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Mobile Network LayerMobile Network Layer
IT351: Mobile & Wireless ComputingIT351: Mobile & Wireless Computing
Objective:– To highlight the requirements of internetworking in wireless networks as opposed to
wired networks.– To detail the operation of common internetworking schemes, including , MobileIP /
migration to IPv6 and CellularIP.
OutlineOutline
• The Internet Protocol (IP) mobility– Motivation and overview
• Mobile IP– Components and terminology
– Protocols: agent discovery, registration, tunneling & encapsulation
– Optimization
– Reverse tunneling
– Problem
• IPv6
• Micro mobility protocols• DHCP
Overview of the main chaptersOverview of the main chapters
Chapter 2: Wireless Transmission
Chapter 3: Medium Access Control
Chapter 4: Telecommunication Systems
Chapter 5: Satellite Systems
Chapter 6: Broadcast Systems
Chapter 7: Wireless LAN
Chapter 8: Mobile Network Layer
Chapter 9: Mobile Transport Layer
Chapter 10: Support for Mobility
Internet Protocol (IP)Internet Protocol (IP)
• IP for normal fixed Internet– Network layer
– Most important protocol
– Packet-switched, connectionless service
– Fragmentation and reassembly
– Error reporting using ICMP (Internet Control Message Protocol)
– Delivery of packets across an internetwork (Routing)
Internet (IP) MobilityInternet (IP) Mobility
• Internet (IP) provides the host with a permanent identity in the form of an IP address
• This IP address is associated with a location, i.e. the IP network domain
• If the host moves within the domain it will probably be ok (depends, e.g. subnetting)
• If the host moves outside the domain it will not have a different IP address (statically assigned IP)
• If the host moves any ‘connections’ (recall – IP is connectionless) will be lost
Problems with fixed IPProblems with fixed IP
• Two ways of assigning IP addresses: – Statically assigned IP
• Host address stays constant over all connections– Common case in PC access to LANs and some ISPs
– IP addresses may be dynamically assigned by DHCP (Dynamic Host Configuration Protocol)
• Host addresses change with each connection– Common with Laptop access and some ISPs
• Problems for mobility– With static addresses the host cannot move
– With dynamic addresses partners can’t communicate
Motivation for Mobile IPMotivation for Mobile IP
• Routing– based on IP destination address, network prefix (e.g. 129.13.42)
determines physical subnet– change of physical subnet implies change of IP address to have a
topological correct address (standard IP) or needs special entries in the routing tables
• Specific routes to end-systems?– change of all routing table entries to forward packets to the right
destination– does not scale with the number of mobile hosts and frequent
changes in the location, security problems
• Changing the IP-address?– adjust the host IP address depending on the current location– almost impossible to find a mobile system, DNS updates take long
time– TCP connections break, security problems
Requirements for Mobile IPv4 (RFC 3344, was: 3220, was: 2002 , Requirements for Mobile IPv4 (RFC 3344, was: 3220, was: 2002 , updated by: 4721)updated by: 4721)
• Transparency– mobile end-systems keep their IP address– continuation of communication after interruption of link possible– point of connection to the fixed network can be changed
• Compatibility– support of the same layer 2 protocols as IP– no changes to current end-systems and routers required– mobile end-systems can communicate with fixed systems
• Security– authentication of all registration messages
• Efficiency and scalability– only little additional messages to the mobile system required – world-wide support of a large number of mobile systems in the whole
Internet
Mobile IP – IP IntegrationMobile IP – IP Integration
• What does Mobile IP do?– Extends IP for mobility not wireless networking– Mobile IP operates between network and transport layers
(i.e. on top of IP but below TCP/UDP)
• Mobile IP provides two addresses:– Fixed address for identification (home address)
– Dynamic address for routing (care-of address/foreign address)
• Benefits:– Stable address for hosts
– Enables TCP to keep track of session data
– Routing based on fixed source/destination
Mobile IP – Components & TerminologyMobile IP – Components & Terminology
• Mobile Node (MN)– system (node) that can change the point of connection
to the network without changing its IP address
• Correspondent Node (CN)– communication partner (cam be fixed or mobile node)
• Home Network– The subnet the MN belongs to with respect to its IP address. No mobile
IP support is needed within the home network.
