2. GSM Network Planning - Transmission Overview/Planning
DISCLAIMER This book is a training document and contains
simplifications. Therefore, it must not be considered as a
specification of the system. The contents of this document are
subject to revision without notice due to ongoing progress in
methodology, design and manufacturing. Ericsson assumes no legal
responsibility for any error or damage resulting from the usage of
this document. This document is not intended to replace the
technical documentation that was shipped with your system. Always
refer to that technical documentation during operation and
maintenance. This document was produced by Ericsson Radio Systems
AB. It is used for training purposes only and may not be copied or
reproduced in any manner without the express written Copyright 2002
by Ericsson Radio Systems AB consent of Ericsson. This document
number, EN/LZT 123 6914/2, R3A supports course number LZU 108
3816/2. EN/LZT 123 6914/1 R3A
3. Revision Record REVISION RECORD Date Revision No. Chapters
Affected 2002-11-03 R3A All EN/LZT 123 6914/2 R3A
7. GSM Introduction - Interfaces and Node Hierarchy Chapter 1
This chapter is designed to provide the student with an
introduction to the GSM system. OBJECTIVES: Upon completion of this
chapter the student will be able to: Draw a PLMN comprising
classical GSM nodes and GPRS nodes SGSN-G 3.0 and GGSN 4.0. List
the interfaces in a GSM PLMN Explain how user data is mapped in
each interface
11. 1 GSM Introduction - Interfaces and Node Hierarchy SYSTEM
ARCHITECTURE IN ERICSSONS GSM SYSTEM The GSM R9 network will be a
multi-service network. It will accommodate the growing number of
interconnections between a variety of networks circuit-switched and
packet-switched, narrowband and broadband, voice and data, fixed
and mobile. For the operator, the GSM R9 network means continuity
of services, optimized end-user application portfolios and
significant cost reductions in transmission, operation and
maintenance. Examples of private corporate applications LAN/MAN
interconnect, file transfer, CAD/CAM PBX extensions and tie line,
Fax G3/G4 Corporate multimedia, video conference X-rays Examples of
coding PCM MPEG2 ADPCM Transfer mode; Bearer network Circuit mode
Private ISDN, Private voice network BGS (ISDN, PSTN), VPN (ISDN,
PSTN), leased lines, Private cellular (DECT) Packet mode Private
X.25, PVC X.25, Private ISDN (X.25), Mobitex Frame mode Private
frame relay, Private PVC (FR), Private ISDN (FR) Cell mode Private
ATM, VLL, Private DQDB Examples of transmission access techniques
Baseband Modem PDH, SDH, TDMA, CDMA, HDSL, ADSL, FDM Medium Copper
pair Fibre (FTTO, FTTR, FTTC...) Radio (macrocell, microcell, pico
cell, radio P-P...) Satellite Coax Figure 1-1: Private, virtual
private and business access. The Core Network of the GSM R9.1 is an
evolved GSM R8 (and R9.0) core network. It supports both Circuit
Switched and Packet Switched services. Figure 1-2 shows Ericssons
GSM/WCDMA system for CN2.0/R9.1. The overall aim of CN2.0 is the
introduction of the new node and layered network architecture. The
physical split between circuit mode servers and MGWs is
implemented. Ericsson has developed Cello-ased MGW R2 as an
external MGW. R9.1 includes functions that, although not related to
the architecture split, are dependent upon its implementation. It
also includes features that could not be implemented in R9.0.
EN/LZT 123 6914/2 Rev R3A 1
12. GSM Network Planning - Transmission Overview/Planning
CN2.0/R9.1 is the first combined WCDMA Systems/GSM release that
will reach full GA for WCDMA. The release is based on 3GPP R99
June-01. It is permitted to combine GSM and WCDMA systems access
technologies within the same node. IP Backbone Cello MGw IP SDH
Network Cello MGwATM Backbone STM/TDM Based Transit Network PSTN
ISDN PLMN Internet, Intranet HLR AuC FNR BSC RNC MSC server SGSN G
SGSN W MSC server AXE MGw GMSC server AXE MGw GMSC server GGSNR IP
R IP R Note: Not all nodes shown and named . Figure 1-2: Ericssons
GSM/WCDMA System for CN2.0/R9.1 To create the architecture split
(layered network architecture), the software of the existing MSC is
upgraded to implement an internal split in MSC Server and AXE based
Media Gateway, which will continue to serve the GSM BSS (and part
of the WCDMA Systems traffic). This split also facilitates the
utilization of the MSC Server part for controlling the WCDMA
Systems traffic in the stand-alone Cello based MGW. When WCDMA
Systems traffic increases further, there will typically be a need
for additional call/session handling capacity. This can be achieved
by deploying the stand-alone MSC Servers (without AXE media gateway
function). MSC may have different configuration scenarios to
support both 2G and 3G networks. 2 EN/LZT 123 6914/2 Rev R3A
13. 1 GSM Introduction - Interfaces and Node Hierarchy MSC/VLR
GSMTDM (Cello) CC MSC/MGW UMTSTDM ATM GSM MSC/VLR GSMTDM MSC-Server
(Cello) MGW ATM UMTS TDM UMTS TDM UMTS ATM UMTS TDM/ATM
UMTS/GSM-TDM UMTS/GSM-ATM UMTS-TDM/GSM-ATM UMTS-ATM/GSM-TDM
UMTS/GSM-TDM/ATM UMTS/GSM-TDM UMTS-ATM/GSM-TDM UMTS TDM UMTS ATM
UMTS TDM/ATM GSM-TDM GSM only GSM and WCDMA WCDMA only MSC-Server
(Cello) MGW ATM UMTS TDM Figure 1-3: Different MSC Configuration
Scenarios NODES GMSC VLR GMSC VLR GG SNGG SN HLRHLR EIREIR AU CAU C
SMS- IW MSC SMS- IW MSC SMS- GMSC SMS- GMSC SGSNSGSN MSC VLR MSC
VLR ISDN PSTN PSPDN CSPD N PDN: -Intranet -Extranet -Internet BSC
RBSSIM SIM MS MS BSC RBSSIM SIM MS MS Core NetworkBSS DTI SOG BGW
FNR MIN Note: Not all nodes and interfaces are shown and named
Figure 1-4: Ericssons GSM Model EN/LZT 123 6914/2 Rev R3A 3
14. GSM Network Planning - Transmission Overview/Planning The
GSM/GPRS system contains the following components: Base Station
System (BSS) Radio Base Station (RBS) Base Station Controller (BSC)
Core Network (CN) Mobile services Switching Center (MSC) Gateway
MSC (GMSC) Visitor Location Register (VLR) Home Location Register
(HLR) Authentication Center (AUC) Equipment Identity Register (EIR)
Short Message Service - Gateway MSC (SMS-GMSC) Short Message
Service - InterWorking MSC (SMS- IWMSC) Serving GPRS Support Node
(SGSN ) Gateway GPRS Support Node (GGSN ) Data Transmission
Interworking unit (DTI) Flexible Number Register (FNR) Additional
items possibly connected - Mobile Intelligent Network (MIN) -
Billing Gateway (BGW) - Service Order Gateway (SOG) Base Station
System (BSS) The Base Station System (BSS) consists of the
functional units described in the following sections. Radio Base
Station (RBS) A Base Transceiver Station (BTS) is the GSM radio
equipment required to serve one cell. It contains the antenna
system, radio frequency power amplifiers, and digital signaling
equipment. The Ericsson product for the BTS is the Radio Base
Station (RBS). 4 EN/LZT 123 6914/2 Rev R3A
15. 1 GSM Introduction - Interfaces and Node Hierarchy The
system versions are: RBS 2000 for GSM 900, GSM 1800, and GSM 1900
RBS 200 for GSM 900 and GSM 1800 Base Station Controller (BSC) The
BSC controls and supervises a number of RBS and radio connections
in the system. It handles the administration of cell data, the
locating algorithm, and orders handovers. The node is based on
Ericsson Digital Switching System AXE 10 switch. Transcoder
Controller (TSC) The TRC performs speech coding and decoding
functions and rate adaptation for data calls. The TRC is not a
standard GSM network element and in Ericssons implementation it can
be a stand-alone node or it can be integrated. Core Network The
Core Network contains the functional units described in the
following sections. Mobile Services Switching Center (MSC) The MSC
is responsible for setting up, routing, and supervising calls to
and from the mobile subscriber (mobility management, handover, ).
