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The role of Software
in Telecommunications
The old networks
• Up to few decades ago Information Technology hadn’t entered the
Telecommunication world yet. The switches were only HW based and IT
devices didn’t need to communicate with each other
• As IT developed, it began to be employed in the design of the network
nodes, in order to take advantage of the enormous benefits that
software could provide, e.g.:
– extended the capabilities of the switches (both the performance and the
service number and complexity)
– allowed for simpler, cheaper and quicker service extension, normally without
any need for hardware modifications, thus speeding up and simplifying the
productive process
– provided for quicker and simpler error and malfunction correction
– extended the flexibility of the Network Elements, e.g.:
easier customization process
better adaptability to the different network contexts
easier paramenter configurability
– allowed for the implementation of more effective redundancy techniques (e.g.
micro-synchronous duplication) thus increasing the system reliability
Adoption of IT technology in TLC
• Computers began being gradually adopted as the basic elements
upon which the network nodes were designed, and the switches
became complex ensambles of cooperating microprocessors
– Languages, real time operating systems, software structures (e.g. the
“automatas”, based on SDL) started to spread out, optimized for the real
time event management
– Dedicated I/O devices, handled via interrupt routines and often working
with DMA, began to be employed, especially for protocol handling (e.g. for
the signaling SS7 protocols)
• A dramatic change happened both in the manufacturer
companies and the telecom operators, since the know how
requested for technical people moved towards the computer
world (even if with characteristics that were deeply different from
those of the commercial computers)
Employment of IT at the network level
• The adoption of IT in the TLC world grew even more extensive as
the requested services started to become more and more
• Some new services were too complex to be effecively provided by
each individual node, and some required service logic and data to
be shared among all the nodes of the network
• The network architecture started to include specialized,
centralized servers to provide such services
The “Intelligent Network” (IN) was developed
Intelligent Network (IN)
• In the IN architecture complex services are realized in a
dedicated node (SCP: Service Control Point) by means of
pure software applications
• To exploit the required service, SCP queries SDP (Service
Data Point) to get user’s related information (e.g. his/her
profile) and invoice information
• SCP is invoked by any switch of the network (through the
SSP: Service Switching Point function) after recognizing that
the user has requested an IN service
• SCP performs the service logic and provides the switch with
commands relative to how the call is to be managed
A few examples of IN services
Number Portability
Green Number
Reverse Charging
Calling card
Personal Number
Universal Number
Call distribution (location / time based - proportional - …)
IN Flexibility
• IN is a clear example of how the great flexibility of SW made
possible the provision of services otherwise too complex to be
• Adding new services or modifying existing ones only required to
act at the SCP/SDP level; at the switch level just adding triggers in
SSP was enough
• In the SCE (Service Creation Environment) dedicated SW
applications provided for easy, quick, flexible and user friendly
inplementation of the service logic
• User friendly software applications also provided for easy and
user friendly service management (management of Users’profile,
service Data Base, etc.)
Computers evolution towards communication
• Meanwhile also the computers began evolving from stand-alone
machines to systems open to the communication with the
external world, especially after PCs started to spread out (one
example for all: the e-mail service)
• This thrusted a big effort that developed in two directions:
1) Integration in the telephone switches of devices and features
providing communication capabilities for the data
equipment, besides the voice ones;
2) The birth of the data networks, both local (LAN, IBM SNA,
etc.) and geographical (e.g. the Italian “Itapac” public packet
Data communication through the telephone
switches (1)
• The most important role in the integration within the same switching
devices of different types of service and equipment was played by the
PABXs, and in particular those based on the ISDN standards (ISPBXs)
• The ISDN specifications were developed with the goal of integrating
voice and data services through one network interface
• Access of IT devices to the telephone switches was realized by means of
“Terminal Adaptors” (TAs) that presented the same interface to the
switch as the telephone sets
• Protocol converters were also available as pools of resources to cope
with protocol differences between the communicating devices
• Access to the external networks (e.g. the public packet ones) was
realized through the development of centralized interfaces, e.g.
Modem pools to communicate thorugh the external telephne network
PAD (Packet Assembler Disassembler) to access external packet networks
SNA emulators to access the IBM SNA networks
Data communication through the telephone
switches (2)
Data communication interface boards required a particular type of
SW to be developed:
• Real time management requirements were very strong
• Typically written in structured low level languages for optimizing
the execution time and the memory use
• Finite state machines (e.g. SDL) were frequently used for protocol
• Often dedicated chips, interrupt driven, were used, able to
autonomously handling the lower level parts of the data link
protocols (e.g. LAPB, LAPD, etc.) thus relieving the CPU from the
most time critical tasks
• DMA was also used as well for data unit buffers management in
conjunction with the transmitting/receiving devices
Data communication through the data networks (1)
• A big acceleration occurred in the definition process of the
computer communication standards, both for geographical
networks (e.g. X.25) and the LANs
• The ISO-OSI model was defined.
