Wi-Fi Detail
Talked about Wi-Fi at the end last time. Look in a little more detail. We're using this wireless packet technology all the time.
Wi-Fi/Ethernet Strategy
- Wi-Fi and Ethernet are LANs, Local Area Networks (e.g. a room)
- "shared" - everybody shares the channel (or wire)
- Every computer has its own address (addr)
- Packet "to:" field is the addr of the intended recipient
- How to receive: listen all the time for a packet to: your addr
- How to send: wait for silence, broadcast the packet to everyone
Wi-Fi Picture
Wi-Fi Broadcast
- Suppose the router has a packet that's supposed to go to computer2
- The router broadcasts that packet .. it goes to everyone on the LAN
- The non-intended recipients are supposed to ignore the packet
Wi-Fi Scenarios
- 1. Bad guy intercepts packets intended for others:
- -Don't ignore packets to: someone else
- -This is why we have encryption/https - a later lecture
- 2. Someone else on the LAN is downloading a big file, what happens?
- -The shared radio channel is busy with their packets (i.e. not silent) - fewer opportunities for everyone else to use it
- 3. Computer receives a packet but the checksum does not match
- -The packet was corrupted in transit
- -In effect, request that a second copy be sent