computaÇÃo ubÍqua e mÓvel - fernando pessoa university

COMPUTAÇÃO UBÍQUA E MÓVEL

Rui Silva Moreira11/5/2012

1Mobile and Ubiquitous Computing

Obectivos do Seminário

� Sistemas Ubíquos e Móveis

� Definição e evolução histórica

� Características e objectivos

� Exemplos UbiCom

� Comunicações sem Fios

� Codificação e Transmissão

� Multiplexagem & Canais & Células

� Normas

� Wi-Fi - 802.11a/b/g/n

� Bluetooth – 802.15.1

� ZigBee – 802.15.4

� Protocolos e Redes Móveis

� Pilha protocolos

� Redes ad hoc

� IP & Integração de Serviços (IMS)

� Localização e Contextualização

� Métodos & tecnologias localização

� Modelização do contexto

� Adaptação dinâmica local/contexto

� Requisitos de Sistema

� Modos/perfis de funcionamento (e.g., poupança de energia)

� Segurança e privacidade em ambientes móveis

11/5/2012

2

Mobile and Ubiquitous Computing

Protocol Layers

Routing Algorithms

IP Protocols and Networks

11/5/2012

3


Protocol Layers

11/5/2012Mobile and Ubiquitous Computing

4

Application Layer(DHCP, DNS, FTP, HTTP)

Transport Layer(TCP, UDP)

Network/Internet Layer(IP, OSPF, ARP, ICMP)

Data Link Layer(Ethernet, Wi-Fi, ZigBee, GPRS/UMTS)

Physical Layer(UTP/STP, Optical Fiber, Coaxial)

Domain Name System (DNS)


5

� Internet users memorize and use names & routing uses IP addresses, hence this requires translating (or resolving) names to IP address and vice-versa;

� DNS service converts names into IP address(es) and IP addresses into names

� hierarchical organization which allows for sub-delegation of name spaces to other DNS servers

Dynamic Host Configuration Protocol


6

� DHCP service dynamically attributes an available IP addresses to each host connecting to the network

� Works on local or access network, avoid static IP configuration

Packets at Different Levels


7

Ethernet

Header Layer 2 (pt-tp link)

Network

Header Layer 3

Ethernet - LANs


8

� Ethernet does not scale� Limited distance

� Flat addresses

� No hop count

� Missing features� neighbor discovery� Fragmentation� error messages� congestion feedback

… hence, we need IP

Basic Pt-Pt Layers (OSI Model)


9

Layer Description

Data Link Transform raw bits into stream of bits without errors;Sender bracks data into data frames (100..200 bytes);Tx data frames sequentially – framming;Reliable service – ack from receiver for each frame;Flow regulation – buffer adapt tx rate between emitter/receiver;Error handling – timers and sequence numbers;Medium Control Access (MAC sublayer) - broadcast networks & shared channels;

Physical Tx data bits over communication channel;Voltage representation for 0/1;Duration of bits (nanoseconds);Physical medium (UTP, air, optical fibers, water);Electrical/light/sound signals; Timings;

Layer Chained by Routers


10

Layer Description

Network Controls operation of subnet;Packets routed from source to destination address;Static routing tables (reflect structure of network);Dynamic routing tables;Congestion control;QoS (delay, jitter)Allow different operation of differetn networks (map addressing, map protocols, map packets);

Layers End-to-End (OSI Model)


11

Layer Description

Session Session establishment;Dialog control (keep track of whose turn to talk);Token managment (prevent use of same critical operation at sametime);Synchronization (tx checkpoint log to allow continuation);

Transport Split data into small units and pass them to network layer;Guarantee all pieces arrive correctly (sequenced/ordered);Type of transport connection (e.g., error-free pt-pt channel(ordered), broadcast message, etc.);End-to-End layer – source process talks to destination process withpre-defined headers and message control;

TCP/IP Reference Model


12

Layer Description

Application Higher-level protocols (e.g., FTP, SMTP, HTTP, etc.)

