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IELM 231: IT for Logistics and Manufacturing

IELM 231: IT for Logistics and Manufacturing. Course Agenda. Introduction. IT applications design: Human-Computer Interface. Fundamental IT tools: sorting, searching. The Client-Server architecture, Interacting applications. IT in logistics, Case study 1: web-search. Search robots

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IELM 231: IT for Logistics and Manufacturing

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  1. IELM 231: IT for Logistics and Manufacturing Course Agenda Introduction IT applications design: Human-Computer Interface Fundamental IT tools: sorting, searching The Client-Server architecture, Interacting applications IT in logistics, Case study 1: web-search Search robots Data processing, Data storage/retrieval (DB, indexes) Data presentation: page ranking techniques IT in logistics, Case study 2: web-based auctions How auctions work Web issues: session tracking Web issues: secure communications Web issues: cash transactions

  2. The Internet and Web searching Part 1. The infrastructure of the web - The architecture of the Internet - The ISO/OSI 7-layer communication protocol - Client-server architecture for applications Part 2. How to use a web search engine [case study: Google] - Basic searching - Advanced searching (Booleans) and filtering (setting up local engines) - Searching data not accessible to search engines Part 3. How search engines work - Crawling the internet - Indexing of information, database design - Page ranking

  3. The Internet and Web searching Part 1. The infrastructure of the web - The architecture of the Internet - The ISO/OSI 7-layer communication protocol - Client-server architecture for applications

  4. Unit of digital communication: Packets All data (files, streamed data e.g. music, video) is transmitted using wires/optic-cables/wireless channels In most cases, there must be no error in the communication  the data on receiving computer is exactly same as data on sending computer Why zero-error ? [hint: uploaded programs] Zero error some error detection and correction technology must be used When is some error acceptable? [hint: video-conf, streaming] Long message  probability (error) is high  Need to re-transmit message ?

  5. To address From address 1/3 data (part 1 of 3) EDC To address From address 2/3 data (part 2 of 3) EDC To address From address 3/3 data (part 3 of 3) EDC Unit of digital communication: Packets Long message  p(error) is high  Need to re-transmit [part] of message Solution: Break message into small “packets”  send packets 1-by-1 To address From address Long message part 1 of 3 part 2 of 3 part 3 of 3 packets transmit Receiver Re-constructs Message from three parts received Typical packet size: 2048 - 4096 Bytes Question: Why do some web pages load in non-sequential fashion (some pictures load first, others later)

  6. Network terminology LAN: Local Area Network A network of communicating devices in a small area (e.g. a building, a factory, etc.) Common ways of physically connecting computers in a LAN: Cables (wires), Bluetooth, Wi-Fi… WAN: Wide Area Network Two or more LAN’s connected to each other, over a large area, e.g. international communication networks. Common ways of connecting between LAN’s in a WAN: Telephone networks, Long-distance cables, Satellites

  7. Network topologies Suppose N computers need to communicate with each other Pairwise connections: How many ? Problems ?

  8. Terminator Network topologies Network topology describes how different devices are (physically) connected to each other.

  9. millions of connected computing devices: hosts = end systems running network applications communication links fiber, copper, radio, satellite transmission rate = bandwidth routers: forward packets router workstation server mobile local ISP regional ISP UST network What is the internet

  10. protocolscontrol sending, receiving of msgs e.g., TCP, IP, HTTP, FTP, PPP Internet: “network of networks” public: Internet private: Intranet Internet standards RFC: Request for comments IETF: Internet Engineering Task Force What is the internet.. router workstation server mobile local ISP regional ISP UST network

  11. Get http://www.awl.com/kurose-ross time What is a protocol protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt a human protocol a computer protocol Hi TCP connection req Hi TCP connection response What’s the time? 2pm <file>

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

  13. End systems (hosts): run application 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 The network edge

  14. Goal: data transfer between end systems handshaking: setup (prepare for) data transfer ahead of time Hello, hello back human protocol set up “state” in two communicating hosts 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 e.g.

