Mobile Communication Networks: Technologies and Protocols

Posted on May 29, 2025 in Computer Engineering

Mobile Communication Challenges and Solutions

Basic Challenges of Mobile Communications and Solution Areas:

Challenges:

1. Mobility: Mobile devices constantly change location, requiring seamless handovers between cell towers or base stations.
2. Interference: Multiple devices sharing the same frequency spectrum can lead to signal interference.
3. Attenuation and Fading: Radio channels can suffer from signal attenuation due to distance and obstacles, leading to signal fading.
4. Bandwidth Limitations: Radio frequency spectrum is limited, demanding efficient bandwidth allocation to meet data demand.

Solutions:

1. Handover: Seamless handover techniques allow devices to switch between cells without disrupting communication.
2. Interference Control: Multiple access methods (e.g., TDMA, FDMA, CDMA) manage interference for concurrent communication.
3. Modulation and Coding: Techniques improve data recovery in challenging radio conditions.

Properties of Radio Channels:

1. Bandwidth: Radio channels have limited bandwidth, affecting data transfer rates.
2. Interference: Interference occurs when multiple signals overlap in the same frequency spectrum.
3. Attenuation: Signals weaken as they propagate through space, especially over long distances or in obstructed environments.
4. Fading: Signal strength can fluctuate during transmission due to multipath propagation and mobility.
5. Noise: Unwanted signals (noise) can degrade communication quality, measured by signal-to-noise ratio (SNR).

Error Correction in Radio Channels

How can the transmission errors of the radio channel be corrected (FEC, ACK, interleaving)?

1. FEC (Forward Error Correction): FEC involves adding redundant information to transmitted data to detect and correct errors at the receiver.
2. ACK (Acknowledgment): ACK relies on the receiver sending acknowledgments to the sender, indicating successful data reception. If no ACK is received, the sender retransmits the data.
3. Interleaving: Interleaving rearranges data before transmission, making it more resilient to burst errors by spreading them out in time.

Mobile Network Structure and Frequency Reuse

Sketch the basic structure of mobile networks. Describe the principle of frequency reuse:

Mobile networks consist of Base stations, Mobile devices, Core networks, Handover and location management.

Principle of Frequency Reuse:

Frequency reuse divides the geographic area into cells. Each cell uses a set of frequency channels. Reuse the same frequencies in cells far apart to minimize interference.

Why Mobile Networks Use Radio Cells:

Radio cells are used due to signal propagation limitations, interference control, capacity management, and support for mobility. They provide efficient and reliable coverage.

OSI Model: First Four Layers

Describe the main functionalities of the first four layers of the OSI layered model.

Here’s a concise description of the main functionalities of the first four layers of the OSI model:

1. Physical Layer (Layer 1): Manages the physical transmission of data through the communication medium, such as cables and wireless signals. Eg: ETHERNET PHY
2. Data Link Layer (Layer 2): Provides error detection and correction, flow control, and logical communication between devices on a shared medium. Eg: ETHERNET
3. Network Layer (Layer 3): Routes data between devices on different networks, uses logical addresses, and establishes logical connections. Eg: IP
4. Transport Layer (Layer 4): Segments and reassembles data, offers error detection, flow control, and establishes end-to-end connections for reliable communication. Eg: TCP and UDP

These layers handle aspects like physical transmission, routing, error detection and correction, and reliable communication in a network.

Circuit Switched vs. Packet Switched Communications

Describe the basic properties of circuit switched and packet switched communications.

Circuit-Switched Communications:

• Establishes a dedicated connection.
• Fixed bandwidth during the call.
• High quality for real-time communication.
• Inefficient for data.
• Examples: Traditional phone networks.

Packet-Switched Communications:

• Data in packets.
• Shared network resources.
• Efficient for data transfer.
• Versatile for various applications.
• Examples: Internet networks.

Digital Transmission Fundamentals

Digital transmission: binary data, basic element, frames, parts of a frame.

Digital Transmission involves sending binary data (0s and 1s) over a communication channel. It is the foundation of digital communication systems.

Basic Element:

The fundamental unit in digital transmission is a “bit,” representing either a 0 or a 1.

Frames:

In digital transmission, data is typically organized into frames. A frame is a structured unit of data that includes not only the binary data but also control information for synchronization and error checking.

Parts of a Frame:

1. Header: Contains control information like source/destination addresses and frame synchronization bits.
2. Data: Carries the actual binary data to be transmitted.
3. Trailer: Often includes an error-checking code (e.g., CRC) to detect transmission errors.

Frames provide a structured and organized way to transmit data, ensuring that it can be correctly interpreted by the receiver.

Real-Time vs. Non-Real-Time Services

What are real time/quasi real time and non-real time services?

• Real-time services: The information is transmitted when it is created (voice call).
• Quasi-real-time services: Live streaming services (latency can be seconds).
• Non-real-time services: Latency is not a concern.
  • Seconds: browsing
  • Tens of seconds: file transfer, email – data loss is not permitted

Communication Network Hierarchy

Describe a typical communication network hierarchy (access, aggregation, core).

The communication network hierarchy consists of three layers that work together to provide end-to-end connectivity and transport of data across the network.

• Access network: Is the segment that reaches subscribers, also known as the last mile. It provides connectivity between end-user devices and the network. There are multiple types such as DSL, ADSL, WiMAX. An example could be residential areas or office buildings.
• Aggregation network: Provides connectivity to the core network. Typically uses IP, GigaBitEthernet or optical. Example could be district or towns.
• Core network: Provides high-speed connectivity between different aggregation networks. Typically uses MPLS, IP or optical technologies. Example could be regional or country-wide networks.

Geographic Scale of Communication Networks

What is the geographic scale of comm. networks (PAN, LAN, MAN, WAN)?