Transport Allow peer enteties on source and destination hosts to carry outconversation;~ Transport Layers (OSI Reference Model)2 end-to-end protocols:

- Transmission Control Protocol (TCP): reliable connection protocol, i.e., tx bytes without errors; byte stream fragmented into discrete packetsand passed to Internet layer; receiver TCP process reassembles packetsinto stream; handles flow control – tx speed;

- User Datagram Protocol (UDP): unreliable connection protocol for applications that require no sequencing nor flow control;

Internet Packet-switching network – connectioless internetwork layer;Defines packet format and IP protocol;Deliver IP packets to destination (routing) and avoid congestion;~ Network Layer (OSI Reference Model)

Host-to-network Connect to network using a variaty of adapters/cards

Connectiviy


13

� Connectionless

� IPv4, IPv6

� Connection-oriented

� X25

� Connection-oriented (datagram)

� ATM, MPLS

Circuit versus Packet Switching

� Connection-oriented

� End-to-end circuit

� Connection setup stores route in router tables

� Each packet carries ID of virtual circuit (notdestination address)

� Connectioless service� No setup is required� Packets are routed

independently(datagrams)

� Routing algorithm maychange router tables

� Each packet carriesdestination address (IP)

11/5/2012

14


Circuit switching Packet switching

Routing

11/5/2012

15


Network Layer (revisited)…


16

� Route packets from source to destination throughhops on intermediate routers;

� Routers need to know subnet topology to chooseappropriate paths and avoid overloading paths;

� Store-and-forward packet switching:

� host/router tx packet to nearest router;

� packet stored until fully arrived (check sum verified);

� then tx to next router… until it gets to destination;

� Bridges deal with different networks;

Routing Algorithms


17

� Two processes:

� Update: dynamically exchange information about all network paths and fill routing tables

� Forward: handle incoming packets and lookup outgoingline in router table

� Properties:

� Correctness and simplicity

� Robusteness and stability

� Fairness and optimallity

Goals of Routing Algorithms


18

� Minimizing mean packet delay

� Maximizing total network throughput

� Minimizing number of hops (improve delay and reduce bandwidth)

� Two groups of routing algorithms:

� Non-adaptive - static routing

� route decisions computed in advance/offline and downloaded to routers at bootstrap

� Adaptive – dynamic routing

� route decisions may change to reflect topology changes, trafficmeasurements, etc.;

� differences are in the place where to get info, e.g., locally, adjacentneighbours, all routers, etc.

Basic Routing Algorithm


19

� Distance Vector: calculate direction and distance (hops)

� Vector: choosing forwarding direction/next hop, i.e., interface through which to send out the incoming packet

� Distance: based on the cost of reaching a destination (e.g., RIP - hop count, IGRP - node delay and bandwidth)

� Count-to-infinit problem (loops)

� Link State: calculate metric based on type and status of router links

� how fast are the links

� how are the links state, i.e., up or down

Distance Vector (e.g., RIP)


20

� Ford-Fulkerson and Bellman-Ford distributedalgorithm (cf. routing loop problem)

� Routers do not have entire path to a destination

� Route table contains:

� best distance & direction to each destination

� Table updates propagation:

� each node exchanges info with neighbours (cf. confidance problem & convergence problem)

Link State (e.g., OSPF)


21

� Every node builds connectivity graph (network map)� node measures delay/cost to each neighbour

� periodically/link failure trigger Link State Packet (LSP):� sequence number + itself + list of pairs (neighbor, cost)

� broadcasts LSPs to all routers

� each router stores latest LSP (with new sequence nº) from other routers and forwards to neighbors - flood

� Based on net map, each node calculates best paths from self to every destinations – routing table� shortest path - Dijkstra’s Algorithm

Example – From C to All


22

A

B

D

E

C

F

G

2

2

6

1

2

2

4

5

1

A

B 6

D 2

D

A 2

E 2

E

B 1

D 2

F 4

F

C 4

E 4

G 1

C

B 2

F 2

G 5

B

A 6

C 2

E 1

G

C 5

F 1

C(0)

B(2) F(2) G(5)

E(4) G(3)

E(3)A(8)

D(5)

A(7)

Shortest Path Algorithm


23

� Build graph of subnet� each node = router;

� each arc = communication line/link

� Choose route based on metrics� number of hops

� bandwidth/average traffic

� measured delay

� communication cost

� mean queue length

� geographic distance (Km)

Shortest path - Dijkstra


24

� Uses tree to store visited nodes

� Uses list of nodes to visit

� Add itself to the tree and then loop until list is null:� All node neighbors added to the visiting list (except nodes

already in the tree or list)

� One at a time, each node in visiting list is transferred to tree –attached to appropriate neighbor

� Tree contains all network nodes – shortest path = tree search (e.g., bread-first)

� Routing table built from node sequences in shortest paths

Routing Table


25

• Network Destination and Netmask describe the Network ID

e.g. 192.168.1.0 & 255.255.255.0 => Net ID 192.168.1.0/24(1st net address & 24 bits net prefix & 8 bits host addressing)

