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CSE401N Computer Networks Lecture-2 Network Structure[KR-1.2+1.3+1.4]

CSE401N Computer Networks Lecture-2 Network Structure[KR-1.2+1.3+1.4]. S. M. Hasibul Haque Dept. of CSE BUET. network edge: applications and hosts network core: routers network of networks access networks, physical media: communication links. A closer look at network structure:.

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CSE401N Computer Networks Lecture-2 Network Structure[KR-1.2+1.3+1.4]

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  1. CSE401NComputer NetworksLecture-2Network Structure[KR-1.2+1.3+1.4] S. M. Hasibul Haque Dept. of CSE BUET CSE401N

  2. network edge: applications and hosts network core: routers network of networks access networks, physical media: communication links A closer look at network structure: CSE401N

  3. end systems (hosts): run application programs e.g., WWW, email at “edge of network” client/server model client host requests, receives service from server e.g., WWW client (browser)/ server; email client/server peer-peer model: host interaction symmetric e.g.: Gnutella, KaZaA The network edge: CSE401N

  4. Goal: data transfer between end sys. handshaking: setup (prepare for) data transfer ahead of time Hello, hello back human protocol set up “state” in two communicating hosts TCP - Transmission Control Protocol Internet’s connection-oriented service Why not connected? TCP service[RFC 793] reliable, in-order byte-stream data transfer loss: acknowledgements and retransmissions flow control: sender won’t overwhelm receiver congestion control: senders “slow down sending rate” when network congested Network edge: connection-oriented service CSE401N

  5. Goal: data transfer between end systems same as before! UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service unreliable data transfer no flow control no congestion control App’s using TCP: HTTP (WWW), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP: streaming media, teleconferencing, Internet telephony Network edge: connectionless service CSE401N

  6. 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” The Network Core CSE401N

  7. End-end resources reserved for “call” link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required Network Core: Circuit Switching CSE401N

  8. 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 Network Core: Circuit Switching • dividing link bandwidth into “pieces” • frequency division • time division CSE401N

  9. Network Core: Circuit Switching CSE401N

  10. Example: 4 users FDMA frequency time TDMA frequency time Circuit Switching: TDMA and TDMA CSE401N

  11. Circuit Switching: Resources (Frequency and Time) • Divide link bandwidth—the resource--into “pieces” • frequency division multiplexing (FDM) • time division multiplexing (TDM) CSE401N

  12. Circuit Switching: The Process • Three phases • circuit establishment • data transfer • circuit termination • If circuit not available: “busy signal” CSE401N

  13. processing delay at Node 1 DATA propagation delay from Host 1 to Node 1 propagation delay from Host 2 To Host 1 data transmission circuit termination Timing Diagram of Circuit Switching Host 1 Host 2 Node 1 Node 2 circuit establishment CSE401N

  14. Delay Calculation in Circuit-Switched Networks • Propagation delay: delay for the first bit to go from source to destination • Transmission delay: time to pump data onto link at reserved rate Propagation delay: • d = length of physical link • s = propagation speed in medium (~2x105 km/sec) • propagation delay = d/s Transmission delay: • R = bandwidth (bps) • L = packet length (bits) • time to send a packet into link = L/R CSE401N

  15. An Example • Propagation delay • suppose the distance between host 1 and host 2 is 4000 km, then one-way propagation delay is: • Transmission delay • suppose we reserve one slot of a T1 line, which • has a bandwidth of 1.536 Mbps • is divided into 24 slots, and thus • each reserved slot has a bandwidth of 64 Kbps • then the transmission delay of a file with 6.4 Kbits is • Suppose the setup message is very small, and the total setup processing delay is 200 ms CSE401N

  16. An Example (cont.) • Then the delay to transfer a 6.4 Kbits file from host 1 to host 2 (from the beginning until host receives last bit of the file) is: DATA 20 + 200 20 20 100 CSE401N

  17. 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 Network Core: Packet Switching 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 CSE401N

  18. Header Data Trailer Packet Switching Each end-to-end data flow divided into packets • Packets have the following structure: • Header and Trailer carry control information (e.g., destination address, check sum) • (where is the control information for circuit switching?) • At each node the entire packet is received, stored briefly, and then forwarded to the next node (Store-and-Forward Networks) • Each packet is passed through the network from node to node along some path (Routing) CSE401N

  19. Packet Switching CSE401N

  20. Inside a Packet Switching Router • A node in a packet switching network node incoming links outgoing links Memory CSE401N

  21. Bandwidth division into “pieces” Resource reservation Dedicated allocation Packet Switching: Resources • Each packet waits for its turn at the output link • On its turn, a packet uses full link bandwidth • Resources used as needed • Aggregate resource demand can exceed amount available • Congestion: packets queue, wait for link use CSE401N

  22. A Taxonomy of Packet-Switched Networks According to Routing • Goal: move packets among routers from source to destination • we’ll study several routing algorithms later in the course • Two types of packet switching • datagram network • each packet of a flow is switched independently • virtual circuit network: • all packets from one flow are sent along a pre-established path (= virtual circuit) CSE401N

  23. Datagram Packet Switching • Example: IP networks • Each packet is independently switched • each packet header contains complete destination address • receiving a packet, a router looks at the packet’s destination address and searches its current routing table to determines the next hop • routes may change during session • routers do not keep any state about a flow An example of datagram-style routing in daily life? CSE401N

