CSC 600 Internetworking with TCPIP Unit 10 Mobile

CSC 600 Internetworking with TCP/IP Unit 10: Mobile IP (Ch. 19) Dr. Cheer-Sun Yang Spring 2001

Mobile IP • How can IP design be changed so that portable computers can be moved from one network to another with disconnection and reconnection?

Why Mobile IP? • A computer can logon to a home network from within an airplane, a car, yacht, etc. • New ways of connection are now available including radio frequency, infrared LAN, etc. • For example, if an access point is installed, a computer user who just finished preparing for the presentation material can carry the laptop to the conference room without shutting down and then restoring the communication links in the new room.

Mobile IP vs. Wireless Communication • When Mobile IP talks about computers, wireless communication has to do with cellular phones. • Wireless communication requires a phone company to make changes in their system, whereas infrared or radio LAN attachments are typically made without charge.

Mobility vs. Portability • Mobility requires a host connecting to a network to change its location without disconnecting the connection. • Portability allows a host to be moved from one location to another with the possibility of reconnection. • Mobility is often associated with wireless technology, e. g. , wireless PC, whereas portability is often associated with laptop computers.

Mobil IP Topics • • • Mobility, Routing, and Addressing Mobil IP Operations Mobil Addressing Foreign Agency Discovery Agent Registration Tunneling: The Two-Crossing Problem

Portability • The protocols such as Point-to-Point (PPP), Dynamic Host Configuration Protocol (DHCP) and Domain Name System (DNS) are devised to supportability.

Mobile IP • Mobile allows a single host to hold two addresses simultaneously. – The primary address is permanent and fixed. It is the address applications and transport protocols use. – The secondary address is temporary and changes as the host moves.

Architectural Model of the IETF Protocol • In the IETF Mobile IP Protocol, the location directory (LD) is present at the same node on the home network that implements the readdressing function. The readdressing node on the home network is called the home agent. • Correspondingly, a foreign agent fulfills the inverse readdressing function when the datagram is delivered to the care-of address. After the readdressing function is performed, the foreign agent delivers the resulting datagram to the mobile node.

Mobile IP Protocol Overview • Mobile IP is, in essence, a way of doing three relatively separate functions: – Agent discovery – Registration – IP-to-IP tunneling

Agent Discovery • Home agents and foreign agents may advertise their availability on each link for which they provide service. A newly arrived mobile node can send a solicitation on the link to learn if any prospective agents are present.

Agent Registration • Before it can receive datagram at a foreign location, a mobile host must register. • The procedure allows a host to: – Register with an agent on the foreign network – Register directly with its home agent to request forwarding – Renew a registration that is due to expire – Deregister after returning home

Registration Message Format

Datagram Routing • Once it has registered, a mobile host can communicate with an arbitrary host. To do so, the mobile creates a datagram with the destination address in the destination field and the mobile’s home address as the source. • The datagram will travel along the shortest path from the foreign network to the destination. • However, a reply will not follow the shortest path directly to the mobile node. Instead, it travels to the mobile node’s home network.

IP-to-IP Tunneling • The home agent, which has learned the current location from the registration, intercepts the datagram and uses IP-in-IP encapsulation to tunnel the datagram to the care-of address.

The Two-Crossing Problem • Major problem of mobile IP: inefficiency. • Because a mobile node uses its home addresses, a datagram sent to the mobile will be forwarded to the mobile’s home network first and then to the mobile. • The problem is especially severe because computer communication often exhibits special locality of reference.

Also referred to as Triangle Routing

Route Optimization • Update binding cache • Managing smooth handoffs between foreign agents • Acquiring registration keys for smooth handoffs • Using special tunnels

Wireless LAN Issues • Medium access – Carrier Sense Multiple Access/Collision Avoidance • IEEE 802. 11 -Wireless LAN (WLAN) specification

Suggested Reading • • • Perkins: RFC 2002 Perkins: RFC 2004 Hanks et. al. : RFC 1701(IP-to-IP tunneling) Montenegro: RFC 2344(reverse tunneling) Perkins and Johnson: optimization for mobile IP