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Wireless and Mobile Networks
Lecture 8. Mobility Management and Wireless Broadband Access
Lecture objectives
• Understand the motivation behind, the key parts, and operation of Mobile IP
• Understand the issues involved and requirements for fixed broadband wireless
access
• Understand the goals and architecture of WiMax
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MOBILITY MANAGEMENT
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Mobile IP
• Enable computers to maintain Internet connectivity while moving from one Internet attachment point to another
• Mobile – user’s point of attachment changes dynamically and all connections are automatically maintained despite the change
• Nomadic – user’s Internet connection is terminated each time the user moves and a new connection is initiated when the user dials back in
– New, temporary IP address is assigned
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Operation of Mobile IP
• Mobile node is assigned to a particular network – home network
• IP address on home network is static – home address
• Mobile node can move to another network – foreign network
• Mobile node registers with network node on foreign network – foreign agent
• Mobile node gives care-of address to agent on home network – home agent
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Mobile IP Scenario
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Capabilities of Mobile IP
• Discovery – mobile node uses discovery procedure to identify prospective home and foreign agents
• Registration – mobile node uses an authenticated registration procedure to inform home agent of its care-of address
• Tunneling – used to forward IP datagrams from a home address to a care-of address
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Protocol Support for Mobile IP
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Discovery
• Mobile node is responsible for ongoing discovery process
– Must determine if it is attached to its home network or a foreign network
• Transition from home network to foreign network can occur at any time without notification to the network layer
• Mobile node listens for agent advertisement messages
– Compares network portion of the router’s IP address with the network portion of home address
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Agent Solicitation
• Foreign agents are expected to issue agent advertisement messages periodically
• If a mobile node needs agent information immediately, it can issue ICMP router solicitation message
– Any agent receiving this message will then issue an agent advertisement
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Move Detection
• Mobile node may move from one network to another due to some handoff mechanism without IP level being aware
– Agent discovery process is intended to enable the agent to detect such a move
• Algorithms to detect move:
– Use of lifetime field – mobile node uses lifetime field as a timer for agent advertisements
– Use of network prefix – mobile node checks if any newly received agent advertisement messages are on the same network as the node’s current care-of address
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Co-Located Addresses
• If mobile node moves to a network that has no foreign agents, or all foreign agents are busy, it can act as its own foreign agent
• Mobile agent uses co-located care-of address
– IP address obtained by mobile node associated with mobile node’s current
network interface
• Means to acquire co-located address:
– Temporary IP address through an Internet service, such as DHCP
– May be owned by the mobile node as a long-term address for use while visiting a given foreign network
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Registration Process
• Mobile node sends registration request to foreign agent requesting forwarding service
• Foreign agent relays request to home agent
• Home agent accepts or denies request and sends registration reply to
foreign agent
• Foreign agent relays reply to mobile node
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Registration Procedure Security
• Mobile IP designed to resist attacks
– Node pretending to be a foreign agent sends registration request to a home
agent to divert mobile node traffic to itself
– Agent replays old registration messages to cut mobile node from network
• For message authentication, registration request and reply contain authentication extension
– Fields = type, length, security parameter index (SPI), authenticator
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Types of Authentication Extensions
• Mobile-home – provides for authentication of registration messages between mobile node and home agent; must be present
• Mobile-foreign – may be present when a security association exists between mobile node and foreign agent
• Foreign-home – may be present when a security association exists between foreign agent and home agent
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Tunneling
• Home agent intercepts IP datagrams sent to mobile node’s home address
– Home agent informs other nodes on home network that datagrams to mobile node should be delivered to home agent
• Datagrams forwarded to care-of address via tunneling
– Datagram encapsulated in outer IP datagram
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Mobile IP Encapsulation Options
