* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Network Edge and Network Core
Survey
Document related concepts
Internet protocol suite wikipedia , lookup
Net neutrality wikipedia , lookup
Asynchronous Transfer Mode wikipedia , lookup
Policies promoting wireless broadband in the United States wikipedia , lookup
Zero-configuration networking wikipedia , lookup
Wireless security wikipedia , lookup
Distributed firewall wikipedia , lookup
Net neutrality law wikipedia , lookup
Recursive InterNetwork Architecture (RINA) wikipedia , lookup
Wake-on-LAN wikipedia , lookup
Computer network wikipedia , lookup
Airborne Networking wikipedia , lookup
Network tap wikipedia , lookup
Deep packet inspection wikipedia , lookup
Cracking of wireless networks wikipedia , lookup
Transcript
Computer Networks Network Edge and Network Core Based on Computer Networking, 4th Edition by Kurose and Ross Stan Kurkovsky What’ What’s the Internet: “Nuts and Bolts” Bolts” View • millions of connected computing devices: hosts PC server wireless laptop cellular handheld access points wired links Mobile network = end systems • running network apps • communication links • fiber, copper, radio, satellite • transmission rate = Global ISP Home network Regional ISP bandwidth • routers: forward packets (chunks of data) Institutional network router Stan Kurkovsky 1 “Cool” Cool” Internet Appliances Web-enabled toaster + weather forecaster IP picture frame http://www.ceiva.com/ Internet phones Shaver with a LAN connectivity Stan Kurkovsky What’ What’s the Internet: “Nuts and Bolts” Bolts” View • protocols control sending, receiving of messages Mobile network • e.g., TCP, IP, HTTP, FTP, PPP, Skype, Ethernet Global ISP • Internet: “network of networks” networks” • loosely hierarchical • public Internet versus private intranet Home network Regional ISP • Internet standards • RFC: Request for comments • IETF: Internet Engineering Task Force Institutional network Stan Kurkovsky 2 What’ What’s the Internet: a Service View • communication infrastructure enables distributed applications: • Web, email, voice over IP, games, ee-commerce, file sharing • communication services provided to apps: • reliable data delivery from source to destination • “best effort” effort” (unreliable) data delivery Stan Kurkovsky What’ What’s a Protocol? human protocols: • “what’ what’s the time?” time?” • “I have a question” question” • introductions network protocols: • machines rather than humans • all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt … specific msgs sent … specific actions taken when msgs received, or other events Hi TCP connection request Hi TCP connection response Got the time? Get http://www.awl.com/kurose-ross 2:00 <file> time Stan Kurkovsky 3 A closer Look at Network Structure • network edge: • applications and hosts • network core: • interconnected routers • network of networks • access networks, physical media: • wired and wireless communication links Stan Kurkovsky The Network Edge • end systems (hosts): • • • run application programs e.g. Web, email at “edge of network” network” • client/server model: • client host requests, receives service from alwaysalways-on server • e.g. Web browser/server; email client/server • peerpeer-peer model: • minimal (or no) use of dedicated servers • e.g. Gnutella, KaZaA, KaZaA, Skype, BitTorrent Stan Kurkovsky 4 Network Edge: Reliable Data Transfer Service Goal: data transfer between end systems • handshaking: setup (prepare for) data transfer ahead of time • Hello, hello back human protocol • set up “state” state” in two communicating hosts • TCP - Transmission Control Protocol • Internet’ Internet’s connectionconnection-oriented service TCP service [RFC 793] • reliable, inin-order bytebyte-stream data transfer • loss: acknowledgements and retransmissions • flow control: • sender won’ won’t overwhelm receiver • congestion control: • senders “slow down sending rate” rate” when network congested Stan Kurkovsky Network Edge: Best Effort (Unreliable) Data Transfer Service Goal: data transfer between end systems • same as before! • UDP - User Datagram Protocol [RFC 768]: • • • • connectionless unreliable data transfer no flow control