Domain Name System A heirarchial, distributed database A service primarily aimed at mapping names to...

Domain Name System

• A heirarchial, distributed database

• A service primarily aimed at mapping names to IP addresses

• Partitioned for ease of administration

DNS Structure (partial).

edu comgov

utexas tamu ibm

cs austin

mac1 mac1solar

DNS -- How it Works

• DNS Servers in a logical tree

• DNS clients on every host

• Iterative Queries

• Recursive Queries

ARP

• Address Resolution Protocol {translate network layer address to physical address}

• Part of general resolution procedure:

name {e.g., neuron.cs.tamu.edu}

IP Address {e.g., 128.194.133.1}

Ethernet address {e.g., 08:00:20:08:58:78}

DNS

ARP

Application Layer• File Transfer, Access and Management

– virtual file store– file servers and requesting clients

• Electronic Mail– process to process traffic expected to dominate Internet– actually email dominates the Internet

• Virtual Terminals– representing the abstract state of the real terminal

• Remote Job Execution– JTM: Job Transfer and Manipulation

ISO Applications

• FTAM ~ FTP File Transfer, Access & Manipulation• VTS ~ TELNET Virtual Terminal Service• JTM ~ ??? Job Transfer & Manipulation {maybe rsh, RPC?}• MHS ~ SMTP Message Handling System (X.400)

ISO Terminology

SASE SASE

CASE

“applications”

[Specific|Common] Application Service Elements

“think of them as programming libraries or APIs”

ISO Service Elements(examples)

• Association Control Service Element (primitives)

• Commitment, Concurrency and Recovery– atomic actions– two phase commit

File Servers

• 1. File Structure

• 2. File Attributes– e.g. identifier, size of storage, access control

• 3. File Operations– create, delete move– OSI has defined virtual filestore operations

Replicated Files

• Why multiple file servers?– 1. To split the workload over multiple servers.

– 2. To allow file access to occur even if one file server is down

– 3. To increase reliability by having independent backups of each file

• Updates

• Voting

Electronic Mail

• Motis and X.400CCITT has aligned them for compatibilityMay replace SMTP

• The user agentuser interface

• Message transfer agentpost office

Virtual Terminals

• Scroll mode terminalsno local resources; dumb display and transmission

• Page mode terminals25 x 80 character displayscreen editing via termcap

• Form mode terminalslocal processing enabled

• Bitmapped terminals

like X stations

Case Study: Internet

• File Transfer

• Electronic Mail

• Virtual Terminals

Getting Started

• RARP

• BOOTP

• TFTP

• DHCP

File Transfer Protocol

• FTP recognizes four file types:• 1. Image

– bit by bit transfer

• 2. ASCII• 3. EBCDIC• 4. Logical Byte files

– binary files which use byte size other than 8 bits

Electronic Mail

• Pioneered by ARPANET

• RFC 822 (widely used)

• Simple Mail Transfer Protocol (SMTP)

• Supports only ASCII text

• name@domain addressing

Virtual Terminals - TELNET

• Designed for scroll mode terminals

• Hit a key , 8-bit bytes are sent

• 95 ASCII and 7 control characters legal

USENET--HOW TO AVOID GRADUATION

• Internet compatible (now)

• Variety of newsgroups

• Moderated newsgroups

• NNTP, Network News Transfer Protocol, allows selective downloading of messagesto multiple sites

The Web

• “the” killer application for the Internet

• Two components for popularity– http combines multiple access (gopher, ftp, etc)

methods– hypertext interface supports point-and-click interface

• Who will organize the information?– No one...– Database experts– Librarians (!)

Web Terminology• Web Browsers

– Netscape– Mosaic

• Web Servers– http daemon

• httd.conf - main server config file

• srm.con - server resource config file• access.conf - global access control file

• Home Page– Eg., www.cs.tamu.edu

• HTML– HyperText Markup Language

HTML Document<HTML>

<HEAD>

<TITLE>Willis Marti’s Homepage</TITLE>

<LINK REV=“OWNER” HREF=“mailto:[email protected]”>

</HEAD>

<BODY>

<IMG SRC=“my-logo.gif” ALT=“logo”>

<H1> Sample HTML Document</H1>

<EM> To demonstrate HTML </EM>

<HR>

....

Web Future Directions

• HTML Enhancements

• Secure Transactions

• Uniform Naming

• Librarians & Brokers

• Information “push” or “pull”

Layer 7 Summary

• Service Element Model

• Not all Apps belong here...

• Common Network Services

Domain Name System A heirarchial, distributed database A service primarily aimed at mapping names to...

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