1. Mobile Networking (I) CS 395T - Mobile Computing and Wireless Networks
Department of Computer Sciences
THE UNIVERSITY OF TEXAS AT AUSTIN
CS 395T - Mobile Computing and Wireless Networks
Mobile Networking (I)
© 2002 Yongguang Zhang

2. Contents Mobility at the Network Layer IETF Mobile-IP Discussions
Other Mobile-IP
Discussions
Architectural issues
Common implementation issues
Future Directions
Spring 2002
© 2002 Yongguang Zhang

3. Mobility at the Network Layer
Where can you manage mobility?
Application
Session
Transport
Network
Data-link
Physical
Mobile-IP: an extension to current IP architecture
To manage mobility at the IP layer
To hide mobility from the upper layers
Spring 2002
© 2002 Yongguang Zhang

4. Terminology Mobile Node (MN or MH) Correspondent Node (CN or CH)
Home Network and Foreign Network
Mobility Agent
Home Agent (HA) and Foreign Agent (FA)
Home Address (HoA) and Care-of Address (CoA)
Binding and Binding Update
Spring 2002
© 2002 Yongguang Zhang

5. IETF Mobile-IP: Basic Concept
MN always uses its home address HoA
When MN visits a foreign network,
Registration with FA
Discover mobile agents and CoA
Registration with HA
Binding update (HoA -> CoA)
When CN communicates with MN, it uses HoA
HA forwards packet from HoA to CoA
Spring 2002
© 2002 Yongguang Zhang

6. Agent Discovery Through Agent Discovery Process
Agent advertisement (beaconing):
Mobile agent broadcast agent advertisement at regular intervals (“I am here”)
Agent solicitation:
MN can solicit advertisement (“anyone here?”)
Mobile agent respond to agent solicitation
Question:
why agent solicitation?
Spring 2002
© 2002 Yongguang Zhang

7. Functions of Agent Advertisement
Allow for the detection of mobility agents
Let the MN know whether the agent is a HA, or a FA
List one or more available care-of addresses
Inform the MN about special features provided by FA
Example: Alternative encapsulation techniques
Let MN determine the network number and status of their link to the Internet
Spring 2002
© 2002 Yongguang Zhang

8. CoA Two types of CoA: Depends on foreign network configuration
FA’s IP address
MN’s temporary address
Locally-assigned address in the foreign network
E.g., DHCP address
Depends on foreign network configuration
Foreign network may or may not hand out addresses to visitors
Spring 2002
© 2002 Yongguang Zhang

9. Implementing Agent Discovery
Protocol details
Built on top of an existing standard protocol: Router Advertisement (RFC 1256)
Simply extends the fields of existing router advertisements
Spring 2002
© 2002 Yongguang Zhang

10. Registering CoA HA must know a MH’s CoA (binding update)
Binding: (HoA->CoA)
Binding has a lifetime (can expire)
Registration process
MH sends a registration request with CoA information
HA authenticate the request
HA approves or disapproves the request
HA adds the necessary information to its routing table
HA sends a registration reply back to MH
Spring 2002
© 2002 Yongguang Zhang

11. Registration Operations
Spring 2002
© 2002 Yongguang Zhang

12. Authentication A malicious node could cause remote redirect
Authentication and protection against replay attacks, and need for unique identification field
Timestamp and Pseudorandom Number
Spring 2002
© 2002 Yongguang Zhang

13. Automatic Home Agent Discovery
Problem: what if MH never knew its HA?
Example: MH reboots and losses all states
Subnet-wise broadcast packet is sent to the home network
Subnet-wise broadcast: cell-cast
HA responds
If more than one, other HAs on the home network send rejection notice
Spring 2002
© 2002 Yongguang Zhang

14. Forwarding to CoA Encapsulation Default encapsulation mechanism:
Sending the original packet (CH->MH) in another packet (HA->CoA)
Default encapsulation mechanism:
IP-within-IP (tunnel)
Tunnel header: A new IP header inserted by the tunnel source (home agent)
Destination IP: CoA
Alternative encapsulation mechanism:
Minimal encapsulation
Spring 2002
© 2002 Yongguang Zhang

15. Tunneling Operations in Mobile IP
Spring 2002
© 2002 Yongguang Zhang

16. The Triangle Routing Problem
MH->CH: direct; CH->MH: CH->HA->MH
Inefficient
Solution: Route optimization in Mobile-IP
Deliver binding updates directly to CH
Spring 2002
© 2002 Yongguang Zhang

17. Discussion
System issues
Spring 2002
© 2002 Yongguang Zhang

18. Home Network Where Can We Put the Home Agent? At the router
As a separate server?
At the router
What if there is multiple routers for the home network?
As a separate server
How can it pick up a packet [CHMH]?
Spring 2002
© 2002 Yongguang Zhang

19. Foreign Network Where is FA? (Router or Separated Server?)
How Can FA deliver MH the packet [CHMH]
Normally, [CHMH] would go straight to a router (because MH is foreign)
Is There Adequate Support at A Foreign Network
What if there is no FA at the network you visit?
Co-located FA
What is the Minimum Requirement from the Foreign Network?
Keep it as small as possible
Spring 2002
© 2002 Yongguang Zhang

20. Security Issues Visitors Are Threats!
How to provision your LAN to support nomadic users
And to protect your LAN from nomadic users
Foreign Network Firewall Traversal
Can firewall allows inbound [HAFA] tunnel?
Can [MHCH] pass through an egress filter?
Bi-directional tunneling
Mutual Authentication
Can you trust MH?
Can you trust FA?
Spring 2002
© 2002 Yongguang Zhang

21. Mobile Computing Model
What is the binding in IETF Mobile-IP?
HoA -> CoA (one level of indirection)
Where is the binding being managed? HA
In the route optimization case: CH
Scale of mobility?
Internet-wide
What is a cell in Mobile-IP?
Subnet
Spring 2002
© 2002 Yongguang Zhang

22. Further Discussions Variants of IETF Mobile-IP Mobility Scope
Implementation issues
Mobility Scope
Macro-mobility: Mobile-IP
Micro-mobility: Hierarchical Mobile-IP, Cellular-IP, HAWAII, TeleMIP, EMA, …
Combining network-layer mobility with link-layer mobility
Features: fast handoff, paging, etc.
Mobility in a higher layer
Transport layer, session layer
Spring 2002
© 2002 Yongguang Zhang

23. Summary IETF Mobile-IP Other versions of Mobile-IP
Other extensions to Mobile-IP
Future Directions
Spring 2002
© 2002 Yongguang Zhang