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1 Networking. 2 Internet History 1961: Kleinrock - queueing theory shows effectiveness of packet- switching 1961: Kleinrock - queueing theory shows effectiveness.

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Presentation on theme: "1 Networking. 2 Internet History 1961: Kleinrock - queueing theory shows effectiveness of packet- switching 1961: Kleinrock - queueing theory shows effectiveness."— Presentation transcript:

1 1 Networking

2 2 Internet History 1961: Kleinrock - queueing theory shows effectiveness of packet- switching 1961: Kleinrock - queueing theory shows effectiveness of packet- switching 1964: Baran - packet- switching in military nets 1964: Baran - packet- switching in military nets 1967: ARPAnet conceived by Advanced Research Projects Agency 1967: ARPAnet conceived by Advanced Research Projects Agency 1969: first ARPAnet node operational 1969: first ARPAnet node operational 1972: 1972: ARPAnet demonstrated publicly NCP (Network Control Protocol) first host- host protocol first e-mail program ARPAnet has 15 nodes 1961-1972: Early packet-switching principles

3 3 Internet History 1970: ALOHAnet satellite network in Hawaii 1970: ALOHAnet satellite network in Hawaii 1973: Metcalfe’s PhD thesis proposes Ethernet 1973: Metcalfe’s PhD thesis proposes Ethernet 1974: Cerf and Kahn - architecture for interconnecting networks 1974: Cerf and Kahn - architecture for interconnecting networks late70’s: proprietary architectures: DECnet, SNA, XNA late70’s: proprietary architectures: DECnet, SNA, XNA late 70’s: switching fixed length packets (ATM precursor) late 70’s: switching fixed length packets (ATM precursor) 1979: ARPAnet has 200 nodes 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 1972-1980: Internetworking, new and proprietary nets

4 4 Internet History 1983: deployment of TCP/IP 1983: deployment of TCP/IP 1982: SMTP e-mail protocol defined 1982: SMTP e-mail protocol defined 1983: DNS defined for name-to-IP-address translation 1983: DNS defined for name-to-IP-address translation 1985: FTP protocol defined 1985: FTP protocol defined 1988: TCP congestion control 1988: TCP congestion control new national networks: Csnet, BITnet, NSFnet, Minitel new national networks: Csnet, BITnet, NSFnet, Minitel 100,000 hosts connected to confederation of networks 100,000 hosts connected to confederation of networks 1980-1990: new protocols, a proliferation of networks

5 5 Internet History Early 1990’s: ARPAnet decommissioned Early 1990’s: ARPAnet decommissioned 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) early 1990s: Web early 1990s: Web hypertext [Bush 1945, Nelson 1960’s] hypertext [Bush 1945, Nelson 1960’s] HTML, HTTP: Berners-Lee HTML, HTTP: Berners-Lee 1994: Mosaic, later Netscape 1994: Mosaic, later Netscape late 1990’s: commercialization of the Web late 1990’s: commercialization of the Web Late 1990’s – 2000’s: more killer apps: instant messaging, peer2peer file sharing (e.g., Naptser) more killer apps: instant messaging, peer2peer file sharing (e.g., Naptser) network security to forefront network security to forefront est. 50 million host, 100 million+ users est. 50 million host, 100 million+ users backbone links running at Gbps backbone links running at Gbps 1990, 2000’s: commercialization, the Web, new apps

6 Structure of the Internet Europe Japan Backbone 1 Backbone 2 Backbone 3 Backbone 4, 5, N Australia Regional A Regional B NAP SOURCE: CISCO SYSTEMS MAPS UUNET MAP KOREA

7 Internet Host Count 1991- 2003 172,000,000 ESTIMATE: 300,000,000 hosts by 2005 “Host”  computer than can be reached by a URL

8 Internet Leverage by Country RankCountryUsers % of Users % of World Leverage 1U.S.166M25.04.525.55 2Japan56M8.42.054.20 3China46M7.020.970.33 4U.K.35M5.30.975.46 5Germany32M4.81.343.58 6 S. Korea 26M3.90.785.00 7Italy20M3.00.933.23 8Russia18M2.72.341.15 9France17M2.60.972.68 10Canada17M2.60.515.10 11Brazil14M2.12.840.74 12Australia11M1.70.325.31 13Netherlands10M1.50.265.77 LEVERAGE = % OF INTERNET USERS ÷ % OF WORLD POPULATION WORLD TOTAL USERS (AUG. 2003): 700,000,000

