Mobile and wireless networking Zilong Ye, Ph.D. zye5@calstatela.edu

Mobile cloud computing Mobile devices have limited computing power, and limited battery, so it is needed to offload the computing tasks to remote cloud. Small-cell, multi-antenna and millimeter wave communications allow gigabits wireless communications to transmit data to cloud.

Limitation of mobile cloud computing Long latency from the end user to the remote cloud High bandwidth consumption to move data from edge to cloud Security and privacy

Mobile edge computing or fog computing

Advantages of fog computing reduction in data movement across the network resulting in reduced congestion elimination of bottlenecks resulting from centralized computing systems improved security of encrypted data as it stays closer to the end user

CLOUD VS FOG: Requirement Cloud computing Fog computing Latency high low Delay jitter High Very low Location of server nodes With in internet At the edge of local n/w Distance between the client and server Multiple hops One hop Security    Undefined Can be defined Attack on data  High probability Very Less probability Location awareness No Yes

Continued……… Requirement Cloud computing Fog computing Geographicaldistribution Centralized Distributed  No. of server nodes Few  Very large Support for Mobility Limited Supported Real time interactions Type of last mile connectivity Leased line Wireless

Fog computing applications

Wireless network Routing Goal: Communication between wireless nodes No external setup (self-configuring) Often need multiple hops to reach dst Limited communication range in each wireless node

Challenges and Variants Poorly-defined “links” Probabilistic delivery, etc. Kind of n^2 links Time-varying link characteristics No oracle for configuration (no ground truth configuration file of connectivity) Short communication range Low bandwidth (relative to wired) Possibly mobile Possibly power-constrained

Types of routing Proactive Routing On-Demand or Reactive Routing Link state Fish-Eye Routing, GSR, OLSR. Table driven: Destination-Sequenced Distance Vector (DSDV), WRP) On-Demand or Reactive Routing Ad hoc On-demand Distant Vector (AODV) Dynamic Source Routing (DSR) Hybrid Schemes Zone Routing ZRP, SHARP (proactive near, reactive long distance) Safari (reactive near, proactive long distance) Geographical Routing Hierarchical: One or many levels of hierarchy Routing with dynamic address Dynamic Address RouTing (DART)

Proactive Protocols Proactive: maintain routing information independently of need for communication Update messages send throughout the network periodically or when network topology changes. Low latency, suitable for real-time traffic Bandwidth might get wasted due to periodic updates They maintain O(N) state per node, N is the number of nodes

On-Demand or Reactive Routing Reactive: discover route only when you need it Saves energy and bandwidth during inactivity Can be bursty -> congestion during high activity Significant delay might occur as a result of route discovery Good for light loads, collapse in large loads

Hybrid Routing Proactive for neighborhood, Reactive for far away (Zone Routing Protocol, Haas group) Proactive for long distance, Reactive for neighborhood (Safari) Attempts to strike balance between the two

Hierarchical Routing Nodes are organized in clusters Cluster head “controls” cluster Trade off Overhead and confusion for leader election Scalability: intra-cluster vs intercluster One or Multiple levels of hierarchy

Geographical Routing Nodes know their geo coordinates (GPS) Route to move packet closer to end point Protocols DREAM, GPSR, LAR Propagate geo info by flooding (decrease frequency for long distances)

Proactive: DSDV - Destination-Sequenced Distance Vector Algorithm By Perkins and Bhagvat Based on Bellman Ford algorithm Exchange of routing tables Routing table: the way to the destination, cost Every node knows “where” everybody else is Thus routing table O(N) Each node advertises its position Sequence number to avoid loops Maintain fresh routes

DSDV details Routes are broadcasted from the “receiver” Nodes announce their presence: advertisements Each broadcast has Destination address: originator No. of hops Sequence number of broadcast The route with the most recent sequence is used

Reactive: Ad-Hoc On-demand Distance Vector Routing (AODV) By Perkins and Royer Sender tries to find destination: broadcasts a Route Request Packet (RREQ). Nodes doesn’t participate in any periodic routing table exchanges State is installed at nodes per destination Does nothing when connection between end points is still valid When route fails Local recovery Sender repeats a Route Discovery

Route Discovery in AODV 1 Propagation of Route Request (RREQ) packet

Route Discovery in AODV 2 Path taken by Route Reply (RREP) packet

In case of broken links… Node monitors the link status of next hop in active routes Route Error packets (RERR) is used to notify other nodes if link is broken Nodes remove corresponding route entry after hearing RERR

Dynamic Source Routing (DSR) Two mechanisms: Route Maintenance and Route Discovery Route Discovery mechanism is similar to the one in AODV but with source routing instead Nodes maintain route caches Entries in route caches are updated as nodes learn new routes. Packet send carries complete, ordered list of nodes through which packet will pass

When Sending Packets Sender checks its route cache, if route exists, sender constructs a source route in the packet’s header If route expires or does not exist, sender initiates the Route Discovery Mechanism

Route Discovery 1 (DSR) Building Record Route during Route Discovery

Route Discovery 2 (DSR) Propagation of Route Reply with the Route Record

Route Maintenance Two types of packets used: Route Error Packet and Acknowledgement If transmission error is detected at data link layer, Route Error Packet is generated and send to the original sender of the packet. The node removes the hop is error from its route cache when a Route Error packet is received ACKs are used to verify the correction of the route links.

The Zone Routing Protocol (ZRP) Hybrid Scheme Proactively maintains routes within a local region (routing zone) Also a globally reactive route query/reply mechanism available Consists of 3 separate protocols Protocols patented by Cornell University

Intrazone Routing Protocol Intrazone Routing Protocol (IARP) used to proactively maintain routes in the zone. Each node maintains its own routing zone Neighbors are discovered by either MAC protocols or Neighbor Discovery Protocol (NDP) When global search is needed, route queries are guided by IARP via bordercasting

Interzone Routing Protocol Adapts existing reactive routing protocols Route Query packet uniquely identified by source’s address and request number. Query relayed to a subset of neighbors by the broadcast algorithm

Potential topic – 1 Each mobile host is associated with a limited amount of cache, e.g., NDN Each mobile host can cache either Interest/Request packet or Data/Reply packet Pending Interest will be cached for a retransmission later When to retransmit, how many times retransmission If retransmission fails, how to discover another path

Potential topic 2 Each mobile host is associated with a geographical coordinate Each mobile host maintain its current location, and its previous location Based on the above two information, it is possible to calculate or predict the moving direction of the mobile host The moving direction will be considered in making the routing decision, in addition to the number of hops