Title: P2P Live Streaming
1P2P Live Streaming
- Yang Gao, Nazanin Magharei, Reza Rejaie, "Mesh or
Multiple-Tree A Comparative Study of Live P2P
Streaming Approaches" INFOCOM 07 - Y Liu, Y Guo, "A survey on peer-to-peer video
streaming systems", Peer-to-peer Networking and
Applications, 2008. - S Ali, A Mathur, "Measurement of commercial
peer-to-peer live video streaming", Recent
Advances in Peer-to-Peer Streaming, 2006 .
Deepak Kumar Agarwal ( 71404423 ) Ajay Narayan (
60006864 ) Nishchint Raina ( 67569992 )
2Paper 1. Mesh or Multiple-Tree A Comparative
Study of Live P2P Streaming Approaches
- - Analyze tree based and mesh based overlays as
content delivery overlays - - Evaluates performance of their content delivery
mechanisms over a properly connected overlay - - similarities and differences
- - ability to tolerate churn
- - mesh based gt tree based by all measures !
3P2P streaming
- Using P2P overlay for streaming live media over
network - Participating end-systems (or peers) actively
contribute their resources by forwarding their
available content to their connected peers. - Push based content delivery over multiple tree
shaped overlays. - The tree-based P2P streaming approach expands on
the idea of end-system multicast by organizing
participating peers into multiple diverse trees. - Mesh-based approach uses swarming content
delivery over a randomly connected mesh.
4Terms
- Churn
- a peer can leave or join the p2p system at
arbitrary time - Deadlock
- In the presence of churn, a tree could become
saturated and thus unable to accept any new leaf
node. - Content Bottleneck
- When a parent does not have sufficient number of
useful packets for a child peer, the bandwidth of
its congestion controlled connection to that
child peer can not be fully utilized. - Bandwidth Utilization
- ratio of the number of data packets to the total
number of delivered packets. - Average Quality
- the average number of descriptions ( of
Multiple Description Coded (MDC) content ) it
receives during a session. - Multiple Description Coding (MDC)
- Encoding streams into multiple sub-streams called
description. Each description can be
independently decoded. Furthermore, receiving
multiple unique descriptions results in a higher
quality.
5Organized view of Random Mesh
6Delivery Trees
Mesh based approach
Tree based approach
7Tree Overlay Construction
- Peer decides number of trees to join based on its
access link bandwidth - Each peer is placed as an internal node in only
one tree and as a leaf node in other trees. - Join
- peer contacts the bootstrapping node to identify
a parent in the desired number of trees - Leave
- subtree nodes rejoin the tree
- Balance tree
- peer is added as an internal node to the tree
that has the minimum number of internal nodes. - Short tree
- a new internal node is placed as a child for the
node with the lowest depth
8Mesh Overlay Construction
- Participating peers form a randomly connected
overlay - Each peer tries to maintain a certain number of
parents (i.e., incoming degree) - Each peer serves a specific number of child peers
(i.e., outgoing degree). - Upon arrival, a peer contacts a bootstrapping
node to receive a set of peers that can
potentially serve as parents.
9...Mesh Overlay Construction
- The bootstrapping node maintains the outgoing
degree of all participating peers. Then, it
selects a random subset of peers that can
accommodate new child peers in response to an
incoming request for parents. - Individual peers periodically report their newly
available packets to their child peers and
request specific packets from individual parent
peers - A parent peer periodically receives an ordered
list of requested packets from each child peer,
and delivers the packets in the requested order.
The requested packets from individual parents are
determined by a packet scheduling algorithm at
each child peer.
10Packet scheduling algorithm ( PRIME )
- Each peer maintains two pieces of information for
individual parents - the available packets, and
- the weighted average bandwidth ( b/w budget )
- Each peer monitors the aggregate incoming
bandwidth from all parents and slowly adapt the
number of requested descriptions (or their target
quality) with the aggregate bandwidth. - Each peer invokes the algorithm every ? seconds
to request packets from parent ( with n target
quality ) as follows - scheduler identifies the packets with the highest
timestamp that have become available among
parents since the last request (during last ?
seconds). - the missing packets for each timestamp (up to n
descriptions per timestamp) are identified and a
random subset of these packets is requested from
all parents to fully utilize their bandwidth. - to balance the load among parents, when a packet
is available at more than one parent, it is
requested from the parent that has the lowest
fraction of its bandwidth budget utilized.
