Application of fiber-optic techniques in the transport and access transmission networks of mobile systems.

Abstract

Fixed access networks widely employ fiber-optical techniques due to the extremely wide bandwidth offered to subscribers. In the recent years enormous increase of user data is visible in mobile systems too. Therefore the importance of fiber-optical techniques within the fixed transmission/transport part of mobile systems is inevitably increasing. This paper summarizes a few reasons and gives examples why and how fiber-optic techniques are employed efficiently in 2G networks.

Full text

Program book

_________________
#978-963-8111-76-0
Application of Fiber-Optic Techniques in the
Transport and Access Transmission Networks
of Mobile Systems
Dr.Attila Hilt László Pozsonyi
NPO, Network Planning and Optimization, NPO, Network Planning and Optimization,
Nokia Siemens Networks Kft., Nokia Siemens Networks,
H-1092 Köztelek utca 6., Budapest, Hungary, A-1030 Guglgasse 15., Wien, Austria,
attila.hilt@nsn.com laszlo.pozsonyi@nsn.com
Abstract — fixed access networks widely employ fiber-optical
techniques due to the extremely wide bandwidth offered to
subscribers. In the recent years enormous increase of user data is
visible in mobile systems too. Therefore the importance of fiber-
optical techniques within the fixed transmission/transport part of
mobile systems is inevitably increasing. This paper summarizes a
few reasons and gives examples why and how fiber-optic
techniques are employed efficiently in 2G networks.
Index Terms — mobile networks, GSM, access transmission,
transport, SDH, IP, mobile data, EDGE deployment,
modernization, network upgrade
I. INTRODUCTION
IGITAL mobile telephony systems have been originally
developed for circuit switched (CS) voice traffic.
Continuously increasing demand for mobile data services such
as mobile Internet access resulted in an evergreen development
and modernization of the initially pure circuit switched digital
mobile networks towards the packet switched (PS) domain.
Such services like mobile Internet, video streaming, gaming,
navigation, banking, or mobile television (TV) require
efficient networks that can provide very high user data rates.
Fig.1 demonstrates the trend of enormous increase of user data
rates in wireless systems in the last decade [1]. As a
comparison wireline techniques are also shown on the chart.
In Europe nowadays, the very first digital mobile networks
(NW) are in operation for already two decades. Therefore in
the past years a continuous upgrade and modernization of
mobile networks were visible in terms of both hardware (HW)
and software (SW) of the existing components. In order to
support higher and higher user data rates, major technology
steps were the introduction of GPRS and EDGE in 2G, as well
as launching 3G or UMTS, WiMax and recently LTE services.
In this paper the main focus is on GSM networks, that are
part of the above mentioned wireless/wireline access field.
Modernization and optimization of actual GSM networks give
a continuous job for both network operators and equipment
vendors. Modernization of mobile networks inherently offers
the possibility of simultaneous optimization [2-5]. GSM
network modernization aspects are presented with special
emphasis on the application of fiber-optical techniques in the
fixed access transmission (TRS) and transport parts of second
generation (2G) mobile systems. The paper shows some
examples for the modernization of the 2G network elements
(NE) in order to enable higher data rates in the existing GSM
networks.
Fig.1. Increasing data in rates in fixed and mobile services
II. MOBILE SYSTEMS: ARCHITECTURE AND
INCREASING ROLE OF FIBER OPTIC TECHNIQUES
The role of fiber-optic techniques in the fixed part of
mobile access networks is continuously increasing. One main
reason is already mentioned in the introduction, namely the
continuously increasing amount of subscribers’ data.
Microwave (MW) radio links and copper-based leased lines
(LL) are extensively used in mobile access and transport
networks (Fig.2.).
However, the offered bandwidths of MW and LL are
limited due to several technical and financial reasons, such as
D

available radio spectrum, bandwidth, interference, hop
distance, radio frequency or leased line fees and installation
costs, etc. (Fig.2.). Recent trend is therefore to further extend
the fiber-optic techniques from the BackBone/Transport part
towards the Access Network. MW and LL technologies are
more and more moving to the last mile of the access networks.
