SieciKomp-02a-TopologieTypySieci

Basic Concepts

• A computer network is a group of interconnected network devices (computers, printers with network cards) functioning as a single communication system.
• Topology definitions:
  • Physical topology: the actual cabling layout and physical connections between devices (nodes).
  • Logical topology: how nodes communicate with each other within the network.
• Key terms: node (węzeł), network medium, and communication protocols.

Local Area Networks (LAN)

• LAN = Local Area Network
• Definition: a telecom network arranged over a small area (e.g., in one building) containing up to several dozen nodes.
• LAN standards and speeds:
  • Ethernet: $10\,\text{Mb/s}$
  • Fast Ethernet: $100\,\text{Mb/s}$
  • Gigabit Ethernet: $2\,\text{Gb/s}$
  • Token Ring: up to $128\,\text{Mb/s}$
  • Fiber Distributed Data Interface (FDDI): up to $100\,\text{Mb/s}$
  • LocalTalk (Apple): $0.2\,\text{Mb/s}$
• Notation: B = byte, b = bit.
• Characteristics of LANs:
  • Limited range (up to about $10\,\text{km}$)
  • High transmission speed (up to $2\,\text{Gb/s}$)
  • Easy to build and expand

Wireless Local Area Networks (WLAN)

• WLAN standards and features:
  • IEEE 802.11b: 2.4 GHz band, throughput $11\,\text{Mbps}$, DSSS modulation (2002).
  • IEEE 802.11a: 5 GHz band, throughput $54\,\text{Mbps}$, no compatibility with 802.11b (1999). Modulation: OFDM.
  • IEEE 802.11g: 2.4 GHz band, throughput $54\,\text{Mbps}$, OFDM modulation.
  • High Performance Radio LAN (HyperLAN): 5.15–5.3 GHz and 17.1–17.3 GHz bands.
  • IEEE 802.15: Bluetooth, synchronous transmission, fast-frequency-hopping, throughput up to $1\,\text{Mbps}$, 2.4 GHz ISM band, modulation: Gaussian Frequency Shift Keying (GFSK).
  • IEEE 802.16: WiMAX, range up to $50\,\text{km}$, throughput up to $70\,\text{Mbps}$, bands: 2.5 GHz, 3.5 GHz licensed and 5.8 GHz unlicensed.
  • Infrared (IR): Infrared Data Association (IrDA), optical signal 850–950 nm, range up to $1\,\text{m}$.
• Notes:
  • Wireless standards provide varying ranges, speeds, and regulatory compliance depending on the band and technology.

Metropolitan Area Networks (MAN)

• MAN = Metropolitan Area Network
• Description: city-scale networks that consist of multiple LANs connected together.

Wide Area Networks (WAN)

• WAN = Wide Area Network
• Purpose: interconnects local networks (LANs) and metro networks (MANs) and networks using wireless technologies.
• WAN technologies and standards:
  • X.25 protocol
  • Frame Relay protocol
  • Integrated Services Digital Network (ISDN): protocol layers 1–3 of the OSI model
  • Point-to-Point Protocol (PPP)
  • Digital point-to-point phone links with typical US and European speeds:
  • USA: T1 = $1.544\,\text{Mbps}$, 24 channels; T2 = $6.312\,\text{Mbps}$, 96; T3 = $44.736\,\text{Mbps}$, 672
  • Europe: E1 = $2.048\,\text{Mbps}$, E2, E3 = $34.368\,\text{Mbps}$
  • Synchronous Optical Network (SONET) / Synchronous Digital Hierarchy (SDH)
  • Asynchronous Transfer Mode (ATM)

VSAT Systems (Satelite Networks)

• VSAT = satellite networks and systems where data is transmitted between nodes via satellites.
• Technologies and standards:
  • GSM (Global System for Mobile Communications)
  • CDMA (Code Division Multiple Access)
  • PCS (Personal Communications Services), ITU standard

Network Topologies

• Topology types:
  • Bus (szyna)
  • Star (gwiazda)
  • Ring (pierścień)
  • Mesh (każdy-z-każdym)
  • Others
• Distinctions:
  • Physical topology: how cables physically connect nodes.
  • Logical topology: how data flows between nodes.
• Reasons for different topologies:
  • Installation and equipment costs
  • Architecture flexibility (ease of expansion and reconfiguration)
  • Reliability of communication
  • Required transmission speed
  • Network security

Medium Access Methods (Dostęp do medium)

