2. Communication Paradigms & Mobile Telecommunications Infrastructures Flashcards
2 major paradigms for data transmission in communication
CIRCUIT-SWITCHED=communication line is used exclusively for communication parties (network resources used even if no data transferred; duration of connection used for billing)
— PACKET-ORIENTED=communication is divided into several packets, which get addressed & transferred using a shared transmission medium (network only used when data is transmitted; amount of transferred data used for billing)
Cellular Network
radio network consisting of several transmitters/base stations which cover a certain area (=cell)
Advantages of CBC
++higher capacity (e.g. by multiplexing*): more users can use infrastructure
++reduced transmission power: reduced power consumption for mobile devices
++robustness: failure of one base station doesn’t affect complete infrastructure
++better coverage: better availability of infrastructure
Disadvantages of CBC
- -required infrastructure to link base stations is complex & costly
- -handover needed when changing from one cell to another (complex)
- -careful frequency planning to minimize interference (LTE 800 & LTE 700 = digital dividends)
Multiplexing
describes how several users can share medium (e.g. mobile network) with minimum or no interference
1st mobile radio network in Germany: “A-Network”/1G
Manual switching by an operator & for a call to a mobile; Operator needed to know the location area of the callee
2nd mobile radio network in Germany: “B-Network”/2G
Automatic dial switching by area code, but caller needed to know that code of callee –> GSM = mobile communication standard for fully digital mobile networks (made cross-border mobile communication possible)
3rd mobile radio network in Germany: “C-Network”/3G
First cell based mobile radio system in Germany;
Change of cells happens automatically by distance measuring to the nearest base station;
Network can automatically detect place of the call partner by use of HLR; telephone number ≠ allocated to the terminal but to a magnetic stripe card & later a chip card
- -> UMTS = Global Uniform Standard - Successor of GSM for mobile multimedia incl. video & audio transmissions
- -> HSPA/HSPA+ = High Speed Packet Access/Evolved HSPA
LTE (Long Term Evolution)/4G
first all-IP mobile network technology -> higher data rates, capacity, etc.
5G
fifth generation of cellular network technology – high bandwidth, low latency, high number of devices connected, …. –> use cases: autonomous driving, virtual reality
– View 1: hyper-connected vision – View 2: next-generation radio access technology
Definition: GSM
(Global System for Mobile Communications) = mobile communication standard for fully digital mobile networks (worldwide roaming among different mobile network operators became possible)
Services of GSM
- Carrier services: Services to transfer signals over GSM network (focus on voice services)
- Telecommunication services: Supports mobile communication among users
- Supplementary services: Specific to network operators -> e.g. caller ID, call redirect, closed user groups, Teleconference
Architecture of GSM (3 main parts)
Network & Switching System (NSS), Operation Subsystem (OSS), Radio Subsystem (RSS) —> Process: PSTN - GMSC - HLR - VLR - MSC - BSC - BTS
Network & Switching System (NSS)
COMPONENTS:
Mobile Switching Center (MSC): Switching Center for initiation, termination & handover –
Home Location Register (HLR): Central Data Base with subscribers’ data (mobile number, location) –
Visitor Location Register (VLR): Data Base assigned to every MSC with data of active subscribers in MSC’s range
Operation Subsystem (OSS)
COMPONENTS:
Operation & Maintenance Center (OMC): supervises each network component & creates status reports –
Authentication Center (AuC):protects identity of participants –
Equipment Identity Register (EIR): data list with identification list for devices
Radio Subsystem (RSS)
COMPONENTS:
Mobile Station (MB): System of mobile terminal (device) & SIM –
Base Transceiver Station (BTS): Radio facility for signal transfer –
Base Station Controller (BSC): Administrates affiliated BTS & supervises e.g. frequency allocation & connection handover between cells
GSM Security Services
ACCESS CONTROL & AUTHENTICATION: authentication of the subscriber to the SIM by input of a PIN & to the GSM network by challenge-response procedure (idea: nobody should make use of your phone or your SIM card without password) –
CONFIDENTIALITY: data & voice transferred between mobile station & BTS = encrypted, but no end-to-end encryption –
PARTIAL ANONYMITY: no transfer of data which can identify the subscriber via radio, instead temporary identification; temporary mobile subscriber ID, TMSI; only the operator, but none of your neighbors should identify your mobile phone due to the data sent
Security in GSM (2G): SIM based Subscriber Authentication
Key K(i) & Algorithm A3 are stored on SIM and deposited in the AuC.
- AuC creates random number
- AuC ecyrypts rand and K(i) via A3 (SRes*)
- AuC transfers rand & SRes* to VLR
- VLR transfers exclusively rand to SIM
- SIM computers with “own” K(i) and A3 response SRes
- SRes computed by SIM is transmitted to VLR & compares with SRes*
- If SRes* = SRes the subscriber is authenticated successfully
Security in GSM (2G): Encryption
- AuC creates random number
- AuC generates K(c) for encryption of transferred data via rand, K(i) & A8
- VLR transfers only rand to SIM
- SIM computed K(c) using A8, the rand received & local K(i)
- Mobile station & mobile radio network use generated K(c) and A5 for encryption & decryption of sent and received data
GSM (2G) Security Model: Shortcomings
Network doesn’t authenticate itself (only authentication of terminal/subscriber): assumption that network is trustworthy per se
- Subscriber localization is almost exclusively controlled by network: centralized movement tracking is possible
- Model bases partly on secret encryption algorithms (A3 & A8 published without authentication)
- No encryption from terminal to terminal but only over air interface (deactivation by network possible, without notification of users)
- Encryption comparatively “weak” because of key length
Definition: UMTS
(Universal Mobile Telecommunication System) = Problem with 2G: different standards in different continents which avoid worldwide roaming -> demand for 3G: globally uniform standard -> Common approach: worldwide reservation of frequencies in 2GHz range
UMTS Architecture
- UMTS Terrestrial Radio Access Network (UTRAN)
- Radio Network Subsystem (RNS) (=RSS)
- Radio Network Controller (RNC): controls the Node Bs (=MSC)
- Node B: UMTS base stations (equivalent to BTS in GSM): not so different as in GSM
- UMTS Core network: corresponds to Network- &Switching Subsystems (NSS) in GSM
UMTS Security Model
- UMTS complements the security mechanisms known by GSM:
- -> enhanced participant authentication (EMSI)
- -> network authentication
- -> integrity protection of data traffic
- -> transferred security keys are also encrypted in the fixed network (e.g. HLR-VLR)
- -> increased key length
- -> end-to-end encryption = possible
LTE
Long Term Evolution -> LTE Advanced (4G) makes use of frequency spectrum more efficiently, resulting in higher data rates (towards 1Gbit/s) & lower latency
5G
Two views of 5G: 1. Hyper-connected vision (everything will be connected) - 2. Next-generation radio access technology (download/upload faster)
Potential Use Cases: autonomous driving, wireless-cloudbased office, machine-2-machine connectivity, AR
Roaming
Denotes a change of network access.
• Change of GSM network operator
• Change between different network systems (UMTS, GSM, WLAN, …)
• Cell change within GSM system (handover): GSM manages handover with a short connection interruption -> reason: update of VLR
