Computer Networking PowerPoint Presentation

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15-744: Computer Networking L-1 Intro to Computer Networks

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L -1; 9-11-02 © Srinivasan Seshan, 2002 2 Outline Administrivia Whirlwind tour of networking

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L -1; 9-11-02 © Srinivasan Seshan, 2002 3 Who’s Who? Professor: Srinivasan Seshan http://www.cs.cmu.edu/~srini srini@cmu.edu Office hours: Wed 1:30-2:30pm TA: Amit Manjhi manjhi@cs.cmu.edu Office hours: Mon 3:00-4:00pm Course info http://www.cs.cmu.edu/~srini/15-744/F02/

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L -1; 9-11-02 © Srinivasan Seshan, 2002 4 Objectives Understand the state-of-the-art in network protocols, architectures and applications Understand how networking research is done Teach the typical constraints and thought process for networked systems How is class different from undergraduate networking (15-441) Training network programmers vs. training network researchers

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L -1; 9-11-02 © Srinivasan Seshan, 2002 5 Web Page Check regularly!! Course schedule Reading list Lecture notes Announcements Assignments Project ideas Exams Student list

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L -1; 9-11-02 © Srinivasan Seshan, 2002 6 Course Materials Research papers Links to ps or pdf on Web page Combination of classic and recent work ~40 papers Optional readings Recommended textbook For students not familiar with networking Peterson & Davie 2nd edition 2 copies on reserve Kurose & Ross (preferably 2nd edition) I have some spare (1st ed) that I can lend out

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L -1; 9-11-02 © Srinivasan Seshan, 2002 7 Grading Homework assignments Problem sets & hands-on assignments (15%) Hand-ins for readings (10%) Class participation (5%) 2 person project (30%) Midterm exam (20%) Final (2nd Midterm) exam (not cumulative) (20%)

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L -1; 9-11-02 © Srinivasan Seshan, 2002 8 Waitlist & HW 0 HW 0 – due next Thursday in class If you are trying to add class HW 0 is due on Tuesday in class I will email enrollment decisions by next Friday

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L -1; 9-11-02 © Srinivasan Seshan, 2002 9 Outline Administrivia Whirlwind tour of networking

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L -1; 9-11-02 © Srinivasan Seshan, 2002 10 What is the Objective of Networking? Communication between applications on different computers Must understand application needs/demands Traffic data rate Traffic pattern (bursty or constant bit rate) Traffic target (multipoint or single destination, mobile or fixed) Delay sensitivity Loss sensitivity

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L -1; 9-11-02 © Srinivasan Seshan, 2002 11 Four Steps to Networking Communicating across a link Connecting together multiple links (internetworking) Finding and routing data to nodes on internetwork Matching application requirements

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L -1; 9-11-02 © Srinivasan Seshan, 2002 12 A First Step Creating a link between nodes Link: path followed by bits Wired or wireless Broadcast or point-to-point (or both) Node: any device connected to a link

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L -1; 9-11-02 © Srinivasan Seshan, 2002 13 Types of Links Point-to-Point Multiple Access …

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L -1; 9-11-02 © Srinivasan Seshan, 2002 14 Packet Transmission Modes Unicast Transmission to single specific receiver Broadcast Transmission to all network nodes Multicast Transmission to specific subset of nodes Anycast Transmission to one of a specific subset of nodes

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L -1; 9-11-02 © Srinivasan Seshan, 2002 15 Switched Network What are Switched Networks? Switch: moves bits between links Packet switching Circuit switching

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L -1; 9-11-02 © Srinivasan Seshan, 2002 16 Back in the Old Days…

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L -1; 9-11-02 © Srinivasan Seshan, 2002 17 Then Came TDM… Multiplex (mux) Demultiplex (demux) Synchronous time division multiplexing

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L -1; 9-11-02 © Srinivasan Seshan, 2002 18 TDM Logical Network View

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L -1; 9-11-02 © Srinivasan Seshan, 2002 19 Packet Switching (Internet) Packets

