1. A Novel Approach to WLAN Mesh Interworking with Multiple Mesh Portals 指導教授：許子衡 教授 學生：王志嘉

2. www.themegallery.com 2 Contents Introduction 1 Previous Work on WLAN Mesh Interworking 2 Interworking with External LANs through Multiple Portals 3 Interworking Example 4

3. www.themegallery.com 3 Introduction (i)  Wireless local area network (WLAN) mesh networking is an emerging technology which can provide affordable and reliable wireless connectivity.  According to the IEEE 802.11 s WLAN mesh standard, a WLAN mesh generally consists of the following components ： 1.Mesh point (MP) 2.Mesh access point (MAP) 3.Mesh portal (MPP)

4. www.themegallery.com 4 Introduction (ii)  An MPP is a gateway point at which a WLAN mesh sends or receives frames to or from other non-mesh networks.  In fact, a traditional bridge as defined in IEEE 802.1D standard will consider a WLAN mesh as a single network segment; thus allowing only one port to access this segment so that broadcast loops can be avoided.  With the use of multiple MPPs on the same LAN segment, the network load can be shared among many MPPs (load balancing) and the network reliability can be increased.

5. www.themegallery.com 5 Introduction (iii)  The path through the port which was left open may not be the best one for forwarding frames between some of the nodes in the mesh and the external network, thus resulting in unnecessary delays and reduced throughput.  The best solution will be to allow the use of multiple MPPs simultaneously for load balancing and provide an algorithm for broadcast loops prevention.

6. www.themegallery.com 6 Interworking with External LANs through Multiple Portals (i)  We consider various network topology scenarios, where the source and destination can be either inside or outside the mesh network with a possibility of both nodes being on separate wired LANs.  Whatever be the topology scenario, when a communication from source to destination is through MPP(s), there are two possible cases: 1.The right MPP is known and then frames are delivered via unicast through the MPP(s). 2.The right MPPs are not known and frames are sent to all MPPs, including those connected to the same wired LAN segment.

7. www.themegallery.com 7 Interworking with External LANs through Multiple Portals (ii)  The latter case is more likely to cause broadcast loops as a frame from the mesh network via one MPP may come back to the mesh through another MPP and keep bouncing back and forth to the non-mesh network as shown by dotted lines in Fig. 1.

8. www.themegallery.com 8 Fig.1

9. www.themegallery.com 9 Interworking with External LANs through Multiple Portals (iii)  Broadcast loops will be created if the MPP simply broadcasts all frames with unknown destination address without considering the frame contents and without the blocking function as normally done through the STP.  A mesh data frame - when transmitted between neighbor MPs - contains a "Mesh Header" field as shown in Fig. 2,which is inspected during the frame filtering process.

10. www.themegallery.com 10 Interworking with External LANs through Multiple Portals (iii)  To prevent the formation of broadcast loops, the following additional information is needed during the frame filtering process: 1.5-bit Bridged LAN segment identification (LAN_ID) 2.5-bit MPP identification (MPP_ID) in every frame forwarded by an MPP to the mesh network. When a frame is internally generated, the MPP_ID value is set to all zero's which is also a default value.  The new PANN element format is shown in Fig. 3 with a 5-bit LAN_ID we introduce. The 5 bits were taken from the flags field, making a maximum capacity of 32 LAN segments to be attached to the mesh network.

11. www.themegallery.com 11 Interworking with External LANs through Multiple Portals (iv)  As for MPP identification, the "Mesh header" field in the Mesh data frame is modified in order to include the portal identification of the MPP which forwards the concerned frame as shown in Fig. 4.

12. www.themegallery.com 12 Interworking with External LANs through Multiple Portals (v)  Every MP will build a table containing the following information: 1.MPP_IDs of all MPPs for which it received PANNs 2.Link cost to MPPs 3.Corresponding LAN_ID for each MPP-LAN segment pair, i.e., the LAN segment which a particular MPP is connected to.

13. www.themegallery.com 13 Interworking with External LANs through Multiple Portals (vi)  When a frame originating from an external LAN reaches an MPP, the MPP_ID will be copied into the "Mesh Header“ field.  There are two possible destinations: 1.If the frame destination address is inside the mesh network,the MP will do the path selection and forwarding for the frame to reach the final destination. 2.If the frame destination address is not known, the MP will forward the frame to all one hop nodes excluding MPPs which are attached to the same LAN segment as the one from which the frame originates.

14. www.themegallery.com 14 Interworking with External LANs through Multiple Portals (vii)  The frame filtering process at MPPs for loop avoidance is described by the flowchart shown in Fig. 5.

15. www.themegallery.com 15 Interworking Examples (i)  We illustrate how the proposed frame filtering process with the new fields enables multiple MPPs in interworking with external LANs through several examples for various network topologies.  We assume the following for the examples considered in this section: 1.The frame filtering process prevents frame forwarding to/from MPPs on the same LAN segment. 2.Interportal communication procedures are triggered by an MPP when receiving a new unicast data frame from either MP or MPP.

16. www.themegallery.com 16 Interworking Examples (ii) 3.In case a destination node is outside the mesh network,its address has been learned by all MPPs connected to the same LAN segment through the learning process of bridging functionality.

17. www.themegallery.com 17 External Source and Internal Destination  In an interworking scenario involving an external source node and an internal destination node as shown in Fig. 6

18. www.themegallery.com 18 Internal Source and External Destination  In this scenario a source node inside the mesh network communicates with a destination outside the mesh network,as shown in Fig. 7.

19. www.themegallery.com 19 External Source and External Destination  In this scenario, both the source and destination are connected to the wired networks, but they communicate via the wireless mesh network. Fig. 8 shows such a scenario involving multiple portals on each wired LAN segment.

20. www.themegallery.com 20 Summary  We suggested a frame filtering process at MPPs which is based on new portal and LAN segment identifications introduced in the mesh header and the PANN element, respectively.  This filtering process can detect and discard frames that have already been forwarded by an MPP on the same LAN segment, thus avoiding looping but ensuring the use of multiple MPPs on the same LAN segment.  This can improve the network reliability and overall performance.