Transport and Network Layers

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Description

Transport Layer

  • Organize data into segments
  • Reliable end-to-end transport
    • Loss recovery
    • Flow control
    • Data ordering
    • Data duplication
  • Or just Best Effort delivery
  • Segmentation
  • Dividing data in small fragments that can be transmitted over network
  • Different networks have different Maximum Transmission Unit (MTU)
  • MTU defines maximum size of one data piece carried through the network
  • Data is being divided and transmitted to recipient via transport layer
  • The MTU size is being acknowledged by transport layer
  • MTU acknowledgment is during discovering routine and while establishing connection with the recipient
  • Reassembly
  • Done at the receiving end
  • Transport layer protocols reconstructs data to its initial form
  • Data can be received in different order
  • Transport layer rearranges pieces of data in the correct order
  • Sequencing
  • Using sequencing identifiers
  • Avoids losses and duplication
  • Fixes the issue of following data different paths
  • Organizing data in groups of subdivided data segments
  • Identifying the order of groups of data sending and interpretation
  • Connection oriented
  • Reliable and more secure
  • Establishing two way connection between the nodes before data transmission
  • When the browser is trying to open the webpage, transport layer would send synchronization packet to the web server
  • Browser expects synchronization-acknowledgement response
  • When it receives response, it sends its own response to the server
  • After this process is done the data can be transmitted
  • Connectionless oriented
  • Not reliable
  • Best-effort delivery
  • No connection establishment prior to data transmission
  • Less security
  • Allows data flooding
  • Used with delay-sensitive data (Real Time)
    • Audio calls
    • Video streaming

 

Network Layer

  • Organize data into packets
  • Responsible of end-to-end addressing and routing
  • Identifies unique logical address for machines
  • Selects the best path for destination
  • Routers work in the network later
  • Performs fragmentation if segmentation is not enough
  • Receives the segments of data from Transport layer
  • Converts them to packets by adding addressing information
    • Source address
    • Destination address
  • Finds a route for data to be delivered to the receiver
  • Routes may differ because it is being determined based on the following:
    • Network overload
    • Quality of Service (QoS)
    • Cost of alternative routes
    • Delivery priorities

 

Logical Address

  • Unique identifier
  • Bound to geographical location
  • Used for end-to-end routing
  • Can be changed
  • Not vendor oriented
  • Common example is the IP address in TCP/IP

 

Network and Transport Layers

  • Network layer defines the following:
    • Source machine
    • Destination machine
  • Transport Layer guarantees either of the following according to the used protocol:
    • End-to-end reliable delivery
    • End-t0-end Best-effort delivery
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