• Methods for sharing the transmission medium:
  • Frequency division (CDMA-like separation by frequency)
  • Time division (TDMA-like access by time slots)
  • CDMA: all nodes have full access with unique coding sequences; many users can transmit simultaneously; requires high chip frequency
  • CSMA: carrier sense multiple access; nodes may sense medium but only one can transmit at a time
  • Token passing: access to medium is granted to the holder of a token
• Specifics by network type:
  • Ethernet: CSMA/CD access
  • Wireless networks: CSMA/CA
  • Token Ring and FDDI: token holder has access

Code Division Multiple Access (CDMA)

• CDMA is used in wireless broadcast channels (satellites, cellular):
  • Each user is assigned a unique code
  • All users share the same frequency band; each user has its own data coding sequence
  • Requires high chip frequency for encoding/decoding
  • Allows multiple users to access the medium simultaneously

Bus Topology (Topologia szyny)

• Physical bus: all nodes connected to a common cable (bus) or backbone
• Logical bus: signals from one node reach all nodes
• Example: Ethernet network
• Advantages:
  • Easy segmentation into smaller subnets
  • Simple installation and expansion
• Disadvantages:
  • Only one transmitting node at a time (single collision domain)
  • Transmitted data reaches all nodes
  • Shared network resources (e.g., media access time)
  • Error handling mechanisms can slow down transmission

Star Topology (Topologia gwiazdy)

• Physical topology: all nodes connect to a common network device (hub/concentrator)
• Logical topology in star: point-to-point communications; a virtual circuit is a collection of point-to-point links
• Benefits:
  • Easy to build and expand
  • Simple administration and monitoring
  • Easy fault localization
• Example visualization shows multiple hosts and devices connected to a central hub

Ring Topology (Topologia pierścienia)

• Physical topology: each node connects to two neighboring nodes forming a closed loop
• In transmission, all nodes between the two communicating nodes participate
• Intermediate nodes retransmit and amplify the signal
• Advantages:
  • Easy fault localization
  • Low cable usage
  • High transmission speed
• Example: ring with hosts, printer, scanner

Physical vs Logical Topology Correlations

• Ethernet: physical topology is often a bus or star; the logical topology can be a bus in practice
• Physical star often results in a logical bus (Ethernet example)
• Physical star + logical bus combinations illustrate how real networks can map different logical flows over physical layouts

LAN Standards Overview

• LAN standards categories:
  • Ethernet
  • Token Ring
  • FDDI

Token Ring (IEEE 802.5)

• Token Ring is IBM’s standard; compatible with other LAN standards (Ethernet) via IEEE 802.5; ring topology
• Transmission speed up to $128\,\text{Mbps}$
• Nodes pass a frame called a token; only the node with the token may transmit
• Logs indicate there are no collisions in Token Ring
• Token details:
  • Frame structure includes: Start Delimiter, Access Control, End Delimiter
• Token Ring frames/types:
  • Token frame
  • Data frame
  • LLC data frame
  • MAC management frames
  • Interrupt frame
• MAC management frames perform network management tasks (MAC layer): test of link, ring initialization, ring clearing, token reporting, active monitor functions
• Managing tokens and frames:
  • A single token exists in the network
  • Transmitting device modifies the token to create data frames
  • Devices without a token cannot create frame headers or transmit
• Data circulation: transmitted signals pass through all nodes and return to the sender
• If a node no longer wants to transmit, the data frame becomes a token and is passed to the next node
• Token frame fields:
  • Start delimiter
  • Access control
  • End delimiter

Token Ring Frames (Detailed Types)

• Types of frames in Token Ring:
  • Token frame
  • Data frame
  • LLC data frame
  • MAC management frames
  • Interrupt frame
• MAC frame purpose: network management and addressing
• MAC management tasks include:
  • Testing node connections (link test)
  • Ring initialization
  • Ring clearing
  • Token reporting
  • Active monitoring functions
• Interrupt frame purpose: terminates transmission and includes start and end markers

Token Ring Network Management and Agents

• Token Ring networks include management and monitoring features:
  • Network monitoring mechanisms
  • Automatic failure detection and notification to other ring nodes
  • Ring management system
  • Ring tuning mechanisms
• Agents and servers used for ring management:
  • Active monitor, standby monitor
  • Ring error monitor
  • Configuration report server
  • Ring parameter server
• Types of agents/servers include: monitor agents, configuration servers, parameter servers

Physical Construction of Token Ring (Cabling and Adapters)

