Control Plane in Network Layer
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Questions and Answers

The two approaches to structuring the network control plane are ______ control and logically centralized control.

per-router

In Software-Defined Networking, the remote ______ computes and installs forwarding tables in routers.

controller

Routing protocols are designed to determine good ______ from sending hosts to receiving hosts.

paths

Routing is considered a top-10 networking ______.

<p>challenge</p> Signup and view all the answers

In link state routing algorithms, the net topology and link costs are known to all ______.

<p>nodes</p> Signup and view all the answers

The link cost from node x to y is denoted as c______,y.

<p>x</p> Signup and view all the answers

Routing decisions are evaluated in terms of a certain ______, such as least cost or fastest.

<p>metric</p> Signup and view all the answers

The ______ state broadcast allows all nodes to acquire information about link states in a network.

<p>link</p> Signup and view all the answers

Graph abstraction involves link costs denoted by c______,b, which represent the cost of direct links.

<p>a</p> Signup and view all the answers

In a routing context, a path is a sequence of routers packets traverse from a given initial ______ host to final destination host.

<p>source</p> Signup and view all the answers

Dijkstra's algorithm is used to find the least cost paths to ______ destinations after k iterations.

<p>k</p> Signup and view all the answers

In Dijkstra's algorithm, the notation cx,y represents the link cost from node x to ______; it is ∞ if not direct neighbors.

<p>y</p> Signup and view all the answers

D(v) indicates the current value of the cost of path from source to destination ______.

<p>v</p> Signup and view all the answers

The set N' consists of nodes whose least cost path is definitively ______.

<p>known</p> Signup and view all the answers

The complexity of Dijkstra's algorithm with n nodes is O(n^2) due to the need to check all nodes not in ______.

<p>N</p> Signup and view all the answers

A more efficient implementation of Dijkstra's algorithm using a priority queue has a complexity of O(n log ______).

<p>n</p> Signup and view all the answers

Each router must broadcast its link state information to ______ other routers.

<p>n-1</p> Signup and view all the answers

The overall message complexity in Dijkstra’s algorithm becomes O(n^2) due to each router’s message crossing O(______) links.

<p>n</p> Signup and view all the answers

An oscillation issue in Dijkstra’s algorithm can occur when link costs depend on ______ volume.

<p>traffic</p> Signup and view all the answers

Routing to destination a can be affected by traffic rates entering from ______, c, and e.

<p>d</p> Signup and view all the answers

Study Notes

Introduction to Control Plane in Network Layer

  • The network layer is responsible for forwarding packets from the source to the destination.
  • Forwarding deals with moving packets between input and output ports of the router (data plane).
  • Routing determines the route packets will take between source and destination (control plane).
  • There are two approaches to structuring the network control plane:
    • Per-router control: Each router has its own control plane elements which interact independently to decide routes.
    • Logically centralized control (SDN): A remote controller calculates and installs forwarding tables in routers.

Routing Protocols

  • Routing protocols are responsible for determining the "best" paths between hosts across a network of routers.
  • The "best" path is defined by a specific metric, such as least cost, fastest route, or least congested path.
  • Networks can be represented as graphs where nodes are routers and edges are links.
  • Link costs are assigned to each link, reflecting the cost of using that link, and determined by network operators.
  • This can be defined in different ways, for example:
    • A fixed cost of 1 for all links.
    • A cost inversely proportional to bandwidth.
    • A cost inversely proportional to congestion levels.

Routing Algorithm Classification

  • Routing algorithms are classified as either link state or distance vector protocols.
  • In link state routing, every node in the network has complete knowledge of the network topology and link costs.
  • Each node broadcasts its link state information to all other nodes, resulting in all nodes having the same information.
  • The goal is to compute the least cost paths from one node to all other nodes in the network.
  • Dijkstra's algorithm is used to calculate these paths, working iteratively by finding the least cost path to progressively larger sets of destination nodes.
  • The algorithm uses a set of variables:
    • c(x, y): Cost of the link from node x to node y (infinity if no direct link).
    • D(v): Cost of the least cost path from the source to destination node v.
    • p(v): Predecessor node on the least cost path from the source to destination node v.
    • N': Set of nodes whose least cost path is definitively known.
  • The algorithm iteratively builds the least cost path tree by tracing predecessor nodes in the graph.

Dijkstra's Algorithm: Discussion

  • Complexity: The complexity of the algorithm is O(n^2) for a network with n nodes.
  • Message Complexity: Each router broadcasts its link state information to all other routers, resulting in O(n^2) message complexity overall.

Oscillation Issue in Dijkstra's Algorithm

  • Link costs can change due to network traffic.
  • This dynamic change in link costs can cause the routing paths to constantly change, a phenomenon called route oscillation.
  • This issue can lead to inefficient network performance.

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Description

Explore the fundamentals of the control plane in the network layer, focusing on packet forwarding and routing protocols. This quiz covers the structural approaches to network control, including per-router control and logically centralized control through SDN. Test your understanding of how networks are represented and the metrics for determining optimal routing paths.

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