Fisheye State Routing (FSR) - Protocol Overview


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Overview of the Fisheye State Routing (FSR) for cellular networks, IDC 2012
By Yoav Francis and Nir Solomon

(Part of a performance comparison of various routing algorithms in cellular networks)

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  • גם node שעוזב את הרשת וכו '
  • Proactive – always know network topology, always know network topology and best send method Requires storage at every node for the routing table, a lot of overhead of update packets – more than data itsself. Reactive (on demend)– do the search for route only when need to find a route. Storage is small, no need to hold topology, less overhead. Route search time is long.
  • Link state = Network Topology (“State of the link”) Distance Vector = Only hold the next hop for each node and the cost (hop distance), not entire/partial network topology. Like a router. Distance – as in number of hops Problem : we may take a “worse” route that indeed has less hops but takes longer than passing through multi-hop route.
  • 2 From UCLA, one from Bell Labs. ICDCS = I nternational Workshop on Wireless Networks and Mobile Computing
  • We only transfer to our close neighbors, every x time. What shall we pass ? Which nodes are in the update ? - as the distance from our node increases, we will update the information regarding those nodes in less frequency than closer ones. - this will cause the update packets size to be smaller + less update packets will be sent (we will only send update packets every x-time) - בעצם , נשלח חלקים מן המידע ולא את כל הטבלה , בהתאם למרחק מן הצומת
  • Neighbor list – all nodes in distance of one hop Topology table – the “link state” (neighbor list) – I save at my node the list of the nodes that every node sees Next hop table / distance table – tables that are computed with shortest path (dijkstra) – each time an update occurs, an algorithm runs that finds the shortest path from our node to every node that was contained in the update. Change exchange periods – in every update packet we send, we choose which nodes to put in our update packet – depending on the frequency and nodes the distance (so, close nodes will be sent an update every x time, far nodes will be sent an update every 2x time, etc.)
  • Central Node = working node (my node) I update ONLY the green nodes. What will be contained in the update – this is something else. תלוי מימוש – T הוא לבחירת המממש וכן זה לא חייב להיות 2 , וגם אפשר להגיד שעד מרחק 5 אני גם מעדכן כל 2T למשל.
  • (בציור) הלבנים – הם באותו scope כי בשניהם המרחק גדול מ- 2 . ככל שצמתים מתרחקים – המידע שיש לנו עליהם הוא פחות עדכני – יכול להיות שבטרם קיבלנו עדכון הטופולוגיה השתנתה, node עזב, התרחק וכו'. תדירות העדכון היא ביחס הפוך למרחק. ככל שהפקטה מתקרבת ליעד, ה- Routing הופך ליותר מדויק (כי כל node יודע במדויק את ה- routing אל ה- nodes הקרובים)
  • Node אפס רואה את 1 , ויש לו הופ 1 אליו – זה מה שבעצם רואים בטבלה. הטבלה של כל node מחזיקה את כל הטופולוגיה. ( LST הוא טבלת הטופולוגיה)
  • סימולציה מן המאמר – מראה שה- overhead אם יש רק סקופ 1 – link state רגיל. ככל שמס' ה- nodes גדלים , מקטינים את ה- accuracy מעט אך יורד ה- overhead – בעצם בציור רואים שככל שמגדילים את ה- scopes (בהינתן אותו מספר' nodes ) – התקורה הכוללת במערכת הולכת וקטנה, כמובן על חשבון accuracy .
  • LINK STATE = טופולוגית הרשת גודל טבלת ה- route – לא scalable מבחינת הסטורג' (כי הוא מכיר את כל ה- nodes ושומר אותם. כאשר יש המון nodes מדובר לשמור את כל הקשרים וכל ה- nodes - הרבה storage )
  • Fisheye State Routing (FSR) - Protocol Overview