• Cables used:
  • IBM twisted-pair type 3
  • Telephone twisted pair (Category 1)
• Connectors:
  • IBM types 1 and 2
  • RJ-45 for UTP (IBM type 3)
  • RJ-11 for telephone cables
• Network interface cards:
  • PC Adapter
  • TRN/A Adapter
• Maximums:
  • Maximum number of nodes: $96$
  • MAU (Medium Attachment Unit) count: $12$ (transceivers)
• Distances:
  • Maximum distance between a node and MAU: $45\,\text{m}$
  • Maximum distance between nodes: $120\,\text{m}$

Fiber Distributed Data Interface (FDDI)

• FDDI = Fiber Distributed Data Interface; ANSI X3T9.5 standard
• Topology: dual ring with a token-based access mechanism; token is time-based (owner can transmit for a limited time)
• Collision behavior: no collisions in FDDI
• Key characteristics:
  • Max data rate: $100\,\text{Mbps}$
  • Physical distances:
  • Between nodes with multimode fiber: up to $2\,\text{km}$
  • Between nodes with single-mode fiber: up to $20\,\text{km}$
  • Token access controlled by the token
  • Mechanism to detect and remove failures
• Cabling:
  • Multimode fiber: 62.5/125 µm
  • Single-mode fiber: 9/125 µm (ANSI/ITU can vary; typical spec shows ~8.3/125 µm in some texts)
• Ring size: up to $100\,\text{km}$
• Maximum nodes: $500$

FDDI Protocol Layers

• MAC (Medium Access Control) layer (OSI Data Link Layer):
  • Governs access to the medium and frame formats
  • Defines: token generation, frame management, physical addressing (MAC), error detection/correction during frame reception
• PHY (Physical Layer):
  • OSI data link equivalent responsible for receiving bit streams and converting to transmission-ready format
  • Provides network timing (clocking) signals; FDDI clocking is 125 MHz
• PMD (Physical Medium Dependent) layer:
  • Specifies medium characteristics, such as cable type, signaling levels, connector types, allowable error rates
  • For FDDI, fiber optic cables are common; copper-based TMDDI (CDD I) exists for copper

FDDI SMT (Station Management) Layer

• SMT = Station Management layer of FDDI
• Purpose: management and monitoring of ring nodes
• Functions:
  • SMT frame handling
  • Connection control
  • Ring control
• SMT services:
  • Station attachment/detachment
  • Statistical data collection
  • Fault identification and removal
• Standard: ANSI INCITS 229-1994 (Information Systems - Fibre Distributed Data Interface (FDDI) - Station Management (SMT))

Summary of Key Concepts and Connections

• LAN/WAN/MAN distinctions map to scale and scope of networks, with corresponding standards and technologies tailored to speed, distance, and topology requirements.
• Topologies (bus, star, ring, mesh) define physical layouts and interact with logical data flow and medium access methods to determine performance and fault characteristics.
• Medium access control strategies directly influence collision domains, efficiency, and reliability in different network types (e.g., CSMA/CD in Ethernet vs. token-based access in Token Ring and FDDI).
• FDDI provides a robust, high-speed fiber-based LAN technology with dual-ring topology and comprehensive SMT/MAC/PHY layering for management, error handling, and scalability.

Notation and Formulas

• Speeds and capacities are often given in bits per second (bps) and may be represented as:
  • $10\,\text{Mb/s}, 100\,\text{Mb/s}, 2\,\text{Gb/s}, 128\,\text{Mb/s}, 100\,\text{Mbps}, 54\,\text{Mbps}$
• Distances and ranges commonly appear as:
  • $10\,\text{km}, 2\,\text{km}, 1\,\text{m}, 45\,\text{m}, 120\,\text{m}$
• Frequency bands and frequencies may be expressed, for example:
  • 2.4 GHz, 5 GHz, and wavelength-related considerations in WLAN standards
• Token and frame concepts are not numeric equations but structural elements (e.g., token fields: Start Delimiter, Access Control, End Delimiter) critical to protocol behavior

Connections to Foundational Principles

• OSI model alignment: MAC and PHY layers in FDDI map to OSI Data Link and Physical layers, illustrating how access control and signaling operate in layered networking models.
• Industry standards evolve to balance performance, compatibility, and deployment costs; examples include Ethernet’s CSMA/CD and Token Ring’s token-based access, both influencing network design trade-offs.
• Real-world relevance: LANs provide the backbone for building-wide communication; WANs connect geographically dispersed sites; WLANs enable mobility; FDDI demonstrates fiber-based high-speed backbones with robust ring-based management.