CS 118 Discussion Week 1: A Brief Introduction to Networking
Slides by Eric Newberry (UCLA) Winter 2021
TA Introduction
• Education
• Ph.D. in Computer Science, UCLA, Started in January 2020
• M.S. in Computer Science and Engineering, University of Michigan, 2020 • B.S. in Computer Science, University of Arizona, 2018
• Research
• Named Data Networking (NDN) with Prof. Lixia Zhang
• Focusing on efficient packet forwarding implementations for NDN
• Prior work on caching in NDN, software-defined NDN, and
automotive network security (at Arizona and Michigan)
• Outside activities (aka when I’m not working or in class)
• I read about history, read science fiction, and play video games of all sorts
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Course Logistics
• My office hours are Wednesdays, 3-5pm PST
• https://ucla.zoom.us/j/99586525253?pwd=RVJ4Nzl6QVVMSE9zR0RKbW94Zit
xQT09
• Email: enewberry@cs.ucla.edu
• If it requires an immediate response, please CC the professor (gpau@cs.ucla.edu) and the other TA (hdellaverson@gmail.com)
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Course Introductions
• Name
• Major
• Year
• (optional) What’s been your go to pastime in lockdown?
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Structure of the Internet
• Network of networks→hierarchical
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https://commons.wikimedia.org/wiki/File:Internet_map_1024.jpg
https://commons.wikimedia.org/wiki/File:Internet_Connectivity_Access_layer.svg
A Brief Step Back in Time
• The first modern computer network was developed in the late 1960s • ARPANET
• The story of “LO”
UCSB
UCLA
SRI
Utah
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Structure of the Internet
• The “edge”
• End devices such as desktops, laptops, smartphones, game consoles, tablets,
IoT devices, etc.
• The “core”
• Networks that interconnect large, geographically disparate networks • Made up of internet service providers (ISPs)
• “Access networks”
• How the edge reaches the core
• E.g., DSL, cable, fiber to the home, 4G, 5G, WiFi, Ethernet
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Access Networks
mobile network
national or global ISP
local or regional ISP
home network
enterprise network
content provider network
datacenter network
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Book slides by Kurose & Ross
Are these “access networks”?
• Your home network (WiFi, routers, and connected devices)?
• Not quite! It includes all of the above except your connected devices.
• Your local ISP?
• No, they would be part of the core
• DSL or Cable link between your home and your local ISP? • Yes!
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Providing Structure to the Internet
• “Network of networks”
• You connect to your ISP
• Your ISP connects to other ISPs
• Some ISPs only have other ISPs as customers
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https://commons.wikimedia.org/wiki/File:Internet_Connectivity_Distribution_%26_Core.svg
Packets
• We have to share the network with other devices
• However, reserving network resources is too complex and inflexible •→Split data stream into “packets” and send via “packet switching”
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Layering and Encapsulation
Application Presentation Session Transport Network Data Link Physical
https://commons.wikimedia.org/wiki/File:UDP_encapsulation.svg
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Layering: Why Bother?
• Different layers have different responsibilities
• Can use different protocols at one layer without needing to change protocol at another layer
• Don’t want network layer to need to understand how your application works to operate correctly
• Don’t want to have to change application when using Wi-Fi instead of wired • Protocols evolve and change over time (e.g., IPv4→IPv6 at network layer)
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Routing and Forwarding
• Routing: how do I reach the final destination of this packet?
• Forwarding: knowing the above, which of my neighbors do I send the
packet to next?
routing
forwarding
forwarding
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Image from main lecture slides
Packet Queuing and Loss
• Routers can only process packets so quickly
• If packets come in faster than they can be sent out, they are queued
• If queue fills up, packets start being dropped!
• What do we do in the event of loss? • Try again! (aka retransmit)
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Sources of Packet Delay
transmission
A B
propagation
nodal
processing queueing
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▪ s: propagation speed (~2×108 m/sec) Book slides by Kurose & Ross 16
dnodal = dproc + dqueue + dtrans + dprop
dproc: nodal processing
▪ check bit errors, determine
output link, typically < μs
dtrans: transmission delay (L/R): ▪ L: packet length (bits)
▪ R: link transmission rate (bps)
dqueue: queueing delay
▪ time waiting at output link for
transmission
dprop: propagation delay (d/s):
▪ d: length of physical link
Throughput
• Definition: Number of bits that can be sent from sender to receiver per unit of time (e.g., bits/second)
• End to end throughput constrained by throughput of “slowest” link • And by how much traffic other hosts are sending through the same link(s)
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Bandwidth-Delay Product
• How much data can be “in flight” on a given link in a given unit of time?
• Bandwidth (theoretical throughput of link, also in bits/second) • BW x Round-trip delay
.........
AB
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Bandwidth-Delay Product
• Fiber-optic link:
• Bandwidth: 10 Gb/s
• Round-trip Delay: 25 μs (25 x 10^-6 seconds) • BDP:
• Slow DSL connection:
• Bandwidth: 1 Mb/s
• Round-trip Delay: 50 ms (50 x 10^-3 seconds)
• BDP:
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Questions?