Communication networks are categorized by their geographic scale:

• PAN (Personal Area Network): Smallest, covering about 10 meters, often for an individual. Uses USB, FireWire, Bluetooth, or infrared connections.
• LAN (Local Area Network): Encompasses limited areas like homes, schools, or offices. Wired LANs use Ethernet, while wireless LANs use standards like 802.11 (a, ac, ad, b, g, n, ac, ax).
• MAN (Metropolitan Area Network): Spans a city or large campus.
• WAN (Wide Area Network): Largest, covering cities, countries, or continents. Utilizes various media such as telephone lines, cables, and airwaves.

Internet Protocol Addressing and Routing

Describe the Internet Protocol’s addressing and routing!

The Internet Protocol (IP) is responsible for addressing and routing data packets across the internet. IP addresses are unique identifiers assigned to each device connected to the internet. Private addresses are used inside a private network and are not routable to the outside network. In contrast, public addresses are globally visible and accessible. IP packets are routed across the internet using routers, which look at the destination address of the packet and use a routing table to determine the output network interface.

Internet Protocol Packet Format and IP Tunneling

What is the Internet Protocol’s packet format? What is IP tunneling?

The Internet Protocol (IP) packet format consists of a header and a payload. The header contains several fields, including the version, header length, type of service, total length, identification… The payload contains the data being transmitted. IP tunneling is a technique used to encapsulate one IP packet within another IP packet. The outer packet is used to transport the inner packet across an intermediate network. This technique is used to create virtual private networks (VPNs) and to provide secure communication between two networks.

ICMP (Internet Control Message Protocol)

Describe the ICMP (with an example)!

ICMP stands for Internet Control Message Protocol. It is a protocol that operates at the IP layer and is used for sending control messages in the payload of IP packets. These messages are used for signaling errors, discovering routes and paths, and checking the availability of a device. One example of ICMP is the “ping” command. When you ping a device, your computer sends an ICMP “echo” message to the device. If the device is available and responds, it sends an ICMP “echo reply” message back to your computer.

IPv4 vs. IPv6: Key Differences

What are the main differences between IPv4 and IPv6?

• Address Space: IPv4 uses 32-bit addresses, which limits the number of unique addresses to about 4.3 billion. IPv6 uses 128-bit addresses, which allows for a virtually unlimited number of unique addresses.
• Address Format: IPv4 addresses are written in decimal notation, while IPv6 addresses are written in hexadecimal notation.
• Header Size: IPv4 headers are 20 bytes long, while IPv6 headers are 40 bytes long.
• Header Fields: IPv6 headers have fewer fields than IPv4 headers, and some fields have been combined or eliminated.
• Fragmentation: IPv4 routers can fragment packets, while IPv6 routers cannot. Fragmentation is done by the source node in IPv6.
• Autoconfiguration: IPv6 supports stateless address autoconfiguration, which allows devices to automatically configure their own addresses without the need for a DHCP server.
• Security: IPv6 includes built-in support for IPsec, which provides encryption and authentication for IP packets.
• Quality of Service: IPv6 includes support for Quality of Service (QoS), which allows packets to be prioritized based on their type or content.
• Multicast: IPv6 includes native support for multicast, which allows a single packet to be sent to multiple devices at once.
• Backward Compatibility: IPv6 is not backward compatible with IPv4, which means that devices that only support IPv4 cannot communicate directly with devices that only support IPv6. However, there are transition mechanisms that allow IPv4 and IPv6 networks to interoperate.

IPv6 Addressing, Packet Format, and Protocol Features

Summarize IPv6 addressing, packet format and protocol features!

IPv6 addresses are written in hexadecimal notation and are divided into eight 16-bit blocks separated by colons. IPv6 packet format includes a 40-byte header and a payload that contains the data being transmitted. The header contains several fields, including the version, traffic class, flow label, payload length, next header, hop limit, source address, and destination address. IPv6 protocol features include faster forwarding and routing, IPSec security, mobility, larger address space, end-to-end connectivity, and simplified header. IPv6 forwarding and routing are faster because the information contained in the first part of the header is adequate for a router to take routing decisions.

TCP (Transmission Control Protocol)

Describe the TCP transport protocol!

TCP (Transmission Control Protocol) is a connection-oriented transport protocol that is used to send large files or data over the internet. TCP defines a bytestream of data that is transmitted between two devices. It is designed to provide reliable and in-sequence delivery of data over an unreliable IP network. TCP uses an acknowledgement/retransmission mechanism to ensure that all data is received correctly and in the correct order. It also includes a flow control mechanism that regulates the amount of data that can be sent at any given time. This mechanism prevents the sender from overwhelming the receiver with too much data.

UDP (User Datagram Protocol)

Describe the UDP transport protocol!

UDP (User Datagram Protocol) is a connectionless and stateless transport protocol that is used to transmit small, time-sensitive data packets over the internet. Unlike TCP, UDP does not provide reliable and in-sequence delivery of data. Instead, it uses a simple transmission model with a minimum of protocol mechanisms. UDP packets are sent without establishing a connection between the sender and receiver, which makes it faster than TCP.

DNS (Domain Name System)

What is the DNS Domain Name System?

DNS stands for Domain Name System. It is a system used to handle the name-to-IP address relations in a network. In other words, it is a hierarchical, distributed directory of names around the world that maps domain names (such as www.example.com) to IP addresses (such as 192.0.2.1). DNS is used to translate human-readable domain names into machine-readable IP addresses that are used to deliver data over the network. DNS is managed by authorities who oversee the name servers for the domains. The DNS concept is based on domains of names, with more domains in domains, and the root name servers at the top of the hierarchy.

Cloud RAN (C-RAN)

What is Cloud RAN? What are the benefits? Examples of functional splits.

