1. IP Mobility & Ad-hoc Network Routing

2. Mobile IP Optimizations
Route optimization
Smooth hand-offs

3. Route Optimizations
Enable direct notification of the corresponding host
Direct tunneling from the corresponding host to the mobile host
Binding cache maintained at corresponding host
Management of cache not stipulated (e.g. least used entry replacement)

4. Route optimizations (contd.)
4 types of messages
Binding update
Binding request
Binding warning
Binding acknowledge

5. Binding Update
When a home agent receives a packet to be tunneled to a mobile host, it sends a binding update message to the corresponding host
When a home agent receives a binding request message, it replies with a binding update message
Also used in the the smooth-handoffs optimization

6. Binding Update (Contd.)
Corresponding host caches binding and uses it for tunneling subsequent packets
Lifetime of binding?
Corresponding host that perceives a near-expiry can choose to ask for a binding confirmation using the binding request message
Home agent can choose to ask for an acknowledgement to which a corresponding host has to reply with a binding ack message

7. Binding update (problem?)
What happens when a mobile host moves?

8. Binding warning
When a foreign agent receives a tunneled message, but sees no visitor entry for the mobile host, it generates a binding warning message to the appropriate home agent
When a home agent receives a warning, it issues an update message to the corresponding host
What if the foreign agent does not have the home agent address (why?) ?

9. Illustration Home Agent BU BW BR BA Foreign Agent Corresponding Host
Mobile Host

10. Smooth Hand-offs
When a mobile host moves from one foreign agent to another …
Packets in flight to the old FA are lost and are expected to be recovered through higher layer protocols (e.g. TCP)
How can these packets be saved?

11. Smooth Hand-offs Make previous FA forward packets to the new FA
Send binding updates to the old FA through the new FA
Such forwarding will be done for a pre-specified amount of time (registration lifetime)
Update can also help old FA free any reserved resources immediately
Why better?

12. Mobile IP in IPv6
Route optimization and smooth hand-offs used in IPv6 mobility
Binding updates easier since IPv6 supports destination caches at sources
IPv6 security inherently stronger than in IPv4. Hence, no explicit security mechanisms needed for mobile IP
Source routing to be used instead of encapsulation (why?)

13. Recap Mobile IP problems Mobile IP Optimizations
Mobility support in IPv6

14. Outline Multicast-based architecture Fast handoffs MosquitoNet
End-to-end approach

15. Multicast-based Architecture
Very different from the mobile-IP model
Based on the IP-multicast approach
Leverages the similarities in the two problems (multicast and mobility)
Minor modifications to IP-multicast required

16. Multicast
Multicast: group membership, packets sent to a multicast address have to be delivered to all members of the group
Members of a multicast group can be located “anywhere”
IP-multicast infrastructure is overlayed on the Internet (construction of infrastructure a separate problem by itself – DVMRP, CBT, etc.)
Forwarding of data happens on the overlayed infrastructure, and routing is group specific

17. Multicast (Illustration)
Tunnels

18. Multicast & Mobility CH Tunnels
Use IP-multicasting to support mobility!

19. MSM-IP Architecture MSM-IP: Mobility support using Multicasting in IP
Addressing: mobile host has multicast address
Tunneling architecture: same as IP multicast (sparse mode algorithm required)
Join and prune mechanisms: hand-offs made more efficient
Resource reservation (RSVP) easier

20. Problems? ARP replies TCP support IGMP registration
ICMP message delivery
Multicast address space
IP-multicast maturity

21. Fast Handoffs
Reduce the latency in resuming operations when a hand-off occurs
Use hierarchical foreign agents
Example: domain foreign agents and subnet foreign agents
Mobility within a domain kept transparent from the home agent by appropriate interactions between domain foreign agent and subnet foreign agents

22. Fast Handoffs (Illustration)
Internetwork FA
Subnet A
Subnet B FA FA

23. MosquitoNet One of the first test-bed implementations of Mobile IP
Introduced the notion of co-located foreign agents
Improves deployability of the mobile-IP approach to support host mobility
Trade-offs?

