In peer-to-peer networks such as gnutella, each host must search out other hosts. When a host finds...

In peer-to-peer networks such as gnutella, each host must search out other hosts. When a host finds another host, these hosts become neighbors. Often a host will continue to search for peers until a sufficient number of hosts have been found. Lets assume that a host will continue to search for hosts until it has N neighbors.

In this project, peer-to-peer neighborhoods are made and maintained. Each host maintains list of neighbors and sends hello packets to these neighbors every 10 seconds. If a host is on the neighbor list, and no hello packet is received from the host for 40 seconds, then this host is removed from the neighbor list. If a node does not have enough neighbors, then it selects an address (e.g., IP and port) at random and tries to become its neighbor.

Objectives

• Find N neighbors– A node is a neighbor if two-way communication is

possible and verified• Two-communication == bidirectional link

• Maintain N neighbors– If two-way communication is no longer verified,

the node is no longer a neighbor

Detecting Bidirectional Links• Node A has a bidirectional with node B if

– Node A can hear node B– Node B can hear node A

• To determine if a link between node A and B is bidirectional– Node A sends a message to node B– Node B sends a message to node A saying that it can hear node A

• Now node A believes the link is bidirectional

– Node A sends a message to node B saying that it can hear node B• Now node B believes the link is bidirectional

• In general, to determine is links are bidirectional– Send hello messages where the message includes a list of all nodes that

have been heard– Upon receiving a hello message,

• If you are listed as one of the nodes that has been recently heard, then the link is bidirectional

• Add the sender of the hello to the list of nodes that you can hear

A B

I am AI have heard: no one

Have heard list Have heard list

A B

I am AI have heard: no one


A

A B

I am BI have heard: A


A

A B


A

I am BI have heard: A

B and B hears me

A B


A

I am AI have heard: B

B and B hears me

A B

Have heard list Have heard listA and A hears me

I am AI have heard: B

B and B hears me

Neighbor States

nothing

one-way (receivable)

bidirectional

Received a hello and this node is not listed

in the hello as a recently heard node

Received a hello with this node listed as

recently heard

No hello received for a long time


recently heard



as recently heard

Neighbor States

nothing

semiActive

active


as recently heard


recently heard



recently heard



as recently heard

Neighbor List Activity Diagram

activeNeighbors – list of nodes in active statesemiActiveNeighbors – list of nodes in semi-active state

waiting

Hello arrived from node B

Node B is semiActiveNeighbors Node B is activeNeighbors

Node B is neither list

This node is listed in the hello as a recently heard

node

Move B from semiActiveNeighbors to ActiveNeighbors

Move B from ActiveNeighbors to

semiActiveNeighbors

This node is NOT listed in the hello as a recently heard node

Put B into semiActiveNeighbors

Put B into activeNeighbors


node


Lists

• C++ Standard template library list• Add the following to the top of cpp file

#include <list>

using namespace std;• E.g., list of ints

– making a list of intslist<int> myList;

– Add an element to myListmyList.push_back(1);myList.push_back(2);myList.push_back(1);

– Iterate through the list and print each elementfor( list<int>::iterator it=myList.begin(); it!=myList.end(); ++it)

printf(“entry=%d\n”,*it);

– Remove an element from the listint elementToRemove = 2;for( list<int>::iterator it=myList.begin(); it!=myList.end(); ++it){

if (*it == elementToRemove){

myList.erase(it);break; // not breaking would result in a crash

}}

– AlternativelymyList.remove(1); // removes all elements == 1. But this requires == operator, which exists for int, but might not for other types

• for( list<int>::iterator it=myList.begin(); it!=myList.end(); ++it)– printf(“entry=%d\n”,*it);

• Boost foreach.hpp

• foreach( int x, mylist)– printf(“entry=%d\n”,x);

Structuresstruct HostID { char ip[16];

unsigned int port;unsigned int lastTimeHelloRec;

};

struct PktStruct {int type;char senderIP[16];unsigned int senderPort;int numberOfRecentlyHeardNeighbors;struct RecentNeighborEntry recentNeighbors[100];

};

struct RecentNeighborEntry {char ip[16];unsigned int port;

};

List

bool checkIfInList(HostID &hid, list<HostID> &L){

list<struct HostID>::iterator it;for (it=listToCheck.begin(); it!=listToCheck.end(); ++it)

if (it->ip == hid.ip && it->port == hid.port)return true;

return false;}

struct HostID { char ip[16];


