Tuesday, May 31, 2011

3G and IPv6 More considerations:

Please note this are pretty much notes I made while going through some literature, I also assume a lot of people reading this have probably worked for ISP's and understand a typical ISP network:

Architecture:
A 'generic' ISP network has functional roles very much like a 3G network. They have an access network, Distribution/aggregation and a core network. 3G is a just a 'little bit' more complex but think along those lines and you'll get it.

The 3G/UMTS network is divided into two main domains:
the packet switched (PS) domain - Where I predominantly work/worked
and the circuit switched (CS) domain - where I know enough theory to run circles around most but I'm by no means an expert.

The core network elements comprise of the GGSN, the SGSN and the IMS (Think of the IMS as a mix of many many systems/applications).The GGSN is really just a customized router between the GPRS network and other networks - the first GGSN I ever run was a cisco CMX based on the 7613 chassis and a bunch of MWAM modules interfacing networks such as the general Internet and customer networks.

The SGSN is again an intermediate router between the GGSN and radio network. It's main responsibity is administrative functions other than routing: AAA, mobility management, and billing, among others - please note you can bill from either SGSN or GGSN's, If you have a DPI/PCRF, the billing function is moved further out of the actual 3G network.

The IMS as mentioned earlier is essentially the server farm, is where content and IP infrastructure servers live. So your DPI, WAP, DNS etc etc

The radio network abbreviated as UTRAN has Radio Access Network Controllers (RNC's) and base stations (BTS), which connect the handsets (UE or User Equipment) to the core network. The radio network is capable of transmitting data at various increments from 64 kbps to 2 Mbps or more - it all depends on issues like the next line describes and the technologies used - google for direct tunnel-.

The actual data rate depends on propagation, velocity of the handset, bandwidth available, and so on. This is important to note especially if you're the kind of guy that escalates issues to me:-) or if you live in South C....:-) thats a joke...laugh

IPv6 view of a 3G network:
As far as IPv6 is concerned the biggest point of concern is the pdp context. This forms the connection between the (UE) - user terminal and the GGSN. It is over this link that we transfer packets. If you're thinking - oh so like PPP - I'll say yes, just like PPP, only we use a protocol called GTP .

PDP contexts are created and torn down every time you attach/detach/re-attach. So IPv6 runs over this PDP context and that is what is referred to as an IPv6 link for a handset.

Resource usage on Handsets:
Now imagine if you are dual stacked, imagine how much power you'll be using or attach reattach for two sets of contexts and you begin to see why I still insist that all mobile handsets should be made to only support IPv6 then use 6to4 mechanisms to transition.

Also imagine a chinese manufacturer and your standard user who will buy a Nokla phone that some 'manufacturer' only enabled IPv6 and you suddenly start having very interesting support calls. I am so sure the black market for IPv6 handsets will show up and one of the key issues will be IPv6/IPv4 misconfiguration. Some intentional, some laziness, some just pure sillines.

You will definately also need slightly more memory to hold the lenghthier IP addresses. This looks trivial but again I expect some issues there.

IPv6 address assignment:
GPRS systems have always supported static and dynamic addresses. This can be stateless or stateful. The key issue with IPv6 here is the simple fact that autoconfiguration requires a mac-address, your handset doesn't have this, to counter this, we'll use rfc 2472's procedures.

There are other issues here with addressing that Im not entirely sure I get, like since we now have so many addresses, doesn't it make sense to assign static addresses? plug each msisdn with an IP on the HLR and call it a day? apparently not

Aa /64 to each handset is a huge number of addresses, however you can very well expect guys to share connections behind mobile devices in which case it actually makes sense. It also makes sense because 'most books' say so, and if you do the binary math carefully, you start seeing why /64's to each endhost is good for the transition. Heck some might even require /48's - think of tethering. Plan how to do addressing carefully.

Whether or not you'll run out of addresses depends on many variables, including size of allocation, customer takeup, and so on. Your planning is also key here. If you were an idiot subnetter in IPv4, I suggest you try cross the idiot barrier fast. IPv6 is a whole 'nother ball game. In reality even with the ratio adjusted to /64 per PDP context, and only addresses from 2xxx:: used, there are still well over 300 trillion addresses available. This should be plenty of room for the next few years. Just plan accordingly, read widely, you should be okay.

Mobility:
The movement of cellular hosts within 3GPP networks is handled by link layer mechanisms. So as far as IPv6 goes, it's handled just as it would be in IPv4.

Following the case above, it means the PDP context would be moved from one location to another without tearing down the pdp context. Now most movements are within base stations - micro mobility? This doesn't change your point of attachment for IP so there's no 'handover from a ggsn to another. You can also have movements that churn your point of attachment between GGSNs - macro mobility. In the initial releases of 3G, macro mobility is taken care of below IP layer by using tunnels to create an apparently flat IP network. ie a tunnel between ggsnA and B ensuring your PDP context remains BUT the more this happens the more delay and other bad things can happen to your connection.

Roaming:
Arghhhh.......throw in another arghhh for the fact that telco's still insist on using simcards for identifying users....the sim card should be killed...swiftly...another rant, another day

Are there motivations to move IPv6:
Where I work, IPv6 is still pretty much driven by technical enthusiasts. Management is still quiet and can be quite unsupportive and a morale drain. However it might be us techies failing to inform them. Am I motivated enough to do that? probably not, for some reason there is always someone higher up, an invisible hand out to discredit or tear them down, or generally just not ready to make things happen fast enough, so unless i can safely do it without asking eg paying for my own ccie or travel to afnog,or test IPv6 I stopped bothering; they can read my blog though:-) to get a grasp of my views.

The move to general IP is however very well taken up. we have come from far, we've done an NGN, we have a unified core so IPv6 will be an easy one to cross once we get widespread acceptance, or its forced on us. Either way it will happen.


I also saw a nice term describing a challenge we can expect. IPv6 brain drain. Since the most senior enough managers to make retention decisions do not know much about IPv6, expect to lose some people to the ones that get it faster than you.

In the US, IPv6 is actually being driven by government. i find it weird that organizations that stand to benefit the most are the ones lagging behind the most.

Probably the clearest motivation for 3G from the telco point of view is that the integration of IP actually helps to reduce the cost of running the network.Ultimately, the goal is to carry voice traffic over packets, enabling statistical multiplexing to kick in. This should save costs on traditional support infrastructure, such as circuit-switched E1-minimum increment backhaul. Furthermore, the mass market economics of IP, when brought to bear upon the production of telecomms equipment, should result in further savings.

- read IPv6 Network Administration By: Niall Richard Murphy; David Malone

References:
http://tools.ietf.org/html/rfc3316
http://tools.ietf.org/html/rfc2472
installation-and-configuration/ipv6na-chp-5-sect-7

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