9 9 What’s the Internet: “nuts and bolts” view millions of connected computing devices: hosts, end-systems millions of connected computing devices: hosts, end-systems PCs workstations, servers PCs workstations, servers PDAs phones, toasters PDAs phones, toasters running network apps communication links communication links fiber, copper, radio, satellite fiber, copper, radio, satellite transmission rate = bandwidth transmission rate = bandwidth routers: forward packets (chunks of data) routers: forward packets (chunks of data) local ISP company network regional ISP router workstation server mobile

10 10 “Cool” internet appliances World’s smallest web server http://www-ccs.cs.umass.edu/~shri/iPic.html IP picture frame http://www.ceiva.com/ Web-enabled toaster+weather forecaster

11 11 What’s the Internet: “nuts and bolts” view protocols control sending, receiving of msgs protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, FTP, PPP e.g., TCP, IP, HTTP, FTP, PPP Internet: “network of networks” Internet: “network of networks” loosely hierarchical loosely hierarchical public Internet versus private intranet public Internet versus private intranet Internet standards Internet standards RFC: Request for comments RFC: Request for comments IETF: Internet Engineering Task Force IETF: Internet Engineering Task Force local ISP company network regional ISP router workstation server mobile

12 12 What’s the Internet: a service view communication infrastructure enables distributed applications: communication infrastructure enables distributed applications: Web, email, games, e- commerce, database., voting, file (MP3) sharing Web, email, games, e- commerce, database., voting, file (MP3) sharing communication services provided to apps: communication services provided to apps: connectionless connectionless connection-oriented connection-oriented cyberspace [Gibson]: cyberspace [Gibson]: “a consensual hallucination experienced daily by billions of operators, in every nation,...."

13 13 What’s a protocol? human protocols: “what’s the time?” “what’s the time?” “I have a question” “I have a question” introductions introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: machines rather than humans machines rather than humans all communication activity in Internet governed by protocols 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

14 14 What’s a protocol? a human protocol and a computer network protocol: Q: Other human protocols? Hi Got the time? 2:00 TCP connection req TCP connection response Get http://www.awl.com/kurose-ross time

15 15

16 16 A closer look at network structure: network edge: applications and hosts network edge: applications and hosts network core: network core: routers routers network of networks network of networks access networks, physical media: communication links access networks, physical media: communication links

17 17 The network edge: end systems (hosts): end systems (hosts): run application programs run application programs e.g. Web, email e.g. Web, email at “edge of network” at “edge of network” client/server model client/server model client host requests, receives service from always-on server client host requests, receives service from always-on server e.g. Web browser/server; email client/server e.g. Web browser/server; email client/server peer-peer model: peer-peer model: minimal (or no) use of dedicated servers minimal (or no) use of dedicated servers e.g. Gnutella, KaZaA e.g. Gnutella, KaZaA

18 18 Network edge: connection-oriented service Goal: data transfer between end systems handshaking: setup (prepare for) data transfer ahead of time handshaking: setup (prepare for) data transfer ahead of time Hello, hello back human protocol Hello, hello back human protocol set up “state” in two communicating hosts set up “state” in two communicating hosts TCP - Transmission Control Protocol TCP - Transmission Control Protocol Internet’s connection- oriented service Internet’s connection- oriented service TCP service [RFC 793] reliable, in-order byte- stream data transfer reliable, in-order byte- stream data transfer loss: acknowledgements and retransmissions flow control: flow control: sender won’t overwhelm receiver congestion control: congestion control: senders “slow down sending rate” when network congested

19 19 Network edge: connectionless service Goal: data transfer between end systems same as before! same as before! UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service unreliable data transfer unreliable data transfer no flow control no flow control no congestion control no congestion control App’s using TCP: HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email) HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP: streaming media, teleconferencing, DNS, Internet telephony streaming media, teleconferencing, DNS, Internet telephony

20 20 The Network Core mesh of interconnected routers mesh of interconnected routers the fundamental question: how is data transferred through net? the fundamental question: how is data transferred through net? circuit switching: dedicated circuit per call: telephone net circuit switching: dedicated circuit per call: telephone net packet-switching: data sent thru net in discrete “chunks” packet-switching: data sent thru net in discrete “chunks”

