P2P and more …
Rumen Stainov
http://www2.hsfulda.de/~stainov/erasmus/TUSofia/
L: TKSoft
P: kommsoft06
rumen.stainov@informatik.hs-fulda.de
2012 © R. Stainov
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Peer-to-Peer – what is this ?
2012© R. Stainov
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Peer-to-Peer – what is this ?
2012© R. Stainov
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System Architectures

Client-Server



Data Centers / Cloud Computing
Peer-to-peer (P2P)
Hybrid Client-Server and P2P
2012 © R. Stainov
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Client-Server Architecture
Server:
 Always-on Host
 Permanent IP address
 Server Farms for Scaling
Clients:

client/server



2012 © R. Stainov
communicate with server
may be intermittently connected
may have dynamic IP addresses
do not communicate directly with
each other
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Google Data Centers



Estimated cost of data center: $600M
Google spent $2.4B in 2007 on new data centers
needs 50-100 Megawatt electricity
2012 © R. Stainov
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Pure P2P Architecture



no always-on server
arbitrary end systems
directly communicate
peers are intermittently peer-peer
connected and change IP
addresses
Highly scalable but difficult
to manage
2012 © R. Stainov
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Server-client vs. P2P: File Distribution Time
Minimum Distribution Time
3.5
P2P
Client-Server
3
2.5
2
1.5
1
0.5
0
0
5
10
15
20
25
30
35
N
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Hybrid of Client-Server and P2P
Skype
 voice-over-IP P2P application
 centralized server: finding address of remote party:
 client-client connection: direct (not through server)
Instant messaging
 chatting between two users is P2P
 centralized service: client presence detection/location
 user registers its IP address with central server
when it comes online
 user contacts central server to find IP addresses of
buddies
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Peer-to-Peer – what is this ?
First Idea – Direct downloading of (music) files
Shawn Fanning, Boston Student, called Napster
2012© R. Stainov
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Napster File Sharing: hybrid center + edge
1. User starts Napster and
connects to the server
2. Napster creates a Dynamic
Directory of the personal .mp3
collection of the user
3. beastieboy enters search
criteria
Title
song1.mp3
song2.mp3
song3.mp3
song4.mp3
song5.mp3
song5.mp3
song6.mp3
song6.mp3
song7.mp3
User
beasiteboy
beasiteboy
beasiteboy
kingrook
kingrook
slashdot
kingrook
slashdot
slashdot
Speed
DSL
DSL
DSL
T1
T1
28.8
T1
28.8
28.8
s ong5
4. Napster shows the hits to
beastieboy
5. beastieboy connects
direcly to kingrook for
file transfer
“beastieboy”
•song1.mp3
•song2.mp3
•song3.mp3
•song5.mp3
“kingrook”
•song4.mp3
•song5.mp3
•song6.mp3
“slashdot”
•song5.mp3
•song6.mp3
•song7.mp3
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Peer-to-Peer Systems
Second Idea, Using Fat Clients for Resources Sharing
 Thin client  Fat client
DEC’S
VT100
No Memory
2012© R. Stainov
IBM 8-bit PC
@ 4.77MHz
360k
Diskette
64-bit PC @ 4-core
4GHz
1 TB HD
Peer-to-Peer (P2P)
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Resources Sharing

What can we share?


Computer-related resources
Shareable related-computer resources:






CPU cycles
Bandwidth
Storage Space
Data
People
Camera, Microphone,
- seti@home, GIMPS
- PPLive, PPStream
- OceanStore, Murex
- Napster, Gnutella
- Buddy Finder
Sensor, Service???
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SETI@Home





SETI – Search for Extra-Terrestrial Intelligence
@Home – On your own computer
A radio telescope in Puerto Rico scans the sky for
radio signals
Fills a DAT tape of 35GB in 15 hours
That data have to be analyzed
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SETI@Home – stat MUX
using parallel computing resources
Peer-to-Peer – what is this ?
Third Idea – Searching for (music) files on all peers
Distributed Hash Table (DHT) - BitTorrent, Kademlia,
eMule
DHT
2012 © R. Stainov
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Peer-to-Peer – what is this ?
Hash function f(x) = x mod 5
0
1
2
10
15
6
2012 © R. Stainov
Hash function f(x) = x mod 6
3
4
23
5
8
19
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Peer-to-Peer – what is this ?
Hash function f(x) = x mod 5
0
1
2
10
15
6
2012 © R. Stainov
Hash function f(x) = x mod 6
3
4
23
5
8
19
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Peer-to-Peer – what is this ?
The virtual DHT address space
0
1
2
10
15
6
3
4
5
DHT
2012 © R. Stainov
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8
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Peer-to-Peer Systems: DHT
Idea:
1. A lookup service similar to a hash table: (key, value) pairs are
stored in the DHT,
2. Responsibility for maintaining the mapping from keys to values is
distributed among the nodes,
3. Scales to extremely large numbers of nodes
Tasks of DHT are:

To find the location of the searched resource (data).

