Skip to content

Latest commit

 

History

History
175 lines (119 loc) · 6.18 KB

SN_chp1.md

File metadata and controls

175 lines (119 loc) · 6.18 KB

1.1 what is the Internet?

inter + network

ex. mobile network, home networks, institutional networks

component

H/W

  • end hosts: running network apps on terminals
  • interconnection devices: router, switch, repeater...
    • packet switches: the way to communicate between hosts in the other networks
  • links: copper, fiber, radio, wireless...
    • transmission rate: bandwidth ⬆ internet speed ⬆

S/W

  • Operating Software
  • application programs
  • protocols: rules for communications
    • ex. message format, order, action
hosts => network edges => network core

1.2 Network Edge

1.2.1 Access Networks

: make network edges(⊃ end hosts) accessible to the network

architecture

my network network core my network
[end host(wireless) --(wireless)--- AP --(wire)-- edge router] (routers) [edge router -----end host]
  • transmission rate: bandwidth(bps) ⬆ internet speed ⬆
  • (central office) shared / dedicated

Digital Subscriber Line

dedicated access network

  1. DSL modem -> splitter
  2. DSL phone line
  3. (central office) DSL Access Multiplexer
  4. voice(4kHz): telephone network | data(4kHz): Internet Service Provider

Cable Network

shared access network

  1. cable modem -> splitter
  2. coaxial cable: cable company provide one signal to multiple users
  3. (central office) Cable Modem Termination System
  4. Hybrid Fiber Coax
  5. Internet Service Provider

Home Network

  1. cable or DSL modem, ONT -> splitter
  2. Fiber To The Home
  3. (central office) Headend
  4. Internet Service Provider

Enterprise / Institutional Network

  1. AP, Ethernet switch
  2. Institutional link to ISP

Wireless Access Networks

shared access network

  • wireless LANs: Wireless Fidelity(shared network)
  • wide-area wireless access(shared network)

1.2.2 Physical Media

: the physical materials that are used to store or transmit information in data communications

  • guided: wired
    • Twisted-pair cable: copper wires, behind the ethernet
    • Coaxial cable: copper conductor, broadband
    • Fiber-optic Cable: high speed, low error rate
  • unguided: wireless
    • radio link types

1.3 Network Core

  • connecting network edges(⊃ end hosts)
  • the mesh of interconnected routers
  • when sending packets, forwarding from a router to the next router
    • routing: Get a path from source host to destination host using routing algorithms
    • forwarding: Move packets from the before router to the next router using forwarding table

1.3.1 Two fundamental approaches to moving data

comparison

circuit switching packet switching
call setup, resource reservation
: the resources needed along a path		 No call setup, no resource reservation
multiple users sharing a link
by Frequency Division Multiplexing , Time Division Multiplexing		 full link capacity
by dividing into small packets which have their own each destination address
using store-and-forward transmission
low speed 3.5x users but after it.. low Quality Of Service
in telephone networks ~

store-and-forward transmission

  • app in source Host ---link(by packets)---> app in destination Host
  • how? storing bits until a packet and then forwarding it
  • => total time

1.3.2 A Network of Networks

Internet = A Network (by ISP) of Networks (end system)

hierarchy structure

host < access ISP < regional ISP (peering link) < Internet eXchange Point < Tier 1 ISP or Content Provider

  • content provider has its own content provider network in its own data center

1.4 Evaluation Metrics in networks

1.4.1 delay

: source~destination seconds

  1. nodal processing delay: before forwarding a packet, should check its error and destination address
    • opt to the quality of router
  2. queueing delay: when forwarding one packet, the other packet should wait in a buffer.
    • opt to the number of network users => so variable
    • traffic intensity = La/R ↑ ~1 infinite
      when packet arrival rate(packet/sec) > output link capacity(L/R)
      <=> over the queue -> dropped
  3. transmission to the link delay when starting to forward: A host send a packet of L bits over a link with transmission rate R bits/sec, then the time to transmit the packet is L/R sec. (link transmission rate = link capacity = link bandwidth)
    • opt to bandwidth of output link
  4. propagation delay in the link: time = length / speed
    • opt to the amount of data
  5. => end-end delay: the number of hop * L/R

1.4.2 loss

: Packet Loss Rate (<-> Packet Delivery Rate)

  • usually in router
  • in a buffer when queueing delay, data > queue capacity => dropped
  • host: re-transmission, network: waste of resource, user: delay

1.4.3 throughput

: sum of traffic <=> how much data has been moved between server and client
=> rate: bits/time unit

  1. instantaneous: throughput at the peak
  2. average: throughput on the average
    • end-end average throughput == bottleneck link == min(Rs, Rc, R/10)

1.5 protocol layers, service models

Internet protocol stack

5 layers explanation protocol encapsulation controlled by
application support network application FTP, SMTP, HTTP message user(app developer)
transport data transfer process <-> process TCP, UDP + segment OS
network find path IP, routing protocols + datagram OS
link data transfer by hop from source to destination Ethernet, WiFi + frame OS
physical on the wire like cable, radio bits Protocol Data Unit OS
  • layering: modulerarization -> maintenance, system update
  • encapsulation: message + headers..
    • source -> switch(link+physical) -> router(network+link+physical) -> destination(only message + segment are from source)
    • always start from physical layer and go up by figuring out the needed info by the headers