Short messages, routed from the SMS-GMSC or sent from the Mobile
Station (MS), are relayed in the MSC. The MSC is implemented using
an AXE 10 switch or AXE 810 switch. AXE 810 is the name of the AXE
version that will be available to the market in CN2.0/R9.1. Gateway
MSC (GMSC) The GMSC is an MSC serving as an interface between the
mobile network and other networks, such as the Public Switched
Telephony Network (PSTN) and Integrated Services Digital Network
(ISDN) for mobile terminating calls. It contains an interrogation
function for retrieving location information from the subscribers
HLR. The GMSC contains functions for rerouting a call to the mobile
subscriber according to the location information provided by the
HLR. EN/LZT 123 6914/2 Rev R3A 5
16. GSM Network Planning - Transmission Overview/Planning The
GMSC is implemented using an AXE 10 switch or AXE 810 switch.
Visitor Location Register (VLR) The VLR temporarily stores
information about the MS currently visiting its service area. In an
Ericssons GSM network, the VLR is integrated with the MSC in the
same AXE 10 switch or AXE 810. Home Location Register (HLR) The HLR
database stores and manages all mobile subscriptions belonging to a
specific operator. The HLR stores permanent data about subscribers,
including the subscriber's supplementary services, location
information, and authentication parameters. When a person buys a
subscription, it is registered in the operators HLR. The HLR can be
implemented with the MSC/VLR or as a stand-alone database. The HLR
uses Mobile Application Part (MAP) signaling to the other nodes
(Except for PC-based AUC). Flexible Number Register (FNR) FNR was
introduced with Ericssons release to provide a flexible number
function which enables mobile operators to allocate subscriber
MSISDN freely without restricting it to the MSISDN series, held in
the HLR where the corresponding IMSI series are held. FNR is
modified to provide the function of number portability with GSM R7
in addition to flexible numbering. Number portability is a network
feature that allows the subscribers to retain their MSISDN when
they change their service provider within one country, based on the
agreement between different network operators. FNR is a database
which stores all the information needed to perform SCCP message
translation before rerouting an incoming call to the correct HLR.
The FNR has the same platform as HLR. It can be implemented as a
stand-alone node or can be co-located with the other As
(Application Module). 6 EN/LZT 123 6914/2 Rev R3A
17. 1 GSM Introduction - Interfaces and Node Hierarchy
Authentication Center (AUC) The AUC database is connected to the
HLR. The AUC provides the HLR with authentication parameters and
ciphering keys by generating triplets or quintuplets depending on
the GSM release. Using these triplets or quintuplets, ciphering of
speech, data, and signaling over the air-interface is performed.
Both provide system security. The AUC is available as a PC or
VAX-based system or as an integrated AUC. The PC-based version is
connected to the Input/Output Group 20 (IOG20) similar to an
operator terminal. The VAX-based version uses MAP signaling and is
connected via S7 signaling links. The integrated AUC is implemented
on an RPD or RPG within the AXE 10 or AXE 810 and can be co-
located with a MSC/VLR. A new and more powerful RPG (RPG3) was
built for AXE 810 switch. The RPG/RPG2 have more than four times
the processing capacity of their predecessor RPD, and RPG3 has more
than 12 times the processing capacity of the RPD. Equipment
Identity Register (EIR) The EIR database validates mobile
equipment. The MSC/VLR can request the EIR to check if an MS has
been stolen (black listed), not type-approved (gray listed), normal
registered (white listed), or unknown. The EIR is connected to the
VLR via the S7 network and uses MAP signaling. The EIR is
implemented as a UNIX operating system or as a VAX computer
platform. Data Transmission Interworking Unit (DTI2) The DTI2
provides the interface necessary for fax and circuit- switched data
communication. Short Message Service - Gateway MSC (SMS-GMSC) The
SMS-GMSC routes MS-terminated short messages. For signaling to GSM
entities, MAP signaling is used. For signaling to an Ericsson SC,
an Ericsson variant of MAP is used. Any MSC/GMSC can be implemented
as an SMS-GMSC. EN/LZT 123 6914/2 Rev R3A 7
18. GSM Network Planning - Transmission Overview/Planning Short
Message Service - InterWorking MSC (SMS-IWMSC) The SMS-IWMSC routes
MS-originated short messages to the SC for delivery. For signaling
to GSM entities, MAP signaling is used. For signaling to an
Ericsson SC, an Ericsson variant of MAP is used. Any MSC/GMSC can
be implemented as an SMS-IWMSC. Serving GPRS Support Node - SGSN
The Serving GPRS Support Node is a primary component in the GSM
network using GPRS. It forwards incoming and outgoing IP packets
addressed to/from an MS that is attached within the SGSN service
area. The SGSN handles packet routing and serves all GSM
subscribers that are physically located within the geographical
SGSN service area. The (packet-switched) traffic is routed from the
SGSN to the BSC, via the BTS to the user equipment. Gateway GPRS
Support Node GGSN The Gateway GPRS Support Node is the second new
node type, introduced to handle GPRS connections. The GGSN handles
the interface to the external IP packet networks and acts like a
router for the IP addresses of all GPRS subscribers in the network.
Additional Nodes Mobile Intelligent Network (Mobile IN) Mobile IN
is used in conjunction with the Public Land Mobile Network (PLMN).