Equal distribution of the resources to the nodes.

Routing to the node storing the resource from any other node.
2012 © R. Stainov
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Peer-to-Peer Systems: DHT


Value
Alexander
Berlin
Ivan
Moskow
Marina
Fulda
Peter
Avignon
Rumen
Fulda
Stefan
Sofia
Each node has a search operation (lookup)


Key
Find the value associated with the key
The nodes maintain routing pointers (Finger poiters) to
other nodes if the resource is not local.
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Peer-to-Peer – what is this ?
The virtual DHT address space
Advantages:
 Load Balancing. Equal distribution of objects and peer in the DHT
address space.
 Scalability. Adding and removing of peers concerns the neighbors
only .
 Fast Lookup. The object‘s ID defines the peer ID
 Availability. No central component (server) exists, which could fail.
 Anonymity. In P2P we address not a computer (e.g. server), but
contents.
0
1
2
3
4
5
DHT
2012© R. Stainov
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Peer-to-Peer Systems: DHT
Lookup in P2P Applications
2012© R. Stainov
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Peer-to-Peer – what is this ?
The virtual DHT address space
Disadvantages:
 Geographic or network location is irrelevant (Overlay)
Routing and data transfer over continents (speed)
 Dealing with disconnected (crashed) nodes
Especially in mobile networks
0
1
2
3
4
5
DHT
2012 © R. Stainov
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Peer-to-Peer Systems:
DHT
The steps for look up in
Consistentent Hashing
Chord are logarithmic
The size of the routing
table is logarithmic
Example:
log2(1000000)≈20
Effective !
2012 © R. Stainov
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Peer-to-Peer Systems: Chord
The nodes build a modulo 2m ring (Chord Ring). The node Ids are
created by hashing of IP addreses and the resource IDs by hashing of
the recource key. Those IDs build a ID ring modulo 2m.
15
0
1
14
2
13
3
12
4
H(a) = 6
H(b) = 5
H(c) = 0
H(d) = 11
H(e) = 2
5
11
6
10
9
7
8
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Each node a,b,c,d,e calculates an ID using the hash function H
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Peer-to-Peer Systems: Chord


The succesor (succ) of an Identificator is the first node
clockwise.
Example:
15
0
1
14
2
13
3
12
4
succ(12)=14
succ(15)=2
succ(6)=6
5
11
6
10
9
2012 © R. Stainov
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Peer-to-Peer Systems: Chord
Each resource calculates an ID using the hash function H. Example:
H(“Marina”)=12, H(“Peter”)=14, H(“Rumen”)=4, H(“Stefan”) = 9.

Resource-Ids are maped in the same or in successor (succ) node and are
stored in this node.
15
0
1
14
2
13
3
12
4
5
11
“Marina”  succ(12) = 0
“Peter”  succ(14) = 0
“Rumen”  succ(4) = 5
“Stefan”  succ(9) = 11
6
10
9
2012 © R. Stainov
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Peer-to-Peer Systems: Chord


Each node points to his successor (succ), the so called succ pointer.
Each node points to his predecessor (pred), the so called pred pointer.
2012 © R. Stainov
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Peer-to-Peer Systems: Chord
Lookup of the key “Rumen” from node 2:
15
0
1
14
2
13
3
12
4
5
11
 Calculate H(“Rumen”) = 9
 Go to succ pointers until „9“ is
found, i.e.
 Lookup the nodes 2, 5,6,11 (BINGO)
 Value „Fulda“ is sent back to node 2
.
6
10
9
7
8
2012 © R. Stainov
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Peer-to-Peer Systems:
Chord
The steps for look up in
Chord
are logarithmic
Speed up of the lookup. Using Succ pointers
in succ(
n+1), we
need in the worse case N steps for N nodes. WeThe
cansize
achieve
a speed
up, if
of the
routing
we use a pointer in succ (n+2M-1). In our example
theisnode
0 should point
table
logarithmic
to the nodes succ (0+1)=2, succ (0+2)=2, succ (0+4)=5, succ (0+8)=11
Example:
zeigen.
0
15
1
14
2
13
3
succ (0+1)=2log (1000000)≈20
2
succ (0+2)=2
Effective !
succ (0+4)=5
succ (0+8)=11
The distance is first the half.
12
4
5
11
6
10
9
7
8
Pointer to succ(n+2M-1)
Finger table node n:
Finger points to the succesor of n + 2i
finger[i] = successor (n + 2i)
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Peer-to-Peer Systems: Chord

