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

• 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

• 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

Reverse TunnelingReverse Tunneling

• The return path from MN to CN looks quite simple. MN can directly send its packets to CN. However, this leads to several problems:– Firewalls

• Most companies have firewalls

• To provide security the firewall rejects a topologically incorrect packet

– Multicast • An MN in a foreign network can not transmit multi-cast packets in a way

that emanate from its home network

• The foreign network might not even provide the technical infrastructure for multicast communication

– TTL (time to live)• TTL might be low to reach the destination

• Adjusting the TTL results in non transparent mobile IP

• To solve these problems, reverse tunneling has been defined as an optional extension to mobile IP.

Reverse tunneling (RFC 3024, was: 2344)Reverse tunneling (RFC 3024, was: 2344)

Internet

receiver

FA

HA

MN

home network

foreignnetwork

sender

3

2

1

1. MN sends to FA2. FA tunnels packets to HA by encapsulation3. HA forwards the packet to the receiver (standard case)

CN

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