January 17, 2002CE80N -- Winter Lecture #51 CE80N Introduction to Networks & The Internet Dr. Chane L. Fullmer UCSC Winter 2002

January 17, 2002CE80N -- Winter Lecture #52 Next Week – Inside the Internet 6. Jan 22 (T) Inside the Internet –Chapter 15, IP: Software to Create a Virtual Network 7. Jan 24 (Th) Inside the Internet –Chapter. 16, TCP: Software For Reliable Communication –Chapter. 19, Why the Internet Works Well

January 17, 2002CE80N -- Winter Lecture #53 More Internet History 1961: Kleinrock - queueing theory shows effectiveness of packet- switching 1964: Baran - packet- switching in military nets 1967: ARPAnet conceived by Advanced Research Projects Agency 1969: first ARPAnet node operational 1972: –ARPAnet demonstrated publicly –NCP (Network Control Protocol) first host- host protocol –first program –ARPAnet has 15 nodes : Early packet-switching principles

January 17, 2002CE80N -- Winter Lecture #54 More Internet History 1970: ALOHAnet satellite network in Hawaii 1973: Metcalfe’s PhD thesis proposes Ethernet 1974: Cerf and Kahn - architecture for interconnecting networks late70’s: proprietary architectures: DECnet, SNA, XNA late 70’s: switching fixed length packets (ATM precursor) 1979: ARPAnet has 200 nodes Cerf and Kahn’s internetworking principles: –minimalism, autonomy - no internal changes required to interconnect networks –best effort service model –stateless routers –decentralized control define today’s Internet architecture : Internetworking, new and proprietary nets

January 17, 2002CE80N -- Winter Lecture #55 More Internet History 1982: smtp protocol defined 1983: deployment of TCP/IP 1983: DNS defined for name-to-IP-address translation 1985: ftp protocol defined 1988: TCP congestion control new national networks: Csnet, BITnet, NSFnet 100,000 hosts connected to confederation of networks : new protocols, a proliferation of networks

January 17, 2002CE80N -- Winter Lecture #56 More Internet History Early 1990’s: ARPAnet decommissioned 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) early 1990s: WWW –hypertext [Bush 1945, Nelson 1960’s] –HTML, http: Berners-Lee –1994: Mosaic, later Netscape –late 1990’s: commercialization of the WWW Late 1990’s: est. 50 million computers on Internet est. 100 million+ users backbone links running at 1 Gbps 1990’s: commercialization, the WWW

January 17, 2002CE80N -- Winter Lecture #57 Reading Chapter 12, Packet Switching Chapter 13, A Network of Networks Chapter 14, ISPs and Network Connections

January 17, 2002CE80N -- Winter Lecture #58 How does a Network work?

January 17, 2002CE80N -- Winter Lecture #59 How Does the Network work ? Circuit switching –Network resources reserved and dedicated from sender to receiver (circuit) –Control signaling and data transfers are separated –Control information processing at circuit setup and termination

January 17, 2002CE80N -- Winter Lecture #510 How Does the Network Work? Sharing is a good thing.. –Saves money… One public phone vs. a cell phone for each individual One central conveyor belt in warehouse –But, costs time… Waiting for the resource to be free –Long winded conversationalist –Big order on the conveyor belt

January 17, 2002CE80N -- Winter Lecture #511 How Does the Network Work Sharing by taking turns… –Conveyor belt model Allow packages to be interspersed –Individual order’s packages are multiplexed with others onto the moving belt.. Networks use a similar idea –Packet Switching Packetize data to transfer Multiplex it onto the wire

January 17, 2002CE80N -- Winter Lecture #512 How Does the Network Work? Packet Switching Example C DDDD CC A D B C

January 17, 2002CE80N -- Winter Lecture #513 How Does the Network Work? Packet Switching… –Avoids some delays Resource is shared by multiplexing packets Short messages do not have to wait for long ones to complete. –Overhead Packetizing does not come for free –Header with labeling information is added

January 17, 2002CE80N -- Winter Lecture #514 How Does a Network Work Packet Switching… –Labeling (Header information) Source (sender’s) address Destination (recipient’s) address Packet size Sequence number Error checking information

January 17, 2002CE80N -- Winter Lecture #515 How Does a Network Work Packet Switching… –Computer Addresses Each computer attached to a network is assigned a unique number – called its address. A packet contains the address of the computer that sent it and the address of the computer to which it is sent.