• IP-within-IP – entire IP datagram becomes payload in new IP datagram – Original, inner IP header unchanged except TTL decremented by 1
– Outer header is a full IP header
• Minimal encapsulation – new header is inserted between original IP header and original IP payload
– Original IP header modified to form new outer IP header
• Generic routing encapsulation (GRE) – developed prior to development of Mobile IP
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FIXED BROADBAND WIRELESS ACCESS
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Fixed broadband wireless access
• Traditional telephone – provided on a wired local loop
• Wired technologies responded to the need for reliable, high-speed
access by residential, business, and government subscribers – ISDN, xDSL, cable modems
• Wireless technologies compete for subscriber access
• Called fixed broadband wireless access (BWA)
– Also called wireless local loop (WLL)
– Provides high-speed two-way voice and data service
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Fixed Broadband Wireless Configuration
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Advantages of BWA over Wired Approach
• Cost – wireless systems are less expensive due to cost of cable installation that’s avoided
• Installation time – BWA systems can be installed in a small fraction of the time required for a new wired system
• Selective installation – radio units installed for subscribers who want service at a given time
– With a wired system, cable is laid out in anticipation of serving every subscriber in a given area
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BWA comparisons
• With wired schemes
– Many in the world do not have cables or telephone wires into their homes – New installations can avoid wires by using BWA
• With mobile cellular technology
– 4G provides broadband support
– BWA can cover larger areas with higher data rates
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WIMAX/IEEE 802.16
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IEEE 802.16/WiMAX Standards Development
• Started in 1999
• Use wireless links with microwave or millimeter wave radios
• Use licensed spectrum
• Create wireless metropolitan area networks (WMANs)
• Provide public network service to fee-paying customers
• Use point-to-multipoint architecture with stationary rooftop or tower- mounted antennas
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IEEE 802.16/WiMAX Standards Development
• Provide efficient transport of heterogeneous traffic supporting quality of service (QoS)
• Use wireless links with microwave or millimeter wave radios
• The WiMAX (Worldwide Interoperability for Microwave Access) Forum
– Industry consortium
– Formed to promote the 802.16 standards and to develop interoperability specifications
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WiMAX network reference model
• Access Service Network (ASN)
– Functions to provide radio access to WiMAX subscribers
• Network Access Provider (NAP)
– Provides path between a WiMAX radio access infrastructure to one or more WiMAX Network
Service Providers.
• Connectivity Service Network (CSN)
– Provides IP connectivity services to WiMAX subscribers • Network Service Provider (NSP)
– A business entity that provides IP connectivity and WiMAX services to WiMAX subscribers
• ASN Gateway
– Connectivity from an ASN to an NSP
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Elements of the WiMAX Network Reference Model
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IEEE 802.16 Protocol Architecture
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Protocol Architecture
• Physical and transmission layer functions: – Encoding/decoding of signals
– Preamble generation/removal
– Bit transmission/reception
• Medium access control layer functions:
– On transmission, assemble data into a frame with address and error detection
fields
– On reception, disassemble frame, and perform address recognition and error detection
– Govern access to the wireless transmission medium
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Protocol Architecture
• Convergencelayerfunctions:
– Encapsulate PDU framing of upper layers into native 802.16 MAC/PHY frames
– Map upper layer’s addresses into 802.16 addresses
– Translate upper layer QoS parameters into native 802.16 MAC format
– Adapt time dependencies of upper layer traffic into equivalent MAC service
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802.16 Physical Layer
• Wireless MAN-SC
– 10-66 GHz bands
– Line of sight required
– TDMA and demand-assignment multiple access
• Wireless MAN-OFDM – Below 11 GHz
– LOS is not necessary
• Wireless MAN-OFDMA
– Enhanced version of Wireless MAN-OFDM for OFDMA
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WiMAX in Australia
• Popular in the end of ’00s as a solution for regional areas connectivity – Mainly areas without fixed line broadband access
– A number of small Internet providers experienced with the technology
• WiMAX is still offered in some regional areas without fixed line broadband access
– SA: Adam Internet
– NSW: CountryTell (for business costumers only)
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Sources for this lecture
Cory Beard, William Stallings. Wireless Communication Networks and Systems, 1st edition. Pearson Higher Education, 2016
(Chapters 15.4, 16.4, and 16.5)
All material copyright 2016
Cory Beard and William Stallings, All rights reserved
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