## 2 Design Principles for Mesh Networks
### IEEE802.15.4-Tg4g  
This section delves into an assessment of ZigBee's cutting-edge performance benchmark known as the smart utility network (SUN). Its scope encompasses the next echelon of intelligent power grids. It is envisaged that a progression toward employing numerous intelligent meters and multiple communication nodes for data exchange with base stations within the communication system architecture will emerge as a prevailing trajectory [19; 20; 21; 22]. This standard lays the groundwork by delineating the initial two layers of the OSI model, catering to low-rate wireless personal area networks (LR-WPANs). The physical (PHY) layer meticulously defines the requisite attributes that wireless radio frequencies should embody. It lends support to two disparate radio frequency spectra, situated at 868 MHz, 915 MHz, and 2450 MHz. The radio frequency range of 2450 MHz bestows the capability of delivering data rates of 250 kbps, accompanied by 16 message channels. In contrast, the 868/915 MHz spectrum designates 868 MHz for a single message channel, operating at a data rate of 20 kbps, while 915 MHz graciously offers ten message channels, with data transmission cruising at 40 kbps. Meanwhile, the Media Access Control (MAC) layer shoulders the mantle of facilitating data interchange among proximate devices. It shoulders the responsibility for forging connections and orchestrating network synchronization, thereby establishing a robust linkage between two devices. ZigBee introduces a triumvirate of network topologies at the network layer: the star topology, tree topology, and mesh topology networks. In Figure 3, we encounter simplified representations of these three network topologies, encompassing (a) the star topology, (b) the tree topology, and (c) the mesh topology [23; 24]. In each topology, a solitary ZigBee coordinator assumes the solemn duties of the inauguration, perpetuation, and governance of the network. Within the precincts of the star topology, devices are confined to the exchange of data solely with the coordinator. In the realms of the tree and mesh topologies, devices engage in reciprocal communication through the agency of a multi-hop routing mode. The structural scaffolding of both tree and mesh topologies consists of a coordinator supported by an array of routers. The discerning contrasts between the three topological paradigms are elucidated in Table 2.  
Upon the network's commencement, the fully fledged devices within its domain engage in a spirited competition, each vying for the esteemed title of ZigBee coordinator. Upon successful ascension to this pivotal role, the coordinator embarks upon a comprehensive survey of all wireless frequency bands, meticulously selecting a well-suited channel for reference. Subsequently, a network address is bestowed upon devices through the auspices of the beacon's transmitting entity, serving as a distinctive insignia for forthcoming data transmissions. Channel scanning, an innate function, is entrusted with the responsibility of  
Figure 3: Diagram of three ZigBee network topologies. detecting activity or extraneous interference within a channel. This physical layer consideration enables network protocols to discern whether any channels within a designated frequency band might impede communication among nodes. Frequency flexibility is a hallmark of the network, endowing it with the capacity to adapt its operating channels for all nodes, ensuring seamless operation even when channels become afflicted by interference. The efficacy of message transmission stands to be enhanced through the incorporation of a confirmation mechanism. Upon a successful reception of a packet, the receiving node dutifully dispatches a confirmation signal to the originating transmitter. This duality of point-to-point acknowledgment and message retries significantly mitigates the probability of packet loss.