Networking Concepts

Evolution of Computer Networks

• Computer networks, also known as Datacom or Data-transmission networks, are a result of the evolution of computing and telecommunication technologies.
• The first computer was the ENIAC in 1946
• Transistors appeared in 1947
• Batch mode arrived in the 1950s
• Interactive computing emerged in the 1960s
• ICs appeared in 1961
• Microprocessors appeared in 1971
• Communications include the telegraph in 1838, the telephone in 1876, radio in 1896, TV in 1923, and microwave and satellite tech

Data Communications

• Data Communications means the exchange of data between two devices through a transmission medium
• The five components of data communication are the message/information, sender, receiver, transmission medium, and protocol
• Information can be conveyed through text, numbers, images, audio, and video
• Communication modes include simplex, half-duplex, and full duplex

Networks

• A network is a set of interconnected devices capable of communication
• Devices can be hosts like computers, laptops, and phones, or connecting devices like routers, switches, and modems

Network Criteria

• Network performance depends on network elements, measured by delay and throughput
• Reliability is measured by the failure rate of network components and availability
• Security involves data protection against loss or corruption

Types of Connection

• Point-to-point connections involve a single transmitter and receiver
• Multipoint connections involve multiple recipients of a transmission

Physical Topology

• Mesh topology connects every device to every other device
• Star topology connects devices to a central hub
• Bus topology connects devices along a single cable with drop lines and taps
• Ring topology connects devices in a circle, with repeaters to maintain signal strength

Types of Transmission

• Unicast transmission sends a packet from a single source to a specific destination
• Broadcast transmission sends information from one point to all other points
• Multicast transmission sends information from one or more points to a set of other points
• IP supports unicast, broadcast, and multicast services

Categories of Networks

• Local Area Networks (LANs) cover short distances and provide local interconnectivity
• Wide Area Networks (WANs) cover long distances and provide connectivity over large areas
• Metropolitan Area Networks (MANs) provide connectivity over areas like a city or campus

Switching

• An internet is a switched network where a switch connects at least two links
• Circuit-switched networks create a dedicated path between two points
• Packet-switched networks break data into packets and route them independently

Internet

• The Internet is a global system of interconnected computer networks using the TCP/IP protocol suite
• Internet history began in the 1950s with point-to-point communication between mainframe computers and terminals
• In 1972, Vint Cerf and Bob Kahn collaborated on the Internetting Project using a Gateway

Protocols

• Protocols set the rules for data communications
• Elements of Protocol
  • Syntax: deals with data structure/format, and reading of bits
  • Semantics: interprets bit meanings, defining field actions
  • Timing: specifies when data should be sent, and the speed for sending/receiving

Layered Architecture Characteristics

• Layered architecture decomposes complex problems into manageable units
• Implementation details are abstracted, separating implementation from the specification
• Layers share services
• A framework implements multiple protocols per layer
• Layer architecture simplifies network design and debugging and makes network management easier
• Network layers adhere to protocols

Network Architecture Requirements

• Network requirements include connectivity, cost-effective resource sharing, support for common services, and reliability
• Network architecture is the framework guiding network design
• The OSI and TCP/IP models are the most widely used architectures

Layering and Protocol

• Services provided by the underlying hardware are augmented with layers for higher service levels
• These services use the services of lower layers
• Layering decomposes network building into manageable components
• Layering offers a modular design

Protocol Definition

• Protocol defines the format of exchanged data
• It also controls the timing for handshake between layers
• A protocol specifies interfaces between layers in the same system and with peer layers
• Two defined interfaces:
  • Service interfaces are the interfaces between objects on same device
  • Peer interfaces are messages exchanged with a peer system
• Protocol specification involves prose, pseudo code, state transition diagrams, packet formats, and abstract notations
• Encapsulation: Wrapping data under a single unit
• Header: Small piece of information for communication between peers
• Payload: Data transmitted by application

7 Layers of the OSI Model

• Application: End user layer (HTTP, FTP, IRC, SSH, DNS)
• Presentation: Syntax layer (SSL, SSH, IMAP, FTP, MPEG, JPEG)
• Session: Synch & send to port (API's, Sockets, WinSock)
• Transport: End-to-end connections (TCP, UDP)
• Network: Packets (IP, ICMP, IPSec, IGMP)
• Data Link: Frames (Ethernet, PPP, Switch, Bridge)
• Physical: Physical structure (Coax, Fiber, Wireless, Hubs, Repeaters)