    1. 1. Fisheye State Routing Protocol Overview By: Nir Solomon Yoav Francis Interdisciplinary Center, Herzliya
    2. 2. Ad-Hoc Network A wireless network between mobile nodes No infrastructure Limited communication distance Low-powered users How to route messages? Flooding/Broadcast Not scalable Using the shortest path from source to destination Requires nodes to keep topology data
    3. 3. Ad-Hoc Network (cont.) Node moves cause network topology changes Results in routes change Nodes need to update their topology information A node disconnecting to or from a neighbor needs to notify other nodes There are many upates – must make update process efficient Low overhead Fast propagation
    4. 4. Ad-Hoc Routing algorithms  Proactive:  Always monitor network topology  Advantage: Always know how to route to any node  Disadvantages: Routing table storage Periodic control traffic overhead  Example protocols: LSR, FSR  Reactive:  Look for a route only when need to send a packet  Advantages: Low routing table storage No periodic control traffic  Disadvantage: route search overhead  Example protocols: TORA, DSR
    5. 5. Link State Routing Each node holds a routing table with the link state of all nodes in the network Periodically or on link change: flood “link state” – list of neighbors (neighbor = 1 hop) Re-broadcasts link state information received from neighbors Use timestamp to distinguish new from stale updates Routing The destination is stored in the message header Each forwarding node finds the shortest path to the destination according to its routing table  On each update of the topology map – each node must calculate the shortest path to all other nodes again.
    6. 6. Link State Routing drawbacks As the number of nodes grow or mobility increases: Routing tables grow linearly Link state overhead grow linearly – the overhead packets will consume most of the bandwidth as network size increases. Not scalable
    7. 7. • Fish do have 360° (or almost) vision. • Fishes (and humans) do have a higher concentration of optic nerves close to they focal point than elsewhere in they eye. • As a result fisheye captures with high detail the points near the focal point Fisheye Vision
    8. 8. Fisheye Vision (Cont.)
    9. 9. Published in “Fisheye State Routing in Mobile Ad Hoc Networks” in 2000, by Guangyu Pei , Mario Gerla , Tsu-Wei Chen at ICDCS. Aim – Reduce routing updates overhead in large ad-hoc networks. Background
    10. 10. Fisheye State Routing (FSR) • Proactive link-state routing protocol. • Similar to link state as it maintains a full topology map at each node – Periodic exchange of Hello packet. – Periodic exchange of topology tables within the local neighbors only (instead of flooding the entire network) . • Topology tables update frequency decreases with distance to destination – Updates for a near destination are propagated more frequently then updates for a remote destination
    11. 11. Fisheye State Routing (Cont.) Every node holds:  Neighbor list  Topology Table  Next Hop Table  Distance Table For large network, in order to reduce the size of the routing update message, the FSR technique uses different exchange periods for different entries in the routing table. Relative to each node, the network is divided into different scopes.
    12. 12. Fisheye State Routing (Cont.) Central Node 1-hop neighbor 2-hops or more neighbor The link state updates of the nodes in scope k are sent every 2k-1 T to all the neighboring nodes •K is the hop distance •T is the link state updates transmission period Scope 1 Scope 2
    13. 13. Fisheye State Routing (Cont.)  Maintain accurate routing information for immediate neighbors.  Progressively less detail as distance increases.  Link state of immediate neighbors are exchanged more frequently.  The exchange frequency decreases proportionally to the distance.  As the packet gets closer to the destination, the accuracy increases.
    14. 14. Fisheye State Routing 0 5 1 2 4 3 0:{1} 1:{0,2,3} 2:{5,1,4} 3:{1,4} 4:{5,2,3} 5:{2,4} 1 0 1 1 2 2 LST HOP 0:{1} 1:{0,2,3} 2:{5,1,4} 3:{1,4} 4:{5,2,3} 5:{2,4} 2 1 2 0 1 2 LST HOP 0:{1} 1:{0,2,3} 2:{5,1,4} 3:{1,4} 4:{5,2,3} 5:{2,4} 2 2 1 1 0 1 LST HOP Entries in black are exchanged more frequently
    15. 15. Simulation Results
    16. 16. FSR – Conclusions  Major scalability benefit: link state overhead decreases significantly  Unsolved problems: Route table size still grows linearly with network size Out of date routes to remote destinations
    17. 17. Our Project
    18. 18. Questions? Thanks!