– It is a clear example of the ultimate importance got by software
development to implement data communication functions
– The SW characteristics were quite different between the network
nodes (which handled only the three lowest levels) where the needs
for processing speed and real time process management were
predominant, and the endpoint host computers where the
communication packages needed to be integrated in the host
environment normally based on high level operating systems and
– Developing the entire stack was quite a complicate matter and it was
typically developed by specialized SW companies which also helped
integrating it within the customers’ machines
Data communication through the data networks (2)
• Further improvement brought to the diffusion of more efficent
protocols (Frame switching, frame relaying, ATM, …)
• The continuous technological evolution allowed for the realization
of more and more powerful, fast, cheap and reliable nodes; as a
– Final replacement of X.25 with the more efficient
connectionless Internet Protocol (IP)
– Abandonment of the OSI stack in favor of TCP/UDP with the
Application Layer directly above
• The long process of evolution of the data networks, in particular
the geographical ones, brought to the birth of the Internet, based
on the TCP/IP protocols
Convergence between voice and data services
• In the same way as the telephone networks evolved towards
including data communication, the data networks began including
voice and, in a later step, video communication (the Internet is an
example of this). This brought to the definition of the VoIP
• VoIP was initially conceived just to transport voice packets
through the Internet, without providing the actual typical
telephone services (e.g. Call Forwarding on busy / on no answer,
Call Park, etc.)
• The full provision of the telephone services will be accomplished
later as the “NGN” networks will provide the real ToIP (Telephony
over IP)
Factors that triggered voice/data convergence
• The quick technological development of the network nodes and
the consequent cost reduction and improvement in terms of
speed, reliability and bandwdith
• The predominance of the packet switching technique over circuit
switching even for the voice services (and for the video ones) as
one of the consequences of the technological improvement. This
brought to a situation where all the information types shared the
same switching technique
• The bigger and bigger demand for new services by the users
Further networks evolution (1)
Technological development
Increase of the demand of new and
more sophisticated services by the users
Urgency of the providers to conquer market areas
with the provision of new and better services
requiring further technological improvement
Further networks evolution (2)
The consequences were:
• Possibility to integrate the different types of media to provide
multimedia services due to the capability of the IP network to
transport all types of information
• The availability of a much wider bandwidth than needed by the
traditional phone calls and the possibility to flexibly allocate it
depending on the service needs
• Independence from the user’s device (fixed or cellular phone,
smartphone, tablet, PC, …)
Loss of the traditional distinction between voice and data networks:
only one type of network (packet switched, IP based) for all stream
types: voice, video, data, images.
Further networks evolution (3)
The transport and switching networks, IP based, became more and
more service independent
The provision of all the services (including, even though not in all the
implementations, the classic telephone call as a particular case)
moved to a higher layer that used the transport and switching
network just as a bandwidth and QoS provider
Multimedia services began to spread out, integrated with users’ data
such as Presence information
Birth of the NGN (New Generation Network)
NGN Architecture
Application Layer
. . .
IP phone
TDM legacy networks
IP phone
IP phone
Legacy phone
Legacy phones
Session Boarder Controller
Signaling Gateway
Media Gateway
Integrated Access Device
• All the calls within the NGN are managed by the Softswitch that:
– acts as network controller
– regulates the users’ access to the network
– doesn’t provide any service directly: it examines the service that the user
has invoked by means of an INVITE message
– depending on the requested service, it selects the appropriate Application
Server and delivers the user’s request to it
• The Application Servers
– are triggered by the softswitch on the basis of the service requested by the
– run the service logic
– command, if needed, the establishment of new sessions with other users’
devices by sending the relative commands to the Softswitch
• Different Application Servers may be involved simultaneously in
the same service (e.g. an IP Centrex user that asks also for a
Manufacturer competence splitting
Coherently with the NGN architecture, a revolutionary scenario
occurred in the TLC world also as far as the role of the main actors
is concerned:
• The traditional network manufacturers are more and more
confined within the Switching and Transport Layer
• The Service Layer is realized by pure software applications
running on commercial servers and has become almost entirely
prerogative of specialized IT companies
• Architectural modularity allows for integration of systems by
different vendors within the same solution, thus achieving
vendor independence
NGN : Application Layer (1)
• Adding new services can simply be accomplished by employing
further Application Servers in the Sevice Layer
• Interoperability tests between a new Applications Server and the
Softswitch are always necessary before activating a new service in
the network
• AS’ are realized by SW applications developed upon state-of-theart computer HW and SW (Operating Systems, Data Bases,
Graphical Interfaces, Communication platforms, etc.)
