Online Social Networks and Network Layers

Transcription

Online Social Networks and Network Layers
Lecture for the Project Group
A Distributed Framework for Social Networks
Dr.-Ing. Kalman Graffi
Email: [email protected]
Fachgruppe Theorie verteilter Systeme
Fakultät für Elektrotechnik, Informatik und Mathematik
Universität Paderborn
Fürstenallee 11, D-33102 Paderborn, Deutschland
Tel.+49 5251 606730, Fax. +49 5251 606697
http://www.cs.uni-paderborn.de/fachgebiete/fg-ti.html
UPB__SS2011__PG-Framework__Lecture-01___Online-Social-Networks-Network-Layer.ppt
This slide set is based on the lecture "Communication Networks 2" of Prof. Dr.-Ing. Ralf Steinmetz at TU Darmstadt
Organizational Information
Homepage:
http://www.cs.uni-paderborn.de/fachgebiete/fg-ti/lehre0/ss2011/pgframework.html
Google Calendar Link
Template for Seminar paper and presentation
next dates
Soon:
www.p2pframework.com
Mailinglist:
pg-framework [at] lists.uni-paderborn.de
Dr.-Ing. Kalman Graffi, FG – Theorie verteilter Systeme
2
Some relevant Books
Monitoring and
Management of
Peer-to-Peer Systems
Kalman Graffi
http://tuprints.ulb.tudarmstadt.de/2248/
Handbook of P2P
Networking
Xuemen Shen,
Heather Yu, John
Buford, Mursalin Akon
Peer-to-Peer Systems
and Applications
Ralf Steinmetz, Klaus
Wehrle (Editors)
www.springerlink.com
/content/g6h805426g7t
H(„m
y 709 1008
data“)
611
=
3107
?
1622
3485
2011
2207
2906
12.5.7.31
peer-to-peer.info 61.51.166.150
planet-lab.org
berkeley.edu
95.7.6.10
86.8.10.18
7.31.10.25
3
Overview
1 Online Social Networks
2 Communications - Objectives
2.1 Computer Network / Communication Network
2.2 Distributed System
3 Overall Network Structure
3.1 Networking Basics
3.2 Reference Model for Open Systems Interconnection
3.3 ISO-OSI Layers: Functions
4 Layer Concept
4.1 Protocol: Communication between same Layers
4.2 Service: Communication between adjacent Layers
5 Other Reference Models and Comparison
5.1 TCP/IP Reference Model: Internet Architecture
5.2 Comparing the Reference Models: 5-Layer Model Used Herein
6 Overlay Networks
4
Current Trends in the Internet: Web 2.0
5
Current Trends in the Internet
Online Social Networks
Popular all over the world
Top ranked besides
Search engines
Media streaming
6
1
Online Social Networks
What are ‘Online Social Networks’ technically?
Web-based applications (StudiVZ, Facebook, MySpace, Xing)
Provide different services for community members
Personal
information
and photos
Events
Plugin
architecture
Games
Friends
Social
interaction
7
Goals and Motivations
Users want
System providers want
Storing and searching for content
High profit
Profiles, friend lists, …
Pictures, shared “Wall” editing, …
User to user interaction
Chatting, VoIP, …
Games
Security
Access control on their data
Secure, confidential communication
Fun!
Many users
Personalized advertisements
Low operational costs
For servers, electricity, cooling …
For personnel, legal issues
Controlled Quality of Service
To attract and keep users
Providing reliable, high quality services
Money!
Can the requirements be implemented in one solution?
8
Usage of Web 2.0 in Germany
9
Ratio of Users in Germany
10
Publicity of Social Networks
11
Facebook
12
StudiVZ
13
Research Gate
14
Bildung im Dialog - OWL
15
At least weekly usage
16
Most used Online Social Networks in Germany
17
Most used Online Social Networks in the World
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Number of Memberships
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Usage Frequency
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Mobile Internet Usage
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General Trend: Online Social Networks
Social networks are „normal“ in private and business world
Daily usage by large part of the society
Various types of communities
Allows new communication patterns
Increased relevance in mobile Internet
Community is created through interactions of users
Revolution in business communication / e-learning / dating?
