Computer Systems and Network Diagram:

Computer Networks and Systems

  • A computing device is a physical artifact that can run a program.
    • Computers
    • Tablets
    • Servers
    • Routers
    • Smart sensors
  • A computer network is a type of computing system
  • A path between two computing devices on a computer network (a sender and a reciever) is a sequence of directly connected computing devices that begins at the sender and ends at the receiver.
  • Routing is the process of finding a path from sender to receiver.
  • The bandwidth of a computer network is the maximum amount of data that can be sent in a fixed amount of time.
  • Bandwidth is usually measured in bits per second.

How Computers Are Connected

  • A computing system is a group of computing devices and programs working together for a common purpose.
  • A computer network is a group of interconnected computing devices capable of sending or receiving data.

Packets

  • A packet is a small amount of data sent over a network. Each packet also includes the source and the destination information.
  • Packet Switching:
    • The message (file) is broken up into packets and sent in any order. The packets are reassembled by the recipient’s device. Ex:
      • Hello. How are you? ==>
      • Hello. You? How are

The Internet

  • The Internet is a computer network consisting of interconnected networks that use standardized, open (nonpropritary) communication protocols.
  • Access to the Internet depends on the ability to connact a computing dvice to an internet connected device.
  • Routing on the Internet is usually dynamic; it is not specified in advance
  • Information is passed through the Internet as a data stream. Data streams contain chunks of data, which are encapsulated in packets
  • Packets contain a chunk of data and metadata used for routing the packet between the origin and the destination on the Internet, as well as for data reassembly
  • Packets may arrive at the destination in order, our of order, or not at all
  • The World Wide Web is a system of linked pages, programs, and files
  • The World Wide Web uses the Internet

Protocols

  • A protocol is an agreed-upon set of rules that specify the behavior of a system.
  • The protocols used in the Internet are open, which allows users to easily connect additional computing devices to the Internet.
  • IP, TCP, and UDP are common protocols used on the Internet
    • TCP does error checking and error recovery so it is slower
    • UDP performs error checking, but it discards erroneous packets
  • HTTP is a protocol used by the World Wide Web

Internet and Transport Layers

  • Transport Layer - How the packets are sent, and for what
    • Reliability - reliable - sender gets a receipt back, resend as needed TCP
    • Unreliability - send and forget. UDP
  • Internet Layer
    • IPv4: Example 192.168.24.1 32 bits, separated into 4 “octets” 8 bits long (0-255)
    • Separated into 2 parts:
      • Network (1-31)
      • Device (32-network bits)
  • Three targets that can be addressed using IP
    • Unicast - A specific device. Internet wide access. TCP is used.
    • Multicast - A group of devices. It is specific range of IP addresses. Internet-wide access. UDP is used.
    • Broadcast - All devices. LAN-wide. Data stops at the router. UDP is used.

Application Layer

  • Key protocols used:
    • http. How to ask and receive data from web servers. Normally uses TCP, Port 80 at the transport layer
    • https. Like http but with security. Usually uses TCP Port 443
  • Web Servers:
    • Programs running on machines connected to the Internet
    • Provides clients web pages - data linked to other pages using URLs (Uniform Resource Locations)
    • Ex, https://www.mycompany.com
    • The World Wide Web (WWW) is this network of linked data and programs, running over the Internet
  • DNS - Domain Name Service
    • Applications that translate a human readable URL (e.g. www.mycompany.com) to an IP address
    • DNS holds a database of mapping of names to IPs. Servers running DNS are spread across the internet
    • There are large computers serving and managing these name/IP Mappings for each Domain (.com, .net, .gov, etc.)
    • You use a DNS server every time you ask for a web page on a browser

Scalibility of the Internet

  • The scalability of a system is the capacity for the system to change in size and scale to meet new demands.
  • The Internet was designed to be scalable
    • Able to change in size and scale to meet new demands
  • Local Area Network (LAN):
    • Physical Connections
    • Limited by hardware and physics
    • 1 to 100s of systems
  • Intranet:
    • LANs connected by Routers within an organization
  • Autonomous Systems (AS):
    • Large intranets linked together under the control and policies of major organizations. Large routers link networks with large telecommunications connections
  • The Internet:
    • Autonomous Systems linked together
    • Large Routers linking Ass via special telecom means (Fiber, T3, Satellites)
    • Major infrastructures - DNS (.com, .net, etc.), Cyber Operations

Authentication

  • Authentication measures protect devices and information from unauthorized access. Ex:
    • Strong passwords
    • Multifactor authentication.
  • A strong passwrod is something that is easy for a user to remember, but would be difficult for someone else to guess based on knowledge of that user.
  • Multifactor authentication is a method of computer access control in which a user is only granted access after successfully presenting several separate pieces of evidence to an authentication mechanism, typically in at least two of the following categories:
    • knowledge (something they know)
    • possession (something they have)
    • ingerence (something they are)
  • Multifactor authentication requires a least two steps to unlock protected information; each step adds a new layer of security that must be broken to gain unauthorized access.

Encryption

  • Encryption: the process of encoding data to prevent unauthorized access
  • Decryption: the process of decoding the data.
  • Two common encryption approaches are:
    • Symmetric key encryption involves one key for both encryption and decryption
    • Public key encryption pairs a public key for encryption and a private key for decryption.
      • The sender does not need the receiver’s private key to encrypt a message, but the receiver’s private key is required to decrypt the message
  • Certificate authorities issue digital certificates that validates the ownership of encryption keys used in secure communications and are based on a trust model.

Viruses and Malware

  • Computer virus and malware scanning software can help protect a computing system against infection.
  • A computer virus is a malicious program that can copy itself and gain access to a computer in an unauthorized way. Computer viruses often attach themselves to legitimate programs and start running independently on a computer.
  • Malware is software intended to damage a computing system or to take partial control over its operation.
    • Can infiltrate a system by posing as legitimate programs or by attaching itself to legitimate programs, like an email attachment
  • Virus scans can help to prevent malicious code from getting into and affecting your system

Prevention

  • All real-world systems have errors or design flaws that can be exploited to compromise them. Regular software updates help fix errors that could compromise a computing system.
  • Users can control the permissions programs they have for collecting user information. Users should review the permission settings of programs to protect their privacy.

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