1. Mobile and wireless networking
Zilong Ye, Ph.D.

2. 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.

3. 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

4. Mobile edge computing or fog computing

5. 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

6. 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

7. 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

8. Fog computing applications

9. 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

10. 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

11. 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)

12. 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

13. 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

14. 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

15. 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

16. 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)

17. 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

18. 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

19. 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

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

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

22. 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

23. 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

24. 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

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

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

27. 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.

28. 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

29. 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

30. 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

31. 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

32. 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