1. Where Does Circuit Switching Make Sense In the Internet?
Pablo Molinero-Fernández
High Performance Networking Group
Stanford University

2. Outline Motivation Packet switching Circuit switching
6/26/2018 1:16 AM
Outline
Motivation
Packet switching
Description and myths
Circuit switching
Where it can be useful
Research: TCPSwitch
Goals, architecture and QoS
Conclusion
I am going to start talking about packet switching, I will describe its characteristics and why researchers thought in the late 60s and early 70s that it would be the perfect technology for computer networks
I will revisit those ideas and reevaluate in the current context of the Internet, and I will show that there are some myths and misconceptions
Next I will describe where circuit switching can be useful to the current Internet, and where it just adds complexity, without providing much benefit
Finally I will be talking about my current research, a TCP Switch for the core of the Internet

3. How We Think the Internet Is

4. How the Internet Really Is
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How the Internet Really Is
$41Bn
$12Bn
Market Size in 2003: Data from RHK
Market Size in 2003 (Data from RHK)
IP routers
SONET/SDH

5. What Dictates Internet’s Performance
Processing power
Link speed

6. Fast Links, Slow Routers
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Fast Links, Slow Routers
Processing Power
Link Speed (Fiber)
SPEC95Int: doubles every 2 ¼ years
FO: doubles every 2 years
DWDM: triples every year, i.e. Doubles every 7 months
Need to optimize router processing not bandwidth efficiency
Optical technology requires:
No buffering
Slow switching
Little logic
Source: SPEC95Int; Prof. Miller, Stanford Univ., 2000

7. Fast Links, Slow Routers
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Fast Links, Slow Routers
Processing Power
Link Speed (Fiber)
2x / 2 years
2x / 7 months
SPEC95Int: doubles every 2 ¼ years
FO: doubles every 2 years
DWDM: triples every year, i.e. Doubles every 7 months
Need to optimize router processing not bandwidth efficiency
Optical technology requires:
No buffering
Slow switching
Little logic
Source: SPEC95Int; Prof. Miller, Stanford Univ., 2000

8. Can We Build All Optical Routers?
Packet switches require buffering
We cannot buffer light
We need other techniques

9. Why was Internet Packet-Switched in the First Place?
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Why was Internet Packet-Switched in the First Place?
Gallager:
“Circuit switching is rarely used for data networks, ... because of very inefficient use of the links”
Tanenbaum:
”For high reliability, ... [the Internet] was to be a datagram subnet, so if some lines and [routers] were destroyed, messages could be ... rerouted”
Breaking message into packets allows parallel transmission across all links, reducing network latency.
In summary the benefits that of packet switched networks can be summarized as follows:
They use the bandwidth efficiently, meaning that a trunk link uses less resources than the sum of its tributaries, as they multiplex and conserve bandwidth
They have little state in the intermediate nodes
They are robust, some claim that they were designed to withstand a nuclear attack
They do not have a central authority from whom we need permission to run experiments

10. Statistical Multiplexing
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Statistical Multiplexing A B C A 2x
1.7x
A+B B
Statistical multiplexing
Important if traffic is bursty
Less expensive
Contention requires buffering
Variable delay => no QoS guarantees

11. How Was Internet Used in the 70s and 80s?
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How Was Internet Used in the 70s and 80s?
Applics: , news, ftp, telnet
Peer-to-peer network
Long lasting and bursty flows (telnet, large ftp’s)
Interactive applications (telnet) could consume pkts as they arrived
Many things have changed since then
Bursty flows=> statistical multiplexing is good

12. How Is It Different Today?
Client-server population
Traffic dominated by short http flows
Average: 5 s, 10 pkts
TCP flows
Connection setup: dominated by RTT
Burst of data: dominated by data rate
Nature of user expectations has changed
telnet: each pkt was useful
Web: only useful when all pkts have arrived

13. How the Internet Was Used Then
Host A R1 R2 R3
Host B

14. How the Internet Is Used Today
Tresponse
Client A R1 R2 R3
Server B

15. How Current Internet Works
Servers
Internet
Clients

16. Paradox: 99% of Circuits Finish Earlier
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An Example
1 server
100 clients
1 Mbps
File = 1Mbit
Paradox: 99% of Circuits Finish Earlier
99% of all clients using a circuit get a better performance than the ones using packets
Shortest Job First obtains the minimum delay, and this is what this example is showing (packet switching is doing processor sharing)
Circuit sw
Packet sw
Bandwidth
1 Mbps
10 Kbps
Average latency
50 sec
100 sec
Worst case latency
100 sec

