1.why computer networks are important
most computer applications are network-relater(e-mail\social\media\wwww\etc)
digital divided
internet-on-things(IOT)
2.Analog、Binary、and Digital Transmission
Telephone Modems
before 1980 ,telephone produces an analogous electrical signal.
Digital signals change abruptly between states
If there are two states ,this is binary transmission.
If there are serveral states ,this is digital transmission.
Binary 2 states
Digital A few states 2,4,8,16……
3.Network Topology
Network topology is the layout of how elements(links,nodes,etc.) of a networkucommunicates of a network communicates with other devices.
Physical topology—Mostly applies
to hardware and describes how computers, other devices, and cables fir together
to form the physical network
Logical topology—Has to do with software and describes how access to the network is controlled
How users and programs initially gain access to the network
Network operating system(NOS)—Controls access
to the entire network
Required by client-server models
Types of Physical Topology
Wired Topology
Ring Topology
Bus Topology
Star Topology
Mesh Topology
Wireless Topology
lInfrastructure Topology
A combination of Wired and Wireless devices
Ad hoc Topology
Mesh Topology
4.peer-to-peer newwork model
- The OS of each computer on the network is responsible for controlling access to its resources.
Computers, called nodes or hosts, form a logical group of computers and users
May share resources
May prevent access to resources
Each computer user has a Windows local account
Works only on that one computer
Advantages
Simple configuration
Less expensive
Compared to other network models
Disadvantages
Not scalable
Not necessarily secure
Not practical for large installations
5.Client-Server Network Model
Resources are managed by the network operating system (NOS) via a centralized directory database
Windows domain—A logical group of computers that a Windows Server can control
Active Directory (AD)—The centralized directory database that contains user account information and security for the entire group of computers
A user can sign on to the network from any computer on the network and gain access to the resources that AD allows
This process is managed by Active Directory Domain Services (ADDS)
Client---A computer making a request from another
Clients don’t share their resources directly with each other
Access is controlled by entries in the centralized domain database
Client computers access resources on another computer by way of the servers controlling the domain database
The NOS is responsible for the following activities:
Manages client data, resources
Ensures authorized user access
Controls user file access
Restricts user network access
Dictates computer communication rules
Supplies application to clients
(Server examples
Windows Server 2016, Ubuntu Server, or Red Hat Enterprise Linux)
Servers that have a NOS installed require:
More memory, processing, and storage capacity
Equipped with special hardware
Provides network management functions
Advantages relative to peer-to-peer networks
User credential assigned from one place
Multiple shared resource access centrally controlled
Central problem monitoring, diagnostics, and correction capabilities
More scalable
Terminal-Hos vs Client/Server
6.Client-Server Applications
Network services—The resources a network makes available to its users
Includes applications and the data provided by these applications
In client-server applications
A client computer requests data or a service from a second computer, called the server
Protocols
Methods and rules for communication between networked devices
Two primary protocols:
TCP (Transmission Control Protocol)
IP (Internet Protocol)
TCP/IP suite of protocols is used by OSs for communication on a network
（List of several popular client-server applications:
Web service
Email services
F T P service
Telnet service
Remote applications
Remote Desktop）
7.Network Hardware
Local area network (LAN)—Usually contained in a small space
Such as an office or building
Switch—Receives incoming data from one of its ports and redirects it to another port or multiple ports
Will send the data to its intended destination
Star topology—All devices connect to one central device (usually a switch)
Network interface card (N I C)—A network port used to attach a device to a network
A LAN can have several switches
Backbone—A central conduit that connects the segments (pieces) of a network
Might use higher transmission speeds and different cabling than network cables connected to computers
Three switches daisy-chained together in a single line is said to use a bus topology
However, each switch is connected to computers via a star topology, making it a star-bus topology
A topology that combines topologies is known as a hybrid topology
Router—A device that manages traffic between two or more networks
Can help find the best path for traffic to get from one network to another
Routers can be used in small home networks to connect the home LAN to the Internet
Called a SOHO (small office-home office) network
Industrial-grade routers can have several network ports, one for each network it connects to
Difference between router and switch:
Router is like a gateway between networks and belongs to two or more local networks
Switch belongs only to its local network
8.MANsand WANs
Metropolitan area network (MAN)—A group of connected LANs in the same geographical area
Also known as a campus area network (CAN)
WAN (wide area network)—A group of LANs that spread over a wide geographical area
Internet is the largest and most varied WAN
MANs and WANs often use different transmission methods and media than LANs
PAN (personal area network)—Smallest network
A network of personal devices such as your smartphone and your computer
8.Major Standards Architectures
In networking, standards agencies first create standards architectures that define the categories of standards to be developed.
