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Questions and Answers
What is the primary function of Medium Access Protocols?
Which of the following standards is NOT classified under the IEEE standards for Medium Access Protocols?
What type of addressing is implemented within the Network Interface Controller (NIC)?
What happens if an acknowledgment (ACK) is not received after a data transmission in the ALOHA protocol?
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How does access to the medium occur in the ALOHA protocol?
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What is a characteristic feature of the ALOHA protocol?
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Which of the following best describes the delay mechanism in ALOHA after sending data?
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Which network topology does the ALOHA protocol primarily support?
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What is the main improvement of slotted ALOHA over pure ALOHA?
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In CSMA/CD, what is the first action taken by a host wanting to transmit?
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What happens when a collision is detected in CSMA/CD?
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What does each station in slotted ALOHA wait for before transmitting?
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What is the outcome of too many collisions occurring in pure ALOHA?
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Which mechanism is used to detect collisions in CSMA/CD?
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In pure ALOHA, when can collisions occur?
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What does the algorithm in CSMA/CD do after too many collisions are detected?
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What is the maximum frame size for Ethernet II?
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What does CSMA/CD stand for in the context of Ethernet?
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Which field indicates the start of a frame in the Ethernet 802.3 Frame Format?
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In an Ethernet MAC address, what does OUI stand for?
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What is the data transmission speed of standard Fast Ethernet?
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Which topology is used by Ethernet?
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What is the purpose of the Control Field in the 802.2 LLC Header?
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What is the delay time between Ethernet frames?
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What does CSMA/CD stand for?
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Which IEEE standard is associated with Wireless PANs?
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Who developed Ethernet and in what year?
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What was the operating speed of the original Ethernet introduced by Dr. Metcalfe?
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Which standard laid out the 10Mbps Ethernet specification?
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Which of the following is NOT part of the IEEE 802 standards for networking?
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The IEEE 802.4 standard is designed for which type of network?
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What layer is covered by the IEEE 802.2 standard?
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What does the acronym PMA stand for in Gigabit Ethernet?
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How many octets does the Destination Address field occupy in the IEEE 802.3 frame format?
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Which layer is responsible for the mapping between physical layer signaling primitives and signals on GMII?
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Which of these components is part of the architecture for Gigabit Ethernet?
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In the Gigabit Ethernet frame format, how many octets are used for the Length/Type field?
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What is the purpose of the Start-of-Frame Delimiter in Ethernet frames?
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Which of the following correctly describes the Medium Access Control layer?
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What medium speed does the Gigabit Ethernet frame format target?
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Study Notes
Medium Access Protocols
- Medium Access Protocols (MAC Protocols) are used to control how devices share a common communication channel in a network.
- MAC protocols define addressing systems that make it possible for each node on a network to be uniquely identified.
- Wired networks use cabling, while wireless networks use radio waves as their shared medium for communication.
- MAC protocols are essential for managing communication in networks with multiple devices sharing resources.
Addressing
- Each Network Interface Controller (NIC) contains the hardware to carry out addressing.
- A MAC header is added to the beginning of each packet to ensure it reaches the correct node on the network.
- This header contains address fields for both the sender (source) and receiver (destination) of the packet.
Access Methods
- Access methods used by MAC protocols are standardized by organizations such as the IEEE, ATM Forum, and ANSI.
- Common IEEE standards include Aloha (pure and slotted), CSMA/CD, Token Bus, Token Ring, and 802.11 (Wi-Fi).
- The ANSI standard is FDDI, Fiber Distributed Data Interface.
- ATM Forum developed the Asynchronous Transfer Mode (ATM) standard.
Aloha
- Aloha is the earliest MAC protocol and was devised by Norman Abramson and colleagues at the University of Hawaii in the early 1970s.
- Aloha operates at layer 2 (Data Link Layer) of the OSI model and uses broadcast topology.
- There is no central control with Aloha, and access to the medium is random.
- Stations can send data at any time.
- After transmission, the sender listens to the channel for a period equal to twice the time it takes for a packet to reach the furthest node.
- If no acknowledgement (ACK) is received within a certain time, the packet is re-transmitted.
- All stations use the same frequency in Aloha.
- Ethernet evolved from Aloha.
Slotted Aloha
- Pure Aloha suffers from decreased throughput when a large number of stations are connected to the network.
- Slotted Aloha organizes the channel time into uniform time slots, where the duration of each slot is equal to packet transmission time.
