Speaker : Junn-Keh Yeh Date : 2010/7/2 1

 IEEE  Forming, Joining, and Rejoining ZigBee Networks ◦ Forming Networks ◦ Joining Networks ◦ Rejoining Networks  ZigBee Packet Routing ◦ Broadcasting ◦ Mesh Routing 2

 IEEE defines: ◦ Mechanisms for discovering networks ◦ Mechanisms for forming and joining networks ◦ Mechanisms for changing channels ◦ Mechanisms for detecting interference and “ noise ” on a particular channel ◦ An acknowledged, single-hop, data-packet delivery method, using CSMA-CA to avoid collisions  Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA) 3

 Starts out with a unique 64-bit IEEE address  Joining the network, each node is assigned a unique (within that network) 16-bit short address. 4 ZC ZED ZR ZED ZR

 ZigBee Coordinator has the following duties: ◦ It forms a network. ◦ It establishes the channel on which the network will operate. ◦ It establishes the extended and short PAN ID for the network. ◦ It decides on the stack profile to use (compile or run-time option). ◦ It acts as the Trust Center for secure applications and networks. ◦ It acts as the arbiter for End-Device-Bind (a commissioning option). ◦ It acts as a router for mesh routing. ◦ It acts as the top of the tree, if tree routing enabled. 5 ZC ZED ZR ZED ZR

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 ZigBee Routers are responsible for: ◦ Finding and joining the “ correct ” network ◦ Perpetuating broadcasts across the network ◦ Participating in routing, including discovering and maintaining routes ◦ Allowing other devices to join the network (if permit-join enabled) ◦ Storing packets on behalf of sleeping children 7 ZC ZED ZR ZED ZR

 ZigBee End-Devices are responsible for: ◦ Finding and joining the “ correct ” network ◦ Polling their parents to see if any messages were sent to them while they were asleep ◦ Finding a new parent if the link to the old parent is lost (NWK rejoin) ◦ Sleeping most of the time to conserve batteries when not in use by the application. 8 ZC ZED ZR ZED ZR

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10 ZC ZE D ZR ZED ZRZED

 There are several reasons why a node might need to rejoin the network: ◦ A ZED has lost contact with its parent ◦ Power has been cycled, and many or all nodes in the network rejoin “ silently ” ◦ Joining a secure network if permit-joining is off 11

 ZigBee employs a variety of methods for routing packets from one node to another: ◦ Broadcasting (from one to many nodes) ◦ Mesh routing (unicast from one node to another) ◦ Tree routing (unicast from one node to another, stack profile 0x01 only) ◦ Source routing (unicast from one node to another, stack profile 0x02 only) 12

 ZigBee does allow a radius of 0x00, which is a special flag that means to repeat the broadcast for the entire network.  This radius set from 0x01 to 0xff, to indicate an actual maximum distance.  There are three special ZigBee broadcast modes: ◦ 0xffff—broadcast to all nodes (even sleeping ZEDs) ◦ 0xfffd—broadcast to all awake devices (including RxOnIdle =TRUE ZEDs) ◦ 0xfffc—broadcast to all routers (excludes all ZEDs) 13

 The Broadcast Transaction Table(BTT) is a critical component of broadcasting.  Broadcasting transmits from one node to many nodes, up to the entire network.  Use broadcasts sparingly, as they consume a lot of bandwidth and resources.  Broadcasts are slow compared to unicasts. 14

 The record that was created actually goes into a table called the Broadcast Transaction Table or BTT. ◦ when a broadcast is transmitted, all devices that receive it will broadcast a copy. ◦ Each time a copy of the broadcast arrives, the address of the sender will be added to the BTT to mark that it has relayed the broadcast. ◦ After a broadcast timeout, if all neighbors haven’t relayed the broadcast, meaning they aren’t present in the BTT, then the original sender will need to do a broadcast retry. 15

 In ZigBee mesh: ◦ The algorithm is based on the publicly available Advanced Ad- hoc On-Demand Distance Vectoring (AODV). ◦ All routers are peers. ◦ The route is distributed: Each node in the route keeps track of the next hop for the route in a routing table. ◦ Routes are unidirectional (a route must be discovered each way for bidirectional communication). ◦ Routes are like goat trails: they continue to be used until they fail. ◦ Failed routes are communicated back to the originating node, allowing it to discover a new route.  Ad hoc On-Demand Distance Vector (AODV):RFC

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18 Note: the least path cost is not the same as the fewest number of hops.

