Migration from PSTN to NGN

Abstract

"Modernization of telecommunication infrastructure of PTK " is a Post and Telecommunication of Kosova (PTK) project. This project was initiated to replace most of the switching and access infrastructue of PTK that was very old, up to semi-automatic exchanges. For this project PTK decided to go for the latest switching technology Next Generation Network (NGN). The project consist of replacement of switches in 6 regions with the new access equipment that would use the same Soft Switch installed at central server room in Prishtina, capital of Kosova. The applied aproach by PTK to make a large step by moving from semi-electronic switches to NGN is presented by this paper.

Full text

49th International Symposium ELMAR-2007, 12-14 September 2007, Zadar, Croatia
Migration from PSTN to NGN
Shkelzen Cakaj
1
, Muharrem Shefkiu
2
1, 2
Post and Telecommunication of Kosova (PTK), PTK Building, Dardania, pn. Prishtina, Kosova
E-mail: shkelzen.cakaj@ptkonline.com; scakaj@yahoo.com
muharrem.shefkiu@ptkonline.com; mshefkiu@yahoo.com
Abstract – “Modernization of telecommunication infrastructure of PTK “ is
a Post and Telecommunication of
Kosova (PTK) project. This project was initiated to replace most of the switching and access infrastructue of
PTK that was very old, up to s
emi- automatic exchanges. For this project PTK decid ed to go for the latest
switching technology Next Generation Network (NGN). The project consist of replacement
of switches in 6
regions with the new access equipment that would use the same Soft Switch installed at central server room in
Prishtina, capital of Kosov
a. The applied aproach by PTK to make a large step by moving from semi-elect ronic
switches to NGN is presented by this paper.
Keywords – Migration, NGN, Vo
IP
1. INTRODUCTION
Post and Telecommunication of Kosova is the
largest telecommunication operator in Kosova
offering Fixed and Mobile services for Voice and
Data. The
majority of switching technology used
until 2007 was semi-electronic, except two
electronic switches. During 2006 PTK started
implementing the project “Modernization and
Extension of the Fixed N
etwork Infrastructure of
PTK-J.S.C.”. The goal of this project was to replace
old switching and access technology into the latest
technology and increase access and switching
cap
acities. Phase one of the project implementation,
which is subject of this paper, contained replacement
of all semi-electronic switches used by PTK fixed
network.
2. SWITCHING NETWORK BEFOR
E
MIGRATION TO NGN
2.1 Switching Topology and Technology
Switching Network has been organized in three
switching levels: Local level, Main level and Transit
level, organized in star topolo
gy, as it is presented in
Fig. 1.
Fig. 1. Switching system topology
Local level exchanges use d to be the lowest
functional level of exchange s. The main role was to
offer access and local swit
ching to subscribers.
Local level switches were connecte d to Main Level
exchanges.
Main level exchanges, used to be one per region,
offering intraregional switching bet
ween local
exchanges and interconnecting all regional traffic to
transit level exchange. Usually main level exchanges
offered access to subscribers also.
Transit level exchange
is installed in PTK HQ in
Prishtina, the role is to offer interconnection to all
regional main switches and interconnect those
switches to international traffic. There were two
transit level exchanges
in Prishtina and both offered
access to subscribers also.
Exchange technology used by PTK fixed network
are presented in Table 1. It is o bvious that the
biggest part of
exchanges were based on FDM
technology and few exchanges based on TDM
technology, using circuit switching.
Table 1. Exchange models used
Exchange level Tec
hnology
Local level Semi – electronic
Main level Semi – electronic
Transit level Electronic
2.2 Numbering Plan
Kosova fixed network numbering plan contains 7
area codes for 7 regions using a particular area code
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49th International Symposium ELMAR-2007, 12-14 September 2007, Zadar, Croatia
for each region. As an international prefix for
incoming calls up to now FRY prefix 381 is used,
outgoing prefix for international calls is 99 and
national access number is 0, numbering plan is
presented in Tab
le 2.