Cloud RAN (C-RAN) is an evolved base station architecture where remote radio heads (RRH) connect to a centralized pool of baseband units (BBU) via high-bandwidth, low-latency networks. It applies data center networking principles to provide cost-efficiency, reliability, low latency, and high bandwidth within the BBU pool. It utilizes open platforms and real-time virtualization, enabling dynamic resource allocation and supporting multi-vendor, multi-technology environments.

Benefits of Cloud RAN:

• Cost-Efficiency: Reduces hardware and site costs by centralizing baseband processing.
• Reliability: Offers high reliability due to centralized control and maintenance.
• Low Latency: Provides lower latency through efficient network connectivity.
• High Bandwidth: Facilitates high-bandwidth interconnectivity within the BBU pool.

Training Sequence and Timing Advance

What is a training sequence? What does timing advance means?

TRAINING SEQUENCE:

• One of 8 standard sequences
• Enables bit-level synchronization of the receiver
• A known sequence (the receiver knows it) → It enables the estimation of the effect of the channel. Hence the data bits can be detected correctly
• Tail bits (3-3): no information, this is needed to let the electronic circuits set their operation point, when turning on/off at the beginning/end of the burst
• Simultaneous transmission/reception is not possible, it would cause big problems
• Not full duplex at radio level
• Therefore there are 3 timeslots difference between reception and transmission
• Although full duplex at service level (voice call is full duplex, both party can talk at the same time)
• Half-duplex at low, radio operation level
• Guard interval
• Due to the different distances of mobiles from the base station, the propagation delay of bursts is also different
• Guard interval prevents bursts of different users to collide when arriving to base station.

TIMING ADVANCE:

• Mobile synchronizes itself to the BTSs signal in downlink
• According to the received frames at the MS, let’s suppose it would have to start transmission at the beginning of a timeslot, at e.g. T0
• However, in downlink, the BS has this info at T0+d/c, where d is its distance, c is speed of light
• It starts transmitting, but on uplink it again has a delay, hence arrives to the bus station at T0+2d/c
• The burst may overlap with that of the user transmitting in the next slot
• Hence the system measures the delay of the burst’s arrival
• Orders the mobile to start the transmission earlier
• Theoretically the mobile should start earlier by 2d/c, compared to when it thinks it should start

GSM Network Subsystems and Functional Entities

What are the subsystems of the GSM network? What kind of functional entities are known?

GSM network consists of four subsystems: Mobile Station (MS), Base Station Subsystem (BSS), Network Switching Subsystem (NSS), Operation SubSystem (OSS).

Three main functional entities: Base Transceiver Station (BTS), Base Station Controller (BSC), TransCoder (TC).

• BTS main functions are channel coding and decoding (error detection), intervaling and de-intervaling, encryption and decryption of voice streams, radio processing and measurement of channel quality.
• BSC main functions are configure and control the radio channel for all base stations and cells under its control and connection point towards NSS.

GSM Radio Basics

Summarize GSM radio basics (medium access, frame structure, bursts)!

GSM radio interface uses TDMA/FDMA/FDD for medium access. FDMA is used to divide the frequency band into 200 kHz wide channels. TDMA is used to divide each channel into 8 timeslots per frame. Each connection is assigned a timeslot in both directions. The GSM frame structure consists of 8 timeslots, and each timeslot is 577 µs long. The transmission of data in GSM is done through bursts, which are short time intervals of transmission. The length of a burst is 15/26 of a timeslot, which is approximately 0.577 ms.

TDMA/FDMA, FDD, PDH, and SDH

What is the difference between TDMA/FDMA and FDD? What is PDH and SDH?

FDMA (Frequency Division Multiple Access):

• Concept: Users’ channels are separated in the frequency domain.
• Implementation: Each user is assigned a unique frequency band for communication.
• Example (e.g., GSM): Allocates a 200 kHz wide band around a carrier frequency for each user.

TDMA (Time Division Multiple Access):

• Concept: Users have different timeslots for communication, and their channels are separated in the time domain.
• Implementation: Time is divided into frames, each containing multiple timeslots. Each user is assigned a specific timeslot for transmission.
• Example (e.g., GSM): Uses a frame structure based on 8 timeslots per frame. A connection has a timeslot in both uplink and downlink directions.

FDD (Frequency Division Duplex):

• Concept: Uplink and downlink communications occur in two separate frequency bands simultaneously.
• Implementation: Allocates distinct frequency bands for uplink and downlink transmissions.
• Example (e.g., GSM): Utilizes separate frequency bands for uplink and downlink communications.

PDH (Plesiochronous Digital Hierarchy):

• Type: Time Division Multiplexing (TDM) network.
• Characteristic: Operates on microwave, copper, or optical fiber.
• Bitrate: High bitrate, providing robust networking for telephony operators.
• Representation of Voice Calls: Voice calls are represented by sending a byte in a timeslot over the link.
• Timeslot Allocation: Timeslots are periodically allocated for a given connection, end-to-end, for the entire duration of the call.
• Signalling: Signalling is found in PDH networks.

SDH (Synchronous Digital Hierarchy):

• Type: Synchronous TDM network.
• Characteristic: Provides a more standardized and synchronized approach compared to PDH.
• Bitrate: High bitrate, ensuring better synchronization across the network.
• Voice Calls Representation: Similar to PDH, voice calls are represented by sending data in predefined timeslots.
• Advantages: Overcomes synchronization issues present in PDH networks.

In summary, TDMA, FDMA, and FDD represent different access methods in wireless communication, utilizing frequency and time to separate users. On the other hand, PDH and SDH are both TDM networks, with SDH providing a more synchronized and standardized approach, overcoming synchronization challenges present in PDH networks.

Handover and Location Management in GSM

What is a handover? Summarize location management in GSM networks, including LAC.

