The Networking
Philosopher’s Problem
Jennifer Rexford
Computer Science Department
Princeton University
http://www.cs.princeton.edu/~jrex
The Internet: An Exciting Time
• One of the most influential inventions
–A research experiment that escaped from the lab
–… to be a global communications infrastructure
• Ever wider reach
–Today: 1.7 billion users
–Tomorrow: more users, computers, sensors
• Near-constant innovation
–Apps: Web, P2P, social networks, virtual worlds
–Links: optics, WiFi, cellular, WiMax, …
2
So, why every two years, when I
teach graduate networking,
I have all sorts of angst...
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What is Networking?
4
A Plethora of Protocol Acronyms?
WAP
SNMP
LLDP
FTP
OSPF
RTP
SIP
ICMP
HTTP
RED
IP
RIP
SMTP
IMAP
MAC
TLS
SACK
VLAN
LISP
VTP
RTCP
CIDR
NAT
SSH
DNS
IGMP
TCP
BFD
RTSP
HIP
ECN
ARP
MPLS
NNTP
POP
PPP
UDP
BGP
PIM
IPX
STUN
DHCP
TFTP
LDP
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A Heap of Header Formats?
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TCP/IP Header Formats in Lego
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A Big Bunch of Boxes?
Router
Label
Switched
Router
Gateway
Load
balancer
Scrubber
Intrusion
Detection
System
Deep
Packet
Inspection
WAN
accelerator
Bridge
DHCP
server
Firewall
NAT
Switch
Hub
DNS
server
Repeater
Route
Reflector
Packet
shaper
Packet
sniffer
Base
station
Proxy
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A Ton of Tools?
arpwatch
tcpdump
syslog
wget
nslookup
traceroute
trat
snort
nmap
whois
rancid
ntop
net-snmp
dig
ipconfig
bro
ping
iperf
wireshark
NDT
dummynet
mrtg
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What Do Peers in Other Fields Say?
• “You networking people are very curious. You
really love your artifacts.”
• “In my college networking class I fell asleep at the
start of the semester when the IP header was on
the screen, and woke up at the end of the
semester with the TCP header on the screen.”
• “Networking is all details and no principles.”
Is networking “just the (arti)facts”?
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An Application Domain?
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Application Domain for Theory?
• Algorithms and data structures
• Control theory
• Queuing theory
• Optimization theory
• Game theory and mechanism design
• Formal methods
• Information theory
• Cryptography
• Programming languages
• Graph theory
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Application Domain for Systems?
• Distributed systems
• Operating systems
• Computer architecture
• Software engineering
•…
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An Exercise in Entrepreneurship?
• Identify a need or desirable capability
– Whether previously known or not
• Invent a new feature or system that provides it
• Determine how it fits in the existing network
• Build and/or evaluate your solution
• Pitch or $ell the problem and solution to others
– Whether to investors or a program committee
• Bask in glory, or lick your wounds
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What Peers in Other Fields Say?
• “Networking papers are strange. They have a lot of text.”
• “What are the top ten classic problems in networking? I
would like to solve one of them and submit a paper to
SIGCOMM.” After hearing that we don't have such a list:
"Then how do you consider networking a discipline?”
• “So, these networking research people today aren't doing
theory, and yet they aren't the people who brought us the
Internet. What exactly are they doing?”
• “Networking is an opportunistic discipline.”
Is networking a problem domain or a scholarly discipline?
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What Do We Teach
Networking Students?
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How Practitioners Learn Networking
• Certification courses
– On how to configure specific pieces of equipment
• “On the job” training
– Aka “trial by fire”
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How Colleges Teach Networking
• Undergraduates: how the Internet works
• Graduates: read the 20 “best” papers
• Few general principles, little “hands-on”
experience
“There is a tendency in our field to believe that everything we
currently use is a paragon of engineering, rather than a snapshot of
our understanding at the time. We build great myths of spin about
how what we have done is the only way to do it to the point that our
universities now teach the flaws to students (and professors and
textbook authors) who don't know better.” -- John Day
• (I’m as guilty as anyone)
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Now That I’ve Bummed You Out…
Or, Why Should You
Stay in This Field?
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So, Why is Networking Cool?
• Tangible, relates to reality
– Can measure/build things (we do “love our artifacts”)
– Can truly effect far-reaching change in the real world
• Inherently interdisciplinary
– Well-motivated problems + rigorous solution techniques
– Interplay with policy, economics, and social science
• Widely-read papers
– Many of the most cited papers in CS are in networking
– Congestion control, distributed hash tables, resource
reservation, self-similar traffic, multimedia protocols,…
– Three of top-ten CS authors (Shenker, Jacobson, Floyd)
– So, somebody is interested in reading this stuff… 
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So, Why is Networking Cool? (Cont)
• Young, relatively immature field
– Great if you like to make order out of chaos
– Tremendous intellectual progress is still needed
– You can help decide what networking really is
• Defining the problem is a big part of the challenge
– Recognizing a need, formulating a well-defined problem
– … is at least as important as solving the problem…
• Lots of platforms for building your ideas
– Programmability: Click, OpenFlow/NOX, NetFPGA
– Routing software: Quagga, XORP, and Bird
– Testbeds: Emulab, PlanetLab, Orbit, GENI, …
– Measurements: RouteViews, traceroute, Internet2, …
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But, That Doesn’t Say What
Networking Really Is
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Maybe networking is defined
more by the questions we ask,
than the techniques we use
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Decomposition of Function
• How to
– Design and operate components and protocols
– That can be used and combined in many ways
– To do many things
• Definition and placement of function
– What to do, and where to do it
• The “division of labor”
– Between the host, network, and management systems
– Across multiple concurrent protocols and mechanisms
• How do we know if we got it right?
– Soul searching? A proof or analysis? A prototype?
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Today’s Divisions of Labor
• End host and the network
– Packet switching
– Best-effort delivery
– Fixed end-points with
IP addresses
• Protocol layers
– IP as the center of the universe
– IP above the link layer
– IP below transport and application
network
Applications
UDP TCP
Data Link
Physical
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Today’s Divisions of Labor
• Network elements
– Data plane: packets
– Control plane: events
– Management: policies
• Administrative domains
– Autonomous Systems
– Destination IP prefixes
– Policy-based path-vector routing
“d: path (2,1)”
3
“d: path (1)”
1
2
data traffic
data traffic
d
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Beyond Today’s Division of Labor
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Between Hosts and the Network
• Networked services hosted in data centers
– Web sites, social networks, video streaming, online
gaming, virtual worlds, ...
– Replicated on servers in multiple data centers
– Churn from mobile users, migrating VMs, failures, …
data centers
• Time to rethink
– Naming and addressing
– Early vs. late binding
– Server and network
load balancing
– End-host network stack
and socket API
..
..
servers
Internet
clients
Between Network and Management
• Smart management,
dumb network
measure
control
• Dumb management,
smart network
– Network elements talk
amongst themselves
– Adapting automatically
Between Administrative Domains
Evolvable Protocols
(under-specified, programmable)
?
Autonomy
Global Properties
(autonomous parties, with
different economic objectives)
(stability, scalability, reliability,
security, managability, …)
Can we have all three? Under what conditions?
Conclusion
• Networking is cool
– Real, important problems
– Opportunities for impact
– Inherently interdisciplinary
• But the field is immature
– More of a “domain” than a “discipline”
– Still searching for its intellectual center
• Please help!
– Master a discipline and apply it to networking
– Define what the networking “discipline” really is
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Random Advice on Being an
Effective Graduate Student
http://www.freedom-totinker.com/blog/jrex/advice-newgraduate-students
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