Network layer purpose
transport segment from sending to receiving host
1, Sender : encapsulates segments into datagrams, passes to link layer
- receiver : delivers segments to transport layer protocol
Explains how router works
- examines header field in all IP datagrams passing through it
- moves datagrams from input ports to output ports to transfer along end-end path
Explains 2 Key network layer functions:
forwarding and routing
- forwarding : move packets from a router input link to appropriate router output link (getting through an interchange)
2, routing : determine route taken by packets from source to destination (planning a trip from source to destination)
What is data plane, control plane, and how those correlates ?
- Data plane : local , per router function. Determines how datagram arriving on router input port is forwarded to router output port
- Control plane : network wide logic. Determines how datagram is routed among routers along end-end path from source host to destination host
Network Layer Service Model
No guarantees on:
- successful datagram delivery to destination
- timing or order of delivery
- bandwidth available to end-end flow
Router architecture overview
routing processor, high speed switching fabric , input ports , output ports. (slide 14 of lecture 15)
before sending packet to switch fabric, input port applies decentralized switching function , what does it do
using header field values, lookup output port using forwarding table in input port memory
- destination based forwarding : forward based on ip address
- generalized forwarding : forward based on any set of header field values
briefly explains Longest Prefix matching when looking up destination based forwarding and etc
when looking for forwarding table entry for given dest address, use longest address prefix that matches destination address (slide 18 lec 15)
What does switching fabric do
transfer packet from input link to appropriate output link
3 types of switching fabric:
- memory : speed is very limited by memory bandwidth (2 bus crossing / datagram)
- bus : only one packet can cross bus at a time; switching speed limited by bus bandwidth
- interconnection network : overcome bus switching lmitations; allows forwarding of multiple packets in parallel; non blocking
where does queueing occur?
both input ports and output ports .
caused by traffic load, switching fabric speed, line speed
In Input port queueing, sometimes we use Head of the line blocking (HOL) blocking.
HOL: queued datagram at front queue prevents others in queue from moving forward
Rest of chapter (lecture 17 and 18) covered:
subnets, IP addressing (CIDR), DHCP , NAT, IPv6
