FDDI Network Architecture Quiz

Point-To-Point Protocol (PPP)

• PPP establishes communication between two devices via a serial interface, often seen with computers linked through phone lines to servers.
• It operates at the data-link layer (Layer 2) of the OSI model, packaging TCP/IP packets for transmission to the Internet.
• The protocol consists of encapsulation, Link Control Protocol (LCP), and Network Control Protocol (NCP).

Link Control Protocol (LCP)

• LCP is crucial for managing PPP links, overseeing configuration, maintenance, and termination phases.
• Phases include:
  • Link Configuration: Negotiation of link parameters.
  • Link Maintenance: Management of the established link.
  • Link Termination: Closure of unnecessary links.
• LCP messages, known as packets or frames, control link operations and are categorized into three frame types for each link phase.

Network Control Protocol (NCP)

• NCP allows various network layer protocols to operate on a single communication link.
• It engages in encapsulation and negotiation of options, with specific NCPs such as IPCP for IP and IPX/SPX for Internetwork Packet Exchange.

Fibre Distributed Data Interface (FDDI)

• FDDI enhances Ethernet speed with dual-ring optical LAN technology, transmitting data up to 100 Mbps over 200 km.
• Utilizes multimode fiber and LEDs for lower costs and can connect thousands of users.
• Features two classes of stations (Class A and B) providing redundancy via dual rings.

FDDI Specifications

• FDDI's specifications consist of MAC, PHY, PMD, and SMT protocols, governing medium access, data encoding, physical transmission characteristics, and station management.

FDDI Encoding

• Uses a 4B/5B encoding scheme to ensure signal transitions, preventing clocking issues by minimizing consecutive zero bits.

Token Bus (802.4)

• Token Bus connects devices in a network that must possess a token to transmit, using a linear or tree-shaped layout.
• Logical organization resembles a ring, passing tokens in sequential order, enhancing efficiency and preventing collisions.

Token Ring (802.5)

• Token Ring operates where stations are interconnected in a ring topology, controlled by token passing.
• Only one token exists within the network, ensuring orderly access to the medium without conflicts.

Networking Devices Overview

• Repeaters: Amplify signals across segments of the same LAN, operating solely at the physical layer and unaware of data packets.
• Hubs: Connect various Ethernet devices, creating a single network segment, and can be passive, active, or intelligent depending on the functionality.
• Bridges: Connect multiple network segments, regenerating signals and filtering frames based on destination addresses. Types include transparent and routing bridges.
• Routers: Forward packets between different networks, operating at the network layer using logical and physical addresses, combining hardware and software components.

Additional Device Functions

• Each device type has specific roles:
  • Switches: Operate like bridges but connect individual computers with dedicated paths, avoiding collision domains.
  • Transport Gateways: Facilitate communication across different transport protocols.
  • Application Gateways: Translate message formats between different systems, such as converting email to SMS formats.### Gateway
• A gateway connects two different networks using distinct protocols, acting as an access point.
• Translates and interprets data formats between incompatible systems.
• Comprises both software and hardware components, functioning across all seven OSI layers.
• Performs additional tasks like format conversion and email forwarding.

Switch

• A network switch links devices or segments within a network, enhancing bridging efficiency.
• Buffers incoming packets and checks the outgoing link's status before forwarding.
• Two primary types:
  • Store and Forward Switch: Holds the entire packet before sending it.
  • Cut Through Switch: Forwards packets immediately upon receipt.

Media Access Control (MAC)

• MAC is a sublayer of the data link layer (Layer 2) in the OSI model.
• Provides addressing and control mechanisms for multiple access networks, allowing shared medium communication.
• The interface between MAC and the physical layer is crucial for unicast, multicast, and broadcast communications.
• Solves collision issues and organizes access using multiple access protocols.

Broadcast Networks

• Use a single shared communication channel allowing all machines on a network to receive transmitted packets.
• Each packet includes an address for the intended recipient, ensuring only relevant nodes process the information.

Need for Protocols in Broadcast Channels

• Necessitates structured management to avoid collisions and data loss.
• Protocols regulate access to the channel, determining who can transmit and when.

Types of Multiple-Access Protocols

• Classified into three categories:
  • Random Access Protocols: Allow nodes to transmit at full channel rate, employing a random backoff mechanism after a collision occurs.
  • Controlled Access Protocols: Grant permission to one node at a time, ensuring organized access.
  • Channelization Protocols: Allocate bandwidth across frequencies or time slots.

Random Access Protocols

• Facilitate multiple nodes sending transmissions without pre-allocated slots.
• Collision detection and random delays help nodes avoid immediate retransmitting after a collision.
• Common examples include ALOHA, CSMA, CSMA/CD, and CSMA/CA protocols.

ALOHA Protocol

• The original ALOHA employs a hub star configuration with distinct inbound and outbound channels.
• Uses acknowledgment packets to confirm successful transmissions, leading to automatic retransmissions in case of collisions.
• Key variants, including Pure ALOHA and Slotted ALOHA, optimize frame handling.

Pure ALOHA

• Transmits without checking channel status, relying on a later retransmission strategy after a collision.
• Efficiency is limited to about 18% due to potential overlapping frame transmissions.