Handover, or handoff, in mobile telecommunications is when a device switches its connection from one cell to another without interruption. In GSM networks, location management involves Location Areas (LAs), each with a unique Location Area Code (LAC) to identify specific areas. Tracking Areas (TAs) are smaller units within LAs, managing a device’s location. Location Updates notify the network of device movements, while Paging locates devices for incoming calls/messages. Handovers ensure communication continuity when devices move between cells within the same or different LAs.

GSM System Databases and Their Roles

What kind of databases can be found in the GSM system and what are the roles of these?

In the GSM system, databases include:

1. Home Location Register (HLR): Stores permanent subscriber information, aiding call routing and service verification.
2. Visitor Location Register (VLR): Temporarily stores subscriber data, including location information.
3. Authentication Center (AuC): Manages authentication keys and verifies SIM card identities.
4. Equipment Identity Register (EIR): Stores data on mobile devices, especially for tracking stolen or malfunctioning devices.
5. Short Message Service Center (SMSC): Handles storage and forwarding of SMS messages, with some variability in implementation.

High Speed Circuit Switched Data (HSCSD)

Briefly describe High Speed Circuit Switched Data (HSCSD)!

High Speed Circuit Switched Data (HSCSD) is the subsequent advancement in GSM technology aimed at achieving higher data transmission rates. Its primary goal is to boost bitrates within the existing GSM network infrastructure by allocating up to a maximum of four timeslots simultaneously to a single data connection. This allocation results in a potential maximum bitrate of 57.6 kbps, comparable to dial-in modems used in fixed phone networks at that time. Advantages of HSCSD include its implementation feasibility within the existing GSM network without requiring new infrastructure. However, to fully utilize HSCSD, new mobile terminals compatible with this technology are necessary. One notable disadvantage is that HSCSD remains circuit switched, meaning the connection stays active throughout the session and is billed based on time duration, irrespective of actual data transmission occurring.

GPRS System: New Nodes and Their Roles

What are the new nodes (compared to GSM) in GPRS system?

In the GPRS system, compared to GSM, the new nodes and their roles are:

• PCU (Packet Control Unit):
  • Acts as an interface between the GPRS core network and the BSS.
  • Transforms data into PCU frames for transmission, similar to voice frames in GSM (TRAU frames).
  • Manages radio resources for packet-switched services:
    • Allocates timeslots and logical channels.
    • Schedules user data transmission.
    • Sets up radio links for GPRS connections.
  • Handles mobility management for GPRS services, including paging and handover.
• SGSN (Serving GPRS Support Node):
  • Routes and forwards packets between PCUs, other SGSNs, and GGSNs.
  • Manages mobility by tracking mobile positions based on routing areas and cells.
  • Collects charging records for packet data traffic.
  • Assists in establishing IP-level sessions between mobile devices and GGSNs.
  • Provides security encryption and optional data compression.
• GGSN (Gateway GPRS Support Node):
  • Collects charging records for communications with external networks (e.g., the internet).
  • Serves as a gateway to the internet and other mobile networks.
  • Assigns IP addresses to mobile devices.
  • Acts as the anchor of mobility in the GPRS network, routing traffic for active sessions.
  • Converts IP addresses if necessary and manages the PDP context (Packet Data Protocol), containing allocated IP addresses, IMSI (International Mobile Subscriber Identity), and other traffic descriptors.

UMTS Network Architecture and Features

Describe the architecture and main features of UMTS network (UTRAN + Core Network).

UMTS Network Architecture:

• UTRAN (UMTS Terrestrial Radio Access Network): Comprises RNSs (Radio Network Systems), consisting of an RNC (Radio Network Controller) and Node Bs. RNCs connect through the Iur interface, while the RNC-NodeB interface is called Iub. RNCs connect to the Core Network via the Iu interface.
• Core Network: Inherits elements from GSM/GPRS networks, involving MSCs, GMSCs (CS domain), SGSNs, GGSNs (for packet data), and supporting databases like VLR, HLR, AuC, and EIR.

Roles of New Devices in UTRAN:

• Node B: Acts similarly to GSM’s BTS but with new hardware, managing physical layer signal processing, translating radio signals to wired signals, and vice versa. Handles modulation, synchronization, coding, scrambling, encryption, and transmit power control.
• RNC (Radio Network Controller): Comparable to GSM’s BSC, controls multiple NodeBs, manages user data transfer, radio resource management (RRM), mobility management, and supports soft handovers.
• RRM: Handles power allocation, code allocation, timeslot scheduling, logical/transport, and physical channels.
• Mobility Management: Controls handovers, admission, scheduling paging messages, and enables soft handovers where the user maintains connections with multiple base stations.
• Macro Diversity: In soft handover scenarios, data streams arrive at the RNC from multiple cells. The RNC combines these streams to minimize data loss.
• Broadcasting System Information: Disseminates crucial network information.

CDMA (Code Division Multiple Access)

Describe the main concept of CDMA. Show the basic principle of CDMA using an example.

CDMA (Code Division Multiple Access):

• Main Concept: CDMA enables multiple users to share the same frequency simultaneously by assigning each user a unique spreading code. The use of orthogonal codes ensures minimal interference.
• Basic Principle:
  1. Each user is assigned a unique spreading code.
  2. Users transmit simultaneously on the same frequency.
  3. Orthogonal codes enable accurate separation of users’ signals at the receiver.
• Example: Users A, B, and C have codes 101010, 110011, and 001100, respectively. Orthogonal codes minimize interference, allowing simultaneous transmission and accurate signal separation at the receiver.
• Code Orthogonality: Orthogonal codes have a dot product of zero, minimizing interference and enabling efficient use of the frequency spectrum in CDMA.

