ICOM6012 Topic 2 The Big Picture

作者: Arthur | 1303 字, 7 分钟 | 2020-10-05 | 分类: Notes

hku, icom6012, internet

翻译: EN

ICOM6012 Internet Infrastructure Technologies

Topic 2 The Big Picture

The Internet: “nuts and bolts” view

  • Billions of connected computing devices
    • Host = end system
    • Running network apps
    • Internet of things (IoT)
  • Packet switches
    • routers
    • switchers
  • Communication links
    • Fiber, copper, radio, satellite
    • Transmission rate: bandwidth
  • Networks
    • Collection of devices, routers, switches, links
    • Managed by an organization
  • Internet: “network of networks”
    • Interconnected ISPs
  • Protocols
    • Control sending, receiving of messages
  • Internet standards
    • RFC: Requests for Comments
    • IETF: Internet Engineering Task Force
    • IEEE: Institute of Electronical & Electronic Engineering

The Internet: a “service” view

  • Infrastructure
    • Web
    • Streaming video
    • Multimedia teleconferencing
    • Email
    • Games
    • E‐Commerce
    • Social media
    • Inter‐connected appliances
  • Programming interface
    • Sending/receiving apps
    • Service options

Protocol

  • Activities in the Internet involving two or more remote entities are governed by a protocol
  • Protocols are running everywhere in the Internet

A protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event.

Network Standards

  • IETF
    • Application
    • Transport
    • Network
  • IEEE
    • Data link
    • Physical

Network Edge

  • Hosts
    • Clients
    • Servers (always in data centers)

Access Networks, Physical Media

  • Residential access networks (cable-based)
    • Frequency Division Multiplexing (FDM)
      • Different channels transmitted in different frequency bands
      • Modem = Modulator + Demodulator
        • A device that converts data from digital format into one suitable for a transmission medium
    • HFC: hybrid fiber coax
      • Asymmetric: up to 40 Mbps – 1.2 Gbs downstream transmission rate, 30‐100 Mbps upstream transmission rate
    • Network of cable, fiber attaches homes to ISP router
      • Homes share access network to cable headend
  • Residential access networks: digital subscriber line (DSL)
    • Use existing telephone line to central office DSLAM
      • Data over DSL phone line goes to Internet
      • Voice over DSL phone line goes to telephone network
  • Wireless access networks
    • Wireless local area networks (WLANs)
      • Within or around building (~100ft)
      • 802.11b/g/n (WiFi) - 11,54,450 Mbps
    • Wide-area cellular access networks
      • Mobile (10km)
      • 4G/5G cellular networks - 10 Mbps
    • IoT
      • BLE
      • ZigBee
      • LoRa
    • Remote areas
  • Enterprise access networks (school, company)
    • Mix of wired, wireless link technologies
      • Ethernet
        • Wired access at 100Mbps, 1Gbps, 10Gbps
      • WiFi
        • Wireless access points at 11, 54, 450 Mbps

History of IEEE 802.11 (Use CSMA/CA)

  • Unlicensed ISM - 1985
  • 802.11 - 1997
    • 2.4GHz
    • DSSS & FHSS
    • 1,2Mbps
  • 802.11b - 1999 (WiFi-1)
    • 2.4GHz
    • DSSS
    • 11Mbps
  • 802.11a - 1999 (WiFi-2)
    • 5GHz
    • OFDM
    • 54Mbps
  • WiFi Alliance - 1999
  • 802.11g - 2003 (WiFi-3)
    • 2.4GHz
    • 54Mbps
  • 802.11-2007 - 2007
    • Combined 802.11a/b/g
  • 802.11n - 2009 (WiFi-4)
    • MIMO, 2.4 or 5GHz
    • 600Mbps
  • 802.11-2012
    • Combined 802.11a/b/g/n
  • 802.11ac - 2013 (WiFi-5)
    • 5GHz
    • 7Gbps
  • 802.11ah - 2017
  • 802.11ax - 2020 (WiFi-6)
    • 5GHz
    • OFDMA
    • 9.6Gbps

Links: Physical Media

  • Twisted pair (TP)
    • Two insulated copper wires
      • Category 5: 100Mbos, 1Gbps Ethernet
      • Category 6: 10Gbps Ethernet
  • Coaxial cable
    • Two concentric copper conductors
    • Bidiretional
    • Broadband
      • Multiple frequency channels on cable
      • 100 Mbps per channel
  • Fiber optic cable
    • Glass fiber carrying light pulse a bit (each pulse a bit)
    • High-speed point-to-point transmission (10-100Gbps)
    • Low error rate
      • Repeaters spaced far apart
      • Immune to electromagnetic noise
  • Wireless radio
    • Signal carried in electromagnetic spectrum
    • No physical “wire”
    • Propagation environment effects
      • Reflection
      • Obstruction by objects
      • Interference

Network Core

Mesh of interconnected routers

  • Packet-switching (hosts break application-layer messages into packets)

    • Forward packets from one router to the next
    • Each packet transmitted a full link capacity
  • Packet transmission delay

packet_switch

	Packet transmission delay = L (bits) / R (bits/sec)
  • End-end delay

store_and_forward

	End-end delay = 2L (bits) / R (bits/sec)
	(Assuming zero propagation delay)
  • Store and forward: entire packet must arrive at router before it can be transmitted on next link

  • Packet queuing and loss

    • If arrival rate > transmission rate, packets will queue
    • If memory fills up, packets can be dropped
    • Bigger buffer can bring lower packet loss but higher delay+buffer cost
  • Two key network-core functios

    • Forwarding
      • Local action: input link -> output link
    • Routing
      • Global action: source -> destinatin
      • Routing algorithms
  • Circuit switching

