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

August 22, 2001 Outline Why might circuit switching be a good idea in the Internet? How might circuit switching be integrated in the Internet?

Stanford University August 22, 2001 How the Internet Looks Like Today

Stanford University August 22, 2001 How the Internet Really Looks Like Today SONET/SDH DWDM

Stanford University August 22, 2001 How the Internet Really Looks Like Today Modems, DSL

Stanford University August 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 University August 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 University August 22, 2001 Internet’s Performance Trends Link capacity Processing power

Stanford University August 22, 2001 Fast Links, Slow Routers Processing PowerLink Capacity (Fiber) Source: SPEC95Int; Prof. Miller, Stanford Univ.

Stanford University August 22, 2001 Fast Links, Slow Routers Processing PowerLink Speed (Fiber) 2x / 2 years2x / 7 months Source: SPEC95Int; Prof. Miller, Stanford Univ.

Stanford University August 22, 2001 Fewer Instructions Instructions per packet since 1996

Stanford University August 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 University August 22, 2001 What Is the Performance of Circuit Switching? Packet swCircuit sw 10 Mb/s1 Gb/sFlow BW 1 s0.505 sAvg latency 1 s Worst latency 99% of Circuits Finish Earlier 1 server 100 clients 1 Gb/s File = 10Mbit x 100

Stanford University August 22, 2001 What Is the Performance of Circuit Switching? sec sWorst latency Packet swCircuit sw 10Mb/s+1Gb/s1 Gb/sFlow BW sec sAvg latency A big file can kill CS if it blocks the link 1 server 100 clients 1 Gb/s File = 10Gbit/10Mbit x 99

Stanford University August 22, 2001 What Is the Performance of Circuit Switching? Packet swCircuit sw 1 Mb/s Flow BW 10,000 sec10,000 sWorst latency 109.9sec 109.9sAvg latency No difference between CS and PS in core 1 server 100 clients 1 Gb/s x 99 1 Mb/s File = 10Gbit/10Mbit

Stanford University August 22, 2001 Outline Why might circuit switching be a good idea in the Internet? How might circuit switching be introduced into the Internet?

Stanford University August 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 University August 22, 2001 TCP Switching Exposes Circuits to IP TCP Switches IP routers

Stanford University August 22, 2001 TCP “Creates” a Connection Router Destina- tion Source SYN SYN+ACK DATA Packets

Stanford University August 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 CircuitPackets ACCEPTED

Stanford University August 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 University August 22, 2001 Software Implementation Results TCP Switching boundary router: Kernel module in Linux 2.4 1GHz PC Forwarding latency –Forward one packet: 21  s. –Compare to: 17  s for IP. –Compare to: 95  s for IP + QoS. Time to create new circuit: 57  s.

Stanford University August 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

Stanford University August 22, 2001 How the Internet Really Looks Like Today

Stanford University August 22, 2001 Design Issues in the Paper State Management Signaling Triggers for circuit establishment/release Integration with current Internet And many more...

Stanford University August 22, 2001 Simulation Results In ns-2, using TCP and HTTP traffic –CS Avg. response time comparable to that of PS in most cases –Sometimes slightly worse because of transmission times over thin circuits 1500 Bytes over a 64 Kb/s circuit takes 188 ms