Unit 4 Mobile IP, Ad Hoc Networks and Mobile TCP

1. Mobile IP

Normal IP routing assumes that an IP address identifies both a host and its network location. Mobile IP separates permanent identity from current location.

Need for Mobile IP

• Continuous connectivity during movement
• Transparent mobility
• Existing applications continue working
• Permanent home address remains unchanged

2. Components of Mobile IP

• Mobile Node: device that changes its network attachment point.
• Home Network: permanent network of the mobile node.
• Home Agent: maintains the current location of the mobile node.
• Foreign Network: network currently visited by the mobile node.
• Foreign Agent: assists the mobile node in the visited network.
• Care-of Address: temporary address representing the current location.
• Correspondent Node: device communicating with the mobile node.

3. Working of Mobile IP

1. The mobile node detects that it has entered a foreign network.
2. It obtains a care-of address.
3. It registers the care-of address with the home agent.
4. The home agent intercepts packets addressed to the home address.
5. Packets are tunneled to the care-of address.
6. The foreign agent or mobile node delivers the packets.
7. Outgoing packets may be sent directly or through reverse tunneling.

Tunneling

Tunneling encapsulates the original IP packet inside another IP packet for delivery to the current location.

4. DHCP

Information Provided

• IP address
• Subnet mask
• Default gateway
• DNS server
• Lease duration

DORA Process

1. Discover: client searches for a DHCP server.
2. Offer: server offers an address.
3. Request: client requests the offered address.
4. Acknowledge: server confirms the lease.

5. Ad Hoc Networks

Characteristics

• Infrastructure-less operation
• Dynamic topology
• Multi-hop communication
• Distributed control
• Limited bandwidth
• Battery-powered nodes
• Rapid deployment

Applications

• Military communication
• Disaster recovery
• Temporary meetings
• Vehicle networks
• Emergency operations

6. Performance Issues in Ad Hoc Networks

• Dynamic topology: routes change frequently.
• Limited bandwidth: wireless medium is shared.
• Energy limitation: nodes depend on batteries.
• Hidden terminal: transmitters may not hear each other.
• Exposed terminal: unnecessary waiting reduces capacity.
• Security: no fixed boundary or central authority.
• Scalability: routing overhead increases with network size.
• Unreliable links: mobility and fading cause packet loss.

7. Routing in Mobile Hosts

Ad hoc routing protocols discover and maintain paths between mobile nodes.

Proactive Routing

Routes are maintained continuously.

• Example: DSDV
• Low route-discovery delay
• High periodic overhead

Reactive Routing

Routes are discovered only when needed.

• Examples: AODV and DSR
• Lower regular overhead
• Initial route-discovery delay

Hybrid Routing

Combines proactive and reactive methods.

8. Wireless Sensor Networks

Sensor Node Components

• Sensing unit
• Processing unit
• Communication unit
• Power unit

Applications

• Environmental monitoring
• Healthcare
• Agriculture
• Industrial automation
• Military surveillance
• Smart cities

Challenges

• Limited energy
• Limited memory and processing
• Coverage and connectivity
• Fault tolerance
• Security

9. Mobile Transport Layer

Traditional TCP treats packet loss as a sign of congestion. Wireless links may lose packets because of fading, handoff or disconnection, causing unnecessary reduction in transmission rate.

Main Problems

• Wireless transmission errors
• Temporary disconnections
• Long and variable delay
• Frequent handoff
• Asymmetric links

10. Indirect TCP

Advantages

• Wireless losses are hidden from the fixed host.
• Different protocols can be used on the wireless link.
• Fast local retransmission is possible.

Limitations

• End-to-end TCP semantics are broken.
• Base station stores connection state.
• Handoff requires state transfer.

11. Snooping TCP

Working

1. Base station caches unacknowledged TCP packets.
2. It observes acknowledgements from the mobile host.
3. If wireless loss is detected, it retransmits locally.
4. Duplicate acknowledgements may be suppressed.

Advantages

• Maintains end-to-end TCP semantics
• No major change at fixed host
• Quick local recovery

Limitation

Encrypted traffic may prevent the snooping agent from reading transport headers.

12. Mobile TCP

Mobile TCP supports mobility and temporary disconnections without causing unnecessary congestion control at the sender.

Main Idea

• A supervisory host monitors the mobile connection.
• During disconnection, the sender is placed in a controlled state.
• After reconnection, transmission resumes without slow-start penalties caused by false congestion assumptions.

13. Timeout Freezing

Working

1. The mobile predicts disconnection.
2. It informs the sender through a special signal.
3. The sender freezes timers and congestion state.
4. After reconnection, the mobile signals the sender.
5. Transmission continues from the previous state.

Limitation

The mobile must detect the disconnection before it occurs.

14. Selective Retransmission

Selective retransmission sends only the packets that were actually lost instead of retransmitting a complete sequence of correctly received packets.

Benefits

• Saves wireless bandwidth
• Reduces delay
• Improves performance on error-prone links
• Avoids unnecessary retransmissions

15. Transaction-Oriented TCP

It is useful for applications that send a small request and receive a small response, such as mobile queries.

Advantages

• Lower setup overhead
• Reduced delay
• Suitable for short transactions

16. Introduction to WAP

WAP Architecture

WAP Protocol Stack

• WAE: Wireless Application Environment
• WSP: Wireless Session Protocol
• WTP: Wireless Transaction Protocol
• WTLS: Wireless Transport Layer Security
• WDP: Wireless Datagram Protocol

Advantages

• Designed for low-bandwidth networks
• Supports limited mobile devices
• Provides session and security services

Unit 4 Summary

• Mobile IP preserves connectivity while a host changes networks.
• DHCP automatically provides IP configuration.
• Ad hoc networks work without fixed infrastructure.
• Routing may be proactive, reactive or hybrid.
• Wireless sensor networks collect and forward environmental data.
• Indirect TCP splits the connection at a base station.
• Snooping TCP performs local retransmission while preserving end-to-end semantics.
• Timeout freezing prevents false TCP timeouts.
• WAP delivers mobile-oriented network services.

Important RGPV Exam Questions

Long Answer Questions

1. Define Mobile IP and explain its components and working.
2. Explain tunneling and triangular routing in Mobile IP.
3. Explain DHCP and the DORA process.
4. Define ad hoc networks and explain their characteristics.
5. Discuss performance issues in ad hoc networks.
6. Compare proactive, reactive and hybrid routing protocols.
7. Explain wireless sensor network architecture and applications.
8. Why does traditional TCP perform poorly over wireless networks?
9. Explain Indirect TCP with advantages and limitations.
10. Explain Snooping TCP and Mobile TCP.
11. Explain timeout freezing and selective retransmission.
12. Explain transaction-oriented TCP.
13. Draw and explain WAP architecture and protocol stack.

Short Answer Questions

1. Define care-of address.
2. What is a home agent?
3. Expand DHCP.
4. Define ad hoc network.
5. What is AODV?
6. Define sensor node.
7. What is Snooping TCP?
8. Expand WAP.

Download Study Resources

Frequently Asked Questions

Related Study Pages