Multimedia Communication Services Traffic Modeling and Streaming

Transcription

1 Multimedia Communication Services Medium Access Control algorithms Simulation of AlohaNet (not slotted) with finite number of nodes Università degli Studi di Brescia A.A. 2014/2015 Francesco Gringoli Master of Science in Communication Technologies and Multimedia

2 Discrete event simulation: multi-node scenario Channel point-to-point: only one node, actually, no nodes!! We simulated only start and end of transmission to evaluate if OK or KO It was not a network! No nodes, no simultaneous transmissions! Aloha Slotted: Hypothesis, if packet received, no ACK More code is needed, existing code should be modified Class representing nodes: class Node;! Unicast messagges generated by nodes and addressed to other nodes New handlers to implement reception Need to have status at every node to keep trace of Status of transmission, reception, IDLE Status of current (multi)reception, (means collisions), Channel is broadcast! 2

3 Message types Messages: STARTTX and STOPTX alone are not enough Nodes can transmit and receive! Add messagges STARTRX and STOPRX Add two additional handler next slides Who triggers reception messages? Node that start/stop TX generate start/stop RX for all other nodes! Remember: channel is broadcast even if messages are unicast! Change class Message to hold Destination node E.g.: when node N creates message, it adds destination to message Node where message should be executed E.g.: when node N create message for node M, it schedules STARTTX on itself! 3

4 Message types/2 Class Message! typedef enum { STARTTX, STOPTX,STARTRX, STOPRX } msg_t; // 4 handlers! class Message {!!// declaration of the new class!!public:!!!!!message(void);!// costructor!!!double time;!// scheduling time!!!int msgid;!// event id!!!msg_t msgtype;!// message type: decides handler!!!int msglen;!// length of message!!!node* node;!// node where message is executed! NEW!!!Node* dst;!// destination node!!!message* next;!!// point to next message! };! 4

5 How to use the new message types Example with 3 nodes (id 0, 1, 2): node 2 starts tx addressed to node 0 T 0 STARTTX on 2;dst 0 2 trasmits to 0 but channel is broadcast! Add two STARTRX for other nodes Same time means propagation time is null! T 0 STARTTX on 2;dst 0 on 0;dst 0 on 1;dst 0 Destination does not change! Who executes message changes! CHANNEL IS BROADCAST! 5

6 How to use the new message types/2 Need to schedule end tx on node 2, packets have duration ΔT T 0 STARTTX on 2;dst 0 on 0;dst 0 on 1;dst 0 T 0 +ΔT STOPTX on 2;dst 0 and next tx on 2: time T 1 according to arrival statistic on 2 T 0 STARTTX on 2;dst 0 on 0;dst 0 on 1;dst 0 T 0 +ΔT STOPTX on 2;dst 0 T 1 STARTTX on 2;dst 1 and destination node according to a given law NOTE: remove requirement T 1 > T 0 +ΔT, we keep status on nodes now! If T 1 < T 0 +ΔT, when event is executed node still txing, reschedules! 6

7 How to use the new message types/3 Remove current event: on 0;dst 0 on 1;dst 0 T 0 +ΔT STOPTX on 2;dst 0 T 1 STARTTX on 2;dst 1 handler will change status of node 0 and 1 to RX handler schedules events STOPRX T 0 +ΔT STOPTX on 2;dst 0 T 0 +ΔT STOPRX on 0;dst 0 T 0 +ΔT STOPRX on 1;dst 0 T 1 STARTTX on 2;dst 1 Handler will verify reception and put status to IDLE on 0: me==dst! Reception OK! on 1: me!=dst! Exit 7

8 Class node and status What happens if a STARTRX at a node is followed by STARTTX? Aloha: hypothesis, when a node has something to tx it starts transmitting Example: T 0 STARTTX on 0;dst 1 T 0.1 STARTTX on 1;dst 2 0 has pkt for 1 1 has pkt for 2 on 1;dst 1 on 2;dst 1 T 0.1 STARTTX on 1;dst 2 T 0 +ΔT STOPTX on 0;dst 1 First message in 1 put it to RX, second put it to TX (and forgets RX) 8

9 Class node and status/2 Temporal diagram Node 0 has pkt for 1 in t = T 0, node 1 has pkt for 2 in t = T 0.1 Signals transmitted over time and nodes states Signal Node 0: T 0 +ΔT T 0 Signal Node 1: State of nodes: 0: IDLE 1: IDLE 2: IDLE 0: TX 1: RX 2: RX T 0.1 0: TX 1: TX 2: RX(?) T 0.1 +ΔT 9

10 Class node and status: collisions More messages STARTRX may arrive at a node in sequence Aloha: hypothesis, when a node has something to tx it starts transmitting Example: T 0 STARTTX on 0;dst 1 T 0.1 STARTTX on 1;dst 2 0 has pkt for 1 1 has pkt for 2 on 1;dst 1 on 2;dst 1 T 0.1 STARTRX on 0;dst 2 T 0.1 STARTRX on 2;dst 2 T 0 +ΔT STOPTX on 0;dst 1 T su First message in 2 put it to RX, second must trigger collision on 2!! 10

11 Class node and status: collisions/2 Temporal diagram Node 0 has pkt for 1 in t = T 0, node 1 has pkt for 2 in t = T 0.1 Signals transmitted over time and nodes states: Node 0: T 0 +ΔT Node 1: T 0 T 0.1 T 0.1 +ΔT When collision occurs, nodes 0 and 1 are TX, they don t realize Node 2 must realize! SOLUTION: COUNT HOW MANY SIGNALS I M RECEIVING! 11

12 Class node typedef enum { IDLE, TX, RX} node_status_t;! class Node {! public:! Node();! int nodeid; node_status_t status; int signals; int collided; };! // unique id for every node! // status of the node! // number of received signals! // state of collision! int nextnodeid = 0; // global variable to trace nodes! Node::Node() { // initialize node:! nodeid = nextnodeid++; // unique id! status = IDLE; // in state IDLE (doing nothing)! signals = 0; // it is not receiving anything! collided = 0; // never experience collisions! fprintf(stderr, "Created node id %d\n", nodeid);! }! 12

13 Managing nodes and handling new arrivals #define N 100! Node *nodes = new Node[N]; int suc = 0; int tot = 0; double now; // keep vector with nodes in global heap! // number of successful receptions! // number of new arrivals! // global time, refreshed by main! void schednewpacket(node* node) {! Message* msg = new Message; // new message! msg->time = now - log(1-drand48()) / MU; // execution time! msg->msgtype = STARTTX; // it s a new transmission! msg->node = node; // for this same node! int j = floor((n-1)*drand48()); // extract destination address:! if(j >= node->nodeid) j++; // trick for avoiding self-sending!! msg->dst = &nodes[j]; // store destination! fprintf(stderr, "%f %d: schednewpacket to %d at %f\n, now, node->nodeid, msg->dst->nodeid, msg->time );! sched->insert( msg ); tot++; // schedules message! // refresh new arrivals! 13

14 Function to send messages in broadcast Channel is broadcast: use a helper function to send messages Simply change the message type Es: handler STARTTX replicates STARTTX message as STARTRX for everybody 14

15 Handler: starttx e stoptx 15

16 Handler: startrx 16

17 Handler: stoprx 17

18 Main loop: changes 18