IP Mobility & Ad-hoc Network Routing

Mobile IP Optimizations Route optimization Smooth hand-offs

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)

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

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

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

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

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?) ?

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

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?

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?

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?)

Recap Mobile IP problems Mobile IP Optimizations Mobility support in IPv6

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

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

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

Multicast (Illustration) Tunnels

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

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

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

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

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

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?

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

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

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?

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…

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

Illustration A B C D

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)

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”

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

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)

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

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

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?

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?

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

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)

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

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?

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

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?

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

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)

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?

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

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

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

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

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

The Core: Illustration CHANNELS NETWORK NODES

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

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

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

State Propagation using Waves LINK GOES UP LINK GOES DOWN

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

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

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)