NGN : Application Layer (1)
• Both SW (e.g. in terms of number of required third party SW
licensees) and HW (server class, number of servers, number of
processors per server, memory size, HD space, etc.) are
dimensioned through an engineering process according to the
estimated load (e.g. the number of users and the estimated access
• Normally the HW platform is modular so that system upgrades can
easily be accomplished by adding new elements (e.g. new servers,
new CPUs, …) or replacing them with more performing ones
• The HW platform is always redunded in high availability
configuration in order to guarantee service continuity even in the
presence of faults
• System redundancy allows for upgrades or release changes without
any service interruption
NGN : Application Layer (2)
• Two configurations are most used (mainly depending on the
number of servers the system is made of):
⁻ in a fully duplicated configuration (2 X N) each server is duplicated and the
two servers of each couple work in load sharing; should one server fail, the
remaining one takes all the functionality, since it is dimensioned to manage
the network load alone;
2 X N redundancy is most used when the system is made of servers
specialized to run different applications which can even be dimensioned in
different ways;
⁻ N + 1 configuration is most used when the system consists of N identical
servers, all sharing the same applications, whose number only depends on
load considerations; a further server is added to the configuration in order
to grant the simultaneous presence of N active servers even in case one
• Communication links and network interface devices are always
redunded as well
NGN: examples of services
• Telephone calls
• Multiple Ringing
• MRBT (Multimedia Ring Back
• Messaging
• Voice SMS
• Unified Messaging
• Voice / video mailing
• Multimedia conferencing
• Presence oriented services
(e.g. conferencing)
• Telepresence
• IP-Centrex
• IVR applications
• Fixed-Mobile Convergence
(VCC: Voice Call Continuity)
• VoicePAD / Web-VoicePad
• Content sharing
• Switchboard
• Multiparty interactive games
• Domotics
• Pre / Postpaid calling cards
• Mass Calling
• Televoting
• ...
Example: Conference AS architecture
Application Server
WEB Server
Service &
System Administr.
Media Server
IMS (1)
• IMS (IP Multimedia Subsystem) is the 3GPP architectural
standardization evolution for the NGN networks
• It is a set of specifications for an unified service architecture
• It defines a complete framework for enabling the convergence of
voice, video, and data communications over an IP-based
infrastructure using SIP
• Provides interoperability with any network, both legacy and new
generation, thus granting access to any user regardless of the
network he/she is connected to
• Is independent of the user’s device (fixed or mobile telephone,
smartphone, PC, Tablet; etc.) regardless of access technology (DSL,
Ethernet, GPRS, WCDMA, etc.)
– Every IP terminal working with SIP (Session Initiation Protocol) can access the
IMS services
– Legacy terminals, connected to legacy networks, can still access IMS services
through gateway functions
IMS (2)
• Rigorous distinction between the lower layers (Access / Transport
and Control), still under the competence of the TLC manufacturers,
and the Service layer, mainly prerogative of the IT companies:
– The Access/Transport layer based on IP protocol; SIP (Session Initiation
Protocol) is used as “signaling” protocol to ask for service requests and call
– The Control layer which contains the main users’ Data Base (HSS: Home
Subscriber Server) and the CSCF functions (Call Session Control Functions)
which are responsible for analyzing the users’ service requests and
determining which Application Server will be in charge of managing the
requested service
– The Service layer, that includes all the Application Servers providing all the
services to the users.
Simplified IMS Architecture
IP network
Access / Transport
IMS: the Service Layer
AS’ interact with the control layer by means of SIP protocol
Legacy servers working with different interfaces can interact
with the Control layer by means of protocol conversion function
Services provided by customized applications for mobile
networks using Camel can be provided to IMS users by means of
the “IM-SSF” function
The AS’ perform as Originating / Terminating User Agents, Proxy
Servers or Back-to-back User Agents
Application Servers
Main characteristics
• Must allow quick development and deployment of new services
• Must provide quick service customization
XML based languages
Voice XML
. . .
• Should provide the customers with control possibilities over their
preference settings
WEB interfaces
CPL (XML based Call Processing Language)
. . .
Management Systems
Management Systems
• Management is of crucial importance in all the TLC networks
• No node, equipment, service or application is never deployed in a
TLC network without the guarantee that it can be properly
• Management is performed by dedicated systems: the OSS
(Operation Support Systems)
• OSS are the means through which operators perform such
activities as:
– monitor the way how the network is behaving, the provided QoS, its traffic
handling capabilities, its faults and the way how they affect the services, etc.
