1. Introduction to Wireless Networking
ECE/CSC 575 – Section 1
Introduction to Wireless Networking
Lecture 12 Dr. Xinbing Wang

2. Part 3: Current Wireless Systems
Cellular network architecture: UMTS (Chapter 10)
Fundamentals of cellular communications
System capacity
frequency reuse
Cell splitting
Admission control
handoff
Universal mobile telecommunication system (UMTS)
Network architecture
Functional units
Quality of service
Mobility management
Mobile IP (Chapter 12)
Wireless LAN (Chapters 11/13/14)
In our daily lives, wireless communication technology is used everywhere, from VCR remote control, to satellite weather forecast. The common characteristics of wireless communication systems is that there is no physical (visible) lines between two communication parties.
Therefore, a wireless system is able to support user roaming. For example, we do not have to use a remote control in a particular position to.., we can use our cellular phones almost everywhere.
However, there are many impairments to a wireless channel, causing a lot of limitations to wireless communications system such as geographical.. (signal fading, additional noise, cochannel interference. Wireless systems also suffers from limit usable spectral width, so that the transmission rate is relatively low.
Specifically, wireless cellular systems based on radio propagation has been evolving from narrow band (1G, late 170s) to wide-band(3G).
With their geographical coverage limitation, wireless systems need a backbone network to extend their geographical coverage to enable global communications.
The interoworking of a wireless network as the front-end and the Internet as the backbone has received much attention in recent years.
So we will first take a look at the network architecture of current wireless systems,…, Then we will talk about the evolution from 2G to 3G systems.
Dr. Xinbing Wang

3. Overview of Mobile IP (Ch. 12)
Is Mobile IP an official standard?
The Internet allocates a fixed address to each and every mobile user. The current approach to forwarding messages from the mobile’s fixed address to it in its new location is Mobile IP.
Mobile IP was approved by the Internet Engineering Steering Group (IESG) in June 1996 and published as a Proposed Standard in November 1996.
Mobile IP was produced by the IP Routing form Wireless/Mobile Hosts (mobileip) working group of the Internet Engineering Task Force (IETF), which was formed in June 1992.
Request for Comments (RFC) 2002 defines the Mobile IP protocol itself.
Dr. Xinbing Wang

4. Requirements for Mobile IP
A mobile node must be able to communicate with other nodes after changing its link-layer point-of-attachment (POA).
Network-prefix-based routing algorithms won’t work
A mobile node must be able to communicate using only its home (permanent) IP address, regardless of its current POA.
Rules out any solution which calls for changing IP-addr
Network services are based on IP-addr such as licenses
A mobile node must be able to communicate with other computers that do not implement the Mobile IP mobility functions.
A mobile node must not be exposed to any new security threats over and above those to which any fixed node on the Internet is exposed.
Dr. Xinbing Wang

5. Design Goals for Mobile IP
Routing protocols, including Mobile IP, require the transmission of routing updates between the various nodes in the network. Therefore, one of the goals was to make the size and the frequency of these updates as small as possible.
For the purpose of memory and processing-constrained devices, to make it as simple as possible to implement mobile node software.
Because of the address limit, to avoid solutions which requires mobile nodes to use multiple addresses. (Solved by IPv6!)
Dr. Xinbing Wang

6. Assumptions in Mobile IP
Assume unicast packets--those destined to a single recipient—are routed without regard to their IP Source address.
That means, Mobile IP assumes that all unicast packets are routed based on Dest-addr, typically only the network-prefix portion of that address.
Assume that the Internet exists ‘always’ and that is capable of delivering packets between any pair of nodes in the network.
Dr. Xinbing Wang

7. Terminology
Home Address: an IP address that is assigned to an MN. It remains unchanged regardless of the MN’s current location.
Home Link: The link on which an MN’s home subnet prefix is defined. Standard IP routing mechanisms will deliver packets destined for an MN’s home address to its home link.
Home Agent: A router with an interface on the MN’s home network link, which the MN keeps informing of its care-of-address, as the MN moves.
Care-of-address: an IP address associated with an MN while visiting a foreign link (other than home link).
Correspondent node: a peer host with which a mobile node communicates.
Foreign Agent: a router with which an interface on an MN’s visiting network. Assists the MN in informing its HA of a CoA.
Dr. Xinbing Wang