It consists of service nodes that provide advanced services to
subscribers. Mobile IN functions include the Service Switching
Point (SSP) and the Service Control Point (SCP), or a combined
Service Switching and Control Point (SSCP). The mechanism to
support operator-specific services which are not covered by
standardized GSM services, even while the UE is roaming outside the
Home PLMN, is provided by the Customized Applications for Mobile
network Enhanced Logic (CAMEL). 8 EN/LZT 123 6914/2 Rev R3A
19. 1 GSM Introduction - Interfaces and Node Hierarchy The SSP
function determines whether the SCP function is required. The SCP
function provides the service. The SSP is typically located in an
MSC. The SCP function may be located in the SSP node or it may be a
stand-alone node. SSP-SCP communication occurs via the Ericsson
Intelligent Network Application Part (INAP) protocol CS 1+. INAP CS
1+ is compatible with the standard protocol INAP CS 1, but offers
additional functions. When the SSP and SCP are co-located, INAP
messages are carried on internal AXE software signals. When the
nodes are remote, INAP messages are carried on S7 links and use the
Transaction Capabilities Application Part (TCAP) function. An
example of an advanced service provided by Mobile IN is Virtual
Private Network (VPN). The VPN service gives the corporate customer
a private numbering plan within the PLMN network. The Mobile IN
functions are implemented on AXE 10 or AXE 810 platforms. Service
Center (SC) The SC receives, stores, and forwards a short message
between the message sender and the MS. Ericsson offers the SC as a
combined messaging system, for example, voice and fax on an MXE
platform. Billing GateWay (BGW) The BGW collects billing
information, Call Data Records (CDRs), in files from the network
elements and immediately forwards the information to
post-processing systems that use CDR files as input. The BGW acts
as a billing interface to all network elements in an Ericsson
network. The flexible interface of the BGW easily adapts to new
types of network elements. Service Order Gateway (SOG) The SOG
connects a Customer Administrative System (CAS) and a set of
Ericsson Network Elements (NEs) to allow the CAS to exchange
service data with the NEs. It provides a safe and reliable
connection for updating the GSM network database and EN/LZT 123
6914/2 Rev R3A 9
20. GSM Network Planning - Transmission Overview/Planning
eliminates the operators need to create his own interface to each
of the NEs. The SOG provides a remote interface to the HLR, the
AUC, and the EIR. This combines the subscription management
functionality of the HLR/AUC and the equipment management
functionality of the EIR. Mobile Station (MS) The MS allows the
subscriber to access the network through the radio interface. It is
not specified as a network node in Ericssons GSM network. The MS
consists of: Mobile Equipment (ME) The ME consists of radio
processing functions and an interface to the user and other
terminal equipment. Subscriber Identity Module (SIM) The SIM
contains information regarding the user subscription and can be
used with any MS. INTERFACES SGSN G MGW MSC Server Backbone Network
ATM SGSN W MSC/VLR Gr Gn/Gom BSC GbAbis Gs Gf BS RNC Iu Iub Gr
Gn/Gom Gf Backbone Network IP Other PLMN Gp GGSN Gi IP Network
GsGSM BSS WCDMA Systems RAN HLRHLR AUCAUC FNR FNR BTS EIREIR MGW Iu
MSC/VLR Other PLMN Fixed Network A Iu C C C H F to MSC Signaling
Signaling and Traffic E Iu WCDMA Systems RAN GMSC SGSN G MGW MSC
Server Backbone Network ATM SGSN W MSC/VLR Gr Gn/Gom BSCBSC GbAbis
Gs Gf BS RNC Iu Iub Gr Gn/Gom Gf Backbone Network IP Other PLMN Gp
GGSN Gi IP Network GsGSM BSS WCDMA Systems RAN HLRHLR AUCAUC FNR
FNR BTS EIREIR MGW Iu MSC/VLR Other PLMN Fixed Network A Iu C C C H
F to MSC Signaling Signaling and Traffic Signaling Signaling and
Traffic E Iu WCDMA Systems RAN GMSC Note: Not all nodes and
interfaces shown. Figure 1-5: Ericsson WCDMA/GSM Network Interfaces
10 EN/LZT 123 6914/2 Rev R3A
21. 1 GSM Introduction - Interfaces and Node Hierarchy Um
Interface The MS RBS (air-) interface uses GSM for the physical
layer. For more information refer to section Um interface later in
this chapter. Abis Interface The RBS - BSC interface is named Abis
interface, which carries both signaling and traffic. For more
information refer to section Um interface later in this chapter. A
Interface The A Interface is the interface between the GSM access
network and core network. GSM L1 GSM L1 Layer 1 Layer 1 LAPDm LAPDm
LAPD LAPD MTP MTP MTP TU P / IS UP SCCP SCCPSCCP BTSMBTSMRR BSSAP
RR BSSAP RR MM CM MAP TCAP RR MM CM Um Abis A MS C BS C BT S M S CM
Connection Management MM Mobility Management RR Radio Resource
Management CM,MM,RR = Radio Interface Layer 3 LAPDm Link Access
Procedures for Dm-channel GSM L1 Air interface layer 1 BTSM BTS
Management BSSAP Base Station System Application Part MAP Mobile
Application Part TCAP Transaction Capabilities Application Part
SCCP Signaling Connection Control Part ISUP ISDN User Part TUP
Telephony User Part MTP Message Transfer Part Figure 1-6: GSM MS
MSC Protocol EN/LZT 123 6914/2 Rev R3A 11
22. GSM Network Planning - Transmission Overview/Planning C
Interface The MSC Server HLR interface is a MAP interface used to
perform the interrogation needed to set up calls to a mobile
subscriber. To forward a short message to a mobile, the SMS gateway
MSC interrogates the HLR to obtain routing information. F Interface
The MSC - EIR interface is an optional MAP based interface for
checking user equipment. H Interface The HLR - AUC interface is for
retrieval of authentication parameters from the AUC. GSM L1 GSM L1
L1 bis L1 bis MAC MAC NS BSSGPBSSGPRLC LLCLLC GMM/SM Um Gb
SGSNBSSMS LLC Logical Link Control RLC Radio Link Control MAC
Medium Access Control BSSGP Base Station System GPRS Protocol GMM
GPRS Mobility Management SM Session Management NS Network Service
RLC NS GMM/SM Figure 1-7: GPRS MS SGSN Signaling 12 EN/LZT 123
6914/2 Rev R3A
23. 1 GSM Introduction - Interfaces and Node Hierarchy Gb
Interface The Gb interface between the SGSN and BSC (PCU) is used
for both user data and signaling. The user data part carries
end-user IP traffic encapsulated in LLC-PDU and transported over
the FR network between the CN and the AN. GSM L1 GSM L1 L1 bis L1
bis MAC MAC NS L1 IPBSSGPBSSGPRLC TCP / UDP LLCLLC SNDCP IP Um Gb
Gn GGSNSGSNBSSMS IP Internet Protocol SNDCP Sub-network Dependent
Convergence Protocol LLC Logical Link Control RLC Radio Link
Control MAC Medium Access Control BSSGP Base Station System GPRS
Protocol GTP GPRS Tunneling Protocol TCP Transmission Control
Protocol UDP User Datagram Protocol L1 Layer 1 L2 Layer 2 NS
Network Service RLC Application NS SNDCP L2 GTP L1 L2 GTP IP IP TCP
/ UDP Gi Figure 1-8: GPRS Transmission Protocol Architecture Gn
Interface The Gn interface is used for control signaling (for
mobility and session management) between the SGSN and GGSN, as well
as for tunneling of end-user data payload within the backbone
network. On the Gn interface the GTP protocol is used for control
signaling and for tunneling user plane data between SGSN and GGSN.
EN/LZT 123 6914/2 Rev R3A 13
24. GSM Network Planning - Transmission Overview/Planning Gi
Interface The Gi interface is used to transport end-user IP data
between the mobile network and external IP networks. It connects
the GGSN to other networks. The Gi interface is also used for GGSN
control signaling to SP servers located in IP networks such as the
ISPs network. This usage involves external servers for end-user
authentication and IP address allocation. Gp Interface The Gp
interface is used for control signaling when the GSNs are located
in different mobile networks. Gp provides a subset of Gn
functionality. Gr Interface The SGSN supports the standard Gr
interface to the HLR. MAP signaling is used over this interface in
order to support storage/retrieval of subscriber data. Gs Interface
The Gs interface is used towards the MSC server, with the BSSAP+
protocol. OPERATION AND MAINTENANCE CENTRE For centralized control
of a network, the installation of a Network Management Center
(NMC), with a subordinate Operation and Maintenance Centers (OMC)
is advantageous. NMC staff can concentrate on system-wide issues,
whereas local personnel at each OMC can concentrate on short-term,
regional issues. The OMC and NMC functionality can be combined in
the same physical installation, or implemented at different
locations. The BTSs are supported through the BSC. Other Ericsson
nodes including Message Center (MXE) can be supported. Core Network
Operation and Support System (CN-OSS) is Ericssons implementation
of OMC and/or NMC. CN-OSS management areas are based on the
Telecommunication Management Network (TMN). TMN is a 14 EN/LZT 123
6914/2 Rev R3A
25. 1 GSM Introduction - Interfaces and Node Hierarchy model
for telecommunication networks management. The most important parts
are: Operation and Support System NMC OMC OMC MIN MSC BSC BTS HLR
AUC / EIR Figure 1-9: Central Supervision of All Network Elements.
