stanford university august 22, 2001 tcp switching: exposing circuits to ip pablo molinero-fernández...
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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
Stanford UniversityAugust 22, 2001
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