24. End-to-End Approach
Internet infrastructure does not change (like in mobile IP)
Changes required at both the sender and receiver
Does connection migration when mobile-host moves

25. E2E Approach (Contd.)
Hostname used as the invariant to identify mobile host
Mobile host uses DNS updates to change hostname to IP address mapping
No consistency problem as DNS entries can be made un-cacheable
If client is mobile, DNS-support not used

26. E2E Approach (Contd.)
When a mobile-host undergoes a handoff, it re-issues a SYN (with a MIGRATE option identifying the previous connection)
A unique token exchanged during initial connection set-up used to identify connection
The receiver of the SYN changes its state to represent the new address of the mobile-host
Connection proceeds as a regular TCP connection from thereon
Trade-offs?

27. Ad-hoc Networks
Infrastructure-less wireless networks dynamically formed using only mobile hosts (no routers)
Network topology dynamic as all hosts are mobile!
Mobile hosts themselves double up as routers!!
Multi-hop paths …
Highly resource constrained
Extreme case of network mobility…

28. Applications … Military – digital battlefield Disaster relief
Sensor networks
Areas with no cellular coverage

29. Illustration A B C D

30. Routing Protocols Proactive approaches Reactive approaches
DSDV (destination sequenced distance vector), LSR (link state routing), OLSR (optimized link state routing)
Reactive approaches
DSR (dynamic source routing), AODV (ad-hoc on-demand distance vector)
Hybrid approaches
ZRP (zone routing protocol), CEDAR (Core extraction distributed ad-hoc routing)

31. Proactive routing protocols…
Unsuitable for such a dynamic n/w
For example, consider link-state routing that sends out network-wide floods for every link-state change …
Even in the absence of any existing connections, considerable overhead spent in maintaining “network state”

32. Goals Low overhead route computation
Ability to recover from frequent failures at low-cost
Scalable (with respect to mobility and number of hosts)
Robust

33. Reactive (On-demand) protocols
Compute routes only when needed
Even if network state changes, any re-computation done only when any existing connections are affected
Example:
Dynamic source routing (DSR)
Ad-hoc On-demand Distance Vector (AODV)

34. Dynamic Source Routing
Based on source routing
On-demand
Route computation performed on a per-connection basis
Source, after route computation, appends each packet with a source-route
Intermediate hosts forward packet based on source route

35. DSR – Basic Operation
When higher layer gives DSR a packet to transmit, and there exists no route in the route-cache, route computation is performed
Source S floods the network with a RREQ (route request) packet for the destination D
Every host I that receives the RREQ packet checks to see if I=D. If not, I adds its identifier to the RREQ packet header and forwards the packet

36. DSR – Basic Operation (contd.)
Each forward is a local broadcast (unlike in a wireline network where a flood would entail multiple local transmissions)
When D receives packet, the RREQ message contains the list of identifiers it traversed through
D responds to the sender S with an RREP (route reply) message containing the route in the RREQ – How?

37. DSR – RREP propagation
If MAC layer assumes bi-directionality (e.g.?), D has to use the same route (reversed) that is being conveyed to S
If not, and if network can have asymmetric links (why?), D has to use an explicitly computed route from D to S
Infinite loop possible?

38. DSR (Contd.)
When S receives the RREP message, it starts using it from thereon
Every packet from S to D has the route in its header
Intermediate hosts merely forward based on the source route

39. DSR – Route Maintenance
Consider path S-X-Y-Z-D
Let Y-Z link break (why?)
Y initiates a route error (RERR) message back to S conveying the link failure
When S receives the RERR, it switches to an alternate route (or re-issues another RREQ if none available)

40. Additional Mechanisms - 1
Caching overheard routes
Every host caches routes that it overhears (how?)
Such routes are later used if needed
Cached routes also used in the next mechanism

41. Additional Mechanisms - 2
Replying to route requests using cached routes
When an intermediate host I receives a route request for D, and has a cached route for D, it replies to the source with the cached route+the route thus far from S-I
Reduces route computation latency
Provides source with multiple route options
Cons?

