Mobile Systems Presented by: Eddy & Kevin Directed by: Professor Joung

Introduction n Computing and communications are becoming inseparable synergistic activities independent of time and location, i.e., with mobility. Mobile Computing Computation MobilityCommunication

Introduction n 3 components: Computation includes the computing devices with their dramatically increasing processing power. Computation includes the computing devices with their dramatically increasing processing power. Communication systems include the different wireless and wired networks and span a wide range of bandwidths. Communication systems include the different wireless and wired networks and span a wide range of bandwidths. Mobility is an aspect of user behavior. Mobility is an aspect of user behavior.

Link Layer Consideration n A great deal of attention is paid to methods for establishing links between mobile computers (or mobile nodes) and base stations (or access points) that make use of both wired and wireless communications.

Link Layer Consideration Hidden terminals  Having multiple computers in a cell can give rise to the hidden terminal problem.  Under this problem, the simultaneous transmission of two mobile nodes can’t hear each other but are both received by the same access point or destination station.

Link Layer Consideration Hidden terminal problem Hidden terminal problem

Link Layer Consideration Hidden terminal problem Hidden terminal problem  Possible solution #1 A sender ask to transmit its data(e.g., by a RTS, or request to send), and then waits until the intended receiver grants permission(e.g., CTS, or clear to send). A sender ask to transmit its data(e.g., by a RTS, or request to send), and then waits until the intended receiver grants permission(e.g., CTS, or clear to send).

Link Layer Consideration Hidden terminal problem Hidden terminal problem  Possible solution #2 Applying CDMA (or code division multiple access) schemes, we assign the minimum number of orthogonal codes to eliminate the hidden terminal interference. Applying CDMA (or code division multiple access) schemes, we assign the minimum number of orthogonal codes to eliminate the hidden terminal interference.  Note : The receivers are code-agile, namely, able to communicate over several codes, in which case it is a transmitter-oriented code assignment (TOCA) scheme.

Link Layer Consideration Code Assignment for hidden terminal interference ~ in a ring network Code Assignment for hidden terminal interference ~ in a ring network

Link Layer Consideration Code Assignment for hidden terminal interference ~ in binary tree networks Code Assignment for hidden terminal interference ~ in binary tree networks

Network Layer Consideration n IP traditionally makes next-hop decisions based on the IP address of the destination, but it is now modified to tunnel packets to a mobile node at it’s current point of attachment to the Internet.

Network Layer Consideration Tunneling A tunnel is the path followed by a first packet while it is encapsulated within the payload portion of a second packet. A tunnel is the path followed by a first packet while it is encapsulated within the payload portion of a second packet. mobile node: a node which can change its point-of- attachment to the Internet from one link to another by using only its (permanent) IP home address mobile node: a node which can change its point-of- attachment to the Internet from one link to another by using only its (permanent) IP home address home agent: a router with an interface on the mobile node’s home link home agent: a router with an interface on the mobile node’s home link foreign agent: a router on a mobile node’s foreign link foreign agent: a router on a mobile node’s foreign link

Network Layer Consideration Tunneling

Triangle Routing vs. Optimized Routing

Network Layer Consideration Triangle Routing Packets sent by a correspondent to a mobile node are routed first to the home agent and then tunneled to the care-of address. Packets sent by a correspondent to a mobile node are routed first to the home agent and then tunneled to the care-of address. Packets sent by the mobile node are routed directly to the correspondent, thus forming a triangle. Packets sent by the mobile node are routed directly to the correspondent, thus forming a triangle. Optimized Routing The mobile node informs correspondents of its care- of address and have them tunnel directly bypassing the home agent, in so-called binding updates. The mobile node informs correspondents of its care- of address and have them tunnel directly bypassing the home agent, in so-called binding updates.

Transport Layer Consideration n Several mechanisms in TCP perform as well, and others need modified to accommodate themselves to the mobile system.

Transport Layer Consideration Asymmetry The mobile node may send directly to some Internet nodes but receive by another routing path around the tunneling, that causes the different data rate. The mobile node may send directly to some Internet nodes but receive by another routing path around the tunneling, that causes the different data rate.  The ACK can’t be supplied normally.

Transport Layer Consideration Congestion The problem comes when errors are mistaken as evidence of congestion. The problem comes when errors are mistaken as evidence of congestion. The packets should be retransmitted right away, but the window-based self-clocking mechanism causes a slowdown in the data rate! but the window-based self-clocking mechanism causes a slowdown in the data rate!

Transport Layer Consideration The WTCP approach n Rate-based transmission control n Inter-packet delay as the main mechanism for transmission control n Predicting the cause of packet loss and adjusting transmission rate accordingly

Transport Layer Consideration The WTCP approach n Performing transmission control computation at the receiver n Variable granularity rate adjustment n Start-up behavior

Transport Layer Consideration Handoff Whenever the process requires the transfer of state information from the old connection point to the new one, a handoff has to occur. Whenever the process requires the transfer of state information from the old connection point to the new one, a handoff has to occur. Issues: any kinds of packets can be lost during the handoff period. Issues: any kinds of packets can be lost during the handoff period.

