Transcript lecture_slides

T-110.6120 Special Course in Data
Communication Software
Mobility in the Internet
25.9.2009
Prof. Sasu Tarkoma
Contents
• Overview
• Mobile IP
• NEMO
• Transport layer solutions
• i3
• SIP mobility
Mobility in the Internet
• This topic pertains to mobility of
– Networks
– Hosts
– Transport connections
– Sessions
– Objects (passive, active)
– Services
– Users
• Many solutions are needed on multiple layers
– Link layer, network, transport, application
– Vertical and horizontal handoffs
Mobility
• What happens when network endpoints start to move?
• What happens when networks move?
• Problem for on-going conversations
– X no longer associated with address
– Solution: X informs new address
• Problem for future conversations
– Where is X? what is the address?
– Solution: X makes contact address available
• In practice not so easy. Security is needed!
Classifying Mobility Protocols
Mobility
Global
Macro
Micro
Hierarchical MIP
(1996)
Cellular IP
(1998)
MIP
(1996)
Hawaii
(1999)
Dynamic Mobility
Agent (2000)
Intra-subnet
TMIP
(2001)
HMIPv6
(2001)
Intra-domain
MIPv6
(2001)
Inter-domain
Time
(evolutionary
path)
Routing vs. mobility
• Topology data aggregation is necessary
– Cannot track all hosts in the world
– IP addresses determined by topology
• Network gives the routing prefix
• Mobile hosts must change their IP addresses
– Causes sockets / connections to break
• How to communicate address changes?
• Two approaches:
– Let routing handle it  not scalable
• Done by ad hoc routing protocols
– Let end-systems handle it  protocol is needed
• Goal of a mobility protocol
– Transport and applications do not see address changes
– Mobility transparency
Rendezvous
• How to find the moving end-point?
– Tackling double jump
• What if both hosts move at the same time?
• Requires a rendezvous point
• Mobility management is needed!
– Initial rendezvous
– Can be based on directories
– Requires fast updates to directories
• Does not work well for DNS
Security issues
• Address stealing
– Alice and Bob communicate
– Mallory tells Alice
• Bob is now at C
• Address flooding
– Mallory downloads from Alice, Bob, etc.
– Mallory tells everybody
• I have moved to C
Mobile IP
• Two versions
– IPv4 (optional)
– integrated into IPv6 (with IPSec security)
• Home Agent (HA)
– Home address
– Initial reachability
– Triangular routing / reverse tunneling
• Route optimization
– Tunnels to bypass HA
– HA as a rendezvous point
Mobility Example:Mobile IP
Triangular Routing
Ingress filtering causes problems for IPv4
(home address as source), IPv6 uses CoA
so not a problem . Solutions:
Correspondent
(reverse tunnelling) or
host
route optimization
Foreign agent left
out of MIPv6. No special
support needed with
IPv6 autoconfiguration
DELAY!
Foreign agent
Home agent
Home link
Foreign link
Mobile host
Care-of-Address (CoA)
Reverse Tunnelling
Correspondent
host
Firewalls and ingress
filtering no longer a
problem
Double triangular routing
leads to overhead and
increases congestion
DELAY!
Router
Home agent
Home link
Foreign link
Mobile host
Care-of-Address (CoA)
Mobility Example:Mobile IPv6
Route Optimization
CH sends
packets using routing header
Correspondent
host
Secure tunnel (ESP)
Home agent
First, a Return Routability test
to CH. CH sends home test and CoA
test packets. When MH receives both,
It sends the BU with the Kbm key.
Router
MH sends a binding update to CH
when it receives a tunnelled packet.
Home link
Foreign link
Mobile host
MIPv6
• MIP6 utilizes IPv6 header options for signalling between the HA
and CN.
• The important changes are a new extension header (mobility
header) for the creation and management of binding, a new
routing header type to allow packets to be routed directly from
CN to a MN CoA (home address in ext), and a new destination
type (MN to CN, home address again)
• MIP6 uses the new IPv6 autoconfiguration mechanism to
determine the CoA, and thus does not need a FA.
• Using autoconfiguration, the MN receives Router Advertisements
that contain the routing prefixes of the visited network. This prefix
information is then combined with the interface ID (MAC address)
of the MN to obtain the CoA.
• MIP6 also supports the dynamic discovery of the HA or HAs.
Security in Mobile IP
• MIPv6 RFC 3775/3776
– Protection of Binding Updates HA, CNs
– IPsec extension headers or the binding authorization data
option
– Binding management key, Kbm, which is established through
return routability procedure
– Protection of mobile prefix discovery
– Protection of the mechanisms that MIPv6 uses for
transporting data
• Protecting binding updates
– Must be secured through IPsec
– ESP is used for updates and acks
• Shoulds: init messages, prefix discovery
Hierarchical Mobile IP
• HMIPv6 is specified in RFC 4140
• Introduces local Mobility Anchor Points (MAP) that are
essentially Home Agents
• MAPs can be located at any level in a hierarchical
network of routers, including the access routers.
• The aim of the HMIPv6 is to minimize the signaling
latency and reduce the number of required signaling
messages.
• As long as the MN stays inside one MAP domain it only
needs to update its location with the MAP.
• The localized mobility management can also be
completely handled on the network side without MN's
involvement at the IP mobility protocol level.
NEMO
• It is also possible for a
whole subnetwork to roam from
one part of the Internet to another.
• Network Mobility (NEMO) is specified in RFC 3963
• The technical solution of NEMO is based on MIP6.
NEMO allows subnetworks to change their location in a
network.
• This is realized using a mobile router that manages
the mobile network. The mobile router updates its HA
regarding the CoA of the mobile router.