};

List

bool checkIfInList(HostID &hid, list<HostID> &L){

std::list<struct HostID>::iterator it;for (it=listToCheck.begin(); it!=listToCheck.end(); ++it)

if (strcmp(it->ip,hid.ip)==0 && it->port == hid.port)return true;

return false;}

struct HostID { char ip[16];


};



waiting


Node B is semiActiveNeighbors Node B is activeNeighbors

Node B is neither list



semiActiveNeighbors




node



node




waiting


checkIfInList(sender,semiActiveNeighbors)

==true

else



semiActiveNeighbors




node


checkIfInList(sender, activeNeighbors)

==true


node


Neighbor List Activity DiagramactiveNeighbors – list of nodes in active statesemiActiveNeighbors – list of nodes in semi-active state

int checkForNewPacket(SOCKET UDPSock, char *pkt, int TimeOut)

Hello arrived


==true

else



semiActiveNeighbors




==true

Extract sender from hello

else


node



node


Receiving a Packet

• PktStruct pkt;• int ret = checkForNewPacket(UDPSock, (char *)&pkt, 2); // time out of 2 seconds

• The pkt object is a string or chunk of bytes• &pkt is the pointer to pkt• (char *)&pkt treats this pointer as a string of bytes

• struct PktStruct {• int type;• char senderIP[16];• unsigned int senderPort;• int numberOfRecentlyHeardNeighbors;• struct RecentNeighborEntry

recentNeighbors[100];• };

Extract Sender from Hello Message• PktStruct pkt;• int ret = checkForNewPacket(UDPSock, (char *)&pkt, 2);

• HostID sender;• sender.ip = pkt.senderIP;• sender.port = pkt.senderPort; • struct HostID {

char ip[16];unsigned int port;unsigned int lastTimeHelloRec;

};

• struct PktStruct {• int type;• char senderIP[16];• unsigned int senderPort;• int numberOfRecentlyHeardNeighbors;• struct RecentNeighborEntry recentNeighbors[100];• };

Extract Sender from Hello Message• PktStruct pkt;• int ret = checkForNewPacket(UDPSock, (char *)&pkt, 2);

• HostID sender;• strcpy(sender.ip , pkt.senderIP);• sender.port = pkt.senderPort; • struct HostID {

char ip[16];unsigned int port;unsigned int lastTimeHelloRec;

};




Hello arrived


==true

else



semiActiveNeighbors




node



==true


else


node


thisHost

int main(int argc, char* argv[]){

HostID thisHost;fillThisHostIP(thisHost); // provided in helper.cppthisHost.port = atoi(argv[1]);…



Hello arrived


==true

else



semiActiveNeighbors



This node is listed in recently heard

nodes

This node is NOT listed in recently

heard nodes


==true


else

checkIfThisHostIsInRecentlyHeardNeighbors(pkt,thisHost)

==true


==false

checkIfThisHostIsInRecentlyHeardNeighbors

• struct HostID { char ip[16];


};


• struct RecentNeighborEntry {• char ip[16];• unsigned int port;• };

for (int i=0; i<pkt.numberOfRecentlyHeardNeighbors; i++){

if (pkt.recentNeighbors[i] == thisHost)return true;

}return false;



Hello arrived


==true

else

Move sender from semiActiveNeighbors to ActiveNeighbors

Move sender from ActiveNeighbors to

semiActiveNeighbors

Put sender into semiActiveNeighbors

Put sender into activeNeighbors

checkIfThisHostIsInRecentlyHeardNeighbors(pkt,

thisHost)==true


==true


else


==true


==false


thisHost)==false



Hello arrived


==true

else



semiActiveNeighbors




thisHost)==true


==true


else


==true


==false


thisHost)==false

Lists• C++ Standard template library list

#include <list>using namespace std;

• Making a list of intslist<int> myList;

• Add an element to myListmyList.push_back(1);myList.push_back(2);myList.push_back(1);

• Iterate through the listfor( list<int>::iterator it=myList.begin(); it!=myList.end(); ++it)

printf(“entry=%d\n”,*it);