• Foreign Network– The current subnet the MN visits and which is not the home network– The current location of the MN from the IP point of view is called Care-
of-Address (COA)
• Tunneling– Packet delivery towards the MN is done using a tunnel
Mobile IP – Components & TerminologyMobile IP – Components & Terminology
• Home Agent (HA)– system in the home network of the MN, typically a router– Provides several services to the MN– registers the location of the MN, tunnels IP datagrams to the COA
• Foreign Agent (FA)– system in the current foreign network of the MN, typically a router– Provides several services to the MN during its visit to the foreign
network– forwards the tunneled datagrams to the MN, typically also the
default router for the MN– FA can also provide security service,
• Care-of Address (COA)– actual location of the MN from an IP point of view– address of the current tunnel end-point for the MN (at FA or MN)– all packets sent to the MN are delivered to the COA– Foreign agent COA: located at the FA – Co-located COA: can be chosen, e.g., via DHCP if IP addresses
are available.
Example networkExample network
mobile end-systemInternet
router
router
router
end-system
FA
HA
MN
home network
foreign network
(physical home networkfor the MN)
(current physical network for the MN)
CN
Data transfer from the mobile systemData transfer from the mobile system
Internet
receiver
FA
HA
MN
home network
foreignnetwork
sender
1
1. Sender sends to the IP address of the receiver as usual, FA works as default router
CN
Data transfer to the mobile systemData transfer to the mobile system
Internet
sender
FA
HA
MN
home network
foreignnetwork
receiver
1
2
3
1. Sender sends to the IP address of MN, HA intercepts packet 2. HA tunnels packet to COA, here FA, by encapsulation3. FA forwards the packet to the MN
CN
OverviewOverview
CN
routerHA
routerFA
Internet
router
1.
2.
3.
homenetwork
MN
foreignnetwork
4.
CN
routerHA
routerFA
Internet
router
homenetwork
MN
foreignnetwork
COA
Mobile IP – The ProtocolsMobile IP – The Protocols
• Three major problems:– Discovery of new point of attachment– Registration of new location with Home domain– Delivery of datagrams to registered locations
• Agent Discovery– Mobility agents advertise availability– MN solicits agent
• Registration– Updating the care-of-address with home network
• Tunneling– Delivery of data to mobile node’s care-of-address, via
permanent home address
1. Agent Discovery1. Agent Discovery
• One initial problem of an MN after moving is how to find a foreign agent– How does the MN discover that it has moved?
• Mobile IP describes two methods:– Agent advertisement– Agent solicitation
• Agent Advertisement– Extends the current ICMP (Internet Control Message Protocol –
Router Advertisement)– HA and FA periodically send advertisement messages into their
physical subnets– MN listens to these messages and detects, if it is in the home or
a foreign network (standard case for home network)– MN reads a COA from the FA advertisement messages
Agent Discovery (cont)Agent Discovery (cont)
• Agent Solicitation– Alternatively, mobile node may solicit agent (Broadcast or
Multicast)
• Mobile node can now proceed to register
preference level 1router address 1#addressestype
addr. size lifetimechecksum
COA 1COA 2
type = 16 sequence numberlength
0 7 8 15 16 312423code
preference level 2router address 2
. . .
registration lifetime
. . .
R B H F M G r reservedT
Agent Advertisement (ICMP – extension)
2. Registration2. Registration
• Mobile Node requests registration from Foreign Agent (or directly for co-located COA)
• Request is forwarded to Home Agent– Includes CAO + home
addresses
• Home Agent replies to Foreign Agent
• Security– Authentication between all
three parties– Mobile-Home auth. is
based on shared secret
From: Perkins, C.E., “Mobile networking through Mobile IP,” IEEE Internet Computing, Volume 2, Issue 1, Jan.-Feb. 1998 Page(s):58 – 69.
