PeertoPeer Based Multimedia Distribution Service

1
Peer-to-Peer Based Multimedia Distribution
Service

• Zhe Xiang, Qian Zhang, Wenwu Zhu, Zhensheng
  ZhangIEEE Transactions on Multimedia, Vol. 6,
  No. 2, April 2004
• Presented by Ho Tsz Kin14/04/2004

2
Agenda

• Introduction
• Architecture
• Topology-ware Overlay
• Replication Strategies
• Intergroup Replication
• Intragroup Replication
• Performance Evaluation
• Conclusion

3
Multimedia distribution services

• Centralized multimedia distribution
• Mirroring, Proxy caching
• Bottleneck bandwidth problem
• Measurement between University of Washington and
  a set of 13,656 servers
• Over 90 is less than 10 Mbps
• Not scalable
• Content distribution network (CDN)
• Deploys a large number of servers at the edge of
  the network
• Objective is to efficiently redirect user
  requests to appropriate servers so that request
  latency is reduced and load among servers are
  balanced

4
Multimedia distribution services

• Capacity of the edge server is not large enough
  to support multimedia service
• Where and when to place those edge servers is a
  difficult problem
• Peer-to-peer network
• Some rely on servers to disseminate information
• Single point of failure
• Overlay network in a P2P system is not aware of
  the underlying topology
• Availability depend on peers reliability
• Cannot provide good QoS-provision
• Propose a novel framework based on P2P network

5
Architecture
Client join the P2P network, and contribute
resources
Determine how many replicas and how they place
Determine grouping among peers
6
Topology-aware Overlay

• Routing overhead is a key performance metric
• If randomly constructed, overlay network may
  actually be far away in the underlying network
• Nearby peers in the underlying network are
  clustered into groups
• A group consists of a set of nodes that are close
  to each other
• Close means if the distance is less than some
  predefined value
• Distance can be network latency, or round trip
  time

7
Topology-aware Overlay

• Two different groups are communicating with each
  other through the shortest distance
• Predefined distance threshold
• Given a certain transmission delay requirement

8
Content delivery

• When a request to obtain certain content is
  issued
• Found within the same group
• Content can be directly distributed to the
  requesting peer
• Peer may decide to replicate according to the
  replication strategies
• Not found, flooding search is carried out
• A shortest communication path is setup between
  two groups
• The content in source will first be sent to some
  host in target group, that host in target group
  will send the content to requester

9
Replication Strategies

• Global level replication decision
• relies on complete information about the network
  such as distances between groups or between
  peers, storage capacity of each group, and each
  peer
• such global information is difficult to obtain in
  a distributed environment
• Divide the problem into two sub-problems
• Intergroup and Intragroup replication

10
Intergroup Replication

• Provide low latency and QoS-aware service within
  group level
• Seed
• Group-level replica
• Number of seeds number of groups holding this
• Seed capacity is the total capacity of a group to
  store different seed
• Minimize
• the average distance between requesting group and
  the group providing content
• Subject to
• the constraint of each groups seed capacity

11
Intergroup Replication

• Variation of K-center problem
• NP-Complete
• Ignore seed capacity of each group, and only
  consider the totally seed capacity
• Idea of heuristic

Seed of each content ci should be uniformly
distributed over the network, let number be
L
Average distance
L
2D Euclidean space
12
Intergroup Replication

• Average access distance

• Modified problem, with S is total capacity,
  popularity of content ci is ri

Weighted average minimum distance
Storage capacity constraints

• Applying Lagrange Function

13
Intergroup Replication

• Substitute back to find the average distance

Estimated using local information

• Proposed heuristic
• If distance between the requestor and the peer
  who has a replica is larger than , then
  replicate

14
Intragroup Replication

• Improving the availability of the content
• Replica is copies of the content within the group

• Replica replication matrix

• Availability of content ci

N peers
Reliability of pj
15
Intragroup Replication

• Optimization problem
• Variation of the knapsack problem
• NP-complete

size of content ci
storage capacity of peer pj
16
Intragroup Replication

• Proposed heuristic
• Climb-hill based algorithm
• Adding a new replica for content cr will improve
  its availability
• Deleting the stored contents cj also decreases
  its availability
• A(cr) availability of content cr
• A(ci)availability of content ci if we delete
  this content
• If A(ci) gt A(cr)
• Deleting ci does not conflict with the objective

17
Performance Evaluation

• Network topology
• Euclidean space model
• Nodes are randomly located
• Edge longitudes are fixed as 3000 ms
• 200 groups are generated
• Latency within group are very small
• Packet loss model mainly due to the congestion
  occurred at routers
• Number of hops between two peers increases
  linearly to the distance between two peers
• Largest hop is ten
• Bandwidth of link range from 800 Kbps to 1.4
  Mbps, and average is about 1.2 Mbps

18
Performance Evaluation

• Content distribution
• 10,000 MPEG-4 format video clips encoded in 1.28
  Mbps
• Length follows a normal distribution in range of
  3 min to 5 min, correspondingly to 37.8 MB to 48
  MB in files sizes
• Request distribution
• Zipf distribution
• Truncated Geometric Distribution (TGD)
• Truncated Pareto Distribution (TPD)

19
Performance Evaluation

• Peer Storage capacity and reliability
• Storage contributed by a peer follows a normal
  distribution in the range of 300 MB and 2 GB,
  which approximately supports 8 to 50 video clips
• Peer reliability of sustaining service follows
  normal distribution in the range of 0.1 to 0.9
• Comparison
• Freenet
• Always makes a replica for each requested content
• LRU replacement policy
• Random replication system
• Contents are uniformly distributed into peers
  storage

20
Performance Evaluation

• Performance metrics
• Average latency
• Average access distance between the requestor
  peer and the content provider peer
• Video quality
• Perceived video quality by the client
• PSNR
• Weighted availability
• Represents the service availability provided by
  contents in a certain area (within distance d)
• Defined as

21
Performance Evaluation

• Average latency
• Varying number of content from 8000 to 12500
• Varying skew factor with 10000 content

22
Performance Evaluation

• Video quality
• Varying peer storage
• Varying average packet loss ratio of network
  links with peer storage capacity as 960 MB

23
Performance Evaluation

• Availability
• Varying distance d

24
Conclusion

• Propose and analyze
• A topology-aware overlay
• Replication strategies
• Intergroup replication
• Intragroup replication
• Comments
• Assume equal sizes in intergroup replication, but
  different sizes in intragroup replication
• Topology-aware techniques can also be applied to
  clustering in SLVoD
• How to formulate and resolve stripping strategies