sadna advanced internet applications and systems: peer to peer
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04:45:11 PM H. Levy, Sadna P2P 2011 1
Sadna Advanced Internet applications and Systems: Peer to Peer
Hanoch Levy & Hillel Avni (hanoch at cs.tau.ac.il, hillel.avni@gmail.com)
Some slides adopted from Y. Mansour, Y. Afek
04:45:11 PM H. Levy, Sadna P2P 2010 2/60
Course Information
Lectures: Tuesday Shreiber 007Teaching Assistant: Hillel Avni Web site: http://www.cs.tau.ac.il/~hanochSearch for sadna
1. An Engineering Approach to Computer Networking / Keshav
2. Computer Networks / Tanenbaum 3. Data Networks / Bertsekas and Gallager
Supporting Books (computer networks – little P2P):
Resources: Articles: Web, UsFramework : Hillel Avni
04:45:11 PM H. Levy, Sadna P2P 2010 3/60
What is P2P + Questions
1. An “unnatural” way to ship traffic in a network:• Pass the traffic between the clients • Instead of: from server to clients
2. “Against nature laws”…3. Rose due to “legal reasons”.. 4. Turned out to have positive technical properties 5. Can it survive 6. Can it operate in a decent environment
04:45:11 PM H. Levy, Sadna P2P 2010 4/60
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)
04:45:11 PM H. Levy, Sadna P2P 2010 5/60
Peer to Peer
A (source) sends to K.
K (client) may become now a server.
K sends to C (another client).
04:45:11 PM H. Levy, Sadna P2P 2010 6/60
Course Objective
1. Get to understand very well P2P systems – with application to Video
2. Understand advantages and limitations 3. Understand “efficiency” and scheduling 4. Hands-on experience5. Gate for Master thesis? ….
04:45:11 PM H. Levy, Sadna P2P 2010 7/60
Structure + Grades
Structure:1) A few general lectures by team.2) Work on your own with team guidance. 3) 3 deadlines for turning in material • Grade:
• Based on what is turned in• Quality:
• How good the program performs• How good the students understand the
problem/solution
04:45:11 PM H. Levy, Sadna P2P 2010 8/60
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
04:45:12 PM H. Levy, Sadna P2P 2010 9/60
Motivation (cont)
Applications / technology / research rapidly change over time
If want to stay in frontier: => Research material very
dynamic => Course material very dynamic
04:45:12 PM H. Levy, Sadna P2P 2010 10/60
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.
04:45:12 PM H. Levy, Sadna P2P 2010 11/60
Objectives (2)
Advanced Material – network development following technology Peer to Peer (P2P): Bittorent, Skype
Songs /movies / video-on-demand/video online
Distributed nets (serve the user) Semi organized nets :
serve the provider (e.g. video provider, Youtube?) Serve Internet Service provider (ISP=Bezeq Intl.)
04:45:12 PM H. Levy, Sadna P2P 2010 12/6012
Backbone ISPISP ISP
Internet Physical InfrastructureResidential access
Cable Fiber DSL Wireless
Campus access, e.g.,
Ethernet Wireless
The Internet is a network of networks
Each individually administrated network is called an Autonomous System (AS)
04:45:12 PM H. Levy, Sadna P2P 2010 13/60
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.
04:45:12 PM H. Levy, Sadna P2P 2010 14/60
Real Network
04:45:12 PM H. Levy, Sadna P2P 2010 15/60
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
each layer implements a service
via its own internal-layer actions
relying on services provided by layer below
Peer entities
04:45:13 PM H. Levy, Sadna P2P 2010 17/60
The seven Layers
Presentation
Application
Session
Transport
Network
Data Link
Physical
Presentation
Application
Session
Transport
Network
Data Link
Physical
Network
Data Link
Physical
End system End systemIntermediate system
There are only 5!!
