index.md (1919B)
1 +++ 2 title = "Data Link: Protocols" 3 +++ 4 5 # Data Link: Protocols 6 **Protocols** 7 8 - link layer commonly implemented as NIC (physical layer, some data link layer processes) and OS drivers (rest of link layer processes) 9 - make sure that receiver is ready for next frame with acknowledgements, timers, etc. 10 - Utopian simplex 11 - does not worry about anything going wrong 12 - simplex — data sent only in one direction 13 - sender is infinite while that gets data from network and puts data on physical 14 - receiver waits until arrival of frame, then puts on network 15 - Simplex Stop-and-Wait 16 - also only one direction 17 - sender passes a packet, then waits for receiver to send back a ‘dummy’ frame to acknowledge 18 - Automatic Repeat ReQuest (ARQ) 19 - receiver acknowledges correctly delivered frames 20 - sender resends on timer if no acknowledge 21 - frames must be numbered (1 bit is enough) 22 - Sliding Window 23 - piggyback with two senders — add acknowledgement to outgoing frame 24 - sending window — at any instant of time, sender maintains set of sequence numbers for frames that i can send 25 - receiving window — receiver has a set of frames that it can accept 26 - Go-back-n 27 - if error while pipelining, discard all subsequent frames without sending acknowledgements 28 - receive window of size 1 29 - can waste a lot of bandwidth 30 - Selective repeat 31 - a bad frame that is received is discarded, any good frames after are accepted and buffered 32 - only oldest unacknowledged frame is resent 33 34 **Example: ADSL (Asymmetric Digital Subscriber Loop)** 35 36 - most popular scenario: 37 38 1. Inside home, PC sends IP packets to DSL modem over Ethernet 39 2. DSL modem sends IP packets to DSLAM (DSL Access Muxer) 40 3. DSLAM extracts IP packets and sends them to ISP network 41 42 