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? Asynchronous communication Sending and receiving occur at different times

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?)

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

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

Internet Schematic Diagram

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

Basic Client/Server Interaction

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

Client/Server Relationships

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

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

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?

IP Addresses

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

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)

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

The .edu Domain

The .edu Domain

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

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

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)

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

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)

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

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

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

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)

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”

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

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

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

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

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