Configuration Management The Configuration Manager enables the
operator to fully configure a node in a fast and efficient manner,
enabling new nodes to be brought into service quickly, and existing
nodes to be updated in a similar manner. Fault Management Ericssons
Fault Management solution is designed to provide a completely
integrated alarm and event handling solution, which provides the
operator with element-level, sub-network as well as full network
and service management. CN-OSS provides core/network support for
all implementations of the FM solution. Performance Management The
Performance Management solution is designed to provide
comprehensive network performance management for all sub-network
domains as well as specific sub-network level performance data
analysis and reporting. CN-OSS offers the customer cost effective
support for centralized, regional and local operations, and
maintenance EN/LZT 123 6914/2 Rev R3A 15
26. GSM Network Planning - Transmission Overview/Planning
activities required by a cellular network. CN-OSS is the functional
entity that allows the network operator to monitor and control the
system. CN-OSS in Ericssons GSM system is based on the new CIF
(Common Integration Framework) platform. The Common Integration
Framework (CIF) from Ericsson is a unified platform that integrates
common functionality of O & M applications for existing and new
types of network elements. It provides operators with one solution
to manage both their existing 2nd generation mobile network and
their 3rd generation mobile network. CIF is a scalable platform
that best meets the needs of the customer, thus avoiding costly
over-dimensioning. Benefits The major CIF benefits are: CIF makes
it possible to run, upgrade and maintain the O&M environment as
one system. CIF is built on state of the art technology, thus
creating a secure foundation upon which the O & M system can
expand. CIF is a multi-technology platform consisting of commercial
IT components facilitating integration in the operators existing IT
environment. CIF provides a Configuration Service which stores a
model of the network where changes can be performed on a planned
configuration before applying to the network elements. CIF provides
common security solution which the applications can use. CIF
supports scalable O & M solutions for management of large
networks. CIF supports distribution of O & M functionality over
several servers. CIF maximizes return on investment by utilizing
extensions of existing HW, rather than replacement. 16 EN/LZT 123
6914/2 Rev R3A
27. 1 GSM Introduction - Interfaces and Node Hierarchy
Description CIF provides numerous services (e.g. Object Request
Broker, Web Server, Databases, Configuration Services, security)
essential to network management. The different O & M systems
exist as applications on top of CIF which acts as a bottom layer.
The applications can be cellular planning tools, network
consistency tools, alarm viewers, network topology viewers etc.
EN/LZT 123 6914/2 Rev R3A 17
28. GSM Network Planning - Transmission Overview/Planning AIR
INTERFACE (Um) The Um interface is the interface between the MS and
the BTS. Here, the communication is carried out using radio waves.
Cell Allocation (CA) is the subset of the total frequency band that
is available for one BTS. It can be viewed as the total transport
resource available for the traffic between the BTS and its attached
MSs. One carrier (pair of frequencies, one uplink and one downlink)
of the CA is used to carry synchronization information and the
Broadcast Control CHannel (BCCH). This carrier is known as the BCCH
carrier or the c0 carrier. High efficiency and quality requirements
have resulted in a rather complex way of utilizing the frequency
resource. This chapter describes the basic principles of how to use
this resource, from the physical resource itself to the information
transport service offered by the BTS. CARRIERS, TIME SLOTS, AND
TDMA FRAMES Table 1-1 shows the frequency bands allocated to each
system. GSM 900 GSM 1800 GSM 1900 Uplink 890 - 915 MHz 1710 - 1785
MHz 1850 - 1910 MHz Downlink 935 - 960 MHz 1805 - 1880 MHz 1930 -
1990 MHz Table 1-1: Frequency Bands Carrier separation is 200 kHz,
which provides: 124 carriers in the GSM 900 band 374 carriers in
the GSM 1800 band 299 carriers in the GSM 1900 band Using Time
Division Multiple Access (TDMA) each of these carriers are divided
into eight Times Slots (TS). A TS has a duration of 3/5200 seconds
(577 s). Eight TSs form a TDMA frame, with a duration of
approximately 4.62 ms. At the BTS, 18 EN/LZT 123 6914/2 Rev
R3A
29. 1 GSM Introduction - Interfaces and Node Hierarchy the TDMA
frames on all radio frequency channels in the downlink direction
are aligned. The same applies to the uplink. The start of a TDMA
frame on the uplink is, however, delayed by a fixed time
corresponding to three time slot periods. The reason for this delay
is to allow for the same TS number to be used in both uplink and
downlink directions without requiring the MS to receive and
transmit simultaneously. 9 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 0 1
2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 Downlink Uplink offset TDMA frame
No. TDMA frame No. MS to BTS transmission BTS to MS transmission
Figure 1-10: TDMA Offset. One TS on a TDMA frame is called a
physical channel, that is, on each duplex pair of carriers there
are eight physical channels. A variety of information is
transmitted between the BTS and the MS. The information is grouped
into different logical channels. Each logical channel is used for a
specific purpose such as paging, call set-up and speech. For
example, speech is sent on the logical channel Traffic CHannel
(TCH). The logical channels are mapped onto the physical channels.
EN/LZT 123 6914/2 Rev R3A 19
30. GSM Network Planning - Transmission Overview/Planning
LOGICAL CHANNELS This section examines how the logical channels are
used in the circuit switched communication between the MS and the
RBS. GPRS channels are not covered in this document. Logical
Channels Control Channels Traffic Channels BCH Broadcast CHannels
CCCH Common Control CHannels DCCH Dedicated Control CHannels Half
Rate Full Rate FCCH SCH BCCH PCH AGCH RACH SDCCH SACCH FACCH Figure
1-11: Logical Channels The logical channels can be divided into two
categories, namely traffic channels and signaling/control channels.
There are two forms of Traffic CHannels (TCH): Bm or full rate TCH
(TCH/F). This channel carries information at a gross rate of 22.8
kbit/s. Lm or half rate TCH (TCH/H). This channel carries
information at a gross rate of 11.4 kbit/s. Signaling channels are
subdivided into three categories: Broadcast CHannels, BCH Common
Control CHannels, CCCH Dedicated Control CHannels, DCCH The
following sections describe specific channels within these
categories. 20 EN/LZT 123 6914/2 Rev R3A
31. 1 GSM Introduction - Interfaces and Node Hierarchy
Broadcast Channels 1. Frequency Correction CHannel (FCCH) On the
FCCH, bursts containing only zeroes are transmitted. This serves
two purposes. Firstly, to ensure that this is the BCCH carrier,
and, secondly, to allow the MS to synchronize to the frequency. The
FCCH is only transmitted downlink on c0 Time Slot 0 (C0TS0). 2.