January 17, 2002CE80N -- Winter Lecture #516 How Does a Network Work? Packet Switching… –Packet sizes are variable There is a maximum packet size –Maximum transmission unit (MTU) No minimum size –But, header size is fixed -- ~40 bytes –Transmission seems fast packets/second on campus LAN

January 17, 2002CE80N -- Winter Lecture #517 How Does a Network Work Packet Switching… –Sharing is automatic and fair Hardware handles the sharing Adapts as more/less computers are active –Remote devices can be shared Printers –Must be network “smart” File Systems

January 17, 2002CE80N -- Winter Lecture #518 Compare and Contrast Circuit-Switched –guaranteed transmission –large setup delays –reliable connection –quality-of-service –idle time is wasted –bandwidth granularity problem Packet-Switched –small setup delays, header overhead –unreliable connection –efficient use of available bandwidth –congestion (queues) result in dropped packets

January 17, 2002CE80N -- Winter Lecture #519 How Does a Network Work? Packet Switching and the Internet All data is transferred across the Internet in packets. A sender divides a message, or document, into packets and transfers the packets across the Internet. A receiver reassembles the original message from the packets that arrive. Packets from many machines traverse the Internet at the same time.

January 17, 2002CE80N -- Winter Lecture #520 The Network Core mesh of interconnected routers 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”

January 17, 2002CE80N -- Winter Lecture #521 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

January 17, 2002CE80N -- Winter Lecture #522 Network Core: Circuit Switching 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 –time division

January 17, 2002CE80N -- Winter Lecture #523 Bandwidth division into “pieces” Dedicated allocation Resource reservation Network Core: Packet Switching each end-to-end data stream is divided into packets user 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 –transmit over link –wait turn at next link

January 17, 2002CE80N -- Winter Lecture #524 Network Core: Packet Switching Packet-switching versus circuit switching: Personal Driving analogy –other human analogies? A 10 Mbs Ethernet D E B C 1.5 Mbs 45 Mbs statistical multiplexing queue of packets waiting for output link

January 17, 2002CE80N -- Winter Lecture #525 Network Core: Packet Switching Store & Forward Behavior

January 17, 2002CE80N -- Winter Lecture #526 Packet switching versus circuit switching 1 Mbit link each user: –100Kbps when “active” –active 10% of time circuit-switching: –10 users packet switching: –with 35 users, probability > 10 active less that.004 Packet switching allows more users to use network! N users 1 Mbps link

January 17, 2002CE80N -- Winter Lecture #527 Packet switching versus circuit switching Great for bursty data –resource sharing –no call setup Excessive congestion: packet delay and loss –protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behavior? –bandwidth guarantees needed for audio/video apps still an unsolved problem Is packet switching a “slam dunk winner?”

January 17, 2002CE80N -- Winter Lecture #528 Packet-switched networks: routing Goal: move packets among routers from source to destination –we’ll look at a couple of path selection algorithms datagram network: –destination address determines next hop –routes may change during session –analogy: driving, asking directions – without a map! virtual circuit network: –each packet carries tag (virtual circuit ID), tag determines next hop –fixed path determined at call setup time, remains fixed thru call –routers maintain per-call state

January 17, 2002CE80N -- Winter Lecture #529 Access networks and physical media Q: 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?

January 17, 2002CE80N -- Winter Lecture #530 Delay in packet-switched networks packets experience delay on end-to-end path four sources of delay at each hop Processing delay: –check bit errors –determine output link Queueing delay: –time waiting at output link for transmission –depends on congestion level of router A B propagation transmission nodal processing queueing

January 17, 2002CE80N -- Winter Lecture #531 Delay in packet-switched networks Transmission delay: R=link bandwidth (bps) L=packet length (bits) time to send bits into link = L/R Propagation delay: d = length of physical link s = propagation speed in medium (~3x10 8 m/sec) propagation delay = d/s A B propagation transmission nodal processing queueing Note: s and R are very different quantities!

January 17, 2002CE80N -- Winter Lecture #532 Queueing delay (revisited) R=link bandwidth (bps) L=packet length (bits)  = average packet arrival rate traffic intensity = (L/R) (L/R) ~ 0: average queueing delay small (L/R) -> 1: delays become large (L/R) > 1: more “work” arriving than can be serviced –average delay approaches infinity!

