Computer Networks 1-1 What s the Internet: nuts and bolts view PC server wireless laptop cellular handheld access points wired links millions of connected compu?ng devices: hosts = end systems running network apps communica?on links fiber, copper, radio, satellite transmission rate = bandwidth Mobile network Global Home network Regional Institutional network router routers: forward packets (chunks of data) 1-2 1
Cool internet appliances Web-enabled toaster + weather forecaster IP picture frame http://www.ceiva.com/ World s smallest web server http://www-ccs.cs.umass.edu/~shri/ipic.html Internet phones 1-3 What s the Internet: nuts and bolts view protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, Skype, Ethernet Internet: network of networks loosely hierarchical public Internet versus private intranet Internet standards RFC: Request for comments IETF: Internet Engineering Task Force Mobile network Global Home network Regional Institutional network 1-4 2
What s the Internet: a service view communica?on infrastructure enables distributed applica?ons: Web, VoIP, email, games, e- commerce, file sharing communica?on services provided to apps: reliable data delivery from source to des?na?on best effort (unreliable) data delivery 1-5 What s a protocol? human protocols: what s the?me? I have a ques?on introduc?ons specific msgs sent specific ac?ons taken when msgs received, or other events network protocols: machines rather than humans all communica?on ac?vity in Internet governed by protocols protocols define format, order of msgs sent and received among network en<<es, and ac<ons taken on msg transmission, receipt 1-6 3
What s a protocol? a human protocol and a computer network protocol: Hi Hi Got the time? 2:00 time TCP connection request TCP connection response Get http://www.awl.com/kurose-ross <file> Q: Other human protocols? 1-7 A closer look at network structure: network edge: applica?ons and hosts network core: interconnected routers network of networks access networks, physical media: wired, wireless communica?on links 1-8 4
The network edge: end systems (hosts): run applica?on programs e.g. Web, email at edge of network client/server model client host requests, receives service from always- on server e.g. Web browser/server; email client/server peer- peer model: minimal (or no) use of dedicated servers e.g. Skype, BitTorrent peer-peer client/server 1-9 Access networks and physical media Q: How to connect end systems to edge router? residen?al access nets ins?tu?onal access networks (school, company) mobile access networks Keep in mind: bandwidth (bits per second) of access network? shared or dedicated? 1-10 5
Dial- up Modem central office telephone network Internet home PC home dial-up modem modem (e.g., AOL) Uses exis?ng telephony infrastructure Home is connected to central office up to 56Kbps direct access to router (o`en less) Can t surf and phone at same?me: not always on Digital Subscriber Line (DSL) home phone Existing phone line: 0-4KHz phone; 4-50KHz upstream data; 50KHz-1MHz downstream data Internet DSLAM splitter telephone network home PC DSL modem central office Also uses exis?ng telephone infrastruture up to 1 Mbps upstream (today typically < 256 kbps) up to 8 Mbps downstream (today typically < 1 Mbps) dedicated physical line to telephone central office 6
Residen?al access: cable modems Does not use telephone infrastructure Instead uses cable TV infrastructure HFC: hybrid fiber coax asymmetric: up to 30Mbps downstream, 2 Mbps upstream network of cable and fiber ajaches homes to router homes share access to router unlike DSL, which has dedicated access 1-13 Residen?al access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html 1-14 7
Cable Network Architecture: Overview server(s) cable headend cable distribution network home 1-15 Cable Network Architecture: Overview FDM (more shortly): 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 A T A D A T A C O N T R O L 1 2 3 4 5 6 7 8 9 cable headend cable distribution network home 1-16 8
Fiber to the Home ONT Internet optical fibers OLT optical fiber ONT central office optical splitter Op?cal links from central office to the home Two compe?ng op?cal technologies: Passive Op?cal network (PON) Ac?ve Op?cal Network (PAN) Much higher Internet rates; fiber also carries television and phone services ONT Ethernet Internet access 100 Mbps Ethernet switch Institutional router To Institution s 100 Mbps 100 Mbps 1 Gbps server Typically used in companies, universi?es, etc 10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet Today, end systems typically connect into Ethernet switch 9