Functions of the 7 OSI Layers

• Physical Layer
  • Defines the interface between devices
  • Specifies transmission medium type
  • Handles bit representation (1s and 0s)
  • And also transmission rate in bits per second (bps)
  • Contains the Clock Synchronization system
• Data Link Layer
• Manages framing (frames)
• Handles physical addressing (MAC Address)
• Maintains flow control to avoid receiver overload
• Provides error control by detecting/retrasnmitting lost or damaged frames
• Performs access control over a shared link with multiple devices
• Network Layer
  • Enables source to destination packet delivery
  • Also utilizes logical addressing (IP)
  • Controls routing using routers and internetworks
• Transport Layer
  • Ensures process-to-process delivery (running programs)
  • Provides service point addressing (port address)
  • Manages segmentation and reassembly (segments)
  • Offers connection control (TCP connection-oriented, UDP connectionless)
  • Performs flow control and end-to-end flow control
  • And also error control via retransmission to ensure delivery without any damage
• Session Layer
  • Opens, closes, and generally manages end-user application processes
  • Supports Inter-host communications
  • And also controls ports and sessions
• Presentation Layer
  • Deals with syntax (formats) and semantics
  • Uses Encryption and compression for security purpose
• Application Layer
  • Provides user interface services like e-mail, or file transfer

TCP/IP Model (Internet Architecture)

Functions of the TCP/IP Layers:

• Application:
  • Allows access to network resources
• Transport:
  • Provides reliable, process-to-process message and error delivery
• Internet:
  • Moves packets from source to destination and makes internetworking possible
• Network Interface:
  • Transmits data between two devices on the same network The TCP/IP protocol suite includes the following layers:
• Application:
  • Uses Application Protocols(FTP, TFTP, SMTP, Telnet, HTTP)
• Transport:
  • Handles TCP(reliable/connection-oriented) and UDP(unreliable/connectionless oriented)
• Internet:
  • IP supports networking tech interconnection
  • Supporting protocols include ARP, RARP, and ICMP
• Network Interface:
  • Uses Network interface protocols (NET1, NET2,..NETn)
  • Includes hardware(i.e. network adapter) and software (network device driver)

Networking Devices

• Networking devices includes all computers, peripherals, interface cards and other equipment needed to perform data-processing and communications within the network

• Common networking devices include network interface cards (NICs), hubs, switches, repeaters, bridges, routers, modems, gateways, and firewalls.

• Network Interface Card (NIC)

  • Used for physical connection between network and computer
  • Referred to as Ethernet adapters, network adapters, LAN cards

• Hub

  • Convergence point of network for data packet transfer
  • Duplicates data packets to be sent

• Switch

  • Joins computers within one LAN
  • Inspects and forwards data packets

• Repeater

  • Amplifies signals that are communicated

• Bridge

  • Creates connection between two LANs and divides one network into two

• Router

  • Connects networks
  • Routes data packets through networks

• Modem

  • Provides internet connectivity

• Gateway

  • Connects multiple Networks
  • Acts as a entrance to another network
  • Operates in all seven layers of the OSI model

• Firewall

  • Prevents unauthorized device access from networks

• Monitors and decides to block incoming and outgoing traffic

Network Standards

Standards

• Allow different computers to communicate
• Increase market making products cheaper Two Categories of Standards
• De facto:
  • "From The Fact" and created without a plan.
  • Example is QWERTY
• De Jure
• "By Law" and Formal legal standards adopted by an organization body
• Example is TCP/IP.

Standard Organizations

• ITU-T: International Telecommunication Union
  • It is Promoting telecommunication networks and services
• ISO: International Organization for Standardization.
• Includes: The OSI Layer
• IETF: Internet Engineering Task Force.
• Publishing RFCs (Request For Comments)
• IEEE: Institute of Electrical and Electronic Engineers
  • Dedicated to advancing technology for the benefit of humanity.

Communication Protocols

• Communication protocol defines the rules, of when transmission station send and received.
• Includes: How data is formatted and error checking.
• MAC (Media Access Control)
  • Protocol that controls access to a shared communications medium among users
  • Stations Transmit at a time

Multiple Access schemes

• In total have three main categories
• Fixed Assignment:
• Include FDMA
• Random Assignment:
• Include CSMA/CD
• Demand Assignment:
• Include DAMA

Poll and Select

• Supervisor stations asks the other station if the current station has data to send and stations can send data only if they are permitted to
• Used in a star topology
  • Polling list is modified in case of high priority stations.

ALOHA Protocols

• Developed for the radio network in 1970
  • Frequency: is 30kHz-300GHz

PURE ALOHA

• Stations listen for other stations to send for round trip propagation If then there is no acknowledgment station re transmits
• If Two frames interfere it indicated increased load and data

CSMA

• Transmitting station that listens to the medium, if another transmission is in progress (carrier sense)
  • If in you use the station waits
  • if you are idle you may transmit in the station
  • Collision happens when more than one begins transiting to the period of propagation delay.

Fast Ethernet

• Low cost Ethernet used in LAN operating at 100mbs.

Token Bus

• Linear cable for which stations are attached
  • Logically stations are organzed to into a ring
  • Speacial frame token is used for stations

Token Ring

• IEEE 802 5 Medium Access protocol frame token is transmitted to stations that can use use this protocol. ,

FDDI Fiber Disributed Data interface

• Operating with 100 MBS in Optical fibers and twisted pairs.