Network Translators translates from one system network to a universal system network for the terminal system to convert to its suitable local network system. Network translators is responsible for the conversion of the protocol, and character, encrypting decrypting data, graphic expansions, and compression of data. It sets up standard systems to give seamless communication in multiple protocol stacks and provides emulation on terminals and encryption compression. Read: Network Architecture

Inter Host Communication or session Layer

It establishes/starts, maintains or progress and ends or stops sessions across the network. For example, it starts log in, maintains browsing/file transfer, and Ends log out. Also, it is responsible for identification or recognition of name so that designated parties can have synchronized planned session interactions in the data stream. When a session fails, the most recent data at the most recent checkpoint is transmitted.

They manage transmission data at a given time, determines the length of time or period (interactive log in and connections related to file transfers) session connects or reconnects if an interruption happens. Recognizes and registers names in the history files for example Telnet, FTP, NetBIOS, TCP, Duplexing etc.

End to End data Delivery or Transport Layer

This describes the Interface between the hardware and the software. It puts into packets or segments large amounts of messages and manages the data’s flow control across the network. Ensures segments or packets deliver by returning acknowledgment for successful transmitted data. Requests a re-transmission of other packets.Re-assembles segments or packets at the receiving end in the order of transmission for completed messages. Examples are switches, TCP, UDP, SPX, ICMP, NetBEUI or NetBIOS.

Network Layer -Path Determination and Logical Addressing

Network Layer

Path Determination and Logical Addressing focuses on issues regarding the internet. It routes packets or segments into different networking routes and adds unique identifiers that address information to packets

Translates MAC

Physical address into an IP- a logical network address and is responsible for routing, addressing and managing problems in the network for example IP, ICMP, IPX, Apple Talk, Switches, and Routers etc.

Data Link Layer or Physical Addressing/Configuration

Data Link Layer or Physical Addressing/Configuration focuses on Local Area Networks. They define methods used in transmission and receiving of Data on the LAN network. Bridge and CSMA as intelligent issues are used in this layer.The receiving end packages raw data/bits into data frames for onward delivery to the actual network layer from the physical layer and is responsible for access control and physical addressing and also error free transfer of frames to other computers via physical layer e.g., CSMA/CD, bridges, switches, NIC, Ethernet.

Physical Layer Media, Signal and Binary Transmission.

It deals with physical connectivity between devices. The hardware and the passive make raw bit stream transmissions over the physical cable. It is responsible for bit control and synchronization, and physical topologies. Examples are NICs, repeaters, amplifiers, modem, hubs, RJ11, RJ45 etc.

TCP/IP Protocol Architecture

Developed by the US Defense Advanced Research Project Agency (DARPA) and used for packet switched networks (ARPANET), It is used by global Internet.

1. Network access layer
2. Internet layer
3. Transport layer
4. Application layer

Its application encapsulates/decapsulates processes in transmission of messages and receiving messages as shown below

Protocol Operation of Sending and Receiving a Message/Data

The HTPP as an application layer protocol delivers the HTML formatted page data to Transport layer. The transport layer  breaks the data into segments called TCP with a header label containing information on the destination computer to receive the message. It has information that enables the destination process reassemble data back into its original formation, encapsulates it and sends to internet layer.Both the Internet layer and IP protocol encapsulates TCP segments to an IP packet by adding a header to the IP which has source and destination host IP address. It also has information necessary to provide deliver the packet to the corresponding destination, then to network access layer.The Access layer of the Network encapsulates it in a header frame and each header has a source and a destination physical address. The destination physical address identifies the device or devices s on the local network. The trailer has error checking information and bits are encoded into the Ethernet media by NIC.

Advantages of Layered Architecture

• Layers can be identified, modified and upgraded without affecting other layers in the network.
• Layering by modularization simplifies the design of the network.
• They can be assigned to different standards, design teams and committees.
• Packet switching, circuit switching mechanisms can be used without affecting one layer after another.
• Can be plugged-in different machines at different layers in the network.
• The different color codes between different control functions can easily be understood easily.
• Functions at lower levels can be removed from the software to hardware and even macrocodes.
• They greatly increase compatibility between different

Disadvantages of Layered Architecture

• The total overhead is much higher
• Two machines in communication can use specific functions which they could do without a layer.
• Functions may not be a cost-effective layer because technology changes all the time.

Additional reading Network Hardware and Computer Networks