A roaming architecture for IP based mobile telephony in WLAN environments

1. A roaming architecture for IP based mobile telephony in WLAN environments Tekn. Lic Jon-Olov Vatn Royal Institute of Technology (KTH) Department of Microelectronics and Information Technology (IMIT) Telecommunication Systems Lab (TSLab) <vatn@imit.kth.se>

2. Outline of presentation • Implications • Background • Current and upcoming requirements • Proposed architecture • Handover procedure • Discussion "Roaming arch. for IP telephony in WLAN env.", Jon-Olov Vatn, KTH/IMIT

3. Implications • WLANs will be used for IP based mobile telephony • User handsets will look like cellular phones, but have WLAN (and possibly WWAN) interface(s), and will support SIP and MIPv6. • Good WLAN coverage will be achieved through access network sharing and roaming. • Telephony and instant messaging will be treated as normal IP services and will be priced as such. • Fast handover support will become crucial; hence it is important to reduce the number of necessary message exchanges during the time critical handover procedure. "Roaming arch. for IP telephony in WLAN env.", Jon-Olov Vatn, KTH/IMIT

4. Background • IEEE 802.11 WLANs first emerged as wireless extensions to company and campus networks. WLANs have now become common in homes and at public hot-spots.We expect (near) full WLAN coverage in urban areas (bus-stops, shops, shopping malls, hotels, public transportation, …) • Due to low cost and VLSI more and more end-user devices have built-in WLAN (PCs, PDAs, IP-phones). • IP telephony is becoming mature and is beginning to take off. Emerging WLAN access infrastructures will certainly be used for IP based telephony. Using them for IP based mobile telephony is a natural next step. "Roaming arch. for IP telephony in WLAN env.", Jon-Olov Vatn, KTH/IMIT

5. Current requirements • Security and access control Valid for WLAN networks in general, not specific to IP telephony services. Standards and products are ready or on their way. • Coverage Existing and new wireless ISPs (WISPs) are about to setup more APs. Infrastructure sharing or roaming will be needed. "Roaming arch. for IP telephony in WLAN env.", Jon-Olov Vatn, KTH/IMIT

6. Results and new requirements • AAA solutions to support roaming • Improves coverage • Model with heterogenous set of actors. • Telephony will be cheap! (Flat rate?) • Authentication to avoid ”phone spamming” • Confidentiality easily added (encryption as default) • Demand for fast handover support • Users want to have mobile phones, not simply cordless phones  Fast handover will be crucial. "Roaming arch. for IP telephony in WLAN env.", Jon-Olov Vatn, KTH/IMIT

7. AAAL AAAL AP AP AP AP Alice Proposed architecture Alice’s ISP Bob’s ISP HA SIP AAAH Bob SIP AAAC Internet "Roaming arch. for IP telephony in WLAN env.", Jon-Olov Vatn, KTH/IMIT

8. Components of the architecture • IP end-to-end • Bypasses PSTN whenever possible; using Intranets and the Internet • IPv6 rather than IPv4 (avoiding NAT; enabling MIPv6 route optimization) • SIP to setup (secure) phone call • Provides confidentiality and defeats phone spamming • IP mobility support using MIPv6 • MIPv6 gives low end-to-end delay (SIP mobility interesting alternative) • Shared access networks • Both sharing and roaming • Enhanced WLAN security • 802.1X to enforce access control • TKIP, CCMP or WPA to secure wireless link • Accounting for network usage using RADIUS (or Diameter) • No explicit accounting for telephony usage - except for gateways to PSTN "Roaming arch. for IP telephony in WLAN env.", Jon-Olov Vatn, KTH/IMIT

9. Seamless mobility? • In-LAN handover delay: • Regular IEEE 802.11 mechanisms (Scanning for APs, authentication, reassociation) • Acquire network access • Authenticating with home AAA server (802.1X)(Ongoing work to handle this locally.) • Establish keys for secure WLAN connection. • Possibly map association to right ISP. "Roaming arch. for IP telephony in WLAN env.", Jon-Olov Vatn, KTH/IMIT

10. Seamless mobility? (cont.) • Cross-LAN handover delay, as for In-LAN handovers plus: • Acquire IP address (IPv6) • Redirect downstream (and upstream) traffic accordingly. "Roaming arch. for IP telephony in WLAN env.", Jon-Olov Vatn, KTH/IMIT

11. Symbolic handover latency expression Tup = T80211,up+T8021X+TIPv6-addr+TMIPv6,up = 8Tbb+21TWLAN+TDAD+Trand,radv Tdown = T80211,down+T8021X+TIPv6-addr+TMIPv6,down = 10Tbb+23TWLAN+Tsearch+TDAD+Trand,radv (here EAP/TLS authentication is assumed for 802.1X) "Roaming arch. for IP telephony in WLAN env.", Jon-Olov Vatn, KTH/IMIT

12. Future and related work • Practical tests on WLAN handover • Arbaugh et al[1] and Velayos et al[2] have published some practical measurements on WLAN handover performance. • I am performing a similar study complementing their work. • I also intend to extend the study to include 802.1X authentication, MIPv6 etc. to verify the latency formulas presented here, and to study the effect of processing delays in the different nodes. • The model should be extended to include roaming brokers. • SIP security • Elisabetta Carrara et al are working on IETF drafts for secure RTP (SRTP)[4] and an associated keying mechanism (MIKEY) • Israel Abad Caballero (KTH) is working on open source SRTP (and MIKEY) implementation for SIP clients as part of his master thesis. "Roaming arch. for IP telephony in WLAN env.", Jon-Olov Vatn, KTH/IMIT

13. References [1] Arbaugh et al, ”An Empirical Analysis of the IEEE 802.11 MAC Layer Handoff Process”, Tech Report, University of Maryland, 2002. [2]Héctor Velayos ”Contributions to IP-based wireless communications”, Lic. Thesis, KTH, May 2002. [3] Carrara et al, ”The Secure Real-time Transport Protocol”, IETF draft, Work in progress. [4] Carrara et al, ”MIKEY: Multimedia Internet KEYing”, IETF draft, Work in progress. "Roaming arch. for IP telephony in WLAN env.", Jon-Olov Vatn, KTH/IMIT

14. Discussion • Accounting? • Coverage? • Quality of Service? (What is acceptable quality?) • Network sharing and/or roaming feasible? • ”Horizontal” or ”Vertical” handover? • … "Roaming arch. for IP telephony in WLAN env.", Jon-Olov Vatn, KTH/IMIT