Transport Layer Consideration Before the handoff Before the handoff

Transport Layer Consideration Handoff between 2 foreign networks Handoff between 2 foreign networks

Transport Layer Consideration After the handoff After the handoff

Transport Layer Consideration Handoff  Possible solution: We may allow the data packets to be stored at the foreign agent; thus when a handoff occurs, the old foreign agent would forward all the stored packets to the new foreign agent. We may allow the data packets to be stored at the foreign agent; thus when a handoff occurs, the old foreign agent would forward all the stored packets to the new foreign agent.

Enter the Mobile IP

Introduction n How does Mobile IP work ?? n OSI Reference Model n Why Mobile IP?? –What happens when a node changes link?? –The existing solution to the problem. n What problems does Mobile IP solve??

How does Mobile IP work ?? n A change-of-address postcard to everyone –These postcards would have to be sent every time you moved to a new location. –You would have to be sure to send a postcard to every conceivable correspondent. –Some prankster form sending bogus change-of- address cards to your correspondents in order to redirect your mail to some undesirable person or place.

How does Mobile IP work ?? n Leave a forwarding notice at your home post office –Arrange with your previous post office to forward any subsequently arriving mail to your current post office. –Inform your correspondents that if they do not see a reply form you within a reasonable period of time then they should resend their letter to you.

How does Mobile IP work ?? n Letter n Forwarding n Post office n Internet Protocol data packet n Tunneling n Mobile IP-enhanced router

How does Mobile IP work ?? n Most network protocols were designed back in the days when almost all computers did not move very often. n Mobile IP –Allows a mobile computer to change its location without restarting its applications and without disrupting any ongoing communication.

OSI Reference Model

IP Network

Why Mobile IP??

n The existing solution to the problem –Host-Specific Routes –Changing IP Address –Some existing link-layer solutions n CDPD n IEEE

Host-Specific Routes

n Minimally, host-specific routes must be propagated to all nodes along the path between a mobile node’s home link and its foreign link. n Some (in the worst case all) of these routes must be updated every time the node moves from one link to another. n We expect millions of mobile nodes to be operation in the Internet within the coming years. Thus, we must multiply the number if host- specific routes suggested by the first two items by a million-or-so in order to determine the full impact of this solution.

Host-Specific Routes n Unless host-specific routes are propagated to a much larger set of routes than the minimal set described in the first item above, then the Internet’s ability to route around isolated node and link failures is negated by host-specific routing. n There are serious security implications to using host-specific routes to accomplish node mobility in the Internet, which would require authentication and complicated key management protocols to address.

Changing IP Address n Terminate any ongoing communications at the old link and then restart them at the new link Mobility vs. Nomadicity Mobility vs. Nomadicity

Some existing link-layer solutions n CDPD (Cellular Digital Packet Data) –Limitations in the media over which they can run n IEEE –Limitations in geographic applicability

What problems does Mobile IP solve?? n If a node moves from one link to another without changing its IP address, it will be unable to receive packets at the new link. n If a node changes its IP address when it moves, it will have to terminate and restart any ongoing communications each time it moves.

Mobile IP n Mobile IP was produced by the IP Routing for Wireless/Mobile Hosts working group of the Internet Engineering Task Force (IETF), which was formed in June n 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 n The Mobile IP standards documents include the following Request For Comments (RFCs): –RFC 2002, which defines the Mobile IP protocol itself –RFC 2003,2004, and 1701,which define three respective types of tunneling used in Mobile IP –RFC 2005, which describes the applicability of Mobile IP –RFC 2006, which defines the Mobile IP Management Information Base(MIB).The Mobile IP MIB is a collection of variables within a node which implements Mobile IP that can be examined or configured by a manager station using version 2 of the Simple Network Management Protocol (SNMPv2) [RFC 1905]

Mobile IP n What problems does Mobile IP solve?? n The scope of the Mobile IP solution n The requirements for Mobile IP n The design goals for Mobile IP n Where does Mobile IP reside?? n At a 10,000-foot level, how does Mobile IP work??

What does Mobile IP solve?? n Mobile IP is a solution for mobility on the global Internet which is scalable, robust, secure, and which allows nodes to maintain all ongoing communications while changing links. Specifically, Mobile IP provides a mechanism for routing IP packets to mobile nodes which may be connected to any link while using their permanent IP address.

The scope of the Mobile IP solution n Mobile IP is a network-layer solution to node mobility in the Internet. –Mobile IP accomplishes its task by setting up the routing tables in appropriate nodes, such that IP packets can be sent to mobile nodes not connected to their home link. n Mobile IP is completely independent of the media over which it runs.

The scope of the Mobile IP solution n Heterogeneous mobility –The ability of a mobile node to move between different media types while retaining its ability to communicate. n Homogenous mobility –CDPD and IEEE n Mobile IP is unique in its ability to accommodate heterogeneous mobility in addition to homogenous mobility.