Routing to 15 (Get (15)) goes in considerable less steps (log2(N) steps
insteat of N steps in the worst case)
2012 © R. Stainov
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Peer-to-Peer Systems: Chord

Prinzip of the lookup – find the next predecessor.
Get(8)
Get(15
)
15
15 0
2
14
0
15
1
1
2
14
13
3
13
3
12
12
4
4
11
5
10
6
9
8
2012 © R. Stainov
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11
5
10
6
9
8
8
7
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Peer-to-Peer Systems: Chord

A new peer joins and informs his
successor.
2012 © R. Stainov
15
13
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Peer-to-Peer Systems: Chord
The new peer takes the corresponding
resources from his successor.
14
0
1
5
1
2
14
2
13
9
3
12
8
12
4
11
5
10
6
9
2012 © R. Stainov
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7
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Peer-to-Peer Systems: Chord
The new peer takes the corresponding
resources from his successor.
15
1
4
0
1
2
14
2
13
3
12
12
4
9
8
11
5
10
9
9
8
2012 © R. Stainov
6
8
7
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MOBILITY SUPPORT
What is the problem ?
1. Internet access over different networks on different cost.
2. The communication with the mobile device could be
temporarily (or even for a longer period) interrupted.
3. Heterogeneous mobile devices according to their
computing, transmission and storage capacity.
2012 © R. Stainov
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Existing Solutions
Proprietary add-on layer to the existing P2P
systems for caching or buffering of data units at
the powerful peers
 broadcast channels, feeds



throw boxes
data MULEs
Emails per POST
0
1
2
3
4
5
DHT
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Our Idea
 Peer Port represents "ordered message buffer" for a
redundant persistent P2P communication.
Difference to the existing approaches:
 Peer Port is redundant to
the primary P2P channel
and is used only in case of
interruption
 Peer Port is a part of the
P2P system and continues
receiving data after the
interruption
Peer Port
PUSH
Data Object
Sending Peer
Receiving Peer
DHT
39
Peer Port
Normal operation with redundant buffering (PUSH)
Peer Port
PUSH
Data Object
Sending Peer
Receiving Peer
DHT
Registration with the Peer
Group:
 creates a peer port.
 defines his size and
validity date/time.
 sets-up a unique
sequence number for
messages.
 creates a ticket for
accessing it over PULL.
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Peer Port
PULL the
missing
messages
at
“low cost”
messages ID = [peer port
ID, message sequence
number]
Data recovery (PULL) after interruption.
Peer Port
Peer Group
PUSH
PULL
Data Object
Sending Peer
Bang
DHT
Receiving Peer
Continue with persistent
communication over the
Peer Port
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Peers as relays - Example

Problem when both Alice
and Bob are behind
“NATs”.


NAT prevents an outside
peer from initiating a call
to insider peer
Solution:



Using Alice’s and Bob’s
SNs, Relay is chosen
Each peer initiates session
with relay.
Peers can now
communicate through
NATs via relay
42
Use Case A famous orthodontist is traveling
WiMAX
His colleague in the practice needs frequently consultations over
video & VoIP, but:

Because of entering a tunnel, the WiMAX connection is
interrupted shortly. A normal P2P channel will lose information,
so that this part has to be repeated.
Solution: the missed information will be taken from the
peer port and can be played, even couple of minutes
later.

The connection over WiMAX is replaced by 3G/GPRS. A normal
P2P channel will be disconnected, and after reconnection the
missing audio and video transmission has to be repeated.
Solution: the transmission continues over the peer port.
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Advantages of Peer Ports




