Transcript Architecture Overview

Communication Topics
 Jason

Hill – [email protected]
http://www.cs.berkeley.edu/~jhill/cs294-8/MiniRetreat.ppt
High Level Communication
Goals

Support low power network devices
 Give intermittently connected devices the
illusion and appearance of continuous IP
connectivity
 Make scalability independent of end device
 Allow application to manage
availability/consistency tradeoffs
 Mask device mobility from services &
applications
 Provide application interface to low level
network information (location)
How?
 Push
as much of the complexity as
possible into the infrastructure
 Assume
compute cycles and network
bandwidth are free once you get to the
wired world
Quick look at existing wireless
systems
 GSM
 Mobitex
 CDPD
GSM Overview….

Mobility achieved through the use of the
Home Location Register (HLR) and the Visitor
Location Register (VLR).
Mobitex Architecture

Used by Palm VII
 Packet Switched
 Guaranteed message delivery (Message
Queues)
 http://www.ericsson.se/wireless
CDPD – “Wireless IP”
 Uses Analog
Cellular System
 19.2 kbps data w/ 128 bit encryption
 Sends small data packets over unused
voice channels
 “Mobile data intermediate systems”
route packets
 Fixed “address”
Possible Architecture
Traditional Clients/Services
IP
Device Proxies
Infrastructure Based Services
Delivery Q’s
Base Stations
Portable Devices
Device Properties

Uniquely identifiable
 Bootstrap to nearest Access Point
 Not directly addressable



AP’s can provide them temporary names
(proximity based naming)
Must phone home to inform proxy of temp. name
Special client of proxy push/pull data to/from
proxy
Access Points/Base Station
Properties
 Permanently
Connected
 Globally Addressable via IP
 Provides
 Queues
route to “local” devices
Data for recently seen devices
 Informs device proxies of “local” devices
that it is in communication with
Proxy Service Properties

Easy to find (immobile)
 Always available
 Has approximation of device state


What is the consistency policy?
Locatable by both devices and services
 Handles all requests to and from mobile
devices – provides scalability
 Can learn temporary route to portable
devices
Optimizations….
 Ninja
style code migration allows layers
to collapse as an optimization
 Higher power devices can take on
additional functionality
 Complex base stations can perform
protocol translations for clients
 Device  communication can avoid
going to proxies
Optimization for data flowing
from the device…

Forward by any base station that hears clear
transmission – minimize retransmissions at
expense of wired bandwidth
 Duplicates removed by proxy
 If all 5 clients try to transmit, 4 would get
through
Data flowing to the device…
 Base
stations uses wired network to
orchestrate communication
 Base stations learn which other base
stations they conflict with for a given
client
 Primary base station transmits to client
but neighboring base stations also
queue data in case client moves into
their area
Last link communication
options
option is use RF Monolithics – Low
Power/Cost
 Device to AP protocol should not
determine lowest power consumption of
devices (i.e. Require device to be active
minimum amount of time.)
 Are there any standard protocols we
could use?
 One
Issues…

What is the internal structure of a device
proxy?
 How inter-related are the designs for the
proxies, mobility support, and last link
communication protocols?


Could a device proxy be built on top of
CDMA/Mobitex providing continuous IP
connectivity?
Naming & Name Discovery

Both proxy names and temp. names
Is this a big naming problem?
 Resolution
and assignment of proximity
based names
 Querying of proximity based name
space?
Strengths…

Complex Device drivers are pushed into the
infrastructure where they are easy to write,
debug, & upgrade
 Devices can be composed by the
infrastructure (Speaker + Camera + Display
 Video Conference Device)
 Allow small devices to reliably service many
clients (device proxies/surrogates)
 Heterogeneity can be masked by software
adapters
Infrastructure Based
Communication Protocols
 Support
mobility in a transparent way
 Provide tiny devices the illusion of IP
connectivity
 Make brief periods of disconnection
invisible to the “real world”
 Buffer
 Attempt
and Cache information for clients
to optimize delivery overhead