• Gateway = Next hop (i.e., gateway to reach network)• Interface = NIC IP to destination (e.g., use192.168.1.65 to LAN 192.168.1.0/24) • Metric indicates = cost of route (efficiency of routes)

Distance Vector vs Link State


26

� Memory: DV smaller than LS

� Simplicity: DV simpler than LS

� Convergence: LS faster than DV

� Functionality: LS better than DV

� Hierarchical networks

� troubleshooting

� sabotage-proof routing

Flooding Algorithm


27

� Static algorithm

� Every incomig packet is sent out on every outgoingline (except the one from it came)

� Avoid infinit duplication (loops)

� Use hop counter decremented in each hop

� Drop packet when hop counter reaches 0

Mobile IP

11/5/2012

28


Node Mobility with IP


29

� Nomadic nodes� Mobile user carries his computer to another network,

changing the attachment point;

� Mobile IP allows a mobile node to use two IP addresses:� home-address – used to identify TCP connections to where

the mobile node “lives”;� care-of-address – the new mobile node’s address in the

foreign network where the mobile node is plugged;� whenever the mobile node moves it registers care-of-

address with its home agent� home agent “tunnels” packet from the home-address to the

care-of-address

Mobile IP


30

Mobile IP


31

IP and Services Integration:

IP Multimedia Subsystem (IMS)

References:� Thomas Magedanz, IP Multimedia System (IMS): Principles, Architecture and

Applications, Fraunhofer FOKUS, 2006.

� Gonzalo Caramillo & Miguel Garcia-Martim, The 3G IP Multimedia System (IMS): Merging the Internet and the Cellular Networks, McGraw Hill, 2008.

� Travis Russel, The IP Multimedia System (IMS): Session control and other network operations, McGraw Hill, 2008.


11/5/2012

32


Convergence (FMC) & Integration


33

Network Convergence


34

Past Market Evolution

� Decrease in PSTN revenues – overcomedby VoIP

� Counter measures:

� ISP launch their ownVoIP services

� Introduce added valuehigh-end SIP-services

� Develop convergencesolutions

11/5/2012

35


IP Multimedia SubSystem


36

� Generic and sclalable architecture

� VoIP, MMoIP, IM, Presence, etc.

� Support for several access types

� IP on top of ADSL, Fiber, Cable, etc.

� Horizontal architecture used by ISPs

� Basic protocols:

� SIP (session initiation)

� Diameter (AAA)

Next Generation Network

11/5/2012

37


� Services: independentservice layer; servicesblunding;

� Control: signalingprotocols for sessioncontrol (SIP) andaccounting (Diameter);

� Transport: conveysignaling and media; multiple accesstechnologies; same core

IMS Layered Architecture


38

IMS Layered Architecture


39

Flexible Services Provision


40

Vertical vs Horizontal Integration

11/5/2012

41


Pre IMS Comm (service islands) IMS Comm (service combination)

Services Interoperability

11/5/2012

42


Replication of agreements Reuse of agreements

Cost saving & Speeds development

11/5/2012

43


Vertical islands – slowdeployment

Horizontal convergence – speeds

development

Component Functional Overview


44

Overlay Session/Service Control Arch.


45

� IMS Core

� S-CSCF (Serving Call Session Control Function): IS anker point in home network

� I-CSCF (Interrogating Call Session Control Function): topology hiding

� P-CSCF (Proxy Call Session Control Function): entrypoint into IMS world

� MS (Media Server): Media Server hosting special resources

� MGF (Media Gateway): interworking with legacy networks

� PDF (Policy Decision Function): QoS Control using Polícies (COPS)

� IMS Application Layer

� HSS (Home Subscriber System): maintaining subscriber & AS profiles

� AS (Application Server Function): hosting applications

� IMS enablers (e.g. Presence, Group Mgt.): specific ASs with generic functions

� IMS end system (IMS Client)

� plays an important role - real multimedia / IMS services

IMS Components


46

� Call Session Control Function (CSCF)� registration of the endpoints

� routing SIP signaling messages to appropriate app server

� works with interworking and transport layer to guarantee QoS across all services

� roles of CSCF servers:� Serving (S-CSCF): session control entity for endpoint devices� Proxy (P-CSCF): entry point to IMS for devices� Interrogating (I-CSCF): entry point to IMS from other

networks

IMS Components


47

� Breakout Gateway Control Function (BGCF)� in IP-PSTN breakout it selects MGCF to receive SIP signaling