no congestion control App’ App’s using TCP: • HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email) (email) App’ App’s using UDP: • streaming media, teleconferencing, DNS, Internet telephony Stan Kurkovsky 5 Access Networks and Physical Media • How to connect end systems to edge router? • residential access nets • institutional access networks (school, company) • mobile access networks • Keep in mind: • bandwidth (bits per second) of access network? • shared or dedicated? Stan Kurkovsky Residential Access: Point to Point Access • Dialup via modem • up to 56Kbps direct access to router (often less) • Can’ Can’t surf and phone at same time: can’ can’t be “always on” on” • DSL: digital subscriber line • deployment: telephone company (typically) • 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 Stan Kurkovsky 6 Residential Access: Cable Modems • HFC: hybrid fiber coax • asymmetric: up to 30Mbps downstream, 2 Mbps upstream • network of cable and fiber attaches homes to ISP router • homes share access to router • deployment: available via cable TV companies Diagram: http://www.cabledatacomnews.com/cmic/diagram.html http://www.cabledatacomnews.com/cmic/diagram.html Stan Kurkovsky Cable Network Architecture: Overview FDM 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 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 Channels cable headend server(s) cable distribution network (simplified) home Typically 500 to 5,000 homes Stan Kurkovsky 7 Company Access: Local Area Networks • company/university local area network (LAN) connects end system to edge router • Ethernet: • 10 Mbs, Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet • modern configuration: end systems connect into Ethernet switch • LANs: chapter 5 Stan Kurkovsky Wireless Access Networks • shared wireless access network connects end system to router • via base station aka “access point” point” • wireless LANs: • 802.11b/g (WiFi ): 11 or 54 Mbps (WiFi): • widerwider-area wireless access • provided by telco operator • ~1Mbps over cellular system (EVDO, HSDPA) • next up (?): WiMAX (10’ (10’s Mbps) over wide area router base station mobile hosts Stan Kurkovsky 8 Home Networks Typical home network components: • DSL or cable modem • router/firewall/NAT • Ethernet • wireless access point to/from cable headend cable modem wireless laptops router/ firewall Ethernet wireless access point Stan Kurkovsky Physical Media • Bit: propagates between transmitter/receiver pairs • physical link: what lies between transmitter & receiver • guided media: • signals propagate in solid media: copper, fiber, coax • Twisted Pair (TP): two insulated copper wires • Category 3: traditional phone wires, 10 Mbps Ethernet • Category 5: 100Mbps Ethernet • unguided media: • signals propagate freely, e.g., radio Stan Kurkovsky 9 Physical Media • Coaxial cable: two concentric copper conductors • bidirectional • baseband: • single channel on cable • legacy Ethernet • broadband: • multiple channels on cable • HFC • Fiber optic cable: glass fiber carrying light pulses, each pulse a bit • highhigh-speed operation: • highhigh-speed pointpoint-toto-point transmission (e.g., 10’ 10’s-100’ 100’s Gps) Gps) • low error rate: repeaters spaced far apart; • immune to electromagnetic noise Stan Kurkovsky Physical Media • • • • Radio: signal carried in electromagnetic spectrum no physical “wire” wire” bidirectional propagation environment effects: • reflection • obstruction by objects • interference • Radio link types: • terrestrial microwave • e.g. up to 45 Mbps channels • LAN (e.g., WiFi) WiFi) • 2Mbps, 11Mbps, 54 Mbps • widewide-area (e.g., cellular) • e.g. 3G: hundreds of kbps • satellite • Kbps to 45Mbps channel (or multiple smaller channels) • 270 msec endend-end delay • geosynchronous versus low altitude Stan Kurkovsky 10 The Network Core • mesh of interconnected routers • the fundamental question: how is data transferred through net? • circuit switching: dedicated circuit per call: telephone net • packetpacket-switching: data sent thru net in discrete “chunks” chunks” Stan Kurkovsky Network Core: Circuit Switching EndEnd-end resources reserved for “call” call” • • • link bandwidth, switch