Stanford University August 22, 2001 TCP Switching: Exposing Circuits to IP Pablo Molinero-Fernández...

Stanford UniversityAugust 22, 2001

TCP Switching: Exposing Circuits to IP

Pablo Molinero-FernándezNick McKeown

Stanford University

Stanford UniversityAugust 22, 2001

Outline

Why might circuit switching be a good idea in the Internet?

How might circuit switching be integrated in the Internet?

Stanford UniversityAugust 22, 2001

How the Internet Looks Like Today

Stanford UniversityAugust 22, 2001

How the Internet Really Looks Like Today

SONET/SDHDWDM

Stanford UniversityAugust 22, 2001

How the Internet Really Looks Like Today

Modems, DSL

Stanford UniversityAugust 22, 2001

Why Is the Internet Packet Switched in the First Place?

• PS is bandwidth efficient

• PS networks are robust

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”

Stanford UniversityAugust 22, 2001

Are These Assumptions Valid Today?

• PS is bandwidth efficient

• PS networks are robust

SONET required to reroute in 50 ms vs. over 1 min for IP [Lavobitz]

10-15% average link utilization in the backbone [Odlyzko]

Stanford UniversityAugust 22, 2001

Internet’s Performance Trends

Link capacity

Processing power

Stanford UniversityAugust 22, 2001

Fast Links, Slow Routers

0,1

1

10

100

1000

10000

1985 1990 1995 2000

Fib

er

Ca

pa

city

(G

bit

/s)

Processing Power Link Capacity (Fiber)

0,1

1

10

100

1000

10000

1985 1990 1995 2000

Spec

95In

t CPU

resu

lts

Source: SPEC95Int; Prof. Miller, Stanford Univ.

Stanford UniversityAugust 22, 2001

Fast Links, Slow Routers

0,1

1

10

100

1000

10000

1985 1990 1995 2000

Fib

er

Cap

acit

y (G

bit

/s)

Fiber optics DWDM0.1

1

10

100

1000

10000

1985 1990 1995 2000

Spe

c95I

nt C

PU

res

ults

Processing Power Link Speed (Fiber)

2x / 2 years 2x / 7 months

Source: SPEC95Int; Prof. Miller, Stanford Univ.

Stanford UniversityAugust 22, 2001

Fewer Instructions

1

10

100

1000

1996 1997 1998 1999 2000 2001

(log

scal

e)

Instructions per packet since 1996

Stanford UniversityAugust 22, 2001

How Can Circuit Switching Help the Internet?

• Simple data path:• No buffering• No per-packet processing• Possible all-optical data

path

• Peak allocation of BW• No delay jitter

Higher capacity switches

Simple but strict QoS

Stanford UniversityAugust 22, 2001

What Is the Performance of Circuit Switching?

Packet swCircuit sw 10 Mb/s1 Gb/sFlow BW

1 s0.505 sAvg latency

1 s1 sWorst latency

99% of Circuits Finish Earlier

1 server100 clients

1 Gb/s

File = 10Mbit

x 100

Stanford UniversityAugust 22, 2001

What Is the Performance of Circuit Switching?

10.990 sec10.990 sWorst latency

Packet swCircuit sw 10Mb/

s+1Gb/s1 Gb/sFlow BW

1.099 sec10.495 sAvg latency

A big file can kill CS if it

blocks the link

1 server100 clients

1 Gb/s

File = 10Gbit/10Mbit

x 99

Stanford UniversityAugust 22, 2001

What Is the Performance of Circuit Switching?

Packet swCircuit sw 1 Mb/s1 Mb/sFlow BW

10,000 sec10,000 s

Worst latency

109.9sec 109.9s

Avg latency

No difference between

CS and PS in core

1 server100 clients

1 Gb/s

x 991 Mb/s

File = 10Gbit/10Mbit

Stanford UniversityAugust 22, 2001

Outline

Why might circuit switching be a good idea in the Internet?

How might circuit switching be introduced into the Internet?

Stanford UniversityAugust 22, 2001

Our Proposed Architecture

• Create a separate circuit for each flow

• IP controls circuits• Optimize for the most

common case– TCP (90-95% of traffic)– Data (9 out of 10 pkts)

TCP Switching

Stanford UniversityAugust 22, 2001

TCP Switching Exposes Circuits to IP

TCP Switches

IP routers

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TCP “Creates” a Connection

Router Router Router Destina-tion

Source

SYN

SYN+ACK

DATA

Packets Packets

PacketsPackets

Stanford UniversityAugust 22, 2001

Let TCP Leave State Behind

Boundary TCP-SW

Core TCP-SW

Boundary TCP-

SW

Destina-tion

Source

SYN

SYN+ACK

DATA

ACCEPTED

One Circuit PacketsPackets

ACCEPTED

Stanford UniversityAugust 22, 2001

State Management Feasibility

• Amount of state– Minimum circuit = 64 kb/s.– 156,000 circuits for OC-192.

• Update rate– About 50,000 new entries per sec for

OC-192.• Readily implemented in hardware

or software.

Stanford UniversityAugust 22, 2001

Software Implementation Results

TCP Switching boundary router:• Kernel module in Linux 2.4 1GHz PC • Forwarding latency

– Forward one packet: 21s.– Compare to: 17s for IP. – Compare to: 95s for IP + QoS.

• Time to create new circuit: 57s.

Stanford UniversityAugust 22, 2001

Conclusion• PS seems unlikely to keep up with link

speeds in the backbone. • CS becomes attractive in core

– Higher capacity (optical) switches – Simple QoS– User response time comparable to PS

• TCP Switching – Integrates CS and PS– Exploits our connection oriented use of

Internet