1. Host Mobility Using an Internet Indirection Infrastructure by Shelley Zhuang, Kevin Lai, Ion Stoica, Randy Katz, Scott Shenker presented by Essi Vehmersalo

2. Introduction and i3 ● Robust Overlay Architecture for Mobility (ROAM) ● Built on top of i3 – Indirection to separate sending from receiving – Chord based overlay of servers – Multicast (several triggers with same identifier), anycast (inexact matching of triggers), service composition (stack of triggers), mobility (updating trigger address)

3. Goals for mobility solution ● Routing efficiency close to IP routing ● Efficient handoff, minimal loss of packets ● Fault tolerance ● Location privacy ● Simultaneous mobility of both endpoints ● Personal/session mobility ● Link layer independence

4. ROAM design ● Efficient routing – Caching trigger servers to minimize hops in overlay – Trigger sampling to select id on close by server – Mobility-aware trigger caching to maintain triggers for different locations ● Efficient handoff – With higher the lattency of location updates, more packets will be lost during cold switch→choosing ids on close by servers – With simultaneous connectivity at two locations, multicast- based soft handoff ● Duplicate detection by comparing MD5 digest of packet with those of recently received packets

5. ROAM design (cont.) ● Location privacy – Choosing ids on nearby servers may expose location of the host – Ids may be chosen close to CH (sharing same prefix) ● Assuming CH doesn't need location privacy ● For fast handoff two triggers one close to CH one to MH

6. ROAM design (cont.) ● Personal/session mobility – Available device may register a trigger representing the user. – Reguires agreement protocol between devices ● Legacy application support with user-level proxy inserting, exchanging and updating triggers

7. Simulation Results ● Comparing ROAM and MIP with bidirectional tunneling and triangular routing to IP routing ● Latency stretch vs. infrastructure size – Two mobility patterns for MH-HN distance and three communication patterns for CH location – ROAM performs better especially with weak points of MIP, when neither MH or CH is close to HN ● ROAM is more fault tolerant than MIP

8. Simulation Results (cont.)

9. Handoff Experiment Results ● ROAM TCP throughput was measured relative to frequency of handoffs – With multicast-based soft handoff the TCP performance degragation was minimal with increasing number of handoffs – Only MD5 digest calculation causes some performance penalty ● ROAM recovered from packet loss during cold switch better than MIP

10. Discussion and Conclusions ● Security can be increased with private triggers, public key cryptography to exchange them and preventing inserting several triggers with same id ● Lower latency can be achieved by using i3 only to exchange location updates ● ROAM achieves location privacy and efficient routing and handoff by giving end-hosts ability to control placement of indirection points ● Also robust and supports well soft handoffs and frequent mobility