Transport and Network Layers

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