Podcast
Questions and Answers
In channel partitioning, the channel is divided into smaller pieces for exclusive use by nodes.
In channel partitioning, the channel is divided into smaller pieces for exclusive use by nodes.
True
TDMA provides each station with a variable length slot in each round.
TDMA provides each station with a variable length slot in each round.
False
FDMA assigns each station a fixed frequency band to use.
FDMA assigns each station a fixed frequency band to use.
True
Random access protocols allow for divided channel usage with no possibility of collisions.
Random access protocols allow for divided channel usage with no possibility of collisions.
Signup and view all the answers
In channel partitioning, if a slot goes unused, it is made available for other nodes during that round.
In channel partitioning, if a slot goes unused, it is made available for other nodes during that round.
Signup and view all the answers
In slotted ALOHA, nodes can transmit at any time without synchronization.
In slotted ALOHA, nodes can transmit at any time without synchronization.
Signup and view all the answers
If a collision occurs in slotted ALOHA, nodes can only retransmit their frames in the subsequent slots with a certain probability.
If a collision occurs in slotted ALOHA, nodes can only retransmit their frames in the subsequent slots with a certain probability.
Signup and view all the answers
The maximum efficiency of slotted ALOHA is 1/e, which is approximately 0.37.
The maximum efficiency of slotted ALOHA is 1/e, which is approximately 0.37.
Signup and view all the answers
Slotted ALOHA allows for continuous transmission by multiple nodes without any limit.
Slotted ALOHA allows for continuous transmission by multiple nodes without any limit.
Signup and view all the answers
Collisions in slotted ALOHA can waste transmission slots.
Collisions in slotted ALOHA can waste transmission slots.
Signup and view all the answers
All frames in slotted ALOHA must be of different sizes to function properly.
All frames in slotted ALOHA must be of different sizes to function properly.
Signup and view all the answers
Slotted ALOHA is a highly decentralized protocol.
Slotted ALOHA is a highly decentralized protocol.
Signup and view all the answers
An ARP table contains IP address and MAC address mappings for nodes on a LAN.
An ARP table contains IP address and MAC address mappings for nodes on a LAN.
Signup and view all the answers
The Time To Live (TTL) for an ARP address mapping is typically 10 minutes.
The Time To Live (TTL) for an ARP address mapping is typically 10 minutes.
Signup and view all the answers
A node will forget an ARP mapping after the TTL expires.
A node will forget an ARP mapping after the TTL expires.
Signup and view all the answers
A sends a datagram to B if B's MAC address is found in A's ARP table.
A sends a datagram to B if B's MAC address is found in A's ARP table.
Signup and view all the answers
A can send a datagram to B without the need for a MAC address.
A can send a datagram to B without the need for a MAC address.
Signup and view all the answers
Each IP node on a LAN has a unique ARP table.
Each IP node on a LAN has a unique ARP table.
Signup and view all the answers
If A's ARP table already contains B’s MAC address, A needs to request it again.
If A's ARP table already contains B’s MAC address, A needs to request it again.
Signup and view all the answers
The MAC address format contains numbers and letters separated by hyphens.
The MAC address format contains numbers and letters separated by hyphens.
Signup and view all the answers
A can send data to B even if B’s IP address is not present in A's ARP table.
A can send data to B even if B’s IP address is not present in A's ARP table.
Signup and view all the answers
A frame is forwarded on the interface indicated by the entry if its destination is known.
A frame is forwarded on the interface indicated by the entry if its destination is known.
Signup and view all the answers
Frames are always dropped if their destination is on the same segment from which the frame arrived.
Frames are always dropped if their destination is on the same segment from which the frame arrived.
Signup and view all the answers
Flooding occurs when no entry is found for the destination.
Flooding occurs when no entry is found for the destination.
Signup and view all the answers
The switch table is initially empty and contains no MAC addresses.
The switch table is initially empty and contains no MAC addresses.
Signup and view all the answers
A switch uses the TTL value in the MAC address table to determine the lifespan of an entry.
A switch uses the TTL value in the MAC address table to determine the lifespan of an entry.
Signup and view all the answers
A switch forwards frames to all connected interfaces regardless of the destination.
A switch forwards frames to all connected interfaces regardless of the destination.
