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

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

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 WAN Operator R WLAN G1 WLAN R1 WLAN R2 WLAN M1 WLAN M2 Provide connectivity in the office using R2 here. Provide connectivity using M2 by cooperating with the independent operator at the café. Shed load in hot spot by handing off to G.

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 IP int. Each device runs a local NAT that replaces IP int with IP aik and tunnels it out of the active interface k to a Mose IP mose that is expected to be near the correspondent host. How it determines IP mose is an open question. The mose is a NAT that replaces IP aik with any available IP address IP fixed. and creates an (IP dest, IP fixed, IP aik ) in a local table.

8. IP aik, IP mose (IP aik,IP dest ) NAT Pure NAT IP fixed,IP dest IP aik,IP dest Tunnel Encap- sulation Tunnel Decap- sulation Mobility Server Application IP int,IP dest IP aik, IP fixed, IP dest NAT Table Mobile Host (MH) Correspondent Host (CH) Schematic of NAT-based Solution 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. CH Mose CH

9. A Comparison of Different Mobility Solutions Session Layer ProxyMobile IPNAT-based solution Violates end-to-end semantics. Does not violate e2e semantics. Does not require a fixed IP address. Requires a fixed IP address Does not require a fixed IP address. Requires > layer 3 state at indirector. Requires only layer 3 state at indirector. Complexity involved at indirector. The least complex scheme. Complexity involved at mobile host. Deals with address scarcity. Does not deal with address scarcity. Deals with address scarcity. Easy IPv4-IPv6 transition. Not clear…Easy IPv4-IPv6 transition.