17. Myths about BW Efficiency
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Myths about BW Efficiency
Most networks lightly utilized on average
Backbone links: 10-15%
Private lines: 3-5%
Ethernet links: extremely low
Links are not congested
BW efficiency not needed
In the core ½ BW devoted to redundancy
This link utilization data from work by Andrew Odlyzko and Kerry Coffman at AT&T Research. ” Data networks are lightly utilized, and will stay that way,” A. M. Odlyzko. And “ The size and growth rate of the Internet,” K. G. Coffman and A. M. Odlyzko,
Andrew Odlyzko and Kerry Coffman from AT&T Research did several studies of the Internet traffic and capacity growth, and they observed that the link utilization average over days ranges between 10 to 15% for backbone links, to 3 to 5 % for private lines, and the almost negligible use of the Ethernet links. Most of us are not continuously sending and receiving data, even when we are sitting in front of a computer
If we compare it to the 30% of average utilization of voice lines, we see that links in the Internet are lightly utilized, so in fact there is not that much statistical multiplexing going on in the Internet
Growth in traffic limited by source (storage and modems), not by network capacity.
Most data processed locally
In private lines, network designers want rapid response during peak times (
Average is average over a full week
Reasons for low usage:
Data lines are symmetric, traffic is not
Data traffic is burstier, and gets less statistical multiplexing
Data traffic growth is less predictable than voice
Lumpy network capacity and sub linear price
Source: A. Odlyzko and K. Coffman, AT&T Research

18. Myths about Robustness
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Myths about Robustness
Link/router failure is rare
0.5% reroute prob. of TCP flow
Rerouting circuits is not hard (if there aren’t too many!)
50 ms reroute delay for SONET
vs. over 30 s for OSPF and BGP
Current products can reroute 1,000’s of STS-1 circuits
Robustness can also be achieved with circuits

19. If we were to start again with what we know today, could we use circuit switching?

20. This Is Where We Are IP routers SONET/SDH 6/26/2018 1:16 AM
Market Size in 2003 (Data from RHK)
IP routers
SONET/SDH

21. Where We Can Go From Here
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Where We Can Go From Here PS CS
Big routers replace circuit switches
MPLS replaces circuit switches
Circuit and packet switching
coexist, as today
We are are a point of transition
Pure CS:
TCP connection is a circuit,
Very short lived ccts
TCP becomes the center of the hourglass (cornerstone)
Like a telephone network, where one has several lines and one can have several conversations in parallel
MP[lambda]S replaces TDM circuit switches
Pure circuit switched Internet,

22. All Packet Switched Network Is Unlikely
Decision making frequency
(for OC-192)
Complexity
Packet
switching
Per-packet
(32 ns)
# pkts (~10,000)
[#conn (~100,000)]
Circuit
Per-connection
(50 μs)
# connections
(~100,000)

23. All Circuit Switched Network Is Unlikely
Hard to change all end hosts
Hard to change mentality of OS and application developers
Too much investment in packet switched LANs

24. Circuits Make Sense in the Core
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Circuits Make Sense in the Core
Where:
electronics cannot keep up with link speeds
performance is more important than price
Broad Picture Is Unlikely to Change
However, provisioning of circuits is primitive
Let’s see how we could change the circuit switches
Both extremes look unlikely

25. What Other People Are Proposing
Burst switching
Mega packets or mini circuits with explicit tear-down
Automatic monitoring of traffic
Queues, utilization, …
Both cases need new provisioning protocol

26. We Want to Propose a Different Approach
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We Want to Propose a Different Approach
Expose circuits to IP
Optimize for the common case
TCP (90-95% of traffic)
Data (9 out of every 10 pkts)
TCPSwitch
90-95% of all traffic is TCP
How do they interoperate with existing IP routers?
What signal and circuit setup mechanisms need to be used for the circuit switches
Not the same fate as IPv6
Replace SS7 and other proprietary SONET control protocols

27. TCPSwitch Objectives Architecture QoS Results Simulation
Implementation

28. Objectives of TCPSwitch
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Objectives of TCPSwitch
Ability to interoperate with:
Normal IP routers
Unmodified end-hosts
Optics and off-the-shelf switches
QoS and best-effort
Not the same fate as IPv6
Reduce blocking probability