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L -1; 9-11-02 © Srinivasan Seshan, 2002 20 Packet Switching Interleave packets from different sources Efficient: resources used on demand Statistical multiplexing General Multiple types of applications Accommodates bursty traffic Addition of queues

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L -1; 9-11-02 © Srinivasan Seshan, 2002 21 Statistical Multiplexing Gain 1 Mbps link; users require 0.1 Mbps when transmitting; users active only 10% of the time Circuit switching: can support 10 users Packet switching: with 35 users, probability that >=10 are transmitting at the same time < 0.0017

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L -1; 9-11-02 © Srinivasan Seshan, 2002 22 Characteristics of Packet Switching Store and forward Packets are self contained units Can use alternate paths – reordering Contention Congestion Delay

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L -1; 9-11-02 © Srinivasan Seshan, 2002 23 Internet[work] Second Step: Internet[work] A collection of interconnected networks Host: network endpoints (computer, PDA, light switch, …) Router: node that connects networks Internet vs. internet

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L -1; 9-11-02 © Srinivasan Seshan, 2002 24 Challenge Many differences between networks Address formats Performance – bandwidth/latency Packet size Loss rate/pattern/handling Routing How to translate between various network technologies

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L -1; 9-11-02 © Srinivasan Seshan, 2002 25 Third Step: How To Find Nodes? Internet Computer 1 Computer 2

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L -1; 9-11-02 © Srinivasan Seshan, 2002 26 Naming Humans use readable host names E.g. www.cmu.edu Globally unique (can correspond to multiple hosts) Naming system translates to physical address E.g. DNS translates name to IP Address (e.g. 128.2.11.43) Address reflects location in network

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L -1; 9-11-02 © Srinivasan Seshan, 2002 27 Domain Name System What’s the IP address for www.cmu.edu? It is 128.2.11.43 DNS server address manually configured into OS Local DNS Server Computer 1

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L -1; 9-11-02 © Srinivasan Seshan, 2002 28 Packet Routing/Delivery Each network technology has different local delivery methods Address resolution provides delivery information within network E.g., ARP maps IP addresses to Ethernet addresses Local, works only on a particular network Routing protocol provides path through an internetwork

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L -1; 9-11-02 © Srinivasan Seshan, 2002 29 Network:Address Resolution Protocol Ethernet Broadcast: who knows the Ethernet address for 128.2.11.43? Ethernet Unicast: Yes, it is 08-00-2c-19-dc-45

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L -1; 9-11-02 © Srinivasan Seshan, 2002 30 Internetwork: Datagram Routing R R R R R H H H H R R H R Routers send packet to next closest point H: Hosts R: Routers

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L -1; 9-11-02 © Srinivasan Seshan, 2002 31 Routing Forwarding tables at each router populated by routing protocols. Original Internet: manually updated Routing protocols update tables based on “cost” Exchange tables with neighbors or everyone Use neighbor leading to shortest path

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L -1; 9-11-02 © Srinivasan Seshan, 2002 32 Fourth Step: Application Demands Reliability Corruption Lost packets Flow and congestion control Fragmentation In-order delivery Etc…

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L -1; 9-11-02 © Srinivasan Seshan, 2002 33 What if the Data gets Corrupted? Internet GET windex.html GET index.html Solution: Add a checksum Problem: Data Corruption 0,9 9 6,7,8 21 4,5 7 1,2,3 6 X

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L -1; 9-11-02 © Srinivasan Seshan, 2002 34 What if Network is Overloaded? Problem: Network Overload Short bursts: buffer What if buffer overflows? Packets dropped Sender adjusts rate until load = resources Called “congestion control” Solution: Buffering and Congestion Control

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L -1; 9-11-02 © Srinivasan Seshan, 2002 35 What if the Data gets Lost? Internet GET index.html Problem: Lost Data Internet GET index.html Solution: Timeout and Retransmit GET index.html GET index.html

