Gateway Forwarding Strategies in Ad hoc Networks ADHOC04, - - PowerPoint PPT Presentation

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Gateway Forwarding Strategies in Ad hoc Networks ADHOC04, - - PowerPoint PPT Presentation

Dec 11, 2022 47 likes •209 views

Gateway Forwarding Strategies in Ad hoc Networks ADHOC04, Johannesberg Erik Nordstr om, Per Gunningberg IT department, Uppsala University Christian Tschudin CS Department, University of Basel The story so far. . . Ad hoc Mobile

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SLIDE 1

Gateway Forwarding Strategies in Ad hoc Networks

ADHOC’04, Johannesberg

Erik Nordstr¨

  • m, Per Gunningberg

IT department, Uppsala University

Christian Tschudin

CS Department, University of Basel

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SLIDE 2

The story so far. . .

Ad hoc ≈ Mobile Multi-hop Wireless Networking IETF started MANET (Mobile Ad hoc NETworks) working group on ad hoc routing in 1995/96. Since then:

  • Four routing protocols going for RFC status (AODV, OLSR,

DSR, TBRPF)

  • AODV implementations ≈ 10
  • Zero deployment

One explanation: No Internet integration

c Erik Nordstr¨

  • m, Uppsala University

ADHOC’04, Johannesberg 2/16

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SLIDE 3

Common MANET Internet connectivity scenarios

  • Extending the reach of wireless LANs
  • Disaster area rescue drones with connection to rescue central
  • Military units communicating with headquarters

– Uppsala students are building rescue robots with ad hoc routing for participation in Robocup.

c Erik Nordstr¨

  • m, Uppsala University

ADHOC’04, Johannesberg 3/16

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SLIDE 4

So what has gone wrong?

Internet and ad hoc networks are very different:

  • Hierarchical vs. Flat addressing and routing
  • Fixed vs. Mobile (macro and micro mobility)

For Internet connectivity many suggest Mobile IP (MIP).

  • It is only half the solution (solves macro mobility)
  • Provides topologically correct (care-of) addresses
  • Operates (mainly) at gateways towards the Internet (i.e., MIP

does not really matter until packets reach the gateway)

c Erik Nordstr¨

  • m, Uppsala University

ADHOC’04, Johannesberg 4/16

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SLIDE 5

Example of an Internet connected ad hoc network

Combining Ad hoc Networking with MIP connectivity:

  • Computers are mobile and use their home

addresses

  • Multiple gateways (MIP agents, FA, HA) to

the Internet

  • Multi-hop paths to gateways

130.238.12.5 63.3.5.23 142.67.8.245 10.0.4.2 130.238.12.1 192.168.6.1 65.43.32.1 66.35.250.151 192.168.1.1 130.238.8.1

MIP Tunnel

HA FA MN

Internet

How do we stitch all this together?

c Erik Nordstr¨

  • m, Uppsala University

ADHOC’04, Johannesberg 5/16

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SLIDE 6

Challenges

  • Gateways have to be discovered and self-configured at nodes
  • Gateway changes have to be trackable so that MIP can

re-register (otherwise return traffic is lost)

  • For smooth operation, hand-over and multi-homing might be

beneficial (i.e., we must support connectivity to more than one gateway at once)

  • Efficient integration with the routing protocol is important (for

example, mixing proactive gateway discovery with reactive routing does not make sense)

c Erik Nordstr¨

  • m, Uppsala University

ADHOC’04, Johannesberg 6/16

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SLIDE 7

Our contribution

A lot of Previous Work on:

  • Address configuration
  • Gateway discovery (efficiency in gateway advertisements)

Our complementary work is a comparison of different gateway forwarding strategies:

  • Default routes – one generic path to a gateway for all external

(Internet) destinations.

  • Tunneling – temporary replace the destination address with the

gateway address

c Erik Nordstr¨

  • m, Uppsala University

ADHOC’04, Johannesberg 7/16

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SLIDE 8

Default Routes – Routing Tables

Destination Next Hop Hop Cnt default 3 66.35.250.151 192.168.1.1 63.3.5.23 63.3.5.23 63.3.5.23 default 192.168.1.1 _ 3 1 (b) Destination Next Hop Hop Cnt 63.3.5.23 63.3.5.23 66.35.250.151 default default 63.3.5.23 1 _ 3 (a)

a) we need host state (to avoid subsequent route lookups on source and intermediate nodes). . . b) but also a gateway route to track gateways (Globalv6 proposal)

  • as much as three routing table lookups might be necessary

(host→default→gateway/next hop)

c Erik Nordstr¨

  • m, Uppsala University

ADHOC’04, Johannesberg 8/16

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SLIDE 9

Default Routes – State Replication Problem

Extra routing table state (host, gateway, default route) introduces problems:

  • states (e.g., SA) must be replicated on intermediate nodes
  • how do we handle repairs or route optimizations?

