- Good developers know how things work. Great developers know why they work.
- Latency - time from source to destination of a packet
- Bandwidth - throughput of comm path
- delay - propagation, transmission, processing, queuing
- propagation delay - time for signal to travel from source to destination
- transmission delay - time to push all bits into link
- processing delay - time to process packet at router
- queuing delay - time to wait at router
- user perceive lag at 100-200ms
- cdn help with this
- last mile latency
- guarantees - in order and reliable bytes
- 3 way handshake
- TFO - tcp fast open - send data in first part of handshake
- congenstion collapse - round trip time exceeds retransmission timeout
- flow control - prevent sender from overwhelming receiver
- tcp connection advertises receiver window
- congestion window - prevent network overload. Sender side limit (slow start, congestion avoidance)
- SSR - slow start restart - resets congestion window
- bandwidth delay product - max amount of data in flight at any point
- datagram - pretty much the same as packet
- no guarantee of message delivery, order, connection tracking, or congestion control
- NAT traversal - inability to establish udp connection between two hosts behind same NAT
- STUN - discover peers - keepalive pings
- TURN - relay peers
- SSL - oberserver can not read or modify the data, just observe its transmission
- uses encryption, authentication, and integrity
- handshake - negotiate encryption keys
- signs messages with MAC
- don't have to repeat full handshake for each connection - abbreviated handshake - start transmitting encrypted data before handshake completes
- session identifiers - server caches session for every client - or can use session tickets
- certificate authorities - verify certificate
- computation cost of encryption
- can optimize handshake with CDN
- network is a group of devices connected to one another
- all comms have max channel capacity
- dependent on signal strength and bandwidth
- gov decides hertz freq
- low freq - long range, larger antenna and more clients
- s/n - signal to noise ratio
- near far - recevier captures a strong signal and can't hear weaker signals
- cell breathing - coverage arae expands or shrinks
- modulation - process of digital to analog conversion
- affect performance - distance, noise, interference intra, interference inter, power, processing
- treat channel as shared medium as random access
- listen before talk
- also has collision detection and avoidance
- wifi has no collision detection
- gigabit plus throughput with ac standard
- wifi provides no bandwidth or latency guarantees
This chapter was a lot of history so I skimmed.
- underlying standars - peak spectral efficiency
- Gs are a set of requirements
- LTE - long term evolution
- continuous reception - highest power state, established network context, allocated resources
- short discontinuous reception
- long discontinuous reception