1. Towards Efficient Simulation of Large Scale P2P Networks
Tobias Hoßfeld
ITG-Fachgruppe “Cooperating and Scalable Networks”
Aachen, Ericsson, J. Sachs,

2. Cartography of P2P Architectures
Two control functions in P2P systems
Resource mediation where are files located
Resource access control who may download a file and when
Mapping of P2P architectures into architectural space
pure P2P
hybrid P2P
classic client/server
Identification of control objectives
resource mediation
centralized
decentralized
operator-centric domain
user-oriented domain X
Chord
Pure P2P X
Gnutella
P2P Cartography
hybrid P2P X
eDonkey
Client/
Server X
BitTorrent
resource access control
centralized
decentralized

3. Peer-to-Peer Architectures
Unstructured P2P-Network (Gnutella)
Information
Provider
Seeker
Information
Seeker
Information
Provider
Information
Mediator
Structured P2P-Network (Chord)
Hybrid P2P-Network (eDonkey)
Index
Information
Mediator
BitTorrent
Tracker
Web-Server
Information
Mediator

4. Basic Functions of P2P Networks
join()
leave()
new node
knows one peer
peer informs its “neighbors” and bootstrap server
bootstrap server
contacts
bootstrap server
position in the P2P network according to the structure: self-organization
node failures detected by periodical updates or not answered requests: resilience

5. Basic Functions of P2P Networks (contd.)
insert(key,data)
retrieve(key)
peer x wants to insert (key,data); using DHTs: key = hash(data)
peer x searches for key
y has (key,data) x x
and asks its neighbors
which redirect requests
key routes to peer y which stores data y
y sends data to x
structure assigns responsibility for data based on hash function: load balancing
y responsible for (key,data)
performance improved by using shortcuts according to the known structure for a given key: scalability

6. Basic Function of P2P Content Distribution
Main feature is multiple source download.
Peers issue several download requests for the same file to multiple providing peers in parallel.
Providing peers serve the requesting peers simultaneously.
downloading peer 2
downloading and providing peer 1
After successfully downloading a whole chunk, it is provided to other peers.
providing peer
downloading peer 1
index server #2
index server #1
providing peer
providing peer

7. Features of P2P Systems and Their Implications
Usually a large number of participating peers
Large-scale: a lot of nodes and even higher number of resources need to be simulated
Peers may arbitrary join or leave
Highly dynamic: a lot of user created event (due to churn, i.e. peers joining and leaving arbitrarily, as key feature of P2P systems)
Cooperative working of peers and robust systems
Complexity:
one event can cause a large number of events at other peers, i.e. system events, due to cooperation among peers
additionally periodic or provisional systems event to cope with the self-organization of p2p systems
Target of Workshop:
Focus on large-scale P2P networks in order to consider key characteristics (e.g. regarding churn for 100 peers reasonable?)

8. Approach For Simulating Large-Scale P2P Systems
System state has to be stored at simulation machine
requires efficient data structures (e.g. calendar queue)
How to model in order to reduce the number of events?
Resource mediation might not require to model bandwidth, only signalling delay
Resource exchange might not require to model delay if large contents are exchanged; requires modelling of bandwidth
other performance influence factors: packet loss, moving users, …
appropriate abstractions & models for investigated application
Clustering of peers to user groups...
might allow parallel simulation of clusters

9. Workshop in Würzburg Efficient Data Structures
Andreas Binzenhöfer, Calendar Queue and Event Design Algorithms
Jens Oberender, Modelling Resource Fragmentation
Abstractions and Models
Kolja Eger, Packet-based Simulation
Gerald Kunzmann, Signaling in Voice/Video over IP Systems
Daniel Schlosser, Tobias Hoßfeld, Periodic and Market-Based Bandwidth Allocation
Parallel Simulation
Ivan Dedinski, Parallel Discrete Event Simulation

10. Talks Today
Hier könnte Ihr Name stehen !

11. Periodic and Market-Based Bandwidth Allocation in eDonkey Networks
Tobias Hoßfeld, Daniel Schlosser

12. Measurements of eDonkey Traffic
Case-by-case measurements of eDonkey file-sharing application in public GPRS/UMTS network
Multiple source download via GPRS

13. eDonkey Data Exchange via UMTS
UMTS upload restricts throughput
UMTS download restricts throughput
Max-min-fair share of available bandwidth is observed
How to model the bandwidth allocation of fair-share P2P file-sharing applications?

