Design issues for layers
Addressing - whom am I going to talk to? i.e., how do we identify senders and receivers?
Rules for data transfer: Simplex (one way channels), half-duplex (two way communication but not simultaneously) and full duplex (2 way)
Logical channels: usually at least 2. One for normal mode and one for urgent transmission.
Reconstituting messages: Out of order messages need to be numbered.
Error control: This is all about communicating along imperfect channels and error correction in such cases. (Issues: Attenuation, delay distortion and noise).
Large messages: Procedures for disassembling, transmitting and reassembling. What to do when messages are very small (compared to packet)? PTO
Network software/Design issues for layers.