Telecommunications 1

Transcription

1 Telecommunications 1 Introduction to ECEN 1200 Peter Mathys Electronic Communication Which examples of electronic communication systems come to your mind? From the time you got up this morning, how many communication systems did you use? What does that tell you about electronic communication?

2 Examples Telephone, pager Radio, TV Internet, WWW Fax CB radio Baby monitor Not So Obvious CD player Walkman, ipod Videotape, DVD IR (infrared) remote control Remote keyless entry system Barcodes, UPC

3 Chances Are You Used Radio (to wake up) Telephone (talk to a friend) ipod (while jogging) (check what s going on) WWW (get the news) Barcodes (at the food store) Remote control (unlock car) What does that tell... Telecommunications is one of the most important and fastest growing technologies of our time. Computers combined with electronic communications have drastically changed the ways in which we work and interact. Practical skills and basic knowledge in telecommunications are vital for everyone.

4 How to Teach/Learn? Learning about telecommunications and data networks and how to use them is not straightforward since knowledge in many diverse disciplines is needed. The best approach appears to be a combination of trying it out and adding bits and pieces of more fundamental knowledge on an as needed basis. Areas of Knowledge Protocols, standards, languages, addresses Databases, electronic publishing, multimedia Signals, analog, digital, binary numbers Data representation, codes, compression Computer hardware/software, programs, files Communication theory, network architecture Sound and image representation/processing Attacks, security, cryptography, authentication

5 Number of Users One way to classify communication systems is in terms of the number of users that are involved: One sender, one receiver: Point-to-point One sender, many receivers: Broadcasting Many senders, one receiver: Multi-user Many senders, many receivers: Network Connectivity Point-to-point Multi-user Half duplex Broadcast Full duplex Network

6 Outreach vs. Complexity Point-to-point communication is easy to manage, but offers the least flexibility. Broadcasting is still quite easy to manage, but vastly increases the outreach. Multi-user communication needs scheduling and arbitration of independent users. Networks are complex to build and maintain, but offer universal service. Telephone Network Suppose we want to call from A to B. What are the 3 most important elements needed? Telephone A Telephone B Public Switched Telephone Network (PSTN)

7 The 3 Elements Are: 1. Common address scheme that assigns unique address to each user. 2. Common protocol that makes sure messages can be exchanged between any two (or more) users. 3. A message format or language that is common to the particular users that communicate with each other. Telephone Network Address is telephone number, e.g., Protocol consists of dialing, picking up phone when it rings, saying hello, etc. Language is any natural language, e.g., English or Chinese, possibly flavored by some specialization, e.g., using words specific to a profession or interest.

8 On the Internet Address scheme uses IP addresses, e.g., , and domain name system (DNS), e.g., spot.colorado.edu. Protocols include ftp (file transfer protocol), smtp (simple mail transfer protocol), telnet (for remote access), http (hyper-text transfer protocol). On the Internet Languages or message formats include ASCII (American standard code for information interchange) text, GIF (graphics interchange format) and JPEG (joint photographic experts group) image files, MPEG (moving pictures experts group) video files, MP3 (MPEG, layer 3) sound files, html (hyper-text markup language).

9 On the Internet URI (uniform resource identifier) format: <scheme>://<authority>/<path>?<query>#<fragment> Example: <authority> contains host address, e.g., (or IP address ) <path> specifies directory/file on host, e.g., ds/hosts.html ( ds is directory, hosts.html is file) Filename extension (.html ) specifies language <scheme> <scheme>://<authority>/<path>?<query>#<fragment> Specifies protocol that is used to retrieve the resource. <scheme> strings are NOT case sensitive. Different protocols on the Internet are: http (hypertext transfer protocol) ftp (file transfer protocol) telnet (remote computer access) mailto (send )

