TCP Switching: Exposing Circuits to IP

TCP Switching: Exposing Circuits to IP Pablo Molinero-Fernández Nick McKeown Stanford University

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

How the Internet Looks Like Today

How the Internet Really Looks Like Today SONET/SDH DWDM

How the Internet Really Looks Like Today Modems, DSL

PS is bandwidthefficient PS networks are robust Why Is the 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”

PS is bandwidthefficient PS networks are robust Are These Assumptions Valid Today? 10-15% average link utilization in the backbone [Odlyzko] SONET required to reroute in 50 ms vs. over 1 min for IP [Lavobitz]

Internet’s Performance Trends Processing power Link capacity

Fast Links, Slow Routers Processing Power Link Capacity (Fiber) Source: SPEC95Int; Prof. Miller, Stanford Univ.

Fast Links, Slow Routers Processing Power Link Speed (Fiber) 2x / 2 years 2x / 7 months Source: SPEC95Int; Prof. Miller, Stanford Univ.

Fewer Instructions Instructions per packet since 1996

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

Circuit sw Packet sw 99% of Circuits Finish Earlier Flow BW 1 Gb/s 10 Mb/s Avg latency 0.505 s 1 s Worst latency 1 s 1 s What Is the Performance of Circuit Switching? File = 10Mbit 100 clients 1 server 1 Gb/s x 100

Circuit sw Packet sw A big file can kill CS if it blocks the link Flow BW 1 Gb/s 10Mb/s+1Gb/s Avg latency 10.495 s 1.099 sec Worst latency 10.990 s 10.990 sec What Is the Performance of Circuit Switching? File = 10Gbit/10Mbit 100 clients 1 server 1 Gb/s x 99

No difference between CS and PS in core Circuit sw Packet sw Flow BW 1 Mb/s 1 Mb/s Avg latency 109.9s 109.9sec Worst latency 10,000 s 10,000 sec What Is the Performance of Circuit Switching? File = 10Gbit/10Mbit 100 clients 1 server 1 Gb/s x 99 1 Mb/s

Outline Why might circuit switching be a good idea in the Internet? How might circuit switching be introduced into the Internet?

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

TCP Switching Exposes Circuits to IP IP routers TCP Switches

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

Source Boundary TCP-SW Core TCP-SW Boundary TCP-SW Destina-tion SYN ACCEPTED SYN+ACK ACCEPTED DATA Packets One Circuit Packets Let TCP Leave State Behind

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.

Software Implementation Results TCP Switching boundary router: • Kernel module in Linux 2.4 1GHz PC • Forwarding latency • Forward one packet: 21ms. • Compare to: 17ms for IP. • Compare to: 95ms for IP + QoS. • Time to create new circuit: 57ms.

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

TCP Switching: Exposing Circuits to IP