P2P technology. The peer port inherits the P2P
advantages like low cost, availability, high bandwidth, scalability
and anonymity.
Delay tolerant. The peer ports overlay will be tailored to
the context of the delay tolerant networking and will be used for
add-on persistent communication with the goal that each
message will eventually be delivered to its destination.
Low cost recovery after interruption. The peers
belonging to the group are chosen to be “near” the receiver,
building on this way a location aware group.
Network independent recovery. Sending peers will
push the data into the peer ports; receiving peers will pull data
from them, if necessary.
44
PEER PORTS FOR LAYERED
P2P STREAMING
Peer Ports Implementation
New Problems:
• received and processed data should be removed
• missing data could be requested from Peer Port
A new Peer Port Sliding Window Protocol is needed.
New Ideas:
 Peer Ports for Layered Streaming.
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Peer Port Sliding Window
During the Normal Operation:
• Transient (direct) communication between Sending and Receiving
Peers
• Sliding Window between the Receiving Peer and the Peer Port.
Peer Port
PUSH
Peer Group
ACK + miss. data
control + req.
Data Object
Sending Peer
Receiving Peer
DHT
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Peer Port Sliding Window
After Interruption:
• Persistent (indirect) communication between Sending and Receiving
Peers
• Sliding window between the Receiving Peer and the Peer Port.
Peer Port
PUSH
Peer Group
PUSH data + ack
control + req.
Data Object
Receiving Peer
Sending Peer
DHT
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Peer Ports for Layered Streaming
Layered coding:
• The basic media stream is first encoded into a base layer providing
the minimum quality and requiring the minimum bandwidth.
• The enhancement layers are encoded separately into separate
packets, where each additional layer contributes to the improving the
quality of the media played.
L4
L3
L2
L1
L2
L1
More enhancement layers introduce better video quality
Base layer
49
Peer Ports for Layered Streaming
Existing Application in P2P:
• Supplier & Receiver Side Schedulers
• Scheduling mechanism to request absent blocks, based on 3
buffering windows: free stage, decision stage and remedy stage.
Our Approach:
Parallel transmission over 2 Peer Ports – one for basic layer stream, the
another for enhancement layers.
50
Peer Ports for Layered Streaming
During Normal Operation :
• The Base Peer Port is used mainly for back up of the packets of the
base layer, and therefore for requesting of missed base layer
messages. The enhancement layer packets are buffered separately,
and deleted first.
Base Peer Port
• If the “control + req.”
message requests missing
base layer and enhancement
layer packets, the reply
message “ACK + miss. Data”
should include them.
Peer Group
PUSH
Data Object
ACK + miss. data
control + req.
Sending Peer
Receiving Peer
control + req.
ACK + miss. data
DHT
Enhancement Peer Port
51
Peer Ports for Layered Streaming
During Normal Operation :
• The Enhancement Peer Port is used mainly for back up of
enhancement packets layer, and therefore for requesting of missed
enhancement layer messages. The base layer packets are buffered
separately, and deleted first.
• Control messages are
used to request missing
enhancement packets
and to implement the
sliding window protocol
to the Receiving Peer.
Base Peer Port
Peer Group
PUSH
Data Object
ACK + miss. data
control + req.
Sending Peer
control + req.
Receiving Peer
ACK + miss. data
DHT
Enhancement Peer Port
52
Peer Ports for Layered Streaming
Persistent Operation (In case of interruption):
• The Base Peer Port will start playing the role of a proxy and will push
the packets to the Receiving Peer, using the Sliding Window Protocol.
… But, the Extra Hop Problem …
Base Peer Port
Peer Group
PUSH
Data Object
 Solution: Pushing Base
Layer Packets trough the
Base Peer Port in parallel
to pushing Enhancement
Layer Packets trough the
Enhancement Peer Port.
PUSH. Data + ack
control + req.
Sending Peer
Receiving Peer
control + req.
PUSH. Data + ack
DHT
Enhancement Peer Port
53
Peer Ports for Layered Streaming
Persistent Operation (In case of interruption):
The Enhancement Peer Port plays the role of backup for Base Layer
Streaming packets.
Implementation: The
request for missing base layer
streaming packets will be sent Data Object
to both Peer Ports, and both
will deliver the missing base
layer streaming packets. The Sending Peer
first message with the base
DHT
layer packet will be processed,
the second will be ignored.
Base Peer Port
Peer Group
PUSH
PUSH. Data + ack
control + req.
Receiving Peer
control + req.
PUSH. Data + ack
Enhancement Peer Port
54
The Peer Port solution for Data Sharing Networks
The Peer Port is representative of the mobile Peer, and forwards the
data chunks received to the mobile Peer.
If several mobile Peers are sharing the same data  a swarm of Peer
Ports, like BitTorrent, Gnutella, etc.
The sliding window protocol:
1.
2.
3.
•
•
•
Bit vector with missed data chunks
for each data sharing session.
The mobile Peer sends periodically
control messages with the last
received chunks.
The missing chunks will be
selectively sent.
DHT
Peer Port m
PUSH. Data + ack
BitTorrent
control + req.
Swarm
mobile Peer m
Peer Port n
PUSH. Data + ack
control + req.
mobile Peer n
55
Peer Port
Problems with mobile Peer-to-Peer Multimedia:
1.
Limitations in the throughput and Quality
of Service (QoS) over the wireless
interface.

gaps in an audio/video presentation
 Layered streaming coding,


The basic media stream is first encoded into a base
layer providing the minimum quality and therefore
requiring the minimum bandwidth.
The enhancement layers are encoded separately into
special packets, where each additional layer contributes
to the improving the quality of the media played.
56
Peer Port
Support for streaming multimedia.


