1. The Networking Philosopher’s Problem
Jennifer Rexford
Computer Science Department
Princeton University

2. 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, …

3. So, why every two years, when I teach graduate networking, I have all sorts of angst...

4. What is Networking?

5. A Plethora of Protocol Acronyms?
WAP
SNMP
IPX
SIP
PPP
MAC
FTP
LLDP
UDP
HIP
ICMP
OSPF
RTP
IMAP
IGMP
BGP
HTTP
ECN
PIM
RED
ARP IP
TCP
RIP
MPLS
RTCP
SMTP
BFD
CIDR
Red: network layer
Green: transport layer
Purple: application layer
Blue: routing
Orange: enterprise/edge networks
Black: other stuff
Most have three or four letters, except IP has just two. But IP is special, as it is the center of the known universe.
RTSP
NNTP
TLS
NAT
SACK
STUN
SSH
DNS
DHCP
VTP
VLAN
LDP
POP
LISP
TFTP

6. A Heap of Header Formats?
Header formats have gotten more colorful in recent years (I am old enough to remember when they were in black and white, and courier font), but they are still awfully boring. Zzzzz…
Have you seen the lego version of the IP and TCP header?

7. TCP/IP Header Formats in Lego

8. A Big Bunch of Boxes? Load balancer Label Switched Router Switch
Scrubber
Repeater
Gateway
Bridge
Intrusion
Detection
System
Route
Reflector
Deep
Packet
Inspection
DHCP
server
Packet
shaper
Firewall
Ask yourself what is the real difference between these components? Do we need to think of them as distinct?
Can a common piece of hardware support many of these functions?
Do ever need to do more than one of these functions at the same time and place?
NAT
Hub
Packet
sniffer
DNS
server
WAN
accelerator
Base
station
Proxy

9. A Ton of Tools? arpwatch tcpdump syslog wget nslookup traceroute trat
snort
nmap
whois
ipconfig
rancid
ntop
bro
net-snmp
dig
ping
iperf
wireshark
NDT
dummynet
mrtg

10. 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”?

11. An Application Domain?
All of the next few slides have an element of truth in them. These are perfectly reasonable ways to think of networking as a “domain” rather than a “discipline”.

12. 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
Algos and data structures: data plane (longest-prefix match, packet classification), control plane (Dijkstra, Bellman-Ford, spanning tree), DHT, …
Control theory: TCP, load-sensitive routing
Queuing theory: justification for packet switching (i.e., studying statistical multiplexing)
Optimization: design/analysis of protocols like TCP congestion control, tuning protocols for traffic engineering
Game theory: interdomain routing, sharing CPU/bandwidth/power in mobile ad hoc networks
Formal methods: design and validation of protocols
Info theory: inference of network properties from limited measurements
Crypto: secure protocols, analysis of security properties of new/existing protocols
PL: configuration languages, software-defined networking
Graph theory: graph algorithms, metrics for characterizing topologies

13. Application Domain for Systems?
Distributed systems
Operating systems
Computer architecture
Software engineering …
Distributed systems: how different from networking? Evolved somewhat separately. DS assumes underlying connectivity of some sort. Yet, common issues, and they are more mature than we are.
Operating systems: end-host networking stack
Computer architecture: network interface card, router hardware, etc.
Software engineering: protocol design, understanding requirements, …

14. 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

15. 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?

16. What Do We Teach Networking Students?

17. How Practitioners Learn Networking
Certification courses
On how to configure specific pieces of equipment
“On the job” training
Aka “trial by fire”

18. How Colleges Teach Networking
Undergraduates: how the Internet works
Graduates: read the 20 “best” papers
Few general principles, little “hands-on” experience
(I’m as guilty as anyone)
“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
No need to be too apologetic here. This is a reflection of where we are as a field. The key point is not that we should feel bad about this, but rather than we should not be satisfied with the current state of our understanding.

19. Now That I’ve Bummed You Out…
Or, Why Should You Stay in This Field?
These next few slides take the critiques in the previous slides and give them a positive spin. It’s not that the earlier slides were wrong, so much as there being an upside to all this…

20. 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… 
The point about widely-read papers is meant to be somewhat glib. High citation count doesn’t necessary mean important or deep – just that the field is large (and perhaps, as is true in networking, interdisciplinary). Or, maybe the networking field is just a large cult, where we all cite each others. ;)

21. 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, …
The “lots of platforms” is relevant to the course, where we will leverage these platforms to Do Great Things.

22. But, That Doesn’t Say What Networking Really Is

23. Maybe networking is defined more by the questions we ask, than the techniques we use

24. 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?

25. 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
UDP
TCP
Data Link
Physical
Applications

26. 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)”
“d: path (1)” 2 3 1
data traffic
data traffic d

27. Beyond Today’s Division of Labor

28. 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, …
Time to rethink
Naming and addressing
Early vs. late binding
Server and network load balancing
End-host network stack and socket API
data centers
. .
. .
servers
Internet
clients

29. Between Network and Management
Smart management, dumb network
Dumb management, smart network
Network elements talk amongst themselves
Adapting automatically
measure
control

30. Between Administrative Domains
Evolvable Protocols
(under-specified, programmable) ?
Programmability determines the space in which the economic incentives play out.
The programmability plus the incentives determines whether/what X-ities can be satisfied.
We’re starting to see some work in this space, though admittedly focused on analyzing existing systems moreso than designing systems that identify the right programming model.
Autonomy
(autonomous parties, with
different economic objectives)
Global Properties
(stability, scalability, reliability, security, managability, …)
Can we have all three? Under what conditions?

31. Conclusion Networking is cool But the field is immature Please help!
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

32. Random Advice on Being an Effective Graduate Student