  24. Datagram Packet Switching Host C Host D Host A Node 1 Node 2 Node 3 Node 5 Host B Host E Node 7 Node 6 Node 4 CSE401N

  25. Packet 1 Packet 1 Packet 1 Packet 2 Packet 2 Packet 2 Packet 3 Packet 3 Packet 3 Timing Diagram of Datagram Switching Host 1 Host 2 Node 1 Node 2 propagation delay from Host 1 to Node 1 processing and queueing delay of Packet 1 at Node 2 transmission time of Packet 1 at Host 1 CSE401N

  26. Virtual-Circuit Packet Switching • Example: Asynchornous Transfer Mode (ATM) networks • Hybrid of circuit switching and datagram switching • each packet carries a short tag (virtual-circuit (VC) #), tag determines next hop • fixed path determined atVirtual Circuit setup time, remains fixed thru flow • routers maintain per-flow state • What advantages do virtual circuit have over datagram? • Guarantees in-sequence delivery of packets • However: Packets from different virtual circuits may be interleaved CSE401N

  27. Virtual-Circuit Switching Host C Host D Host A Node 1 Node 2 Node 3 Node 5 Host B Host E Node 7 Node 6 Node 4 CSE401N

  28. Virtual-Circuit Packet Switching • Three phases • VC establishment • Data transfer • VC disconnect CSE401N

  29. Packet 1 Packet 1 Packet 1 Packet 2 Packet 2 Packet 2 Packet 3 Packet 3 Packet 3 Timing Diagram of Virtual-Circuit Switching Host 1 Host 2 Node 1 Node 2 propagation delay between Host 1 and Node 1 VC establishment data transfer VC termination CSE401N

  30. Discussion: Datagram Switching vs. Virtual Circuit Switching • What are the benefits of datagram switching? • What are the benefits of virtual circuit switching? CSE401N

  31. Delay at a Router in Packet Switching • A packet experiences delay at each hop • Four types of delay at each hop • nodal processing delay: check errors & routing • queueing: time waiting for its turn at output link • transmission delay: time to pump packet onto a link at link speed • propagation delay: router to router propagation CSE401N

  32. Packet 1 Packet 1 Packet 1 Packet 2 Packet 2 Packet 2 Packet 3 Packet 3 Packet 3 Delay in Datagram Networks Host 1 Node 1 Node 2 Host 2 nodal processing and queueing delay of Packet 1 at Node 2 propagation delay between Host 1 and Node 2 transmission time of Packet 1 at Host 1 CSE401N

  33. Packet-switching versus circuit switching: human restaurant analogy other human analogies? D E Network Core: Packet Switching 10 Mbs Ethernet C A statistical multiplexing 1.5 Mbs B queue of packets waiting for output link 45 Mbs CSE401N

  34. 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 than .0004 Packet switching allows more users to use network! Packet switching versus circuit switching N users 1 Mbps link CSE401N

  35. 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 (chapter 6) Is packet switching a “slam dunk winner?” Packet switching versus circuit switching CSE401N

  36. Q: How to connection 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? Access networks and physical media CSE401N

  37. Dialup via modem up to 56Kbps direct access to router (conceptually) ISDN: integrated services digital network: 128Kbps all-digital connect to router ADSL: asymmetric digital subscriber line up to 1 Mbps home-to-router up to 8 Mbps router-to-home ADSL deployment: happening Residential access: point to point access CSE401N

  38. HFC: hybrid fiber coax asymmetric: up to 10Mbps upstream, 1 Mbps downstream network of cable and fiber attaches homes to ISP router shared access to router among home issues: congestion, dimensioning deployment: available via cable companies, e.g., MediaOne Residential access: cable modems CSE401N

  39. Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html CSE401N

  40. company/univ 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 happening now LANs: chapter 5 Institutional access: local area networks CSE401N

  41. shared wireless access network connects end system to router wireless LANs: radio spectrum replaces wire e.g., Lucent Wavelan 11 Mbps wider-area wireless access CDPD: wireless access to ISP router via cellular network router base station mobile hosts Wireless access networks CSE401N

  42. Typical home network components: ADSL or cable modem router/firewall Ethernet wireless access point Home networks wireless laptops to/from cable headend cable modem router/ firewall wireless access point Ethernet (switched) CSE401N

  43. 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 Physical Media CSE401N

  44. Coaxial cable: wire (signal carrier) within a wire (shield) baseband: single channel on cable broadband: multiple channel on cable bidirectional common use in 10Mbs Ethernet Physical Media: coax, fiber Fiber optic cable: • glass fiber carrying light pulses • high-speed operation: • 100Mbps Ethernet • high-speed point-to-point transmission (e.g., 5 Gps) • low error rate CSE401N

  45. signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects: reflection obstruction by objects interference Physical media: radio Radio link types: • microwave • e.g. up to 45 Mbps channels • LAN (e.g., WaveLAN) • 2Mbps, 11Mbps • wide-area (e.g., cellular) • e.g. CDPD, 10’s Kbps • satellite • up to 50Mbps channel (or multiple smaller channels) • 270 Msec end-end delay • geosynchronous versus LEOS CSE401N

  46. Thank YOU CSE401N

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