History and Definitions of Communication

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Questions and Answers

What is the purpose of using bit stuffing in bit-oriented protocols like HDLC?

To increase the maximum frame size

To avoid special sequences from appearing in data (correct)

To eliminate the need for acknowledgements

To prevent frame collisions during transmission

Which protocol uses a flag sequence of 01111110 for framing?

HDLC (correct)

DDCMP

PPP (correct)

BISYNC

What technique is employed in the Aloha protocol to address collisions?

Slot assignment

Exponential backoff (correct)

Token passing

Frequency hopping

How is error detection accomplished using the CRC method?

By padding data with trailing zeros and dividing by a polynomial Signup and view all the answers

Which of the following definitions describes the Internet as a 'network of networks'?

Network of networks Signup and view all the answers

In which MAC method does each station get a fixed time slot to transmit data?

Channel partitioning Signup and view all the answers

Who invented the Ethernet, which is crucial for network communication?

R. Metcalf Signup and view all the answers

What term describes a single source node sending data to all other nodes in a network?

Broadcast Signup and view all the answers

Which mechanism is characterized by establishing a dedicated circuit across links for data transmission?

Circuit Switching Signup and view all the answers

What does the packet switching method primarily use to manage data communication?

Store and forward technique Signup and view all the answers

Which communication protocol invention by Tim Berners Lee significantly impacted the development of the World Wide Web?

HTTP Signup and view all the answers

Which characteristics do network operators specify when designing a network system?

List system characteristics for easy administration Signup and view all the answers

When nodes are connected through a link that allows multiple endpoints, what type of link is it described as?

Multiple-access Signup and view all the answers

What is the main function of Layer 3 in the 5 Layer Internet Model?

To handle address definitions and routing protocols Signup and view all the answers

Which of the following devices operates at Layer 1 and Layer 3 in the 5 Layer Internet Model?

Router Signup and view all the answers

In the IP service model, which description best characterizes its connection type?

Connectionless, does not guarantee delivery Signup and view all the answers

How is transfer time calculated according to the performance formulas?

RTT/2 + size/bandwidth + handshake time Signup and view all the answers

Little's Law in queuing theory formulates the relationship between which three elements?

Arrival Rate, Mean Response Time, Mean Number of Jobs Signup and view all the answers

Which of the following best describes the encapsulation process in networking?

Wrapping data in headers at multiple layers Signup and view all the answers

What is the primary purpose of the transport layer in the 5 Layer Internet Model?

To control the logical channels for end-to-end communication Signup and view all the answers

What does the 'Best Effort' characteristic of the IP service model imply?

Delivery cannot be guaranteed, but transmission will occur Signup and view all the answers

What is a key characteristic of a hub in networking?

Repeats signals received on one port to all other ports Signup and view all the answers

What is the maximum number of repeaters that can be placed between two hosts in a classical Ethernet network?

4 Signup and view all the answers

Which access method allows nodes to distinguish between idle and busy links?

CSMA/CD Signup and view all the answers

What must the minimum frame length ensure in a CSMA/CD environment?

It must be long enough for collision detection Signup and view all the answers

Which statement about broadcast addresses in Ethernet is correct?

They consist of all 1's and send to all hosts Signup and view all the answers

What does the exponential backoff algorithm in CSMA/CD help to manage?

Collisions on the network Signup and view all the answers

How does a switch differ from a hub in terms of traffic management?

A switch creates separate collision domains Signup and view all the answers

What happens when a collision is detected on a CSMA/CD network?

The node sends a jam signal and retries after a wait Signup and view all the answers

What characterizes a base station in a network?

It has no mobility but is connected to the internet via a wired connection. Signup and view all the answers

How does the hidden node problem manifest in a network?

A sending node transmits without knowing another sending node is active. Signup and view all the answers

What is the main function of Multiple Access with Collision Avoidance (MACA)?

To ensure only one node transmits at a time, preventing interference. Signup and view all the answers

What is indicated when a node receives a Clear To Send (CTS) message?

The node is not hidden and can send data without issue. Signup and view all the answers

Which statement accurately describes the association protocol in a wireless distribution system?

The node sends a probe frame, and access points respond with probe frames. Signup and view all the answers

What role do routers/gateways play in a network stack?

