Lecture Computer Networks WS 2016/2017

Transcription

1 Lecture Computer Networks WS 2016/2017 Prof. Dr. Werner Filip 1-1 References James F. Kurose, Keith W. Ross, Computer Networking, A Top-Down Approach, (6th Edition), Pearson, Andrew S. Tanenbaum Computer Networks, (5th Edition), Pearson, Douglas E. Comer, Computer Networks and Inters, (6th Edition), Pearson,

2 Lecture: Computer Networks Chapter 1 Introduction Chapter 2 Application Layer Chapter 3 Transport Layer Chapter 4 Network Layer Chapter 5 Data Link Layer and LANs Chapter 6 Network anagement Introduction 1-3 Chapter 1 Introduction A note on the use of these ppt slides: We re making these slides freely available to all (faculty, students, readers). They re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) that you mention their source (after all, we d like people to use our book!) If you post any slides on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. Thanks and enjoy! JFK/KWR All material copyright J.F Kurose and K.W. Ross, All Rights Reserved Computer Networking: A Top Down Approach 6 th edition i Jim Kurose, Keith Ross Addison-Wesley arch 2012 Introduction 1-4 2

3 Chapter 1: Introduction Our goal: get feel and terminology more depth, detail later in course approach: use Inter as example Overview: what s the Inter? what s a protocol? edge: hosts,, physical media core: packet/circuit switching, Inter structure protocol layers, service models history Introduction 1-5 Chapter 1: roadmap 1.1 What is the Inter? 1.2 Network edge end systems, s, links 1.3 Network core circuit switching, packet switching, structure 1.4 Protocol layers, service models 1.5 History Introduction 1-6 3

4 What s the Inter: nuts and bolts view PC server wireless laptop smartphone router wireless links wired links millions of connected computing devices: hosts = end systems running apps communication links fiber, copper, radio, satellite transmission rate: bandwidth Packet switches: forward packets (chunks of data) routers and switches institutional mobile home global ISP regional ISP Introduction 1-7 Cool inter appliances IP picture frame Web-enabled toaster + weather forecaster World s smallest web server Inter phones Introduction 1-8 4

5 What s the Inter: nuts and bolts view protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, Skype, Ether Inter: of s loosely hierarchical public Inter versus private intra Inter standards RFC: Request for comments IETF: Inter Engineering Task Force mobile institutional home global ISP regional ISP Introduction 1-9 What s the Inter: a service view communication infrastructure enables distributed applications: Web, VoIP, , games, e-commerce, file sharing communication services provided to apps: reliable data delivery from source to destination best effort (unreliable) data delivery mobile institutional home global ISP regional ISP Introduction

6 What s a protocol? human protocols: what s the time? I have a question introductions specific msgs sent specific actions taken when msgs received, or other events protocols: machines rather than humans all communication activity in Inter governed by protocols protocols define format, order of msgs sent and received among entities, and actions taken on msg transmission, receipt Introduction 1-11 What s a protocol? a human protocol and a computer protocol: Hi Hi Got the time? 2:00 time TCP connection request TCP connection response Get <file> Introduction

7 Chapter 1: roadmap 1.1 What is the Inter? Network edge end systems, s, links 1.3 Network core circuit switching, packet switching, structure 1.4 Protocol layers, service models 1.5 History Introduction 1-13 A closer look at structure: edge: applications and hosts s, physical media: wired, wireless communication links core: interconnected routers of s mobile institutional home global ISP regional ISP Introduction

8 The edge: end systems (hosts): run application programs e.g. Web, at edge of client/server model peer-peer client host requests, receives service from always-on server client/server e.g. Web browser/server; client/server peer-peer model: minimal (or no) use of dedicated servers e.g. Skype Introduction 1-15 Access s and physical media Q: How to connect end systems to edge router? residential i s institutional s (school, company) mobile s Keep in mind: bandwidth (bits per second) of? shared or dedicated? Introduction

9 Access : digital subscriber line (DSL) central office telephone DSL modem splitter voice, data transmitted at different frequencies over dedicated line to central office DSLA DSL multiplexer ISP use existing iti telephone line to central office DSLA data over DSL phone line goes to Inter voice over DSL phone line goes to telephone < 2.5 bps upstream transmission rate (typically < 1 bps) < 24 bps downstream transmission rate (typically < 10 bps) Introduction 1-17 Access : cable cable headend cable modem splitter V I D E O V I D E O V I D E O V I D E O V I D E O Channels V I D E O D D A A T T A A C O N T R O L frequency division multiplexing: different channels transmitted in different frequency bands Introduction

10 Access : cable cable headend cable modem splitter data, TV transmitted at different frequencies over shared cable distribution CTS ISP cable modem termination system HFC: hybrid fiber coax asymmetric: up to 30bps downstream transmission rate, 2 bps upstream transmission rate of cable, fiber attaches homes to ISP router homes share to cable headend unlike DSL, which has dedicated to central office Introduction 1-19 Access : home wireless devices often combined in single box to/from headend or central office cable or DSL modem wireless point (54 bps) router, firewall, NAT wired Ether (100 bps) Introduction