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2
Communications - Objectives
Shared usage of resources
resources are
programs
data
devices
Allows for/to
enhance reliability
load balancing
cost reduction
e.g. shared usage of a data server (a.o. with X-terminal)
easier extensibility
High-performance communication media
person to person (e.g. E-mail, interactively)
person to machine (e.g. data bases, WWW, video server)
machine to machine (e.g. often Peer-to-Peer)
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2.1
Computer Network / Communication Network
Computer Network
several autonomous computers/end-systems interconnected with the aim to exchange information
here "connected" means:
data can be exchanged
but, no distribution transparency
Typical approach to implement online social networks
Main server operated by provider
Hosting all information
Contacted by user clients to modify / submit their information
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2.2 Distributed System
Examples
operating systems
database systems
middleware
Distributed system
is based on several independent
CPUs/systems
objective:
among others: optimized load distribution operating system usually allocates
physical units
user perspective:
centralized knowledge (i.e. for example no explicit "login")
the existence of single objects/units/systems is not visible
distribution transparency
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3
Overall Network Structure
Basics
Reference Model for Open Systems Interconnection
ISO-OSI Layers: Functions
26
Networking Protocol Map … (Source www.javvin.com)
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3.1 Networking Basics
Problem: engineering communication means
multitude of partially very complex tasks
interaction of differing systems and components
Simplification:
to introduce abstraction levels of varying functionalities
general module, preferable: layer, level
Example
biologists with translator and e.g. secured encrypted FAX-office
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3.2
Reference Model for Open Systems Interconnection
ISO OSI (Open Systems Interconnection) Reference Model
model for layered communication systems
defines fundamental concepts and terminology
defines 7 layers and their functionalities
7
Application Layer
6
Presentation Layer
5
Session Layer
4
Transport Layer
3
Network Layer
2
Data Link Layer
1
Physical Layer
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OSI Architecture
Actual data flow between two systems:
30
OSI Architecture
Real data flow with intermediate systems:
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3.3 ISO-OSI Layers: Functions
Layer
Function
sending bit 1 is also received as bit 1
(and not as bit 0):
1
Physical
mechanics: connector type, cable/medium,..
electronics: voltage, bit length,..
procedural:
unidirectional or simultaneously bidirectional
initiating and terminating connections
reliable data transfer between
adjacent stations with frames
2
Data Link
introducing data frames and acknowledgement frames
error recognition and correction within the frame:
manipulation, loss, duplication
fast sender, slow receiver:
flow control
distribution network requires access control:
Medium Access Control (MAC)
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Functions of Layers in Communications
Layer
Function
connection (as relationship between entities)
end system to end system
3
Network
(subnets) with packets
routing, i. e. among others
fixed, defined during connect, dynamic
congestion control (too many packets on one path)
quality of service dependent
varying subnets, Internetworking,
i. e. among others
addressing, packet size
comment: at broadcast networks:
routing often simplified or non-existent,
i. e. this layer does often not exist here
example: IP
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Layer
Function
connection (as relationship between entities)
From source (application/process)
to destination (application/process)
4
Transport
optimize required quality of service and costs
1 L4 connection corresponds to 1 L3 connection
increase throughput:
1 L4 connection uses several L3 connections (splitting)
minimize costs:
several L4 connections multiplexed onto 1 L3 connection
process addressing, connection management
fast sender, slow receiver:
flow control
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Layer
Function
support a “session” over a longer period
5
Session
synchronization
(during interrupted connection)
token management
(coordinate the simultaneous processing of different applications)
data presentation independent from the end system
6
Presentation
negotiating the data structure,
conversion into a global data structure
examples:
data types: date, integer, currency,
ASCII, Unicode, …
application related services
7
Application
examples:
electronic mail, directory service
file transfer, WWW, P2P, …
Comment:
layer does not necessarily correspond to the process of the implemented unit
otherwise loss of efficiency
35
4
Layer Concept
N-Layer
abstraction level with defined tasks
N-Entity
active elements within a layer
process or intelligent I/O module
peer entities: corresponding entities on different systems
N-Service Access Point, N-SAP
service identification
N-Protocol:
a multiple of rules for transferring data between N-entities
36
4.1
Protocol: Communication between same Layers
Protocol
rules for syntax (format) and semantics (contents)
of the data transfer (frames, packet, message) occurring
between the respective, active peer entities
analogy: programming, protocol corresponds to
realization of the data type (procedures, etc.)