Synchronization CHannel (SCH) The MS must synchronize to the time
structure within this particular cell, and also needs to ensure
that the chosen BTS is a GSM base station. By listening to the SCH,
the MS receives information about the frame number in this cell and
about the BSIC (Base Station Identity Code) of the selected BTS.
The BSIC can only be decoded if the base station belongs to the GSM
network. The SCH is only transmitted downlink on c0TS0. 3.
Broadcast Control CHannel (BCCH) The MS must receive some general
information concerning the cell to perform these functions: start
roaming, wait for calls to arrive, or make calls. The required
information is broadcast on the Broadcast Control CHannel (BCCH)
and includes the Location Area Identity (LAI), maximum output power
allowed in the cell, and the BCCH carriers for neighboring cells,
on which the MS performs measurements. The BCCH is only transmitted
downlink on c0TS0. Using FCCH, SCH, and BCCH, the MS tunes to a BTS
and synchronizes with the frame structure in that cell. The BTSs
are not synchronized to each other. Therefore, every time the MS
decides to camp on another cell, it must listen to the FCCH, SCH
and BCCH in the new cell. Common Control Channels (CCCH) 1. Paging
CHannel (PCH) At certain time intervals, the MS listens to the PCH
to check if the network wants to get in contact with the MS. The
network may want to contact the MS because of an incoming call or
an incoming short message. The information on the PCH is a paging
message, including the MSs identity number (IMSI) or a temporary
number (TMSI). The PCH is transmitted downlink on c0TS0 (possibly,
also on other physical channels on c0). EN/LZT 123 6914/2 Rev R3A
21
32. GSM Network Planning - Transmission Overview/Planning 2.
Random Access CHannel (RACH) The MS listens to the PCH to know when
it is paged. When the MS is paged, it replies by requesting a
signaling channel on the RACH. The RACH can also be used if the MS
wants to contact the network, for example, when setting up a call.
The RACH is transmitted uplink on c0TS0 (possibly, also on other
physical channels on c0). 3. Access Grant CHannel (AGCH) The
network assigns a signaling channel (the Stand alone Dedicated
Control CHannel, SDCCH) to the MS. This assignment is performed on
the AGCH. The AGCH is transmitted downlink on c0TS0 (possibly, also
on other physical channels on c0). Dedicated Control Channels
(DCCH) 1. Stand alone Dedicated Control CHannel (SDCCH) The MS (as
well as, the BTS) switches over to the assigned SDCCH. The call
set-up procedure is performed on the SDCCH, as is the textual
message transmission (short message and cell broadcast) in idle
mode. The SDCCH is transmitted both uplink and downlink. The
default in the Ericsson implementation is C0TS2 (possibly, also on
any other physical channel) When call set-up is performed, the MS
is told to switch to a TCH. 2. Slow Associated Control CHannel
(SACCH) The SACCH is associated with the SDCCH or TCH (that is,
sent on the same physical channel). On the uplink, the MS sends
averaged measurements on its own BTS (signal strength and quality)
and neighboring BTSs (signal strength). On the downlink, the MS
receives information concerning the transmitting power to use and
also instructions on the timing advance. The SACCH is transmitted
both uplink and downlink. 3. Fast Associated Control CHannel
(FACCH) If a handover is required, the FACCH is used. The FACCH
works in stealing mode, which means that one 20 ms segment of
speech is exchanged for signaling information necessary for the
handover. Under normal conditions the subscriber 22 EN/LZT 123
6914/2 Rev R3A
33. 1 GSM Introduction - Interfaces and Node Hierarchy does not
notice the speech interruption because the speech coder repeats the
previous speech block. CHANNEL COMBINATIONS Only certain
combinations of logical channels are permitted according to the GSM
recommendations. Figure 1-12 below shows the way in which logical
channels can be combined onto Basic Physical Channels (BPC). The
numbers appearing in parenthesis after the channel designations
indicate sub-channel numbers. A sub-channel is formed by a specific
subset of BPCs within a multiframe structure. (i) TCH/F + FACCH/F +
SACCH/TF (ii) TCH/H(0.1) + FACCH/H(0.1) + SACCH/TH(0.1) (iii)
TCH/H(0) + FACCH/H(0) + SACCH/TH(0) + TCH/H(1) (iv) FCCH + SCH +
BCCH + CCCH (v) FCCH + SCH + BCCH + CCCH + SDCCH/4(0...3) +
SACCH/C4(0...3) (vi) BCCH + CCCH (vii) SDCCH/8(0...7) +
SACCH/C8(0...7) Where CCCH = PCH + AGCH + RACH Figure 1-12:
Permitted Channel Combinations (DL). GPRS- Specific Channels Are
Not Listed. SACCH/T indicates that the SACCH is associated with a
TCH whereas SACCH/C is associated with a control channel. If the
SMSCB is supported, the CBCH replaces the SDCCH sub-channel 2 in
cases (v) and (vii) above. A combined CCCH/SDCCH allocation (case
v) above can only be used when no other CCCH channel is allocated.
The difference between channel combinations (ii) and (iii) is that
combination (ii) addresses two different MSs, whereas combination
(iii) addresses one single MS using both half rate traffic
channels, for example, one for speech and the other for data.
EN/LZT 123 6914/2 Rev R3A 23
34. GSM Network Planning - Transmission Overview/Planning Abis
INTERFACE The interface between the BSC and RBS is called Abis. The
BSC and the RBS are connected via E1 links. Radio network planning
provides information that is vital for planning the Abis part of
the network, such as the number of E1 links required. When planning
the radio network the cell planners consider, for example, the
number of subscribers, subscriber behavior, grade of service (GoS),
costs, possible sites for the RBSs, radio wave propagation,
interference. The output will be the Channel Loading Plan (CLP):
number of sites, site types (including number of TRUs/TRXs per
site), and, possibly, also a map showing the location of the sites.