  15. Goal: data transfer between end systems App’s using TCP: HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP: Streaming media, Teleconferencing, DNS, Internet telephony Network edge: connection-less service e.g. UDP - User Datagram Protocol: connectionless unreliable data transfer no flow control no congestion control

  16. Network core Network core: a mesh of inter-connected routers Basic methods to transfer data through the net: Circuit switching Dedicated circuit per call, e.g. telephone net Packet-switching Data sent through net in discrete “chunks”

  17. 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

  18. 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 allocation: • total 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

  19. Packet Length: L bits Baud rate: R bps Time to push packet on link: L/R sec Entire packet must arrive at router before it can be transmitted on next link: store and forward delay = 3L/R Example: L = 7.5 Mbits R = 1.5 Mbps delay = 15 sec Packet switching: store and forward L R R R

  20. Q: How to connect end systems to edge router? residential access nets institutional access networks (school, company) mobile access networks Access networks and physical media

  21. Phone modem up to 56Kbps direct access to router (often less) Can’t surf and phone at same time: can’t be “always on” Residential access: point to point access • ADSL: asymmetric digital subscriber line [similar to NOW Broadband] • up to 1 Mbps upstream • up to 8 Mbps downstream

  22. Residential access: Cable modems cable headend home cable distribution network (simplified)

  23. Residential access: Cable modems.. Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

  24. company/univ local area network (LAN) connects end system to edge router Ethernet: shared or dedicated link connects end system and router 10 Mbs, 100Mbps, Gigabit Ethernet Company access: local area networks

  25. Shared wireless access network connects end system to router via base station aka “access point” Wireless LANs: 802.11b (WiFi): 11 Mbps (good for networks) bluetooth: 720Kbps (good for device-to-device) router base station mobile hosts Wireless access networks

  26. Typical home network components: ADSL or cable modem router/firewall/NAT Ethernet wireless access point Home networks wireless laptops to/from cable headend cable modem router/ firewall wireless access point Ethernet

  27. a packet passes through many networks! Tier 3 ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP Network Access Point Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP

  28. Networks are complex! many “pieces”: hosts routers links of various media applications protocols hardware, software Protocol “Layers”

  29. Analogy: Organization of air travel ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing (departure) ticket (complain) baggage (claim) gates (unload) runway landing airplane routing (arrival) airplane routing [intermediate air-traffic control points]

  30. Layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below airplane routing airplane routing Layering of airline functionality ticket ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing baggage gate takeoff/landing airplane routing departure airport intermediate air-traffic control centers arrival airport

  31. Dealing with complex systems: explicit structure allows identification, relationship of complex system’s pieces layered reference model for discussion modularization eases maintenance, updating 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 layering considered harmful? Why layering?

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

  33. network link physical link physical M M Ht Ht M M Hn Hn Hn Hn Ht Ht Ht Ht M M M M Hl Hl Hl Hl Hl Hl Hn Hn Hn Hn Hn Hn Ht Ht Ht Ht Ht Ht M M M M M M Encapsulation source message application transport network link physical segment datagram frame switch destination application transport network link physical router

  34. What’s inside a router Internet Protocol and IP addresses How packets are routed The Network Layer: Internet Protocol Internet Protocol (IP) The Internet Protocol (IP) is a network-layer (Layer 3) protocol that contains addressing information and some control information that enables packets to be routed.

  35. routing algorithm local forwarding table header value output link 0100 0101 0111 1001 3 2 2 1 value in arriving packet’s header 1 0111 2 3 Network layer functions: Forwarding and Routing Forwarding: determines which link to take at a specific router; Routing: plan of a series of forwarding data that can take the packet from source to destination DATAGRAM

  36. IP protocol version number 32 bits total datagram length (bytes) header length (bytes) type of service head. len ver length for fragmentation/ reassembly fragment offset “type” of data flgs 16-bit identifier max number remaining hops (decremented at each router) upper layer time to live Internet checksum 32 bit source IP address 32 bit destination IP address upper layer protocol to deliver payload to E.g. timestamp, record route taken, specify list of routers to visit. Options (if any) data (variable length, typically a TCP or UDP segment) IP datagram format how much overhead with TCP? • 20 bytes of TCP • 20 bytes of IP • = 40 bytes + app layer overhead

  37. Packets forwarded using destination host address packets between same source-dest pair may take different paths application transport network data link physical application transport network data link physical Datagram networks 1. Send data 2. Receive data Main router functions: • run routing algorithms/protocol (RIP, OSPF, BGP) • forwarding datagrams from incoming to outgoing link