January 17, 2002CE80N -- Winter Lecture #533 How Does a Network Work? Various network technologies are incompatible… –Many tradeoffs – cost, speed, extensibility, etc.. It is impractical, or infeasible, to require all computers to use the same network technology –Needs of Engineering vs. Administration

January 17, 2002CE80N -- Winter Lecture #534 How Does a Network Work Extending a network is simple…. Network POTS Direct Wire Optical Fiber Dial-Up Line Wireless

January 17, 2002CE80N -- Winter Lecture #535 How Does A Network Work A computer can have multiple NICs –Each NIC can connect to a separate network Network A Network A Network B Network B

January 17, 2002CE80N -- Winter Lecture #536 How Does a Network Work Interconnecting Networks –A dedicated computer –Special software Restarts automatically on power up –Goal is to forward packets from one network to another – quickly, efficiently and correctly Process is called routing Computers are called routers

January 17, 2002CE80N -- Winter Lecture #537 How Does a Network Work Routers – Building blocks of the Internet The Internet is not a conventional network. It consists of thousands of computer networks interconnected by dedicated special purpose computers called routers –Routers can interconnect LANs and WANs

January 17, 2002CE80N -- Winter Lecture #538 How Does a Network Work Wide Area Backbone LAN Net  A Happy Router

January 17, 2002CE80N -- Winter Lecture #539 How Does the Network Work? Interconnecting networks was a revolutionary idea…. –Simply connect to your closest neighbor and you are in! –Issues now arise Privacy Politics Borders

January 17, 2002CE80N -- Winter Lecture #540 How Does a Network Work? Getting connected... –Connection service provided by an Internet Service Provider (ISP) Provides connection to the Internet –ISP agrees to route your packets to/from Internet – server –Web page presence –Other file space

January 17, 2002CE80N -- Winter Lecture #541 How Does a Network work Getting connected… –ISPs …. Provides access to/from your machine –“The Last Mile”.. Dial-up modem, ADSL, wireless, cable modem It isn’t free… –Pay for the Internet connection –Pay for “The last mile”…

January 17, 2002CE80N -- Winter Lecture #542 How Does a Network Work ? Getting Connected –Direct line, leased digital circuit 24/7 availability; very expensive -- $500+/mo High speed 1.5Mbps  …. –Dial-up modem $10-20/mo; not 24/7 Slow link (56Kbps, or less)

January 17, 2002CE80N -- Winter Lecture #543 How Does the Network Work ? Getting connected… –New technologies (A)DSL – (Asymmetric) Digital Subscriber Line –24/7; $50/mo; medium speed (384Kbps) –Multiplexes data and voice on same wires Cable modem –24/7; $50/mo; medium to high speed (  10Mbps) –Wire already in place in most (suburban) homes –Multiplexes data and TV signals on same wire Wireless –24/7; $??; slow to medium (10Kbps  10Mbps)

January 17, 2002CE80N -- Winter Lecture #544 How Does the Network Work? Residential access: point to point access –Dialup via modem up to 56Kbps direct access to router (conceptually) –ISDN: integrated services digital network: 128Kbps all-digital connect to router (overcome by ADSL) –ADSL: asymmetric digital subscriber line up to 1 Mbps home-to-router up to 8 Mbps router-to-home ADSL deployment: happening

January 17, 2002CE80N -- Winter Lecture #545 How Does the Network work ? Residential access: cable modems –HFC: hybrid fiber coax asymmetric: up to 1 Mbps upstream, 10 Mbps downstream –network of cable and fiber attaches homes to ISP router shared access to router among homes issues: congestion, dimensioning –deployment: available via cable companies

January 17, 2002CE80N -- Winter Lecture #546 How Does the Network Work? Institutional access: local area networks Corporate/University local area network (LAN) connects end system to edge router Ethernet: –shared or dedicated cable connects end system and router –10 Mbs, 100Mbps, Gigabit Ethernet deployment: institutions, home LANs soon

January 17, 2002CE80N -- Winter Lecture #547 How Does the Network Work? Wireless access networks shared wireless access network connects end system to router wireless LANs: –radio spectrum replaces wire –e.g., Lucent Wavelan 10 Mbps wider-area wireless access –CDPD: wireless access to ISP router via cellular network base station mobile hosts router

