The OSI model vs the TCP/IP Model, Network Protocols and Messages

The OSI model — The Open Systems Interconnection (OSI) model defines a networking framework to implement protocols in layers, with control passed from one layer to the next. It is primarily used today as a teaching tool. It conceptually divides computer network architecture into 7 layers in a logical progression. The lower layers deal with electrical signals, chunks of binary data, and routing of these data across networks. Higher levels cover network requests and responses, representation of data, and network protocols as seen from a user’s point of view.

The 7 layers —

  1. Physical Layer, responsible for ultimate transmission of digital data bits from the Physical layer of the sending device over network communications media to the Physical layer of the receiving device.
  2. Data Link Layer, checks for physical transmission errors and packages bits into data “frames”. Also manages physical addressing schemes.
  3. Network Layer, adds the concept of routing above the Data Link layer. When data arrives at the Network layer, the source and destination addresses contained inside each frame are examined to determine if the data has reached its final destination.
  4. Transport Layer, delivers data across network connections.
  5. Session Layer, manages the sequence and flow of events that initiate and tear down network connections.
  6. Presentation Layer, it handles syntax processing of message data.
  7. Application Layer, supplies network services to end-user applications.

TCP/IP Model — Like the OSI model, it describes general guidelines for designing and implementing computer protocols.
It consists of four layers: Network Access, Internet, Transport, and Application

The 4 Layer:

  1. Application, standardizes data exchange for applications. Protocols include HTTP, FTP, POP3, SMTP, and SNMP.
  2. Transport, handles communications between hosts and is responsible for flow control, reliability and multiplexing. Protocols include TCP and UDP.
  3. Internet, connects independent networks to transport the packets containing the data across network boundaries. Protocols are IP and ICMP.
  4. Network Access, consists of methods and protocols that operate only on a link, which is the network component that interconnects nodes or hosts in the network. Protocols in the layer include Ethernet and ARP.

Network Protocols:

Internet Protocols, contains a set of related network protocols. Beside Internet Protocol (IP) itself, higher-level protocols like TCP, UDP, HTTP, and FTP all come together with IP to provide more capabilities. Similarly, lower-level Internet Protocols like ARP and ICMP also co-exist with IP.

Wireless Network Protocols, Network protocols designed for use on wireless networks must support roaming mobile devices and deal with issues such as variable data rates and network security.

Network Routing Protocols, A routing protocol can identify other routers, manage the pathways (called routes) between sources and destinations of network messages, and make dynamic routing decisions. Common routing protocols include EIGRP, OSPF and BGP.

Encapsulation — Encoding is the process of converting information into another acceptable form, for transmission. Decoding reverses this process in order to interpret the information. A message being sent from source to destination, must use a specific format or structure. The message size matters, when a message is sent the information is broken to other smaller pieces and then puzzled back again when it reaches the destination, the larger the data, the longer it’ll take to send. Message timing. Access Method determines when someone is able to send a message. Flow Control, affects how much information can be sent and the speed.

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