11Similarities
- Both approaches leverage MDC to accommodate the
bandwidth heterogeneity among participating
peers. - Superimposed view of multiple diverse trees is
same as directed random mesh overlays. - Content delivery in both enables individual peers
to receive different pieces of content. - All peers receive data from multiple parents and
send it down to different child peers. - Both require peers to maintain a loosely
synchronized playout time that is sufficiently (t
seconds) behind sources playout time.
12Differences
Tree based approach Mesh based approach
Delivery tree for all packets of a particular description is corr overlay tree for that description Delivery tree for individual packets is dynamically shaped as packet travels through the overlay. When a connection has lower bandwidth than description b/w, its descendant peers can still receive packets from alternate path from other parents.
Push based content delivery over multiple tree shaped overlays extending idea of end-system multicast 1 content delivery over a randomly connected mesh extending file swarming mechanisms like in bitTorrent.
Inferior performance due to static mapping of content to a particular tree. The placement of each peer as an internal node in one tree and as a leaf in all other trees. Superior performance as there mutiple type of connections among peers and parents. More dynamic to increase in description bandwidth.
Sweet spot for peer bandwidth where it can effectively utilize available resources and provide the desired quality. Swarming content delivery couples push content reporting with pull content requesting.
13Delivery Tree in Mesh
- Maximize outgoing bandwidth
- Diffusion Phase Once a new packet becomes
available at the source, a single peer p in
level, i pulls the packet during the next
interval ? s. - Swarming Phase During the swarming phase, peers
on different diffusion subtrees exchange their
new packets to contribute their outgoing
bandwidth. - Delivery tree of a packet consists of two parts
- top portion shall be a diffusion subtree
- bottom portion is a collection of swarming
connections hanging from the diffusion subtree.
14Connection Rules of Delivery Tree
- C(i,s) and C(l,s) can be attached at any part of
the bottom portion of the delivery tree. - C(l,s) and C(l,d) ? C(l,s) or C(i,s) .
Otherwise, they form an ending branch for the
delivery tree. - C(i,d) and C(l,d) can only be attached to the
diffusion subtree. - C(i,s) and C(i,d) can only be attached as an
ending branch of the delivery tree.
15Effect of Per Connection Bandwidth
- Tree-based approach has a sweet spot for the
ratio of per-connection bandwidth to description
bandwidth where high resource utilization and
thus high delivered quality is achieved.
16Effect of Peer Degree (Number of Trees)
17Effect of bandwidth heterogeneity
- Mesh as the of high bandwidth peers increases,
the aggregate performance improves - Tree increasing the of high bandwidth peers
rapidly drops depth of all trees which in turn
improves both utilization and the delivered
quality.
18Performance Evaluation Properly Connected
Static Overlays
Tree Based Overlay Mesh Based Overlay
Content has to be delivered through a particular tree extending the adverse effect of a low bandwidth connection to all downstream peers on that tree. Minimizes the impact of a low bandwidth connection on the connected child peer by providing the required content through other parents.
19Performance Evaluation Responsiveness to
Churn !
Procedure / property Tree Mesh
A. Produce distorted overlay remove a random subset of participating peers from a properly connected overlay without repairing it Subtrees isolated would not receive content Alternate paths to subtree still exist via swarming connections
B. Cohesion of the overlay structure under persistent churn a) ancestor changing rate b) avg degree of connectivity c) frequency of deadlocks a) not stable b) less c) sometimes a) stable longevity ? stability ? quality b) more c) no deadlocks !
20Summary
- Identifies the key differences between mesh-based
and tree-based approaches to P2P streaming. -
- This in turn sheds an insightful light on the
inherent limitations and potentials of these two
approaches - Identifies the underlying causes for the observed
differences between tree- and mesh-based
approaches.
21Paper 2
A survey on peer-to-peer video streaming systems
Yong Liu Yang Guo Chao Liang
22Introduction
- Classification of Video Streaming
- Live Streaming
- Video on Demand
- Different models to achieve video streaming over
internet - Client-Server Model
- Content Delivery Network
- Peer-to-Peer Networking
23P2P Live Streaming
- Live video content is disseminated to all users
in real-time. Video playbacks on all users are
synchronized. - Overlay Structures for P2P live streaming
- Tree Based Systems
- Single-tree streaming
- Multi-tree streaming
- Mesh-based Systems
24Tree Based System P2P Live Streaming
- Tree Based Systems
- A peer has only one parent in a single streaming
tree and downloads all content of the video
stream from that parent. - Single Tree Streaming
- Users form a tree at the application layer,
rooted at the video server. - Considerations while constructing a streaming
tree - Depth of the tree.
- Fan out of the tree.