• Remove an element from the listint elementToRemove = 2;for( list<int> iterator::it=myList.begin(); it!=myList.end(); ++it){

if (*it == elementToRemove){

myList.erase(it);break; // not breaking would result in a crash

}}

• AlternativelymyList.remove(1); // removes all elements == 1. But this requires == operator, which exists for int,

but might not for other types

Objectives

• Find N neighbors– A node is a neighbor if two-way communication is

possible and verified• Two-communication == bidirectional link

• Maintain N neighbors– If two-way communication is no longer verified,

the node is no longer a neighbor

To do

• While (1)– Receive hello• Process neighbor states (sort of like what we did)

– Search for more neighbors?• Check and if so, search

– Update neighbor set• If some neighbors have timed out, remove them

– Send hello messages to neighbors• Send every 10 sec

To do





Search for more neighborsint main(int argc, char* argv[]){

bool searchingForNeighborFlag = false;readAllHostsList(argv[2], allHosts); // provided

while (1){

if (activeNeighbors.size() + semiActiveNeighbors.size() < DESIRED_NUMBER_OF_NEIGHBORS && searchingForNeighborFlag ==false){

searchingForNeighborFlag = true;tempNeighbor = selectNeighborAtRandom(activeNeighbors, semiActiveNeighbors, allHost, thisHost); // provided

}….

To do





Process Hello


Hello arrived


==true

else



semiActiveNeighbors




thisHost)==true


==true


else


==true


==false


thisHost)==false

sender==tempNeighbor

searchingForNeighborFlag = false


==false


==true



To do





Process Hello


Hello arrived


==true

else



semiActiveNeighbors




thisHost)==true


==true


else


==true


==false


thisHost)==false

sender==tempNeighbor

searchingForNeighborFlag = false


==false


==true



updateLastReceivedTime(sender,

activeNeighbors)


semiActiveNeighbors)


activeNeighbors)






activeNeighbors)

Lists

• C++ Standard template library list• #include <list>• using namespace std;• Making a list of ints

– list<int> myList;

• Add an element to myList– myList.push_back(1);– myList.push_back(2);– myList.push_back(1);

• Iterate through the list– for( list<int>::iterator it=myList.begin(); it!=myList.end(); ++it)

• printf(“entry=%d\n”,*it);

• Remove an element from the list– int elementToRemove = 2;– for( list<int>::iterator it=myList.begin(); it!=myList.end(); ++it)– {

• if (*it == elementToRemove)• {

– myList.erase(it);– break; // not breaking would result in a crash

• }

– }– Alternatively

• myList.remove(1); // removes all elements == 1. But this requires == operator, which exists for int, but might not for other types



};



To do





Send hello messages to neighbors every 10 sec

• #include <time.h> • #include <sys/types.h>• #include <sys/timeb.h>• int main(int argc, char* argv[])• {• ….

struct _timeb lastTimeHellosWereSent;_ftime_s( &lastTimeHellosWereSent ); struct _timeb currentTime;

while (1){ _ftime_s( &currentTime );if (currentTime.time > lastTimeHellosWereSent.time + 10){

lastTimeHellosWereSent = currentTime;sendHellos(…)

}….

Send hello messages to neighbors every 10 sec

• #include <time.h> • #include <sys/types.h>• #include <sys/timeb.h>• int main(int argc, char* argv[])• {• ….

struct _timeb lastTimeHellosWereSent;lastTimeHellosWereSent.time = 0;_ftime_s( &lastTimeHellosWereSent ); struct _timeb currentTime;

while (1){ _ftime_s( &currentTime );if (currentTime.time > lastTimeHellosWereSent.time + 10){

lastTimeHellosWereSent = currentTime;sendHellos(…)

}….

sendHellos(…)

• sendHelloToANeighbor• Hello must include all heard neighbors

– activeNeighbors– semiActiveNeighbors– Not tempNeighbor

• void sendHelloToNeighbor(SOCKET UDPSock, HostID destination, list<HostID> &activeNeighbors, list<HostID> &semiActiveNeighbors, HostID &thisHost);

• Hello must be sent to – activeNeighbors– semiActiveNeighbors– AND tempNeighbor



};



for(it= activeNeighbors.begin(); it!=activeNeighbors.end() ++it){

sendHelloToNeighbor(UDPSock, *it, activeNeighbors, semiActiveNeighbors, thisHost);

}….

Date post:	19-Dec-2015
Category:	Documents
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In peer-to-peer networks such as gnutella, each host must search out other hosts. When a host finds...

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