� in IP-IP networks it becomes the peering control point between boundary points

� Media gateway control function (MGCF)� manages the distribution of sessions across multiple media

gateways

� Media Server Function Control (MSCF)� manages the use of resources on media servers

� SIP Applications Server (SIP-AS)

Convergence Architecture


48

� support plethora of services over fixed and mobile access networks

� single unified network supporting all major access technologies

� single set of services that:

� apply network-wide

� available anytime, anyplace, anywhere

Convergence Network


49

ISP - Get Control of IP Services

11/5/2012

50


IP networks allow freecommunication between endpoints

IMS allows controlling services on IP networks (QoS, Security, Charging)

Standard Interfaces

� IMS is based onstandard Internet protocols:

� SIP (session control)

� DIAMETER (AAA)

� COPS for QoS

� RTP (media stream)

11/5/2012

51


Session Initiation Protocol (SIP)


52

� Protocol to initiate, terminate, and modify service sessions� Voice and Multimedia sessions; Point-to-point and multiparty

� Support for� registration and modification of multiple user location information

� caller and callee authentication / call authorization

� privacy for call signaling and media streams

� Media path with ensured QoS

� Flexible service creation� support through SIP servers (located inside and outside the network)

� Extensible protocol to cover new communication aspects� e.g., presence and instant messaging

� Used together with Session Description Protocol� No Bearer support (RTP and RTCP are used for that)

� Developed and maintained by IETF (MMUSIC and SIP WGs)

� RFC 3261: www.ietf.org/html.charters/sip-charter.html

Local SIP Architecture


53

SIP Requests


54

� REGISTER: allows clients to register their current location (one or more addresses)

� INVITE: used by client to initiate a call� ACK: sent by client to confirm reception of final

response from server, e.g., 200 OK� BYE: sent either by calling or caller agent to abort a

call� CANCEL: sent to abort a request that was sent

previously as long as the server has not yet sent a final response

� OPTIONS: allows clients to learn servers capabilities; server sends back list of supported methods

More SIP Requests


55

� SUBSCRIBE: starts/stops session or user supervision (event monitoring)

� NOTIFY: informs subscribed entity about occurred events

� PUBLISH: enables entity to modify presence information� MESSAGE: allows to send an instant message� REFER: informs recipient to contact dedicated SIP user

(e.g. MWI)� PRACK: PRovisional ACKnowledgement� UPDATE: Change of media (SDP) during session setup� INFO: Exchange of application layer info (e.g. DTMF)

SIP Responses


56

� SIP Responses defined as (HTTP-style):� Status-Line = SIP-Version SP Status-Code SP Reason-Phrase CRLF

(SP=Space, CRLF=Carriage Return & Line Feed)

e.g., SIP/2.0 404 Not Found

� First digit gives Class of response:

SIP Message Body


57

� Message body can be any protocol

� In most implementations it is SDP (Session DiscriptionProtocol)

� RFC 2327 4/98, http://www.ietf.org/rfc/rfc2327.txt

� Specify info about a multi-media session.

� SDP fields have a required order

� For RTP (Real Time Protocol Sessions)� RTP Audio/Video Profile (RTP/AVP) payload descriptions

are often used

SIP – enabler converged comm


58

Diameter Protocol (AAA)


59

� Protocol for Authentication, Authorization and Accounting (AAA)� RFC 3588 DIAMETER Base Protocol (2003)

� Development based on 3G network operators

� Used in 3GPP IMS for HSS access

� Extends RADIUS functionalities:� Introduction of Agent roles (cf. proxy, relay, redirect & translation)

� Enables server-initiated messages

� Uses UDP, TCP and SCTP protocol for reliable message transport

� Backward compatible to RADIUS by using translation agents

� Explicit modular structure => extendible

Wireless Ad Hoc Networks / Mobile Ad Hoc Networks (MANETs)

Ad Hoc = for a particular end or case

E. Royer, Chai-Keong Toh, A Review of Current Protocols for Ad Hoc Mobile WirelessNetworks, IEEE Personal Communications, April 1999


11/5/2012

60


Wireless Networks


61

� Topologies with organized infrastructure

� Fixed and wired routers/gateways

� Disperse Base stations (BS): bridges used by mobile nodes to access wired infrastructure