Each TRX/TRU can handle a maximum of eight TCHs on the Um
interface. Normally, the TRX/TRU for the c0 carrier handles six
TCHs, plus two physical channels for signaling. The other TRXs/TRUs
handles eight TCHs as long as no further physical channel is needed
for signaling. MSC/VLR BSC RBS MS A interface Air interface A-bis
Interface A-ter Interface TRC Figure 1-13: CS interfaces in a GSM
network On the Abis interface, resources are allocated for each
TRX/TRU. Normally, one TS (on the E1) is reserved for signaling
(LAPD signaling) and two TSs (on the E1) are reserved for traffic
(each TS carries four traffic channels). This means that three TSs
on Abis are required for each TRX/TRU. 24 EN/LZT 123 6914/2 Rev
R3A
35. 1 GSM Introduction - Interfaces and Node Hierarchy BSC S =
Signaling T = Full rate traffic S T S T T T T T TRX 1 S T S T T T T
T T T T T T T T T TRX 2 T T T T T T T T 0 1 2 3 4 5 6 . 31 Synch S
T T T T T T T T TRX 1 S T T T T T T T T TRX 2 c0 Figure 1-14: Um
Abis relation. In the cell given in Figure 1-14, there are two
carriers, that is, two TRXs. On the Um interface, TRX1 handles the
c0 carrier (up- and downlink) with two physical channels for
signaling and six for full rate traffic, and TRX2 handles eight
full rate traffic channels. On the Abis interface three E1 TSs (64
kbit/s) are required for each TRX one for signaling and two for
traffic. One E1 TS carries four full rate traffic channels (13
kbit/s for each traffic channel plus three kbit/s for inband
signaling). =E1 frame synchronization S1 S2 S1 S2 T1 T1 T1 T1 T1 T1
T2 T2 T2 T2 T2 T2 T2 T2 .... S1 T1 T1 T1 T1 T1 T1 T1 .... S4 S3 T1
T1 T1 T1 T2 T2 T2 T2 T2 T2 T2 T2T1 T1 T1 T1 T1 T1 T1 T1 T3 T3 T3 T3
T3 T3 T3 T3 T4 T4 T4 T4 T4 T4 T4 T4 S2 S1 S3 S4 .... LAPD-M LAPD-C
Figure 1-15: Um Abis , if the optional features LAPD- multiplexing
and LAPD-concentration are used. The numbers refer to a specific
TRX. EN/LZT 123 6914/2 Rev R3A 25
36. GSM Network Planning - Transmission Overview/Planning LAPD
concentration offers a more efficient usage of the signaling
transmission between Base Transceiver Station (BTS) and Base
Station Controller (BSC). The improved utilization of the signaling
transmission is achieved by sharing the same 64 kbit/s time slot
for several Transceivers with low signal transmission. By
concentrating up to four LAPD signaling links upon one 64 kbit/s
A-bis PCM timeslot, the required signaling transmission capacity
can be reduced by approximately 25%. One TRX requires 2.25 TS in
the PCM link. The LAPD concentration is most efficient for RBS
sites with three TRXs or more per cell. LAPD concentration can be
used when RBS 200 and RBS 2000 are cascaded in the same
transmission link. This feature can not be used simultaneously with
LAPD multiplexing. LAPD multiplexing offers another example of
efficient usage of the signaling transmission between Base
Transceiver Station (BTS) and Base Station Controller (BSC). This
is especially useful for small sites (typically two TRXs or less).
The improved utilization of the signaling transmission is achieved
by multiplexing of A-bis LAPD signaling links and traffic links on
the same 64 kbit/s link. One TRX requires two TSs on the PCM link.
Sub rate switching on RBS site is required and it is only supported
in RBS 2000. This feature can normally not be used together with
LAPD concentration in the same DXU. See the next section. 26 EN/LZT
123 6914/2 Rev R3A
37. 1 GSM Introduction - Interfaces and Node Hierarchy A-ter
INTERFACE AND REMOTE BSC R7 introduced the A-ter interface between
a distributed BSC and the TRC (Transcoder Controller) which allow
the migration from a coverage solution to a high capacity solution
in a cost efficient way. The introduction of a limited number of
remote BSCs can be justified by savings in transmission cost due to
the dynamic utilization of transmission resources on the interface
between the remote BSCs and the Transcoders. The market- unique
Ericsson feature, Dynamic Allocation of Transcoder Resources, makes
it possible for up to 16 BSCs to share the same transcoders in the
TRC (Transcoder Controller) node integrated with the central BSC.
However, remote BSCs should be introduced at a limited number of
strategically chosen locations when the transmission savings on the
link from the remote BSC to the central BSC/TRC justifies the
investment cost, the increased O&M costs and spare part costs
associated with the remote BSC node. DXC Hub Node AA A Ring, Tree,
etc. MSC BSC/TRC BSC DXC Hub Node AA A Ring, Tree, etc. MSC BSC/TRC
BSC Figure 1-16: Remote BSC EN/LZT 123 6914/2 Rev R3A 27
38. GSM Network Planning - Transmission Overview/Planning
RBS2000 X-Bus PSUs Mains Supply DC System Supply Timing Bus Power
Communication Loop External alarm OMT interface Test A-bis
interface Local Bus Antenna System Interface Antenna System
Interface RF-Path RF-Path CDU-Bus Antenna System Interface Antenna
System Interface RF-Path RF-Path CDU-Bus Antenna System Interface
Antenna System Interface RF-Path RF-Path CDU-Bus TRU TRU TRU TRU
TRU ECU CDU CDU CDU Mobile Station Test Point (MSTP) Mobile Station
Test Point (MSTP) Mobile Station Test Point (MSTP) Mobile Station
Test Point (MSTP) Mobile Station Test Point (MSTP) Mobile Station
Test Point (MSTP) DXUDXU TRU X-Bus PSUs Mains Supply DC System
Supply Timing Bus Power Communication Loop External alarm OMT
interface Test A-bis interface Local Bus Antenna System Interface
Antenna System Interface RF-Path RF-Path CDU-Bus Antenna System
Interface Antenna System Interface RF-Path RF-Path CDU-Bus Antenna
System Interface Antenna System Interface RF-Path RF-Path CDU-Bus
TRU TRU TRU TRU TRU ECU CDU CDU CDU Mobile Station Test Point
(MSTP) Mobile Station Test Point (MSTP) Mobile Station Test Point
(MSTP) Mobile Station Test Point (MSTP) Mobile Station Test Point
(MSTP) Mobile Station Test Point (MSTP) DXUDXU TRU DXUDXU TRU
Figure 1-17: Radio Base Station 2000 (RBS2000) There are two
different RBS families: RBS 200 RBS 2000 The following overview
relates to RBS 2000. The major functional units are (refer to
Figure 1-17): The Distribution Switch Unit (DXU) provides an
interface to the link towards the BSC. It is in charge of the link
resources and connects the traffic between the BSC and the TRUs.
