1. IT351: Mobile & Wireless Computing
Mobile Network Layer
Objective:
To highlight the requirements of internetworking in wireless networks as opposed to wired networks.
To detail the operation of common internetworking schemes, including , MobileIP / migration to IPv6 and CellularIP.

2. Outline The Internet Protocol (IP) mobility Mobile IP IPv6
Motivation and overview
Mobile IP
Components and terminology
Protocols: agent discovery, registration, tunneling & encapsulation
Optimization
Reverse tunneling
Problem
IPv6
Micro mobility protocols
DHCP

3. Overview of the main chapters
Support for Mobility
Chapter 9:
Mobile Transport Layer
Chapter 8:
Mobile Network Layer
Chapter 4:
Telecommunication Systems
Chapter 5:
Satellite
Systems
Chapter 6:
Broadcast
Systems
Chapter 7:
Wireless
LAN
Chapter 3:
Medium Access Control
Chapter 2:
Wireless Transmission

4. Internet Protocol (IP)
IP for normal fixed Internet
Network layer
Most important protocol
Packet-switched, connectionless service
Fragmentation and reassembly
Error reporting using ICMP (Internet Control Message Protocol)
Delivery of packets across an internetwork (Routing)

5. Internet (IP) Mobility
Internet (IP) provides the host with a permanent identity in the form of an IP address
This IP address is associated with a location, i.e. the IP network domain
If the host moves within the domain it will probably be ok (depends, e.g. subnetting)
If the host moves outside the domain it will not have a different IP address (statically assigned IP)
If the host moves any ‘connections’ (recall – IP is connectionless) will be lost

6. Problems with fixed IP Two ways of assigning IP addresses:
Statically assigned IP
Host address stays constant over all connections
Common case in PC access to LANs and some ISPs
IP addresses may be dynamically assigned by DHCP (Dynamic Host Configuration Protocol)
Host addresses change with each connection
Common with Laptop access and some ISPs
Problems for mobility
With static addresses the host cannot move
With dynamic addresses partners can’t communicate

7. Motivation for Mobile IP
Routing
based on IP destination address, network prefix (e.g ) determines physical subnet
change of physical subnet implies change of IP address to have a topological correct address (standard IP) or needs special entries in the routing tables
Specific routes to end-systems?
change of all routing table entries to forward packets to the right destination
does not scale with the number of mobile hosts and frequent changes in the location, security problems
Changing the IP-address?
adjust the host IP address depending on the current location
almost impossible to find a mobile system, DNS updates take long time
TCP connections break, security problems

8. Efficiency and scalability
Requirements for Mobile IPv4 (RFC 3344, was: 3220, was: 2002 , updated by: 4721)
Transparency
mobile end-systems keep their IP address
continuation of communication after interruption of link possible
point of connection to the fixed network can be changed
Compatibility
support of the same layer 2 protocols as IP
no changes to current end-systems and routers required
mobile end-systems can communicate with fixed systems
Security
authentication of all registration messages
Efficiency and scalability
only little additional messages to the mobile system required
world-wide support of a large number of mobile systems in the whole Internet

9. Mobile IP – IP Integration
What does Mobile IP do?
Extends IP for mobility not wireless networking
Mobile IP operates between network and transport layers (i.e. on top of IP but below TCP/UDP)
Mobile IP provides two addresses:
Fixed address for identification (home address)
Dynamic address for routing (care-of address/foreign address)
Benefits:
Stable address for hosts
Enables TCP to keep track of session data
Routing based on fixed source/destination

10. Mobile IP – Components & Terminology
Mobile Node (MN)
system (node) that can change the point of connection to the network without changing its IP address
Correspondent Node (CN)
communication partner (cam be fixed or mobile node)
Home Network
The subnet the MN belongs to with respect to its IP address. No mobile IP support is needed within the home network.
Foreign Network
The current subnet the MN visits and which is not the home network
The current location of the MN from the IP point of view is called Care-of-Address (COA)
Tunneling
Packet delivery towards the MN is done using a tunnel

