ECE537/3 #1Spring 2009© 2000-2009, Richard A. Stanley

ECE537 Advanced and High Performance Networks

3: Mobile Networking

Professor Richard A. Stanley, P.E.

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Overview of Tonight’s Class

• What do we mean by mobile networking?

• How does the cellular telephone network deal with mobility?

• What about mobile data users?

• Are there protocols to facilitate mobile networking under IP?

• What is ad hoc networking?

• How can we implement ad hoc networking?

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What Do We Mean by Mobile Networking?

• Telephone network designed to route calls to fixed sockets, always at the same location

• Mobile refers to the ability of users to join or leave a network more or less at will, whether it is their “home” or not

• Mobile does not necessarily refer to physical movement of the user while communicating

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The Way it Was

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Cellular Architecture (GSM)

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GSM Nomenclature

• Home Location Register (HLR) • Visitor Location Register (VLR) • Equipment Identity Register (EIR) • Authentication Center (AuC) • SMS Serving Center (SMS SC) • Gateway MSC (GMSC) • Chargeback Center (CBC) • Transcoder and Adaptation Unit (TRAU)

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What is Going On Here?

• Many steps to set up, conduct, and break down a call

• More steps to locate the handset and connect to it, without user input

• Driving force?

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Mobile Networking

• How does the cellular model relate to data networking?– Addressing– Authentication– Host location– Billing

• Could we use a similar model to achieve mobile data networking?

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Mobile IP

• Why?– Increasing numbers of mobile (i.e. peripatetic)

computers seeking network access– Manual network updates to accommodate this

are not feasible

• How?– What about the cellular approach?– Could we do this with IP?

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The Problem

• A mobile node must change its IP address whenever it changes its point of attachment, so that packets destined for the node are routed correctly

• But to maintain existing TCP/UDP connections, the mobile node has to keep the same IP address– Changing the IP address will cause the

connection to be disrupted and lost

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Mobile IP: A Solution

• Each mobile node has two IP addresses:– One IP address is the permanent home address that is

assigned at the home network and is used to identify communication endpoints

– The other IP address is a temporary care-of address that represents the current location of the host

• Objective of Mobile IP is to make mobility transparent to higher level protocols and to make minimum changes to the existing network infrastructure

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Mobile IP Architecture

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Concepts• Home network

– The network within which the device receives its identifying IP address (home address).

• Home address– The IP address assigned to the device within its home network.

• Foreign network– Network in which a mobile node is operating when away from its home network.

• Care-of address– Physical IP address of the device when operating in a foreign network.

• Home agent– A router on a mobile node’s home network which tunnels datagrams for delivery to the mobile node when it

is away from home. It maintains current location (IP address) information for the mobile node. It is used with one or more foreign agents.

• Foreign agent– A router that stores information about mobile nodes visiting its network. Foreign agents also advertise care-

of-addresses which are used by Mobile IP.

• Binding– The association of the home address with a care-of address

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Mobility Agents

• Two sorts: – Home agents

– Foreign agents

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Home Agent

• Designated router in the home network of the mobile node

• Maintains the mobility binding in a mobility binding table – each entry is identified by the tuple <permanent

home address, temporary care-of address, association lifetime>

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Mobility Binding Table

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Foreign Agent

• Specialized routers on the foreign network where the mobile node is currently visiting– Maintains a visitor list which contains

information about the mobile nodes currently visiting that network

– Each entry in the visitor list is identified by the tuple: < permanent home address, home agent address, media address of the mobile node, association lifetime>

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Visitor List

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Stages in Mobile IP

• Agent discovery

• Registration

• In-service

• Deregistration

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Agent Discovery

• Mobility agents advertise their presence by periodically broadcasting Agent Advertisement messages– Agent Advertisement message lists one or more care-of addresses

and a flag indicating whether it is a home agent or a foreign agent.