Signup and view all the answers
Switches can be interconnected to enhance network communication.
Switches can be interconnected to enhance network communication.
Signup and view all the answers
Self-learning is the process by which a switch learns the MAC addresses of devices in the network.
Self-learning is the process by which a switch learns the MAC addresses of devices in the network.
Signup and view all the answers
When sending a frame from A to G, the frame will always take the shortest path through the switches.
When sending a frame from A to G, the frame will always take the shortest path through the switches.
Signup and view all the answers
Link-level reliability is seldom used on low bit-error links like fiber.
Link-level reliability is seldom used on low bit-error links like fiber.
Signup and view all the answers
Error correction allows the receiver to identify and correct bit errors without requiring retransmission.
Error correction allows the receiver to identify and correct bit errors without requiring retransmission.
Signup and view all the answers
In half-duplex communication, nodes can transmit simultaneously.
In half-duplex communication, nodes can transmit simultaneously.
Signup and view all the answers
The link layer is typically implemented in an adaptor, also known as a network interface card (NIC).
The link layer is typically implemented in an adaptor, also known as a network interface card (NIC).
Signup and view all the answers
Flow control manages pacing between sending and receiving nodes.
Flow control manages pacing between sending and receiving nodes.
Signup and view all the answers
Error detection is 100% reliable.
Error detection is 100% reliable.
Signup and view all the answers
Cyclic redundancy check is a more powerful error-detection coding method.
Cyclic redundancy check is a more powerful error-detection coding method.
Signup and view all the answers
The Internet checksum is used at the network layer.
The Internet checksum is used at the network layer.
Signup and view all the answers
Two-dimensional bit parity can only detect single bit errors.
Two-dimensional bit parity can only detect single bit errors.
Signup and view all the answers
Errors can still occur even if the checksum matches.
Errors can still occur even if the checksum matches.
Signup and view all the answers
Larger EDC fields generally lead to better detection and correction.
Larger EDC fields generally lead to better detection and correction.
Signup and view all the answers
Parity checking can detect both single and multiple bit errors.
Parity checking can detect both single and multiple bit errors.
Signup and view all the answers
A cyclic redundancy check (CRC) can detect all burst errors less than r+1 bits.
A cyclic redundancy check (CRC) can detect all burst errors less than r+1 bits.
Signup and view all the answers
Multiple access protocols only function effectively in point-to-point links.
Multiple access protocols only function effectively in point-to-point links.
Signup and view all the answers
Collision occurs when one node receives signals from multiple other nodes simultaneously.
Collision occurs when one node receives signals from multiple other nodes simultaneously.
Signup and view all the answers
An ideal multiple access protocol requires synchronization between nodes.
An ideal multiple access protocol requires synchronization between nodes.
Signup and view all the answers
In a broadcast channel, each node can send data at the same rate regardless of the number of other nodes transmitting.
In a broadcast channel, each node can send data at the same rate regardless of the number of other nodes transmitting.
Signup and view all the answers
Ethernet is an example of a point-to-point link.
Ethernet is an example of a point-to-point link.
Signup and view all the answers
The communication about channel sharing must use the channel itself.
The communication about channel sharing must use the channel itself.
Signup and view all the answers
A point-to-point link can include a PPP connection for dial-up access.
A point-to-point link can include a PPP connection for dial-up access.
Signup and view all the answers
R in a broadcast channel signifies the total transmission rate that can be shared by nodes.
R in a broadcast channel signifies the total transmission rate that can be shared by nodes.
Signup and view all the answers
TDMA allows each station access to the channel in fixed length slots during each round.
TDMA allows each station access to the channel in fixed length slots during each round.
Signup and view all the answers
In FDMA, each station is assigned a variable frequency band.
In FDMA, each station is assigned a variable frequency band.
Signup and view all the answers
Random access protocols require nodes to synchronize before transmitting data.
Random access protocols require nodes to synchronize before transmitting data.
Signup and view all the answers
Channel partitioning MAC protocols include techniques such as TDMA and FDMA.
Channel partitioning MAC protocols include techniques such as TDMA and FDMA.
Signup and view all the answers
In random access protocols, collisions between nodes are not permitted.
In random access protocols, collisions between nodes are not permitted.
