What are the responsibilities of the Presentation Layer od the ISO/OSI model?
Key Responsibilities:
Translation: Converts data formats (e.g., character encoding).
Encryption/Decryption: Secures data for transmission.
Compression/Decompression: Optimizes data size for faster transfer.
What is handled by the session layer?
Role: Manages and controls the establishment, maintenance, and termination of communication sessions between applications.
Session Establishment, Management, and Termination Starts, maintains, and ends sessions between systems.
Synchronization Adds checkpoints to track progress and enable recovery in case of failures.
Dialog Control Manages the direction of communication (half-duplex or full-duplex).
Services like Authtification and Authorization are offered (+potentially restoration).
What are constraints of the transport layer?
Packets are transported on different paths.
Some paths are faster/ longer than others
Paths can malfunction
packets have size restriction (e.g. 1500 bytes)
thus ->
reception of data:
not at all
or
not completely
doubled message
and
order not guaranteed + readiness of the remote station is unknown.
Transport Layer has to cope with all errors of the Network Layer!
Trade-Off: reliability v speed
Why do we need a Transport Layer?
Purpose: The Transport Layer ensures reliable, ordered, and error-checked delivery of data between devices across a network.
Key Functions:
Reliable Data Transfer (e.g., TCP): Guarantees data arrives intact and in sequence.
Flow Control: Prevents overwhelming the receiver with too much data at once.
Error Detection and Correction: Ensures data integrity during transmission.
Multiplexing: Manages multiple communication sessions simultaneously on a single device.
Connection establishment
Contrast and explain the terms Connection Oriented Service and Connection Less Transport Service and name exmaple protocols for both.
CONNECTION ORIENTED SERVICE
connection establishment (Handshake SaE!)
virtual channel
ensure data reception
correct order
labeled as reliable not secure!
TCP (Transmission Control Protocol)
Pros: Reliable, ordered delivery. Good for apps needing data integrity (e.g., web browsing, email, file transfers).
Cons: More overhead and slower due to connection setup and error checking.
CONNECTION LESS TRANSPORT SERVICE
just a simple message -> fire and forget
UDP (User Datagram Protocol)
Pros: Fast, low overhead. Ideal for time-sensitive applications (e.g., video streaming, VoIP, online games).
Cons: No reliability—packets can be lost, duplicated, or arrive out of order.
Decribe the packet structure on the transport layer.
What are the main tasks of the Network layer?
Provide a common addressing scheme across different Data Link Layer networks (e.g., IP addressing).
Transmit packets across multiple nodes and diverse Data Link Layers.
Determine the best path to deliver packets to their destination (routing).
Packet forwarding to the destination host.
Packet fragmentation when the Data Link Layer can’t handle large packet sizes.
Packet reassembly at the destination to reconstruct fragmented messages.
What is described by a network topology?
A network topology describes the interconnection scheme of a network. It focuses on the interconnection of individual nodes and how these nodes pass information through this network.
How does a Binary Tree topology look and what are its advantages and disadvantages?
Advantages
• one way from one node to any other node
• simple structure
Disadvantages
• the disruption of one line can create a net split
• bottlenecks because one line may connect many nodes
What does a Ring topology look like and what are its advantages and disadvantages?
The ring is a very old network topology. It may send information in one directly only or in both directions!
Redundancy when transmission in both diections is supported.
Simple structure.
Many hops leading to bad latency
Bottlenecks because of limited amount of connecting paths.
What does a Mesh topology look like and what are its advantages and disadvantages?
The mesh is a very modern network topology.
Multiple ways to reach destination (redundancy)
No bottlecks due to redundancy
Disrupted links can easily be compensated for.
Very complicated path finding
Requires greater computing power and memory perfomance
What does a Crossbar topology look like and what are its advantages and disadvantages?
A crossbar is typically used in Integrated Circuits (ICs) or System on Chips (SoCs).
Easy and cheap broadcast
Direct and fast connection between nodes
No redundancy
No scalability
What does a Bus topology look like and what are its advantages and disadvantages?
Abus is also a very old network topology. In most cases one node is a dedicated master node which organizes the access to the shared medium. A bus is often used in computer processors, ICs, and SoCs.
What classifications exist for computer networks?
Using the Aerial Classification system:
A network connecting components within a single chip or sometimes between different chips.
The distance between participants is typically around 0.1 mm.
Commonly used in multiprocessor systems and system-on-chip (SoC) designs.
A network that spans around one person.
Connects wearable devices, smartphones, headsets, etc., often using Bluetooth or Infrared.
Typical distance between participants: 1 m to 10 m.
A network focused on a specific organization or company.
Covers a room, building, or campus owned and managed by the same organization.
Maximum distance typically up to 2000 m.
Common technologies: Ethernet, Wi-Fi.
A network that covers large geographic areas, such as countries, continents, or the entire world (e.g., the Internet).
Larger than a LAN, often composed of multiple LANs connected together.
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