– collect statistical performance data to identify critical points or as support to
network upgrade policies
– react to critical situations like traffic congestions, serious faults, configuration
errors, etc.
– set the configuration of the network nodes and check the current one
– deploy and configure the services
– perform customer management
– collect accounting information and provide billing data
– ...
Management Systems
• OSS functionalities are normally placed at different levels
Network Element level (Element Managers)
Network Level
Service Level
Business Level
• The main management areas of the Network Element and the
Network management levels are the “FCAPS” ones, as specified
by the ISO TMN Model:
• At the Service Management Level Service Provisioning and
Monitoring are performed
• The Business Management level is focused on commercial and
customer management issues
Management Systems
• OSS are implemented as state-of-the-art servers with standard
Operationg Systems and proprietary software applications
• The splitting of the management functions into four layers is a
theoretical one and doesn’t necessarily correspond to actual
system implementations: in practical circumstances features
belonging to different layers can sometimes coexist within the
same system
Element Managers
• Every network node is individually managed by its own Element
Manager (EM)
• EMs allow for the complete set of management operations to be
performed directly onto the Network Elements, via a user friendly
GUI, by operators for which deep knowledge of the detailed
structure of the NE is required
• For large nodes (e.g. a softswitch) they are dedicated servers,
normally based on redunded commercial HW platform, with
standard O.S., running proprietary SW applications each
dedicated to a FCAPS function
• For smaller nodes (e.g. an IP router) they can consist of a set of
SW applications running on the node itself, accessible by the
operator via standard PC running dedicated applications (client)
• EMs are interfaced with the higher layers management systems
through standard or, sometimes, proprietary protocols in order to
(e.g. configuration
measurements, call detail records, alarms, etc.) and receive
commands to be activated on the NEs (e.g. configuration
parameter setting, traffic control commands, etc.)
Network Managers (1)
• At the network level the management systems perform the same
FCAPS features as the EMs, but with a global network view
• They collect configuration data, alarms, measurements and
accounting data from the Network Elements, through the
respective Element Managers, and integrate them in a global view
of the entire network
• They act upon the network by sending configuration data and
commands to the Network Elements through the interfaces with
the Element Managers
Network Managers (2)
• To provide network level view from the information gathered
from the individual nodes, Network Management System perform
such processing activities as:
– normalization among data collected from NE by different
– integration of alarm indications coming from different NEs to
identify the “Root cause alarms”
– integration of fault indications and traffic measurements to identify
possible impacts on the QoS provided to the customers (Service
– aggregation of the performance measurements of different NEs to
identify the traffic loss causes or to anticipate future potentially
critical situations, e.g. during the next busy hour
– integration of configuration data from different NE to identify
possible configuration inconsistencies
– network behavior simulation with new configuration parameters
before their actual activation on the network nodes
– ...
Main Network Management features (1)
• Fault Management
– Fault detection
– Fault localization
– Trouble Ticketing (workflow over the whole lifecycle of the alarm, from
its rising up to its resolution)
• Configuration Management
– Users’ configuration
– Network configuration
For both users and network:
– Configuration setting (Provisioning)
– Configuration Data acquisition and storage (Inventory)
Main Network Management features (2)
• Traffic and Performance Management
– Real time Traffic Management
• Traffic surveillance (near real time detection of critical situations)
• Traffic control (action performed to minimize traffic losses and QoS
– Off-line Performance Management (mainly statistical reports)
• Accounting: collection of users’ related usage data (number and
type of placed calls, traffic volume through the IP network, etc.)
– Accounting data are sent to Billing systems at the Business Level to bill the
– Can also be used by the Performance Management systems as detailed
data to complete the statistical reports or to support detailed analysis of
the network problems
Network Managers main characteristics
• Network Management systems are realized by SW applications,
developed by the same manufacturers as the Network Elements or by
specialized companies, upon state-of-the-art computer HW and SW
(Operating Systems, Data Bases, Graphical Interfaces, Object Oriented
platforms, Communication platforms, etc.)
• Both SW (e.g. in terms of number of licensees of third party SW) and
HW (computer class, number of CPUs, RAM and HD size, etc.) are
dimensioned through an engineering process according to the size of
the network, the traffic volume, the estimated event rate, etc.
• The HW platform is always redounded in a high availability
configuration, in order to guarantee service continuity even in the
presence of serious faults
• Redundancy also allows for upgrades or release changes to be
performed without any service interruption
• Modularity allows for system upgrades, due to network size / traffic or
event volume increase, to be easily accomplished by adding new
elements (e.g. new CPUs) or replacing them with more performing ones