Wireless Internet Routing. IEEE s

Transcription

1 Wireless Internet Routing IEEE s 1

2 Acknowledgments Cigdem Sengul, Deutsche Telekom Laboratories 2

3 Outline Introduction Interworking Topology discovery Routing 3

4 IEEE a/b/g /n /s IEEE s: draft IEEE amendment for mesh networking o How to interconnect wireless devices to create an ad-hoc network o Draft 3.0 as of March

5 What is the current picture? 5

6 Removing the paradox 6

7 Zooming in s architecture Device classes o Mesh point (MP) o Establishes peer links with MP neighbors o Mesh access point (MAP) o MP + AP functionality o Mesh portal (MPP) o Gateway o Station (STA) STA MP AP External Network Portal MP STA Mesh Portal Station STA Mesh Point MP AP MP Mesh AP STA 7

8 What is the target? Unmanaged WLAN mesh networks Enabling interoperability with low complexity Internal behavior is transparent to higher layers 8

9 IEEE s LAN metaphor, bridging support Single-hop/multihop neighbor discovery, Extensible path selection & forwarding Mesh Interworking with other 802 networks Mesh Topology Learning, Routing & Forwarding Mesh Security Medium Access Coordination Discovery & Association Mesh Measurement MAC enhancements i link security based service integration Mesh Configuration & Management PHYs Unmanaged, autonomic management Legacy a/b/g/n 9

10 Goal of s Interworking Achieving LAN segment behavior Through mesh o Broadcast LAN (transparent forwarding) o Overhearing of packets (bridge learning) o Support for bridge to bridge communications (Mesh portals being a part of the spanning tree protocol) 10

11 802.11s Interworking: How? Need to determine if the destination is inside or outside the mesh Inside mesh o Layer-2 mesh path discovery/forwarding Outside mesh o Which MPP is the right one? o If known, unicast to this node o If unknown, send to all MPPs 11

12 Topology discovery Mesh Points o Passive scanning o Periodic beacons o Active scanning o Probes o Look for matching profiles o (Mesh ID, Path Selection Protocol ID, Link Metric ID) o Membership is determined by secure peer links with neighbors X Mesh Identifier: Mesh 1 Mesh Profile: (HWMP, airtime metric) Capabilities: Path Selection: HWMP, Metrics: airtime, latency

13 IEEE s Topology Multi-radio support o Each MP may have one or more logical radio interface o Each interface belongs to one Unified Channel Graph 13

14 Channel Selection Simple channel unification mode o Follow rules to coalesce into a common, fully connected graph on one channel Advanced mode (multi-radio, multi-channel) o Multi-radio capability creates alternative paths o Framework for flexible channel selection algorithms beyond the standard scope 14

15 802.11s Routing Optimizations for unicast traffic Might support for multicast/broadcast s Routing o Layer-2 routing based on MAC addresses o HWMP o Hybrid Wireless Mesh Protocol o Default routing protocol o RA-OLSR o Radio-Aware Optimized Link State Routing o Optional routing protocol 15

16 HWMP - Routing Typical routing categorization o On-demand Routing o Discover routes only when they are needed o Pros: Low routing overhead o Cons: Extra route discovery delay and data buffering o Proactive Routing HWMP o Each node maintains routes to all reachable destinations at all times o Pros: Low delay o Cons: High routing overhead o Combines the advantages of on-demand and proactive routing 16

17 HWMP Link Metric Airtime Others are possible o Power-aware, load-balancing, QOs c a = O ca + O p + B t 1 r 1 e r: link bit rate e pt : frame error rate pt Parameter Value (802.11a) Value (802.11b) Description O ca 75 s 335 s Channel access overhead (depends on PHY) O p 110 s 364 s Protocol overhead B t Number of bits in test frame 17

18 Link Metric Example 48Mb/s, 10% PER 54Mb/s, 8% PER 12Mb/s, 10% PER 54Mb/s, 2% PER 54Mb/s, 2% PER 48Mb/s, 10% PER This path having the minimum airtime cost is the Best! 18