January 17, 2002CE80N -- Winter Lecture #548 Physical Media physical link: transmitted data bit propagates across link guided media: –signals propagate in solid media: copper, fiber unguided media: –signals propagate freely e.g., radio Twisted Pair (TP) two insulated copper wires –Category 3: traditional phone wires, 10 Mbps Ethernet –Category 5 TP: 100Mbps ethernet

January 17, 2002CE80N -- Winter Lecture #549 Physical Media: coax, fiber Coaxial cable: wire (signal carrier) within a wire (shield) –baseband: single channel on cable –broadband: multiple channels on cable bidirectional common use in 10Mbs Ethernet Fiber optic cable: glass fiber carrying light pulses high-speed operation: –100Mbps Ethernet –high-speed point-to-point transmission (e.g., 5 Gbs) low error rate

January 17, 2002CE80N -- Winter Lecture #550 Physical media: WireLess signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects: –Line of sight obstruction by objects –Reflection –Interference Radio link types: microwave –e.g. up to 45 Mbps channels LAN (e.g., waveLAN) –2Mbps, 11Mbps.. 54Mbps wide-area (e.g., cellular) –e.g. CDPD, 10’s Kbps satellite –up to 50Mbps channel (or multiple smaller channels) –270 msec end-to-end delay –geosynchronous versus LEOS

January 17, 2002CE80N -- Winter Lecture #551 How Does a Network Work? Instantaneous Access & Continuous Availability –Compare Dial-up vs dedicated connection A dedicated Internet connection that provides instantaneous access 24/7 changes the way people view the Internet, because it encourages frequent and casual use….

January 17, 2002CE80N -- Winter Lecture #552 How Does the Network Work? Summary –Circuit Switching Reserves resources –Packet Switching Shares resources Increased overhead – headers –Packets are labeled with destination info Efficient – resources used as needed Unreliable – packets can be dropped

January 17, 2002CE80N -- Winter Lecture #553 How Does the Network Work? Summary… –Packet Switching Store and Forward –Packets move one hop at a time –Decisions are made at each hop Delay.. –Processing delay –Queueing delay –Transmission delay –Propagation delay

January 17, 2002CE80N -- Winter Lecture #554 How Does the Network Work? Summary –A router is used to interconnect networks LANs to LANs or LANs to WANs Routers forward packets from one network to another –Process is called Routing Routers are the building blocks of the Internet

January 17, 2002CE80N -- Winter Lecture #555 How Does the Network Work? Summary –ISPs provide the connection service to access the Internet “The Last Mile” –Dialup –ADSL –Cable modem –Wireless Also may provide , web space or other services

January 17, 2002CE80N -- Winter Lecture #556

January 17, 2002CE80N -- Winter Lecture #557 Glossary Destination Address –A numeric value in a packet that specifies the computer to which the packet has been sent. Network Printer –A printer that attaches directly to a network where it can be accessed by any computer on the network.

January 17, 2002CE80N -- Winter Lecture #558 Glossary Packet –Used informally to describe the unit of data sent across a packet switching network. Packet Switching –A technique used on computer networks that requires a computer to divide a message into small packets of data before sending them.

January 17, 2002CE80N -- Winter Lecture #559 Glossary Fiber –a thin, flexible glass fiber used to transmit information using pulses of light. Network of networks –A phrase used to describe the Internet. Source Address –The address of the computer sending data.

January 17, 2002CE80N -- Winter Lecture #560 Glossary Route –In general, a route is the path that network traffic takes from its source to its destination. Router –A special purpose, dedicated computer that attaches to two or more networks and routes IP datagrams from one to the other.

January 17, 2002CE80N -- Winter Lecture #561 Glossary Cable Modem – A device that allows Internet service to be provided over the same coaxial cable wiring used for cable television. Dial-up Access –A technique used to access the Internet using a conventional telephone call.

January 17, 2002CE80N -- Winter Lecture #562 Glossary (A)DSL –((Asymmetric)Digital Subscriber Line) Any of several technologies used to deliver high- speed Internet access over the same wires used for telephone service. Wireless network –A network that uses radio waves to transmit in place of wires.