They facilitate global connectivity by moving packets between networks. Signup and view all the answers

How are IPv4 addresses structured?

They are 32 bits in total, separated by dots. Signup and view all the answers

Which statement about access points (APs) in a distribution system is correct?

APs periodically send beacons to advertise their capabilities. Signup and view all the answers

Study Notes

History of Communication

1876: Alexander Graham Bell invented the telephone.
1940: Claude Shannon conducted groundbreaking research on telecommunications.
1958: Satellite communication and fiber optics were introduced.
1967: RAND Corporation developed the Arpanet plan.
1972: Arpanet and the Network Control Protocol (NCP) were established.
1973: Robert Metcalfe invented Ethernet.
1991: Tim Berners Lee invented the Hypertext Transfer Protocol (HTTP).

Definitions of the Internet

Infrastructure to support applications: The underlying structure allowing various applications to function.
Network of networks: Composed of interconnected individual networks.
Collection of protocols: A set of standardized rules governing communication within the internet.

Groups Specifying Internet Requirements

Application programmers: Define the services required by their applications.
Network operators: Prioritize system characteristics for ease of administration and management.
Network designers: Focus on cost-effective design properties.

Abstract Perspective of Networks/Internet

Nodes and Links: Networks consist of nodes (devices) connected by links (transmission paths).
Link types:
- Point-to-point: A link with two endpoints.
- Multiple-access: A link with multiple endpoints.
Indirect connection methods:
- Switched Networks:
  - Packet Switch: Packets are stored and forwarded.
  - Circuit Switch: A dedicated circuit is established for direct communication.
- Internetwork:
  - Network of networks: Networks interconnected by routers.
  - Routers: Devices connecting multiple networks, operating on the Internet Protocol (IP).
Communication modes:
- Unicast: One source, one destination.
- Multicast: One source, multiple destinations.
- Broadcast: One source, every other node.

Internet Perspective of Networks/Internet

General data flow:
1. User sends an HTTP request.
2. Packet sent to a router (home switch).
3. Router multiplexes traffic onto the network.
  - Multiplexing methods:
    - Synchronous time-division: Time division into equal quanta for round-robin data transmission.
    - Frequency-division: Different frequencies are used for different data flows.
    - Statistical: Packets are sent whenever possible, buffered, and prioritized.
4. Packet is sent to a modem for translation to internet-compatible format.
5. Switches forward packets within a network.
6. Routers forward packets between networks:
  - Routing: Establish forwarding tables to determine the best path for packets.
7. Packet reaches the desired server.

Architectural Perspective of Networks/Internet

Five Layer Internet Model:
- Layer 1: Physical: Hardware specifications and bit representation on physical media.
- Layer 2: Link: Host access to physical media (Ethernet, DSL, Cable, Fiber).
- Layer 3: Network: Uses the Internet Protocol (IP) for addresses and routing protocols.
- Layer 4: Transport: TCP and UDP for end-to-end logical channels.
- Layer 5: Applications: Data and headers are pushed to the transport layer via sockets.
Encapsulation and Decapsulation: Headers are wrapped and unwrapped during transmission.
Device roles:
- Hosts: Operate at all five layers.
- Switches: Operate at layers 1 and 2.
- Modem: Operates at layer 1.
- Router: Operates at layers 1 to 3.
Narrow Waist: Protocols define interfaces between layers on the same machine (service) and between machines on the same layer (peer).

IP Service Model

Connectionless: Connectivity is not guaranteed before sending data.
Packet-Based: Data is divided into packets.
Best Effort: No guaranteed delivery or quality of service.
Destination-Based: Packets are routed to the destination based on the IP address.

Performance

Throughput: Data transfer rate (bits per second).
Transfer time: Time taken to transfer data (RTT + size/bandwidth).
Round Trip Time (RTT): Time for a signal to travel to and from a destination.
Propagation delay: One-way travel time (RTT/2).
Number of Packets: Transfer size divided by bandwidth.
Delay x Bandwidth product: Represents the amount of data that can be sent before receiving feedback.

Queuing

Little's Law: A fundamental queuing theory principle:
- Mean number of jobs in a system = Arrival Rate x Mean Response Time.