3. Tunneling & Encapsulation3. Tunneling & Encapsulation
Home Agent
IP Host
Foreign Agent
Mobile Node
1
2
34
(triangular routing)
IP tunnel
• Communication between an IP node and a Mobile Node
• Delivery of data to mobile node’s COA via permanent home address
• Tunneling is achieved by encapsulation
Encapsulation Encapsulation • Encapsulation of one packet into another as payload
– e.g. IPv6 in IPv4 , Multicast in Unicast
– here: e.g. IP-in-IP-encapsulation
• IP-in-IP-encapsulation (mandatory, RFC 2003)– tunnel between HA and COA
original IP header original data
new datanew IP header
outer header inner header original data
Mobile IP – EncapsulationMobile IP – Encapsulation
• IP-within-IP encapsulation
IP Header
IP Payload IP Payload
MobileIP Header
IP Header
EncapsulationEncapsulation
Care-of address COAIP address of HATTLIP identification
IP-in-IP IP checksumflags fragment offsetlengthDS (TOS)ver. IHL
IP address of MNIP address of CNTTLIP identification
lay. 4 prot. IP checksumflags fragment offsetlengthDS (TOS)ver. IHL
TCP/UDP/ ... payload
Optimization of packet forwardingOptimization of packet forwarding
• Problem: Triangular Routing– sender sends all packets via HA to MN
– higher latency and network load
• “Solution”
– Avoid routing through Home Agent
– Corresponding IP host is given care-of-address
– sender learns the current location of MN
– direct tunneling to this location
– HA informs a sender about the location of MN
– big security problems!
Optimization of packet forwarding (cont.)Optimization of packet forwarding (cont.)
• Requires authentication (to prevent hijacking)
• Process is entitled mobility-binding
– Request
– Update – Authorization
– Acknowledgement
– Warning (if needed)
• If a packet is sent to a wrong FA
Request
Update
ACK
CN HA
Optimization: Change of Foreign Agent Optimization: Change of Foreign Agent
• Change of FA– packets on-the-fly during the change can be lost
– new FA informs old FA to avoid packet loss, old FA now forwards remaining packets to new FA
– this information also enables the old FA to release resources for the MN
Problems with Mobile IPProblems with Mobile IP
• Inefficient routing– Indirect routing via Home Agent may be slow
– Home Agent may get overloaded with traffic
• Firewalls
What happens when Firewalls are operating?– typically mobile IP cannot be used together with
firewalls, special set-ups are needed (such as reverse tunneling)
– Internal addresses appear to enter a network
– Mobile IP cannot handover connections
Problems with mobile IPProblems with mobile IP• Security
– authentication with FA problematic, for the FA typically belongs to another organization
– no protocol for key management and key distribution has been standardized in the Internet
• QoS– many new reservations in case of RSVP (resource
reservation)– tunneling makes it hard to give a flow of packets a
special treatment needed for the QoS
• Security, firewalls, QoS etc. are topics of research and discussions
Mobile IP and IPv6 (RFC 3775)Mobile IP and IPv6 (RFC 3775)
• Mobile IP was developed for IPv4, but IPv6 simplifies the protocols– security is integrated and not an add-on, authentication of
registration is included -Protocols for registration, discovery etc. are available as standard, not layered above IP
– COA can be assigned via auto-configuration (DHCPv6 is one candidate), every node has address auto-configuration
– no need for a separate FA, all routers perform router advertisement which can be used instead of the special agent advertisement; addresses are always co-located
– MN can signal a sender directly the COA, sending via HA not needed in this case (automatic path optimization)
– „soft“ hand-over, i.e. without packet loss, between two subnets is supported
• MN sends the new COA to its old router• the old router encapsulates all incoming packets for the MN and
forwards them to the new COA• authentication is always granted
IP Micro-mobility supportIP Micro-mobility support
• Mobile IP (and MIPv6) problems
– Designed to Internetwork mobile nodes across wide
areas
– Concentrates on address migration issues
– Not suitable for fast migration and handoff within a
defined geographical area
• Micro mobility protocols: Keep the frequent updates
generated by local changes away from the home
network
IP Micro-mobility supportIP Micro-mobility support
• Micro-mobility support:– Efficient local handover inside a foreign domain
without involving a home agent– Reduces control traffic on backbone– Especially needed in case of route optimization
• Example approaches (research, not products):– Cellular IP– HAWAII– Hierarchical Mobile IP (HMIP)
• Important criteria:Security Efficiency, Scalability, Transparency, Manageability
DHCP: Dynamic Host Configuration ProtocolDHCP: Dynamic Host Configuration Protocol
• Application– simplification of installation and maintenance of networked
computers– supplies systems with all necessary information, such as IP
address, DNS server address, domain name, subnet mask, default router etc.
– enables automatic integration of systems into an Intranet or the Internet, can be used to acquire a COA for Mobile IP