EECS122 Midterm Review

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EECS122Midterm Review

• Department of Electrical Engineering and Computer
  Sciences
• University of California
• Berkeley

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TOC Midterm Review

• Network
• Web Browsing
• Layers Protocols
• Inside a Router
• Check List

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Review Network
WAN
MAN
4
Review Network
WAN
LAN
MAN
5
Review Network
WAN
LAN
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Review Web Browsing

• Example
• Locating Resource DNS
• Connection
• End-to-end
• Packets
• Bits
• Points to remember

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Web Example

• Click Link or URL
• ? get content from localor remote computer
• URL
• http//www.google.com/string
• Specifies
• Protocol http
• Computer www.google.com
• String
• Computer (server) selects
• contents based on string

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Web Locating Resource

• www.google.com is the name of a computer
• Network uses IP addresses
• To find the IP address, the application uses a
  hierarchical directory service called theDomain
  Name System

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Web Connection

• The protocol (http) sets up a connection between
  the host and cnn.com to transfer the page
• The connection transfers the page as a byte
  stream, without errors pacing error control

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Web End-to-end

• The byte stream flows from end to end across many
  links and switches routing ( addressing)
• That stream is regulated and controlled by both
  ends retransmission of erroneous or missing
  bytes flow control

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Web Packets

• The network transports bytes grouped into packets
• The packets are self-contained and routers
  handle them one by one
• The end hosts worry about errors and flow
  control
• Destination checks packet for errors (using error
  detection code CKS) and sends ACKs with sequence
  number
• Source retransmits packets that were not ACKed
  and adjusts rate of transmissions

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Web Bits

• Equipment in each node sends the packets as a
  string of bits
• That equipment is not aware of the meaning of the
  bits

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Review Layers Protocols
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Mapping Layers to Network Devices

• Two broad classes of devices
• Hosts
• Routers
• Both sets of devices run applications
• Hosts mainly run user applications
• Routers run infrastructure applications
• E.g. Topology discovery, Network Management
  Protocols, BGP etc.
• Dont be confused by thinking that routers dont
  run application protocols because they are layer
  3 devices

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Layers Transport Services
HTTP
DNS
RA
Application
Transport
IP
A B p1 p2
UDP Not reliable TCP Ordered, reliable,
well-paced
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Layers - TCP MPX, Error, Flow and Congestion
Control
65KB

• window minRAW - OUT, W

W
3DA
3DA
TO
X0.5
X0.5
X0.5
X0.5
3
3
TO
1
CA
SS
SS
CA
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TCP Algorithm AIMD
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Flow Control

• Objective Avoid saturating destination
• Algorithm Receiver avertizes window RAW

window minRAW OUT, W where OUT
Oustanding Last sent last ACKed W Cong.
Window from AIMD refinements
RAW
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Layers IP Internet Protocol

• Addressing
• Class-Based Fixed Prefix M-tree
• Classless CIDR LPM-Patricia Trie
• Routing

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Class-base Addressing

• Addressing reflects internet hierarchy
• 32 bits divided into 2 parts
• Class A
• Class B
• Class C

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Classless Internet Domain Routing

• Suppose fifty computers in a network are
  assigned IP addresses 128.23.9.0 - 128.23.9.49
• Range is 01111111 00001111 00001001
  00000000 to 01111111 00001111 00001001
  00110001
• They share the first 26 bits of 128.23.9.0
• Convention 128.23.9.0/26 prefix
• There are 32-276 bits for the 50 computers
• 26 64 addresses

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IP Routing

• Intradomain
• Formulate the routing problem as a Shortest Path
  Problem
• Link State v/s Distance Vector
• Both work reasonably well in a well engineered
  network

4
4
6
B
BGP
6
7
5
IntraDomain
2
2
4
8
RIP
6
3
13
3
13
11
2
10
IntraDomain
IntraDomain
3
1
13
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• Interdomain
• BGP
• Path Vector, Policies

C
OSPF
IGRP
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Route Computation

• Dijkstra Link State
• Use a flooding protocol to discover the entire
  topology
• Find the shortest paths in order of increasing
  path length from node i.
• Bellman Ford Distance Vector
• D(i,d) minjeN(i) c(i,j) D(j,d)
• BGP Path Vector
• Policy routing Receive and advertise entire
  routes
• AS numbers describe the path to a CIDR address

Choose best route
accept, deny, set preferences
forward, not forward set MEDs
Routes received from neighbors
Routes sent to neighbors
Import Policy Engine
Export Policy Engine
Routes used by router
Decision process
IP Routing table
BGP table
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Review Inside Router

• Input and output interfaces are connected through
  an interconnect
• A interconnect can be implemented by
• Shared memory
• low capacity routers (e.g., PC-based routers)
• Shared bus
• Medium capacity routers
• Point-to-point (switched) bus
• High capacity routers

Scheduling
GPS WFQ
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Router GPS/WFQ

• Why service disciplines?
• Understand GPS and WFQ well
• GPS properties
• WFQ tracking result
• No later than one packet transmission

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Review Check List

• Big Picture
• Layers
• Network Structure (L2, L3)
• Where protocols are implemented
• Switching Techniques
• Applications
• DNS
• HTTP
• Transport
• TCP Service Go Back N Flow Control Congestion
  Control AIMD SS 3DA Phases
• UDP Service
• Network
• Class-Based Classless Addressing
• Dijkstra Bellman-Ford
• Hierarchical routing
• Inside Router
• Architecture Input, Output
• Scheduling Fairness, GPS, WFQ