notes

Chapter 1

Terms

  • Hosts: end systems that run apps
  • Apps
  • Devices: run apps
  • Packet switches (chucks of data)
  • Communication links: transmission forms like fiber, radio, etc
  • Access Network: A network that bottlenecks to one router (edge router) to get back to isp
  • Edge Router: A router on the "edge" of a network
  • Protocols: Control sending, receiving.
  • Internet Standards
  • TCP connection
  • RFC: Request for comments
  • IETF: Internet Enginering Task Force
  • AP: wireless access point
  • NAT: firewall, router

Nuts and bolts

  • Hosts run apps
  • Devices at the core of the network (routers, switches)
  • Router decides what to do with chunk of data
  • TCP, HTTP are protocols
  • RFC:

Access networks

  • Digital subscriber line (DSL)
  • cable-based access
    • HFC hybrid fiber coax
      • fiber optics connect neighborhood junctions
      • coaxial cable connects homes to neighborhood junctions
      • cable modem has higher downstream than upstream
    • Network of cables,fiber optics connect to ISP router
  • Fiber to the homer (FTTH)
    • fiber leaving CO is shared
    • splitter (100 homes)
    • Gbps range
    • Optical Network Terminator (ONT) is an analog for modems
    • Optical

5g fixed wireless

Data is sent wirelessy to modem in home

Wireless access networks

  • Wireless local area networks (wlans)

Wide-area cellular access networks

  • 4g/5g cellular networks

enterprise networks

  • switches connect to modem which goes to isp

Packets of data

  • length L bits
  • tranmission rate (packets per time) R
  • link capacity = link bandwitch = capacity
  • transmission delay

links

  • bit: tranmitter/reciever pairs
  • physical link: what lies between tranmitter and reciever
  • guided media (cables, fiber, etc)
  • unguided media (wireless)
  • TP (twisted pair) cables (cat6): 10gbs

Packet queuing and loss

  • packets can be lost(dropped) if packets exceed memory of router
  • queuing delay: packets have higher latency depending on the length of the queue

Two key network-core functions

  • local forwarding table
  • forwarding table is constructed by the router using "routing algorithms"
  • routing is a global action
  • forwarding table is a local action

Circuit switching

  • end-end resources allocated to reserved for "call" between source and destination
  • restaurant reservation
  • Signal cannot share connection

Fequency Division Multiplexing (FDM)

  • Divide signal into frequency bands
  • each user can utilize 1 band
  • Telephone networks (4KHz bands)

Time Division Multiplexing (TDM)

  • Time is divided into "frames"
  • User gets full access to transmit data, but only during time slot in the frame.

Packet switching

  • More users can use network
  • Adjusts to intermittent data transmission better

Isp structure

  • Tier 1 isp is at the top
  • regional isp connects user to internet exchange point connects back to tier 1
  • Point of presence
  • \(d_{nodal} = d_{proc}+d_{queue}+d_{trans}+d_{prop}\)

dproc

  • <

transmission delay

\(d_{trans} = L/R\)

Propegation

Length/Rate

Traffic intensity

  • R (bits per second)
  • L packet length (bits)
  • a: average packet arrival rate
  • La/R = traffic intensity
  • Average queueing delay \(= \infty\) when \(La/R=1\)
  • traceroute shows delay between packet transmission

Throughput

  • Bits/time
  • Instantaneous: rate at given point in time
  • average: rate over longer period of time

TCP

  • reliable transport
  • flow control
  • congestion control
  • Connection-oriented

Vanilla

  • no encryption
  • cleartext passwords sent into socket traverse in cleartext

TLS

  • provides encrypted TCP
  • Data integrity
  • https

UDP

  • Send message and hope for reply
  • Does not provide: anything that tcp has
  • Used for fast transfer of non-essential items

HTTP/2

  • increased flexibility at server
  • MTU
  • packet loss still stalls object transfer

Http/1.1

  • client requests 1 large object

DNS

  • hostname tp IP address translation
  • host aliasing
    • canonical, alias names
  • each ISP has local DNA nae server

Finite state machines

Rdt2.0 channel with bit errors

  • acknowledgments
  • Check FSM in slides for more details (lots of verbal description about this)
  • state of receiver isn't known to sender
  • Fatal flaw (sender doesn't knwo what happend at reciever)
  • discards duplicate pkt

Rdt2.1 sender, handling garbled ACK/NAKS

  • check slides (walk through each step)

Rdt3.0

App