zigbee学习笔记2008-06-14 17:38Every PAN has a unique 16 bit ID and a single ZigBee
coordinator
每个网络有一个独立的16比特的id和唯一的一个zigbee cordinator（协调器）
For ZigBee V1.0, merging PANs after they have formed
is not possible without re-commissioning the two systems
对于zigbee 1.0版来说，在两个网络建成之后，再合并他们是不可能，除非两个网络重新建立
The ZigBee coordinator has a special 16 bit network
address of 0x0000
zigbee协调器有一个特殊的网络地址0x0000
Every device has a 64 bit MAC address (unique)
每个设备有一个唯一的64位的mac地址
Upon association, every device receives a 16 bit network address
(unique)
经过协商，每个设备受到一个16位的网络地址（单独的）
Only the 16 bit network address is used to route packets within the
network.
只有16位的网络地址被网络路由包使用
Devices retain their 16 bit address if they disconnect from the network,
however, if LEAVE the network, the 16 bit address is re-assigned
当设备断开网络时保留16位的网络地址，但当设备离开网络时，地址就重新分配了
NWK broadcast implemented above the MAC:
– NWK address 0xFFFF is the broadcast address
– Special algorithm in NWK to propagate the message
– “Best Effort” or “Guaranteed Delivery” options
网络广播在mac层上面执行
网络地址0xffff是广播地址
特殊的算法传递信息
有最优传输和保证传输两个选项可选
Two channel access mechanisms
– Beacon-enabled network
– Non-beacon network
两种频道访问机制
允许beacon网络
没有beacon网络
Beacon-enabled Network
– For dedicated bandwidth and low latency
– Set up by network coordinator to transmit in predetermined intervals
– Beacon frame is transmitted on the first slot of each superframe
– Beacons are used to: synchronize attached devices, identify the PAN
(PAN ID), describe the structure of a superframe
– Devices wishing to communicate during CAP (Contention Access
Period) between two beacons compete using CSMA-CA
– All transactions must be completed by the time of the next network
beacon
beacon允许网络
带宽制定和低传输速率
由网络协调器建立，以固定的时间间隔传输数据
beacon帧在每个超级帧的第一个solt被传输
beacons被用来同步设备，识别网络，描述超级帧的结构
所有的传输都必须被下一个beacon时间结束
Non-Beacon Mode
– A simple, traditional multiple access system used in simple peer and near-peer
networks
– Think of it like a two-way radio network, where each client is autonomous and
can initiate a conversation at will, but could interfere with others unintentionally
– However, the recipient may not hear the call or the channel might already be in
use
? Beacon Mode
– A very powerful mechanism for controlling power consumption in ex
tended
networks like cluster tree or mesh
– Allows all clients in a local piece of the network the ability to know when to
communicate with each other
– Here, the two-way radio network has a central dispatcher who manages the
channel and arranges the calls
? As you’ll see, the primary value will be in system power consumption
Beacons add a new level of functionality to a network
beacons 对网络增加了个新级别的功能
? Client devices can wake up only when a beacon is to be broadcast, listen for
their address, and if not heard, return to sleep
客户端设备被一个beacon广播到时将会被唤醒， 侦听地址，如果不匹配继续转如到睡眠状态
? Beacons are important for mesh and cluster tree networks to keep all of the
nodes synchronized without requiring nodes to consume precious battery
energy listening for long periods of time
beacons是对个网络和树形网络保持所有节点同步，without消耗很多昂贵的电池啊能量，侦听很长时间
Data Frame format
数据帧格式
One of two most basic and important structures in 15.4
? Provides up to 118 byte data payload capacity
有118个字符的载荷能力
? Data sequence numbering to ensure that packets are tracked
数据序列数据保证包可被跟踪
? Robust structure improves reception in difficult conditions
鲁棒结构增强了在恶劣环境下的接受能力
? Frame Check Sequence (FCS) validates error-free data
帧检查序列验证错误数据
Acknowledgement Frame format
应答帧格式
The other most important structure for 15.4
? Provides active feedback from receiver to sender that packet was
received without error
提供激活的反馈从接受者到发送者告诉其，帧是错误的还是正确的.
? Short packet that takes advantage of standards-specified “quiet time”
immediately after data packet transmission
短帧利用标准指定的安静时间，再数据帧传输后
MAC Command Frame format
mac控制帧格式
Mechanism for remote control/configuration of client nodes
用来进行远程控制和配置
? Allows a centralized network manager to configure individual
clients no matter how large the network
对一个星型网络来说，控制单独的终端，不管这个网络有多大
Robustness
健壮性
? Carrier sense multiple access with collision
avoidance: CSMA-CA
载波监听，冲突避免
? Frame Acknowledgement
应答帧
? Data Verification:
– Cyclic Redundancy Check (CRC)
使用crc进行错误分析
Security Services
安全服务
? Access Control
访问控制
? Data Encryption
数据加密
? Frame Integrity
？
? Sequential freshness
？
MAC Layer Task
MAC层任务
? Generating network beacons if the device is a
coordinator.
当设备时一个coordinator时，生成网络beacons
? Synchronizing to the beacons.
同步到beacons
? Supporting PAN association and disassociation.
支持pan组织，也可不组织
? Suppor
ting device security.
支持设备安全
? Employing the CSMA-CA mechanism for channel
access.
? Handling and maintaining the GTS mechanism.
处理和维护的GTS机制
? Providing a reliable link between two peer MAC
entities.
提供一个可靠的连接，在两个mac节点之间