Where Does Circuit Switching Make Sense In the Internet? Pablo Molinero-Fernndez High Performance Networking Group Stanford University Outline Motivation Packet switching Description and myths Circuit switching Where it can be useful Research: TCPSwitch

Goals, architecture and QoS Conclusion How We Think the Internet Is How the Internet Really Is $41Bn $12Bn IP routers SONET/SDH

Market Size in 2003: Data from RHK What Dictates Internets Performance Processing power Link speed Fast Links, Slow Routers Processing Power Link Speed (Fiber) 1000

1000 100 100 10 10 1 1 1985 0,1

1990 1995 2000 1985 1990 1995 2000 0,1

Source: SPEC95Int; Prof. Miller, Stanford Univ., 2000 Fiber Capacity (Gbit/s) 10000 Spec95Int CPU results 10000 Fast Links, Slow Routers Processing Power Link Speed (Fiber) 1000

1000 2x / 2 years 2x / 7 months 100 100 10 10 1

1 1985 1990 1995 2000 1985 1990 1995

2000 0,1 0,1 Fiber optics DWDM Source: SPEC95Int; Prof. Miller, Stanford Univ., 2000 Fiber Capacity (Gbit/s) 10000

Spec95Int CPU results 10000 Can We Build All Optical Routers? Packet switches require buffering We cannot buffer light We need other techniques Why was Internet PacketSwitched 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 Statistical Multiplexing A

C A B A+B B 2x 1.7x How Was Internet Used in the 70s and 80s? Applics: email, news, ftp, telnet Peer-to-peer network

Long lasting and bursty flows (telnet, large ftps) Interactive applications (telnet) could consume pkts as they arrived Many things have changed since then 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 How the Internet Was Used Then T0 Host A R1 R2 R3

Host B T1 How the Internet Is Used Today Tresponse Client A R1 R2 R3 Server B

How Current Internet Works Servers Internet Clients An Example 100 clients 1 server 1 Mbps File = 1Mbit

Circuit sw Packet sw Bandwidth Average latency Worst case latency 1 50Mbps sec 100 sec 10 100Kbps sec 100 sec

Paradox: 99% of Circuits Finish Earlier Myths about BW Efficiency Most networks lightly utilized on average Backbone links: 10-15% Private lines: 3-5% Ethernet links: extremely low BW

efficiency not needed Links are not congested Source: A. Odlyzko and K. Coffman, AT&T Research Myths about Robustness Link/router failure is rare 0.5% reroute prob. of TCP flow Rerouting circuits is not hard (if there arent too many!) 50 ms reroute delay for SONET vs. over 30 s for OSPF and BGP Current products can reroute 1,000s of STS-1 circuits

Robustness can also be achieved with circuits If we were to start again with what we know today, could we use circuit switching? This Is Where We Are IP routers

SONET/SDH Where We Can Go From Here Big routers replace circuit switches PS MPLS replaces circuit switches Circuit and packet switching coexist, as today CS MP[lambda]S replaces TDM circuit switches Pure circuit switched Internet,

All Packet Switched Network Is Unlikely Decision making frequency (for OC-192) Complexity (for OC-192) Packet switchin g Per-packet (32 ns)

# pkts (~10,000) Circuit switchin g Per-connection (50 s)s) # connections (~100,000) [#conn (~100,000)] 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 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 Lets see how we could change the circuit switches 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 We Want to Propose a Different Approach TCPSwitch Expose circuits to IP Optimize for the common case TCP (90-95% of traffic)

Data (9 out of every 10 pkts) TCPSwitch Objectives Architecture QoS Results Simulation Implementation Objectives of TCPSwitch Ability to interoperate with: Normal IP routers Unmodified end-hosts

Optics and off-the-shelf switches QoS and best-effort TCPSwitch Exposes Circuit Switching to IP IP routers TCPSwitches Source TCP Creates a Connection Router

Router Router Destina -tion SYN SYN+ACK DATA Packets

Permanent Circuits Packets Source Let TCP Leave State Behind Ingress TCP-SW Core TCP-SW Egress


Packets Complexity of Switches Ingress: Like a packet-swed router Admission control Outgoing port creates circuits Core: Regular TDM/Optical switch Egress: Like core, but with packet reassembly Design Issues

Layer-4 lookup Exact match Path rerouting SYN-packet not seen Hard state vs. soft state 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

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 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 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 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

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