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Questions and Answers
What is the primary purpose of multiple access protocols in a communication channel?
Which of the following random access protocols requires a station to wait for an acknowledgment before resending data?
What does the throughput formula for pure ALOHA indicate about successful transmissions?
What is one of the main improvements of slotted ALOHA over pure ALOHA?
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What are the two common transfer modes provided by HDLC?
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In a pure ALOHA network, if the average frame transmission time is 1 ms, what is the vulnerable time?
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Which type of frame is NOT defined by HDLC?
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What condition must be met for maximum throughput in pure ALOHA?
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What command does node A send to request a connection in the example provided?
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Which protocol is commonly used for point-to-point access?
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Which random access protocol uses a 'back-off time' mechanism for collision handling?
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What method does PPP use to handle framing?
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In Carrier Sense Multiple Access with Collision Detection, how does a station identify a collision?
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What does the Medium Access Control (MAC) sublayer primarily provide?
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What type of response does node B send to acknowledge the connection establishment request?
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In the Stop-and-Wait protocol used by HDLC, what occurs after a data transfer?
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Study Notes
HDLC (High-level Data Link Control)
- HDLC is a bit-oriented protocol designed for point-to-point and multipoint communication links.
- Implements the Stop-and-Wait protocol for data transfer.
- Offers two primary transfer modes: Normal Response Mode (NRM) and Asynchronous Balanced Mode (ABM).
- Defines three frame types:
- Information frames (I-frames) for data transfer.
- Supervisory frames (S-frames) for control purposes.
- Unnumbered frames (U-frames) for various control commands.
U-Frame Usage in Connection Management
- Node A requests a connection using the Set Asynchronous Balanced Mode (SABM) U-frame.
- Node B responds with an Unnumbered Acknowledgment (UA) frame.
- Data transfer occurs after the initial handshake between nodes.
- Connection release is initiated by Node A using a DISC frame, confirmed by a UA frame from Node B.
Point-to-Point Protocol (PPP)
- PPP is a widely used byte-oriented protocol for point-to-point communication.
- Uses byte stuffing with the escape byte 01111101 to handle data integrity.
- Supports various transition phases and encapsulation of packets such as PAP, CHAP, and LCP.
Media Access Control (MAC) Sub-layer
- MAC provides addressing and channel access control in multiple access networks.
- Ensures multiple nodes can communicate over a shared medium.
- If a dedicated link exists, data link control is sufficient; otherwise, multiple access protocols are needed to manage collisions.
Random Access Protocols
- In random access methods, no single station has control over others, promoting an egalitarian approach to communication.
- Stations independently decide when to send data based on protocol-defined procedures.
- Common random access protocols include:
- ALOHA (Pure and Slotted)
- Carrier Sense Multiple Access (CSMA)
- CSMA with Collision Detection (CSMA/CD)
- CSMA with Collision Avoidance (CSMA/CA)
Pure ALOHA
- Allows stations to transmit data whenever ready.
- Stations wait for an acknowledgment after transmission; if not received in time, they utilize a random back-off time before retrying.
- Throughput given by S = G × e^(-2G), with maximum throughput Smax = 0.184 when G = 1/2.
Slotted ALOHA
- Designed to enhance Pure ALOHA efficiency by dividing time into discrete slots.
- Data transmission is permitted only at the beginning of each time slot to minimize collision probability.
- Throughput is calculated as S = G × e^(-G), with a maximum throughput Smax = 0.368 when G = 1.
Example of Pure ALOHA Calculation
- For a pure ALOHA network transmitting 200-bit frames at 200 kbps:
- Frame transmission time (Tfr) = 1 ms.
- Vulnerable time for collisions = 2 × Tfr = 2 ms, indicating the need for timing coordination to reduce collisions.
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Description
This quiz focuses on the Data Link Layer, specifically the High-level Data Link Control (HDLC) protocol. It covers the key features and transfer modes of HDLC, including the Stop-and-Wait protocol and configurations for communication over various links. Test your understanding of this essential aspect of computer networking.