The TRU includes all functionality needed for handling one radio
carrier. Transceiver Unit (TRU) provides functionality for
transmitting, receiving and signal processing for the TS handling
on the radio interface. 28 EN/LZT 123 6914/2 Rev R3A
39. 1 GSM Introduction - Interfaces and Node Hierarchy The
Combining and Distribution Unit (CDU) is the interface between the
TRUs and the antenna system. The Energy Control Unit (ECU) controls
both power and climate (heating/cooling). MULTIDROP BSC RBS A B RBS
A B RBS A B RBS A B RBS A B RBS A B RBS A B Figure 1-18: Multidrop
In RBS 2000, the feature of cascading several RBSs is called
multi-drop. The functionality is implemented in the TRI
(Transmission Radio Interface) for RBS 200, and in the DXU for RBS
2000. The functionality enables the E1 to be passed on to the next
site. The total number of TSs, required for the RBSs, must not
exceed 31. The signaling to control the multi-drop facility in the
DXU is sent together with LAPD signaling. Protection switching
which forwards the incoming signal to the outgoing signal protects
the chain in case one RBS goes down. EN/LZT 123 6914/2 Rev R3A
29
40. GSM Network Planning - Transmission Overview/Planning
DIGITAL CROSS CONNECT A DXC helps to organize the traffic, thereby
reducing the need for transmission capacity. It facilitates the
design of optimized network topologies. The network flexibility,
introduced by a DXC and the variety of DXC interfaces, facilitates
the smooth growth of the network. The following features can be
accomplished using a DXC: Add-drop / Daisy chain. Traffic can be
dropped and added within the capacity limit in the site. Grooming /
Consolidation Traffic from various sites can be allocated in the
same E1 frame, thus reducing the number of E1s required. Protection
with ring configurations. Rerouting of traffic, in case of link
failure, is required. This type of ring configuration may not be
supported by all DXCs types. Voice compression (Adaptive
Differential PCM, ADPCM). Used for conversion of analog
transmission into digital transmission, and also for compression of
the signal. Not all DXC types support ADPCM. 30 EN/LZT 123 6914/2
Rev R3A
41. 1 GSM Introduction - Interfaces and Node Hierarchy NODE
HIERARCHY BSC A HLR TGMSC TGMSC HLR TGMSC TGMSC MSC MSC MSC MSC MSC
MSC PLMN, PSTN, ISDN, ... E TGMSC/TG MSC/VLR BTS BTS BSC/TRC A AREA
A AREA B HLR TGMSC TGMSC HLR TGMSC TGMSC MSC MSC MSC MSC MSC MSC
PLMN, PSTN, ISDN, ... E HLR TGMSC TGMSC HLR TGMSC TGMSC MSC MSC MSC
MSC MSC MSC PLMN, PSTN, ISDN, ... E TGMSC/TG MSC/VLR BTS BTS
BSC/TRC A AREA A AREA B BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS
BTS BTS BTS DXCBSC A A A Backbone (Core) (Trunk) NW Access NW BSC A
HLR TGMSC TGMSC HLR TGMSC TGMSC MSC MSC MSC MSC MSC MSC PLMN, PSTN,
ISDN, ... E HLR TGMSC TGMSC HLR TGMSC TGMSC MSC MSC MSC MSC MSC MSC
PLMN, PSTN, ISDN, ... E TGMSC/TG MSC/VLR BTS BTS BSC/TRC A AREA A
AREA B HLR TGMSC TGMSC HLR TGMSC TGMSC MSC MSC MSC MSC MSC MSC
PLMN, PSTN, ISDN, ... E HLR TGMSC TGMSC HLR TGMSC TGMSC MSC MSC MSC
MSC MSC MSC PLMN, PSTN, ISDN, ... E TGMSC/TG MSC/VLR BTS BTS
BSC/TRC A AREA A AREA B BTS BTS BTS BTS BTS BTS BTS DXCBSC A A A
Backbone (Core) (Trunk) NW Access NW BTS BTS BSC/TRC A AREA A AREA
B BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS DXCBSC A
A A Backbone (Core) (Trunk) NW Access NW Figure 1-19: National /
Regional PLMN Architecture GSM networks are built in a hierarchical
manner with independent regional areas with access networks, each
one controlled by an MSC. In small PLMNs the MSCs are connected in
a meshed network. However, as PLMN grow large the backbone network
is divided into a transit layer and a regional MSC layer. In order
to simplify routing and traffic prediction, a ring topology can be
implemented in the transit layer. It is also recommended that all
incoming and outgoing traffic be in the transit layer. This enables
the operator to choose the most cost-effective solution in terms of
far-end drop or near- end drop. Each regional MSC should be
connected to at least two transit layer nodes. This is called dual
homing and it enables them to have full protection or to have load
sharing. The most common option is something in between. EN/LZT 123
6914/2 Rev R3A 31
42. GSM Network Planning - Transmission Overview/Planning In
the access network the RBSs are linked to the BSC directly or via
chains or hubsites where DXC equipment can be used. Every BSC that
is going to support packet switched traffic must be equipped with a
packet control unit (PCU) that is connected to an SGSN via the Gb
interface. With small or large BSCs there are a number of factors
to be considered: Capacity factor, i.e. when will their capacity
run out? Where should small BSCs be located in the network? O&M
factor, i.e. does it cost more to have many small- capacity SCs
compared to having a few large ones? Network robustness, i.e. would
the network be more robust with many more BSCs rather than a few
large ones? Transmission efficiency, i.e. is it more efficient to
have concentrated large BSCs rather than many smaller ones? Spare
parts handling, the practical issues with holding spare parts in
different places and the management of spare parts. Other costs,
such as the cost of new sites against co- location. Placing many
small BSCs in the network would entail more site costs, especially
if they are to be spread out geographically. Co-location must be
considered. Would the network topology of one, which consists of a
few large BSCs or one, that has many small BSCs be more flexible
for expansion? 32 EN/LZT 123 6914/2 Rev R3A
43. Media Chapter 2 This chapter is designed to provide the
student with an introduction to the types of transmission media and
their basic properties. OBJECTIVES: Upon completion of this
chapter, the student will be able to: List two common types of
copper wiring and list its features in terms of bandwidth and
length List frequency and bridging distance of a typical radio link
List the requirements on a geostationary satellite, and one
disadvantages and one advantage that it has Make a comparison with
low orbiting satellites and state one disadvantage and one
advantage that they have List two wavelengths used in optical fiber
communication systems List two reasons for attenuation and
dispersion respectively in an optical fiber List two light sources
and two light detectors used in optical fiber communication
systems
45. 2 Media 2 Media Table of Contents Topic Page METAL CABLE
...................................................................................33
OPEN WIRE
.................................................................................................................33
PAIRED
CABLE............................................................................................................33
COAXIAL CABLE
.........................................................................................................34
RADIO WAVES
...................................................................................36
RADIO LINK
.................................................................................................................36
SATELLITE...................................................................................................................38
OPTICAL
FIBER..................................................................................41
TYPES OF OPTICAL
FIBER........................................................................................44
OPTICAL TRANSMITTERS AND
RECEIVERS...........................................................46
WAVELENGTH DIVISION MULTIPLEXING (WDM)
...........................48 RECENT ADVANCES IN OPTICAL
COMMUNICATIONS..................50 EN/LZT 123 6914/2 Rev R3A i
47. 2 Media METAL CABLE OPEN WIRE In the early days of
telegraph lines, the only transmission medium was the open wires in
the form of non-isolated copper or iron wires. The first
application example of open wires was the 60 km
Washington-Baltimore telegraph line set up in 1845. Open wires were
generally used in Frequency Division Multiplex (FDM) systems in the
1940s. They are still in use in some rural areas, but for only 3.1
kHz bandwidth voice communications. Figure 2-1: Open wire metal
cables The advantages of using open wire cables are: Very low
attenuation for voice frequencies Very simple and cheap Easy
installation in rural areas The main disadvantage of this type of
transmission media is that it is vulnerable to electromagnetic
disturbances and mechanical damage. Figure 2-1 shows a well-known
rural open wire application. PAIRED CABLE Twisted pair, an example
of paired cable, is probably the most commonly used transmission
media. An example from our daily life is the cable connecting our
telephone to the wall socket. These types of cables are mainly used
in access networks, between the subscribers and the exchange, and
rarely in trunk EN/LZT 123 6914/2 Rev R3A 33
48. GSM Network Planning - Transmission Overview / Planning
networks between the exchanges. Figure 2-2 shows a typical paired
cable structure. Paired cable can be found as 2, 5, 10, 100 and 500
etc. pairs in a plastic or paper cover and is generally buried
underground. The conducting material is normally copper with a
diameter of 0.4 to 0.8 mm diameter. The wires inside the cable are
twisted together to form pairs with two conductors, or quads with
four conductors. Figure 2-2: Paired cable There are two types of
paired cable according to its shielding structure. If the cable
core is covered with a metal sheath (lead or aluminium) inside the
plastic cover structure, it is protected against mechanical
external damage, electrical and electromagnetic interference.
Sometimes metal sheath is armoured with steel wires to increase its
mechanical strength. For aerial applications, paired cables are
reinforced with a steel core. Electrical characteristics, for
example attenuation, of paired cables strictly depend on their
conductor diameter size, conductor material and the frequency used.