42. Additional Mechanisms - 3
Preventing route reply storms
Too many route replies can be generated if reply-from-cache is enabled
Each node waits for a period t (proportional to the hop-count of cached path) before it replies
Reply suppressed if source starts using new route

43. Additional Mechanisms - 4
Expanding ring search
Instead of network wide flood, send RREQ with TTL=1
If no reply, send RREQ with TTL=2, and so on …
Reduces route computation overhead
Trade-offs?

44. Additional Mechanisms - 5
Packet salvaging
If Y-Z fails in S-X-Y-Z-D, Y sends back RERR
Y also tries to salvage packets by using any cached route it might have for D

45. Additional Mechanisms - 6
Route shortening
Consider path S-X-Y-Z-D
If Y moves within range of S (and still remains connected to Z & D), Y issues an unsolicited route reply to S conveying shorter route (S-Y-Z-D)

46. AODV Ad-hoc on-demand distance vector
Hop-by-hop routing as opposed to source routing
On-demand
When RREQ propagates, routing tables updated at intermediate nodes (for route to source of RREQ)
When RREP is sent by destination, routing tables updated at intermediate nodes (for route to destination), and propagated back to source
Trade-offs?

47. Comparison Link state Local Low maintenance overhead
Low update overhead
High access overhead
Dynamic networks
Local
Low maintenance overhead
Low access overhead
High update overhead
Static networks
Link state

48. Broadcast Storms
When a packet is flooded in an ad-hoc network, the flood is performed through a series of local broadcasts
A series of local broadcasts results in the broadcast storm problem
Broadcast storms result in lowered throughput performance or utilization

49. Broadcast storms (contd.)
When C Forwards the flood message:
Redundant transmissions
41% additional (useful) coverage for first time re-broadcast
19% for second time
Contention with other neighbors
Collisions with transmissions of neighbors A B C D E

50. Virtual Infrastructure to Solve Broadcast Storms - CEDAR
Extract a subset of the nodes in the network to perform state management: The CORE
Support an efficient and low-cost flooding protocol for the core that avoids the broadcast storm problem: The Core Broadcast mechanism
Support a novel state propagation mechanism that uses the core broadcast: The WAVES based State Propagation

51. The Core Approximates the minimum dominating set of the network
“minimum”  small number of core nodes
dominating set  low update and access overhead
Self configuring mesh structure
mesh  robust (unlike a tree or the spine)
self-configuring  adaptive to topology change

52. The Core: Illustration
CHANNELS
NETWORK NODES

53. Core Broadcast
Mechanism for flooding on the core using only unicast transmissions
Unicast  eliminates broadcast storms
Extensions to the MAC protocol used to snoop messages, cache message IDs, and send negative clear to sends (NCTS)
reduced overhead for flooding

54. Core Broadcast: Illustration
RTS1
RTS1
CTS1 A
DATA1
CTS1
RTS1 B
NCTS
NCTS
CTS1
CTS1
Snooped
C got DATA1
RTS1
RTS1
Snooped DATA1 C

55. State Propagation
Convey non-local information to core nodes in an intelligent manner
Restrict the propagation of stale information to very few nodes

56. State Propagation using Waves
LINK GOES UP
LINK GOES DOWN

57. The Add/Delete Waves Add waves Delete waves
carries information about addition of link
travels slowly (delayed at each of its hops)
Delete waves
carries information about deletion of link
travels fast (preferential transmission)
When a delete wave catches up with an add wave, it kills the add wave
Allows CEDAR to dynamically adapt point of operation based on network dynamics

58. DSR/AODV on CEDAR
Existing on-demand routing protocols can be operated on CEDAR with significant performance enhancements
Only core used in all route computation/forwarding processes

59. Puzzle Muddy children problem N kids playing in the mud
Only the foreheads of K kids get dirty
A kid does not know if his/her forehead is dirty
One of the parents comes and asks all “dirty” kids to step forward. He keeps asking till all the dirty kids step forward.
How many times does the parent need to ask before kids step forward (all kids are honest, smart, and obedient)