mobility beyond third generation cellular feb 5 1998
TRANSCRIPT
MOBILITY
Beyond Third Generation Cellular
Feb 5 1998
Overview
• Mobile IP
• IMHP
• Mobility in GSM
Mobility & IP: The Problem
• Hierarchical IP addressing based on physical location
• The same address is used for identification as well as location
• For identification, an unchanging address is required
• For mobility, a dynamic address is required
Solution
• A level of indirection– Use two addresses– Home address (identification)– Foreign address (location)
• How to obtain a foreign (care-of) address?
• How to manage the binding between the two addresses?
• How to forward packets?
Why handle mobility at the Network Layer?
• Higher layers should not be concerned with mobility
• Mobility management independent of physical layer– can move from one physical network to another
• The problem of mobility is transformed to one of routing
Goals
• Mobility
• Communicate with nodes that run old IP
• Messages about the location of a mobile should be authenticated
• No constraints on assignment of IP addresses
Previous Approaches
• Sony MHP, Columbia MHP, IBM’s MHP
• Use IP options
• Use a mobility router backbone or home gateways
• Use of multicast in the backbone
• Propagation of bindings for route optimization
Mobile IP: Architecture
Home Network
Foreign Network
Specifications
• Agent Discovery
• Registration
• Tunneling
Agent Discovery
• Agents advertise their presence
• Mobile can send solicitation messages
• Mobile-IP modifies the ICMP router discovery procedure
Registration
• Mobile registers its care-of address with its HA
• This could be strongly authenticated– shared secret between mobile & HA
• Registration request & reply messages
• UDP port 434 is used
Tunneling (forwarding)
• HA should intercept messages coming for the mobile (may use proxy ARP)
• HA tunnels the IP packet to the care-of address
Care-of Address
• Could be FA’s address– the FA de-tunnels the packet and sends it to the
mobile
• Mobile could have its own foreign address (obtained through DHCP)– the mobile de-tunnels the packets itself
New Concerns
• Inefficiency: triangle routing
• Security concerns: Any node on the internet can do “remote redirection”
FA
HA
MobileHost talkingto mobile
Internet Mobile Host Protocol
• Aims to provide– routing efficiency– authentication
• Route optimization + Security is difficult
• Security == Current Internet security
• Ideal solution would require key distribution
Route Optimization
• Cache Agents (CA):– cache bindings– cache entries are authenticated– entries are timed out
• A node that wishes to optimize its communication should function as CA
Binding Management
• Lazy notification
• Mobile host always notifies its HA when it moves (registration)
• Node N (CA/HA/LA) receives a packet to be tunneled to the mobile ==> N sends binding notification to source node S
• Binding notifications are re-sent with back-off
Authentication
• Mobile to HA:– strong authentication based on shared secret– secret exchanged while mobile is at home
• Authenticating a binding at CA– send request to mobile/HA with random
number– get reply and check random number
Authentication (Continued…)
• Visitor-List entries at FA– need not be authenticated (since binding is
authenticated)
• Visitor-List entry deletion– mobile exchanges a secret with the LA when
entry is created– this shared secret is used to authenticate visitor-
entry deletion
Other features
• Binding advertisement may be suppressed optionally
• Intermediate CA’s may provide partial optimization– snoop to detect location update messages
Mobility in GSM
• Designed for mobility: integrated approach– Identification is not tied with location
information– Cryptographic keys for authentication
• Other differences– scale– connection oriented nature
Architecture
HLR
VLR
EIR
Location UpdateMobile Base-Station
channel request
location update request
immediate assignment
authentication request
authentication response
location updating accept
TMSI allocation complete
channel release
When a mobile• moves from one cell to another• or when it powers upit initiates a location update procedure
Hand-overMobile Base-Station
conversation
conversation
measurement report
hand-over command
hand-over access
physical information
hand-over complete
conversation
Hand-over may involve:• Only one BSC• Only one MSC• More than one MSC
When more than one MSC is involved, the old MSC is still in control of call-management
Authentication
• Authentication request, response, reject messages
• Ki: Secret Authentication key in SIM
• Identification request, response messages:– IMSI, IMEI, TMSI
• Ki is used to compute Kc - to encrypt data & control messages