Access Network,
Last mile
BackBone,
Aggregation
Eth
Microwave Radios NG-SDH/SONET
Copper-based
Broadband Access
Carrier Ethernet
(L2 MPLS, PBB-TE)
Fiber-optics in
Broadband Access ATM, L3 MPLS, IP
BTS
E1/T1
Cell sites
BTS
Eth
NB
NB
E1/T1 Eth
I-HSPA
LTE
Eth
WiMAX
Eth
BSC
E1/T1
BSC
GE
RNC RNC
GE
GGSN
eGSN-U
GE
STM1/
OC1
ASN-
GW
GE
Controller /
gateway site
Access Network,
Last mile
BackBone,
Aggregation
Eth
Microwave Radios NG-SDH/SONET
Copper-based
Broadband Access
Carrier Ethernet
(L2 MPLS, PBB-TE)
Fiber-optics in
Broadband Access ATM, L3 MPLS, IP
BTSBTS
E1/T1E1/ T1
Cell sites
BTSBTS
EthEth
NBNB
NBNB
E1/T1E1/ T1 EthEth
I-HSPA
LTE
EthEth
WiMAXWiMAX
EthEth
BSC
E1/T1E1/T1
BSC
GEGE
RNC RNC
GEGE
GGSN
eGSN-U
GEGE
STM1/
OC1
STM1/
OC1
ASN-
GW
GEGE
Controller /
gateway site
Fig.2. Fiber-optic techniques in the fixed part of mobile broadband access
Without completeness, two more important reasons are
discussed here focusing only on 2G systems. First we refer to
modernization projects that involve the network elements of
the mobile systems. Then the access transmission and transport
part mentioned briefly. Both within the last-mile and in the
aggregation layer parts there are several modernization and
optimization possibilities. Proper selection of transmission
protocols and physical media significantly influence the life-
time of the network and in longer term may lead to future
proof investments for the network operators.
A. Architecture of GSM Networks
In second generation mobile systems the BSC (Base
Station Controller) is responsible for the control of the base
transceiver stations (BTS). In third generation (3G) systems
similar task is performed by the Radio Network Controller
(RNC). The general architecture of GSM network is shown in
Fig.3. The first technology supporting data calls in GSM was
High Speed Circuit Switched Data (HSCSD). Even though
HSCSD has very limited data speed, it is still in use in several
networks. Next evolution step was General Packet Radio
Service (GPRS), which employs packet-switching (PS)
protocols in GSM networks. Supporting GPRS in GSM
networks, SGSN (Serving GPRS Support Node) and GGSN
(Gateway GSN) have to be installed as shown in Fig.3. GGSN
provides interworking functions with external PS networks.
SGSN on the other hand, keeps track of individual mobile
stations’ location and provides security and access control. The
advantage of GPRS compared to HSCSD is in the more
efficient resource utilization at the air-interface. One GSM air-
timeslot (TSL) can be shared between several GPRS users.
Gn
GGSN
Gb
SGSN
Abis
MGW and MSS
BSC
Ater
Circuit Switched
Core Network
BTS
BTS
Access
Transmission
Network
Radio Network
Packet Switched
Core Network
Gn
GGSN
Gb
SGSN
Abis
MGW and MSS
BSC
Ater
Circuit Switched
Core Network
BTS
BTS
Access
Transmission
Network
Radio Network
Packet Switched
Core Network
Fig.3. Architecture of the GSM network supporting PS data services
EDGE (Enhanced Data rates for GSM Evolution) became
the next step after HSCSD and GPRS to provide data services
with further increased user throughputs (TP) [2-9]. The
Gaussian Minimum Shift Keying (GMSK) modulation method
of GSM is replaced with eight-state Phase Shift Keying (8-
PSK) in EDGE. Due to three bits that are sent in one symbol,
8-PSK allows higher bit rate. The price paid for higher bit
rates is the smaller coverage that affects the radio frequency
(RF) network planning. EDGE and GSM use the same
200 kHz carrier spacing so they coexist within 2G mobile
networks. The main differences between EDGE and GPRS are
summarized in [2-9]. EDGE allows up to 59.2 kbit/s user
throughput per air-TSL. Increased mobile user data rates
require increased capacities in the fixed access TRS NW
serving the base stations (BTS) [1-17].
B. Network Elements with Optical Interfaces
One typical goal in network modernization projects is to
reduce the number of old radio controller elements (BSCs or
RNCs), thus achieving OPEX reduction in the network
operation and maintenance. New BSCs (and RNCs) can
control more BTSs (or Node-Bs), serve more cells, handle
bigger traffic and have increased performance. Last but not
least new generation BSCs provide more logical and physical
ports for connectivity. There are optical interfaces available for
the required transmission methods and protocols. The
transmission cards of the new generation BSCs provide
electrical and optical ports with PDH/SDH and Ethernet
interfaces (e.g. Fast or Gigabit Ethernet) (Fig.4.) [7-15].
Optical ports are necessary in order to handle the significantly
increased amount of traffic via fiber-optical connections. New
base stations provide optical interfaces for mobile
backhauling. One good example is NSN multiradio (MR) with
optical Gigabit Ethernet connection as shown in Fig.5.