19 HWMP - Details On-demand route discovery o Used in intra-mesh routing for routing optimizations o Radio Metric AODV (RM-AODV) RFC 3561 Proactive routing o Used when a root portal (MPP) is present o Tree-based routing 19

20 HWMP On-demand Main idea (very similar to AODV) o Route discovery o Reverse paths set up by path requests (broadcast/unicast) o Path replies are sent unicast by destination or the intermediate nodes 20

21 HWMP On-demand: Algorithm Source broadcasts PREQ (path request) o the destination and metric initialized Upon receiving PREQ, MPs o update the path to source o if sequence number is greater and offers a better metric o May forward PREQ o If a new path is created or the existing one is modified Target Only and Reply and Forward Flags o If TO=1 o Only destination sends PREP (path reply) o If TO=0 and RF =0 o Intermediate node with path sends a unicast PREP to the source MP and does not forward PREQ o If TO=0 and RF =1 o The first intermediate node with the path to the destination sends a PREP and forwards PREQ setting TO =1 to avoid other intermediate nodes to send back PREP 21

22 HWMP On-demand Loop freedom o Supported by using a destination sequence number Route maintanence o When a link error is detected, a route error is sent by unicast o Route errors are rate-controlled 22

23 HWMP Tree-based routing Proactive RREQ mechanism o Root issues a broadcast RREQ (Route request) o MPs may respond with unicast RREP (Route reply) o 2-way handshaking Proactive RANN mechanism o Root issues a broadcast Root announcement o MP responds with a RREQ o Root responds with a RREP o 3-way handshaking 23

24 Proactive RREQ Mechanism The root MP periodically propagates a PREQ into the network o o Destination address set to all 1s TO=1 and RF=1 Upon reception of a PREQ, each MP has to create or refresh a path to the root MP o o Proactive PREP = 0, MP may send a proactive PREP if required Proactive PREP =1, MP shall send a proactive PREP 24

25 HWMP Tree-based routing Tree maintanence o MPPs monitor the root and take over if the root fails (Root arbitration) o MPs monitor upstream links and may switch to back up links o o RERRs sent for failing links o Downstream nodes o May select their own back up paths o AODV path holders 25

26 HWMP Example 1 On-demand path setup to inside of the mesh MP4 MP9 o MP4 sends a RREQ o MP9 sends back a RREP 26

27 HWMP Example 2 On-demand set up to outside mesh MP4 X o MP4 does not have a route o Broadcasts a RREQ o MP4 does not receive a response o MP4 directs messages for X to MP1 o MP1 sends to X 27

28 HWMP- Example 3 Routing through root to outside of mesh MP4-X o MP4 learns MP1 via Root announcement messages o MP4 sends to MP1 o MP1 sends to X 28

29 HWMP Example 4 Routing through root to inside of the mesh MP4 MP9 o MP4 sends to MP1 o MP1 knows MP9 is inside the mesh o Forwards to MP9 o MP9 may send a RREQ to MP4 to discover a shorter path 29

30 Radio Aware OLSR Optional Proactive o Changes in the link state are advertised to neighbors Works like o OLSR o (Optional) FSR (Fisheye State Routing) 30

31 RA-OLSR Key Concepts Multi-point relays (MPRs) o Cover 2-hop neighborhood o Only MPRs send updates o Message reduction in space Link state reduction (optional) o Main idea o Farther away nodes are updated with less frequency o Message reduction in time 31

32 Addressing for Data Forwarding 6-Address scheme 32

33 Addressing Example 1 33

34 Addressing Example 2 34

35 IEEE s Summary Question o What does IEEE s provide? Answer o It fills the gray boxes in the picture 35

36 1 st IEEE s implementation One Laptop per Child All open source o Mesh code available Partially implements IEEE s o HWMP without treebased routing o Operates simultaneously as mesh point and station 36