- Tree maintenance
25Tree Based Streaming Single Tree
26Tree Maintenance Single Tree
27Single Tree Construction Maintenance
- Achieved in 2 ways
- Centralized
- central server controls the tree construction and
recovery - Disadvantage Performance bottleneck and the
single point of failure - Distributed
- cannot recovery fast enough to handle frequent
peer churn.
28Multi tree Streaming
- Server divides the stream into multiple
sub-streams - One sub-tree for each sub-stream
- Each peer joins all sub-trees to retrieve every
sub-stream. - Each peer has a different position in different
sub trees.
29Multi-tree Streaming
30Mesh-based Systems
- Peers establish and terminate peering
relationships dynamically - A peer maintains peering relationship with
multiple neighboring peers - Extremely robust against peer churn
31Mesh formation and Maintenance
- A mesh streaming system maintains a tracker.
- Keeps track of the active peers in the video
session. - Each peer, when joining the network, contacts the
tracker - Peer reports its IP address, port number etc.
- Tracker returns a subset of active list of peers
in the session.
32 Mesh Maintenance
- Peers identify new node by exchanging peer list
with neighbors. - Also request for active peer list from tracker.
- Graceful departure of a peer is informed to the
tracker. - Unexpected Peer departure
- Peers regularly exchange keep-alive messages
33P2P Video on Demand
- Video on Demand VoD
- allows users to watch any point of video at any
time - offers more flexibility and convenience to users
- key feature to attract consumers to IPTV service
- Overlays to support VoD
- Tree based P2P systems
- Mesh based P2P systems
34Tree Based P2P Systems
- Users grouped into sessions based on arrival
time. - The server and users in the same session form an
application level multicast tree.Base tree - Server streams entire video over the base tree.
- Users who join the session later, should obtain
the patch Content that is missed
35Tree Based P2P Systems
- Users act like peers in a P2P network. Each of
them provide the following 2 functions - Base Stream Forwarding
- Users forward the received base stream to child
nodes - Patch Serving
- Users cache initial part of stream and forward to
peers joining newly.
36Tree Based P2P Systems
37Cache-and-relay P2P VoD
- Based on the concept of interval caching.
- Server caches a moving window of video content.
- Efficiently utilizes memory at the server
- Serve clients whose viewing point falls into the
caching window. - Serves all clients asynchronously.
38Cache-and-relay P2P VoD
- Each peer buffers a moving window of video
content around the point where they are watching. - Serves other users who are watching around that
point by forwarding the stream.
39Cache-and-relay P2P VoD
40Mesh-based P2P VoD
- Achieves fast file downloading by swarming
- Server disperses data blocks to different users.
- Diversity Requirement
- The data blocks at different users are better-off
to be different from each other so that there is
always something to exchange. - Fully utilize users upload bandwidth
- Achieve highest downloading throughput.
41Mesh-based P2P VoD
- Challenges face in building a mesh based P2P
- effective rate of video play back is poor as data
blocks are retrieved in a fairly random order. - availability of different content blocks is also
skewed by users behavior - Requires right balance between the overall system
efficiency and the conformation to the sequential
playback - Example of Mesh-based P2P VoD BiToS
42BiToS Mesh-based P2P VoD
43BiToS Mesh-based P2P VoD
- BiToS has 3 components
- Received Buffer Stores all data blocks that
have arrived. - High Priority Set Contanins the list of data
blocks that are close to playback but are not
downloaded yet. - Remaining Pieces List of all blocks that are
yet to be downloaded.
44Mesh-based P2P VoD
- Availability of Content in Mesh-based P2P
- If video is downloaded in the order of playback
- newly arrived user can make little contribution
- Not many have content earlier users are looking
for - Earlier arrived peers serve content to the newly
arrived users. - The number of peers that serve content to
earlier arrived peers constantly reduces, as
users might leave the network. - One Solution is to introduce a source server.
45Conclusion
- Existing Limitations in P2P systems
- Quality of Experience is not comparable to
traditional TV. - Long channel start up times and channel delays.
- Considerable lag among peers.
- Low resolution videos due to limited uploading
capacity.
46Conclusion
- High traffic volumes pose a challenge to ISPs
network capabilities. - Video content distribution load is shifted to the
ISPs without any profit to them. - Requires further investigation to identify an
effective method to regulate and manage P2P video
streaming traffic and maintain stability of the
ISPs network infrastructure.
47Measurement of Commercial Peer-To-Peer Live Video
Streaming
48Agenda
- Challenges with analyzing P2P apps
- How is measurement done?
