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