11 Enterprise s (Ether) institutional link to ISP (Inter) institutional router Ether switch institutional mail, web servers typically used in companies, universities, etc. 10 bps, 100bps, 1Gbps, 10Gbps transmission rates today, end systems typically connect into Ether switch Introduction 1-21 Wireless s shared wireless connects end system to router via base station point wireless LANs: within building (100 ft) b/g (WiFi): 11, 54 bps transmission rate wide-area wireless provided by telco (cellular) operator, 10 s km between 1 and 10 bps 3G, 4G: LTE to Inter to Inter Introduction

12 Physical edia Bit: propagates between transmitter/rcvr pairs physical link: what lies between transmitter & receiver guided media: signals propagate in solid media: copper, fiber, coax unguided media: signals propagate freely, e.g., radio Twisted Pair (TP) two insulated copper wires Category 3: traditional phone wires, 10 bps Ether Category 5: 100bps Ether Introduction 1-23 Physical edia: coax, fiber Coaxial cable: two concentric copper conductors bidirectional baseband: single channel on cable legacy Ether broadband: multiple channels on cable HFC (hybrid fiber coax) Fiber optic cable: glass fiber carrying light pulses, each pulse a bit high-speed operation: high-speed point-to-point transmission (e.g., 10 s s Gps) low error rate: immune to electromagic noise Introduction

13 Physical media: radio signal carried in electromagic spectrum no physical wire bidirectional propagation environment effects: reflection obstruction by objects interference Radio link types: terrestrial microwave e.g. up to 45 bps channels LAN (e.g., Wifi) 11bps, 54 bps wide-area (e.g., cellular) 3G cellular: ~ 1 bps satellite Kbps to 45bps channel (or multiple smaller channels) 270 msec end-end delay Introduction 1-25 Chapter 1: roadmap 1.1 What is the Inter? 1.2 Network edge end systems, s, links 1.3 Network core circuit switching, packet switching, structure 1.4 Protocol layers, service models 1.5 History Introduction

14 The Network Core mesh of interconnected routers the fundamental question: how is data transferred through? circuit switching: dedicated circuit per call: telephone packet-switching: data sent through in discrete chunks Introduction 1-27 Network Core: Circuit Switching End-end resources reserved for call link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required Introduction

15 Network Core: Circuit Switching resources (e.g., bandwidth) divided into pieces pieces allocated to calls resource piece idle if not used by owning call (no sharing) dividing link bandwidth into pieces frequency division time division multiplexing Introduction 1-29 Circuit switching: FD versus TD FD Example: 4 users frequency TD time frequency time Introduction

16 Packet Switching: Statistical ultiplexing A 100 b/s Ether statistical multiplexing C B queue of packets waiting for output link 1.5 b/s D E Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand statistical multiplexing. Introduction 1-31 Inter structure: of s End systems connect to Inter via ISPs Residential, company and university ISPs Access ISPs in turn must be interconnected. So that any two hosts can send packets to each other Resulting of s is very complex Evolution was driven by economics and national policies Let s take a stepwise approach to describe current Inter structure Introduction

17 Inter structure: of s Question: given millions of ISPs, how to connect them together? Introduction 1-33 Inter structure: of s Option: connect each ISP to every other ISP? connecting each ISP to each other directly connections. (doesn t scale) Introduction

18 Inter structure: of s Option: connect each ISP to a global transit ISP? Customer and provider ISPs have economic agreement. global ISP Introduction 1-35 Inter structure: of s But if one global ISP is viable business, there will be competitors ISP A ISP B ISP C Introduction

19 Inter structure: of s But if one global ISP is viable business, there will be competitors. which must be interconnected Inter exchange point ISP A IXP IXP ISP B ISP C peering link Introduction 1-37 Inter structure: of s and regional s may arise to connect s to ISPS ISP A IXP IXP ISP B ISP C regional Introduction

20 Inter structure: of s and content provider s (e.g., Google, icrosoft, ) may run their own, to bring services, content close to end users ISP A IXP Content provider IXP ISP B ISP B regional Introduction 1-39 Inter structure: of s Tier 1 ISP Tier 1 ISP Google IXP IXP IXP Regional ISP Regional ISP ISP ISP ISP ISP ISP ISP ISP ISP at center: small # of well-connected large s tier-1 commercial ISPs (e.g., Level 3, Sprint, AT&T, NTT), national & international coverage content provider (e.g, Google): private that connects it data centers to Inter, often bypassing tier-1, regional ISPs Introduction

21 Tier-1 ISP: e.g., Sprint POP: point-of-presence to/from backbone peering to/from customers Introduction 1-41 Chapter 1: roadmap 1.1 What is the Inter? 1.2 Network edge end systems, s, links 1.3 Network core circuit switching, packet switching, structure 1.4 Protocol layers, service models 1.5 History Introduction