the "interior" of the object
37
4.2
Service: Communication between adjacent Layers
Service
multiple of primitives/operations/functions
which one layer offers to the upper next layer
characterized by the "interface"
does not reveal anything about the implementation
analogy: programming, service corresponds to
abstract data type
object
38
Service Provider and Service User
Service Provider
Service User
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Nested Protocol Data Units (PDUs)
40
Nested Protocol Data Units (PDUs)
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5
Other Reference Models and Comparison
OSI (Open Systems Interconnection) Reference Model
7
Application Layer
6
Presentation Layer
5
Session Layer
4
Transport Layer
3
Network Layer
2
Data Link Layer
1
Physical Layer
TCP/IP Reference Model Internet Architecture
ISO-OSI presentation, session and application layer merged
ISO-OSI data link layer and physical layer merged to form Network Interface
42
5.1
TCP/IP Reference Model: Internet Architecture
43
Well-Known Internet Protocols
SMTP
HTTP
FTP
TELNET
NFS
RTP
SCTP
TCP
UDP
IP + ICMP + ARP
WANs
ATM, …
ARP
FTP
HTTP
IP
ICMP
LLC
MAC
NFS
SMTP
TELNET
TCP
UDP
SCTP
LLC & MAC
Physical
LANs, MANs
Ethernet, …
= Address Resolution Protocol
= File Transfer Protocol
= Hypertext Transfer Protocol
= Internet Protocol
= Internet Control Message Protocol
= Logical Link Control
= Media Access Control
= Network File System
= Simple Mail Transfer Protocol
= Remote Login Protocol
= Transmission Control Protocol
= User Datagram Protocol
= Stream Control Transmission Protocol
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Comparing the Reference Models: 5-Layer Model
Used Herein
5.2
ISO-OSI: standardized too late
implementations usually worse than those of Internet protocols
in general, however, mainly good concepts
TCP/IP (Internet)
TCP/IP already prevalent, SMTP too, now e. g. WWW
integrated into UNIX
Considered here:
Layer
Function
5
Application
application related services incl. ISO-OSI L5 and L6
(as far as necessary)
4
Transport
connection end/source (application/process) to
end/destination (application/process)
3
Network
connection end-system to end-system
2
Data Link
reliable data transfer between adjacent stations
1
Physical
sending bit 1 is also received as bit 1
45
6
Overlay Networks
Overlay Services
Service B
Service A
Service C
Peers identified by PeerID
Overlay Network
Firewall + NAT
Relay
TCP/IP
TCP/IP
Network
Network
TCP
HTTP
TCP/IP
TCP/IP
Network
Network
TCP/IP
TCP/IP
Network
Network
Underlay Networks
46
Overlay Networks
Overlay Network
Peers
TCP/IP
TCP/IP
TCP/IP
TCP/IP
TCP/IP
TCP/IP
Underlay Networks
A network
provides services (service model)
defines how nodes interact
needs for addressing, routing, …
Overlay network
= network built ON TOP of one or more existing networks
adds an additional layer of
abstraction
indirection/virtualization
47
Overlay Networks
Overlay Network
Peers
TCP/IP
TCP/IP
TCP/IP
TCP/IP
E.g. P2P networks form an
overlay network
on top of the Internet (IP network)
IP networks form an
overlay network
politically and technically
over the underlying telecom
infrastructure
TCP/IP
TCP/IP
Underlay Networks
Both
introduce their own addressing scheme:
e.g. user names, IP addresses
emphasize fault-tolerance
are based on the end-to-end principle
i.e. provide as much intelligence
as possible at end nodes
48
Overlay Networks: Advantages
Introduction of a new functionality
New layer fastens search/lookup of requested information
additional layer solves this problem for higher layers
Do not have to
deploy new equipment
modify existing software/protocols
Allow for bootstrapping
Make use of existing environment
by adding new layer
Not all nodes have to participate in maintaining
But free riding is still a problem
E.g.,
adding IP on top of Ethernet
does not require modifying Ethernet protocol or driver
49
Overlay Networks: Disadvantages
Overhead
Adds another layer in networking stack
Additional packet headers, processing
Complexity
Layering does not eliminate complexity, it only manages it
More layers of functionality
Introducing interdependecies between layers
Misleading behavior
E.g. corruption drops on wireless links interpreted as congestion drops by
TCP
Redundancy
Features may be available at various layers
Some restricted functionality
Some features that a “lower layer” does not provide cannot be added on top
E.g. non real-time capabilities (for QoS)
50
Overlay Networks: Others
Overlay Network
Peers
TCP/IP
TCP/IP
TCP/IP
TCP/IP
Peer-to-Peer overlay network
Content-centric networking / routing
Storage and retrieval
Search / recommender services
Friend-of-a-friend network
User-centric networking
TCP/IP
TCP/IP
Underlay Networks
Other (non P2P) overlay network
VPNs (virtual private networks)
IP over ad hoc networks
Application-layer multicast
TOR – anonymizer proxies
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Online Social Networks and Network Layers

Transcription

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