However, the removal of old BSCs from the existing
network results in increased load on the transmission/transport
network. It is due to the fact that the radio controllers perform
concentration task. Therefore increased traffic can be expected

in the existing access and transport part of the network when
old BSCs are removed. The following examples in part III will
show the effect of the removal of the BSCs and the calculated
traffic increase on the existing fiber-optical SDH network.
Fig.4. NSN FlexiBSC with configurable electrical/optical interfaces. ETS2
card is shown beside the BSC cabinet. The ETS2 card has four optical
ports, each having STM-1.
Fig.5. NSN MultiRadio (2G/EDGE/3G/LTE base station) with transport
module providing electrical/optical (Gigabit Ethernet) transmission
interfaces.
C. Modernization in GSM, in Access and Aggregation Layers
The main aspects that are usually considered in the case of
modernization of existing 2G networks are typically the
following:
 deployment of EDGE service to provide higher data
rates than that of HSCSD or GPRS [2-4],
 coverage or capacity extension of existing EDGE
service (e.g. to reduce congestion of data calls in the
existing radio network) [2-4],
 BSC modernization projects (SW and/or HW upgrades,
swaps resulting in BTS re-homings) [10-16],
 removing transcoders (TCSM) from the 2G network
(as transcoding function is possible in MGWs in
Rel.4 networks) [15],
 Gb interface migration from FR (Frame Relay) to IP,
 core network modernization projects (e.g. from Rel.99
to Rel.4 core networks),
 introducing ‘multipoint A’ interface (IF) feature for the
new BSCs,
 introducing A interface over IP,
 MSS pooling for load balancing and resource sharing
 transition of signalling from SS7 to SIGTRAN,
 OAM / OSS modernization (e.g. introduction of OSS
over IP instead of old X.25 or CNLS),
 changing the access transmission of 2G from TDM
based PDH / SDH to packet transmission (Ethernet/IP),
 protection planning e.g. diversity routes or introducing
ring topology for redundancy [4, 5, 19-22].
Furthermore, there are several other scenarios that are not
directly related to the modernization of the existing 2G
network itself, however inherently offer optimization and
modernization possibilities:
 launching 3G, HSPA or LTE services on co-sites and
therefore providing optical fiber for 2G sites too [17],
 providing a common transmission / mobile backhaul
solution to the same physical location for all radio
layers in case of 2G, 3G and/or LTE co-siting (Fig.5.),
 refarming (e.g. extending UMTS in 900 MHz GSM
radio-frequency band),
 changing the ATM / SDH based 3G access
transmission to hybrid (e.g. ATM for real-time and
packet for non-real time applications) or pure Iub over
IP (packet transmission fro all 3G services),
 multi-layer optimization (MLO) projects [23, 24].
All of the above have significant influence on the traffic
over the existing access networks. Careful strategic decisions
should be done to support future-proof network investments
meanwhile preserving the quality of the network and the
offered services. As an example, Fig.6 shows the typical
evolution path of a mobile backhaul network that is used
commonly for 2G/3G/LTE.
2G
3G
I-HSPA
LTE
WiMAX
2G
3G
I-HSPA
LTE
WiMAX
2G
3G
I-HSPA
LTE
WiMAX
PDH/SDH/ATM
PDH/SDH/ATM
Packet
Packet
ClassicHybrid
Packet
cell site controller
cell site controller
controller
cell site
2G
3G
I-HSPA
LTE
WiMAX
2G
3G
I-HSPA
LTE
WiMAX
2G
3G
I-HSPA
LTE
WiMAX
PDH/SDH/ATM
PDH/SDH/ATM
Packet
Packet
ClassicHybrid
Packet
cell site controller
cell site controller
controller
cell site
Fig.6. Different connection possibilities within mobile networks between
controller and cell sites

The mobile backhaul modernization starts from the
classical transmission methods of PDH/SDH for 2G and
PDH/SDH/ATM for 3G. Introducing HSPA and LTE requires
packet based transmission for more efficient usage of available
bandwidths over the access network. In case of 2G BTS co-
sited with 3G Node-B or LTE site, this may result in offering
packet-transmission based 2G services as discussed later. In
co-siting scenarios of Fig.6 we quickly reach the transmission
bandwidth demands in the range of 100…200 Mbit/s per
single site. Cell sites and controller site NEs therefore must
have optical interfaces and the application of fiber-optical
techniques becomes straightforward [16].
D. Protection Principles for Optical Ater Connections
Different protection possibilities in the aggregation and
core parts increase the overall network reliability and
redundancy. However, they may also require increase of
existing capacities in the actual transmission network. A few
examples are mentioned here. Port and card level MSP SDH
protection methods are shown in Fig.7 and Fig.8, respectively.