Table 2. PTK fixed network numbering plan
Region Prefix Number of digits
Prishtina 038 6
Mitrovica 028 5
Prizreni 029 5
Peja 039 5
Gjilani 0280 5
Gjakova 0390 5
Ferizaji 0290 5
2.3 Capacities and Services
The majority of exchange offered analog lines only,
detailed information about capacities for each region
are presented in Table 3.
Table 3. Access capacities per reg
ion
Services provided by old switching system are:
Bearer services:
 Circuit-mode 64 kbit/s bearer service.
 BRI - Basic Rate Interface ISDN
 PRI – Primary
Rate Interface I SDN
Basic and Supplementary Services:
 Point-to-point bidirectional voice service;
 Point-to-point facsimile service and medium-
speed and low-speed data servic
e
 Call Barring
 Call Forwarding
 Line Hunting
Switching network topology and local area codes
(LAC) of PTK fixed network are presented in Fig. 2.
Fig. 2. Switching network topology and LAC
3. NGN STRUCTURE
NGN implementation at PTK has been planned into
two phases. Phase one was planned mainly to
substitute subscribers from semi-electronic swit
ches,
and phase two was planned to extend the access
capacities and install additional IN services. As
described in Fig.3. network build during phase one
contains five main network
notions:
 Access Network
 Edge/Core Network
 Voice Control Subsystem
 Supplementary Services and IN Subsystem
 Broadband Data Services
3.1 Access Network
The
access network consists of:
Multi-service access nodes
- able to deliver different
services including: telephony, data, High Speed
Internet Access and Video services, where the same
copper pair is used for various mix of ser vices
, in
PTK case POTS and ADSL services.
DSLAM - (Digital Subscriber Line Access
Multiplexer) in PT K network this type of equipment
are used exclusively to offer high speed internet
access through ADSL for urban areas.
Narrowband Management
component for the
narrowband services of the multi-service access
nodes includes the management for: POTS, LL and
ISDN. ISDN part is not used in PTK network since
there is no ISD
N line installed.
Region Analog Lines Digital Lines
Mitrovica 24024 0
Gjilani 16112 0
Prizreni 20036 0
Ferizaji 12701 0
Prishtina 37704 752
Peja 18878 0
Gjakova 11112 0
Total: 140567 752
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49th International Symposium ELMAR-2007, 12-14 September 2007, Zadar, Croatia
Fig.3. Network notions and elements used to build NGN.
Broadband Management
- is the management
component designed to manage broadband access
services for Multiservice Access Nodes and
DSLAM.
3.2 Edge/Core network
Edge/Core network build in PTK u
ses label
switching technology MPLS (Multiprotocol Label
Switching) which provides the ability to set up
connection-oriented paths over a connectionless IP
network. Edge/Core network in
clude:
Ethernet Service Switch (ESS)
is the edge
component of the network able to offer the
following types of services: Ethernet pipe (Epipe)
Frame-Relay (Fpipe), Virtual Private LAN Service
(VPLS), Internet
Enhanced Service (IES). In PTK
network there is an ESS per region (totally 7),
offering separate VPL for voice, data and OAM.
Service Router (SR)
– is the core router able to offer
the following services: Ethernet pipe (Epipe), ATM
VLL (Apipe), Frame-Relay (Fpipe), Virtual Private
LAN Service VPLS, Internet Enhanced Serv
ice
(IES), V irtual Private Routed Network (VPRN).
Routing Management
– is the application offering
provisioning, assurance and element management
for ESS and SR. This application offers the
following means: Node mediation, Equipment
Management, Security Management, Inventory
and
Reporting, CLI/Telnet Access to NE, Backup and
Restore of NE configuration, Equipment Na vigation,
Equipment Statistics configuration, Equipment
Accounting configuration.
