Obras de alimentación

Simulation Scenarios

To evaluate the routing protocols described in Section 3.2, we used the three different next hop selection options, which meaning and description is presented in Section 3.2.2:

(i) UPath:The first set of results is performed for selecting next hops from the FIB table that have the lowest counter value. When multiple next hops have the same counter value, the most recently added is selected.

(ii) SLPath: The second approach is based on the average latency of the next hops in the routing entries. The next hop with the lowest latency is chosen for transmitting an Interest.

(iii) USLPath: The last approach is based on the combination of the previous two. As mentioned in Section 3.2.2, we select the next hop with the lowest counter. If there are multiple next hops with the same counter, the one with the lowest latency is selected.

Simulation Parameters

Moreover, to evaluate our routing protocols we used the ndnSIM simulator [18], v2.0. NdnSIM is a software module providing the basic NDN implementation [18, 19, 106] for the ns-3 network simulator [8]. To obtain the network traffic simulation we used SUMO [36]. For the topology, for MMM-VNDN we chose the MANHATTAN scenario, 1km x 1km, with the number of nodes (cars) varying from 60 to 100. Each vehicle is equipped with three interfaces, to send and receive Interest and Data messages simultaneously, using Wi-Fi 802.11a (We use IEEE 802.11a since 802.11p is not available in ndnSIM v2.0). For iMMM-VNDN we have chosen two different topologies to evaluate the algorithms, the Manhattan map, and the Luxembourg map [47]. In the Manhattan map, the number of nodes (cars) chosen is varying from

3.3. Performance Evaluation Table 3.2: Simulation Parameters

STRATEGY PROPAGATION LOSSMODEL STANDARD- TRANSMISSION RANGE DATA RATE CHANNEL BANDWIDTH MMM- VNDN Three Log Distance and Nakagami IEEE802.11a 200m 24 Mbps 20MHz iMMM-

VNDN Two Ray Ground

IEEE802.11p 250m 6 Mbps 10MHz Broadcasting Three Log Distance and Nakagami IEEE802.11a 200m 24 Mbps 20MHz Best-route Three Log Distance and Nakagami IEEE802.11a 200m 24 Mbps 20MHz NCC Three Log Distance and Nakagami IEEE802.11a 200m 24 Mbps 20MHz

CCVN Two Ray Ground IEEE802.11p

250m 6 Mbps 10MHz

CODIE Two Ray Ground IEEE802.11p

250m 6 Mbps 10MHz

20 to 100 and the average speed is around 15m/s. In the Luxembourg map, we have chosen an area of 1km x 1km in the city centre. Luxembourg traces are available for 24 hours. We have chosen different times during these 24 hours to extract the mobility traces. Then, in these different mobility traces, we have extracted the density of vehicles, varying from 109 to 396. The average speed of cars depends on the time slot when the mobility traces were extracted. The parameters of the algorithms are shown in Table 3.2. In Table 3.2 the standard defines the transmission range, the data rate and the channel bandwidth. We used the IEEE 802.11a standard for MMM-VNDN, Broadcasting and NCC strategies because these strategies were developed in ndnSIM v2.0 and ndnSIM v2.0 is not compatible with IEEE 802.11p. The propagation models include the Three Log Distance model, which is a log distance path loss propagation model with three distance fields [4], the Nakagami model, which accounts for the variations in signal strength due to multipath fading [5], and the Two Ray Ground model, where the gain of the signal depends on the reflection of the signal from

roads [6].

For the next hop selection options chosen (Section 3.3.1(i), (ii), (iii)), one node is sending Interest messages and there exists one content source in the network. For each of the above next hop selection options, we first compare MMM-VNDN with the flooding strategy, which next hop an Internet message into the network. Then, we compared iMMM-VNDN with MMM-VNDN to show the advantages that the improved protocol offers. Finally, for the third next hop selection option, we compared iMMM- VNDN with the broadcasting strategy, which broadcasts every Internet message into the network, the best route strategy, which chooses the best face to send an Interest according to its cost [19], the NCC strategy [7], which chooses the best face to send the Interest and tracks the RTT of faces, the Content-Centric Vehicular Networking (CCVN) algorithm [24], described in Section 2.3 and the Controlled Data and Interest packet propagation strategy (CODIE) [21], where the Interest contains a hop counter and the Data propagation is controlled by this hop counter. The presented results have a confidence interval of 95%. Since the proposed algorithms are developed for VANETs, new nodes could enter the network at any time. This leads to intermittent connections and consequently to breaking the paths from the requester to the content source. To cope with these problems, we broadcast one Interest message every 10 seconds. By broadcasting only one instead of every Interest, routing entries are created or updated and broadcast storms are avoided. This is accomplished by not broadcasting the network with unnecessary Interest transmissions.

For all scenarios chosen, we experiment with three different Interest Lifetime (IL) times, i.e. the time that the Interest is transmitted into the network before it expires. We note that the IL lifetime depends on the application, i.e. how much an application should wait before requesting again its Data. We propose our algorithm in scenarios where vehicles request infotainment data, e.g. a video of a road, where there is a tolerance for a small delay in receiving the Data. Therefore, we choose different ILs: 4 seconds, 8 seconds and 12 seconds. We consider these values to be realistic for infotainment application with delay constrains. Moreover, such small values are widely used in the literature [29, 32]. We highlight here that using large values for the I.L. could result in prevention of forwarding similar Interests because the request is already pending (a node has an entry to its PIT.

3.3. Performance Evaluation

Simulation Metrics

To evaluate the routing protocols three metrics were used:

• Interest Satisfaction Rate (ISR) describes the number of received Data messages that were received by the requester divided by the total number of Interest messages being sent.

• Average Latency: The average latency for all received Data messages describes the average time that passed from the time a requester sent an Interest message to the time that the requester received the Data message. When a Data message has not been received until its expiration time, the requester node retransmits the Interest message and the initial time is reset.

• Average Jitter: Jitter is defined as the mean deviation of the difference in packet spacing at the receiver node compared to the sender for a pair of packets [64].

The above metrics describe the main characteristics that we consider important to the V2V communication in a VANET for an infotainment application. ISR is a core metric, but it is insufficient, when a VANET application has delay constraints. Hence, latency and jitter are being measured in our experiments.