14. Simulation of Fair-Share Bandwidth Allocation
Events which influence the bandwidth allocation are that a peer…
starts the download of a file
finishs a download
goes offline while downloading
continues downloading a file after joining the network again
We consider eDonkey-like file-sharing networks
Aim: Modeling of bandwidth allocation in fair-share networks
Events t Dt Dt Dt Dt Dt Dt Dt Dt Dt Dt Dt
Computation of
allocated bandwidth t

15. Stream-based or packet-based approach?
TCP can be neglected if conditions are fulfilled (540 kB blocks)
Signaling vs. data exchange: RTT vs. bandwidth

16. What means fair-share? All peers get the same bandwidth
If a peer cannot consume completely the allocated bandwidth, the surplus is distributed among the remaining peers
Peer 3
11 kbps
Peer 2
3 kbps
11 kbps
3 kbps
uploading
Peer 1
40 kbps
Peer 4
20 kbps
Peer 5
40 kbps
13 kbps
13 kbps

17. Periodic Bandwidth Allocation
For each Dt, for each peer: compute bandwidth allocation
Peer 3
Peer 2
Allocated bandwidth can be overbooked or underbooked
Peer 1
Peer 4
Peer 5

18. Market-Based Bandwidth Allocation
For each event, consider affected, i.e. connected, peers
All affected peers make a bid
Strategy
If there are no other bids, propose x = not allocated bandwidth / #peers
If minimal bid y of all affected peers is smaller than x, then keep bid y and compute x‘
If all bids are larger than x, then bid x on these connections
Finish: If lower bid of a connection is the minimal bid of a peer and is repeated

19. Market-Based Bandwidth Allocation
Downloading
network links
Uploading
network links 20
NL3: 40kbps
3.333 15
NL4: 30kbps
NL0: 10kbps 10
NL1: 10kbps 5
NL5: 10kbps 5
NL2: 80kbps
NL6: 10kbps 20 10
NL7: 10kbps
Initial bid: x = BW / #peers 40
NL8: 40kbps

20. MBBA Example Downloading network links Uploading network links 20
NL3: 40kbps
3.333 15
3.333
NL4: 30kbps
NL0: 10kbps
26.667 10
NL1: 10kbps 5
NL5: 10kbps 5 25
3.333
NL2: 80kbps 5
NL6: 10kbps 25
6.667 25 20 10
NL7: 10kbps
If minimal bid y of all connected peers holds y<x, then set bid y and compute x‘ x = BW / #peers.
If all y<x, keep x. 40
NL8: 40kbps

21. MBBA Example Downloading network links Uploading network links 20
NL3: 40kbps
3.333
3.333
NL4: 30kbps
NL0: 10kbps
26.667 10
NL1: 10kbps 5
NL5: 10kbps 25
3.333
NL2: 80kbps 5
NL6: 10kbps 25
6.667 25 10
NL7: 10kbps
Finish: If lower bid of a connection is the minimal of a peer and is repeated 40
NL8: 40kbps

22. MBBA Example Downloading network links Uploading network links
NL3: 40kbps
3.333
NL4: 30kbps
NL0: 10kbps 5
26.667
NL1: 10kbps
NL5: 10kbps
24.444 5 25
NL2: 80kbps
6.667
NL6: 10kbps
6.667
24.444
24.444 10
NL7: 10kbps
Finish: If lower bid of a connection is the minimal of a peer and is repeated
Minimal bid y<x, set y and compute x‘ 40
NL8: 40kbps

23. MBBA Example Downloading network links Uploading network links
NL3: 40kbps
3.333
NL4: 30kbps
NL0: 10kbps 5
26.667
NL1: 10kbps
NL5: 10kbps
24.444
31.667
6.667
NL2: 80kbps
NL6: 10kbps 10
24.444
31.667
24.444 10
NL7: 10kbps
Finish: If lower bid of a connection is the minimal of a peer and is repeated
If all y<x, keep x. 40
NL8: 40kbps

24. MBBA Example Downloading network links Uploading network links
NL3: 40kbps
3.333
NL4: 30kbps
NL0: 10kbps 5
26.667
NL1: 10kbps
NL5: 10kbps
6.667
NL2: 80kbps
NL6: 10kbps
36.666
31.667 10
NL7: 10kbps
Finish: If lower bid of a connection is the minimal of a peer and is repeated 40
NL8: 40kbps

25. MBBA Example Downloading network links Uploading network links
NL3: 40kbps
3.333
NL4: 30kbps
NL0: 10kbps 5
26.667
NL1: 10kbps
NL5: 10kbps
6.667
NL2: 80kbps
NL6: 10kbps 10
NL7: 10kbps
36.666
NL8: 40kbps

26. Comparison PBA vs. MBBA
Exchange of small files

27. Comparison PBA vs. MBBA Exchange of large files
MBBA: computes and allocates immediately fair-share bandwidth -> in real systems this requires some time
PBA: bandwidth overbooked or underbooked for Δt -> in next step bandwidth is adapted

28. Conclusion
For P2P content distribution networks, like eDonkey, resource access control is crucial point
Fair-share bandwidth allocation has to be modeled
We have proposed two stream-based approaches which are valid in the considered scenarios
Periodic bandwidth allocation PBA
Market-based bandwidth allocation MBBA
Depending on the number of events influencing the resource access control PBA or MBBA has to be preferred