Signup and view all the answers
TDMA is designed such that unused time slots go idle.
TDMA is designed such that unused time slots go idle.
Signup and view all the answers
FDMA divides the channel spectrum into time slots.
FDMA divides the channel spectrum into time slots.
Signup and view all the answers
In ‘taking turns’ protocols, nodes with more data can take longer turns.
In ‘taking turns’ protocols, nodes with more data can take longer turns.
Signup and view all the answers
Channel partitioning MAC protocols allow for simultaneous communication by all nodes.
Channel partitioning MAC protocols allow for simultaneous communication by all nodes.
Signup and view all the answers
Study Notes
Chapter 5: Link Layer
- PowerPoint slides are freely available for faculty, students, and readers
- Slides can be modified, added to, and edited to suit needs
- Slides are the result of considerable work
- In return for use, only ask that origin is cited if used in a class or on a website
- Copyright of the material should be noted
- Slides are freely available for faculty, students, and readers.
Goals
- Understand principles behind link layer services
- Error detection and correction
- Sharing a broadcast channel (multiple access)
- Link layer addressing
- Local area networks (e.g., Ethernet, VLANs)
- Various link layer technologies
Link Layer, LANs: Outline
- Introduction and services
- Error detection and correction
- Multiple access protocols
- LANs (addressing, ARP, Ethernet, switches, VLANs)
- Link virtualization (MPLS)
- Data center networking
- A day in the life of a web request
Link Layer: Introduction
- Hosts and routers are nodes
- Communication channels connect adjacent nodes along communication paths (links)
- Links include wired and wireless links
- Layer-2 packet (frame) encapsulates datagram
Link Layer: Context
- Datagram transfer by different protocols over different links (e.g., Ethernet on first link, frame relay on intermediate links, 802.1 on last link)
- Different link protocols provide different services (e.g., may or may not provide reliable data transfer (RDT) over a link)
- A transportation analogy explaining concepts like trip, tourist, transportation mode can be useful.
Link Layer Services
- Framing and link access: encapsulate datagram into frame, add header and trailer for channel access if shared medium. Use MAC addresses to identify source and destination, which differ from IP addresses
- Reliable delivery between adjacent nodes
- Wireless links exhibit higher error rates than wired links
Link Layer Services (More)
- Flow control: pacing between adjacent sending and receiving nodes
- Error detection: errors from signal attenuation and noise, receivers detect errors and signals sender about need for retransmission.
- Error correction: receiver identifies and corrects any bit errors without resorting to retransmission.
- Half-duplex and full-duplex: with half-duplex both ends can transmit, but not simultaneously.
Where is the Link Layer Implemented?
- Link layer is implemented in each host
- Implementation takes place in a network adapter card (NIC) or chip
- Components include Ethernet card, 802.11 card, Ethernet chipset, implementing link, and physical layer that attaches to host's system buses. The implementation combines hardware, software, and firmware
Adaptors Communicating
- Sending side: encapsulates datagram into frame, adds error checking bits, manages RDT and flow control.
- Receiving side: looks for errors and uses RDT and flow control to extract and pass datagram to upper layer.
Ethernet Frame Structure
- Preable: 7 bytes with pattern 10101010 followed by 1 byte with pattern 10101011, used to synchronize receiver and sender clock rates.
- Addresses: 6-byte source and destination MAC addresses
- Type: indicates higher-layer protocol (commonly IP, but others like Novell IPX, AppleTalk are possible)
- Data (payload): actual data being transmitted
- CRC: cyclic redundancy check at receiver; used to detect errors and dropped if detected
Ethernet: Unreliable, Connectionless
- Connectionless: no handshaking (no acknowledgment) between sending and receiving network interface cards (NICs)
- Unreliable: data recovery depends on higher-layer protocols, such as TCP, to handle lost segments.