10 <authority> <scheme>://<authority>/<path>?<query>#<fragment> Specifies a host address (server) in the form of a fully qualified domain name or of a numeric IP (Internet Protocol) address. <authority> strings are NOT case sensitive. Examples: Domain names: search.yahoo.com, foldoc.doc.ic.ac.uk Dotted decimal address: , <path> <scheme>://<authority>/<path>?<query>#<fragment> Specifies a file name on the server and is generally case sensitive. Special characters to avoid in file names: SP > < # % { } \ ^ ~ [ ] ` ; /? = & Note: SP stands for space Such characters need to be escaped in URLs, e.g., space is %20. OK to use: $ - _. +! * ( ),

11 OSI 7 Layer Model Open Systems Interconnect (OSI) Reference Model for computer networking Level where applications access network services, e.g., , WWW Intermediary format that specifies/handles presentation of data, e.g., html Used to establish, use and end sessions between applications, e.g., http Does packetizing, error recognition/recovery between end users, e.g., TCP Physical/logical addressing, routing, switching, flow control, e.g., IP Package bits into frames, media access, point-to-point comm, e.g., Ethernet Transmits bits over physical medium such as optical fiber, twisted pair wire, etc Examples Applications: WWW, , newsgroups Telnet, FTP DNS, network management, time Physical/Data Link Layer: Twisted pair, coax, optical fiber, wireless Ethernet, DSL, ISDN, FDDI, ATM

12 WWW and Internet Web Browser/WWW Server HTML (Hypertext Markup Language) HTTP (Hypertext Transfer Protocol) Telnet, ftp, SMTP TCP (Transmission Control Protocol) IP (Internet protocol) Ethernet, ATM, PPP Twisted pair wire, optical fiber, wireless OSI Model Networking

13 A Peek at HTML HTML (hyper-text markup language) was originally conceived as a method to describe documents in terms of their logical structure as opposed to their visual appearance. An HTML document consists of text interspersed with markup tags that may include links to other documents or files. A Peek at HTML <html> <head> <title>title of Document for Indexing</title> </head> <body> <h2>heading Inside the Body of the Document</h2> <p>the first paragraph of text in the document. It is up to the browser to decide where to break lines so that they fit in the browser window, or how to display text marked as <em>emphasized</em> or <strong>strongly emphasized</strong>.</p> <p>the second paragraph of text with a <a href="index.html"> link</a> to the file <tt>index.html</tt>.</p> <p></p><pre> /\_/\ There are special tags to include images and ( o.o ) even sounds. But to keep things simple you > ^ < can also use ASCII art with the pre -format tag. </pre> <hr> </body> </html>

14 A Peek at HTML Cascading Style Sheets HTML was conceived as a language to describe the logical structure of documents and not their appearance. As the WWW became more popular and more commercial, people started trying to abuse HTML tags to control the appearance of documents. Cascading Style Sheets (CSS) were introduced as a specific mechanism to control the appearance of web pages.

15 CSS Example The preferred way to specify text and background color for html pages is: <head> <style type= text/css > body { color: orange; background: black; font-family: sans-serif; } </style> </head> Related to HTML SHTML: server-parsed HTML XHTML: extensible HTML. HTML rewritten as an application of XML. XML: extensible Markup Language. Richer subset of SGML than HTML. SGML: Standard Graphics Markup Language (1986: ISO 8879). HTML and XML are subsets of SGML.

16 Standards What are standards? Standards are documented agreements containing technical specifications or other precise criteria to be used consistently as rules, guidelines, or definitions of characteristics, to ensure that materials, products, processes and services are fit for their purpose. Standards The more parties that become involved in a communication system, the more important standardization becomes. Examples of standards organizations: ISO (International Organization for Standardization), ISO is not acronym, comes from Greek isos meaning equal, ITU (International Telecommunication Union),

17 Standards Organizations ANSI (American National Standards Institute), EIA (Electronic Industries Alliance), IEEE (Institute of Electrical and Electronics Engineers), Internet Standards ISOC (Internet Society), IAB (Internet Architecture Board), IANA (Internet Assigned Numbers Authority), IESG (Internet Engineering Steering Group), IETF (Internet Engineering Task Force), W3C (World Wide Web Consortium), RFC (Request for Comment),