Application
04:45:13 PM H. Levy, Sadna P2P 2010 18/60
The seven Layers - protocol stack
Presentation
Application
Session
Transport
Network
Data Link
Physical
Presentation
Application
Session
Transport
Network
Data Link
Physical
data
DH+data+DT
bits
data
data
data
data
AH
PH
SH
TH
Network
Data Link
Physical
dataNH
Session and presentation layers are not so important, and are often ignoredSession and presentation layers are not so important, and are often ignored
04:45:13 PM H. Levy, Sadna P2P 2010 19/60
עיקרון השכבות
Application
Transport
Network
Data-Link
Application
Transport
Network
Data-Link
Network
Identical message
Identical message
Identical message
Source Destination בשכבהXמתקבלת הודעה זהה להודעה ששכבה
Xמסרה בצד המקור
04:45:22 PM H. Levy, Sadna P2P 2010 20/60
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”
application
transport
network
link
physical
04:45:22 PM H. Levy, Sadna P2P 2010 21/60
applicationtransportnetwork
Linkphysical
applicationtransportnetwork
Linkphysical
source destination
M
M
M
M
Ht
HtHn
HtHnHl
M
M
M
M
Ht
HtHn
HtHnHl
message
segment
datagram
frame
Protocol layering and data
04:45:22 PM H. Levy, Sadna P2P 2010 22/60
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.
04:45:22 PM H. Levy, Sadna P2P 2010 23/60
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
04:45:22 PM H. Levy, Sadna P2P 2010 24/60
Datalink layer (contd.)
Datalink layer protocols are the first layer of software Very dependent on underlying physical link properties Usually bundle both physical and datalink in hardware.
Ethernet (broadcast link) end-system must receive only bits meant for itneed datalink-layer addressalso need to decide who gets to speak nextthese functions are provided by Medium ACcess sublayer (MAC)
04:45:22 PM H. Levy, Sadna P2P 2010 25/60
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
04:45:22 PM H. Levy, Sadna P2P 2010 26/60
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
Network layer (contd.)
04:45:22 PM H. Levy, Sadna P2P 2010 27/60
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
Network layer (contd.)
At end-systems
primarily hides details of datalink layer segments and reassemble detects errors
04:45:22 PM H. Levy, Sadna P2P 2010 28/60
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
04:45:22 PM H. Levy, Sadna P2P 2010 29/60
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
04:45:23 PM H. Levy, Sadna P2P 2010 30/60
Session layer
Not common Provides full-duplex service, expedited
data delivery, and session synchronization
Internet doesn’t have a standard session layer
04:45:23 PM H. Levy, Sadna P2P 2010 31/60
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
Session layer (cont.)
04:45:23 PM H. Levy, Sadna P2P 2010 32/60
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
04:45:23 PM H. Levy, Sadna P2P 2010 33/60
Application layer
The set of applications that use the network Doesn’t provide services to any other layer
04:45:23 PM H. Levy, Sadna P2P 2010 34/60
עיקרון השכבות
3אפליק
UDP
Network (IPv4)
Ethernet
Application
Transport
Network
Data-Link
Network
Source Destination
2אפליק 1אפליק
TCP
WiFiModem
04:45:37 PM H. Levy, Sadna P2P 2010 35/60
עיקרון השכבות
Network
Source Destination
3אפליק
UDP
Network (IPv4)
Ethernet
2אפליק 1אפליק
TCP
WiFiModem
3אפליק
UDP
Network (IPv4)
Ethernet
2אפליק 1אפליק
TCP
WiFiModem
04:45:53 PM H. Levy, Sadna P2P 2010 36/60
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)
04:45:54 PM H. Levy, Sadna P2P 2010 37/60
Peer to Peer
A (source) sends to K.
K (client) may become now a server.
K sends to C (another client).
04:45:54 PM H. Levy, Sadna P2P 2010 38/60
Peer to Peer – WHY ??
Legal (this is how it started…) Broadcast is not really implemented
If implemented – not easy Need at intermediate routers to keep
state of conversation For each packet to memorize who got it. Large overhead when traffic speed is
high A is bottleneck Resource Utilization: K is idle X%
(95?)of the day Communications (costs!!) CPU
04:45:54 PM H. Levy, Sadna P2P 2010 39/60
Peer to Peer – WHY ??
Scalability Can reach N clients at very low cost; By doubling the load on each recipient
(which needs to become server now) can reduce the server load from N to 1.
The network traffic is less than doubled.
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