An A lways B est C onnected S ervice

1. An Always Best Connected Service Sridhar Machiraju (machi@cs.berkeley.edu) Per Johansson (Per.Johansson@ericsson.com)

2. Motivation Cingular Starts 3G Migration Nokia Unveils Roaming Solution Using GSM, WLANs Ericsson Takes Lead In GPRS Race AT&T Wireless Expands GPRS Three airlines racing to provide public high-speed wireless LAN service at gates

3. So… Can wide area wireless operators leverage the proliferating use of high-speed local area networks and other wide area networks to augment their Always Connected Service to an Always Best Connected Service while preserving the seamless nature of connectivity.

4. How to Support Mobility? • Mobility is known to require a level of indirection that is provided by Mobility servers (e.g. Home Agents, Session layer proxies etc). How do different mobility solutions compare in an ABCS scenario w.r.t scalability, robustness, security ? • A device may use a single Mose or multiple Moses. How may this be achieved and what are the pros and cons of either approach? • What are the placement issues to be considered by a Mobility service provider?

5. Why, When and How to Cooperate? • By cooperating providers could increase the ``best`` part of ABCS, reduce operational costs. Disadvantages include the absence of differentiation between services offered by different operators, potential abuses. • Use inter-provider handoff as a means of shedding load. • Assuming its necessity, how may cooperation be realized? Some possible mechanisms include automated auctions or capacity clearing houses etc. WAN Operator G WLAN G1 WLAN M1 WLAN M2 WAN Operator R WLAN R2 WLAN R1 Shed load in hot spot by handing off to G. Provide connectivity in the office using R2 here. Provide connectivity using M2 by cooperating with the independent operator at the café.

6. QoS and Security • In an ABCS scenario, what should be the nature of QoS guarantees and how are they guaranteed. • Since users would like to have a single provider (And consequently, a single bill) how are a provider’s users authenticated (in real-time) with other access providers while limiting the number of logons to be performed. • As with any cooperative scenario, verification of the agreements of peers is an important requirement. How is this performed?

7. A NAT-based Solution for ABCS – Ongoing Work • Traditional Mobile IP drawbacks - • Traditional Mobile IP requires hosts to possess a fixed (home) IP address. This is unsuitable for wireless devices such as cellphones, PDAs. • Triangle routing could result in high overhead since the active network interfaces list could change frequently. • A possible solution – • All applications of a device use an internal IP address IPint. • Each device runs a local NAT that replaces IPint with IPaik and tunnels it out of the active interface k to a Mose IPmose that is expected to be near the correspondent host. How it determines IPmose is an open question. • The mose is a NAT that replaces IPaik with any available IP address IPfixed. and creates an (IPdest, IPfixed, IPaik) in a local table.

8. Schematic of NAT-based Solution Application Mobility Server IPint,IPdest Tunnel Encap-sulation Tunnel Decap-sulation PureNAT NAT IPaik,IPdest IPaik, IPmose (IPaik,IPdest) IPaik,IPdest IPfixed,IPdest NATTable Mobile Host (MH) Correspondent Host (CH) IPaik, IPfixed, IPdest CH It is important that the mobility servers (which is dependent on the correspondent host) be as near the correspondent host as possible in order to reduce the inefficiency that could occur due to triangular routing. Mose CH CH CH

9. A Comparison of Different Mobility Solutions