Metadata Modularization Concepts and Tools Carl Lagoze CS502 2001-03-14.
Basic Concepts and Principles Chapter 1 Copyright 2001 Panko.
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Transcript of Basic Concepts and Principles Chapter 1 Copyright 2001 Panko.
Basic Concepts and Principles
Chapter 1
Copyright 2001 Panko
2
Network
Network
A Network is an Any-to-Any Communication System– Can connect any station to any other
3
“Connect to GHI”
Network
Each Station has a Unique Network Address– To connect, only need to know the receiver’s address– Like telephone number
ABC
DEF GHI
JKLMNO
4Data Communications
Originally, There was a Sharp Distinction:– Voice and Video Communication versus
– Data Communications, in which one or both parties is a computer
Database Electronic mail World Wide Web
– Distinction is fading because voice and video communication are increasingly computer-based
5Voice and Video Networks
Telephone Network– Customer premises (home or office)– Local loop (access line) connects customer premises to
first switching office
Connection
Switching OfficeLocal Loop
(Access Line)
CustomerPremises
CustomerPremises
6Voice and Video Networks
Hierarchy of switches Trunk lines connect switches
Switch
Trunk Line
7Voice and Video Networks
Circuit– End-to-End Connection between Phones– May pass through multiple switches– And trunk lines– Reserved (guaranteed)
capacity during call
CircuitCircuit
8Voice and Video Networks
Reserved Circuit Capacity is Expensive– Good for voice, because conversations are fairly
constant
– Bad for data, because most data transmission is bursty; e.g., in World Wide Web, download, then stare at screen for average of 60 seconds between brief downloads
– Capacity is wasted between bursts; still must pay of capacity
9Packet-Switched Data Networks
Packet Switching– Circuit switching is expensive due to reserved capacity – Packet switching breaks transmissions into messages
– Messages are short (averaging a few hundred bytes) because switches handle short messages efficiently
– Messages are called packets (sometimes, frames or other names)
Message Packets
10Packet-Switched Data Networks
Packet Switching Decision– When a packet arrives at a switch, the switch must
decide which of several ports (connections) to use to send the packet back out
– Complex– Made at each packet switch
B?
D?
C?
Switch A
B
C
DPacket
11Packet Switched Data Networks
Multiplexing– Packets from many conversations are mixed
(multiplexed) over each trunk line– Only pay for the trunk line capacity used– Dramatic trunk line cost savings– The reason for packet switching
Multiplexing onTrunk Line
12Analog Transmission
In analog transmission, rising and falling smoothly in intensity among an infinite number of states– State may be voltage, frequency or other line signal
characteristic
In digital transmission, time is divided into periods of fixed length called clock cycles
Line is in one state (voltage level, etc.) during each clock cycle; at end of cycle, stays same or changes abruptly.
TimeStrength
Clock Cycle Time
State 1 Stays Same
Abrupt Change
State 2
13Digital Communication
Modems– Computers have digital output
– Telephone network assumes analog input
– Modem translates between digital device and analog line for data transmission over the phone system
DigitalSignal
Modem
AnalogSignal
14LANs and WANs
Networks Have Different Geographical Scopes
Local Area Networks (LANs)– Small Office– Office Building– Industrial Park / University Campus
Wide Area Networks (WANs)– Connect corporate sites or– Connect corporate sites with sites of customers and
suppliers
15Elements of a Simple LAN
Hub or Switch
Wiring
Hub or Switch connects all stations housing NIC
Wiring is standardbusiness telephone wiring
(4 pairs in a bundle)
16Terminal-Host Systems
Created in the 1960s– Central host computer does all the processing– Terminal is dumb--only a remote screen and keyboard– Largest hosts are mainframes (file storage & retrieval)
– Legacy systems--systems created by your predecessors
– Would not use the same platform today if built new; however, too expensive to rewrite all legacy applications at once
Terminals Host
17PC Networks
The Most Common Platform in Organizations– Allows PCs to share resources
File Servers– Store files (data files and programs)
Programs are downloaded to client PC for execution, not on file server– The most common type of server in PC networks– Almost all file servers are themselves PCs
Network
ClientPC
ClientPC
PC Server
PC Server
18Client/Server Processing
Client and Server Machines– Neither has to be a PC (Although the client usually is)
