# Routing Protocols for Delay Tolerant Networks:
## 3 Performance Evaluation
### Reference Benchmarking Scenario  
We examine the performance of each protocol and classify its performance using a reference scenario that is general enough to address specifications derived from real-world applications. We consider that nodes that participate in the opportunistic network are smart phones carried by humans, and as such, they do not have control on their mobility (_i.e._, passively mobile). In terms of wireless communication technology for _ad hoc_ connectivity, we consider 802.15.1 (Bluetooth), which is supported by the reference implementation for DTN, as proposed in [2]. According to Bluetooth specifications, transmission speed is about 0.2 Mbps = 25.00 kBps and transmission range about 10 m.  
To evaluate the effects of the buffer size on the performance, we combined different message and buffer sizes. In the small buffer size case, there are an average of 70 messages in the queue, while in the larger case, the messages are about 700. We vary the number of nodes from 10-70 nodes moving in the reference area. Each node generates a new message to a random destination every 1-3 min. Messages never expire, namely their TTL is set to infinity. These technical specification have been derived from the application scenario presented in [1; 12; 19; 43; 44]. We consider two different cases for the area covered by the network nodes (_i.e._, within which humans are moving):  
_Indoor environment_: a rectangular area of 400 m \(\times\) 400 m that may represent a conference hall or an office space;  
_Outdoor environment_: a rectangular area of 8 km \(\times\) 8 km that represents a city center or a town. The area is further analyzed using a 32 \(\times\) 32 grid, with each grid cell covering a square area of 250 m \(\times\)250 m [24]. Clearly, the way in which nodes move within this area is a critical factor that affects the performance of the network [45; 46]. Essentially, movement affects nodes' opportunity to meet other nodes, that is the probability to reach the destination and the inter-contact probability. Consequently, the messages' likelihood to be delivered before being dropped depends on the pattern of the mobility of the nodes. In order to evaluate this effect, we incorporate two approaches: (1) synthetic mobility patterns: we use three mobility models for simulating mobility by humans, a group of humans and robots; (2) real-world traces of mobility: we use traces acquired from real-world experiments in order to reproduce the mobility of the nodes. In all cases considered, the average speed of nodes (used in different mobility models and as observed in the real-world traces) for the indoor environment is chosen to be in the range of walking speed (2.8... 7.2 km/h), while for the outdoor environment, to be in the range of driving speed in the city center (5... 50 km/h), with an average speed of 12.29 km/h [24]. More specifically, the mobility patterns considered are the following:  
* _Random Waypoint (RWP)_[20]: In RWP, nodes randomly choose the next destination and move there with a random speed. Upon arrival at the destination, the node pauses for a while and then chooses a new destination. This mobility pattern is suitable for simulating the mobility of robots. * _Levy Walk (LW)_[16]: This mobility model tries to emulate human walk patterns in outdoor environments. The next direction is uniformly selected at random, while distance from the current position and speed are selected according to a power law distribution. In this model, the authors extended their preliminary work in [47], where they proposed a mobility model called SLAW (Self-similar Least Action Walk) in order to produce synthetic walk traces containing features of human walk traces. * _Community (CM)_[6; 22]: This model emulates communication within groups of people. The network area is divided into the so-called communities, and each node has a probability to get in/out of a community, as well as transit from one community to another [22]. Our implementation follows the specification given in [6].