Seminar on Advanced Internet applications and Systems

1
Seminar on Advanced Internet applications and
Systems
Hanoch Levy (hanoch at cs.tau.ac.il) Some
slides adopted from Y. Mansour, Y. Afek
2
Course Information

• Lectures Wed 10-12 Kaplun324

Web site http//www.cs.tau.ac.il/hanoch/
Resources A list of articles (web site class)

Supporting Books

1. An Engineering Approach to Computer Networking /
   Keshav
2. Computer Networks / Tanenbaum
3. Data Networks / Bertsekas and Gallager

3
Course Objective

1. Get exposed to the advanced material in Computer
   Networks
2. Learn how to
3. Read professional articles
4. Give Professional presentations
5. Exposition to what required of at Master Thesis.

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Structure Grades

• Structure
• Every week one lecture by a student.
• Lecturer is encouraged to encourage students to
  participate.
• Students are encouraged to participate.
• Grade
• Based on material understanding quality of
  presentation
• Bonus for active participation

5
Motivation

• Last 10-15 years communications revolution
• Internet Computer communications
• Is a key factor of the Information revolution
• Implications
• A drastic change of some aspects of life
• Revolution is affected by life
• Technology drives applications
• Applications drive technology

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Motivation (cont)

• Applications / technology / research ? rapidly
  change over time
• If want to stay in frontier
• gt Research material very dynamic
• gt Course material very dynamic

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Objectives

• Computer Networking course Internet
  infra-structure
• 1 Introduction and Layering
• 2 Physical Layer, Data Link Layer, MAC Protocols
• 3 Hubs, Bridges, SwitchesData Link Layer
• 4 Switching UnitsSTP, Switching Fabric
• 5 Scheduling Buffer Management Scheduling, WFQ
  example
• 6 Network Layer RoutingRouting
• 7 Reliable Data TransferIP
• 8 End to End ProtocolsARQ
• 10 Flow Control, Congestion ControlTCP flow
  congestion control
• 11 Network SecurityNetwork Sniffing (no slides)
• 12 DNS, HTTPTCP (state chart)
• 13 DDoS
• ALL operations of network of networks.

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Objectives (2)

• Advanced Material network development following
  technology
• Peer to Peer (P2P) Bittorent, Skype
• Songs /movies / video-on-demand/video online
• Wireless ? AdHoc delay tolerant networks
• Social networks
• Security / DDoS

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Internet Physical Infrastructure

• Residential access
• Cable
• Fiber
• DSL
• Wireless

• The Internet is a network of networks
• Each individually administrated network is called
  an Autonomous System (AS)

• Campus access, e.g.,
• Ethernet
• Wireless

9
10
Data Networks

• Set of interconnected nodes exchange information
• sharing of the transmission circuits
  "switching".
• many links allow more than one path between every
  2 nodes.
• network must select an appropriate path for each
  required connection.

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Real Network
12
Layers
Person delivery of parcel Post office counter
handling Ground transfer loading on trucks
Airport transfer loading on airplane Airplane
routing from source to destination
Peer entities

• each layer implements a service
• via its own internal-layer actions
• relying on services provided by layer below

13
ISO OSI reference model

• Reference model
• formally defines what is meant by a layer, a
  service etc.
• Service architecture
• describes the services provided by each layer and
  the service access point
• Protocol architecture
• set of protocols that implement the service
  architecture
• compliant service architectures may still use
  non-compliant protocol architectures

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The seven Layers
There are only 5 !!
Application
Intermediate system
End system
End system
15
The seven Layers - protocol stack
data
TH
Network
Data Link
DHdataDT
Physical
bits

• Session and presentation layers are not so
  important, and are often ignored

16
?????? ??????
????? X ?????? ????? ??? ?????? ????? X ???? ???
?????
Destination
Source
Application
Application
Identical message
Transport
Transport
Identical message
Network
Network
Identical message
Data-Link
Data-Link
Network
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Internet protocol stack

• application supporting network applications
• ftp, smtp, http
• transport host-host data transfer
• tcp, udp
• network routing of datagrams from source to
  destination
• ip, routing protocols
• link data transfer between neighboring network
  elements
• ppp, ethernet
• physical bits on the wire

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Protocol layering and data
source
destination
message
application transport network Link physical
segment
datagram
frame
19
Physical layer L1

• Moves bits between physically connected
  end-systems
• Standard prescribes
• coding scheme to represent a bit
• shapes and sizes of connectors
• bit-level synchronization
• Internet
• technology to move bits on a wire, wireless link,
  satellite channel etc.

20
Datalink layer L2

• (Reliable) communication over a single link.
• Introduces the notion of a frame
• set of bits that belong together
• Idle markers tell us that a link is not carrying
  a frame
• Begin and end markers delimit a frame
• Internet
• a variety of datalink layer protocols
• most common is Ethernet
• others are FDDI, SONET, HDLC

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Datalink layer (contd.)

• Ethernet (broadcast link)
• end-system must receive only bits meant for it
• need datalink-layer address
• also need to decide who gets to speak next
• these functions are provided by Medium ACcess
  sublayer (MAC)

• Datalink layer protocols are the first layer of
  software
• Very dependent on underlying physical link
  properties
• Usually bundle both physical and datalink in
  hardware.

22
Network layer L3

• Carries data from source to destination.
• Logically concatenates a set of links to form the
  abstraction of an end-to-end link
• Allows an end-system to communicate with any
  other end-system by computing a route between
  them
• Hides individual behavior of datalink layer
• Provides unique network-wide addresses
• Found both in end-systems and in intermediate
  systems

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Network layer (contd.)

