[1Day-1CS] Cross-Tier Data Sending and Receiving Courses & PDUs

Encapsulation & decapsulation process

Encapsulation: embedding the header and data of a higher layer into the data portion of a lower layer and inserting the header of that layer.

• Application → Transport → Internet → Pass to link layer

• Passed to transport layer, where it is segmented or datagrammed + TCP (Layer 4) headers added

• Passes to the Internet layer, where an IP (Layer 3) header is added = packet

• Passes to the link layer and adds a frame header + frame trailer = frame

Decapsulation: the process of removing the header portion of each layer as it goes from lower to higher layers

• Decapsulation proceeds in reverse

• Frame → Packet → Segment, Datagram → Message

• Eventually delivered as Transmission Data Unit (TDU) messages in the application

Protocol Data Unit

A unit of chunk when data is passed from layer to layer

• Different layers have different names, such as message, segment, datagram, packet, frame, bit, etc.

• Transmitting in bits is fastest and most efficient

• String-based sending and receiving at the application layer (due to ease of scaling)