Fig.7. Port level MSP SDH protection of the Ater interface between BSC
and MGW. Protection port is located on the same transmission card.
Fig.8. Transmission card level MSP SDH protection of Ater interface
between BSC and MGW. At the BSC side the protection port is on a
separate transmission card.
Fig.9 shows the network scenario when SDH MSP is
combined with ‘multi A’ feature. In this example the BSC is
connected to two different MGWs by optical fibers. The
connection is at SDH STM-1 level and the SDH optical ports
are protected at transmission card level at the BSC side.
Fig.9. Transmission card protection at BSC side combined with
implementation of multipoint A interface feature.
III. CAPACITY UPGRADE EXAMPLES DUE TO
NETWORK MODERNIZATION
Let us consider a mobile network modernization case with
NW parameters that are typical for a medium or small size
European country. The initial 2G network consists of 48 old
generation BSCs and 2400 sites. This means that in average
there are 50 BTS connected to each old BSC. EDGE is not yet
or only partly deployed in the initial network. The typical
access transmission bandwidth provided for each BTS is
therefore only 1 E1. In the modernized network the goal is to
have only 6 new BSCs. The new BSCs should be located only
at a few Core Nodes (CN). Finally the target is to enable
EDGE service on all the sites.
As shown in Fig.10, one new generation BSC will replace
in average 8 old BSCs. This means that the new BSC should
serve in average 400 BTS. The PDH access network connects
the BTSs to the old BSCs. The access network is typically a
combination of PDH, hybrid or Ethernet microwave links
(MW) and Leased Lines (LL). LLs are either copper cables or
more and more often optical-fibers, when the 2G site is co-
located with a UMTS NodeB or LTE site.
Each node in the figure is an old BSC and simultaneously
an SDH equipment location. The old BSCs are connected to
the core nodes by the high capacity transport network. The
transport network is typically composed of SDH sections,
where the physical media of the SDH transport network is
mainly optical-fiber. In very few cases –where the
implementation of the fiber-optical cables would be very
difficult e.g. time consuming or too expensive – SDH network
may contain SDH level MW links. In our example the SDH
network is composed of STM-4 connections.

The actual utilization rate of the SDH network is around
75% (which value is quite a good assumption, however it is
very difficult to get the exact values from real networks). In
other words within the STM-4 level backbone one entire STM-
1 is available for network expansions. It is recommended for
network operational efficiency that the SDH utilization should
remain always below 95%. The example is calculated first for
the simplest chain/star topology. Then SDH ring scenarios are
considered.
A. Chain/star topology
A regional portion of the entire access transmission and
transport network of the mobile system is shown in Fig.10.
400 sites are connected to 8 old BSCs in chain/star topology.
As each BSC location is an SDH node, each old BSCs can
reach the core network via fiber-optical network. The core
node hosts the old TCSM and MSC and the new MGW and
MSS. The SGSN is located in the CN location too.
old BSC
new Flexi BSC
SDH node
core node:
MGW & SGSN
SDH STM-4
access PDH
old BSC
new Flexi BSC
SDH node
core node:
MGW & SGSN
SDH STM-4
access PDH
Fig.10. Fiber-optic network providing SDH STM-n backbone for
GSM network - chain topology
Now the old BSCs must be removed due to modernization.
As shown in Fig.11, the modernized network will contain only
one new BSC, which is located at the same core node where
the new MGW, MSS and SGSN are located. All the 400 BTSs
will be connected to the new BSC after modernization. For the
sake of roll-out speed the PDH network is neither re-designed
nor optimized. This means that majority of the Abis
connections should contain SDH portion after the
modernization. In our example 350 BTS – BSC lines that were
originally at PDH level will have now an SDH portion too. As
seen in Fig.11, capacity upgrades are required due to the fact
that concentration elements (old BSCs) have been removed
from the network. Naturally, such a modernization project
cannot be carried out without a careful assessment of the
existing SDH network.
new
STM-1
no SDH
upgrade but
utilization
75% →89%
no SDH
upgrade
no SDH
upgrade
no SDH
upgrade but
utilization
75% →89%
old BSC
removed
old BSC
new Flexi BSC
SDH node
core node:
MGW & SGSN
SDH STM-4
access PDH
new
STM-1
no SDH
upgrade but
utilization
75% →89%
no SDH
upgrade
no SDH
upgrade
no SDH
upgrade but
utilization
75% →89%
old BSC
removed
new
STM-1
no SDH
upgrade but
utilization
75% →89%
no SDH
upgrade
no SDH
upgrade
no SDH
upgrade but
utilization
75% →89%
old BSC
removed
old BSC
new Flexi BSC
SDH node
core node:
MGW & SGSN
SDH STM-4
access PDH
old BSC
new Flexi BSC
SDH node
core node:
MGW & SGSN
SDH STM-4
access PDH
Fig.11. The GSM network after BSC modernization. 8 old BSCs removed
from the network. New STM-1 connections are needed in three cases.
