deployment

of converged services will be made possible by open softswitch architecture.

Third party software companies will revolutionize data and voice

communications. By using standards-based protocols and open APIs such as

SIP, JAIN, XML or even H.323, service providers will be able to harness

converged services from third party vendors within a fraction of the time and

cost compared with today's PSTN.

Qualities Imparted:

Changeability Extensibility

Interoperability

Portability

Distributed architecture

The next-generation architecture requires a transition from a mainframe-type

telephony system to a distributed system, which will drive modular systems,

and provide cost-effectiveness. The switch is decomposed into three layers

i.e. layered architecture. The softswitch will be the strategic component in

service providers' networks because it has the potential to function as thenetwork operating system of the new public network. The softswitch gives

the service provider the freedom and flexibility to add ports where it needs

to by simply adding to an existing media gateway or by rapidly bringing a

new media gateway online. In addition to the quick turn-up time, service

providers can also penetrate new markets without the multi-million dollar

class switch investment. Service providers can add a media gateway with a

low port count to a new market. As business grows, more ports or additional

media gateways can be added. The softswitch controls the media gateway

via a media gateway protocol such as the Media Gateway Control Protocol(MGCP). To reduce operational training and back office complexity,

functionality can be located remotely, controlling media gateways across an

entire region. The call control elements can be collocated with the media

gateways or distributed across service providers' backbones.

Qualities imparted:


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Ease of creation

Ease of Maintenance

Localization of changes

Layered Architecture

Simplified Design

Fault-tolerant architecture

The softswitch architecture is fully modular and has the ability to distribute

modules in the network any way the service provider wants. It is a fully

distributed, highly scalable and fault-tolerant architecture. Faults are easy to

locate, and their impact is localized. The fixes do not have any global

significance and maintenance becomes easier.

Qualities imparted:

Reliability

Modularity

High Availability

Maintainability

Existing infrastructure support

Interoperability with the existing Public Telephone Network is critical

during the transition to the new public network. The softswitch interfaces to

media devices and feature servers and receives call signaling from the PSTN

over SS7 links. Additionally, a softswitch can utilize backhauled channelassociated signaling for interfacing with customerpremises equipment. Withthis combined capability, a service provider obtains a complete solution for

optimizing its circuit network and migrating traffic to the packet network. A

softswitch with these capabilities offers a cost-effective way for service

providers to migrate to next-generation networks, while they continue to use

their legacy class 4 and 5 TDM switch equipment until those reach their end-

of-life.Qualities imparted:

Cost Efficiency Reduced Time to Market

Reuse of Existing Investments


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Chapter 7

USAGE


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USAGE OF A SOFTSWITCH

Softswitches can support a wide variety of services. It is important to

understand the business focus of the switching applications in order to select

the most appropriate suite of services for the environment. This allows thebusiness to maximize its return on investment in Softswitch technologies. In

the telephone industry, there are many services that can be given but require

better switching facilities. Many popular enhanced services include call

forwarding, call hold, call transfer, call waiting, caller ID, three-way and

multi-party conferencing. The advent of Internet usage over telephone

system has resulted in new services such as click-to-dial and Internet call

waiting. Several companies currently offer these features.

The integration of the telephone network with wireless networks and cable

networks presents major opportunities to offer value-add services. These

types of services are best supported by the Softswitch approach. MostSoftswitch services are usually related to revenue, in which billing becomes

an important function. There are many variations in call plans, group plans,

and business arrangements with external service providers, applicable rates

and the type of connection circuits. It is required to work with the existing

Operations Support System (OSS) that handle many types of operational

details, as well as the Business Support System (BSS) which also performs

the actual billing. The flexibility of Softswitch technology allows a provider

to support a wide variety of billing options. Softswitches can support

traditional features offered to telephone systems customers such asconsultation hold, call forwarding, conferencing, etc., as described in the

local telephone directory.

Other services that can be given by the Softswitch are:

Emergency calling (911)

Toll-free 800 calls

Calling cards and pre-paid calling cards

Virtual call center

IP Centrex


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Chapter 8

AN EXAMPLE


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subscriber places the request after dial tone is fed to him and the digits are

carried to the call control plane. It is now the duty of the control plane to

ensure the circuit set up and tear down and for this the media controller

which resided in the Call Control and Signaling Plane would hand over the

message in the required format for the corresponding media manager e.g.

SS7 signaling media manager which will direct it to the stack which is a part

of the Transport Plane. The signaling media manager based on the response

from the SS7 stack would handle and complete the required operations like

allocating the circuit and stuff.

Consider the case that the customer wants to call the number 1-800-PIZZA-

HUT. The intention of the subscriber and the nature of the number demand

that the nearest Pizza hut be connected. Here is where the Services and

Application Plane comes in to the picture. The call control analyzes the

directory number of the subscriber and has triggers defined for different

nature of numbers. Here the trigger for an intelligent service which is basedon say number 1-800 invokes the services of an intelligent relational

database handler Service Control Point (SCP) which resides in the Service &

Application Plane. The Call Control would forgo the control at this moment

and the service and application plane takes over returning the new number

based on the data supplied by the call control plane. This is the nearest Pizza

Hut directory number and the call control plane once again on getting the

correct destination number proceeds with the rest of the routing sending the

messages to the stack to set up the call and allocate a circuit the details of

which are beyond the scope of this document. The service and application

frame makes addition of the services easier since they can be creating

without disturbing the call control plane. Newer services can be added to the

switch by putting most of the logic in SCP. Similarly for mobile and other

applications there could be other feature servers, which can take care of easy

addition of newer services, which are required for in a competitive market.

To see the functionality of the management plane lets consider that the

telephone company wants to see if the call control plane or the transport

plane operations are working fine. This is done utilizing the functionality of

the Management Plane, which can be designed using the fault tolerance

patterns mentioned. The Management Plane also takes care of the billingdata of the subscriber, provides the operator interface for maintenance,

performs functions like invoking alarms and diagnostics, monitoring of the

switch functionality collects traffic data, creates, deletes and modifies entries

like say addition of Data Link Card or new hardware alarm monitor or ATM

concentrator.


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CONCLUSION

CONCLUSION


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This describes a migration path for broadband packet-voice access: a

migration moving from a transport-only solution that relies on a

conventional local-exchange switch toward a full-fledged local-exchange

softswitching and access solution that delivers packet voice dial tone.

By far the most important ingredient in this migration path is to the

softswitch technology that forms the basis of the MGC. The softswitch is

where all the service intelligence resides for the delivery of local telephone

services. A far higher level of capability is required for this type of

softswitch than for todays tandem softswitch applications where

functionality is limited to Interworking between PRI, SS7, and VoIP

signaling. For local telephony, the softswitch must not only deliver a critical

mass of local telephony features but also provide a feature creationenvironment that enables service providers to develop differentiated

services.

The development of a local-exchange softswitch that is truly capable of

meeting these requirements is a major undertaking. But for those who

succeed in reaching this goal, an awesome prospect lies ahead: nothing less

than the total transformation of the local telephone network.


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Documents

Softswitch Report