UMTS Radio Interface Properties and Channel Distinguishing

Describe main properties of UMTS radio interface. How are channels of users distinguished?

Main Properties of UMTS Radio Interface:

1. Technology: UMTS uses Wideband Code Division Multiple Access (W-CDMA) technology.
2. Multiple Access: Employs Code Division Multiple Access (CDMA) for simultaneous user communication.
3. Frequency Bands: Operates in various bands around 2 GHz.
4. Duplexing: Supports Time Division Duplex (TDD) or Frequency Division Duplex (FDD).
5. Variable Data Rates: Adapts to different service requirements.

Channel Distinguishing:

1. Spreading Codes (W-H Codes): Assigns unique Walsh-Hadamard codes to users.
2. Scrambling Codes: Adds a security layer and helps mitigate interference.

Physical Gross Bitrates: Gross Bitrate=Chip Rate * Number of Channels

Typical Implemented Bitrates:

• Downlink: HSDPA (up to 14 Mbps), HSPA+ (up to 42 Mbps).
• Uplink: HSUPA (up to 5.76 Mbps), HSPA+ enhances uplink speeds.

HSDPA and HSUPA Features and Solutions

Describe the features and solutions of HSDPA and HSUPA.

HSDPA (High-Speed Downlink Packet Access):

Features:

1. Increased Downlink Data Rates: Enhances downlink data rates.
2. Adaptive Modulation and Coding: Optimizes transmission based on channel conditions.
3. Fast Packet Scheduling: Prioritizes and allocates resources dynamically.
4. Reduced Latency: Improves responsiveness for applications like video streaming.
5. Shared Channel: Introduces HS-DSCH for efficient simultaneous data transmission.

Solutions:

1. Hybrid ARQ: Combines FEC and repeat requests for enhanced reliability.
2. Link Adaptation: Adjusts modulation and coding dynamically.
3. Fast Cell Selection: Enables rapid cell selection and reselection.
4. Fast Retransmission: Minimizes impact of packet errors.

HSUPA (High-Speed Uplink Packet Access):

Features:

1. Increased Uplink Data Rates: Focuses on improving uplink data rates.
2. Enhanced Uplink Throughput: Utilizes advanced modulation and coding schemes.
3. Fast Scheduling: Employs fast scheduling algorithms for efficient resource allocation.
4. Cell-FACH State: Introduces Cell-FACH state for optimized power consumption during idle periods.

Solutions:

1. Fast Hybrid ARQ: Enhances uplink data reliability and minimizes retransmission delays.
2. Category Upgrades: Offers flexibility with multiple categories for varying uplink data rates.
3. Uplink Shared Channel: Introduces HS-SCCH for efficient uplink signaling.
4. Fast Cell Selection: Supports seamless mobility with rapid cell selection and reselection.

LTE Network Architecture and Main Features

Describe the architecture and main features of LTE network (EUTRAN + EPC).

LTE Network Architecture (EUTRAN + EPC):

1. EUTRAN (Evolved Universal Terrestrial Radio Access Network):
   • eNodeB: Base station managing radio communication with UEs, handling resource management, and facilitating handovers.
2. EPC (Evolved Packet Core):
   • MME (Mobility Management Entity): Manages UE mobility, authentication, and security.
   • SGW (Serving Gateway): Routes user data packets, acts as a mobility anchor, and manages handovers.
   • PGW (PDN Gateway): Connects LTE to external networks, assigns IP addresses, and manages QoS.
   • PCRF (Policy and Charging Rules Function): Defines and enforces service policies for QoS, charging, and resource allocation.

Roles of Nodes in LTE Network:

1. UE (User Equipment):- Communicates with eNodeB for radio access, manages data sessions, and handles mobility.2. eNodeB (Evolved Node B):- Manages radio resource, facilitates handovers, and handles radio links with UEs.3. MME (Mobility Management Entity):- Manages UE mobility, authenticates users, and facilitates handovers.4. SGW (Serving Gateway):- Routes user data, acts as an anchor for mobility, and manages handovers.5. PGW (PDN Gateway):- Connects LTE to external networks, assigns IP addresses, and manages QoS.6. PCRF (Policy and Charging Rules Function):- Defines and enforces policies for QoS, charging, and resource allocation based on service agreements.

34. Describe the problem of LTE resource scheduling. 

LTE resource scheduling involves assigning frequency, time, and power resources to user equipment (UE) by evolved NodeBs (eNB) to meet QoS, prioritize users, and avoid interference. Key Aspects:•Shared Channel and Resource Grid: LTE employs a shared channel with a resource grid combining frequency and time, allocated by eNBs to UEs.•Scheduler Algorithm: eNBs use flexible scheduling algorithms to assign resources based on QoS, priorities, and fairness.•Interference Management: Coordinated scheduling among eNBs through the X2 interface minimizes interference, adapting power levels and reuse schemes.•Cell Border Considerations: Resource allocation for UEs near cell borders is carefully managed to prevent interference, employing different reuse schemes.System Approaches:•Coordinated Scheduling: eNBs coordinate to manage interference and optimize resource use.•Adaptive Power Control: Adjusts power levels to maintain signal quality without excessive consumption.•Reuse Schemes: Differentiation between nearby and remote terminals for optimized resource utilization and interference control. In essence, LTE resource scheduling efficiently allocates limited resources among UEs, managing interference and meeting QoS by employing flexible scheduling, adaptive power control, and coordinated strategies.