� Handoff: transfer node communication from one BS to another BS

� Limitations

� Requires a domain entity for structuring/managing network

� Static organization and coverage area

� Topologies with Ad Hoc organization

� No fixed routers/gateways

� Arbitrary dynamic connections through existing mobile nodes

Wireless Mesh Networks


62

� Similar to Mobile Ad hoc NETworks (MANETs) but where nodes are standing (do not move)� MANETs must deal also with route mobility

� Communication is accomplished through routing protocols or flooding schemes

� Usually there are several alternative paths between different nodes

� Self healing characteristics that allow routing in the presence of bad links or node malfunction

� ZigBee is a low “cost-power-bandwidth” standard supporting both star and tree wireless mesh networks

Ad Hoc Routing

� Pro-active routing process that periodically refreshes list of all routes (regardless of usage)

� Nodes maintain consistent/up-to-date routing information

� Each node keeps 1+ tables that store routing info to all nodes

� Consistency maintenance => update messages overload net traffic

� Reactive routing discovery and maintenance

� Demand-driven protocols => source node triggers Route Discovery process (RRequest) when needed

� Lazy route maintenance => reduces traffic overload

� High latency/reaction to changes on net topology

11/5/2012

63


Table Drive Source-Initiated On-Demand

Ad Hoc Routing Protocols


64

Ad Hoc

Routing Protocols

Table Driven

Destination-Sequenced Distance-

Vector (DSDV)

Clusterhead Gateway Switch Routing

(CGSR)

Wireless RoutingProtocol (WRP)

Source-Initiated On-Demand

Ad Hoc On-DemandDistance Vector

(AODV)

Dynamic SourceRouting (DSR)

Lightweight Mobile Routing (LMR)

Temporally OrderedRouting Algorithm

(TORA)

Associativity BasedRouting (ABR)

Signal StabilityRouting (SSR)

Table Driven Protocols


65

DSDV

CGSR

WRP

� Maintain consistent (up-to-date) routing information

� Each node keeps 1+ tables that store routing info� e.g., routes from each node to every other node

� Changes in the network topology originate propagation updates to maintain consistent net view

� Protocols differ essentially in:� Number of routing tables� Methods by which topology changes are

broadcasted

DSDV (Destination-Sequenced Distance-Vector)


66

� Uses improved version of Bellman-Ford algorithm to achieve free-loop routing tables

� Every mobile node maintains routing table:� All possible destinations in the network� Number of hops to each routing table� Each entry marked with sequence number assigned by destination node

– distinguish stable from new routes

� Route table updates transmitted periodically (table consistency)� Uses 2 types of packets (avoid traffic overload):

� FULL DUMP: carries all available routing info (may require several Network Protocol Data Units)

� INCREMENTAL: relay only info that changed since last FULL DUMP (each update fits into 1 standard-size NPDU)

DSDV (Destination-Sequenced Distance-Vector)


67

� New Route broadcasts contain:� Address of destination� Number of hops to reach destination� Sequence number of info received regarding destination� Sequence number unique to the broadcast

� Choose route with� Most recent sequence number� For same sequence number choose smaller metric (shortest

path)

� Mobile nodes keep track of Settling Time (ST) of routes� Used to delay route updates = ST (reduce broadcasts if

better route discovered in near future)

CGSR (Clusterhead Gateway Switch Routing)


68

� Uses different type of addressing and net organization scheme� Instead of flat net it uses clustered multi-hop structure� Clusterhead node

� elected by peer nodes (e.g., bully, ring)� controls group of ad hoc nodes

� Advantages: code separation among clusters; Bandwidth allocation; Channel access; Use of routing heuristics

� Disadvantages: frequent changes can adversely affect routing performance (successive elections diminish node capacity for packet relay)

� Uses Least Cluster Change (LCC) algorithm - clusterhead changes only when:� i) 2 clusterheads come into contact� ii) node moves out of contact of all clusterheads

CGSR (Clusterhead Gateway Switch Routing)


69

� Uses underlying DSDV routing scheme but with hierarchical clusterhead-to-gateway routing scheme

� Gateway:� node within communication range of 2+ clusterheads

� Packet sent by mobile node: 1st goes to clusterhead; 2nd goes to gateway; goes to another clusterhead (until reaches destiny)

� Each node has Cluster Member Table (CMT): stores destination clusterhead for each mobile node - broadcasted periodically

� Each node maintains also a Routing Table (RT): determine next hop in order to reach destination

� When node receives packet:� 1st checks CMT to determine nearest clusterhead to destination;� 2nd checks RT to determine next hop to reach selected clusterhead

CGSR Example


70

1

4

2

3

5

6

7

8

N G

H

Clusterhead (H)Gateway (G)Node (N)