29. TCPSwitch Exposes Circuit Switching to IP
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TCPSwitch Exposes Circuit Switching to IP
What we change from today’s picture
Granularity of the circuit: TCP flow
Replace SONET control protocol
Access Network:
Ethernet, packet-switched
Best-effort only
Like the taxi coming from the airport
Outer backbone:
TCP Switches
Best-effort and reserved traffic
Like checking-in and boarding the plane
Inner backbone:
Lambda- and SONET switches
Reserved traffic only, circuit switched
Like the airplane itself
IP routers
TCPSwitches

30. TCP “Creates” a Connection
Router
Destina-tion
Source
SYN
SYN+ACK
DATA
Permanent Circuits
Packets

31. Let TCP Leave State Behind
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Let TCP Leave State Behind
Ingress TCP-SW
Core TCP-SW
Egress TCP-SW
Destina-tion
Source
SYN
SYN+ACK
DATA
ACCEPTED
Circuits
Packets
Connection establishment using TCP SYN
Admission control
No buffering in the core

32. Complexity of Switches
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Complexity of Switches
Ingress:
Like a packet-sw’ed router
Admission control
Outgoing port creates circuits
Core:
Regular TDM/Optical switch
Egress:
Like core, but with packet reassembly
Ingress has all the buffering

33. Design Issues Layer-4 lookup Path rerouting Exact match
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Design Issues
Layer-4 lookup
Exact match
Path rerouting
SYN-packet not seen
Hard state vs. soft state
Soft state, because less than 0.5% of cases there is a reroute (little leakage)
Admission control based on (priority, BW) pair given by an oracle (SLA database or TCP options)
Circuit establishment via out-of-band circuit (less processing when idle, because there is no polling of idle channels). However this limits the circuit establishment rate

34. Design Issues (2) Admission control Circuit establishment/tear-down
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Design Issues (2)
Admission control
Priority+BW request
blocking prob. vs dropping prob.
Circuit establishment/tear-down
In-band vs out-of-band
Minimum granularity
Soft state, because less than 0.5% of cases there is a reroute (little leakage)
Admission control based on (priority, BW) pair given by an oracle (SLA database or TCP options)
Circuit establishment via out-of-band circuit (less processing when idle, because there is no polling of idle channels). However this limits the circuit establishment rate

35. Simplifies QoS In PS: In CS:
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Simplifies QoS
In PS:
Very complex schemes for isolation, jitter and reserved BW
In CS:
dedicated BW
Jitter and isolation fall naturally
Can mix premium customers (QoS) as well as best-effort in a single network
QoS:
Result of BW reservation
Easy to explain to customers (nice SLA)
Admission control is easier problem than QoS with packets (done on a per-connection basis rather than a per-packet basis)

36. Simulation Results In ns-2 Paradox verified using TCP and http traffic
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Simulation Results
In ns-2
Paradox verified using TCP and http traffic
Avg response: 50% and 90% improvement, for some blocking prob (0%-3%)
Some TCP inefficiencies noticeable with very short flows
Work in progress
Avg delay smaller, the bigger the BW reservation
Connection establishment will retry for 3min (that is what RFC says)
However Microsoft waits for only 45 sec.
TCP inefficiencies are noticeable for short flows
But what we want is low response time
Can have starvation if client is rejected immediately

37. Implementation Results
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Implementation Results
Ingress TCPSwitch
Linux 2.4 router using netfilter (iptables) and iproute2
Module in user space for proof of concept
Big penalty for crossing kernel-user boundary
Data switching: similar performance as a router with a classifier (e.g. policer)
Now being ported into kernel
Penalty of the order of 3-4 ms for the connection setup
Penalty of the order of 60 us for the data forwarding (we are doing some classification now)

38. Conclusion Circuit switching is already there
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Conclusion
Circuit switching is already there
CS makes sense in the core:
Electronics can keep up with link speed
Use of Internet fits well with CS
TCPSwitch
Exposes circuits to IP
Optimized for TCP and data
CS unlikely to go away
TCPSwitch: a circuit-aware core with fine circuit granularity
Core, where performance is more important than cost
Cost amortized over many users, or connections
Lower complexity at the edges, more complexity in the core
Can use optical switches
Provides QoS at the cost of BW inefficiencies
TCPSwitch , a circuit-aware core