They define categories in terms of layers.
They then design standards for the individual categories.
There are two major standards architectures.
1. Open Systems Interconnection model (OSI)
Beginning in 1977, the International Organization for Standardization (ISO) conducted a program to develop general standards and methods of networking.
A similar process evolved at the International Telegraph and Telephone Consultative Committee (ITU-T). Both bodies developed documents that defined similar networking models.
The OSI model was first defined in raw form in Washington, DC in February 1978 by Hubert Zimmermann of France and the refined but still draft standard was published by the ISO in 1980.
ISO (the International Organization for Standardization) is a computer standards agency.
The ITU-T is the International Telecommunications Union—Transmission Standards Agency.
Don’t confuse ISO the organization with OSI the architecture.
2. TCP/IP
This is the standards architecture for the Internet and many corporate internets.
Its standards agency is the Internet Engineering Task Force (IETF).
Most of its documents are called requests for comment (RFCs).
Some (but not all) RFCs are official Internet standards.
OSI divided application communication into three layers.
Session (5) creates a managed session between applications. If there is a break in communication, the communication only has to go back to the last roll-back point.
Presentation (6) was designed to translate between data formats on different computers. In practice, it is used as a category for file format standards, such as jpg and mp3.
Application (7) handles other details of application communication.
9.Birth of the Internet
Forerunner of the Internet
Funded by the Advanced Research Projects Agency (ARPA) of the United States Department of Defense
Now the Defense Advanced Research Projects Agency (DARPA)
To explore packet switching
To give researchers access to ARPA-funded software on hosts computers in distant cities
First four nodes began operation in 1969
Called their standards Requests for Comment (RFCs)
Did not feel that they had the authority to create standards, so they used the weaker term RFC
The NWG evolved into today’s standards body for the Internet, the Internet Engineering Task Force (IETF)
Internet standards today are still called RFCs
DARPA needed a way for researchers on one network to be able to use resources on another network.
Packets would have to travel across multiple networks.
It came up with the idea of connecting multiple networks by devices called routers.
(The original name was gateways.)
Generically, networks of networks are internets.
TCP/IP standards evolved in the 1970s.
Hosts could run either TCP/IP or NCP standards.
1983
All hosts were required to run TCP/IP.
NSFNET
In the 1980s, the NSFNET funded by NSF was the core of the Internet.
NSF had an Acceptable Use Policy barring commercial activity such as e-commerce.
1995
NSFNET replaced by commercial ISPs.
No longer was e-commerce forbidden.
The e-commerce revolution began.
The World Wide Web became popular just before that.
Internet2 is a not-for-profit United States computer networking consortium led by members from the research and education communities, industry, and government.[2]
The Internet2 consortium administrative headquarters are located in Ann Arbor, Michigan, with offices in Washington, D.C. and Emeryville, California
Internet2 operates the Internet2 Network, an Internet Protocol network using optical fiber that delivers network services for research and education, and provides a secure network testing and research environment.
In late 2007, Internet2 began operating its newest dynamic circuit network (the Internet2 DCN) an advanced technology that allows user-based allocation of data circuits over the fiber-optic network.