Final Exam Flashcards
What is hot potato routing?
A network routing strategy is where a data packet is forwarded to the next nearest node as quickly as possible, regardless of the overall path efficiency. The main goal is to minimize the time a packet spends in transit within a network, as opposed to optimizing for the shortest or least congested path.
Give a technique that addresses the count-to-infinity problem incurred by the distance vector algorithm.
Implementation of a split horizon with poison reverse. Split horizon prevents a node from advertising a route back to the node it learned the route from. Poison reverse actively advertises an infinite metric for routes learned from a neighboring node back to that node.
What is split horizon?
A loop prevention technique used in distance vector routing algorithms. It prohibits a router from advertising a route back to the node it learned the route from.
What is poison reverse?
A loop prevention technique used in distance vector routing algorithms. It involves a router advertising an infinite metric back to the source node for the routes it has learned from that node.
In a wireline local area network implementing the carrier sensing multiple access (CSMA) based medium access control, what factors may negatively impact the network
throughput?
Collisions, overhead, propagation delay, limited channel capacity, hidden and exposed node problems.
What is a collision?
A collision is when two or more nodes transmit data simultaneously. This can lead to data loss and retransmissions. Reducing the overall throughput.
What is overhead?
The non-data communication, such as control messages, acknowledgments, and protocol-specific mechanisms required to maintain a network. Overhead consumes a portion of the network’s bandwidth and reduces the effective throughput available for data transmission.
What is propagation delay?
The time it takes for a signal to travel from the sender to the receiver in a network. Determined by factors such as physical distance between nodes, transmission medium, and the signal’s speed.
What is channel capacity?
The maximum data rate that can be transmitted through a communication channel. Limited channel capacity arises when the demand or transmission from multiple nodes exceeds the available bandwidth of the shared medium.
What is the hidden node problem?
Occurs when two nodes, A and C, are unable to directly communicate or detect each others signals but share a common node, B, that can communicate with A and C. A may not be aware of C and send a transmission to B, causing a collision.
What is the exposed node problem?
When a node B, can hear transmission from both the sender and intended receiver. Node B might necessarily defer its own transmission thinking it would cause a collision at the receiver.
In a data center network, what technique can help improve the host-to-host communication throughput?
Using multi-path routing as it enables the distribution of network traffic across multiple paths between source and destination nodes. (ex. equal-cost multi-path routing and the use of multi-rooted, fat-tree topologies)
What is CSMA?
Carrier sense multiple access. Listens before transmitting. If the channel is idle, the entire frame is sent. If the channel is busy, the transmission is deferred. (ex. don’t interrupt others)
What is ALOHA?
A random access protocol. A node transmits data whenever it has a packet to send. If the transmission is successful, the node receives an acknowledgement from the receiver. If not, the node waits for a random period of time and retransmits the packet.
What are the drawbacks of ALOHA?
Low efficiency due to frequent collisions when the network is heavily loaded.
What is S-ALOHA?
Slotted ALOHA. An improved ALOHA. Divides time into discrete intervals or slots, and nodes can only transmit data at the beginning of a time slot. This reduces the probability of collisions.
What is CSMA/CD?
CSMA is primarily used in wired Ethernet networks. Adds collision detection to allow nodes to identify when a collision occurs during transmission. If a collision is detected, the node stops transmitting and waits for a random period, and tries again. Reduces the duration of collisions.
What is CSMA/CA?
Another variation of CSMA is often used in wireless networks such as Wi-FI. Focuses on collision avoidance. Nodes use a random backoff mechanism after sensing an idle channel helping to reduce the probability of simultaneous transmissions and collisions.
When people design a wireless medium access control (MAC) protocol, why the collision detection mechanism (used in Ethernet) could not be applied effectively?
Wireless signals are susceptible to fading, interferences, and attenuation as they propagate. As a result, detecting the difference between a collision and a weak signal is challenging. Also, the hidden node problem would deem the collision detection mechanism ineffective.
What is random backoff?
Used in MAC protocols such as CSMA to reduce the probability of collisions when multiple nodes attempt to transmit data simultaneously. When a node sense a busy channel or collision, it waits a random period before attempting to transmit again.
What is a centralized routing algorithm?
A single node or controller computes and maintains the routing information for the entire network. Requires global knowledge of the network topology and state. More computationally intensive due to processing times.