The accurate figure of traffic concentration thanks to BSCs
in 2G mobile networks is very network dependent. It is
determined by several parameters, such as allowed Ater
blocking ratio (typically 0.1%), Gb interface type, network
topology and protection methods used. The traffic increase
over the SDH portion per demolished old BSC can be
approximated in terms of required new E1 lines as the
difference of new Abis lines and the sum of old Ater and Gb
interface lines. With the simplified assumption of old Abis/old
(Ater+Gb) ratio of ~ 3.6 we will need 36 new E1 lines over the
SDH network for each removed BSC. Naturally, the ratio of
Abis ~ 3.6(Ater+Gb) is a rough assumption. Exact values
should come from real NW planning and measurement data.
However, our figure describes reasonably well several recent
modernization cases. This value is even higher if
simultaneously to the BSC modernizations the EDGE service
is launched or capacity upgraded.
As a result of the example, the requirement of 36 new E1s
per demolished old BSC mean a significant traffic increase.
For star connected BSCs the utilization over the SDH transport
network will increase from 75% to 89%. In the STM-4 chains
of the existing SDH network in practice only one old BSC can
be removed without capacity extension.
B. Ring topology
Fig.12 shows a more realistic scenario when –instead of
chains- a ring topology is employed in the transport network
part [19]. With the same parameters that were used in the

chain/star topology, now in the ring topology case only two
old BSCs can be removed from the existing network without
capacity upgrade on the SDH part. The two BSCs that can be
removed without SDH upgrade are the one connected directly
to the new BSC/MGW location and any other one from the
ring (or chain connected to the ring).
no SDH
upgrade
STM-4 ring,
actual 75% utilization →
only 2 BSCs can be removed
without SDH upgrade: the one
connected directly to new
BSC/MGW location and one
from the ring or chain
connected to the ring
old BSC
new Flexi BSC
SDH node
core node:
MGW & SGSN
SDH STM-4
access PDH
no SDH
upgrade
STM-4 ring,
actual 75% utilization →
only 2 BSCs can be removed
without SDH upgrade: the one
connected directly to new
BSC/MGW location and one
from the ring or chain
connected to the ring
old BSC
new Flexi BSC
SDH node
core node:
MGW & SGSN
SDH STM-4
access PDH
old BSC
new Flexi BSC
SDH node
core node:
MGW & SGSN
SDH STM-4
access PDH
Fig.12. Fiber optic network example with ring topology providing
STM-4 backbone
Finally, the last scenario is shown in Fig.13 where Add
Drop Multiplexers (ADMs) are also taken into account [19-
22]. Here several sites are connected to the BSCs by a
combination of access network types. A portion of the access
network is composed of MW links or leased lines reaching the
ADM. Then, from the ADM to the BSC the Abis traffic is
carried via SDH over fiber. In the example it is assumed that
20% of the sites reach their BSC over ADM and SDH. As seen
in Fig.13, 3 old BSCs can be removed and the one in the core
node can be replaced by the new generation BSC. The removal
of the remaining four old BSCs requires capacity upgrade in
the SDH ring.
no SDH
upgrade
STM-4 ring,
actual 75% utilization →
only 3 BSCs can be removed
without SDH upgrade: the one
connected directly to new
BSC/MGW location and two
from the ring or chain
connected to the ring
2 old BSC can
be removed
1 old BSC
can be
removed
old BSC
new Flexi BSC
SDH node
core node:
MGW & SGSN
SDH STM-4
access PDH
ADM (no BSC)
old BSC
new Flexi BSC
SDH node
core node:
MGW & SGSN
SDH STM-4
access PDH
ADM (no BSC)
Fig.13. Fiber optic network with ring topology and ADM
The conclusions of the presented examples are:
 Application of fiber-optic techniques play essential role
in mobile network modernizations.
 NW modernization projects need very careful
assessment of the existing transmission/transport
network (topology, utilization, redundancy, upgrades).
 The concentration of major network elements into a
few core nodes may significantly increase the load on
the existing transmission/transport network.
 Insufficient capacities on transmission/transport
network may slow down or block modernization
projects.
 The concentration of major network elements into a
very few core nodes may reduce network flexibility and
reliability. Outage of any major network element or
entire core node may have crucial impact on the
network and the availability of the offered services.
Therefore proper protection/redundancy methods must
be applied.
 Decision of having a highly centralized versus
decentralized network should be a trade – off
considering not only technical but economical factors
too (OPEX/CAPEX).