    • End-end resources allocated to, reserved for “call” between source&dest

circuit_switching

  • Frequency Division Multiplexing (FDM)

fdm

  • Time Division Multiplexing (TDM)

tdm

Packet Switching vs. Circuit Switching

  • Packet switching is great for bursty data
    • Resource sharing
    • Simpler, no call setup
  • Packet switching can cause excessive congestion
  • Combined: Virtual Circuit Packet Switching

Internet Structure: Network of networks

  • Hosts connected to internet
  • Access ISPs (Internet Service Providers)
    • To ensure every two hosts can send packets to each other, access ISPs must be interconnected

isp_tiers

  • Tier-1 ISP
    • Sprint, AT&T, NTT
    • National & international coverage
  • Content provider network (private network)
    • Google
    • Facebook

Delay and Loss

  • Nodal processing
  • Queueing delay
  • queueing_delay
    • R: link bandwidth (bps)
    • L: packet length (bits)
    • a: average packet arrival rate
    • Traffic intensity = La / R
    • E(x) = La/R / (1 - La/R)
  • Transmission delay
    • L(packet length) / R (link bandwidth)
  • Propagation delay
    • d (length of physical link) / s (propagation speed)

packet_delay

	d(nodal) = d(proc) + d(queue) + d(trans) + d(prop)

Example

	Number of hops = M
	Per-hop processing delay = d(proc)
	Link propagation delay = d(prop)
	Packet transmission delay = d(trans)
	Message size = N packets

	End-to-end Delay (ignoring queueing delay)
	= M * d(prop) + N * d(trans) + (M-1) * d(trans) + (M-1) * d(proc)

timing_diagram

“Real” Internet delays and routes: traceroute YouTube (macOS)

➜  ~ traceroute youtube.com
traceroute to youtube.com (216.58.197.110), 64 hops max, 52 byte packets
 1  172.24.172.1 (172.24.172.1)  14.211 ms  1.584 ms  1.635 ms
 2  118.140.125.65 (118.140.125.65)  13.122 ms  23.362 ms  7.402 ms
 3  10.30.31.17 (10.30.31.17)  7.024 ms  23.736 ms  54.474 ms
 4  10.28.21.37 (10.28.21.37)  5.924 ms  3.565 ms  2.954 ms
 5  * * *
 6  * 218.188.28.165 (218.188.28.165)  214.507 ms  3.344 ms
 7  108.170.241.65 (108.170.241.65)  3.595 ms
    72.14.222.9 (72.14.222.9)  10.840 ms  3.377 ms
 8  108.170.241.65 (108.170.241.65)  3.156 ms
    216.239.62.59 (216.239.62.59)  3.495 ms
    216.239.62.57 (216.239.62.57)  2.733 ms
 9  216.239.62.59 (216.239.62.59)  4.698 ms
    hkg12s01-in-f14.1e100.net (216.58.197.110)  3.252 ms  4.355 ms

Packet Loss

  • Queen (buffer) preceding link in buffer has finite capcity
  • Packet arriving to full queue dropped (lost)
  • Lost packet may be retransmitted by previous node, end system or not at all

packet_loss

Throughput

  • Rate (bits/time) at which bits transferred from sender to receiver
    • Instantaneous: rate at given point in time
    • Average: rate over longer period of time
  • Bottleneck link
    • link on end-end path that constrains end-end throughput
    • throughput
    • Per-connection end-end throughput
      • min(Rc, Rs, R/10)
      • In practice, Rc or Rs is often bottleneck

Why Layering

  • Explicit structure allows identification, relationship of complex system’s pieces
  • Modularization eases maintenance, updating of system

Internet Protocol Stack

  • Application - supporting network applications
    • FTP
    • SMTP
    • HTTP
  • Transport - process data transfer
    • TCP
    • UDP
  • Network - routing of datagrams from source to destination
    • IP
    • Routing protocol
  • Link - data transfer between neighboring network elements
    • Ethernet
    • WiFi
    • PPP
  • Physical - bits “on the wire”

ISO/OSI Reference Model (Implemented in Application)

  • Presentation
    • Allow applications to interpret meaning of data
  • Session
    • Synchronization, checkpoint, recovery of data exchange

Encapsulation

encapsulation

Network Security

  • Fields of network security
    • How bad guys can attack computer networks
    • How we can defend networks against attacks
    • How to design architectures that are immune to attacks
  • Internet not originally designed with much security in mind

Bad Guys

  • Malware
    • From
      • Virus
      • Worm
    • Spyware malware
    • Usage
      • Botnet
      • Spam
      • DDos attacks
  • Denial of service (DoS)
    • Make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with fake traffic
    • Procedures
      1. Select target
      2. Break into hosts around the network
      3. Send packets to target from compromised hosts
  • Packet interception
    • Packet “sniffing”
    • packet_sniffing
      • Broadcast media (shared ethernet, wireless)
      • Promiscuous network interface reads/records all packets
  • Fake identity
    • IP spoofing: send packet with false source address
    • ip_spoffing

Use’s View Of Internet

  • Single large (global) network
    • Achieved through software that implements abstractions
  • User’s computers all attach directly
  • No other structure visible

user_view_internet Internet History

  • Early packet-switching principles (1961-1972)
  • Internetworking, new and proprietary nets (1972-1980)
  • New protocols, a proliferation of networks (1980-1990)
  • Commercialization, the Web, new apps (1990’s, 2000’s)
  • More new applications, Internet is “everywhere” (2005-Present)

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Arthur

作者

Arthur

区块链(Golang)开发工程师,香港大学计算机系硕士在读。喜欢探索学习新科技,空闲时也折腾Notion等效率工具。 在GitHub关注我