Prescriptive Network Theories

Jon Crowcroft, http://www.cl.cam.ac.uk/~jac22

Existing Theories

Much existing network theory is Theoretical (models, simulation) Descriptive Possibly Predictive (queuing, control, graph,insert yours

here) Disjoint in ownership and application

Identifiers, Paths and Protocols What is really needed to design them

right?

Prescriptive

Tells you what to do… not just what its like, when you’ve done it.

Architects use design patterns - but this is after the innovation - It’s a way of scaling out their work

So prescriptive architecture isn’t patterns - it is some higher level methodology It’s generative

1. Layers and Constraints

John Doyle (caltech) talks about de-constraining constraintsHighly optimized tolerant systems

Specifically, the constraint of IP In the narrow waist of the hourglass Afords design freedoms below IP And above

One could argue that midboxen+TCP has moved this up a level to the HTTP appspace So in modular systems, a careful choice of limitations in

a key module (with high centrality in the “call graph” can allow great flxibility later

Architecting Middleboxes

So if we want to do prescriptive arch for middle box

What is the minimum functionality that is simple enough, but no simpler? Would you include caches in the arch? What about integrity of content there (c.f. DTN

custody protocol)? How about flow and object naming? -Unify (and

crypto-assigned?)? If we got this right, could combine DTN,

CCN and IPng

Getting it wrong - SIP

SIP was about the most extensible protocol ever VOIP signaling/call setup protocol Basic job is easy (MJH’s 1st code worked

in a couple of hours - see rat) So why have a turing complete call

handler as part of any protocol Now cannot write SIP DDoS defense coz

SIP proxy can be hit by halting problem :-(

2. Counter examples - identifiers

Internet Addresses - serve several functions Interface id Routing hint Part of flow tuple Implicit part of IPC end point (socket) Lack of precision allowed “innovation”

Aggregation/Longest prefix match NATs…

2 continued [ack Brian Carpenter]

IPv6 isn’t innovative - inherits most the same properties but doesn’t prescribe or afford much new

IPNL is innovative (see also signpost) -Name based end point frees up IPC end point to support Referrals Multihome Failover Multipath TCP Migration/Roaming Renumbering Virtualisation/Better scale aggregation …

Why combine these?

Resource pooling extended to storage

Traffic management extended over both space and time

Decoupling transmission/publication from reception, subscription, consumption

Disruption and delay tolerant…

Multipath, mobility etc again

The future context is multiscale 1024 core is a couple of years off - what

is IPC on OS on that? Data center systems > 1 M cores

abound The net of mobile end systems is 5B

devices (-> Interet of Things etc) We need to matchmake in this

impedence mismatched world, and It would be good to retain a single

system to do it

3 Graph Theory and Routing

Huge effort measurind and modeling graphs

No-one’s using it to design routing LS&DV&PV routing + Hierarchy are

heavy handed tools Why not start from path properties of

graph And derive a routing algorithm… … …

Conclusions, Discussion

Keep it as simple as possible… …but no simpler

Ack Cambridge Mphil students On Network Architecture module