IV. ACCESS TRANSMISSION NETWORK:
MIGRATION FROM PDH TOWARDS ETHERNET/IP
Mature mobile operators heavily utilize the available
access transmission network capacities [3-5, 17, 19, 23, 24].
To satisfy bandwidth demand increases network costs may
lead to unacceptable levels. Therefore any new capacity
demand may require optimization. Modernization projects
inherently offer the possibilities of optimizing and upgrading
the transmission networks. Use of IP protocol within 2G Abis
transmission will result in significant capacity savings. It may
have different implementation methods. Fig.14. shows a
legacy TDM network. Over existing TDM network Packet
Abis can implemented using MLPPP. MLPPP is a protocol
providing packet transport for 2G over TDM E1 lines. The
operator can utilize the existing installed TDM Infrastructure,
easing the introduction of the Packet Abis solution. Packet
Abis over TDM offers significant bandwidth savings in
comparison with traditional TDM transport since it introduces
a very efficient and fully integrated Abis optimization
capability. Bandwidth can be shared by CS, PS and signalling
traffic as transmission resources are used as pools. Pooling
results as reduced number of TDM lines or reduced bandwidth
with Microwave radios/SDH transmission. Resource
overbooking is also possible. This solution offers the
advantage that network operators can partly or entirely keep
the existing access transmission network until that is
modernized to be fully Ethernet capable. This is especially
important for sites that are running over LLs where the LL
provider cannot transform its actual service to Leased Ethernet
(LE). Another example is existing PDH/TDM MW radios.

TDM
TDM
TDM
Network
MLPPP
Packet Abis
E1/T1/FB
MLPPP
Packet Abis
E1/T1/SDH
FlexiEDGE
TDM
TDM
TDM
Network
MLPPP
Packet Abis
E1/T1/FB
MLPPP
Packet Abis
E1/T1/SDH
FlexiEDGE
BSC
Fig.14. Packet Abis over legacy TDM network
Finally we mention the packet Abis over Ethernet solution
(Fig.15). On one hand significant bandwidth savings are
available compared to TDM based 2G access transmission
networks. The difficulties discussed in part III can be
significantly reduced by the bandwidth savings that expected
to reach 50%. However, on the other hand some new problems
are arising too. Technical considerations must be taken into
account about quality of service (QoS), packet loss, delay,
synchronization and data security. In mobile networks the base
stations derive their frequency reference signals from the
timing inherently provided by the TDM links carrying the
incoming traffic itself. When these TDM based links (Fig.14)
are replaced by Ethernet-based ones (Fig.15) the frequency
reference is lost. Timing over Packet (ToP) is one solution that
is already used in several networks successfully [18]. But one
main drawback still remains: just a few network operators
have their own PS network already countrywide available with
sufficient bandwidth and QoS.
BSC
Eth
Eth
Packet Switched
Network
UDP/ IP
Packet Abis
Ethernet
UDP/ IP
Packet Abis
Ethernet
FlexiEDGE
BSC
Eth
Eth
Packet Switched
Network
UDP/ IP
Packet Abis
Ethernet
UDP/ IP
Packet Abis
Ethernet
FlexiEDGE
Fig.15. Packet Abis over Ethernet
V. CONCLUSIONS
First GSM networks are already 20 years old in Europe.
Better system performance, increasing number of subscribers,
growing traffic as well as introduction of new services require
continuous upgrades, modernizations and replacements in the
existing GSM networks. Modernization of mobile networks
must lead to significant increase in offered traffic and available
user data rates. Higher data rates and better network
performance are only possible with the efficient employment
of fiber-optic techniques. This paper showed some examples
of using optical fibers in the access transmission and transport
part of mobile systems. Effect of BSC modernization was
investigated. It was shown that BSC removals may
significantly increase the load on the existing transmission
network. Some possibilities were mentioned how to cope with
these challenges.
ACKNOWLEDGMENTS
The authors acknowledge Zsolt Borcsiczky, Ivan Lesic,
László Lisztes, Marc Rinofner, Szabolcs Sülle and Pál
Szabadszállási for their valuable comments and support during
the projects that gave contribution to the paper preparation.
