What s the Internet? Hardware view: What s the Internet? Hardware view: PC server wireless laptop cellular handheld access points wired s connected computing devices: hosts = end systems running apps communication s fiber, copper, radio, satellite transmission rate = bandwidth s: forward packets (chunks of data) obile Home Global Regional Institutional Introduction 1-1 Protocols control sending and receiving TCP, IP, HTTP, Ethernet Internet: of s Internet standards RFC: Request for comments IETF: Internet Engineering Task Force obile Global Home Regional Institutional Introduction 1-2 What s the Internet? Service view: What s a protocol? distributed s: Web, VoIP, email, games, e-commerce, file sharing communication services provided to apps: reliable data delivery best effort (unreliable) data delivery human protocols: what s the time? I have a question introductions protocols: protocols define format, order of msgs sent and received among entities, and actions taken on msg transmission, receipt machines rather than humans all communication activity in Internet governed by protocols Introduction 1-3 Introduction 1-4 What s a protocol? A closer look at structure: a human protocol and a computer protocol: Hi Hi Got the time? 2:00 time TCP connection request TCP connection response Get http://www.awl.com/kurose-ross <file> Introduction 1-5 edge: s and hosts access s, media: wired, wireless communication s core: interconnected s of s Introduction 1-6 1
The edge: end systems (hosts): run programs e.g. Web, email at edge of client/server model client host requests, receives peer-peer service from always-on server client/server e.g. Web browser/server; email client/server peer-peer model: minimal (or no) use of dedicated servers e.g. Skype, BitTorrent Access s and media Q: How to connect end systems to edge? residential access nets institutional access s (school, company) mobile access s Introduction 1-7 Introduction 1-8 Digital Subscriber Line (DSL) Cable Network Architecture: Overview home phone Existing phone line: 0-4KHz phone; 4-50KHz upstream data; 50KHz-1Hz downstream data Internet home PC DSL modem splitter central office telephone up to 30 bps downstream dedicated line to telephone central office cable headend cable distribution (simplified) home Introduction 1-9 Introduction 1-10 Fiber to the Home Ethernet Internet access ONT Internet OLT central office optical fiber optical s to the home two technologies: Passive Optical (PON) Active Optical Network (PAN) optical splitter optical fibers uch higher rates; also television and phone ONT ONT 100 bps 100 bps 100 bps Ethernet switch 1 Gbps server institutional to institution s typically used in companies, universities, etc 10 bps, 100bps, 1Gbps, 10Gbps Ethernet end systems typically connect into Ethernet switch Introduction 1-11 Introduction 1-12 2
Wireless access s Home s wireless access via base station aka access point wireless LANs: 802.11 wider-area wireless access provided by telco operator 3G, 4G WiAX over wide area??? base station mobile hosts Typical home components: DSL or cable modem /firewall Ethernet wireless access point to/from cable headend cable modem / firewall Ethernet wireless access point wireless laptops Introduction 1-13 Introduction 1-14 Physical edia Physical edia: coax, fiber : what lies between transmitter & receiver guided media (cables): 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 Ethernet Category 5: 100bps Ethernet Coaxial cable: two concentric copper conductors bidirectional baseband: single channel on cable broadband: multiple channels on cable Fiber optic cable: high-speed operation: high-speed point-to-point transmission (e.g., 10 s- 100 s Gpbs) low error rate repeaters spaced far apart immune to electromagnetic noise Introduction 1-15 Introduction 1-16 Physical media: radio signal carried in electromagnetic spectrum no wire bidirectional propagation environment effects: reflection obstruction by objects interference Radio types: terrestrial microwave e.g. up to 45 bps channels LAN (e.g., WiFi) 11bps, 54 bps wide-area (cellular) 3G, 4G satellite 270 msec end-end delay geosynchronous versus low altitude The Network Core mesh of interconnected s the fundamental question: how is data transferred through net? circuit switching: dedicated circuit per call: telephone net packet-switching: data sent thru net in discrete chunks Introduction 1-17 Introduction 1-18 3
Network Core: Circuit Switching Network Core: Circuit Switching end-end resources reserved for call bandwidth, switch capacity dedicated resources: no sharing Guaranteed performance call setup required resources (e.g., bandwidth) divided into pieces pieces allocated to calls resource piece idle if not used by owning call (no sharing) dividing bandwidth into pieces frequency division time division Introduction 1-19 Introduction 1-20 Circuit Switching: FD and TD Network Core: Packet Switching FD TD frequency time Example: 4 users each end-end data stream divided into packets user packets share resources each packet uses full bandwidth resources used as needed resource contention: demand can exceed amount available congestion: packets queue store and forward: packets move one hop at a time frequency time Introduction 1-21 Introduction 1-22 Packet switching versus circuit switching Is packet switching a winner? great for bursty data resource sharing simpler, no call setup congestion: packet delay and loss protocols needed for reliable data transfer, congestion control How to provide quality of service? bandwidth guarantees for audio/video apps still an unsolved problem Introduction 1-23 Internet structure: of s roughly hierarchical at center: small # of well-connected large s tier-1 commercial s (e.g., Verizon, Sprint, AT&T, Qwest, Level3), national & international coverage large content distributors (Google, Akamai, icrosoft) treat each other as equals Tier-1 s & Content s, interconnect (peer) privately or at Internet Exchange Points s Tier 1 Tier 1 Tier 1 Introduction 1-24 4
Tier-1 : e.g., Sprint Internet structure: of s tier-2 s: smaller (often regional) s connect to one or more tier-1 (provider) s each tier-1 has many tier-2 customer nets tier 2 pays tier 1 provider tier-2 nets sometimes peer directly with each other (bypassing tier 1), or at Tier 1 Introduction 1-25 Tier 1 Tier 1 Introduction 1-26 Internet structure: of s Tier-3 s, local s customer of tier 1 or tier 2 last hop ( access ) (closest to end systems) Internet structure: of s a packet passes through many s from source host to destination host Tier 1 Tier 1 Tier 1 Tier 1 Tier 1 Tier 1 Introduction 1-27 Introduction 1-28 Protocol Layers Networks are complex, with many pieces : hosts s s of various media s protocols hardware, software Question: Is there any hope of organizing structure of? Or at least our discussion of s? Why layering? Dealing with complex systems: structure allows identification, relationship of complex system s pieces layered reference model 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 Introduction 1-29 Introduction 1-30 5
Internet protocol stack ISO/OSI reference model : supporting s FTP, STP, HTTP : process-process data transfer TCP, UDP : routing of datagrams from source to destination IP, routing protocols : data transfer between neighboring elements Ethernet, 802.11 (WiFi) : bits on the wire presentation: allow s to interpret meaning of data, e.g., encryption, compression, machinespecific conventions session: synchronization, checkpointing, recovery of data exchange Internet stack missing these layers! these services, if needed, must be implemented in presentation session Introduction 1-31 Introduction 1-32 message segment H t datagram H n H t frame H l H n H t source Encapsulation switch H t H t H n H t H n H l destination H t H n H t H n H l H t H n Introduction 1-33 6