21 21 Network Core: Circuit Switching End-end resources reserved for “call” link bandwidth, switch capacity link bandwidth, switch capacity dedicated resources: no sharing dedicated resources: no sharing circuit-like (guaranteed) performance circuit-like (guaranteed) performance call setup required call setup required

22 22 Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces” pieces allocated to calls pieces allocated to calls resource piece idle if not used by owning call (no sharing) resource piece idle if not used by owning call (no sharing) dividing link bandwidth into “pieces” dividing link bandwidth into “pieces” frequency division frequency division time division time division

23 23 Packet switching versus circuit switching 1 Mbit link 1 Mbit link each user: each user: 100 kbps when “active” 100 kbps when “active” active 10% of time active 10% of time circuit-switching: circuit-switching: 10 users 10 users packet switching: packet switching: with 35 users, probability > 10 active less than.0004 with 35 users, probability > 10 active less than.0004 Packet switching allows more users to use network! N users 1 Mbps link

24 24 Network Taxonomy Telecommunication networks Circuit-switched networks FDM TDM Packet-switched networks Networks with VCs Datagram Networks Datagram network is not either connection-oriented or connectionless. Internet provides both connection-oriented (TCP) and connectionless services (UDP) to apps.

25 25 Access networks and physical media Q: How do connection end systems connect to edge router? residential access nets residential access nets institutional access networks (school, company) institutional access networks (school, company) mobile access networks mobile access networks Keep in mind: bandwidth (bits per second) of access network? bandwidth (bits per second) of access network? shared or dedicated? shared or dedicated?

26 26 Residential access: point to point access Dialup via modem Dialup via modem up to 56Kbps direct access to router (often less) up to 56Kbps direct access to router (often less) Can’t surf and phone at same time: can’t be “always on” Can’t surf and phone at same time: can’t be “always on” ADSL: asymmetric digital subscriber line ADSL: asymmetric digital subscriber line up to 1 Mbps upstream (today typically < 256 kbps) up to 1 Mbps upstream (today typically < 256 kbps) up to 8 Mbps downstream (today typically < 1 Mbps) up to 8 Mbps downstream (today typically < 1 Mbps) FDM: 50 kHz - 1 MHz for downstream FDM: 50 kHz - 1 MHz for downstream 4 kHz - 50 kHz for upstream 4 kHz - 50 kHz for upstream 0 kHz - 4 kHz for ordinary telephone 0 kHz - 4 kHz for ordinary telephone

27 27 Residential access: cable modems HFC: hybrid fiber coax HFC: hybrid fiber coax asymmetric: up to 10Mbps upstream, 1 Mbps downstream asymmetric: up to 10Mbps upstream, 1 Mbps downstream network of cable and fiber attaches homes to ISP router network of cable and fiber attaches homes to ISP router shared access to router among home shared access to router among home issues: congestion, dimensioning issues: congestion, dimensioning deployment: available via cable companies, e.g., MediaOne deployment: available via cable companies, e.g., MediaOne

28 28 Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

29 29 Cable Network Architecture: Overview home cable headend cable distribution network (simplified) Typically 500 to 5,000 homes

30 30 Cable Network Architecture: Overview home cable headend cable distribution network (simplified)

31 31 Cable Network Architecture: Overview home cable headend cable distribution network server(s)

32 32 Company access: local area networks company/univ local area network (LAN) connects end system to edge router company/univ local area network (LAN) connects end system to edge router Ethernet: Ethernet: shared or dedicated link connects end system and router shared or dedicated link connects end system and router 10 Mbs, 100Mbps, Gigabit Ethernet 10 Mbs, 100Mbps, Gigabit Ethernet deployment: institutions, home LANs happening now deployment: institutions, home LANs happening now

33 33 Wireless access networks shared wireless access network connects end system to router shared wireless access network connects end system to router via base station aka “access point” via base station aka “access point” wireless LANs: wireless LANs: 802.11b (WiFi): 11 Mbps 802.11b (WiFi): 11 Mbps wider-area wireless access wider-area wireless access provided by telco operator provided by telco operator 3G ~ 384 kbps 3G ~ 384 kbps Will it happen?? Will it happen?? WAP/GPRS in Europe WAP/GPRS in Europe base station mobile hosts router

