data link 3

Data-Link Layer: This is the second layer in the TCP/IP protocol suite1 .... It is responsible for communication between two adjacent nodes (node-to-node communication), whether the link is dedicated or broadcast3 . The data-link layer at one device communicates logically with the data-link layer at the next device in the path1 . This layer is the foundation on which local area networks (LANs) and wide area networks (WANs) are built4 .

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Nodes: In the context of the data-link layer, nodes refer to the two end hosts and any intermediate routers that a data unit passes through in an internetwork5 ....

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Links: The networks (LANs and WANs) that connect the nodes are referred to as links5 ....

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Point-to-Point Link: A type of link where the connection is dedicated to communication between two devices, utilizing the full capacity of the medium6 . An example is a traditional home phone line in use6 .

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Broadcast Link: A type of link where the transmission medium (like air or a shared cable) is shared among several pairs of devices, meaning the capacity is not dedicated6 . Cellular phone communication is an example6 ....

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Data-Link Control (DLC): This is one of the two sublayers of the data-link layer3 .... It deals with procedures for communication between two adjacent nodes, regardless of whether the link is dedicated or broadcast3 . Its functions include framing and error control3 .

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Media Access Control (MAC): This is the second sublayer of the data-link layer4 .... It specifically deals with issues related to broadcast links, managing how multiple devices share the common transmission medium7 ....

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Framing: A function of the data-link layer (specifically the DLC sublayer) that involves packing bits received from the physical layer into frames3 .... This makes each message distinguishable by adding a sender and a destination address9 .... Flags can be used to delimit variable-size frames11 .

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Error Control: A responsibility of the DLC sublayer that deals with detecting and possibly correcting data corruption that occurs during transmission3 .... Techniques like checksum can be used for error detection, although in the Internet, checksum is mostly used at the network and transport layers13 . Block codes are a category of error-detecting (and correcting) codes14 .

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High-Level Data-Link Control (HDLC): A bit-oriented data-link control protocol used for communication over point-to-point and multipoint links12 .... It defines three types of frames: information frames (I-frames) for user data, supervisory frames (S-frames) for control information, and unnumbered frames (U-frames) for system management16 . HDLC supports transfer modes like normal response mode (NRM), where one primary station controls multiple secondary stations, and asynchronous balanced mode (ABM), used for point-to-point links where each station acts as a peer15 .... HDLC frames contain fields like a beginning flag, address, control, information, frame check sequence (FCS) for error detection, and an ending flag16 ....

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Point-to-Point Protocol (PPP): A byte-oriented data-link control protocol commonly used for point-to-point links12 .... PPP uses a set of protocols for establishing the link (Link Control Protocol (LCP)), authenticating parties (Authentication Protocols (APs)), and carrying network-layer data (Network Control Protocols (NCPs))18 .

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Media Access Protocols: These are protocols designed to manage access to a shared link (broadcast links) when multiple users or devices need to transmit8 .... They are categorized into random access methods (like Aloha and CSMA), controlled access methods (like polling), and channelization19 .

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Random Access: In these methods, no station has priority, and each station decides whether to transmit based on the state of the medium (idle or busy) following predefined procedures19 . Examples include pure ALOHA and slotted ALOHA12 ....

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Controlled Access: In these methods, the access to the shared medium is controlled. Polling is an example where a primary device queries secondary devices to see if they have data to transmit19 .... The primary uses a select function to alert a secondary about an upcoming transmission21 .

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Link-Layer Addresses: These are addresses that belong to the data-link layer and are used to identify the source and destination of a frame within a specific link in a connectionless internetwork22 .... They are also called physical addresses or MAC addresses and are added to the frame header23 . These addresses change as the frame moves from one link to another23 .... Ethernet LANs commonly use 48-bit (6-byte) unicast and multicast link-layer addresses26 .

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Address Resolution Protocol (ARP): An auxiliary protocol defined in the network layer that is used to map network-layer addresses (like IP addresses) to link-layer addresses (like MAC addresses)24 .... This is necessary because in a connectionless internetwork like the Internet, IP addresses alone are not sufficient to route a datagram through each link to its destination22 .

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Hamming Distance: This is the number of differing bits between two codewords. It is a concept used in error detection and correction5 .

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Normal Response Mode (NRM): A transfer mode in HDLC where one primary station controls communication with multiple secondary stations6 .

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Asynchronous Balanced Mode (ABM): A transfer mode in HDLC used for point-to-point links where each station acts as a peer (both can initiate transmission)6 . This is the common mode used today6 .

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Information Frames (I-frames): One of the three types of frames defined in HDLC. I-frames are used to transport user data and control information related to user data (piggybacking)6 .

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Supervisory Frames (S-frames): Another type of HDLC frame used solely for transporting control information6 .

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Unnumbered Frames (U-frames): The third type of HDLC frame, reserved for system management. Information carried by U-frames is intended for managing the link itself6 .

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Frame Check Sequence (FCS): A field in an HDLC frame used for error detection6 .

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Random Access or Contention Methods: A category of media access protocols where no station is superior, and each decides whether to transmit based on the medium's state following predefined procedures7 .

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Vulnerable Time: In the context of random access protocols like ALOHA and CSMA, this is the time period during which a collision can occur if another station transmits8 .

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Persistence Methods: These methods define what a station should do if the shared channel is busy or idle in CSMA protocols. The three main methods are 1-persistent, nonpersistent, and p-persistent8 .

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1-Persistent: After finding the line idle, the station transmits immediately with a probability of 18 . Ethernet traditionally used this method8 ....

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Nonpersistent: If the channel is busy, the station waits a random amount of time before sensing the channel again8 .

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p-Persistent: When the channel is idle, the station transmits with a probability p. With a probability of (1-p), it waits for the beginning of the next time slot and repeats the process8 . This method is used in systems with slotted channels8 .

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Carrier Sense Multiple Access (CSMA): A random access method where a station senses the medium before attempting to transmit. It tries to avoid collisions by listening8 .

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Carrier Sense Multiple Access with Collision Detection (CSMA/CD): An enhancement of CSMA where a station monitors the medium for collisions after it starts transmitting. If a collision is detected, the transmission is stopped10 . Traditional Ethernet (10 Mbps) used a 1-persistent CSMA/CD method9 .

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Jamming Signal: A short signal sent by a station in CSMA/CD after detecting a collision to ensure all other stations become aware of it10 .

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Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA): Another variation of CSMA used in wireless LANs to avoid collisions rather than detect them after they occur9 . The discussion of CSMA/CA is postponed until Chapter 4, which covers wireless LANs9 .

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Address Resolution Protocol (ARP): An auxiliary protocol defined in the network layer used to map network-layer addresses (like IP addresses) to link-layer addresses (like MAC addresses)11 ....

These terms are crucial for understanding the concepts and protocols discussed in Chapter 33 .... Reviewing their definitions will provide a more comprehensive understanding of the data-link layer