1. Seminar on Advanced Internet applications and Systems
Hanoch Levy (hanoch at cs.tau.ac.il)
Some slides adopted from Y. Mansour, Y. Afek
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Course Information
Lectures: Wed Kaplun324
Web site:
Resources: A list of articles (web site + class)
Supporting Books:
An Engineering Approach to Computer Networking / Keshav
Computer Networks / Tanenbaum
Data Networks / Bertsekas and Gallager
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Course Objective
Get exposed to the advanced material in Computer Networks
Learn how to:
Read professional articles
Give Professional presentations
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
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Motivation
Last 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:
=> Research material very dynamic
=> 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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9. Internet Physical Infrastructure
Residential access
Cable
Fiber
DSL
Wireless
Backbone ISP
ISP
The Internet is a network of networks
Each individually administrated network is called an Autonomous System (AS)
Campus access, e.g.,
Ethernet
Wireless
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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
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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
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The seven Layers
There are only 5 !!
Application
Presentation
Application
Session
Transport
Network
Data Link
Physical
Presentation
Application
Session
Transport
Network
Data Link
Physical
Network
Data Link
Physical
Intermediate
system
End system
End system
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14. The seven Layers - protocol stack
data AH PH SH
Presentation
Application
Session
Transport
Network
Data Link
Physical
Presentation
Application
Session
Transport
Network
Data Link
Physical TH
data
Network
data NH
Data Link
DH+data+DT
Physical
bits
Session and presentation layers are not so important, and are often ignored
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עיקרון השכבות
בשכבה X מתקבלת הודעה
זהה להודעה ששכבה
X מסרה בצד המקור
Source
Destination
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
transport
network
link
physical
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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17. Protocol layering and data
source
destination
application
transport
network
Link
physical M H t n l
message M H t n l
application
transport
network
Link
physical
segment
datagram
frame
2nd break ?!
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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.
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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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20. 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.
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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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25. 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
doesn’t 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
Doesn’t provide services to any other layer
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עיקרון השכבות
Source
Destination
אפליק 3
אפליק 2
אפליק 1
Application
UDP
TCP
Transport
Network (IPv4)
Network
Modem
Ethernet
WiFi
Data-Link
Network
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עיקרון השכבות
Source
Destination
אפליק 3
UDP
Network (IPv4)
Ethernet
אפליק 2
אפליק 1
TCP
WiFi
Modem
אפליק 3
אפליק 2
אפליק 1
UDP
TCP
Network (IPv4)
Modem
Ethernet
WiFi
Network
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32. 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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33. 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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34. 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
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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)
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43. Delay tolerant networks
Network of wireless mobiles
Not necessarily connected all the time
Application can afford DELAY (not real time). E.g:
Non urgent
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)
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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?
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