The transient communication channel is used for the base layer
and for as many enhancement layer packets as possible.
When the mobile connection deteriorates, the lost packets can
be recovered eventually on-time from the Base Peer Port (Base
Packets), and/or from Enhancement Port (Enhancement
packets).
Base Peer Port
Peer Group
PUSH
Data Object
ACK + miss. data
control + req.
Sending Peer
mobile Peer
control + req.
ACK + miss. data
DHT
Enhancement Peer Port
57
Peer Port
Support for streaming multimedia.
Interruption Persistent Communication


Base Peer Port for storing forwarding mainly base layer packets.
The Enhancement Peer Port for handling mainly enhancement
layer packets.
Base Peer Port
Peer Group
PUSH
Data Object
Sending Peer
control + req.
PUSH. Data + ack
mobile Peer
control + req.
PUSH. Data + ack
DHT
Enhancement Peer Port
58
Peer Port
Support for streaming multimedia.
Layered Streaming using a Swarm of Peer Ports


When a live multimedia stream has to be sent to group of mobile Peers
a class listening on a distance education lecture, or a live IPTV
The one-to-many multimedia streaming seems to be a problem in the
traditional Client-Server networks because of




Bandwidth bottleneck at the sending node.
Bad scaling
Pure efficiency
P2P Networks in a swarm are:


Self-scaling
The content delivery can effectively use the outgoing bandwidth of all the
peers – statistical multiplexing.
59
Peer Port
Support for streaming multimedia.
Layered Streaming using a Swarm of Peer Ports
 The first layer represents the swarm of Peer Ports
only.




Peer Ports only on powerful stationary computers.
Efficient delivery and scheduling of live video chunks.
Statistical multiplexing and therefore efficiency of the video data
sent to a group of peers.
The second layer represents the mobile Peers
receiving the same multimedia content.




Do not participate directly in the swarm.
Order to the corresponding Peer Port to gather, and to forward to
him the desired multimedia stream.
The Base Peer Port forwards mainly the base layer packets.
The Enhancement Peer Port mainly the enhancement layer packets.
60
Problems with Ambient
Assisted Living (AAL):
Mobile
Mobile Care
attendants
Doctors
Family
members
Sending/Receiving
• Alternative comm.
media
• Can be interrupted for a
short, or long period
SENDING
• Alternative comm.
media
• Can be interrupted for
a short, or long period
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Peer Port
The Peer Port solution for AAL
Delay tolerant communication with the mobile
SENDING device.
1.



Sending device pushes data via normal transient P2P communication
(enhanced security).
Back-up during the normal communication locally (in the mobile
device) and to the Peer Port.
Add-on persistent communication and recovery in case of interruption.
Peer Group Peer Port
ACK + miss.
control + req. data
Cache Data
Object
Mobile
PUSH
Receiving Peer
Sending Peer
DH
T
62
Peer Port
The Peer Port solution for AAL
2.
Network independent recovery for the mobile RECEIVING device.



Sending Peer pushes the data into the Peer Ports and to the receiver.
Mobile receiving peers will pull data from Peer Ports, only if some data are missing.
Disconnection: The Peer Ports are using for persistent communication.
Peer Port
PUSH
Peer Group
ACK + miss. data
control + req.
Data Object
Sending Peer
mobile Peer
DHT
63
Peer Port
The Peer Port solution for AAL
3.
Direct mobile-to-mobile communication in case of
emergency

Mobile receiving peers will pull emergency data directly from the
Peer Port of the mobile sending device, if the stationary assistance
system at home is not accessible.
Peer Port
Peer Group
PUSH
ACK + miss. data
control + req.
Data Object
Mobile Sending
Peer
Mobile Receiving Peer
DHT
64
Implementation

We are using Chord to implement experimentally the above ideas.
Our approach however, can be applied to an arbitrary P2P system.

We started to experiment with the peer port for two different P2P
applications:
(1) Data messages and file transfer
(2) Audio and video transmission.
65
Future Work

The efficiency of P2P is the stat MUX at the application layer.

The future work will include algorithms for performance
improvements using a swarm of Peer Ports.
66