ABBREVIATIONS
A interface between BSC and MSC in GSM
Abis interface between BSC and BTSs in GSM
ADM Add Drop Multiplexer
ADSL Asymmetrical Digital Subscriber Line
Ater interface between BSC and TCSM (or MGW) in GSM
ATM Asynchronous Transfer Mode
BER Bit Error Rate
BSC Base Station Controller
BTS Base Transceiver Station (or base station)
CAPEX Capital Expenditure
CLNS (ISO/OSI) ConnectionLess Network Service
CN Core Node: location of core NW elements
CS Circuit Switched
DSM L3 Dynamic Spectrum Management Level 3
E1 European primary rate, 2 Mbit/s path, often called as PCM
channel
EDGE Enhanced Data rates for GSM Evolution
EGPRS enhanced GPRS
ETSI European Telecommunications Standards Institute
FR Frame Relay (means also Full Rate CODEC)
Gb interface between BSC and SGSN
GGSN Gateway GPRS Support Node
GMSK Gaussian Minimum Shift Keying
GPON Gigabit Passive Optical Network
GPRS General Packet Radio Service
GSM Global System for Mobile Communications
HSCSD High Speed Circuit Switched Data
HSDPA High Speed Downlink Packet Access
HSPA High Speed Packet Access
HSUPA High Speed Uplink Packet Access
HW hardware
IP Internet Protocol
Iub interface between NodeB and RNC
LL Leased Line
LTE Long Term Evolution
MGW Media GateWay
MIMO multiple-input multiple-output (antenna system)
MLO Multi-layer optimization
MLPPP Multi Link Point to Point Protocol
MSC Mobile Switching Center
MSP Multiplex section protection (as in ITU-T Rec.G841)
MSS MSC Server
MW microwave (frequency, radio or link, e.g. 38 GHz)
NE Network Element

NG PON Next Generation PON
NG SDH Next Generation SDH
Node-B 3G base station (often simply called as BTS too)
NSN Nokia Siemens Networks
NW network
OAM Operation and Maintenance
OSI Open Systems Interconnection
OSS Operations Support System
OPEX Operating Expenditure
PCM Pulse Code Modulation
PCU Packet Control Unit (in BSC)
PDH Plesiosynchronous Digital Hierarchy
PON Passive Optical Network
PS Packet Switched or packet-switching protocol
QoS Quality of Service
RF Radio Frequency
RNC Radio Network Controller
SDH Synchronous Digital Hierarchy
SGSN Serving GPRS Support Node
STM Synchronous Transfer Mode
STM-1 155 Mbit/s or 63 E1s
STM-4 4 x 155 Mbit/s
SW software
TC transcoder, transcoding
TCSM TransCoder and SubMultiplexer
TDM Time Domain Multiplexing
ToP Timing over Packet
TP throughput
TRS transmission
UDP User Datagram Protocol
UMTS Universal Mobile Telecommunications System
VDSL Very-high-speed Digital Subscriber Line
VDSL2 Very-high-speed Digital Subscriber Line 2 (ITU-T G.993.2)
is an enhancement to VDSL (ITU-T G.993.1)
WiMAX Wireless Microwave Access
X.25 ITU-T standard protocol that is step-by-step replaced by
less complex protocols (e.g. IP), but still often in use in
several mobile networks
2G second generation mobile system
3G third generation mobile system
REFERENCES
[1] NSN: “Broadband Access for All – A Brief Technology Guide”,
white paper, 2007.
[2] T.Halonen, J.Romero, J.Melero: “GSM, GPRS and EDGE
performance: evolution towards 3G/UMTS”, John Wiley &
Sons, 2nd edition, ISBN 0-470-86694-2, 2003.
[3] P.Petrás, A.Hilt, M.Suuronen: “Mobile network upgrade for
EDGE in Hungary”, Proc. of the 13th Conference on Microwave
Techniques, COMITE 2005, pp.111-114, Prague, Czech
Republic, September 2005.
[4] A.Hilt, P.Petrás, D.Emsley, G.Rybarczyk: “Access Transmission
Network Upgrade in a Nationwide Mobile Network
Modernization Project for EDGE Deployment”, Networks 2008,
13th International Telecommunications Network Strategy and
Planning Symposium, Budapest, Hungary, October 2008.
[5] A.Hilt, P.Berzéthy: “Recent trends in reliable access networking
for GSM systems”, Proceedings of the Conference on Design of
Reliable Communication Networks, DRCN’2000, pp.91-98,
Budapest, Hungary, October 2001.
[6] ETSI TS 145 001 V5.7.0: “Digital cellular telecommunications
system (Phase 2+); Physical layer on the radio path; General
description”, Technical Specification, 3GPP TS 45.001 version
5.7.0 Release 5, http://www.etsi.org, Nov. 2003.
[7] ETSI TS 145 002 V5.11.0: “Digital cellular telecommunications
system (Phase 2+); Multiplexing and multiple access on the
radio path”, Technical Specification, 3GPP TS 45.002 version
5.11.0 Release 5, http://www.etsi.org, Aug. 2003.
[8] ETSI TS 145 003 V5.10.0: “Digital cellular telecommunications
system (Phase 2+); Channel coding”, Technical Specification,
3GPP TS 45.003 version 5.10.0 Release 5, http://www.etsi.org,
Aug. 2004.
