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Comparing Communication Types

Comparing Communication Types. Basic communication vocabulary Synchronous Communication Asynchronous communication Broadcast Multicast Point-to-point communication. General Communication. Synchronous communication Both sender and receiver active at same time Example?

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Comparing Communication Types

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  1. Comparing Communication Types • Basic communication vocabulary • Synchronous Communication • Asynchronous communication • Broadcast • Multicast • Point-to-point communication

  2. General Communication • Synchronous communication • Both sender and receiver active at same time • Example? • Asynchronous communication • Sending and receiving occur at different times • Example?

  3. General Communication • Based on number of receivers • Broadcast communication: single sender and many receivers (example?) • Multicast: many receivers, but usually a specific group (mailing list) • Point-to-point communication: one specific sender and one specific receiver (example?)

  4. Internet’s Communication Properties • Internet supports point-to-point, asynchronous communication • Internet provides a general communication “fabric”

  5. Internet’s Communication Properties • Internet is fast enough to mimic synchronous communication • Multicasting is also possible • Chat rooms • Streaming video accessible by anyone (broadcasting)

  6. Internet Schematic Diagram

  7. Client/Server Structure • Server stores info; client requests it • Most interactions (like loading web page) over the Internet use client/server interaction protocol • Click Web link • Client, requests page (file) from server • Web server responds with page contents • Client/server relationship ends

  8. Basic Client/Server Interaction

  9. Client/Server Structure • Relationships are brief, so a server can serve many clients “at the same time” • Ask, receive, done • Yahoo, Google, eBay… • One client computer can ask for services from many servers

  10. Client/Server Relationships

  11. Getting More Connected • Internet is primarily a point-to-point asynchronous communication system • Software has been built to implement the many forms of communication • E.g., Skype “slices up” signals from computer’s microphone and video camera into packet-size blocks

  12. Getting More Connected • Content is transferred to other party, whose client reassembles sound and image • Process relies on fast and reliable transmission

  13. Computer Addresses • IP Addresses • Each computer connected to Internet has unique address • Series of four numbers separated by dots • E.g., 166.66.86.42 • Range of each number is 0–255 • How many possible addresses?

  14. IP Addresses

  15. Computer Addresses • Domain Names • IP addresses hard to remember • Internet uses symbolic names for computers based on a hierarchy of domains • A domain is a related group of networked computers

  16. Computer Addresses • Domain Names • Example: turing.cs.millersville.edu • Name of computer is turing • Part of the CS department domain (cs) • Part of the MU domain (millersville) • Which is part of the educational domain(edu)

  17. Computer Addresses • Domains are hierarchical • Each is a member of the next larger domain • edu is a peer of other top-level domains such as com

  18. The .edu Domain

  19. The .edu Domain

  20. DNS Servers • Domain Name System (DNS) translates hierarchical, human-readable names into IP addresses • Every Internet host knows the IP address of its nearest DNS name server • Hostname needs to be translated to IP address by DNS server for communications

  21. DNS Servers • DNS uses client/server model • Name is sent to closest DNS server • If not on DNS server, it contacts an authoritative name server (ANS) • ANS has complete list of IP address/domain name mappings for all computers in its domain • Server returns address

  22. DNS Servers • Root name servers know addresses of name servers for edu, com, org, etc. domains • Their addresses are preprogrammed into your computer’s net software • Servers listed at www.root-servers.org (13 + mirrors)

  23. Top-Level Domains • Top-level domain names (TLDs) • .edu for educational groups • .com for commercial enterprises • .org for organizations • .net for networks • .mil for the military • .gov for government agencies

  24. Top-Level Domains • TLDs were expanded to include biz, info, name, travel, etc. • Full list can be found at www.icann.org(ICANN is Internet Corporation for Assigned Names and Numbers)

  25. Top-Level Domains • Also country code TLDs (ccTLDs) • ca (Canada) • uk (United Kingdom) • fr (France) • Allow domain names to be grouped by their country of origin

  26. Following Protocol Protocol describes the specific technical steps involved in a communication TCP/IP (Transmission Control Protocol/Internet Protocol) is key protocol used on Internet

  27. TCP/IP • TCP/IP Postcard Analogy • Internet communication is like sending a novel to your publisher using postcards • Novel is broken into small units that fit on a postcard • “postcards” are numbered to indicate where each belongs in the novel • As each postcard is completed, it is mailed

  28. TCP/IP • TCP/IP Postcard Analogy • Your publisher eventually receives postcards, but not necessarily in sequential order • Nor do they take the same route • Cards are finally ordered • These “postcards” are really IP packets • They hold: one unit of information, the destination IP, and their sequence number (which packet they are)

  29. Packets Are Independent • Each TCP/IP packet can take different route • Congestion and service interruptions do not delay transmissions • The TCP/IP protocol works under adverse conditions • Under heavy traffic packets may be “dropped”

  30. Packets Are Independent • If a packet is dropped, recipient can request a resend • Packets can arrive out of order

  31. Moving Packets: Wires & More • Internet uses • telephone carriers for long-distance connections • fiber optics (e.g., see http://www.submarinecablemap.com/) • dedicated lines for connections • Transmissions may rely on multiple technologies

  32. Far and Near: WAN and LAN • Internet is a collection of wide area networks (WAN) • Machines aren’t geographically close • Internet is a collection of point-to-point channels • Packets take several must visit a sequence of computers (or hops) before they reach their destination

  33. A ping is a “please reply” message See ping.eu or network-tools.com

  34. Far and Near: WAN and LAN • Local area network (LAN) • Computers are geographically close • Usually linked by a single cable or pair of wires • Ethernet is the main technology • Used in labs or buildings

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