Table of contents
1. Functions provided by the network layer
3. Data plane and control plane
Fourth, the service model of the network layer
1. Functions provided by the network layer
The network layer implements communication between hosts and hosts
Transfer a segment from the sender host to the receiver host:
- The sending host encapsulates the segments into datagrams
- The receiving host submits the segment to the transport layer
A network layer protocol needs to be running on every host and router
- The router checks the header fields of all IP datagrams passing through it
- Then forward the datagram according to the destination IP address
datagram network
2. Routing and Forwarding
Routing and forwarding are the two main functions of the network layer
routing: Determining the path or route that a packet takes to travel from a sender to a receiver.
- determined by the routing algorithm
Forwarding: Diverting a packet from a router's input port to the correct router's output port.
analogy:
- Routing is similar to the process of planning a travel route from a sender to a receiver
- Forwarding is similar to the process of driving through an overpass
The Interaction of Routing and Forwarding
3. Data plane and control plane
The network layer can be decomposed into: data plane and control plane
1. Data plane
- exists locally
- The function of the data plane is equal to the function of each router itself
- Determines how datagrams arriving at a router's input ports are forwarded to that router's output ports
2. Control plane
- Exists across the entire network
- Determines how datagrams are routed between routers on the end-to-end path
Implementation of the control plane:
- Traditional Routing Algorithms: Implemented in Routers
- Software Defined Networking SDN: Implementing it on a Remote Server
SDN：software-defined networking
3. Control Plane: The Traditional Way
Method: Each router has a separate routing algorithm component, and the control plane is realized through interaction between routers.
4. Control plane: SDN approach
Way: through a remote controller to interact with the local control agent CA of the router.
- RC needs to know the state of the whole network
- RC needs to deliver the routing table to the router
Fourth, the service model of the network layer
Network service model: defines the end-to-end transmission characteristics of packets between sending and receiving hosts.
1. Possible services provided by the network layer
- Ensure Delivery: Ensure that the packet will eventually reach its destination.
- Guaranteed delivery with an upper bound on latency: Delivery within a specified host-to-host latency.
- Ordered Packet Delivery: Arrives at the destination in the order sent.
- Guaranteed minimum bandwidth: As long as the sender sends bits at a rate below a certain bps, the packet will eventually reach its destination.
- Guaranteed maximum latency jitter: The sender sends two consecutive packets at the same time interval as they received them.
2. Services provided by the network layer of the Internet
Provide a single service that is a best effort service.
- Final delivery of packets is not guaranteed
- End-to-end latency cannot be guaranteed
- Not guaranteed to be received in the order sent
- There is no guarantee of minimum bandwidth