Internet RealTime Laboratory Wing Ho Andy Yuen Columbia University

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Internet Real-Time LaboratoryWing Ho (Andy)
YuenColumbia University

• IRT Internet Real-Time Lab
• Affiliated with the Computer Science Department
  at Columbia University
• conducts research in the areas of Internet and
  multimedia services Internet telephony, wireless
  and mobile networks, streaming, quality of
  service, resource reservation, dynamic pricing
  for the Internet, network measurement and
  reliability, service location, network security,
  media on demand, content distribution networks,
  multicast networks and ubiquitous and
  context-aware computing and communication.
• Project Title
• Performance Evaluation of Time-based and
  Hop-based TTL Schemes in 7DS Systems

• Qualitative Comparison of TB and HB
• For ?gtgt?, EM?bmax, Hop-based scheme has storage
  cost and storage-time cost independent of node
  encounter rate Variance of storage cost is
  negligible
• Both mean and variance of storage cost and
  storage-time cost of time-based scheme is
  exponential in TTL a priori knowledge of node
  encounter rate and AP encounter rate is needed to
  compute minimal TTL that guarantees Pd1

What is 7DS? 7DS is a peer-to-peer data sharing
network that exploits node mobility for data
dissemination. Any two nodes communicate when
they are in proximity. Under this transmission
constraint, any pair of nodes is intermittently
connected as mobility shuffles node locations.
Three Categories of Applications Upload Mobile
nodes anycast data to an AP e.g.
email delivery P2P Data dissemination between
mobile nodes e.g. mp3 file exchanges
among iPod users Download Content distribution
of popular data e.g. movie and news
video clip download

• Simulation Study
• Analysis compares TB and HB without feedback
• Simulations compare TB and HB with and without
  feedback
• Three scenarios ?1/1000,1/2000 and 1/5000 per
  sec, (17, 33 and 83 minutes to AP on average)
• Node encounter rate ? 1/20 (20 sec per
  encounter)
• For each scenario, select TB and HB schemes that
  has packet delivery ratio Pd1 then consider
  schemes with minimum hmax for each bmax
• Scenario I (hmax,bmax)(2,6),(3,4),(4,3),(7,2)
  yields Pd1 and consumes least overhead

• Email Delivery Application
• A node generates an email message to be delivered
  to an AP. Random delay ranges from hours to days
• Message delay of email delivery can be
  drastically reduced through packet replication
  at node encounters
• Trade off message delay with resource consumption
  (storage cost and energy cost)
• Duplicated packet should be purged periodically
  to prevent buffer overflow
• Packet Purge Mechanisms
• Time-based (TB) A message is purged when the TTL
  field expires
• Hop-based (HB) Each message is appended with
  duple (b,h) to limit the breadth and depth of
  data dissemination tree
• Feedback (FB) When email message is delivered to
  the network, 7DS may provide explicit feedback
  message to purge packets at all nodes
• Four schemes TB, HB, TB-FB, HB-FB

• Performance Metrics
• Storage cost/ Energy cost (CTB and CHB) Each
  packet replication incurs one unit of
  transmission cost at Tx node and one unit of
  storage cost at Rx node
• Storage-time cost (STB and SHB) sum of packet
  storage time over all nodes. Packet storage time
  of node j is given by ?jte-ta , where ta is the
  time when node j receives the packet and te is
  the time node j purge the packet

• Quantitative Comparison of TB and HB
• With no feedback, mean and variance of storage
  cost and storage-time cost of TB scheme is much
  larger than HB schemes
• With feedback, mean and variance of storage cost
  and storage-time cost of TB scheme is on par with
  HB schemes
• Among all HB schemes, two hop scheme often yields
  the least storage and storage-time costs
• In practice, we can select smallest bmax such
  that HB(bmax,2) yields Pd1
• Conclusion
• Although 7DS does not offer delay guarantee for
  packet delivery, reliable and expedite data
  delivery is still possible, at a moderate
  resource overhead
• All schemes under consideration have Pd1. Packet
  delivery time is at the order of 100sec for all
  schemes in scenario I. Storage cost 50 packets
  without feedback, 18 packets with feedback

Time Based Xn1XnYn-Rn
EXn1(1-??)n1
VarXn(1?)n-1((1?)n-1) For
??0 ECTB(1?)TTL ESTB((1?)TTL1-1)/? VarCT
B(1?)TTL-1((1?)TTL-1) VarSTB((1?)2TTL1-(1
?)TTL?(2TTL1)-1)/?2
Assumptions Single email message upload Discrete
time model Poisson node encounter and AP
encounter Number of nodes gtgt number of duplicated
packets Notations Xn number of duplicated packets
at time n Yn number of offspring nodes receiving
a packet copy at time n Zj,n number of offspring
of node j at time n Rn number of nodes that
arrives at an AP at time n
Hop-Based For ?0 ECHB(bmaxhmax-1)(bmax-1) Var
CHB0 ESHB(bmaxhmax-1)(bmax-1)
bmax/? VarSHB(bmaxhmax-1)(bmax-1) bmax/?2 For
?gt0 ECHB(EMhmax1-1)(EM-1)
For More detailed information about this project
please contact andyyuen_at_cs.columbia.edu.