Platform independence: not limited to PC server– Two programs: client and server programs
Example: browser and webserver application program
Servers usually Workstation Servers– Look like PCs but…
More powerful (and expensive) than PCs
Do not use standard Intel PC microprocessors
Usually run the UNIX operating system
Client Machine ServerClient
ProgramServer
Program
Request
Response
19Program Functionality (Size)
High program functionality requires large program size
File Server Program Access– Poor: client PCs are small, can only execute small
programs
Client/Server Processing– Good: not limited to client PC processing power– Heavy work can be done on the server machine
Terminal-Host Systems– Good: Hosts can be very large
20Platform Independence
File Server Program Access– Poor: Only works with PC clients and PC file servers
Client/Server Processing– Excellent: use any server you want, also any client
Terminal-Host Systems– Poor: Hosts require terminals and only work with a few
terminal types
21Scalability
Ability to grow as demand grows
File Server Program Access– Poor: client PCs do not get very large
Client/Server Processing– Very good: Platform independence allows servers to be
larger than PCs– To grow, leave client machine the same, increase the
size of the server machine
Terminal-Host Systems– Excellent: have an enormous range of processing power
22User Interface
File Server Program Access– Very good: uses local PC processing power
Client/Server Processing– Very good: uses local PC processing power for user
interface
Terminal-Host System– Poor: Relies on distant hosts; user interface quality
limited by high long-distance transmission costs– Monochrome, text-only screen; no animation
23Response Time (When User Hits a Key)
File Server Program Access– Very good: uses local PC processing power
Client/Server Processing– Very good: local PC processing power for user interface– But retrievals from the server can cause delays
Terminal-Host System– Poor: Relies on distant hosts; long delays if overloaded
24The Internet
The Internet is a Worldwide Group of Networks– Not a single network
– Individual networks on the Internet are called subnets
Routers– Connect the Internet’s individual networks (subnets)– Cooperate to give an end-to-end route for each packet
(message)Routers
RouteHost
Host
25The Internet
Network deliver messages based on network addresses– The Internet has two addressing systems for hosts
IP addresses (computer friendly) Host names (user-friendly)
Host IP addresses (required)– Strings of 32 ones and zeros– Usually represented by four number segments separated by dots:
dotted decimal notation– For example, 128.171.17.13– Official addresses for hosts
127.18.47.145 127.47.17.47
26The Internet
Dotted Decimal Notation
– IP addresses are really strings of 32 bits (1s and 0s) 10000000101010100001000100001101
– To convert this to dotted decimal notation, first, divide them into four bytes (also called octets)
10000000 10101010 00010001 00001101
– Both octets and bytes are collections of eight bits But “octet” is used in networking
27
Binary to Decimal Conversion
Value(2N) Bit Decimal
128 1 128
64 0 0
32 1 32
16 0 0
8 0 0
4 0 0
2 1 2
1 1 1
163
Position(N)
7
6
5
4
3
2
1
0
Binary10100011
=Decimal
163
Note: Starts with 0
Position7
Position0
28The Internet
Host Names (otional)– Two or more text “labels” separated by dots
www.microsoft.com Mtsu.edu No relationship between segments and labels Usually, only servers have host names
29The Internet
Internet Service Providers (ISPs)– Connects you to the Internet, via Carrier Access Line
May provide other services (e-mail account, etc.)– Costs
ISP = Approx. $20 per month, sometimes more– % for ISP expenses
– % for Internet backbone to carry your messages
Carrier Access Line fee separate from ISP
ISPCarrier
Access Line Internet Backbone
ISP
Carriers
30Standards
Standards are rules of operation that most or all vendors follow
Open standards are created and owned by public standards organizations– No single vendor controls these standards
31Standards Are Layered
For Internet Access to a Webserver, standards are set at five layers– Application– Transport– Internet– Data Link– Physical
Together, these standards provide all that is needed for application programs on different hosts on different networks to work together
32Internet Standards
Messages are Exchanged at Multiple Layers
AppApp
TransTrans
IntInt
DLDL
PhyPhy
User PC
IntInt
DLDL
PhyPhy
Router
AppApp
TransTrans
IntInt
DLDL
PhyPhy
Webserver
HTTP
TCP
IP
PPP
Modem
IP
?
