Abstract
Mobile communication systems were initially designed to carry voice traffic with limited support for packet and messaging services. The constant increase in demand for packet traffic evolved the mobile networks to ultimately become data pipes with support for mobility. While the mobile applications changed dramatically over time, the fundamental principles for mobile service delivery remain the same to a large extend in every network generation. These principles are important to form the investigative context and identify the sources of network evidence with the highest probative value. This chapter details the mobile service delivery fundamentals together with the key features implemented in each mobile network generation. In practice, the sources of mobile network evidence belong to network segments from different generations; therefore, the fundamentals are necessary to establish an effective forensics plan and maximize the investigative outcome.
TopThe Evolution Of Mobile Network Systems
Mobile networks have so far evolved through four generations of networking technologies with the fifth one envisioned for commercial rollout from 2020 onwards. Wireless telephony systems from the first generation needed to support mobility and large user capacity with a limited frequency bandwidth. To overcome this problem, the network service area was organized into smaller logical units called cells (the network coverage map resembles the organization of biological cells). This concept, introduced in the 1970s by Bell Laboratories, was used to develop and deploy the 1G cellular networks1 based on different radio transmission and mobility management technologies, with no support for international roaming. Examples of 1G systems are AMPS in the United States, NMT in Scandinavia, and TACS in the UK.
The widespread adoption of the 1G networks was limited by the unreliability of the analogue wireless interface, modest mobility management, and lack of security and roaming support. The second generation of mobile systems or 2G addressed these issues with a digital network implementation supporting encryption in the radio interface, extended user capacity, new mobility management techniques and support for global roaming. Examples of 2G systems are Global System for Mobile (GSM) in Europe, IS-95 Code Division Multiple Access (CDMA) and IS-136 Time Division Multiple Access (TDMA) in the United States. GSM is by far the most widely deployed of these systems and became the global de-facto standard for 2G mobile network infrastructures.
Both the 1G and 2G systems were design to support voice services, with 2G systems providing limited support for instant messaging and packet data access. In response to the demand for packet data access as a result of the World Wide Web (WWW) proliferation, GSM networks were enhanced to 2.5G and 2.75G with the General Packet Radio Service (GPRS) and Enhanced Data rates for GSM Evolution (EDGE), respectively. Compared to the 76.8 Kb/s rates of GSM, GPRS provided theoretical maximum bitrate of 160 Kb/s and EDGE of 473.6 Kb/s. These speeds were insufficient to provide an acceptable browsing experience or use of multimedia applications that were already supported in the wired broadband networks. The demand for higher data rates on a global level impelled the International Telecommunication Union (ITU) to start working on a third generation or 3G with harmonized specifications for mobile communications for global interoperability (Ghosh et al., 2010). The data requirements for the 3G systems (known as IMT 2000) were 2 Mb/s for fixed or in-building environments, 384 Kb/s for pedestrian or in urban environments, and 144 Kb/s for wide area or vehicular environments. In addition, 3G systems were required to provide better Quality-of-Service (QoS) for conversational (voice services), streaming (video, multimedia), interactive (web browsing), and background (telemetry, emails) classes of services.
Key Terms in this Chapter
WWW: Worldwide web.
A/D: Analog to digital conversion.
SAE: System architectural evolution.
FDMA: Frequency division multiple access.
eMBB: Enhanced mobile broad band.
UTRAN: UMTS RAN.
TD-SCDMA: Time division synchronous CDMA.
1G: 1 st generation of mobile networks.
SOA: Self-organizing networks.
5G: 5 th generation of mobile networks. Still in standardization phase, the first 5G deployments are envisioned for 2020.
ISI: Inter symbol interference.
RF: Radio frequency.
FDD: Frequency division duplex.
IoT: Internet-of-things.
MBMS: Multimedia broadcast multicast services.
EPC: Evolved packet core.
UE: User equipment.
E-UTRAN: Evolved UTRAN.
4G: 4 th generation of mobile networks. The 4G technologies are long term evolution (LTE) and the advanced version, LTE-advanced. Colloquially, the terms LTE/LTE-A are used as a synonym for 4G as they are the only global standard for mobile communication from the fourth generation.
RN: Relay nodes.
EV-DO: Evolution data only.
EDGE: Enhanced data rates for global evolution.
URLLC: Ultra reliable and low latency communication.
IMT Advanced: International mobile telecommunications advanced (ITU’s name for the family of 4G standards).
eICIC: Enhanced inter-cell interference coordination.
UMTS: Universal mobile telephone system.
HSDPA: High speed downlink packet access.
U-NII: Unlicensed national information infrastructure spectrum in the 5 GHz frequency segment.
SC-FDMA: Single carrier FDMA.
2G: 2 nd generation of mobile networks. The most dominant technology is the global system for mobility (GSM).
RAN: Radio access network.
IMT-2020: International mobile telecommunications 2000 (ITU’s name for the family of 5G standards).
S/P-GW: Serving/packet gateway.
SECAM: Security assurance methodology.
E-UTRA: Evolved-universal terrestrial radio access.
CoMP: Coordinated multi-point operation.
OFDMA: Orthogonal FDMA.
CA: Carrier aggregation.
HSPA+: HSPA advanced.
NMT: Nordic mobile telephony.
TIA: Telecommunication Industry Association.
USIM: Universal SIM.
MIMO: Multiple in multiple out.
TDMA: Time division multiple access.
SDMN: Software-defined mobile network.
3GPP: 3 rd generation partnership project.
HSPA: High speed packet access.
QAM: Quadrature amplitude modulation.
3G: 3 rd generation of mobile networks. The most dominant technology is universal mobile telecommunication system (UMTS).
MME: Mobility management entity.
ITU: International Telecommunication Union.
HARQ: Hybrid ARQ.
W-CDMA: Widespread CDMA.
UL: Uplink.
HSS: Home subscriber server.
ARQ: Automatic repeat request.
DL: Downlink.
CDMA: Code division multiple access.
BPSK: Binary phase shift keying.
IMT-2000: International mobile telecommunications 2000 (ITU’s name for the family of 3G standards).
GSM: Global system for mobile.
MS: Mobile station.
GPRS: General packet radio service.
UWB: Ultra-wide band.
D/A: Digital to analog conversion.
IEEE: Institute of Electrical and Electronics Engineers.
OSI: Open system for interconnection.
MTC: Machine type communications (MTC).
TACS: Total access communication system.
GERAN: GPRS/EDGE RAN.
HSUPA: High uplink packet access.
IMS: Internet multimedia subsystem.