35. List at least five versions of the IEEE 802.11 standards, with their prop

•802.11-1997 (802.11 legacy): original standard 2.4 GHz ISM band, 1 or 2 Mbps bitrate•802.11a-1999: 5 GHz ISM band, OFDM waveform, max. 54 Mbps•802.11b-1999: this became popular, extension of 802.11, 11 Mbps•802.11g-2003:2.4 GHz ISM band, waveform is like in 802.11a, 54 Mbps•802.11n-2009: 5 and 2.4 GHz ISM band, OFDM, MIMO, higher bandwidth, up to 600 Mbps bitrate

36. Describe the elements, functionalities and notions of WiFi networks.

WiFi networks, operating on IEEE 802.11 standards, connect devices wirelessly using access points (APs) and wireless clients like laptops, smartphones, and tablets. APs extend wireless coverage and link wireless clients to the wired network. Clients connect via the WiFi radio interface, communicating within the network and with the wired network through APs. The WiFi MAC protocol manages the shared radio channel with two modes: Distributed Coordination Function (DCF) and Point Coordination Function (PCF). DCF employs CSMA/CA for client access, while PCF enables AP-controlled channel access and client transmission scheduling. The WiFi PHY protocol sets physical transmission characteristics, including modulation, channel bandwidth, coding rate, and transmit power. Operating in 2.4 GHz and 5 GHz bands, WiFi networks support various data rates from Mbps to Gbps. Security measures like WEP, WPA, and WPA2 safeguard transmissions from unauthorized access and eavesdropping.

37. Describe the operation of the WiFi MAC protocol’s DCF function.

The Distributed Coordination Function (DCF) is a mechanism used by stations (STAs) to access the shared radio channel without any central coordinator. In DCF, STAs use the same simple rule to get access to the channel, which is the Carrier Sense Multiple Access mechanism with Collision Avoidance (CSMA/CA). Before transmitting a MAC frame, the STA senses the channel to check if it is empty. If the channel is idle, the STA waits for a randomly chosen time interval, called the backoff time, before transmitting the frame. The backoff time is chosen randomly by the STA and is a random number between 0 and the Contention Window (CW). The CW depends on the number of trials to transmit the given frame. In WiFi, the Contention Window grows as powers of 2, as the number of trials grow. If the channel is busy, the STA waits until it becomes idle and then starts the backoff process again. If two or more STAs start transmitting at the same time, a collision occurs, and the STAs involved in the collision wait for a random time interval before retrying the transmission.

38. Describe the hidden terminal problem and how to mitigate it. Describe the basic ideas of

Hidden Terminal Problem: Occurs when stations communicating with a common station are out of each other’s range, leading to collisions. To resolve this:Virtual Carrier Sense:•NAV (Network Allocation Value): Stations use MAC frame headers to set NAV, indicating ongoing transmission duration to avoid collisions.•RTS/CTS Handshake: Prior to transmission, RTS frames specify the recipient and transmission duration. After a SIFS, the recipient responds with a CTS frame, indicating the transmission duration. Overhearing stations set their NAV to prevent collisions.•RTS Threshold: Considers factors like bitrates and packet length. Frames fitting within a single time slot might skip RTS/CTS, reducing overhead. In essence, virtual carrier sense using NAV, RTS/CTS handshakes, and RTS Threshold resolves hidden terminal issues by coordinating channel access, enhancing wireless communication reliability and efficiency

39. Outline what kind of frames are used and for what purposes in WiFi.

In WiFi networks, the MAC protocol defines three frame types: Data frames, Control frames, and Management frames, each serving distinct purposes: Data frames: These carry payload data between wireless clients and the wired network, transporting higher-layer protocols like TCP/IP. They are identified by the “Type” field in the frame header. Control frames: They manage access to the shared radio channel and oversee data frame transmission. Subtypes include RTS (Request to Send) and CTS (Clear to Send) used to reserve channels and prevent collisions, ACK to confirm successful data frame reception, and BA (Block Acknowledgment) for confirming blocks of data frames. Management frames: These handle WiFi network management and information exchange between clients and APs. Subtypes include Association/Reassociation Request and Response for establishing or re-establishing connections, Probe Request and Response for discovering available APs, Beacon for AP presence and capability advertisement, Authentication/Deauthentication for client authentication or disconnection, and Action frames for vendor-specific information exchange between clients and APs. Each frame type has a specific format with relevant fields and is transmitted via the WiFi PHY protocol. Wireless clients and APs process these frames according to the WiFi MAC protocol.

40. Define how power save mode is working in WiFi.

Power save mode in WiFi enables mobile devices to conserve battery by entering a sleep state when not actively listening to the communication channel. Despite being in sleep mode, these devices remain available to receive data. The Access Point (AP) maintains a list of sleeping mobiles and stores incoming packets for them. Periodically, the AP sends beacon frames to notify sleeping mobiles about pending packets. The sleeping mobiles wake up at scheduled intervals to listen to these beacon frames. Once awakened, a mobile sends a power-save poll message to the AP, explicitly signaling its wakefulness. The AP may respond with an acknowledgment (ACK) and deliver the packet later, requiring the mobile to remain awake, or it may transmit the packet immediately. In summary, WiFi power save mode allows devices to enter a sleep state, periodically waking up to check for incoming data through beacon frames, thereby optimizing energy consumption.

41. Outline the basic radio properties and procedures of Bluetooth.

Bluetooth operates within the 2.4 GHz ISM (Industrial, Scientific, and Medical) band and utilizes frequency-hopping spread spectrum (FHSS) as its basic radio procedure. Frequency Band: Bluetooth operates in the 2.4 GHz ISM band. Frequency Hopping Spread Spectrum (FHSS): Utilizes 79 carriers (1 MHz each) from 2402 MHz to 2480 MHz (2402 + k MHz, where k ranges from 0 to 78). Executes 1600 hops per second, with 625 Ps (pseudorandom sequence) per symbol. Modulations: Basic Rate (BR) uses Gaussian Frequency Shift Keying (GFSK) at 1 Mbps. Enhanced Data Rate (EDR) uses Differential Quadrature Phase Shift Keying (DQPSK) at 2 Mbps and 8DPSK at 3 Mbps. Transmission Power Classes: Class 1: Maximum power of 20 dBm (100 mW) with a range of around 100 meters. Class 2: Maximum power of 4 dBm (2.5 mW). Class 3: Maximum power of 0 dBm (1 mW). Range: Bluetooth typically has an approximate range of about 10 meters (though this can vary based on the class of device and transmission power).