34 34 Home networks Typical home network components: ADSL or cable modem ADSL or cable modem router/firewall/NAT router/firewall/NAT Ethernet Ethernet wireless access wireless access point point wireless access point wireless laptops router/ firewall cable modem to/from cable headend Ethernet (switched)

35 35 Physical Media Bit: propagates between transmitter/rcvr pairs Bit: propagates between transmitter/rcvr pairs physical link: what lies between transmitter & receiver physical link: what lies between transmitter & receiver guided media: guided media: signals propagate in solid media: copper, fiber, coax signals propagate in solid media: copper, fiber, coax unguided media: unguided media: signals propagate freely, e.g., radio signals propagate freely, e.g., radio Twisted Pair (TP) two insulated copper wires two insulated copper wires Category 3: traditional phone wires, 10 Mbps Ethernet Category 5 TP: 100Mbps Ethernet

36 36 Physical Media: coax, fiber Coaxial cable: two concentric copper conductors two concentric copper conductors bidirectional bidirectional baseband: baseband: single channel on cable single channel on cable legacy Ethernet legacy Ethernet broadband: broadband: multiple channel on cable multiple channel on cable HFC HFC Fiber optic cable: glass fiber carrying light pulses, each pulse a bit glass fiber carrying light pulses, each pulse a bit high-speed operation: high-speed operation: high-speed point-to-point transmission (e.g., 5 Gps) high-speed point-to-point transmission (e.g., 5 Gps) low error rate: repeaters spaced far apart ; immune to electromagnetic noise low error rate: repeaters spaced far apart ; immune to electromagnetic noise

37 37 Physical media: radio signal carried in electromagnetic spectrum signal carried in electromagnetic spectrum no physical “wire” no physical “wire” bidirectional bidirectional propagation environment effects: propagation environment effects: reflection reflection obstruction by objects obstruction by objects interference interference Radio link types: terrestrial microwave terrestrial microwave e.g. up to 45 Mbps channels e.g. up to 45 Mbps channels LAN (e.g., WaveLAN) LAN (e.g., WaveLAN) 2Mbps, 11Mbps 2Mbps, 11Mbps wide-area (e.g., cellular) wide-area (e.g., cellular) e.g. 3G: hundreds of kbps e.g. 3G: hundreds of kbps satellite satellite up to 50Mbps channel (or multiple smaller channels) up to 50Mbps channel (or multiple smaller channels) 270 msec end-end delay 270 msec end-end delay geosynchronous versus LEOS geosynchronous versus LEOS

38 38 Tier-1 ISP: e.g., Sprint Sprint US backbone network

39 39 Protocol “Layers” Networks are complex! many “pieces”: many “pieces”: hosts hosts routers routers links of various media links of various media applications applications protocols protocols hardware, software hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks?

40 40 Why layering? Dealing with complex systems: explicit structure allows identification, relationship of complex system’s pieces explicit structure allows identification, relationship of complex system’s pieces layered reference model for discussion layered reference model for discussion modularization eases maintenance, updating of system modularization eases maintenance, updating of system change of implementation of layer’s service transparent to rest 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 e.g., change in gate procedure doesn’t affect rest of system layering considered harmful? layering considered harmful?

41 41 Network abstractions International Standards Organization (ISO) developed the Open Systems Interconnection (OSI) model to describe networks: International Standards Organization (ISO) developed the Open Systems Interconnection (OSI) model to describe networks: 7-layer model. 7-layer model. Provides a standard way to classify network components and operations. Provides a standard way to classify network components and operations.

42 42 OSI model physical mechanical, electrical data link reliable data transport network end-to-end service transport connections presentation data format session application dialog control application end-use interface

43 43 OSI layers Physical: connectors, bit formats, etc. Physical: connectors, bit formats, etc. Data link: error detection and control across a single link (single hop). Data link: error detection and control across a single link (single hop). Network: end-to-end multi-hop data communication. Network: end-to-end multi-hop data communication. Transport: provides connections; may optimize network resources. Transport: provides connections; may optimize network resources.