- Stations must wait until the start of the next slot to send data, eliminating overlapping of packets and reducing collisions.
CSMA/CD
- CSMA/CD stands for Carrier Sense Multiple Access with Collision Detection.
- This protocol encapsulates data into frames and waits for the network to be free before beginning transmission.
- Transmission starts after the network has been idle for a period known as the Interframe Gap (IFG).
- If a collision is detected during transmission, a jam signal is sent and the station waits for a random amount of time before trying again.
- Collisions are detected by monitoring changes in voltage.
IEEE LAN Standards
- IEEE 802.3 defines CSMA/CD.
- IEEE 802.4 defines Token Bus.
- IEEE 802.5 defines Token Ring.
- IEEE 802.11 defines Wireless Local Area Networks (Wi-Fi).
- IEEE 802.15 defines Wireless Personal Area Networks (WPANs).
- IEEE 802.16 defines WiMAX, a broadband wireless access technology.
Ethernet
- Ethernet was developed by Robert Metcalfe while he was a researcher at Xerox PARC in 1976.
- The first iterations of Ethernet had a data rate of 2.94 Mbps, which is significantly slower than contemporary networks.
Ethernet Versions
- Ethernet II was developed in 1980 by a consortium of companies (DEC, Intel, Xerox) called DIX.
- Ethernet II was an early standard that used thick coaxial multidrop cables and supported 10 Mbps data rates.
- Ethernet in conjunction with IEEE 802.3 standardizes the PMD, PHY, and MAC layers of Ethernet.
- The LLC layer of Ethernet conforms to the IEEE 802.2 standard, which is used for a variety of networking technologies.
Ethernet II
- Ethernet II utilizes Manchester coding for signaling and operates at a fixed rate of 10 Mbps.
- The protocol uses CSMA/CD for bandwidth sharing and supports frames between 64 and 1518 bytes.
- Additionally, the protocol uses a 64-bit preamble at the beginning of a frame and requires a gap of 9.6μs between frames.
- Ethernet uses bus topology and is considered a passive network, meaning only transmitting stations are detectable.
Ethernet 802.3 Frame Format
- Ethernet 802.3 frames have the following components:
- Preamble: 7 bytes for synchronization.
- Start Frame Delimiter (SFD): 1 byte to mark the beginning of a frame.
- Destination Address: 6 bytes.
- Source Address: 6 bytes.
- Length/Type: 2 bytes, where type describes the protocol in the frame and length indicates the size of the data.
- Data: 46 to 1500 bytes, containing the actual information being transmitted.
- Frame Check Sequence (FCS): 4 bytes, used to error detection.
- The IEEE 802.2 Logical Link Control (LLC) header is added within the data, containing:
- Destination Service Access Point (DSAP): 1 byte that identifies the receiving protocol.
- Source Service Access Point (SSAP): 1 byte that identifies the sending protocol.
- Control Field: 1 to 2 bytes that represent the message type (e.g., supervisory, information, or unnumbered).
The 802.3 MAC Address
- The 802.3 MAC address is 48 bits long and divided into three sections:
- Individual/Group (I/G): 1 bit that indicates whether the address is for an individual station or a group of stations.
- Universal/Local (U/L): 1 bit that indicates the scope of the address (universal: global scope; local; local network)
- Organizationally Unique Identifier (OUI): 22 bits, identifies the manufacturer of the NIC.
- MAC addresses are unique and are assigned to each NIC by the manufacturer.
Gigabit Ethernet
- Gigabit Ethernet is a high-speed evolution of Ethernet that provides data rates of 1 Gbps (1000 Mbps), significantly faster than traditional Ethernet.
- Gigabit Ethernet incorporates the GMII (Gigabit Media Independent Interface) and includes a separate physical layer for signaling at higher speeds.
- The reconciliation layer in Gigabit Ethernet maps signals between the GMII and the physical layer of the network.
- The physical layer of Gigabit Ethernet is subdivided into PMA, PCS, and PMD:
- PMA: Physical Media Attachment, responsible for controlling the physical interface.
- PCS: Physical Coding Sublayer, performs data encoding and decoding.
- PMD: Physical Media Dependent, manages transmission and reception of signals over the medium.
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Description
Test your knowledge on Medium Access Protocols and their role in network communication. This quiz covers MAC protocols, addressing methods, and access methods that facilitate network resource sharing. Understand how devices are uniquely identified and how they communicate over wired and wireless networks.