11. Mobile IP – Components & Terminology
Home Agent (HA)
system in the home network of the MN, typically a router
Provides several services to the MN
registers the location of the MN, tunnels IP datagrams to the COA
Foreign Agent (FA)
system in the current foreign network of the MN, typically a router
Provides several services to the MN during its visit to the foreign network
forwards the tunneled datagrams to the MN, typically also the default router for the MN
FA can also provide security service,
Care-of Address (COA)
actual location of the MN from an IP point of view
address of the current tunnel end-point for the MN (at FA or MN)
all packets sent to the MN are delivered to the COA
Foreign agent COA: located at the FA
Co-located COA: can be chosen, e.g., via DHCP if IP addresses are available.

12. Example network HA MN FA CN Internet router home network
mobile end-system
(physical home network
for the MN) FA
foreign network
router
(current physical network for the MN) CN
end-system
router

13. Data transfer from the mobile systemHA 1 MN
Internet
home network
sender FA
foreign network
1. Sender sends to the IP address of the receiver as usual, FA works as default router CN
receiver

14. Data transfer to the mobile systemHA 2 MN
Internet
home network 3
receiver FA
foreign
network
1. Sender sends to the IP address of MN,
HA intercepts packet
2. HA tunnels packet to COA, here FA,
by encapsulation
3. FA forwards the packet to the MN 1 CN
sender

15. Overview COA foreign network router FA MN home network router HA
Internet CN
router
foreign
network 3.
router FA MN
home
network
router HA 2. 4.
Internet 1. CN
router

16. Mobile IP – The Protocols
Three major problems:
Discovery of new point of attachment
Registration of new location with Home domain
Delivery of datagrams to registered locations
Agent Discovery
Mobility agents advertise availability
MN solicits agent
Registration
Updating the care-of-address with home network
Tunneling
Delivery of data to mobile node’s care-of-address, via permanent home address

17. 1. Agent Discovery
One initial problem of an MN after moving is how to find a foreign agent
How does the MN discover that it has moved?
Mobile IP describes two methods:
Agent advertisement
Agent solicitation
Agent Advertisement
Extends the current ICMP (Internet Control Message Protocol – Router Advertisement)
HA and FA periodically send advertisement messages into their physical subnets
MN listens to these messages and detects, if it is in the home or a foreign network (standard case for home network)
MN reads a COA from the FA advertisement messages

18. Agent Discovery (cont)
Agent Solicitation
Alternatively, mobile node may solicit agent (Broadcast or Multicast)
Mobile node can now proceed to register
Agent Advertisement
(ICMP – extension)
preference level 1
router address 1
#addresses
type
addr. size
lifetime
checksum
COA 1
COA 2
type = 16
sequence number
length 7 8 15 16 31 24 23
code
preference level 2
router address 2
. . .
registration lifetime R B H F M G r
reserved T

19. 2. Registration
Mobile Node requests registration from Foreign Agent (or directly for co-located COA)
Request is forwarded to Home Agent
Includes CAO + home addresses
Home Agent replies to Foreign Agent
Security
Authentication between all three parties
Mobile-Home auth. is based on shared secret
From: Perkins, C.E., “Mobile networking through Mobile IP,” IEEE Internet Computing, Volume 2,  Issue 1,  Jan.-Feb Page(s):58 – 69.