44 44 OSI layers, cont’d. Session: services for end-user applications: data grouping, checkpointing, etc. Session: services for end-user applications: data grouping, checkpointing, etc. Presentation: data formats, transformation services. Presentation: data formats, transformation services. Application: interface between network and end-user programs. Application: interface between network and end-user programs.

45 45 Internet protocol stack application: supporting network applications application: supporting network applications FTP, SMTP, STTP FTP, SMTP, STTP transport: host-host data transfer transport: host-host data transfer TCP, UDP TCP, UDP network: routing of datagrams from source to destination network: routing of datagrams from source to destination IP, routing protocols IP, routing protocols link: data transfer between neighboring network elements link: data transfer between neighboring network elements PPP, Ethernet PPP, Ethernet physical: bits “on the wire” physical: bits “on the wire” application transport network link physical

46 46 Layering: logical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical Each layer: distributed distributed “entities” implement layer functions at each node “entities” implement layer functions at each node entities perform actions, exchange messages with peers entities perform actions, exchange messages with peers

47 47 Layering: logical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data E.g.: transport take data from app take data from app add addressing, reliability check info to form “datagram” add addressing, reliability check info to form “datagram” send datagram to peer send datagram to peer wait for peer to ack receipt wait for peer to ack receipt analogy: post office analogy: post office data transport ack

48 48 Layering: physical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data

49 49 Protocol layering and data Each layer takes data from above adds header information to create new data unit adds header information to create new data unit passes new data unit to layer below passes new data unit to layer below application transport network link physical application transport network link physical source destination M M M M H t H t H n H t H n H l M M M M H t H t H n H t H n H l message segment datagram frame

50 50 TCP/UDP

51 51 Transport protocols Transform host-to-host communication, offered by network layer, to process-to-process communication Transform host-to-host communication, offered by network layer, to process-to-process communication Deliver important services to application layer: Deliver important services to application layer: 1. Guaranteed message delivery 2. In-order delivery 3. Detect/eliminate message replication 4. Support arbitrarily large messages 5. Support synchronization between sender & receiver 6. Allow receiver to apply flow control to sender 7. Support multiple application processes on each host 8. Other services? (congestion control, quality-of-service, …) Overview: Overview: UDP: unreliable message delivery protocol UDP: unreliable message delivery protocol TCP: reliable stream transfer protocol TCP: reliable stream transfer protocol

52 52 User Datagram Protocol (UDP) Connectionless, unreliable, message delivery Connectionless, unreliable, message delivery But, optional checksum provides limited error detection But, optional checksum provides limited error detection Computed over UDP header, message, and IP pseudoheader Computed over UDP header, message, and IP pseudoheader Pseudoheader: IP src & dst addresses, protocol #, and UDP length Pseudoheader: IP src & dst addresses, protocol #, and UDP length If source does not want to compute checksum, it sets it to zero If source does not want to compute checksum, it sets it to zero Allows process demultiplexing using ports Allows process demultiplexing using ports 16 bits per port: 65536 possible channels per host 16 bits per port: 65536 possible channels per host No flow control: sender can overrun receiver’s buffers No flow control: sender can overrun receiver’s buffers

53 53 Transmission Control Protocol (TCP) Reliable, connection-oriented, byte-stream delivery service Reliable, connection-oriented, byte-stream delivery service Full duplex connection Full duplex connection Supports flow control (and congestion control; to be covered later) Supports flow control (and congestion control; to be covered later) Supports application layer demultiplexing using ports Supports application layer demultiplexing using ports Segments vs application-layer “writes”: when does TCP transmit a segment? Segments vs application-layer “writes”: when does TCP transmit a segment? Maximum Segment Size (MSS), Push operation, Send-Timer Maximum Segment Size (MSS), Push operation, Send-Timer Application process Write bytes TCP Send buffer Segment Transmit segments Application process Read bytes TCP Receive buffer … ……

54 54 TCP segment format Ports: as in UDP Ports: as in UDP SeqNum, AckNum, AdvWindow: used in sliding-window algorithm for reliable, in-order, unique delivery, and for flow-control SeqNum, AckNum, AdvWindow: used in sliding-window algorithm for reliable, in-order, unique delivery, and for flow-control Flags: SYN, FIN, RESET, PUSH, URG, ACK Flags: SYN, FIN, RESET, PUSH, URG, ACK Checksum: computed as in UDP (but required) Checksum: computed as in UDP (but required) HdrLen: in 32-bit words; TCP header may include options HdrLen: in 32-bit words; TCP header may include options TCP options: Maximum Segment Size (MSS), timestamp, window scale TCP options: Maximum Segment Size (MSS), timestamp, window scale