SA SA SA SA SA A B C A B GW GW C D D (b) (a)

c Erik Nordstr¨

  • m, Uppsala University

ADHOC’04, Johannesberg 9/16

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SLIDE 10

Default Routes – Gateway Tracking Problem

A default route might not stay consistent along a hop by hop path when there are multiple gateways

  • Breaks two-way communication (e.g., TCP)

GW2

A B C

RREP GW1 GW2

A B C

mismatch GW1 GW2

A B C

Default route pointing to GW1 Default route pointing to GW2

RREQ GW1

c Erik Nordstr¨

  • m, Uppsala University

ADHOC’04, Johannesberg 10/16

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SLIDE 11

Tunneling – Routing Tables

Next Hop Hop Count Flags Destination Next Hop Hop Count Flags Destination Next Hop Hop Count Flags Destination

Internet

66.35.250.151 192.168.1.1 63.3.5.23 63.3.5.23 1 1 3 G I 192.168.4.3 63.3.5.23 192.168.1.1 65.3.5.23 63.3.5.23 192.168.1.1 2 1 1 192.168.4.3 192.168.4.3 65.43.32.1 65.43.32.1 192.168.1.1 65.43.32.1 1 1 2 192.168.4.3 65.43.32.1 65.43.32.1 65.43.32.1 3 1 Flags Hop Count Next Hop Destination 63.3.5.23 192.168.1.1

66.35.250.151 63.3.5.23 130.238.12.5

Ad hoc src node

192.168.1.1 130.238.8.1

Gateway

Tunnel

Encapsulation 63.42.32.1 Decapsulation

  • Gateways addressed in packets – not in nodes (some overhead)
  • No extra state at intermediate nodes – only a gateway route
  • Can be done one-way to gateway only

c Erik Nordstr¨

  • m, Uppsala University

ADHOC’04, Johannesberg 11/16

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SLIDE 12

Tunneling – Benefits

  • Protocol transparency
  • Route aggregation
  • Stability (no gateway tracking problem)
  • Multiple gateways (multi-homing, load-balancing, hand-over)

(a) (b) (c)

Figure 1: (a) Default route. (b) & (c) Tunnel configurations.

c Erik Nordstr¨

  • m, Uppsala University

ADHOC’04, Johannesberg 12/16

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SLIDE 13

Comparison

ns-2 simulations with:

  • Two gateways, 10 - 20 mobile nodes, fixed density
  • Tunneling to gateways
  • Globalv6-draft style default routes
  • Modified default routes – A reference implementation that

forwards all traffic on a default route, ignoring host route state (we have no traffic among ad hoc nodes)

c Erik Nordstr¨

  • m, Uppsala University

ADHOC’04, Johannesberg 13/16

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SLIDE 14

Some simulation results – CBR Traffic (UDP)

70 75 80 85 90 95 100 8 10 12 14 16 18 20 CBR Delivery ratio (%) Number of nodes Tunneling Default routes Default routes mod. 2 4 6 8 10 12 8 10 12 14 16 18 20 Control traffic / data (%) Number of mobile nodes Tunneling Default routes Default routes mod.

  • Default routes have state replication problems – ignoring state

helps

c Erik Nordstr¨

  • m, Uppsala University

ADHOC’04, Johannesberg 14/16

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SLIDE 15

Some simulation results – TCP Traffic (FTP)

0.1 0.2 0.3 0.4 8 10 12 14 16 18 20 TCP Throughput (Mbps) Number of nodes Tunneling Default routes Default routes mod. 1 2 3 4 5 6 7 8 9 10 8 10 12 14 16 18 20 Control traffic / data (%) Number of mobile nodes Tunneling Default routes Default routes mod.

  • With TCP we also need to track gateways – ignoring state does

not help as much here

c Erik Nordstr¨

  • m, Uppsala University

ADHOC’04, Johannesberg 15/16

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SLIDE 16

Conclusions

Internet connectivity is critical for MANET deployment. Our comparison shows:

  • The default route concept does not transfer well to MANETs
  • Default routes operate incorrectly with multiple gateways
  • Tunneling is efficient, simple, transparent and works with

multiple gateways at the cost of a small overhead We will demo ad hoc network Internet connectivity today!

c Erik Nordstr¨

  • m, Uppsala University

ADHOC’04, Johannesberg 16/16