Wide Area Network Emulation on the Millennium

1
Wide Area Network Emulation on the Millennium

• Bhaskaran Raman
• Yan Chen
• Weidong Cui
• Randy Katz
• bhaskar, yanchen, wdc, randy_at_cs.berkeley.edu

2
Why WAN Emulation Testbed

• Realistic, controlled and reproducible WAN
  experiments needed to drive design and test for
• SAHARA next-generation telecommunication service
  infrastructure
• Content Distribution Network (CDN)
• Dynamic Service Composition (constrained routing)
• Routing and content-based routing
• Traffic Engineering and QoS
• Network Measurement and Monitoring Services
• Emulate the critical end-to-end performance
  characteristics
• By various WAN situations (e.g. congestion, loss)
• By various underlying subnetwork technologies
  (e.g. xDSL, cable modem)

3
Why WANE Overlay Network Issues

• Study issues of
• Routing algorithms recovery from failures,
  stability, scaling
• Overlay node placement in physical network
• Service placement in overlay network

4
Simulation vs. Emulation vs. Live Testing

• Simulation
• Very slow
• Bad fidelity to real network
• Implementation in simulator is different from
  actual application
• Emulation
• Fast and good scalability
• Can run actual application
• Can interact with a live environment
• Opportunity Millennium cluster (100s of nodes)
• Live Testing
• Wide-area implementation not always possible
• Too few nodes may be available
• Not reproducible

5
Testbed Requirements

• Fast and minimal overhead
• Close to real network environment
• Scalable
• O(1000) nodes
• Configurable
• Network topology, latency, bandwidth, loss-rates,
  queuing policies
• Flexible
• Testbed should be independent of applications
• Reliable
• Integration with Millennium testbed
• Should not affect other millennium users

6
Emulator Option 1 Kernel-based

• Implemented as kernel module extension to
  operating systems
• Pros
• Small simulation
• overhead more
• realistic network
• performance
• Software packages
• available
• Cons
• Hard to modify and debug
• Hard to deploy on
• millennium platform

User program
User program
User-level
User-level
Kernel
Kernel
Emulator
Emulator
IP Stack
IP Stack
Machine 2
Machine 1
7
Existing Kernel-level Emulators

• NISTNet by National Institute of Standards
  Technology
• On Linux, source code available
• X-window based interactive GUI
• allows the user to select and monitor specific
  traffic streams
• Emulate numerous complex performance scenarios
• tunable packet delay distributions
• congestion and background loss
• bandwidth limitation
• packet reordering / duplication
• Real traces driven allowed
• Extensible for user defined packet handlers
• Dummynet by Luigi Rizzo of Univ. of Pisa, Italy
• On FreeBSD, source code available
• Emulate queue and bandwidth limitations, delays,
  packet losses, and multipath effects

8
Emulator Option 2 User-Level
Configure WAN parameters here
User program
User program
User-level daemon
User-level daemon
User-level library
User-level library
User-level
User-level
pppd pty/tty
pppd pty/tty
Kernel
Kernel
TCP/IP stack
TCP/IP stack
PPP/UDP
Machine 1
Machine 2
9
Emulator Option 2 User-Level

• Advantages
• Flexibility
• Configuration environment can be built as
  required
• Multiple virtual nodes per physical node?
• Disadvantages
• Has to be written from scratch
• Unpredictable latency
• Due to scheduling jitter O(10ms)
• Could lead to considerable slow-down in emulation

10
Proposed Plan

• Study NISTNet
• Run experiments on crash box computers
• Test the performance and reliability
• Learn more features and requirements of the
  Millennium testbed
• Design and implement WAN emulator