55 55 Connection establishment Caller (active open) and callee (passive open) Caller (active open) and callee (passive open) 3-way handshake algorithm 3-way handshake algorithm Why don’t we set the initial sequence numbers to zero? Why don’t we set the initial sequence numbers to zero? What if any of the 3WHS messages get lost/delayed? What if any of the 3WHS messages get lost/delayed? What if the server wants to deny the connection? What if the server wants to deny the connection? Map the Unix system calls socket(), bind(), connect(), listen(), accept() to the following diagram Map the Unix system calls socket(), bind(), connect(), listen(), accept() to the following diagram Active participant (client) Passive participant (server) SYN, SequenceNum = x SYN + ACK, SequenceNum = y, ACK, Acknowledgment = y + 1 Acknowledgment = x + 1

56 56 Connection termination Graceful close: independent termination of each direction of the connection Graceful close: independent termination of each direction of the connection Initiated by close() system call Initiated by close() system call After all pending data have been sent and ACKed, send last segment with FIN bit set After all pending data have been sent and ACKed, send last segment with FIN bit set That direction of the connection is closed 2*MSL seconds (2*120secs) after the remote end ACKs the FIN message That direction of the connection is closed 2*MSL seconds (2*120secs) after the remote end ACKs the FIN message Why do we need to wait before closing the connection? Why do we need to wait before closing the connection? Why to wait for 2* MSL instead of 1*MSL? Why to wait for 2* MSL instead of 1*MSL? Abrupt connection termination Abrupt connection termination Initiated by abort(), or by error conditions Initiated by abort(), or by error conditions Send segment with RST bit set, discarding any pending data Send segment with RST bit set, discarding any pending data

57 57 TCP connection establishment & tear- down state-transition diagram CLOSED LISTEN SYN_RCVDSYN_SENT ESTABLISHED CLOSE_WAIT LAST_ACKCLOSING TIME_WAIT FIN_WAIT_2 FIN_WAIT_1 Passive openClose Send/SYN SYN/SYN + ACK SYN + ACK/ACK SYN/SYN + ACK ACK Close/FIN FIN/ACKClose/FIN FIN/ACK ACK + FIN/ACK Timeout after two segment lifetimes FIN/ACK ACK Close/FIN Close CLOSED Active open/SYN

58 58 IP

59 59 Internet Protocol (IP) Designed by Kahn & Cerf in early 70s Designed by Kahn & Cerf in early 70s Most scalable and successful internetworking protocol Most scalable and successful internetworking protocol R1 ETH FDDI IP ETH TCP R2 FDDI PPP IP R3 PPP ETH IP H1 IP ETH TCP H8

60 60 IP in communication physical data link network transport presentation application session physical data link network transport presentation application session physical data link network node A router node B IP

61 61 IP service model Service model of an internetwork should be feasible by any underlying network technology Service model of an internetwork should be feasible by any underlying network technology IP service model: IP service model: host-to-host best-effort datagram delivery “Best-effort” means no guarantees for reliable or timely delivery “Best-effort” means no guarantees for reliable or timely delivery IP was designed to “run over anything” IP was designed to “run over anything”

62 62 IP header Important enough to remember its fields! Important enough to remember its fields! VersionHLen TOSLength IdentFlagsOffset TTLProtocolChecksum SourceAddr DestinationAddr Options (variable) Pad (variable) 048161931 Data

63 63 IP addresses IP vs MAC addresses IP vs MAC addresses Uniqueness requirement Uniqueness requirement Scalability requirement: hierarchy Scalability requirement: hierarchy Network Network Host (interface) Host (interface) Classful addressing: Classful addressing: Classes A, B, C, D, E Classes A, B, C, D, E In mid-90s, addressing became classless In mid-90s, addressing became classless see CIDR (later) see CIDR (later) Example: Example: GAtech web server (www.gatech.edu): 130.207.165.120 GAtech web server (www.gatech.edu): 130.207.165.120 NetworkHost 724 0 (a) NetworkHost 1416 10 (b) NetworkHost 218 110 (c)


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