4: The Network Layer Flashcards
What is a network service model?
A list of criteria and desired properties of network functionality
What is switching via a bus?
Packets directly transferred from input to output ports over a shared bus, which allows 1 packet through at a time. High traffic can cause buffering in the bus.
What is priority scheduling?
Assigning priorities to each packet, and sending the packet with the highest priority first.
What is generalised forwarding?
A variant of decentralised switching in which packets can be forwarded according to any combination of their header values.
Whar is the control plane?
The section of a router’s architecture that provides the logic determining the topology of the whole network.
What is a subnet?
A subset of a network divided by an interface on a router. The subnet part of an IP address is the high order bits; the low order bits distinguish hosts within a subnet.
What is software-defined networking?
Remote servers contain the control plane logic for routers.
What is the ICMP protocol?
The Internet Control Message Protocol (ICMP) is a network-level protocol that seeks to assist network functionality be reporting errors and operational information, including to routers.
What is decentrailised switching?
Using header values in inbound segments to forward them to an output port as per the forwarding table in the memory of the port they came in on.
What are switching fabrics?
The topology of a network using switches that defines how the switches are placed and connected, and how data are switched in the network.
What is a forwarding table?
A mapping of input to output interfaces used in forwarding in a router.
What is longest prefix matching?
Using the longest address prefix that matches destination address when looking for forwarding table entry for a given destination address, to minimise the number of hops to the destination after the next one.
What is FIFO (first in first out) scheduling?
Sending out packets in a buffer/queue in the same order they arrive.
What is a network bus?
A common linear half-duplex link to which all nodes are connected.
What is switching via memory?
When a traditional computer acts as a switch, taking a packet into memory, processing it to find the associated output port, then sending it there.
What is an interconnection network?
High-speed computer networks with ndoes specialised to memory and processing.
What is switching via interconnection network?
When you use the distributed processors in interconnection networks to process the packets being switched in parallel to optimise performance and overcome bus bandwidth limitations.
What is the concept of IP fragmentation and reassembly?
Networks have MTUs - the largest possible link-level frames - so if these are exceeded then IP datagrams are fragmented into smaller ones and reassembled at the final destination.
What is Head-of-the-Line (HOL) blocking?
When a slow datagram at the front of the queue at an input port in a switch prevents others in the queue from moving forward.
What is buffering?
When high traffic means packets are entered into a queue and processed one at a time, in the order they arrived.
What is a scheduling discipline?
Algorithms used for distributing resources among parties which simultaneously and asynchronously request them.
What is the NAT protocol?
Network address translation is a method of using one IP address to represent a private subnet to relieve IPv4 address exhaustion.
What is output port queueing?
When you buffer multiple packets contending for access to the same output port on a switch, and the arrival rate of packets exceeds the output line speed of the port.
What is Round Robin (RR) scheduling?
Sort packets into groups called classes and cyclically output a packet from each class, internally ordered chronologically.