  38. IP address: 32-bit identifier for host- router interface (128bits in Vista, OS-X) interface: connection between host/router and physical link router’s: 2 or more interfaces host 1 or more interfaces each interface has an IP address 223.1.1.2 223.1.3.27 223.1.3.1 223.1.2.1 223.1.2.2 223.1.3.2 223.1.1.1 223.1.2.9 223.1.1.4 223.1.1.3 223.1.1.1 = 11011111 00000001 00000001 00000001 223 1 1 1 IP Addressing IP Address is a locator to allow one IP device to ‘find’ another IP device

  39. IP address: subnet part (high order bits) host part (low order bits) What’s a subnet ? device interfaces with same subnet part of IP address can physically reach each other without intervening router Access networks and physical media 223.1.1.1 223.1.2.1 223.1.1.2 223.1.2.9 223.1.1.4 223.1.2.2 223.1.1.3 223.1.3.27 LAN 223.1.3.2 223.1.3.1 network consisting of 3 subnets

  40. 223.1.1.0/24 223.1.2.0/24 223.1.3.0/24 Subnets To determine the subnets, detach each interface from its host or router, creating islands of isolated networks. Each isolated network is called a subnet. Subnet mask: /24

  41. Subnets.. 223.1.1.2 How many ? 223.1.1.1 223.1.1.4 223.1.1.3 223.1.7.0 223.1.9.2 223.1.9.1 223.1.7.1 223.1.8.1 223.1.8.0 223.1.2.6 223.1.3.27 223.1.2.1 223.1.2.2 223.1.3.1 223.1.3.2

  42. Subnets… Subnets allow us to create sub-collection of IP devices, e.g. a LAN IP address is made of two parts: - Network address - Host (i.e. device) address How many bits (and which ones) of the IP address are used for Network address, and for Host ? Depends on the LAN: e.g. only 4 devices  we may only use 2 bits. Subnet mask specifies which bits are used for Host name:

  43. How does host get IP address? 1. Hard-coded by system administrator in a file Control-panelNetworkConfigurationtcp/ipproperties or 2.DHCP:Dynamic Host Configuration Protocol: Dynamically get address from a server (plug-and-play) IP Address: how to get one?

  44. People: many identifiers: HKID, name, passport # Internet hosts, routers: IP address (32 bit) - used for addressing datagrams “name”, e.g., www.yahoo.com - used by humans Q: map between IP addresses and name ? Domain Name System: distributed database implemented in hierarchy of many name servers application-layer protocol host, routers, name servers to communicate to resolvenames (address/name translation) DNS: Domain Name System Suppose a client wants to connect to a host www.amazon.co.uk (1) the “network” must tell us the IP address of a host www.amazon.co.uk (2) the client sends a “connect” request to that IP address.

  45. DNS.. How to find IP address of a named host? A DB of {Name  IP address} is stored on computers, Name Servers resource record name  IP, … zone of authority, managed by Name Server High level Name server Lower level Name server, can allocate, store names to computers below it in hierarchy

  46. provide logical communication between app processes running on different hosts Most common transport protocol: TCP application transport network data link physical application transport network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical logical end-end transport Transport services and Protocols The TCP provides a reliable, continuous stream of data - protocol for automatically requesting missing data - reordering IP packets that arrive out of order - converting IP datagrams to a streaming protocol - routing data within a computer to the correct application.

  47. Principles of network applications Web and HTTP FTP Electronic Mail SMTP, POP3, IMAP DNS Socket programming with TCP Building a Web server The Application Layer

  48. Write programs that run on different end systems and communicate over a network Example: Web server software communicates with browser software No software written for devices in network core Network core devices do not function at application layer This design allows for rapid app development application transport network data link physical application transport network data link physical application transport network data link physical Creating a network application

  49. Client-Server Architecture server: • always-on host • permanent IP address clients: • communicate with server • may be intermittently connected • may have dynamic IP addresses • do not communicate directly with each other

  50. Addressing processes For a process to receive messages, it must have an identifier (i.e. address) A host has a unique 32-bit IP address Does the IP address of the host on which the process runs suffice for identifying the process? Ans: No, many processes can be running on same host Problem: Most computers have only one “internet connection”, usually a serial port. How to manage multiple processes (e.g. mail, internet, ftp, telnet) sending/receiving packets of data through that line? Ans: The Operating system must somehow separate out one channel into multiple channels  Sockets

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