Latency & Scaling Issues in Mobile-IP Sreedhar Mukkamalla Bhaskaran Raman

Motivation ICEBERG project: –packet switched cellular telephony network –flexible service architecture Universal INBOX Location based services etc. In search of the right mobility architecture…

Project Goals Mobile IP: IETF Standard for mobility –Is it suitable for ICEBERG ? Wide area registration latency –Is it a problem ? Large number of cell-phone users –How many mobile hosts can an agent handle ?

Basic Mobile IP Triangle routing problem Wide-area registration latency Registration mechanism: –MH registers with HA through FA –If registration times out, retry with exponential back-off –Minimum RTO = 1 second IP tunnel

Ping measurements to Rutgers - used in simulation No congestion: 70 ms latency; During congestion: 1600 ms latency Congestion during day time: 7am-5pm PST; RTT = 540 ms With no back-off during losses, 1200 ms average latency Wide area registration latency vs Time

But... Machine at CMU: –average latency around 190 ms –latency > 200 ms only 3% of the time Machines at MIT & UNC –average < 100 ms –latency > 200 ms less than 0.2% of the time Machine at UMD: –average 1200 ms –latency > 1 sec for more than 1/6th of the time

Scaling Measurements Experimental Setup –FreeBSD implementation of Mobile-IP –Pentium (300MHz) machines on 100 Mbps Ethernet –Mobility emulated by modifying code at MH Measurements to determine: –Hand-off rate that an agent can handle –Data traffic that an agent can handle

Results FA can handle about 2500 registrations per second –User-level handling of registration messages HA/FA can handle data traffic (tunneling/de- tunneling) at 20,000 packets per second –160 byte packets –Equivalent to about 1000 two-way audio streams –Ethernet gets saturated Conclusion: An agent can handle at least a few hundred mobile hosts

Conclusions Processing is not the bottleneck –at least for up to a few 100 users per agent Wide-area registration latency –Very less for some sites, unacceptably high for others Should we optimize the architecture at the IP layer for performance ? –End-to-End argument => IP mobility support required –But, optimizations should probably be made at the link layer