802.3 Ethernet Standards
- Many Ethernet standards exist for different speeds and physical media
- A common protocol and frame format exists
Ethernet Switch
- Takes an active role and store / forwards Ethernet frames
- Examines MAC addresses and selectively forwards frames to the appropriate port
- Uses CSMA/CD protocol to access the segment
Switch: Multiple Simultaneous Transmission
- Hosts have dedicated connections to the switch, switches buffer incoming packets, no collisions
- Each link is a collision domain
Switch Forwarding Table
- Addresses how a switch determines how to reach a destination via a specific interface. The contents of the switch table are similar in structure to a routing table
- Entries contain (MAC address of destination, interface to reach destination, time stamp)
Switch: Self-Learning
- Switches learn which hosts are on which interfaces
- Upon receiving a frame, the switch learns the sender’s location (incoming LAN segment)
- Records the sender/location pair in the switch table
Interconnecting Switches
- One or more switches can be connected together. If a switch learns a new MAC address, it will be added to all switch tables.
VLANs: Motivation
- VLANs allow users to change location without changing network connections
- Users are put into the same virtual LAN (VLAN). The same physical switch can handle multiple VLANs concurrently
VLANs
- Port-based VLANs: grouped by switch management software; single physical switch can support multiple VLANs.
- VLANs can be configured to define multiple virtual LANs over one physical LAN.
- Dynamic membership: ports can be dynamically assigned to multiple VLANs
- Forwarding between VLANs: done via routing
VLANs Spanning Multiple Switches
- Trunk ports are used to carry frames across multiple switches
802.1Q VLAN Frame Format
- 802.1q protocol adds an extra header to the frame to provide Virtual Local Area Network (VLAN) identification
Multiprotocol Label Switching (MPLS)
- Goal: High-speed forwarding for IP packets using fixed-length labels instead of IP addresses
- Fast lookups use fixed-length identifiers, borrowed from virtual circuit (VC) approach
MPLS Capable Routers
- Forward packets based on label values without inspecting the IP address
- MPLS forwarding tables distinct from IP forwarding tables
MPLS vs. IP Paths
- In IP routing, the path is determined only by the destination address
- MPLS can use different routes for the same destination (often based on source address or other parameters)
MPLS Signaling
- Modifies OSPF, IS-IS link-state flooding protocols to include information used in MPLS routing (e.g., link bandwidth information)
MPLS Forwarding Tables
- Forwarding tables within MPLS routers show routing entries for forwarding packets based on labels
Data Center Networks
- Large numbers of closely coupled hosts (tens or hundreds of thousands) often located in close proximity
- Common applications include e-business, content services, and search engines
Data Center Networks: Load Balancers
- Application-layer routing distributes incoming application requests among server racks based on various parameters (e.g. workload balancing)
Data Center Networks: Interconnection
- Rich interconnection between switches and racks is common in data centers
- This approach increases throughput, and redundancy
Synthesis: A Day in the Life of a Web Request
- Protocol stack (application, transport, network, link) work together
- The scenario outlines the interactions of the client's browser, network, DNS server, web server, and other components
A Day in the Life: scenario
- Illustrates the steps involved in a typical internet request from browser to website, including DHCP, DNS, ARP, TCP, and HTTP protocols
A Day in the Life... Connecting to the Internet
- The steps in the process of a laptop connecting to the Internet via DHCP include a request for DHCP, the router running DHCP, and the DHCP server providing the requested IP address information
A Day in the Life... ARP (before DNS, before HTTP)
- Steps involved in ARP, encapsulating the request in a packet, and broadcasting the request on the network; routing the received reply back
A Day in the Life… Using DNS
- Explains the use of different protocols (e.g., DNS, IP, various networking protocols involved in routed traffic) to determine the IP address of the desired web server
A Day in the Life… TCP Connection Carrying HTTP
- The steps in the 3-way handshake process necessary to establish TCP connection to send a web request through the network. The steps involve SYN, SYNACK, and ACK
A Day in the Life… HTTP Request/Reply
- Steps in the HTTP request/reply process to access and display a webpage (includes transmission/reception of the desired HTML page)
Chapter 5: Summary
- Principles of data link layer services, technologies (e.g., Ethernet, VLANs, switched LANs, MPLS)
- Overview of a day's worth of networking protocols for a web request
Chapter 5: Let's Take a Breath
- Overview of network principles and practices, important to consider additional topics if needed
- Topics for consideration: Wireless, multimedia, security, and network management
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
This quiz covers key concepts of channel partitioning and multiple access protocols, particularly focusing on TDMA, FDMA, and slotted ALOHA. Explore how these protocols handle channel usage, manage collisions, and optimize efficiency in communication systems.