capacity dedicated resources: no sharing circuitcircuit-like (guaranteed) performance • call setup required • network resources (e.g., bandwidth) divided into “pieces” pieces” • pieces allocated to calls • resource piece idle if not used by owning call (no sharing) • dividing link bandwidth into “pieces” pieces” • frequency division • time division Stan Kurkovsky 11 Circuit Switching: FDM and TDM Example: FDM 4 users frequency time TDM frequency time Stan Kurkovsky Numerical Examples • How long does it take to send a file of 640,000 bits from host A to host B over a circuitcircuit-switched network? • All links are 1.536 Mbps • Each link uses TDM with 24 slots/sec • 500 msec to establish endend-toto-end circuit • All links are 1.536 Mbps • Each link uses FDM with 24 channels/frequencies • 500 msec to establish endend-toto-end circuit Stan Kurkovsky 12 Network Core: Packet Switching each endend-end data stream divided into packets • user A, B packets share network resources • each packet uses full link bandwidth • resources used as needed resource contention: • aggregate resource demand can exceed amount available • congestion: packets queue, wait for link use • store and forward: packets move one hop at a time • Node receives complete packet before forwarding Bandwidth division into “pieces” pieces” Dedicated allocation Resource reservation Stan Kurkovsky Packet Switching: Statistical Multiplexing 10 Mb/s Ethernet A B statistical multiplexing C 1.5 Mb/s queue of packets waiting for output link D E Sequence of A & B packets does not have fixed pattern, shared on demand Î statistical multiplexing TDM: each host gets same slot in revolving TDM frame Stan Kurkovsky 13 Packet Switching: StoreStore-andand-Forward L R R R • Takes L/R seconds to transmit (push out) packet of L bits on to link or R bps • Entire packet must arrive at router before it can be transmitted transmitted on next link: store and forward • delay = 3L/R (assuming zero propagation delay) • Example: • • • L = 7.5 Mbits R = 1.5 Mbps Transmission delay = 15 sec Stan Kurkovsky Packet Switching versus Circuit Switching • Packet switching allows more users to use network! • Great for bursty data N users • resource sharing • simpler, no call setup 1 Mbps link • Excessive congestion: packet delay and loss • protocols needed for reliable data transfer, congestion control • Q: How to provide circuitcircuit-like behavior? • bandwidth guarantees needed for audio/video apps • still an unsolved problem • Q: What are human analogies? • reserved resources (circuit switching) • onon-demand allocation (packet(packet-switching) Stan Kurkovsky 14 Internet Structure: Network of Networks • roughly hierarchical • at center: “tiertier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coverage • treat each other as equals Tier-1 providers interconnect (peer) privately Tier 1 ISP Tier 1 ISP Tier 1 ISP Stan Kurkovsky TierTier-1 ISP: e.g., Sprint POP: point-of-presence to/from backbone peering … … . … … … to/from customers Stan Kurkovsky 15 Internet Structure: Network of Networks • “TierTier-2” ISPs: smaller (often regional) ISPs • Connect to one or more tiertier-1 ISPs, possibly other tiertier-2 ISPs Tier-2 ISP Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet Tier-2 ISP is customer of tier-1 provider Tier-2 ISP Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISPs also peer privately with each other. Tier-2 ISP Tier-2 ISP Stan Kurkovsky Internet Structure: Network of Networks • “TierTier-3” ISPs and local ISPs • last hop (“ (“access” access”) network (closest to end systems) local ISP Local and tier3 ISPs are customers of higher tier ISPs connecting them to rest of Internet Tier 3 ISP Tier-2 ISP local ISP local ISP local ISP Tier-2 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP local local ISP ISP Tier 1 ISP Tier-2 ISP local ISP Tier-2 ISP local ISP Stan Kurkovsky 16 Internet Structure: Structure: Network of Networks • a packet passes through many networks local ISP Tier 3 ISP Tier-2 ISP local ISP local ISP local ISP Tier-2 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP local local ISP ISP Tier 1 ISP Tier-2 ISP local ISP Tier-2 ISP local ISP Stan Kurkovsky 17