无线传感器网络技术与Zigbee标准综述

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"这篇文档是关于无线传感器网络(WSN)和Zigbee技术的白皮书概述，主要探讨了这种新兴技术在低成本、无人值守环境监控中的应用，以及IEEE 802.15.4标准和即将推出的Zigbee标准对WSN的影响。文章还强调了对能量效率、网络构建、数据管理和安全性的研究进展，以及对比这些标准化解决方案的必要性。" 在无线传感器网络(WSN)领域，这项技术通过微小的传感器节点收集环境信息，并通过无线通信进行传输和处理。这些网络通常用于远程监控，例如环境监测、工业自动化、健康监护和灾害管理等场景。WSN的核心优势在于其部署的便捷性、成本效益和自组织能力。提到的IEEE 802.15.4标准定义了物理层和媒体访问控制(MAC)层的规范，这是WSN的基础，尤其适用于低数据速率、低功耗的应用。该标准为WSN提供了统一的通信框架，提高了不同设备之间的互操作性。而Zigbee标准则进一步扩展了这个框架，涵盖了网络层和应用层，旨在提供更高级别的网络管理和应用服务，如网络组建、安全性和服务质量(QoS)保障。随着WSN研究的快速发展，尤其是在能量效率方面，研究人员致力于开发节能算法和技术，以延长传感器节点的寿命，因为电池替换或充电在许多应用中可能是不可行的。网络构建方面，WSN需要适应性强的路由协议，能处理节点故障、动态拓扑变化和有限的通信范围。此外，数据管理方面，有效的数据聚合和压缩策略可以减少网络流量，提高整体效率。安全问题也是WSN的关键关注点，包括防止数据篡改、窃听和节点被恶意接管。由于WSN的资源限制，安全解决方案必须在保证安全性的同时，兼顾能耗和计算复杂度。比较标准化解决方案与当前研究进展，有助于推动WSN技术的进步和应用。这篇白皮书的作者来自英国布拉德福德大学、意大利比萨的科学研究和技术信息研究所以及计算机科学系，他们对WSN和Zigbee标准的深入分析，为读者提供了理解这一领域最新动态和标准的重要参考。

the node discards the RREP message; otherwise it updates the RDT entry (residual cost) and the RT entry (next

hop). A node that is not the RREP originator must also forward the RREP towards the originator. Note that

intermediate nodes never change the RT entry status to Active as a result of receiving a RREP message. They will

only change the entry status upon reception (and routing) of a data message for the given destination. Figure 7

illustrates the RREP message processing.

Field Name Description

RREQ ID Unique ID (sequence number) given to

every RREQ message being broadcasted

Source Address Network address of the initiator of the route request

Sender Address Network address of the device that

sent the most recent lowest cost RREQ

Forward Cost The accumulated path cost from the

RREQ originator to the current device

Residual Cost The accumulated path cost from the

current device to the RREQ destination

Table 4: Content of the Route Discovery Table

Figure 6: The RREQ processing

Figure 7: The RREP processing

3.2.2 The Application Layer

A ZigBee application consists of a set of Application Objects (APOs) spread over several nodes in the network. An

APO is a piece of software (from an application developer) that controls a hardware unit (transducer, switch, lamp)

available on the device. Each APO is assigned a locally unique endpoint number that other APOs can use as an

extension to the network device address to interact with it. The ZigBee Device Object (ZDO) is a special object

which offers services to the APOs: it allows them to discover devices in the network and the service they

implement. It also provides communication, network and security management services. The Application Sublayer

(APS) provides data transfer services for the APOs and the ZDO. Figure 2 illustrates the various components in the

Application Layer.

A ZigBee application must conform to an existing (ZigBee Alliance-accepted) application profile. An application

profile defines message formats and protocols for interactions between APOs that collectively form a distributed

application. The application profile framework allows different developers to independently build and sell ZigBee

devices that can interoperate with each other in a given application profile. Each APO encapsulates a set of

attributes (data entities representing internal state, etc.) and provides functionalities (services) for setting/retrieving

values of these attributes or being notified when an attribute value changes. In the context of a profile, a group of

related attributes is termed a "cluster" and identified with a numeric id. Typically a cluster represents a sort of

interface (or part of it) of the APO to the other APOs.

The application profile must specify one of two possible communication service types. For the Key Value Pair

(KVP) service type the ZigBee standard has predefined message layouts which must be suitably filled by APOs to

request a given operation on attributes residing on a remote APO. The interactions between APOs is limited by the

operations supported on attributes. The Generic Message service type is suitable for applications that do not fit in

the KVP service type and leaves responsibility to the application profile for specifying message types and their

contents.

A special application profile, named the Device Profile, must be implemented by all nodes in a ZigBee network.

The object responsible for this profile is the ZDO. The Device Profile requires its implementing objects (ZDOs) to

support device/service discovery procedures wherein a node attempts to discover existing nodes in the network,

active endpoints on some node and/or the services they implement (available cluster ids).

Discovery procedures are crucial to APO addressing. In direct addressing mode a message is addressed to a specific

destination address (16-bit network address) and endpoint number and the sending node is responsible for

discovering both via the ZDO discovery services. Indirect addressing mode only requires the sender to supply a

cluster id but needs support from a neighbouring (or local) ZigBee router (or coordinator) to locate the destination

node(s) for the message. This is possible thanks to the APS of the ZigBee router that maintains a binding table

associating (source address, source endpoint, cluster id) tuples to a list of (destination address, destination endpoint)

tuples, one for each device the message must reach. A message sent by an end-device with indirect addressing

reaches the parent node. Here the APS consults its binding table in order to determine the actual destinations and

send them appropriate messages with direct addressing. Adding and removing entries in the binding table is

commanded by the ZDO in response to local/remote binding requests, as defined in the Device Profile.

3.3 Security in ZigBee

Security services provided for ZigBee include methods for key establishment, key transport, frame protection, and

device management [ZIG05]. The ZigBee Alliance describe the security functionalities based on an open trust

model for a device whereby the different layers of the communication stack and all applications running on a

single device trust each.

The ZigBee specifications provide different means to achieve the following security requirements:

• Freshness: ZigBee devices maintain incoming and outgoing freshness counters to maintain data freshness.

These counters are reset every time a new key is created. Devices that communicate once per second will not

overflow their freshness counters for 136 years.

• Message Integrity: ZigBee specifications provide options of providing 0, 32, 64 or 128 bit data integrity for the

transmitted messages. The default is 64 bit integrity.

• Authentication: Network level authentication is achieved by using a common network key. This prevents

outsider attacks while adding very little in memory cost. Device level authentication is achieved by using

unique link keys between pairs of devices. This prevents insider and outsider attacks but has higher memory

cost.

• Encryption: ZigBee uses 128-bit AES encryption. Encryption protection is possible at network level or device

level. Network level encryption is achieved by using a common network key. Device level encryption is

achieved by using unique link keys between pairs of devices. Encryption can be turned off without impacting

freshness, integrity, or authentication as some applications may not need any encryption.

The ZigBee architecture includes security mechanisms at the MAC, NWK and APS Layers of the protocol stack.

Furthermore, the APS sub-layer provides services for the establishment, and maintenance of security relationships.

The ZigBee Device Object (ZDO) manages the security policies and the security configuration of a device [ZIG05].

The following architectural design choices for security are made in ZigBee specifications:

• The layer that originates a frame is responsible for initially securing it. For example, the MAC layer frames and

NWK command frames are secured by MAC layer security and Network Layer security respectively.

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无线传感器网络技术与Zigbee标准综述

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