Class 1 devices with higher transmission power (100mW) can achieve a range of about 100 meters. Power Classes: Class 1: Max 20 dBm (100mW) – approximately 100 meters range. Class 2: Max 4 dBm (2.5mW). Class 3: Max 0 dBm (1mW). These properties and procedures allow Bluetooth devices to communicate wirelessly over short distances, employing frequency hopping to reduce interference and offering varying transmission speeds based on the modulation schemes used.

42. Describe the basic networking properties of Bluetooth.

Fundamental Concepts of Bluetooth Networking:- Piconet: A communicating group of Bluetooth devices.- Ad hoc: A piconet formed using an automated mechanism.- Piconet Structure: Consists of 1 Master and a maximum of 7 actively communicating slaves.- Dynamic Roles: Being a master or slave can change over time and is specific to a given piconet.- Active Members: Active Member Address (AM_ADDR) is represented by 3 bits.- Master Capacity: More slaves can be registered to the master, even in sleep mode.- Multiple Memberships: A device can be a member of multiple piconets, serving as a master in one and a slave in others.- Scatternet: Several piconets connected through devices that are members of two piconets.- Frequency Hopping: Each piconet uses a unique pseudo-random frequency hopping sequence based on the master’s address.- Time Division Duplexing (TDD): Master transmits in downlink, and slaves transmit/respond in uplink during different timeslots.- Communication Pattern: Follows a M->S; S->M; M->S; S->M sequence.- No Slave-to-Slave Communication: Communication is strictly between master and slaves.- Packet Transmission: Each packet fits into a designated timeslot.- Sequential Packets: Subsequent packets are transmitted in the next timeslot and on the next frequency, following the hopping pattern.- Frequency Hopping Pattern: Unique for each piconet, minimizing interference with neighboring piconets.- Collision Mitigation: Patterns are designed to minimize collisions in neighboring piconets.- Non-Interfering Piconets: Piconets are constructed to avoid disturbing each other.

43. Present the link types used in Bluetooth.

Types of Links:1. SCO (Synchronous Connection Oriented)– Symmetric: Equal data transfer in both M->S and S->M directions.- Point-to-Point: Links between the Master (M) and a Slave (S).- Maximum 3 SCO connections in a piconet.- Periodic Allocation: Slot pairs (M->S and S->M slots) are assigned at fixed time intervals, creating a fixed bitrate connection.- Voice Transmission: Mainly designed for voice and telephony communication.- Example: Connection between a headset and a phone.- No Retransmission: There is no retransmission in case of lost packets.- Error Correction: Error correction coding can be implemented.2. ACL (Asynchronous Connection-Oriented Link)– Symmetric or Asymmetric: Can support equal or unequal data transfer in both directions.- Packet Switching: Designed for packet-switched data transmission.- Point-to-Point or Point-to-Multipoint: Supports connections between a single point or multiple points.- Best Effort Link: Can have one ACL per slave device.- Polling Mechanism: Master sends a poll to a slave, and the slave responds; the poll itself can carry data.- Variable Packet Lengths: ACL links may use 1-3-5 slot packets.- Error Correction: Error correction coding can be applied.- ACK and Retransmission (ARQ): Supports acknowledgment and retransmission for reliability.- Forward Error Correction (FEC): Additional error correction mechanism available.

44. Describe the low power modes of Bluetooth.

Bluetooth Classic, which is distinct from Bluetooth Low Energy (BLE), includes several low-power modes to conserve energy. Three key low-power modes in Bluetooth Classic are Sniff Mode, Hold Mode, and Park Mode:1. Sniff Mode:- Purpose: Sniff Mode is designed to reduce power consumption during idle periods while maintaining a connection between two Bluetooth devices.- Operation: In Sniff Mode, the slave device periodically wakes up to check for incoming data, allowing it to consume less power during the idle periods. The master device can adjust the sniff interval, determining how frequently the slave wakes up to check for data. 2. Hold Mode: – Purpose: Hold Mode is used to temporarily suspend communication between two Bluetooth devices while conserving power.- Operation:- When a device enters Hold Mode, it suspends data exchange without terminating the connection.- Devices negotiate a hold time, during which data transmission is paused. After the hold time expires, normal communication resumes.3. Park Mode: – Purpose: Park Mode is an extended low-power state where a Bluetooth device relinquishes its active connection but can be quickly reactivated.- Operation:A device in Park Mode gives up its active connection slot but retains a reserved spot within the piconet.The parked device consumes minimal power and periodically wakes up to synchronize with the master device. If the master device needs to communicate with the parked device, it can be quickly activated without the need for a complete reconnection process.

45. What is Virtualization? What types of virtualizations exist? What is a virtual switch?

Virtualization: Enhancing Efficiency in Computing. Virtualization, the abstraction of physical resources into logical representations, is a powerful technology deployed across various layers of computing environments. Layered Implementation: Storage Virtualization: Centralizes storage management for efficient allocation. Server Virtualization: Allows multiple virtual machines on a single server, optimizing resource utilization. Network Virtualization: Decouples network functionality, creating a flexible virtualized infrastructure. Virtual Switch (vSwitch):Facilitates packet exchange within a host computer or server for seamless communication between virtual machines. Implemented by the hypervisor, with Open vSwitch being a notable example. Operates without physical switching, achieving high-speed communication directly through memory operations. Virtualization, exemplified by vSwitches, continues to drive efficiency, resource optimization, and adaptability in modern computing environments.

