quartz/content/notes/19-network-layer-data-plane.md

title	aliases	tags
19-network-layer-data-plane		cosc203 lecture

• transport layer messages are divided into segments
• passed to network layer
  • sender: encapsulates segments into IP packets, passes to link layer
  • reciever: deliver segments to tranport layer protocol
  • sender and reciever are connected by multple routers
• routers
  • examine header fields in all IP packets passing through it
  • moves IP packers from input ports to output ports to transfer packets along end-end path
• network layer protocols
  • IP
  • internet control message protocol (ICMP)
    • use for troubleshooting type things

Forwarding

forwarding

• move packets from a routers input link to appropriate output link
• local, per-router function
• function in data plane

routing

• determine route taken by packets from source to destination
  • network-wide logic
  • function in control plane
  • chooses shortest path through routers

network layer service model

best effort

• try its best to deliver packet
• does not guarantee successful delivery
• transport layer provides reliability
• no big deal if packet is lost
• does not guarantee timing or order of delivery
  • each packet sent individually, possibly through different paths
• does not guarantee bandwidth available
  • network layer uses packet switching which unlike socket switching does not reserve resources

Routers

destination-based forwarding: foward based only on destination IP address

input port queueing: if datagrams arrive faster than fowarding rate into switch fabric

IP addressing

• unreliable host-to-host communication protocol
  • datagram formatting, IP addressing, packet switching

• ver: IP protocol versin number
• head len: header length in bytes
• type of service: diffserv(0:5) or ECN (6:7)
• length: total datagram length (bytes)
• time to live: remaining max hops (decremented at each router)
• upper layer: which protocol use at transport layer
• 16-bit id, flgs, fragment offset: fragmentation/reassembly
• header checksum
• source IP
• destination IP
• options: e.g., timestamp, record route taken

overhead:

• 20 bytes TCP
• 20 bytes IP
• = 40 bytes

IPv6