Although they were originally developed for analog communications,
they can also be used for digital communications with a maximum
capacity of 100 kbps. The main disadvantage for this type is the
cross talk between the conductors. COAXIAL CABLE Some well-known
applications of coaxial cables are cable-TV networks, local data
networks and radio antenna feeders. They are preferred for both
analog FDM and digital TDM (Time Division Multiplexing) systems
with a capacity up to 200 Mbps. Figure 2-3 shows a schematic of a
coaxial cable and detailed cross-section. The cable consists of an
inner conductor surrounded by a tube-shaped outer conductor. The
best insulator 34 EN/LZT 123 6914/2 Rev R3A
49. 2 Media between these conductors is air. However sometimes
plastic materials are also used for the same purpose. Typical
coaxial cable dimensions for telephony applications are 2.6/9.5 mm
or 1.2/4.4 mm for inner/outer radius. The outer conductor also
provides a shielding for surrounding effects such as
electromagnetic interference. There are some coaxial cables with a
multi-wire inner conductor, twisted multi-wire and plastic
insulator between them. These types are very useful for
applications requiring flexible cabling. Outer shield Insulator
Conductor Figure 2-3: Coaxial cable schematic and cross-section
details Previously coaxial cables were used mainly in trunk
networks but today they are replaced by optical fibers and their
main application area has shifted towards the access network. One
important feature of coaxial cable is that the main electrical
characteristics are completely governed by conductor diameters.
Roughly speaking, the attenuation is inversely proportional to the
conductor diameter. EN/LZT 123 6914/2 Rev R3A 35
50. GSM Network Planning - Transmission Overview / Planning
RADIO WAVES Radio as a transmission medium has great a many
applications in telecommunications. It can be used, in local or
intercontinental networks, for fixed or mobile communications
between network nodes or between users and network nodes. The most
well known applications are cordless, GSM and satellite mobile
phones, radio and TV broadcasting, radar, etc. The radio spectrum
shown in Figure 2-4 extends from 3 kHz to 300 GHz is a part of the
electromagnetic spectrum, in the same way as infrared, visible,
X-ray etc. spectrums. Very low frequency Low frequency Medium
frequency High frequency Very high frequency Ultra-high frequency
Super high frequency Extremely high frequency 3 k 30 k 300 k 3 M 30
M 300 M 3 G 30 G 300 G [Hz] f VLF LF MF HF VHF UHF SHF EHF Very low
frequency Low frequency Medium frequency High frequency Very high
frequency Ultra-high frequency Super high frequency Extremely high
frequency 3 k 30 k 300 k 3 M 30 M 300 M 3 G 30 G 300 G [Hz] f VLF
LF MF HF VHF UHF SHF EHF Figure 2-4: Radio spectrum The main
feature of radio waves is that their propagation is strictly
frequency-dependant. Radio waves having frequency below 30 MHz are
reflected by certain layers of the atmosphere and the ground.
Because of this, frequencies below 30 MHz are generally used in
maritime radio, telegraphy and telex applications with a small
information capacity. Certain parts of VHF and UHF bands are used
for TV broadcasting, FM radio, mobile telephony, etc. Frequencies
greater than 3 GHz suffer attenuation caused by the objects in
their way, such as buildings. For this reason they require free
line of sight to establish good communication between the
transmitter and the receiver (e.g. radio links using the 2-40 GHz
part of the spectrum and satellite communication systems using the
2-14 GHz frequency band). The information carried by these systems
range from a few Mbps to several hundreds Mbps. In this chapter, we
will give some details about radio link and satellite applications.
RADIO LINK The radio links can be used for both analog and digital
communications systems. The physical distance between the
transmitter and the receiver is known as the hop length and is 36
EN/LZT 123 6914/2 Rev R3A
51. 2 Media strictly dependant on which frequency, climate,
output power, antenna size, antenna type and what quality
objectives the hop is designed for. The information can also be
transferred through several hops with active or passive nodes at
both ends. In passive systems, the signal is neither regenerated
nor amplified. Instead, it is received by the receiver antenna and
directed to the transmitted antenna. The only thing changed in a
passive station is the direction of the signal - in order to solve
line of sight problems. A typical point-to-point radio link system
is shown in Figure 2- 5. Figure 2-5: Point-to-point radio link The
main advantages of radio link systems can be summarized as: Fast
installation No fixed infrastructure requirement Easy access over
difficult areas (compared to other techniques such as fiber) Need
for only a few landowner permits Point-to-multi point systems are
generally used in high-speed internet-intranet, LAN-LAN
interconnection, TV broadcast, IP services, leased lines, etc. In
other words, they are very useful and cost effective in providing
communications to scattered populations compared to wire line or
point-to-point systems. A typical point-to-multipoint radio system
is shown in Figure 2-6. EN/LZT 123 6914/2 Rev R3A 37
52. GSM Network Planning - Transmission Overview / Planning
Figure 2-6: Point-to-multipoint radio system The main problems with
radio links can be summarized as: Attenuation due to rain
Refraction from atmosphere Reflection from ground and obstacles
such as buildings SATELLITE Satellite communications had first been
mooted with the prophetic article of Arthur C. Clarke
Extra-Terrestrial Relays in 1945. In this article, Clark proposed
three geostationary satellites to provide world coverage. After
various experiments in USSR and US, the following historical
developments took place: 1958 - Christmas greeting from SCORE
satellite 1960 - First reflector satellite, ECHO 1960 - First
satellite recorded message 1962 - First active communications
satellites, TELSTAR and RELAY 1963 - First geostationary satellite,
SYNCOM 1965 - First commercial geostationary satellite, INTELSAT 1
1965 - First Russian communications satellite, MOLNYA A satellite
network in its simplest form consists of two earth stations
communicating with each other via a satellite as shown in Figure
2-7. 38 EN/LZT 123 6914/2 Rev R3A
53. 2 Media Figure 2-7: A typical satellite communication
system There are several satellite services, which are classified
as: Fixed satellite services Earth stations - Satellite(s) - Earth
station Mobile satellite services Mobile earth stations
Broadcasting satellite service TV and radio Earth exploration
satellite service For example, meteorological Space research
service Scientific and technical research The frequency range for
satellite communications lies between L band (0.4-0.46 GHz) and Q
band (33-50 GHz), but does not cover the whole range. The most
commonly used frequencies are 6/4, 14/11 and 30/20 GHz for
uplink/downlink. Satellites are placed at previously defined orbits
in the space. A satellite remains in that orbit as long as its
centrifugal force is in balance with the gravitational attraction
of the earth and other cosmic influences. There are four distinct
altitude ranges used for telecommunication satellites. These orbits
are: Low Earth orbit (LEO) between 500 and 2000 km, approximately
14 ms signal delay Medium Earth orbit (MEO) between 5000 and 15000
km (also called intermediate circular orbit, (ICO)), approximately
100 ms signal delay EN/LZT 123 6914/2 Rev R3A 39
54. GSM Network Planning - Transmission Overview / Planning
Geostationary Earth orbit (GEO) at 35786 km (also called Clark
orbit), approximately 240 ms signal delay Highly elliptical orbit
(HEO) beyond GEO The main problems with satellite communications
are: Attenuation due to atmosphere and ionosphere, Attenuation due
to precipitation and clouds, Losses due to antenna depointing,
Delay. 40 EN/LZT 123 6914/2 Rev R3A
55. 2 Media OPTICAL FIBER Optical fibers have been extensively
used in communications systems due to their unique features, such
as: Low attenuation High capacity Small volume Low weight
Insensitive to electromagnetic interference No cross-talk After the
proposal of Gao and Hockham in 1966, the first low loss fiber
(