Framing

Byte Oriented Protocols: Use bytes as frame boundaries.
- Sentinel-based approaches (Character Stuffing):
  - BISYNC:
    - Special framing characters to indicate start and end.
    - Character stuffing to escape specific characters in data.
  - PPP:
    - Flag characters are used to define frame boundaries.
    - Character stuffing to escape flag characters.
- Byte-counting approach: Frame header includes the number of bytes.
  - DDCMP:
    - Data is transmitted in blocks.
Bit-Oriented Protocols: Use bits for framing.
- HDLC:
  - Frames bounded by specific bit sequences.
  - Bit stuffing is used to avoid the use of the start/stop bit sequence.
- Error Detection:
  - Cyclic Redundancy Check (CRC):
    - Pads data with zeros and divides by a CRC polynomial.
    - Remainder is the CRC code.
    - Division with the CRC code allows detection of errors.
  - 2-D Parity: Adds extra bits for row and column parity checks.
  - Internet Checksum Algorithm: Performs checksum calculation for error checking.

Layer 2: Link

Link Coordination Methods (Medium Access Control):
- Channel Partitioning: Divides the channel into smaller units using multiplexing (frequency, time, statistical).
- Taking Turns: Nodes access the channel in a predefined order (token-based, polling).
- Random Access: Nodes access the channel randomly (Aloha protocol).
Aloha Protocol:
- Any node can transmit at any time.
- Receiver sends an ACK.
- If no ACK is received, random exponential backoff is triggered.
- After the backoff, the transmission is retried.
- No interframe gap or carrier sense enforcement.

802.3 Ethernet Standard

Based on Aloha with added features.
Physical Properties:
- Repeaters: Forward digital signals (bits only), limited to 4 devices between hosts.
- Hubs: Multi-way repeaters, broadcasting signals to all ports.
- Bridges: Connect collision domains, using forwarding tables to route frames.
- Switches: More complex than bridges, implementing spanning tree algorithms to prevent forwarding loops.
- Collision Domain: A shared link where collisions can occur when multiple nodes transmit simultaneously.
Access Protocol: Carrier Sense Multiple Access with Collision Detection (CSMA/CD).
- Carrier Sense: Nodes listen for activity before transmitting.
- Multiple Access: Multiple nodes share the same link.
- Collision Detect: Nodes listen for collisions and transmit a jam signal.
Frame format:
- Preamble: Clock synchronization.
- Interframe Gap (IFG): Required pause between frames.
- Runt Frame: A frame shorter than the minimum length.
Addressing:
- Unicast Address: Individual address for each Ethernet device.
- Broadcast Address: Address for all hosts.
- Multicast Address: Address for a subset of hosts.

802.11 (WiFi) Standard

Wireless link sharing: All nodes use the same transmission medium.
Endpoints:
- Base Station: Fixed location with wired connection to the network.
- Mesh/Ad Hoc: No dedicated base station, messages are forwarded between nodes within range.
Access Control: Nodes cannot send and receive at the same time.
- Hidden Node Problem: Nodes outside each other's range can interfere with each other's transmissions.
- Exposed Node Problem: A node within range of the receiver but not the sender can interfere with the transmission.
- MACA (Multiple Access with Collision Avoidance): The sender sends an RTS (Request To Send) and the receiver replies with a CTS (Clear To Send) to coordinate transmissions.
Distribution System:
- Base station oriented: Access Points (APs) serve as central access points.
- Roaming: Nodes can move between APs.
- Association Protocol: Nodes find APs and establish connections.
- Beacon Frames: APs broadcast information about their capabilities.

Layer 3: Network

Internetworking: Moving packets between networks.
IP Addresses: Facilitate global connectivity.
- IPv4: A 32-bit address format commonly used.
Routers (Gateways): Interconnect different networks.
Internet Service Provider (ISP): Provides internet access and infrastructure.

3 Essential Components of an ISP

Network: The physical infrastructure for communication.
Access to the Internet: Connecting to the global internet backbone.
Customer service: Providing support and troubleshooting to customers.

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Description

Explore the evolution of communication technologies from the invention of the telephone to the development of the internet and its protocols. This quiz covers key milestones and definitions that shape our understanding of modern communication systems.