Network layer functions and protocols.

Network layer functions and protocols:)

Network layer:

• Transport segment from sending to receiving host.
• On the sending side encapsulates segments into datagrams.
• On the receiving side, it delivers segments to the transport layer.
• Network layer protocols in every host, router.
• The router examines header fields in all IP datagrams passing through it.

Two key network-layer functions:

1. Network-layer functions:
Forwarding: move packets from router’s input to appropriate router output
Routing: determine the route taken by packets from source to destination routing algorithms
2. Analogy: taking a trip:
Forwarding: the process of getting through a single interchange
Routing: the process of planning a trip from source to destination
Network layer: data plane, control plane

Data plane:
the local, per-router function that determines how datagram arriving on router input a port is forwarded to the router output port and forwarding function.
Control plane:
Network-wide logic that determines how datagram is routed among routers along the end-end path from the source host to destination host
Two control-plane approaches:
1. Traditional Routing Algorithms: implemented in routers
2.  Software-Defined Networking (SDN): implemented in (remote) servers
The per-router control plane (Traditional Approach): Individual routing algorithm components in each and every router interact in the control plane.
The logically centralized control plane (SDN Approach): A distinct (typically remote)  Controller interacts with local and Control agents (CAs).