H. Levy, Sadna P2P Sadna Advanced Internet applications and Systems: Peer to Peer Hanoch Levy & Hillel Avni ( hanoch at cs.tau.ac.il, ) hanoch at cs.tau.ac.il Some slides adopted from Y. Mansour, Y. Afek

H. Levy, Sadna P2P /60 Course Information Lectures: Tuesday Shreiber 007 Teaching Assistant: Hillel Avni Web site: Search 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, Us Framework : Hillel Avni

H. Levy, Sadna P2P /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

H. Levy, Sadna P2P /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)

H. Levy, Sadna P2P /60 Peer to Peer A (source) sends to K. K (client) may become now a server. K sends to C (another client).

H. Levy, Sadna P2P /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 experience 5.Gate for Master thesis? ….

H. Levy, Sadna P2P /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

H. Levy, Sadna P2P /60 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

H. Levy, Sadna P2P /60 Motivation (cont) Applications / technology / research  rapidly change over time If want to stay in frontier: => Research material very dynamic => Course materialvery dynamic

H. Levy, Sadna P2P /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.

H. Levy, Sadna P2P /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.)

H. Levy, Sadna P2P /60 12 Backbone ISP ISP Internet Physical Infrastructure Residential access Cable Fiber DSL Wireless Campus access, e.g., m Ethernet m Wireless r The Internet is a network of networks r Each individually administrated network is called an Autonomous System (AS)

H. Levy, Sadna P2P /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.

H. Levy, Sadna P2P /60 Real Network

H. Levy, Sadna P2P /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

H. Levy, Sadna P2P /60 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

H. Levy, Sadna P2P /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 Intermediate system There are only 5 !! Application

H. Levy, Sadna P2P /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 AH PH SH TH Network Data Link Physical dataNH Session and presentation layers are not so important, and are often ignored Session and presentation layers are not so important, and are often ignored

H. Levy, Sadna P2P /60 עיקרון השכבות Application Transport Network Data-Link Application Transport Network Data-Link Network Identical message Source Destination בשכבה X מתקבלת הודעה זהה להודעה ששכבה X מסרה בצד המקור

H. Levy, Sadna P2P /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

H. Levy, Sadna P2P /60 application transport network Link physical application transport network Link physical source destination M M M M H t H t H n H t H n H l M M M M H t H t H n H t H n H l message segment datagram frame Protocol layering and data

H. Levy, Sadna P2P /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.

H. Levy, Sadna P2P /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

H. Levy, Sadna P2P /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 it need datalink-layer address also need to decide who gets to speak next these functions are provided by Medium ACcess sublayer (MAC)

H. Levy, Sadna P2P /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

H. Levy, Sadna P2P /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.)

H. Levy, Sadna P2P /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

H. Levy, Sadna P2P /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

H. Levy, Sadna P2P /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

H. Levy, Sadna P2P /60 Session layer Not common Provides full-duplex service, expedited data delivery, and session synchronization Internet doesn ’ t have a standard session layer

H. Levy, Sadna P2P /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.)

H. Levy, Sadna P2P /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

H. Levy, Sadna P2P /60 Application layer The set of applications that use the network Doesn ’ t provide services to any other layer

H. Levy, Sadna P2P /60 עיקרון השכבות אפליק 3 UDP Network (IPv4) Ethernet Application Transport Network Data-Link Network Source Destination אפליק 2 אפליק 1 TCP WiFiModem

H. Levy, Sadna P2P /60 עיקרון השכבות Network Source Destination אפליק 3 UDP Network (IPv4) Ethernet אפליק 2 אפליק 1 TCP WiFiModem אפליק 3 UDP Network (IPv4) Ethernet אפליק 2 אפליק 1 TCP WiFiModem

H. Levy, Sadna P2P /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)

H. Levy, Sadna P2P /60 Peer to Peer A (source) sends to K. K (client) may become now a server. K sends to C (another client).

H. Levy, Sadna P2P /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

H. Levy, Sadna P2P /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.