46. What is Software Defined Networking? What are the benefits of SDN? Why do modern

Software Defined Networking (SDN) separates network control (control plane) from data forwarding (data plane), allowing centralized management via software. Its benefits include automation, scalability, flexibility, resource optimization, and fostering innovation. Modern networks require SDN due to growing complexity, scalability demands, rigid architectures, and the need for agile, adaptable infrastructures. The SDN architecture involves: SDN Controller: Centralized control software managing network behavior. Control/Data Plane Separation: Decoupling decision-making from packet processing. Programmable Data Planes: Flexibility in traffic handling based on controller-defined policies. Overlay Networks: Virtual networks providing logical separation. APIs and Orchestration: Enabling communication and optimal resource allocation. In essence, SDN transforms network management by offering flexibility, automation, and centralized control to address the challenges of modern, dynamic networks.

47. What is OpenFlow?

OpenFlow is a communication protocol and interface used as the southbound interface in Software Defined Networking (SDN). It acts as a standardized protocol between the control plane (managed by an SDN controller) and the forwarding plane (network devices such as routers or switches). Essentially, OpenFlow enables the SDN controller to instruct and manage how packets are forwarded and processed by these network devices. It provides an open and standardized API (Application Programming Interface) that allows programming of the data plane switches, similar to how an x86 instruction set functions for computers. OpenFlow allows visibility and control into the otherwise closed or proprietary aspects of networking devices, enabling greater openness and flexibility in managing and controlling network traffic. In an OpenFlow switch, the data path consists of a Flow Table, where each flow entry has associated actions. Meanwhile, the control path involves a controller that programs these flow entries into the flow table. This protocol is primarily based on Ethernet switches and provides a standardized way to add, modify, and remove flow entries in the flow table, thereby controlling the behaviour of network traffic in a programmable manner.

48. What is Network Function Virtualization?

Network Function Virtualization (NFV) is a paradigm shift in networking where traditionally dedicated network appliances, such as routers, switches, firewalls, and load balancers, are replaced by software running on standardized servers and hardware. NFV leverages virtualization and cloud technologies to emulate these network functions on standard servers, allowing multiple network functions to be consolidated onto a single physical hardware infrastructure. NFV aims to: Decouple Network Functions from Hardware: Instead of relying on specialized hardware devices, NFV virtualizes and abstracts network functions, allowing them to run on commodity servers or cloud infrastructure. Enable Rapid Service Deployment: By using software-based solutions, NFV enables quick and flexible deployment of network services without the need for deploying dedicated hardware. Increase Operational Efficiency: NFV reduces costs by consolidating and sharing hardware resources, automating network management tasks, and providing scalability and flexibility in network service provisioning. Improve Network Agility: It allows for dynamic scaling, automation, and orchestration of network functions, leading to enhanced agility in responding to changing network demands. NFV utilizes concepts such as cloud computing, virtualization mechanisms, orchestration, and standard high-volume servers to achieve these goals. It faces challenges related to portability, performance trade-offs, interoperability, migration with legacy networks, and ensuring compatibility with existing systems. Overall, NFV represents a shift towards a more flexible, cost-effective, and agile networking model by virtualizing network functions and deploying them on standard IT infrastructure.

49. What is 5G Network Slicing? What is Mobile Edge Computing (MEC)? Describe some MEC

5G Network Slicing involves creating tailored virtual networks called “slices” for specific communication needs, while Mobile Edge Computing (MEC) brings computing servers closer to base stations. MEC’s key benefits include proximity advantages, low latency, and location-awareness. MEC Use Cases: RAN Caching: Storing popular content at base stations for faster access. Augmented Reality: Real-time analytics for automatic event triggers and optimizations. Video Analytics: Enhancing user experiences in museums or points of interest. Intelligent Video Acceleration: Optimizing video quality and throughput. Connected Vehicles: Facilitating vehicle-to-infrastructure communication for rapid hazard warnings.

51. What types of configuration are known and how can they be described?

52. Summarize indoor positioning methods and their properties

Indoor positioning methods include: Absolute Methods: Triangulation, Trilateration, Multilateration. Fingerprinting: Learning and recognizing unique patterns. Proximity-based Methods: Determining position based on nearby points. Relative Methods: Using acceleration and direction for assessment.Specific Techniques: GPS: Outdoor accuracy (3-5 meters). Cellular Networks: Timing and sectoring for positioning. Dead Reckoning (DR): Estimates movement directions. Ultra-wideband (UWB): High accuracy (5-30 cm) with active infrastructure. RFID, NFC, Rubee: Varying costs and proximity requirements. Ultrasound: Precise (. Each method has different accuracies, infrastructure needs, and practical limits, tailored for specific applications based on accuracy, range, and environmental constraints.

19. Describe Ethernet protocol (addressing, switching and speeds)!

Ethernet is a layer 2 protocol used in IP networks. It was originally designed as a local networking technology, but it is now used in networks of various sizes, from local to metropolitan networks. Ethernet uses frames to transmit data between devices, and it operates at different speeds, such as 10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps, 40 Gbps, and 100 Gbps. Ethernet uses MAC addresses (also known as physical addresses) to address devices on the network. MAC addresses are 6-byte addresses that are unique to each network interface. Ethernet switches use the destination MAC address in the Ethernet header to forward frames to the correct device. Switches learn MAC addresses by observing the source MAC address of incoming frames and associating them with the port on which they arrived. Ethernet frames can be switched within a LAN or routed between LANs. Ethernet switches are used to switch frames within a LAN based on the destination MAC address. Ethernet routers are used to route frames between LANs based on the destination IP address.