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L -1; 9-11-02 © Srinivasan Seshan, 2002 36 Problem: Packet size Solution: Fragment data across packets What if the Data Doesn’t Fit? On Ethernet, max IP packet is 1.5kbytes Typical web page is 10kbytes GET inde x.ht ml GET index.html

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L -1; 9-11-02 © Srinivasan Seshan, 2002 37 Solution: Add Sequence Numbers Problem: Out of Order What if the Data is Out of Order? GET x.ht inde ml GET x.htindeml GET index.html ml 4 inde 2 x.ht 3 GET 1

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L -1; 9-11-02 © Srinivasan Seshan, 2002 38 Network Functionality Summary Link Multiplexing Routing Addressing/naming (locating peers) Reliability Flow control Fragmentation Etc….

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L -1; 9-11-02 © Srinivasan Seshan, 2002 39 What is Layering? Modular approach to network functionality Example: Link hardware Host-to-host connectivity Application-to-application channels Application

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L -1; 9-11-02 © Srinivasan Seshan, 2002 40 Protocols Module in layered structure Set of rules governing communication between network elements (applications, hosts, routers) Protocols define: Interface to higher layers (API) Interface to peer Format and order of messages Actions taken on receipt of a message

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L -1; 9-11-02 © Srinivasan Seshan, 2002 41 Layering Characteristics Each layer relies on services from layer below and exports services to layer above Interface defines interaction Hides implementation - layers can change without disturbing other layers (black box)

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L -1; 9-11-02 © Srinivasan Seshan, 2002 42 Layering Host Host Application Transport Network Link User A User B Layering: technique to simplify complex systems

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L -1; 9-11-02 © Srinivasan Seshan, 2002 43 Layer Encapsulation Get index.html Connection ID Source/Destination Link Address User A User B

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L -1; 9-11-02 © Srinivasan Seshan, 2002 44 Protocol Demultiplexing Multiple choices at each layer FTP HTTP TFTP NV TCP UDP IP NET1 NET2 NETn … TCP/UDP IP IPX Port Number Network Protocol Field Type Field

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L -1; 9-11-02 © Srinivasan Seshan, 2002 45 E.g.: OSI Model: 7 Protocol Layers Physical: how to transmit bits Data link: how to transmit frames Network: how to route packets Transport: how to send packets end2end Session: how to tie flows together Presentation: byte ordering, security Application: everything else

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L -1; 9-11-02 © Srinivasan Seshan, 2002 46 OSI Layers and Locations Switch Router Host Host Application Transport Network Data Link Presentation Session Physical

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L -1; 9-11-02 © Srinivasan Seshan, 2002 47 Example: Transport Layer First end-to-end layer End-to-end state May provide reliability, flow and congestion control

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L -1; 9-11-02 © Srinivasan Seshan, 2002 48 Example: Network Layer Point-to-point communication Network and host addressing Routing

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L -1; 9-11-02 © Srinivasan Seshan, 2002 49 Is Layering Harmful? Sometimes.. Layer N may duplicate lower level functionality (e.g., error recovery) Layers may need same info (timestamp, MTU) Strict adherence to layering may hurt performance

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L -1; 9-11-02 © Srinivasan Seshan, 2002 50 Class Coverage No coverage of physical and data link layer Students expected to know this Focus on network to application layer We will deal with: Protocol rules and algorithms Investigate protocol trade-offs Why this way and not another?

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L -1; 9-11-02 © Srinivasan Seshan, 2002 51 Lecture Topics Traditional Layering Internet architecture Routing (IP) Transport (TCP) Queue management (FQ, RED) Naming (DNS) Recent Topics Multicast Mobility Active networks QOS Security Network measurement Overlay networks P2P applications

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L -1; 9-11-02 © Srinivasan Seshan, 2002 52 Next Lecture: Design Considerations How to determine split of functionality Across protocol layers Across network nodes Assigned Reading [Cla88] Design Philosophy of the DARPA Internet Protocols [SRC84] End-to-end Arguments in System Design [Cla02] Tussle in Cyberspace: Defining Tomorrow’s Internet