Slotted ALOHA

• Introduces discrete time slots for transmissions, minimizing collision probabilities.
• Offers improved efficiency of approximately 37% with properly optimized parameters.

Carrier Sense Multiple Access (CSMA)

• Nodes check for signal presence prior to transmitting, ensuring minimal collisions.
• Simple implementation with fair efficiency; however, may waste medium time during collisions.

CSMA/CD (Collision Detection)

• Enhances CSMA by terminating transmissions upon collision detection and signaling other nodes to wait.
• Follows a structured algorithm for handling transmission processes and collision responses.

CSMA/CA (Collision Avoidance)

• A wireless adaptation of CSMA that prevents collisions by listening to the channel before transmitting.
• Utilizes an Interframe Space (IFS) to avoid immediate channel conflicts and provides prioritized access.

Controlled Access Protocols

• Utilize centralized control mechanisms to manage transmissions and avoid collisions.
• Examples include Reservation, Polling, and Token-Based methods.

Reservation Protocols

• Divide time into intervals, allowing stations to reserve slots for data transmission.
• Each station makes reservations to transmit in their designated miniblock.

Polling Protocols

• A central controller cycles through network stations, giving each the opportunity to transmit.
• Common strategies include Round Robin and Priority Order polling.

Token Passing

• Features a passing token that grants transmission rights to nodes in a controlled sequence.
• Eliminates collisions, improving channel utilization despite increased latency when demand is light.

Channelization Protocols

• Allocate network bandwidth among users through time, frequency, or code divisions.
• Examples include FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access), and CDMA (Code Division Multiple Access).

FDMA

• Assigns users exclusive frequency bands for data transmission, commonly seen in satellite communication.

TDMA

• Divides the signal into time slots for each user to ensure shareable frequency usage, widely used in 2G cellular systems.

CDMA

• Assigns unique codes to users for simultaneous transmission across the same frequency, suitable for cellular and satellite systems.

Multiplexing

• Combines multiple signals into one over a shared medium for efficient transmission.
• Devices that manage this process are called multiplexers (MUX) and demultiplexers (DEMUX).### Multiplexing Technologies
• Multiplexing allows multiple signals to use a single communication channel.
• Types include Space-Division Multiplexing (SDM), Frequency-Division Multiplexing (FDM), Time-Division Multiplexing (TDM), and Code Division Multiplexing (CDM).

Frequency-Division Multiplexing (FDM)

• FDM allocates distinct frequency bands for each user, enabling simultaneous analog signal transmission.
• Common examples include microwave transmission lines and AM/FM radio broadcasts.
• Each input signal is shifted to a separate frequency range, maintaining exclusivity.

Time-Division Multiplexing (TDM)

• TDM works by allocating time slots to users, allowing each to use the entire bandwidth during its allocated time.
• Applications include wireline telephone systems and some cellular networks.
• TDM exploits existing transmission lines and requires synchronization to prevent information loss due to timing discrepancies.

Synchronization in TDM

• Essential for maintaining consistent clock rates across communication nodes, preventing 'clock slip.'
• Clock recovery mechanisms are implemented to accommodate potential delays and ensure strict compliance with synchronization standards.
• Packet-based synchronization methods utilize timestamps from a master server for timing distribution.

Differences between FDM and TDM

• FDM divides the channel into non-overlapping frequency ranges; TDM allocates time periods to channels.
• FDM signals always use a portion of the bandwidth; TDM allows full bandwidth use for allocated time.
• TDM is more flexible, dynamically assigning time based on signal needs, while FDM lacks this adaptability.
• FDM is less efficient in channel capacity utilization compared to TDM.

Wavelength Division Multiplexing (WDM)

• WDM enables multiplexing of various optical signals onto a single fiber by using different light wavelengths.
• Facilitates bidirectional communication and increases fiber capacity, utilizing prisms for multiplexing and demultiplexing.

MAC (Medium Access Control) Sublayer

• MAC sublayer manages channel access in broadcast networks to prevent conflicts during transmission.
• Important in LANs using multi-access channels, MAC protocols address how to allocate channels and avoid collisions.

Multiple Access Protocols

• Focus on channel addressing, assignment, and collision avoidance.
• ALOHA system allows any user to transmit without prior scheduling, leading to possible collisions.

Pure ALOHA

• Users can transmit at any time, resulting in potential data loss during collisions.
• Users receive feedback to determine whether their transmission was successful or not.

Slotted ALOHA

• Introduced discrete time slots for transmission, allowing for improved channel utilization and reduced collision risks.
• Users wait for the beginning of designated time slots to transmit, enhancing overall efficiency compared to Pure ALOHA.

Carrier Sense Multiple Access Protocols

• CSM protocols involve listening for ongoing transmissions before sending data, improving performance.

P-persistent C.S.M.A

• For slotted channels; users sense if the channel is idle and transmit with a certain probability, deferring otherwise.

1-Persistent C.S.M.A

• Users listen for an idle channel and transmit immediately when it's available; if a collision occurs, they retry after waiting a random time.

Test your knowledge on the FDDI dual ring architecture and its specifications. This quiz covers the differences between Class A and Class B stations, their connectivity, and the fault tolerance features of the network. Ideal for students and professionals interested in networking concepts.