• The mobile node receiving the Agent Advertisement message observes whether the message is from its own home agent and determines whether it is on the home network or a foreign network

• If a mobile node does not wish to wait for the periodic advertisement, it can send out Agent Solicitation messages that will be responded by a mobility agent

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Registration

• If a mobile node discovers that it is on the home network, it operates without any mobility services

• If the mobile node is on a new network, it registers with the foreign agent by sending a Registration Request message which includes the permanent IP address of the mobile host and the IP address of its home agent

• The foreign agent performs the registration process on behalf of the mobile host by sending a Registration Request containing the permanent IP address of the mobile node and the IP address of the foreign agent to the home agent

• When the home agent receives the Registration Request, it updates the mobility binding by associating the care-of address of the mobile node with its home address

• The home agent then sends an acknowledgement to the foreign agent • The foreign agent in turn updates its visitor list by inserting the entry for the

mobile node and relays the reply to the mobile node

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Registration Process

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In-service• When a correspondent node wants to communicate with the mobile node, it sends an IP packet addressed

to the permanent IP address of the mobile node• The home agent intercepts this packet and consults the mobility binding table to find out if the mobile

node is currently visiting any other network• The home agent finds the mobile node's care-of address and constructs a new IP header that contains the

mobile node's care-of address as the destination IP address– Original IP packet is put into the payload of this IP packet– Packet is sent– This is tunneling

• When the encapsulated packet reaches the mobile node's current network, the foreign agent decapsulates the packet and finds out the mobile node's home address. It then consults the visitor list to see if it has an entry for that mobile node.

• If there is an entry for the mobile node on the visitor list, the foreign agent retrieves the corresponding media address and relays the packet to the mobile node

• When the mobile node wants to send a message to a correspondent node, it forwards the packet to the foreign agent, which in turn relays the packet to the correspondent node using normal IP routing.

• The foreign agent continues serving the mobile node until the granted lifetime expires. If the mobile node wants to continue the service, it has to reissue the Registration Request.

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In-service Tunneling

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Deregistration• If a mobile node wants to drop its care-of address, it has to

deregister with its home agent• This is done by sending a Registration Request with the

lifetime set to zero• No need for deregistering with the foreign agent as

registration automatically expires when lifetime becomes zero

• However if the mobile node visits a new network while the old care-of address is still valid, the old foreign network does not know the new care-of address of the mobile node. Thus datagrams already forwarded by the home agent to the old foreign agent of the mobile node are lost.

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Security Issues

• During registration, home agent should be convinced that it is getting a Registration Request from authentic mobile node and not receiving information from a bogus node

• Mobile IP deals with this problem by specifying a security association between the home agent and the mobile node– Security association is at present manually configured

• Registration message should contain a mobile node-home agent aunthentication extension which contains an Security Parameters Index(SPI) followed by an authenticator.

• SPI is an index to the mobility security association and it defines the security context (i.e., the algorithm and the secret) used to compute and check the authenticator.

– The default algorithm is keyed MD5 with a key size of 128 bits. Also each registration contains unique data to avoid valid registration recording by malicious nodes.

– Timestamps and nonces are used to generate the unique data

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Basic Mobile IP: Triangle Routing

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Route Optimization

• Extension to the basic Mobile IP protocol• Messages from the correspondent node are routed

directly to the mobile node's care-of address without having to go through the home agent

• Route Optimization provides four main operations: – Updating binding caches– Managing smooth handoffs between foreign agents– Acquiring registration keys for smooth handoffs– Using special tunnels

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Updating binding caches

• Binding caches are maintained by correspondent nodes for associating the home address of a mobile node with its care-of address. A binding cache entry also has an associated lifetime after which the entry has to be deleted from the cache. If the correspondent node has no binding cache entry for a mobile node, it sends the message addressed to the mobile node's home address. When the home agent intercepts this message, it encapsulates it and sends it to the mobile node's care-of address. It then sends a Binding Update message to the correspondent node informing it of the current mobility binding.

