Networks – Basics

Networking has happened to be very boring for all of us. We take most of the technologies, protocols and network mechanisms as granted and don’t actually think about how it works on the lower end. Whereas we can not live with the network products we use daily in our professional life. Knowing the basics of Networks for tech guys is a must in my understanding. Otherwise, it would not be fair and without that knowlegde we can not reach to the crux of the technology and hence can not use the technology to its full potential. 

This series is focused on the Network Structure and basic Network Components.

OSI Model

OSI model is an idealized abstract model. Parts of the main protocols will lie in different layers of the model.

Physical Layer

  • Physical HW and Cabling. Responsible for physical data transmission between devices in the form of signals. Connectors, pinouts, electrical specifications and defined here. Puts the data in the form of bits and receives it in the same way.
  • Common Protocols: DSL, IEEE 802.3, IEEE 802.11a/b/g/n, USB, RS232, RS485
  • Scope: Signals between devices
  • Type: Bits

Data Link Layer

  • MAC and Logical Link Control(LLC). Deals with data movement accross networks using physical addresses.
  • Common Protocols: ATM, SDLC, HDLC, ARP, PPP
  • Scope: Low Level messages between devices
  • Type: Frames

Network Layer

  • Network and Logical Addressing. Deals with data movement accross networks using logical addresses.
  • Common Protocols: IP (v4/v6), ICMP, IPsec, IGMP, IPX
  • Scope: Messages between devices
  • Type: Datagrams/Packets

Transport Layer

  • Error Checking and Segmentation. This layer establishes a logical connection between two hosts and provides delivery, flow control and error recovery mechanisms.
  • Common Protocols: TCP, UDP, SCTP, DCCP
  • Scope: Communication between software instances
  • Type: Datagrams/Packets

Session Layer

  • Data Synchronization and session management. Different instances/applications can request data accross the network. Sessions layer keep the data separate for each such session. It is responsible for creation, management and destruction sessions.
  • Common Protocols: NetBIOS, SAP, SIP, PPTP, L2TP
  • Scope: Sessions between local and remote devices
  • Type: Session

Presentation Layer

  • Data Conversion and File Types. Presents data to Application layer. This defines how the data should be formatted. This includes encryption, decryption, compression, decompression.
  • Common Protocols: MIME, TLS, SSL
  • Scope: Application data representation
  • Type: Encoded User Data

Application Layer

  • User Application Services, User requests and files. This layer is the INTERFACE between the software application and the network. This layer does not include the application itself.
  • Common Protocols: HTTP, FTP, DNS, SMPP, NTP, SNMP, DHCP
  • Scope: Application Data
  • Type: User Data (packets)

Similarly, Internet Protocol Suite is an other conceptual model and a set of communications protocols. Referred as TCP/IP. TCP/IP suite actually predates OSI model. This has four layers.

  • Application Layer
  • Transport Layer
  • Internet Layer
  • Link Layer

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