22 Chapter 1: roadmap 1.1 What is the Inter? 1.2 Network edge end systems, s, links 1.3 Network core circuit switching, packet switching, structure 1.4 Protocol layers, service models 1.5 History Introduction 1-43 Protocol Layers Networks are complex! many pieces : hosts routers links of various media applications protocols hardware, software Question: Is there any hope of organizing structure of? Or at least our discussion ssi of s? Introduction

23 Organization of air travel ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing airplane routing a series of steps Introduction 1-45 Layering of airline functionality ticket (purchase) ticket (complain) ticket baggage (check) baggage (claim baggage gates (load) gates (unload) gate runway (takeoff) runway (land) takeoff/landing airplane routing airplane routing airplane routing airplane routing airplane routing departure airport intermediate air-traffic control centers arrival airport Layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below Introduction

24 Why layering? Dealing with complex systems: explicit structure allows identification, relationship of complex system s pieces layered reference model for discussion modularization eases maintenance, updating of system change of implementation of layer s service transparent to rest of system e.g., change in gate procedure doesn t affect rest of system layering considered harmful? Introduction 1-47 Inter protocol stack application: supporting applications FTP, STP, HTTP transport: process-process data transfer TCP, UDP : routing of datagrams from source to destination IP, routing protocols link: data transfer between neighboring elements PPP, Ether physical: bits on the wire application transport link physical Introduction

25 ISO/OSI reference model (International Organization for Standardization / Open Systems Interconnection) presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machinespecific conventions session: synchronization, checkpointing, recovery of data exchange Inter stack missing these layers! these services, if needed, d must be implemented in application needed? application presentation session transport link physical Introduction 1-49 Inter protocol stack and data Each layer gets data from the next layer above (except appl. layer) Adds header information and creates a new Data Unit Forwards new Data Unit to next lower layer Protocol Data Unit (PDU) Source Destination Ht Hn Ht Hl Hn Ht application transport data link physical application transport data link physical Ht Hn Ht Hl Hn Ht essage Segment Datagram Frame Introduction

26 message segment H t datagram H n H t frame H l H n H t source application transport link physical Encapsulation link physical Protocol Data Unit (PDU) switch H l H t H n H t H n H t destination application transport link physical H n H t H l H n H t link H n H t physical router Introduction 1-51 Chapter 1: roadmap 1.1 What is the Inter? 1.2 Network edge end systems, s, links 1.3 Network core circuit switching, packet switching, structure 1.4 Protocol layers, service models 1.5 History Introduction

27 Chapter 1: roadmap 1.1 What is the Inter? 1.2 Network edge end systems, s, links 1.3 Network core circuit switching, packet switching, structure 1.4 Protocol layers, service models 1.5 History Introduction 1-53 Inter History : Early packet-switching principles 1961: Kleinrock - queueing theory shows effectiveness of packetswitching 1964: Baran - packetswitching in military s 1967: ARPA conceived by Advanced Research Projects Agency 1969: first ARPA node operational 1972: ARPA public demonstration ti NCP (Network Control Protocol) first host-host protocol first program ARPA has 15 nodes Introduction

28 Inter History : Intering, new and proprietary s 1970: ALOHA satellite in Hawaii 1974: Cerf and Kahn - architecture for interconnecting s 1976: Ether at Xerox PARC late70 s: proprietary architectures: DEC, SNA 1979: ARPA has 200 nodes Cerf and Kahn s intering principles: ples minimalism, autonomy - no internal changes required to interconnect s best effort service model stateless routers decentralized control define today s Inter architecture Introduction 1-55 Inter History : new protocols, a proliferation of s 1983: deployment of TCP/IP 1982: STP protocol defined 1983: DNS defined for name-to-ipaddress translation 1985: FTP protocol defined 1988: TCP congestion control new national s: Cs, BIT, NSF (National Science Foundation), initel 100,000 hosts connected to confederation of s Introduction

29 Inter History 1990, 2000 s: commercialization, the Web, new apps Early 1990 s: ARPA decommissioned 1991: NSF lifts restrictions on commercial use of NSF (decommissioned, 1995) early 1990s: Web hypertext [Bush 1945, Nelson 1960 s] HTL, HTTP: Berners-Lee 1994: osaic, later Netscape late 1990 s: commercialization of the Web Late 1990 s 2000 s: more killer apps: instant messaging, P2P file sharing security to forefront est. 50 million hosts, 100 million+ users backbone links running at Gbps Introduction 1-57 Inter History 2007: ~ 500 million hosts Voice, Video over IP P2P applications: Skype (VoIP) more applications: YouTube, gaming wireless, mobility 2014: ~ 2,9 billion (2,9 x 10 9 ) Inter Users Introduction

30 Inter History 2016: ~ 4 billion (4 x 10 9 ) Inter Users Introduction 1-59 Introduction: Summary Covered a ton of material! Inter overview what s a protocol? edge, core, packet-switching versus circuit-switching Inter structure layering, service models history You now have: context, overview, ew, feel of ing more depth, detail to follow! Introduction