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Managing smooth handoffs between foreign agents

• When a mobile node registers with a new foreign agent, basic Mobile IP does not specify a method to inform the previous foreign agent. Thus the datagrams in flight which had already tunneled to the old care-of address of the mobile node are lost.

• Problem is solved in Route Optimization by introducing smooth handoffs. Smooth handoff provides a way to notify the previous foreign agent of the mobile node's new mobility binding

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Smooth Handoffs• If a foreign agent supports smooth handoffs, it indicates this in its Agent Advertisement

message• When the mobile node moves to a new location, it requests the new foreign agent to inform

its previous foreign agent about the new location as part of the registration procedure• New foreign agent constructs a Binding Update message and sends it to the previous foreign

agent of the mobile node. – Thus if the previous foreign agent receives packets from a correspondent node having an out-of-

date binding, it forwards the packet to the mobile node's care-of address.

• New foreign agent then sends a Binding Warning message to the mobile node's home agent• Home agent sends a Binding Update message to the correspondent node. • These notifications allow datagrams sent by correspondent nodes having out-of-date

binding cache entries to be forwarded to the current care-of address. • Notifications allow resources consumed by the mobile node at the previous foreign agent to

be released immediately, instead of waiting for the registration lifetime to expire.

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Acquiring registration keys for smooth handoffs

• For managing smooth handoffs, mobile nodes need to communicate with the previous foreign agent. This communication needs to be done securely as any careful foreign agent should require assurance that it is getting authentic handoff information and not arranging to forward in-flight datagrams to a bogus destination. For this purpose a registration key is established between a foreign agent and a mobile node during the registration process.

• The following methods for establishing registration keys have been proposed in the order of declining preference: – If the home agent and the foreign agent share a security association, the home agent can choose the

registration key.– If the foreign agent has a public key, it can again use the home agent to supply the registration key. – If the mobile node includes its public key in its Registration Request, the foreign agent can choose

the new registration key.

• The mobile node and its foreign agent execute the Diffie-Hellman key exchange protocol as part of the registration protocol

• Registration key is used to form a security association between the mobile node and the foreign agent

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Using special tunnels

• When a foreign agent receives a tunneled datagram for which it has no visitor list entry, it concludes that the node sending the tunneled datagram has an out-of-date binding cache entry for the mobile node

• If the foreign agent has a binding cache entry for the mobile node, it re-tunnels the datagram to the care-of address indicated in its binding cache entry

• If the foreign agent has no visitor list or binding cache entry for the mobile node, it constructs a special tunnel datagram

• The special tunnel datagram is constructed by encapsulating the datagram and making the outer destination address equal to the inner destination address. – Allows the home agent to see the address of the node that tunneled the datagram and

prevent sending it to the same node. – Avoids a possible routing loop that might have occured if the foreign agent crashed

and lost its state information.

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Minimal Encapsulaton• Encapsulation in Mobile IP is done by putting the original datagram (=IP

header+payload) inside another IP envelope• Fields in the outer IP header add overhead to the final datagram --several

fields are duplicated from the inner IP header• To prevent this waste of space a Minimal Encapsulation Scheme has been

defined where instead of inserting a new header, the original header is modified to reflect the care-of address and a minimal forwarding header is inserted to store the original source and destination address– Care-of address of the mobile node becomes the destination address of the IP packet

and the home agent's address becomes the source address– The minimal forwarding header stores the original source and destination addresses.

• When the foreign agent decapsulates, it restores the fields in the forwarding header to the IP header and removes the forwarding header.

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Minimal Encapsulaton

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Mobile IP in IPv6• Exploits the larger address space• Route Optimization is a fundamental part of Mobile IPv6 unlike Mobile IPv4

where it is an optional set of extensions that may not be supported by all nodes. • Foreign Agents are not needed in Mobile IPv6. The enhanced features of IPv6

like Neighbor Discovery and Address Autoconfiguration enable mobile nodes to function in any location without the services of any special router in that location.