The requirements for Mobile IP n A mobile node must be able to communicate with other nodes after changing its link-layer point-of-attachment to the Internet. n A mobile node must be able to communicate using only its home (permanent) IP address, regardless of its current link-layer point-of- attachment to the Internet.

The requirements for Mobile IP n A mobile node must be able to communicate with other computers that do not implement the Mobile IP mobility functions. n A mobile node must not to be exposed to any new security threats over and above those to which any fixed node on the Internet is exposed.

The design goals for Mobile IP n To make Mobile IP suitable for use over a wide range of wireless links and the increasing number of nodes using it. –Make the size and the frequency of these updates as small as possible. –Make it as simple as possible to implement mobile node software. –Avoid solutions which require mobile nodes to use multiple addresses, or which require large pools of address to be made available for use by mobile nodes,unless absolutely necessary.

Where does Mobile IP reside?? n Mobile Node –A node which can change its point-of- attachment to the Internet from one link to another while maintaining any ongoing communications and using only its (permanent) IP home address.

Where does Mobile IP reside?? n Home Agent –A router with an interface on the mobile node’s home link which: a.the mobile node keeps informed of its current location, as represented by its care-of address, as the mobile node moves from link to link. b.in some cases, advertises reachability to the network- prefix of mobile node’s home address, thereby attracting IP packets that are destined to the mobile node’s home address. c.intercepts packets destined to the mobile node’s home address and tunnels them to the mobile node’s current location; I.e, to the care-of address.

Where does Mobile IP reside?? n Foreign Agent –A router on a mobile node’s foreign link which: a.assists the mobile node in informing its home agent of its current care-of address; b.in some cases, provides a care-of address and de- tunnels packets for the mobile node that have been tunneled by its home agent; and c.serves as a default router for packets generated by the mobile node while connected to this foreign link.

Where does Mobile IP reside??

n Tunneling –A tunnel is the path followed by a first packet while it is encapsulated within the payload portion of a second packet. n Home address –An IP address assigned to the mobile node “permanently”. n Home link –The link which has been assigned the same network-prefix as the network-prefix of the mobile node’s ho,e address.

Where does Mobile IP reside??

n Care-of address –A care-of address is specific to the foreign link currently being visited by a mobile node. –A mobile node’s care-of address generally changes every time the mobile node moves from one foreign link to another. –Packets destined to a care-of address can be delivered using existing Internet routing mechanisms.

Where does Mobile IP reside?? n Care-of address –A care-of address is used as the exit-point of a tunnel from the home agent toward the mobile node. –A care-of address is almost never used as the IP Source or Destination Address in a mobile node’s conversations with other nodes.Specifically, the care-of address will never be returned by a Domain Name Sever when another node looks up the mobile node’s hostname. –Foreign agent care-of address vs. collocated care- of address

At a 10,000-foot level, how does Mobile IP work?? n Home agents and foreign agents advertise their presence on any attached links by periodically multicasting or broadcasting special Mobile IP messages called Agent Advertisements. n Mobile nodes listen to these Agent Advertisements and examine their contents to determine whether they are connected to their home link or a foreign link.While connected to their respective home links, mobile nodes act just like stationary nodes—that is, they make use of no other Mobile IP functionality. The rest of the steps which follow, therefore, assume that a mobile node has discovered that is connected to a foreign link.

At a 10,000-foot level, how does Mobile IP work?? n A mobile node connected to a foreign link acquires a care-of address. A foreign agent care-of address can be read from one of the fields within the foreign agent’s Agent Advertisement. A collocated care-of address must be acquired by some assignment procedure, such as the Dynamic Host Configuration Protocol, the Point-to-Point Protocol’s IP Control Protocol, or manual configuration.

At a 10,000-foot level, how does Mobile IP work?? n The mobile node Register the care-of address acquired in step3 with its home agent, using a message-exchange defined by Mobile IP. In the registration procedure, the mobile node asks for service from a foreign agent, if one is present on the link. In order to prevent remote denial-of-service attacks, the registration messages are required to be authenticated.

At a 10,000-foot level, how does Mobile IP work?? n The home agent or some other router on the home link advertises reachability to the network-prefix of the mobile node’s home address, thus attracting packets that are destined to the mobile node’s home address. The home agent intercepts these packets, possibly by using proxy ARP, and tunnels them to the care-of address that the mobile node registered in step4.

At a 10,000-foot level, how does Mobile IP work?? n At the care-of address—at either the foreign agent or one of the interfaces of the mobile node itself—the original packet is extracted form the tunnel and then delivered to the mobile node. n In the reverse direction, packets sent by the mobile node are routed directly to their destination, without any need for tunneling. The foreign agent serves as a router for all packets generated by a visiting mobile node.

At a 10,000-foot level, how does Mobile IP work??

Future Topics & Open Issues n Mobility for IP version 6 n Performance of TCP n Support for real-time traffic

Conclusion n A total mobility solution involves more than simply the ability to route IP packets to mobile computers, the latter being solved by Mobile IP.