Wireless access networks shared wireless access network connects end system to router via base sta?on aka access point wireless LANs: 802.11b/g (WiFi): 11 or 54 Mbps wider- area wireless access provided by telco operator ~1Mbps over cellular system (EVDO, HSDPA) next up (?): WiMAX (10 s Mbps) over wide area router base station mobile hosts 1-19 Home networks Typical home network components: DSL or cable modem router/firewall/nat Ethernet wireless access point to/from cable headend cable modem router/ firewall Ethernet wireless access point wireless laptops 1-20 10
Physical Media Bit: propagates between transmijer/rcvr pairs physical link: what lies between transmijer & 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: tradi?onal phone wires, 10 Mbps Ethernet Category 5: 100Mbps Ethernet 1-21 Physical Media: coax, fiber Coaxial cable: two concentric copper conductors bidirec?onal baseband: single channel on cable legacy Ethernet broadband: mul?ple channels on cable HFC Fiber op?c cable: glass fiber carrying light pulses, each pulse a bit high- speed opera?on: - high- speed point- to- point transmission (e.g., 10 s- 100 s Gps) low error rate: repeaters spaced far apart ; immune to electromagne?c noise 1-22 11
Physical media: radio signal carried in electromagne?c spectrum no physical wire bidirec?onal propaga?on environment effects: reflec?on obstruc?on by objects interference Radio link types: terrestrial microwave e.g. up to 45 Mbps channels LAN (e.g., Wifi) 11Mbps, 54 Mbps wide- area (e.g., cellular) 3G cellular: ~ 1 Mbps satellite - Kbps to 45Mbps channel (or mul?ple smaller channels) - 270 msec end- end delay - geosynchronous versus low al?tude 1-23 The Network Core mesh of interconnected routers the fundamental ques?on: how is data transferred through net? circuit switching: dedicated circuit per call: telephone net packet- switching: data sent thru net in discrete chunks 1-24 12
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 Network 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?me division 1-25 Circuit Switching: FDM and TDM Example: FDM 4 users frequency TDM time frequency time 1-26 13
Network Core: Packet Switching each end- end data stream divided into packets user A, B packets share network resources each packet uses full link bandwidth resources used as needed Bandwidth division into pieces Dedicated allocation Resource reservation resource conten?on: aggregate resource demand can exceed amount available conges?on: packets queue, wait for link use store and forward: packets move one hop at a?me Node receives complete packet before forwarding 1-27 Packet- switching: store- and- forward L R R R takes L/R seconds to transmit (push out) packet of L bits on to link at R bps store and forward: en?re packet must arrive at router before it can be transmijed on next link delay = 3L/R (assuming zero propaga?on delay) Example: L = 7.5 Mbits R = 1.5 Mbps transmission delay = 15 sec 1-28 14
Packet switching versus circuit switching Packet switching allows more users to use network Is packet switching a slam dunk winner? great for bursty data resource sharing simpler, no call setup excessive conges?on: packet delay and loss protocols needed for reliable data transfer, conges?on control Q: How to provide circuit- like behavior? bandwidth guarantees needed for audio/video apps s?ll an unsolved problem Q: What are human analogies? reserved resources (circuit switching) on- demand alloca?on (packet- switching) 1-29 Internet structure: network of networks roughly hierarchical at center:?er- 1 s (e.g., Verizon, Sprint, AT&T, Cable and Wireless), na?onal/interna?onal coverage treat each other as equals Tier-1 providers interconnect (peer) privately Tier 1 Tier 1 Tier 1 1-30 15
Tier- 1 : e.g., Sprint POP: point-of-presence to/from backbone peering. to/from customers 1-31 Internet structure: network of networks Tier- 2 s: smaller (o`en regional) s Connect to one or more?er- 1 s, possibly other?er- 2 s Tier-2 pays tier-1 for connectivity to rest of Internet tier-2 is customer of tier-1 provider Tier-2 Tier-2 Tier 1 Tier 1 Tier 1 Tier-2 s also peer privately with each other. Tier-2 Tier-2 Tier-2 1-32 16
Internet structure: network of networks Tier- 3 s and s last hop ( access ) network (closest to end systems) Local and tier- 3 s are customers of higher tier s connecting them to rest of Internet Tier 3 Tier-2 Tier 1 Tier-2 Tier 1 Tier-2 Tier 1 Tier-2 Tier-2 1-33 Internet structure: network of networks a packet passes through many networks! Tier 3 Tier-2 Tier-2 Tier 1 Tier 1 Tier 1 Tier-2 Tier-2 Tier-2 1-34 17