• In Mobile IPv4, when a mobile node communicates with a correspondent node, it puts its home address as the source address of the packet. Thus “ingress filtering routers” are used to filter out the packets as the source address of the packet is different from the network from which the packet originated. This problem is tackled in Mobile IPv6 by putting the care-of address as the source address and having a Home Address Destination option, allowing the use of the care-of address to be transparent over the IP layer.

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Goals of IPv6 Mobility

• Always on IP connectivity• Roaming between different L2 technologies

WLAN, WiMAX, UMTS, fixed• Roaming between different (sub)networks

– huge WLAN deployments mostly use different L3 subnets

• Application continuity (Session persistence)• Static IP Adresses for mobile nodes• Mobile devices may act as servers

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Bidirectional Tunnel Mode (1)

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Bidirectional Tunnel Mode (2)

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Triangle Routing?

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Route Optimization (1)

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Route Optimization (2)

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Secure Binding

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Return Routeability Procedure (1)

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Return Routeability Procedure (2)

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Coming Up• Bootstrapping MIPv6

– No static configuration of HA address and HoA on mobile nodes• Network mobility (NEMO) (Instead of node mobility)

– IETF working group with focus on mobile networks (e.g. prefix delegation)

• Mobile ad hoc networks (MANET)– Interworking of Mobile Ad-hoc networks and Mobile IPv6 Networks– Mobile node roaming in between MIPv6 and MANET– MANET roaming as a MIPv6 client

• Signaling and Handoff Optimization– Fast Handovers for Mobile IPv6 (FMIPv6, RFC4068)– Hierarchical MIPv6 mobility management (HMIPv6, RFC4140)

• Cryptographically generated (IPv6) addresses (RFC 3972)– MN can prove that it owns its HoA by including its public key in the

binding update and by signing the resulting message (No PKI needed)

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Mobile IP Standards• Mobile IPv4: RFC3344• Mobile IPv6: RFC3775• Mobile IPv4 Challenge/Response

Extensions: RFC 4721• Reverse Tunneling for Mobile IP: RFC

3024• Using IPsec to Protect Mobile IPv6

Signaling between Mobile Nodes and Home Agents: RFC3776

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Mobile Ad Hoc Networking

• MANET

• Allows self-configuration of network– Wireless links

– Handles arrival/departure of nodes

• Topology generally a mesh

• Traffic passed by multiple relay

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Formal Definition

• “An ad hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any centralized administration or standard support services regularly available on the wide-area network to which the host may normally be connected.”

» David B. Johnson, “Routing in Ad Hoc Networks of Mobile Hosts,” Proceedings of the IEEE Workshop on Mobile Computing Systems and Applications, pages 158-163, December 1994

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Simple MANET

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Airport Scenario

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Characteristics of MANETs

• Dynamic Network Topology

• Bandwidth-Limited and Fluctuating Capacity Links

• Low-Power and Resource-Limited Operation

• Constrained Physical Security

• Decentralized Network Control

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MANET Challenges

• Route discovery from source to target

• Minimizing network management overhead

• Dealing with constantly changing topology

• Assured packet delivery

• Security

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Summary

• Mobile networking needs are growing

• Two basic networking needs:– Mobile nodes in established networks– Ad hoc networking

• Coexistence of IPv4 and IPv6 complicates sharing of data across different mobile protocols

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Homework

• Research mobile ad hoc networking. How is the network organized? How is a path for datagrams discovered and established? What challenges exist if one network is on IPv6 and wishes to communicate with one on IPv4? Other issues?

• Be prepared to discuss your findings with the class for 5-10 minutes next week. You may use slides if you desire.

ECE506/4 #56Spring 2009© 2000-2009, Richard A. Stanley

Disclaimer

Parts of the lecture slides contain original work of Tarmo Anttalainen, Wikipedia, Debalina Ghosh, Holger Zuleger, and Jin-Hee Cho and remain copyrighted materials by the original owner(s). The slides are intended for the sole purpose of instruction of computer networks at Worcester Polytechnic Institute.