8. How Does Mobile IP Work? Each MN has two IP addresses:
A fixed home address for identification, and
A care-of-address (CoA) for routing. The CoA can be created by “stateless address auto-configuration (RFC 2462)” and “stateful address autoconfiguration, e.g., DHCP).
Mobile IP uses an agent concept.
Home agent (HA) intercepts packets on the home link destined to the MN’s home address, encapsulates them, and tunnels them to the MN’s registered CoA.
Foreign agent (FA) is a router with which an MN establishes an association when it moves away from home. Therefore, the MN updates its locations with the HA through an FA.
Dr. Xinbing Wang

9. Mobile IP Operation
Home subnet prefix: the IP subnet prefix corresponding to an MN’s home address.
Foreign subnet prefix: the IP subnet prefix other than the MN’s home subnet prefix.
address B
Subnet prefix B
Internet Backbone
address B
& address C
Subnet prefix C
A node moves from a link with the prefix B to a link eith the prefix C. On link C the node gets an additional address which has the prefix of this link.
Dr. Xinbing Wang

10. Mobile IP Operation (2) HA Agent advertisement FA FA Home network/
Subnet
Correspondent
Node (CN) HA
Internet Backbone
Agent advertisement FA FA
Foreign Network/
Subnet 2
Foreign Network/
Subnet 1
Dr. Xinbing Wang

11. Three Processes
Agent Discovery: an MN determines its new attachment point or IP address through agent advertisements.
Determine to which link it is connected
Detect if it has changed its point of attachment
Obtain a CoA if it is connected to a foreign link
Allowed to send agent solicitation requests to agent
Agent discovery messages are carried by the ICMP packets.
Registration: an MN requests service from an FA and inform its HA of a new CoA.
Involve registration and deregistration with its HA
Registration message is carried by the UDP packets.
Tunneling (routing): Mobile IP tunnels datagram to the MN, whether it is away from its home network or not.
Encapsulation at the entering point of a tunnel
Decapsulation at the exit point of a tunnel
Dr. Xinbing Wang

12. Agent Discovery Agent solicitation message
Identical to ICMP router solicitations, except having IP time to Live field set to 1.
When an HA or FA receives one, it should immediately respond by transmitting an Agent Advertisement .
Vers = Type of service Total length
Identification Flags Fragment Offset
Time to Live = 1 Protocol = ICMP header Checksum
Source Address = Mobile node’s home address
Desti Addr = (broadcast) or (multicast)
Type = 10 Code = 10 Checksum
Reserved
4 bytes (32 bits)
Dr. Xinbing Wang

13. Agent Discovery (2) Agent advertisement messages
They are formed by appending one or more of the extensions defined by Mobile IP to the ICMP router advertisement message (RFC 1256).
The mobility agent advertisement extension must be included by agents.
IP Header (RFC 791)
20 bytes
ICMP Router Advertisement (RFC 1256)
Type = 16 Length Sequence number
(maximum) registration lifetime Reserved
Mobility agent
Advertisement
Extension
(RFC 2002)
Care of Address (1)….
Type = Length Prefix-length [1] Prefix-length [2]
(Optional)
4 bytes (32 bits)
Dr. Xinbing Wang

14. Registration and Deregistration
When an MN moves to a visiting location, it needs to register with its HA. When it returns to its home network, it also needs to deregister with its HA to update its current CoA (home address).
Registration with care-of-address
Internet Backbone HA FA
Home network/
Subnet
Registration request
Registration reply
Foreign Network/
Subnet
Dr. Xinbing Wang

15. After Class Reading materials Exercise Chapter 12.1 What is tunneling?
How can Mobile IP detects mobile users?
What is Mobile IP registration?
What are home agent, mobile agent, foreign agent?
Dr. Xinbing Wang