?
33Internet Standards
Application Layer Standards– specify how two application programs communicate – Example: browser on user PC and webserver application program
on webserver Webservice = HyperText Transfer Protocol (HTTP)
Transport Layer Standards
– specify how two host computers will work together,regardless of platform types (PCs, workstations, mainframes)
– Gives platform independence HTTP Requires the Use Transmission Control Protocol
(TCP)
34Internet Standards
Internet Layer Standards– specify how hosts and routers will act to route packets from source host to destination host, across many
single networks (subnets) connected by routers Internet Protocol (IP) The IP in “TCP/IP”
– All internet layer messages are called packets– Subnets
single networks (LANs, WANs, point-to-point link) on Internet Packets pass through several subnets in route across Internet Different Subnets Can Have Different Subnet Protocols
RouteSingle Network
(Subnet)Host
Host
35Subnets Standards
Subnet Standards Divided into Two Layers– Physical layer standards govern the transmission of
individual bits within a subnet
Interpretation of bits is left to data link layer
SerialPort
External Modem TelephoneWire Wall Jack
36Subnets Standards
– Data Link layer standards govern the transmission of messages within a subnet
Organize individual bits into structured messages or frames
Controls timing of message transmission Point-to-Point Protocol (PPP) when accessing
Internet from home via telephone modem Only used between home and ISP! Other subnets connecting routers are likely to use
different subnet protocols!
37Standards Organizations and Architectures
Architecture – a Design or framework for Standards Creation– Specifies what types of standards are needed
(application, transport, etc.)– After architecture is designed, individual standards of
each type are created Analogy: architecture of house specifies what rooms
will be needed and their relationships. After architecture is settled, individual rooms are
designed
38Standards Organizations and Architectures
TCP/IP Architecture– Under the Internet Engineering Task Force (IETF)– TCP/IP is the architecture, while TCP and IP are individual standards
– IETF standards dominate in corporations at the application, transport, and internet layers
OSI Standards (Reference Model of Open Systems Interconnection)– Reference Model of Open Systems Interconnection– Created by the International Telecommunications Union-
Telecommunications Standards Sector (ITU-T) And the International Organization for Standardization
(ISO)– OSI standards dominate the data link and physical layers (subnet)
Other architectures specify the use of OSI standards at these layers
39Internet Standards
5-Layer Hybrid TCP/IP-OSI Architecture– Most widely used architecture in organizations today– Used on the Internet
Application TCP/IP
Transport TCP/IP
Internet TCP/IP
Data Link OSI
Physical OSI
40TCP/IP versus OSI
Lowest Four Layers are Comparable in Functionality
TCP/IP OSI
Application ApplicationPresentationSession
Transport TransportInternet NetworkData Link (use OSI) Data LinkPhysical (use OSI) Physical
41Quality of Service (QoS)
Congestion & Speed– Latency: amount of time packets are delayed due to
congestion. Measured in milliseconds (ms), Desired Latency = 50 ms maximum
– Throughput: transmission speed. Measured in bits per second (bps)
Desired Throughput = 1 Million bps
42Quality of Service (QoS)
Reliability – Availability: percentage of time network is available.
Desired Availability = 99.999%– Error Rate: percentage of bits or messages with errors
1999 average = 3% - 6% of all packets Desire much lower average
43Security
Encryption for Confidentiality– Sender encrypts (scrambles) messages before transmission– Receiver decrypt messages to original form
Access Control– Prohibits or authorizes access to various resources (files, programs)
– Access control lists specify what & how a person may use a resource
Authentication– Sender of a message must prove their identity