• Internet
• network layer is provided by Internet Protocol
  (IP)
• found in all end-systems and intermediate systems
• provides abstraction of end-to-end link
• segmentation and reassembly
• packet-forwarding, routing, scheduling
• unique IP addresses
• can be layered over anything, but only
  best-effort service

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Network layer (contd.)

• At end-systems
• primarily hides details of datalink layer
• segments and reassemble
• detects errors

• At intermediate systems
• participates in routing protocol to create
  routing tables
• responsible for forwarding packets
• schedules the transmission order of packets
• chooses which packets to drop

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Transport layer L4

• Reliable end-to-end communication.
• creates the abstraction of an error-controlled,
  flow-controlled and multiplexed end-to-end link
• (Network layer provides only a raw end-to-end
  service)
• Some transport layers provide fewer services
• e.g. simple error detection, no flow control, and
  no retransmission

• Internet
• TCP provides error control, flow control,
  multiplexing
• UDP provides only multiplexing

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Transport layer (contd.)

• Error control
• GOAL message will reach destination despite
  packet loss, corruption and duplication
• ACTIONS retransmit lost packets detect,
  discard, and retransmit corrupted packets detect
  and discard duplicated packets
• Flow control
• match transmission rate to rate currently
  sustainable on the path to destination, and at
  the destination itself
• Multiplexes multiple applications to the same
  end-to-end connection
• adds an application-specific identifier (port
  number) so that receiving end-system can hand in
  incoming packet to the correct application

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Session layer

• Not common
• Provides full-duplex service, expedited data
  delivery, and session synchronization
• Internet
• doesnt have a standard session layer

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Session layer (cont.)

• Duplex
• if transport layer is simplex, concatenates two
  transport endpoints together
• Expedited data delivery
• allows some messages to skip ahead in end-system
  queues, by using a separate low-delay transport
  layer endpoint
• Synchronization
• allows users to place marks in data stream and to
  roll back to a prespecified mark

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Presentation layer

• Usually ad hoc
• Touches the application data
• (Unlike other layers which deal with headers)
• Hides data representation differences between
  applications
• characters (ASCII, unicode, EBCDIC.)
• Can also encrypt data
• Internet
• no standard presentation layer
• only defines network byte order for 2- and 4-byte
  integers

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Application layer

• The set of applications that use the network
• Doesnt provide services to any other layer

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?????? ??????
Destination
Source
????? 3
Application
????? 2
????? 1
UDP
Transport
TCP
Network (IPv4)
Network
Ethernet
Data-Link
WiFi
Modem
Network
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?????? ??????
Destination
Source
????? 3
????? 2
????? 1
UDP
TCP
Network (IPv4)
Ethernet
WiFi
Modem
Network
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Advanced Topics this course

• Peer to Peer systems (files, video on demand,
  streaming)
• Wireless Networks
• Mobility
• Delay tolerant networks
• Social network
• Denial of service (network security) network
  maliciousness ??

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Network Maliciousness Denial of service

• Network fundamental design principle
• User is polite/obey rules
• User aims at maximizing his/her own performance
• Today Some users aim
• DEGRADE NETWORK PERFORMANCE
• Many aspects of network design may collapse
• Research subject
• How much damage malicious user to innocent users
• How vulnerable network mechanisms to malicious
  behavior

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Network Maliciousness Cont

• Anything studied in Data structures /algorithms
  / Computer networks
• If one user becomes malicious
• How much damage can she pose
• How should we pick our algorithms/design
• Examples Hash Table (open / closed)
• Data structure course Equivalent O(1) avg per
  insert/delete/member
• Malicious analysis (our master student)
• Closed much more vulnerable
• Attacker can hurt performance of innocent much
  more
• ? if you design a net ? pick open

closed
open
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Peer to Peer

• Historical Internet send data from A to K.
• Client-server model
• A server data source
• K client data consumer
• If C wants too get from A (unicast or broadcast)

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Peer to Peer

• A (source) sends to K.
• K (client) may become now a server.
• K sends to C (another client).

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Peer to Peer WHY??

• Legal (this is how it started)
• Broadcast is not really implemented
• A is bottleneck
• Resource Utilization K is idle X (95?)of the
  day
• Communications (costs!!)
• CPU
• Issues
• BW cost? Free ride?
• Files? Video on demand? Stream (video Broadcast)

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Wireless Networks

• Cellular net base stations tx to mobiles

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Wireless Networks

• Multihop wireless use wireless devices as
  forwarding mechanisms
• Difficulty when node x transmits the whole area
  must be quiet (avoid colision).
• How much spatial capacity the network has?

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Wireless Networks
1

• Questions
• Difficulty (1) when node x transmits the whole
  area must be quiet (avoid collision).
• How much spatial capacity the network has?
• Paper 2.1
• Difficulty (2) How connected is the network
• Paper 2.2

X
2
42
Wireless Networks
1

• Questions
• How do you allocate resources fairly
  efficiently among users?
• Difficulty (3) x can be noisy on purpose, or
  can request many resources ? denial of service to
  others.
• Paper 2.3

X
2
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Wireless Mobility

• Wireless devices move around.
• Movement can determine
• Density/ Load on network
• Connectivity
• Ability to transfer data from place to place
• Need to understand the mobility patterns
• Papers (3)

44
Delay tolerant networks

• Network of wireless mobiles
• Not necessarily connected all the time
• Application can afford DELAY (not real time).
  E.g
• Non urgent email
• Copy of a song
• General news
• handheld mobility assist in transfering the info
  over the net.
• Delay Tolerant Net
• E.g use the buss system over a campus
• Papers (4)

45
Social networks

• The new (old?) hot thing on the net.
• Data generated by users for users YouTube.
• Understanding its properties 5.1
• Social contacts can be used to transfer data
• E.g spread info in campus.
• Understanding the social interaction is needed.
• Paper (5.2)

Spreading info in university? In conference?