Nothing says “Reading Time” like a having six hours between sound-check and gig. So with this in mind, I’ve read another couple of papers relating to Mobile IPv6. What is nice about academic reading, is that the more you read, the more you seem to understand. Now that sounds a bit obvious, but if you’ve ever read an academic paper, you’ll know that it’s a bit like wading through treacle.
So what I’m trying to say is, perseverance is the key and you’ll soon find that as you go from one paper to the next, you see the same concepts being explained in different ways which all helps with understanding what the heck you’re doing!
So here’s the first of the two papers with a summary and critique. WARNING! This is a LONG post!
Pérez-Costa, X., Torrent-Moreno, M., and Hartenstein, H. 2003. A performance comparison of Mobile IPv6, Hierarchical Mobile IPv6, fast handovers for Mobile IPv6 and their combination. SIGMOBILE Mob. Comput. Commun. Rev. 7, 4 (Oct. 2003), 5-19.
This is the first ‘long’ paper I’ve read thus far at 14 pages in length, but has been the most useful and relevant with regards to my project. This paper introduces some of the ideas and experiments that I may decide to use when designing and running my own experiments.
As the title suggests, the paper compares the performance of the base specification of MIPv6, Hierarchical MIPv6 (HMIPv6) and Fast Handovers for MIPv6 also known as Fast MIPv6 (FMIPv6).
As this is just a summary of the paper, the base specification of Mobile IPv6 will be described in my report so is omitted here. Hierarchical MIPv6 attempts to improve handover times by introducing a ‘micro-mobility’ protocol. What this means in essence, is that if a Mobile Node (MN) moves from one point of attachment to another within a particular IP subnet, then HMIPv6 manages the handover with a Mobile Anchor Point (MAP). It does this by acting as ‘local’ Home Agent (HA) which assigns a Regional Care of Address (RCoA) to the MN when it enters the MAP domain.
Next, the MAP informs the HA and correspondent nodes (CN) within the subnet of the RCoA of the MN. Finally, the MAP intercepts all packets and then forwards them on to the MN to its on-link care of address (LCoA). This means thatonly the MAP need know about the movement of the MN while it is in that particular MAP’s domain.
Fast Handovers for MIPv6 work by anticipating the next move of the MN. Essentially, this involves the old Access Router (AR) to act as a proxy to the MN while the MN attaches to a new AR. There follows a short period of time where the old AR forwards packets for the MN to the new AR before a Fast Binding Update is sent and the old AR link is severed.
There are a couple more papers referenced within the text that go into more depth which I hope to read soon.
The paper goes onto describe a combination of the two extensions called Hierarchical MIPv6 + Fast Handovers for MIPv6 or H+F MPIv6 which I won’t go into as a new internet-draft proposing a combination has been released.
What becomes interesting is that the paper describes the setup for the simulation using ns-2. The key phrase here was:
“…large enough to proveide realistic results but to be small enough to be handled efficiently within ns-2.”
Also the Internet was modelled by adjusting the Link Delay and non-deterministic movement of the Mobile Node was modelled using the random waypoint model. The wireless medium used the 2Mbps WLAN 802.11 DCF (Distributed Coordination Function) provided by ns-2. The simulated network was small, but contained four distinct subnets, each of which was a Micro-Mobility Domain.
One interesting point that was raised in this paper was the issue that 802.11 and similar technologies do not allow the receipt of IP flows at different frequency bands simultaneously from two access routers. That is unless you have multiple wireless interfaces.
The simulations utilised the following performance metrics:
- Handoff Latency
- Packet Loss
- Signalling load
- Bandwidth per Station (The number of stations was increased from 1 up to 50)
Another key point was that each experiment had to be run a number of times in order to get an average value. This appears to be the best way of getting an accurate result be smoothing out extreme results.
The types of traffic sources used in the experiments were:
- Streaming Video
- File download with TCP (Testing bandwidth)
The experiments focused on the results from one Mobile Node moving in a deterministic and non-deterministic manner with an increasing number of competing stations. The traffic sources were used one at a time before the experiments were done using all of the traffic sources at the same time to simulate a ‘realistic’ scenario.
What I took away from this paper was that designing experiments was not an easy task and that the authors had obviously gone to great depths to investigate the peformance of theses extensions fully. However, some questions still arose whilst reading:
- Why did other nodes move randomly all the time? What if many mobile nodes were moving in the same direction at the same time? For example this could be commuters on a train.
- Why did the authors decide to not implement Binding Acknowledgements to Correspondent Node Binding Updates? Surely to provide a realistic scenario it is necessary to include all features even if it incurs additional overhead.
- Was the simulated network an over-simplification? Is modelling the Internet so difficult? I guess the answer to that is probably!
So to sum up, I’ve learnt a lot about what I’m going to have to do regarding the experiments I’ll need to design. And I also learnt a lot about the workings of MIPv6 and its proposed extensions.
My thanks if you’ve gotten to the end of this post and I’ll post the details of the (much) shorter paper tomorrow!