[9] ETSI TS 145 004 V6.0.0: “Digital cellular telecommunications
system (Phase 2+); Modulation”, Technical Specification, 3GPP
TS 45.004 version 6.0.0 Release 6, http://www.etsi.org, Jan.
2005.
[10] Nokia BSC/TCSM, Rel. S12, Product Documentation S11.5,
S12, © Nokia Siemens Networks.
[11] Nokia GSM/EDGE BSS, Rel. BSS13, BSC and TCSM, Rel.
S13, Product Documentation, Nokia BSS Transmission
Configuration, v.4, DN9812391, Issue 13-1 en
[12] Nokia Siemens Networks GSM/EDGE BSS, rel.RG10 (BSS),
operating documentation, issue 04, Plan and dimension, Abis
EDGE Dimensioning for BTSplus at the Flexi BSC product
family, DN0933269
[13] Nokia Siemens Networks GSM/EDGE BSS, rel.RG10 (BSS),
operating documentation, issue 04, Engineering for Flexi BSC,
DN70590621, Issue 1-0
[14] Nokia Siemens Networks GSM/EDGE BSS, rel.RG10 (BSS),
operating documentation, issue 04, Integrate and configure, BSS
Integration, DN9812243, Issue 20-0
[15] Nokia Siemens Networks GSM/EDGE BSS, rel.RG10 (BSS),
operating documentation, issue 06, BSC/TCSM description
Product description of Flexi BSC, DN70577137 Issue 1-3, 2010.
[16] Nokia Siemens Networks GSM/EDGE BSS, rel.RG10 (BSS),
operating documentation, issue 06, ETS2 DN0592447 Issue 1-1.
[17] H.Holma, A.Toskala editors: “HSDPA/HSUPA for UMTS”,
John Wiley & Sons, 2006.
[18] NSN: “Timing over Packet, Technical Brief”, C401-00106-B-
200803-2-EN, 2008.
[19] Trevor Manning: “Microwave Radio Transmission Design
Guide”, 2nd edition, Artech House, 2009.
[20] NSN: “SURPASS hiT 7025, Multi-Service Provisioning
Platform”, C401-00066-DS-200710-1-EN, 2007.
[21] NSN: “Technical Description, SURPASS hiT 7025”, Issue 06,
2008.
[22] NSN: “Technical Description, SURPASS hiT 7080”, Issue 1.6,
June 2008.
[23] NSN: “Multi-Layer Optimized Networks”, white paper, 2010.
[24] NSN: “A vision of tomorrow’s connected world - converged
networks and flexible business models”, white paper, Nov. 2007.

ICUMT2011 - 3rd International Congress on Ultra Modern
Telecommunications and Control Systems
17
OCTOBER 6, 2011 I THURSDAy
ROOM 7
13:00-14:50
FOAN
Session III: Integrated and fiber optics - Part I.
Chair: Edvin Škaljo
1.
INVITED TALK
JACKET MATRIX CODING IN ACCESS NET WORK
Ho Moon Lee
2. ANALYTICAL EVALUATION OF SPLICE AND BENDING LOSSES OF PHOTONIC CRYSTAL FIBERS BASED ON EMPIRICAL RELATIONS
George Kliros
3. LOWCROSSTALK 3X3 OPTICAL CROSSCONNECT USING FIBER BRAGG GRATINGS
Shien-Kuei Liaw
4. PRACTICAL ASPECTS OF ACCESS NETWORK INDOOR EXTENSIONS USING MULTIMODE GLASS AND PLASTIC OPTICAL FIBERS
Gerd Keiser
14:50-15:10 Coffee break
15:10-15:30
FOAN
Session III: Integrated and fiber optics - Part II.
Chair: Edvin Škaljo
1. PHOTONIC SAMPLED AND ELECTRONICALLY QUANTIZED ANALOGUE TO DIGITAL CONVERSION IN ACCESS NETWORKS
Mohammadreza Behjati
15:3017:00
FOAN
Session IV: Radio over fiber and wireless networking
Chair: Attila Gábor Hilt
1. HIGH SPEED MIMO LTE APPLICATIONS BASED ON MATRIX INVERSION ALGORITHMS USING FLOATING POINT DSP
Md. Sarker
2. ULTRAWIDEBAND IMPULSE RADIO OVER FIBRE SYSTEM
Gábor Fehér
3. APPLICATION OF FIBEROPTIC TECHNIQUES IN THE TRANSPORT AND ACCESS TRANSMISSION NETWORKS OF MOBILE SYSTEMS
Attila Gábor Hilt
4. CLOSING
Gerd Keiser