• A NEMO compliant HA can act also as a MIP6 HA. The
basic solution creates a bi-directional tunnel between
the mobile router and the HA, which effectively keeps
the mobile network reachable.
• Hosts behind the mobile router do not need to be aware
of mobility in any way.
Multi-layer Operation
• Mobility and multi-homing can be realized on different
layers
– Network
• Mobile IP, HMIP, NEMO
– Between network and transport
• Host Identity Protocol (HIP)
– Transport (SCTP)
• TCP extensions, SCTP (TrASH)
– Application
• SIP, Wireless CORBA, overlays
• Re-establish TCP-sessions after movement
Host Identity Protocol
• New cryptographic namespace
• Connection endpoints mapped to 128 bit host identity
tags (hashes of public keys)
• Mapping at HIP layer
• 4-phase Base Exchange with cryptographic puzzle for
DoS prevention
• IPSec for network-level security
Mobility protocol
Corresponding
Mobile
UPDATE: HITs, new locator(s), sig
UPDATE: HITs, RR challenge, sig
ESP from MN to CN
UPDATE: HITs, RR response, sig
ESP on both directions
Basic HIP rendezvous
Rendezvous
server
I1
R1
I2
R2
Client
Rendezvous
registration
Server
Application-layer mobility
• Many application-layer protocols are, in principle,
similar to Mobile IP
• Moving entity may differ
– Instead of host we have object, session, entity, or
interests
• For example:
– Object mobility
• Wireless CORBA
– Session mobility
• SIP
– Interest mobility
• Content-based routing
– Generic mobility
• i3 overlay, service composition
SIP Mobility
• Session mobility allows a user to maintain and manage
a media session across devices
• Terminal mobility allows a device to move between IP
subnets while continuing to be reachable for incoming
requests and maintaining sessions across subnet
changes
• Personal mobility allows the addressing of a single user
• Located at different terminals by using the same logical
address
• Service mobility allows users to maintain access to
services while moving or changing devices and network
service providers
• SIP implements these using URLs, proxies, and
redirect servers. The home domain keeps track of users
and devices. Message forking
IMS
• Example of call routing
CSCF = Call State Control Function
HSS = Home Subscriber Service
Interrogating
Location Query
CSCF
HSS
Invite
From: sip:[email protected]
To: sip:[email protected]
Call-ID
User A
Serving
CSCF
Serving
CSCF
Multimedia session
Ok
User B
Internet Indirection Infrastructure (i3)
• An Overlay infrastructure.
• Every packet is associated with an identifier.
• Receiver receives using identifier
A Trigger
Movement with a
different address
(Natural Support for Mobility)
[Source: http://i3.cs.berkeley.edu/]
Mobile Web Server
Webserver
2
Browser
1
3
2.5/3G
Operator
Firewall
DNS
Gateway
By courtesy of Johan Wikman
Presented in EuroOSCON 2006
Internet
Mobile Middleware I
• Middleware is typically designed and implemented for
fixed-network hosts
– High bandwidth, low latency, reliable
communication
– Persistent storage and sufficient computing power
– No mobility
• Mobile environment requires new solutions
– Existing middleware services do not scale
– Previous lectures: mobility is challenging
– Small devices / embedded systems pose totally
different challenges
Mobile Middleware II
• Goals for middleware:
– fault-tolerance, adaptability,
heterogeneity,scalability, resource sharing
• Mobile middleware
– dynamically changing context
– decoupled
• events, tuple spaces
– Basic solution for wireless
• Use a proxy
Wireless CORBA
• CORBA does not support accessing mobile objects or
wireless communication
– Wireless CORBA specification
• Three basic requirements
– Invocations from mobile objects
– Invocations to mobile objects
– Wireless communication
• Home bridge
• Access bridges
• Tunnelling over wireless
• Handoff protocols
Mobile IP vs. WCORBA
• MIP addresses host mobility, not object mobility
• MIP does not specifically support wireless protocols
• MIP hides all handoff events
– location-aware services difficult to implement
Architecture
• Redirects requests for
services on the terminal
• Abstract transport-independent
• Keeps
track of the current
• Encapsulates,
forwards
or ignores
tunnel
for
GIOP
messages
• Other side end of the Access Bridge
access bridge
incoming
GIOP
messages
•
Concrete
tunnels
for
TCP/IP,
• Encapsulate/decapsulates msgs
• Decapsulates
andWDP.
forwards
UDP/IP
andevents
WAP
• Generates
mobility
messages
from reliable
the GIOP
tunnel
• Protocol
requires
and
• Generates
mobility events
ordered
delivery
• Lists available services
Handoffs
• Network initiated handoff
– started by an external application
– optional to support make-before-break
• Terminal initiated handoff
– terminal discovered a new Access Bridge
– make-before-break is required
• Access recovery
• The Home Location Agent is updated
• Old Access Bridges are informed
• Mobility events are generated in the visited domain and
the terminal domain
Indirection Points
• Mobility may be characterized by indirection points
– Mobile IP
• Single fixed indirection point
– Location / Identity split
• Single indirection point
– SIP
• Single fixed indirection point (home domain)
(other are possible)
– Content-based routing
• Many indirection points
Lessons to learn
• Hierarchical routing likely to stay
– Addresses carry topological information
– Efficient and well established
• Applications face changing connectivity
– QoS varies
– periods of non-connectivity
• Identifiers and locators likely to split
• Mobility management is needed
• Probably changes in directory services
– Overlays have been proposed
Summary
• Topology based routing is necessary
• Mobility causes address changes
• Address changes must be signalled end-to-end
– Alternative: use triangular routing as in Mobile IP
• Mobility management needed
– Initial rendezvous: maybe a directory service
– Double jump problem: rendezvous needed
• Many engineering trade-offs