H

G

H

N

N

WRP (Wireless Routing Protocol)


71

� Maintains routing info among all nodes

� Each node responsible for 4 tables:� Distance Table (DT)

� Routing Table (RT)

� Link-Cost Table (LCT)

� Message Retransmission List (MRL) Table� Sequence number of update message� Retransmissions counter� ACK message flag vector (1 entry per-neighbor)� List of updates sent in update message



72

� MRL Table records

� which update (in an update message) needs to be reTX

� which neighbor should ACK reTX

� Mobile nodes inform each other of link changes through update messages between neighbors

� Update contains:� list of updates (destination, distance to destination,

predecessor of destination)

� list of responses (which nodes should ACK update)



73

� Mobile nodes send update package after:� processing update from neighbor

� detecting lost link to neighbor

� Update message to neighbors for:� Modifying their Distance Tables

� Checking new paths through other nodes

� New paths/routes relayed back to original node

� Nodes learn existence of neighbors through their:� ACK packages

� HELLO packages (TX periodically when no ACKs necessary)



74

� Mobile nodes receives HELLO message and:

� Adds neighbor to Routing Table (RT)

� Replies copy of RT

� Nodes TX Distance and Second-to-Last hop info for each destination

� WRP is path find algorithm

� Avoids Count-to-infinite problem / loop freedom� Forces each node to perform consistency checks of

predecessor info reported by all nodes

Source-Initiated On-Demand


75

AODV

DSR

LMR

TORA

ABR

SSR

� Demand-driven protocols

� Source node creates route only when necessary� Route Discover: process through which a

route to a node is found or all possible route permutations have been examined

� Route Maintenance: procedure repeated until:� destination becomes inaccessible along every

path from source� Route no longer desired

AODV (Ad-Hoc On-Demand Distance Vector)76

� Improves DSDV algorithm:� Does not maintain complete list of routes� Builds routes only when necessary – diminishes number of broadcasts� Routes that are not on the selected path do not maintain routing info neither

exchange table info

� Path discovery process initiated by source node� Route Request (RREQ):

� Source node broadcasts RREQ packet to neighbor nodes� Each node records previous node ID (and broadcast ID) of node that sent RREQ

� Info used to forward back RREP afterwards (reverse path record)� Info deleted if no RREP received after given timeout

� Each node forwards RREQ to neighbors until reaches destination or intermediate node aware of path

� Route Reply (RREP):� Destination or intermediate node replies back (unicast) with RREP packet� Each node forwards RREP back to previously recorded neighbor ID (using reverse path)� Each node records previous node ID that sent RREP (forward path record – routing next

data packets)� Source may receive several RREP but uses shortest path (less hops)

AODV Example


77

1

3

4

5

6

7

8

Source

2

RREQ

AODV (Ad-Hoc On-Demand Distance Vector)78

� Uses destination sequence number (DSN) to ensure loop-free routes and identify most recent route (higher DSN => more up-to-date)

� Each node maintains its own:� Sequence number used on transmitted packets (as source on RREQ/destination on

RREP)� Broadcast ID (incremented for every initiated RREQ)

� RREQ carries:� Source ID + Destiny ID� Source Sequence Number (SSN)� Destination Sequence Number (DSN)

� The higher is the DSN the more up-to-date is the route� If intermediate node has route to destination with DSN >= DSN of RREQ then

replies/unicast RREP

� Broadcast ID� Nodes only forward unique RREQs (discard RREQ with repeated Source ID + Broadcast ID)

� Time-to-Live (TTL)� TTL limits number of retransmissions for each RREQ

� RREQ can only be issued after 2xT (where T = timeout of previous RREQ)

AODV (Ad-Hoc On-Demand Distance Vector)


79

� Route Maintenance:� Source node moves => it reinitiates route discovery

� Intermediate node moves => noticing neighbor propagates link failure message (RREQ with infinite metric) through neighbors� when reaches source it may reinitiate route discovery

� Liveliness:� HELLO messages used periodically to inform neighbors

� Nodes listen neighbor retransmission (forward) of data packets => ensure next hop is alive/reachable

DSR (Dynamic Source Routing)


80

TORA (Temporarily Ordered Routing Algorithm)


81

ABR (Associatitivy-Based Routing)


82

SSR (Signal Stability Routing)


83

LMR (Lightweight Mobile Routing)


84

computaÇÃo ubÍqua e mÓvel - fernando pessoa university

Documents