Chapter 4 : Network Layer , Data Plane

Question 1

Network layer purpose

Answer 1

transport segment from sending to receiving host

1, Sender : encapsulates segments into datagrams, passes to link layer

2. receiver : delivers segments to transport layer protocol

Question 2

Explains how router works

Answer 2

1. examines header field in all IP datagrams passing through it
2. moves datagrams from input ports to output ports to transfer along end-end path

Question 3

Explains 2 Key network layer functions:

forwarding and routing

Answer 3

1. 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)

Question 4

What is data plane, control plane, and how those correlates ?

Answer 4

1. Data plane : local , per router function. Determines how datagram arriving on router input port is forwarded to router output port
2. Control plane : network wide logic. Determines how datagram is routed among routers along end-end path from source host to destination host

Question 5

Network Layer Service Model

Answer 5

No guarantees on:

1. successful datagram delivery to destination
2. timing or order of delivery
3. bandwidth available to end-end flow

Question 6

Router architecture overview

Answer 6

routing processor, high speed switching fabric , input ports , output ports. (slide 14 of lecture 15)

Question 7

before sending packet to switch fabric, input port applies decentralized switching function , what does it do

Answer 7

using header field values, lookup output port using forwarding table in input port memory

1. destination based forwarding : forward based on ip address
2. generalized forwarding : forward based on any set of header field values

Question 8

briefly explains Longest Prefix matching when looking up destination based forwarding and etc

Answer 8

when looking for forwarding table entry for given dest address, use longest address prefix that matches destination address (slide 18 lec 15)

Question 9

What does switching fabric do

Answer 9

transfer packet from input link to appropriate output link

Question 10

3 types of switching fabric:

Answer 10

1. memory : speed is very limited by memory bandwidth (2 bus crossing / datagram)
2. bus : only one packet can cross bus at a time; switching speed limited by bus bandwidth
3. interconnection network : overcome bus switching lmitations; allows forwarding of multiple packets in parallel; non blocking

Question 11

where does queueing occur?

Answer 11

both input ports and output ports .

caused by traffic load, switching fabric speed, line speed

Question 12

In Input port queueing, sometimes we use Head of the line blocking (HOL) blocking.

Answer 12

HOL: queued datagram at front queue prevents others in queue from moving forward

Question 13

Rest of chapter (lecture 17 and 18) covered:

Answer 13

subnets, IP addressing (CIDR), DHCP , NAT, IPv6