 Routes are discovered automatically by ZigBee.  ZigBee Mesh route discovery is initiated when a node sends a packet to another node.  Routes are discovered along the least cost path. 19

 The Handoff Procedure for Real Time Voice Communication in ZigBee Environment  Efficient Mechanism for GTS Allocation (EMGA) inIEEE LR-WPAN 20

 (1) 能量檢測通道搜尋 (energy detection channel scan) ：完全功能裝置 (FFD) 要形成 ZigBee 個人區域網路 時所執行的，讓 FFD 得知每一個所搜尋頻道上的最高峰 之能量。  (2) 主動頻道搜尋 (active channel scan) ：在無信標環 境下讓裝置能尋找出所有相鄰之協調器或路由器之狀態。  (3) 被動頻道搜尋 (passive channel scan) ：與主動頻 道搜尋目的相同，主要在信標環境下只做接收信標訊號 之搜尋方式。  (4) 孤兒頻道搜尋 (orphan channel scan) ：裝置發生 同步遺失 (synchronization loss) 狀態時，搜尋所有頻 道來尋找已建立連線之父節點 ( 協調器或路由器 ) 。 21

 若一個裝置 ( 協調器或路由器 ) 擁有路由表 (routing table) 與 路由找尋表 (routing discovery table) 則稱為具有路由能力 (routing capacity) ，  如下頁圖所示 ，當有路由能力的 node 0 要傳送資料到 node 4 時，發現其路由表中並沒有到達目的端 node 4 的 路由時，將會發送廣播訊息 RREQ(Route request) 來啟動路 由尋找機制 (routing discovery) 。  當裝置 2 接收到 RREQ 訊息時會先計算與來源端之間的 link cost ，並且記錄到 RREQ 訊息內，若該裝置 2 接收到相同目 的端訊息 RREQ ，將會保留最低 link cost 的路由。  由於裝置 2 並沒有路由能力，因此將使用樹狀網路機制發送 詢問訊息 RREQ 給 node 4 ，此時目的端 node 4 則按照下一 跳躍 (next hop) 節點的原有路由方式，回傳 RREP(Route reply) 訊息給來源端 node 0 ，完成路由尋找的程序。 22

 MLME ( Media Access Control (MAC) sublayer Management Entity) Media Access Control ◦ 若裝置為協調者則產生訊標 (beacon) ； ◦ 普通裝置根據訊標訊框來與協調者達到同步 (synchronizing) ； ◦ 提供 PAN 網路聯結 (association) 和取消聯結 (disassociation) 功能； ◦ 提供裝置資料加密安全性 (security) ； ◦ 使用載波檢測多重存取 / 碰撞避免 (CSMA/CA) 機制來競爭 通道； ◦ 支援保證時槽 (guaranteed time slots ； GTSs) 之機制； ◦ 在不同的媒介存取控制副層間提供可靠傳輸 (reliable link) ； 23

 網路層資料訊息通道（ Network Layer Data Entity, NLDE ） ◦ a. 將 APL 所傳來的資料（ APDU ）轉成 Network level PDU （ NPDU ） ◦ b. 根據網路的拓樸架構決定資料訊框路由的路徑。  網路層管理訊息通道（ Network Layer Management Entity, NLME ） ◦ 設定網路參數包含以及設備參數 ◦ 負責初始化及建立一新的 ZigBee 網路 ◦ 加入或是離開一網路 ◦ ZigBee 網路協調者以及路由器負責配發網路位址給新加入網路 的終端點，尋找並且記錄鄰近網路設備的所有資訊 ◦ 尋找並且記錄網路封包路由路徑 24

 Stack profile 0x01 tends to be used in applications where cost is one of the major concerns. Its main characteristics are: ◦ Predictable address assignment ◦ Tree routing ◦ Smaller code size ◦ Up to 10 hops in the network 25

 Stack profile 0x02 tends be used where cost is less of an issue, and larger networks are more important. Its main characteristics are: ◦ Random (stochastic) address assignment ◦ Source routing ◦ Multicast ◦ Larger code size ◦ Up to 30 hops in the network 26

 There are two ZigBee stack profiles: 0x01 (ZigBee) and 0x02 (ZigBee Pro).  Stack Profiles define alternate routing methods and maximum number of hops.  ZigBee nodes may join either stack profile. 27

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 ZigBee uses one of two address schemes to assign the short address: ◦ Cskip  Cskip address assignment, available in stack profile 0x01 (the stack profile simply called ZigBee)  stack profile 0x01 uses a calculated number for each “ depth ” (the number of hops from the ZigBee Coordinator), called Cskip (child skip).  allows tree routing in addition to mesh. ◦ Stochastic (random)  Stochastic addressing is available in stack profile 0x02 (the stack profile called ZigBee Pro). 30