20. 3. Tunneling & Encapsulation
Communication between an IP node and a Mobile Node
Delivery of data to mobile node’s COA via permanent home address
Tunneling is achieved by encapsulation
IP tunnel
Home Agent
Foreign Agent 2 3 1
4 (triangular routing)
IP Host
Mobile Node

21. Encapsulation Encapsulation of one packet into another as payload
e.g. IPv6 in IPv4 , Multicast in Unicast
here: e.g. IP-in-IP-encapsulation
IP-in-IP-encapsulation (mandatory, RFC 2003)
tunnel between HA and COA
original IP header
original data
new IP header
new data
outer header
inner header
original data

22. Mobile IP – Encapsulation
IP-within-IP encapsulation
MobileIP Header
IP Header
IP Header
IP Payload
IP Payload

23. Encapsulation ver. IHL DS (TOS) length IP identification flags
fragment offset
TTL
IP-in-IP
IP checksum
IP address of HA
Care-of address COA
ver.
IHL
DS (TOS)
length
IP identification
flags
fragment offset
TTL
lay. 4 prot.
IP checksum
IP address of CN
IP address of MN
TCP/UDP/ ... payload

24. Optimization of packet forwarding
Problem: Triangular Routing
sender sends all packets via HA to MN
higher latency and network load
“Solution”
Avoid routing through Home Agent
Corresponding IP host is given care-of-address
sender learns the current location of MN
direct tunneling to this location
HA informs a sender about the location of MN
big security problems!

25. Optimization of packet forwarding (cont.)
Requires authentication (to prevent hijacking)
Process is entitled mobility-binding
Request
Update – Authorization
Acknowledgement
Warning (if needed)
If a packet is sent to a wrong FA CN HA
Request
Update
ACK

26. Optimization: Change of Foreign Agent
Change of FA
packets on-the-fly during the change can be lost
new FA informs old FA to avoid packet loss, old FA now forwards remaining packets to new FA
this information also enables the old FA to release resources for the MN

27. Problems with Mobile IP
Inefficient routing
Indirect routing via Home Agent may be slow
Home Agent may get overloaded with traffic
Firewalls
What happens when Firewalls are operating?
typically mobile IP cannot be used together with firewalls, special set-ups are needed (such as reverse tunneling)
Internal addresses appear to enter a network
Mobile IP cannot handover connections

28. Problems with mobile IP
Security
authentication with FA problematic, for the FA typically belongs to another organization
no protocol for key management and key distribution has been standardized in the Internet
QoS
many new reservations in case of RSVP (resource reservation)
tunneling makes it hard to give a flow of packets a special treatment needed for the QoS
Security, firewalls, QoS etc. are topics of research and discussions

29. Mobile IP and IPv6 (RFC 3775)
Mobile IP was developed for IPv4, but IPv6 simplifies the protocols
security is integrated and not an add-on, authentication of registration is included -Protocols for registration, discovery etc. are available as standard, not layered above IP
COA can be assigned via auto-configuration (DHCPv6 is one candidate), every node has address auto-configuration
no need for a separate FA, all routers perform router advertisement which can be used instead of the special agent advertisement; addresses are always co-located
MN can signal a sender directly the COA, sending via HA not needed in this case (automatic path optimization)
„soft“ hand-over, i.e. without packet loss, between two subnets is supported
MN sends the new COA to its old router
the old router encapsulates all incoming packets for the MN and forwards them to the new COA
authentication is always granted

30. IP Micro-mobility support
Mobile IP (and MIPv6) problems
Designed to Internetwork mobile nodes across wide areas
Concentrates on address migration issues
Not suitable for fast migration and handoff within a defined geographical area
Micro mobility protocols: Keep the frequent updates generated by local changes away from the home network

31. IP Micro-mobility support
Efficient local handover inside a foreign domain without involving a home agent
Reduces control traffic on backbone
Especially needed in case of route optimization
Example approaches (research, not products):
Cellular IP
HAWAII
Hierarchical Mobile IP (HMIP)
Important criteria: Security Efficiency, Scalability, Transparency, Manageability

32. DHCP: Dynamic Host Configuration Protocol
Application
simplification of installation and maintenance of networked computers
supplies systems with all necessary information, such as IP address, DNS server address, domain name, subnet mask, default router etc.
enables automatic integration of systems into an Intranet or the Internet, can be used to acquire a COA for Mobile IP