3.3 VoIP Control Subsystem
V
oIP Subsystem i s the platform processing IP
Telephony signaling, it consists of:
Soft Switch (SS)
is the telephony signaling platform
which contains four functional blocks:
1. Residential Gateway Controller (RGC)
2. Call and Session Controller (CSC)
3. Subscription Location Server (SLS)
4. Media
Gateway Controller (MGC)
Media Gateway (MG)
is the equipment that converts
the voice traffic from TDM into VoIP. Media
Gateway offered services are: VoIP Ter mination,
VoIP Trunking, TDM Hair pinning, TDM to
Primary Rate Interfac
e (PRI) grooming, Private
Branch Exchange (PBX) Access. MGC does all
signaling for MG.
Management Center
Is the management application
converging all management elements from VoIP
subsystem and OSP (Open System Platform). It
gives centralized access from single server to all
GUI-s used by
operation application.
3.4 Supplementary Services
OSP handles an application serving as Multimedia
Phone Server (MMPS) and together in
interconnection with the Media Server provide the
follow
ing Supplementar y Services to subscribers:
 Call Forwarding: unconditional, no reply, busy
 Fixed Announcement
 Presentation services: (CLIP, CLIR, COLR,
CO
LP, CLNP, CLNR)
 Incoming Call screening
 Outgoing call barring
 3 party conference
 Explicit call transfer
 Call hold
 Call waiting
 Line hunting
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49th International Symposium ELMAR-2007, 12-14 September 2007, Zadar, Croatia
3.5 Capacities
The majority of access capacities installed is analog
lines, but still ever y M ultiservice node offeres a
certain number of ADSL lines, this number will be
increased durin
g phase 2 of the project. Detailed
information a bout capacities for each region are
presented in Table 4.
Table 4. Access capacities installed
Region
Access
Nodes POTS ADSL
Leased
line
Prishtina 18 8456 5232 80
Mitrovica 15 18683 360 120
Peja 16 19252 384 144
Ferizaj 16 17874 1872 120
Gjakova 9 13980 216 80
Prizren 22 26048 528 176
Gjilani 14 18708 336 112
Each access node includes a VoIP Server Board
able to manage 96 simultaneous VoI P calls.
There are seven ESS installed, one per region,
and all a ccess nodes from the region
are
connected to regional ESS. ESS is handling
intraregional traffic and while all regional ESS
are connected to the Service Routes installed in
central server room in Prishtina.
There are two separate Soft
Switches installed,
each capable of serving to 100,000 subscribers.
Media Gateway is interconnected to PSTN world
via 96 E1 and it is the only gateway to the
external networks. M
edi Gateway Controller is
the SoftSwithc component handling the signaling
between PSTN and NGN through 8 E1 links.
OSP is dimensioned to offer supplementar y
services to 200,000 subscribers.
The broadban
d services platform is dimensioned
for 16,000 subscribers.
Network topology and a more detailed view for
the interconnection of the system elements
installed is presented in the Fig. 4.
Fig.4. Network topology for the network build during phase 1
4. CONCLUSIONS
As it is presented in this paper, PTK made a big
change by moving from very old switching
te
chnology to the latest technology. Old exchanges
were hardware based systems and limited to a very
few services. Newly installed NGN technology is
software based system and offer
s many services by
merging voice and data tr affic networks. The
advantages of the NGN installed at PTK are: more
services, easier interoperability and easier
management. Because of the centralized call
control logic a higher reliability of the transmission
network is required. By this PTK did one step
towards the triple play services.
REFERENCES
[1] M. Kalaratna, D. Dias, “Essentials of Modern
Telecommunications”, Artech House
Publishers, 2004.
[2] R. A. Thompson, “Telephone Switching
Systems”, Artech House INC, 2004.
[3] M. Duchaine, “High Level Net
work
Description of PTK NGN”, (Alcatel - PTK
Internal document) Alcatel 2006.
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