Depending on the size of the geographical location, the link layer is divided into LAN and WAN, using HDLC and PPP respectively, and the IP layer has nothing to do with the realization of the physical router
WIFI is the cable channel transmission of medium=air;
function of embeded layers
Reliable transmission: every frame sent by the sender is accepted by the receiver and accepted in sequence;
flow control:
actual window size=min{cwnd, rwnd}, indicating how many frames can be sent,
The sender adjusts the sending window cwnd's size according to the received confirmation frame, conducted in transport layer
Congestion control:
All data in the network (subnet as unit) can be sent normally
Involve (relate to) host, router, switcher table, global comprehend factor
establish connection:
In telegram transmission, the transmission delay and queuing delay can be eliminated after the connection is established;
SSL can be further used for confirmation in the connection,
After the connection, subsequent messages can be sent continuously without confirmation;
congestion control
Redundant ACK: The receiver receives an out-of-sequence message and sends redundant ACK, in SR/GBN
TCP connection establishment or timeout, full start and congestion avoidance
TCP receives 3 redundant ACKs, fast retransmission and fast recovery cwnd=ssthresh