- Analysis of Control Protocols
- Defining Metrics
- Analysis of Data Plane
- Summary and Conclusion
49P2P Systems
- Bright side
- Ubiquity, Resilience, Scalability
- Distributed Applications
- Academic interest generated for Video
applications - Popular
- Not-so-bright side
- Little understanding of protocols
- Proprietary nature makes it difficult
50Challenges with proprietary apps
- No specification of protocols
- Forced to conduct black-box tests
- No documentation or API
- Cant write test scripts
- Manual interaction to be done
51How is it done?
- Collecting packet traces with Ethereal
- Separating control traffic from data traffic
- Reverse engineering the protocols
- By analyzing control traffic
- Data plane analysis on some metrics
- Applications
- PPLive
- SOPCast
52Test Machines
- Intel Pentium 4 computers
- Windows XP OS
- Ethereal Software
53Control Protocols
- Software Update
- Version checking and downloading updates
- Channel Lists
- Downloading channel lists from webserver
- Bootstrap
- Getting initialization information from webserver
- Maintaining Peers
- Getting initial list of hosts and updating them
regularly - Requesting data
54Separating control and data traffic
- Observing packet size
- Packet size lt 40 bytes ACKs (40)
- Packet size gt 1KB Data packets (40 50)
- In between Control packets (10 20)
- Measuring flow rate
- If gt 4KB/s, its a data flow
55PPLive
- Protocol analysis done on PPLive
- SOPCast working very similar
- Both based in Asia with strong American following
- Attract large number of users
56PPLive Protocol Analysis
- Software Update
- GET message sent to update.pplive.com
- Checks for update.inf
- Scalability concerns
- Channel List
- Contact centralized server at http//list.pplive.c
om - Get all.xml file which lists channels
- Channel lists specify trackers
- Flash crowd point in the system
-
57PPLive Protocol Analysis
- Software Update
- GET message sent to update.pplive.com
- Checks for update.inf
- Scalability concerns
- Channel List
- Contact centralized server at http//list.pplive.c
om - Get all.xml file which lists channels
- Channel lists specify trackers
- Flash crowd point in the system
-
58PPLive Protocol Analysis
- Software Update
- GET message sent to update.pplive.com
- Checks for update.inf
- Scalability concerns
- Channel List
- Contact centralized server at http//list.pplive.c
om - Get all.xml file which lists channels
- Channel lists specify trackers
- Flash crowd point in the system
-
59Definitions
- Flow
- F(A1, X1) IPA, PA1, IPX, PX1
- Rate of Flow
- Given by
- Duration of flow
- Parent and Child
- Relationship between peers
- Distance
- Cost
- Miles per byte
- Stability
60Data Plane Analysis
- Network Resource Usage
- Bandwidth
- Number of children supported
- Connectivity
- Locality of peers
- Cost of downloading/uploading
- Stability
61Network Resource Usage
- Bandwidth
- Number of children supported
- Connectivity
62Bandwidth
- Expected
- Fairness
- Limit on upload, download and ratio between them
- Reality
- No policy control over upload
- Increases 3x if 3 instances used (bottom)
63Children Supported
- Number of parents
- Between 3-5
- Same for high capacity (top) and low capacity
(bottom) nodes - 1 parent not possible due to group dynamics
- Unfair children distribution 15 -20 HC, 0 LC
64Bandwidth
- Expected
- Fairness
- Limit on upload, download and ratio between them
- Reality
- No policy control over upload
- Increases 3x if 3 instances used (bottom)
65Connectivity
- Data plane structure
- Very small fraction of hosts connected are
defined parent or child - Unstructured data plane connectivity maintained
through randomness
66Locality of Peers
- Cost of Downloading
- Cost of Uploading
67Visibility
- 3 Levels of visibility
- We measure at the host
68Cost of Download
- High capacity nodes
- High cost of download
- Parents in Asia
- Low Capacity nodes
- Lower cost of download
- Parents in America
- Reason?
69Cost of Upload
- Cost v/s Time
- Done on HC Nodes
- Average suggests low cost
- CDF
- Above 60 children in Asia
- Parents in America
- Inefficiency of System
- Data sent back to Asia in majority cases
70Stability
71Stability
- Stability v/s Time
- 30 of parents change between intervals
- Cause?
- Group dynamics and random nature of data plane
72Summary
- Unfairness
- Improper NAT handling
- Inefficient Distribution of Data
- Transport Protocol
- Not ideal for real-time/overhead
- Delay associated
- Security
- Control protocols are not encrypted
73Contributions
- Gained valuable insight in working of apps
- High resource usage
- Fairness unsatisfactory
- Metrics defined can be used to study other apps
- Brings up issues to be addressed
74Questions ?