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Transport Layer - Coggle Diagram
Transport Layer
Responsibilities
- Tracking individual conversations
- Segmenting data and reassembling segments
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- Identify, separate, and manage multiple conversations
- Uses segmentation and multiplexing to enable different communication conversations to be interleaved on the same network
TCP Basic Functions
- Number and track data segments transmitted to a specific host from a specific application
- Acknowledge received data
- Retransmit any unacknowledged data after a certain amount of time
- Sequence data that might arrive in wrong order
- Send data at an efficient rate that is acceptable by the receiver
TCP Features
- Establishes a Session - TCP is a connection-oriented protocol that negotiates and establishes a permanent connection (or session) between source and destination devices prior to forwarding any traffic.
- Ensures Reliable Delivery - For many reasons, it is possible for a segment to become corrupted or lost completely, as it is transmitted over the network. TCP ensures that each segment that is sent by the source arrives at the destination.
- Provides Same-Order Delivery - Because networks may provide multiple routes that can have different transmission rates, data can arrive in the wrong order.
- Supports Flow Control - Network hosts have limited resources (i.e., memory and processing power). When TCP is aware that these resources are overtaxed, it can request that the sending application reduce the rate of data flow.
UDP Feature
- Data is reconstructed in the order that it is received.
- Any segments that are lost are not resent.
- There is no session establishment.
- The sending is not informed about resource availability.
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UDP Characteristics
Best Effort
Message can be lost, duplicated and corrupted
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UDP Basic Functions
- UDP is a connectionless protocol.
- UDP is known as a best-effort delivery protocol because there is no acknowledgment that the data is received at the destination.
TCP Header
- TCP is a stateful protocol which means it keeps track of the state of the communication session
- TCP records which information it has sent, and which information has been acknowledged.
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TCP Characteristics
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TCP Flow Control
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Maximum Segment Size
A common MSS is 1,460 bytes when using IPv4.
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A host determines the value of its MSS field by subtracting the IP and TCP headers from the Ethernet maximum transmission unit (MTU), which is 1500 bytes be default.
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Congestion Avoidance
When congestion occurs on a network, it results in packets being discarded by the overloaded router.
To avoid and control congestion, TCP employs several congestion handling mechanisms, timers, and algorithms.
Role
- Responsible for logical communications between applications running on different hosts.
- The link between the application layer and the lower layers that are responsible for network transmission.
UDP Header
The UDP header is far simpler than the TCP header because it only has four fields and requires 8 bytes (i.e. 64 bits).