Lect 10 Mobile IP and GSM Handoff.pdf

University of Science & Technology Faculty of Computer Science & Information Technology Department of information for communication and technology Mobile communications & wireless technology_ it 709 4year/sem 7 Tawffeeg Mohammed Tawfeeg...

University of Science & Technology Faculty of Computer Science & Information Technology Department of information for communication and technology Mobile communications & wireless technology_ it 709 4year/sem 7 Tawffeeg Mohammed Tawfeeg 1 Mobile IP 2  Mobile IP RFC 3344 has many features we’ve seen: – home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet) three components to standard: – indirect routing of datagrams – agent discovery – registration with home agent Wireless, Mobile Networks 3 Agent discovery Mobile IP defines the protocols used by a home or foreign agent to advertise its services to mobile nodes, and protocols for mobile nodes to solicit the services of a foreign or home agent. Agent Discovery A mobile IP node arriving to a new network, whether attaching to a foreign network or returning to its home network must learn the identity of the corresponding foreign or home agent. Wireless, Mobile Networks 4  Agent discovery Indeed it is the discovery of a new foreign agent, with a new network address, that allows the network layer in a mobile node to learn that it has moved into a new foreign network. This process is known as agent discovery. Agent discovery can be accomplished in one of two ways: 1. Using agent advertisement 2. Using agent solicitation Wireless, Mobile Networks 5 Agent discovery 1. agent advertisement a foreign or home agent advertises its services using an extension to the existing router discovery protocol [RFC 1256]. The agent periodically broadcasts an ICMP message with a type field of 9 (router discovery) on all links to which it is connected. The router discovery message contains the IP address of the router (that is, the agent), thus allowing a mobile node to learn the agent’s IP address. Wireless, Mobile Networks 6-2 6  Agent discovery The router discovery message also contains a mobility agent advertisement extension that contains additional information needed by the mobile node. Among the more important fields in the extension are the following: Home agent bit (H). Indicates that the agent is a home agent for the network in which it resides. Foreign agent bit (F). Indicates that the agent is a foreign agent for the network in which it resides. Wireless, Mobile Networks 6-2 7 Agent discovery Registration required bit (R). Indicates that a mobile user in this network must register with a foreign agent. In particular, a mobile user cannot obtain a care of address in the foreign network and assume the functionality of the foreign agent for itself, without registering with the foreign agent. M, G encapsulation bits. Indicate whether a form of encapsulation other than IP-in-IP encapsulation will be used. Care-of address (COA) fields. provided by the foreign agent.Wireless, Mobile Networks 6-2 8 Agent discovery Figure below illustrates some of the key fields in the agent advertisement message. Wireless, Mobile Networks 6-2 9 Agent discovery 2. agent solicitation a mobile node wanting to learn about agents without waiting to receive an agent advertisement can broadcast an agent solicitation message, which is simply an ICMP message with type value 10. An agent receiving the solicitation will unicast an agent advertisement directly to the mobile node, which can then proceed as if it had received an unsolicited advertisement. Wireless, Mobile Networks 10 Registration with the Home Agent Once a mobile IP node has received a COA, that address must be registered with the home agent. This can be done either via the foreign agent (who then registers the COA with the home agent) or directly by the mobile IP node itself. But how the foreign agent register the COA? Wireless, Mobile Networks 11 Registration with the Home Agent Four steps are involved. 1. Following the receipt of a foreign agent advertisement, a mobile node sends a mobile IP registration message to the foreign agent. The registration message is carried within a UDP datagram and sent to port 434. 2. The foreign agent receives the registration message and records the mobile node’s permanent IP address. The foreign agent then sends a mobile IP registration message (again, within a UDP datagram) to port 434 of the home agent. Wireless, Mobile Networks 6-2 12 Registration with the Home Agent 3. The home agent receives the registration request and checks for authenticity and correctness. The home agent sends a mobile IP registration reply containing the HA, MA, actual registration lifetime, and the registration identification of the request that is being satisfied with this reply. 4. The foreign agent receives the registration reply and then forwards it to the mobile node. At this point, registration is complete. Wireless, Mobile Networks 13 Mobile IP: registration example visited network: 79.129.13/24 home agent foreign agent HA: COA: 79.129.13.2 128.119.40.7 mobile agent MA: ICMP agent 128.119.40.186 adv. COA: …. 79.129.13.2 registration req. registration req. COA: 79.129.13.2 COA: 79.129.13.2 HA: 128.119.40.7 HA: 128.119.40.7 MA: 128.119.40.186 MA: 128.119.40.186 Lifetime: 9999 Lifetime: 9999 identification:714 identification: 714 …. encapsulation format …. registration reply HA: 128.119.40.7 registration reply MA: 128.119.40.186 HA: 128.119.40.7 Lifetime: 4999 MA: 128.119.40.186 Identification: 714 Lifetime: 4999 encapsulation format Identification: 714 …. …. tim e 14  Mobile IP: indirect routing foreign-agent-to-mobile packet packet sent by home agent to foreign dest: 128.119.40.186 agent: a packet within a packet dest: 79.129.13.2 dest: 128.119.40.186 Permanent address: 128.119.40.186 Care-of address: dest: 128.119.40.186 79.129.13.2 packet sent by correspondent 15 Components of cellular network architecture recall: correspondent wired public telephone network MSC MSC MSC MSC MSC different cellular networks, operated by different providers 16 Handling mobility in cellular networks home network: network of cellular provider you subscribe to (e.g., Sprint PCS, Verizon)  home location register (HLR): database in home network containing permanent cell phone #, profile information (services, preferences, billing), information about current location (could be in another network) visited network: network in which mobile currently resides  visitor location register (VLR): database with entry for each user currently in network 17  could be home network GSM: indirect routing to mobile home HLR network correspondent 2 home Mobile home MSC consults HLR, Switching gets roaming number of Center mobile in visited network 1 call routed to home networ 3 Public VLR switched Mobile telephone Switching network Center 4 home MSC sets up 2nd leg of call to MSC in visited network mobile user MSC in visited network completes visited call through base station to network mobile Wireless, Mobile Networks 18 GSM: handoff 19  GSM: handoff with common MSC  handoff goal: route call via new base station (without interruption) VLR Mobile Switching  reasons for handoff: Center  stronger signal to/from new BSS (continuing connectivity, less old new battery drain) routing routing  load balance: free up channel in old BSS new BSS current BSS  GSM doesnt mandate why to perform handoff (policy), only how (mechanism)  handoff initiated by old BSS 20  GSM: handoff with common MSC 1. old BSS informs MSC of impending handoff, provides list of 1+ new BSSs 2. MSC sets up path (allocates resources) VLR Mobile to new BSS Switching 3. new BSS allocates radio channel for Center 2 1 4 use by mobile 7 8 4. old 5. newBSS BSStells signals MSC, mobile: old BSS: perform handoff to 3 ready new BSS old BSS 5 6 new BSS 6. mobile, new BSS signal to activate new channel 7. mobile signals via new BSS to MSC: handoff complete. MSC reroutes call 8 MSC-old-BSS resources released 21 GSM: handoff between MSCs  anchor MSC: first MSC visited during call home network correspondent  call remains routed Home through anchor MSC MSC  new MSCs add on to end anchor MSC PSTN MSC of MSC chain as mobile MSC moves to new MSC MSC  optional path minimization step to shorten multi-MSC chain (a) before handoff Wireless, Mobile Networks 22 GSM: handoff between MSCs  anchor MSC: first MSC during call visited home network correspondent  call remains routed Home MSC through anchor MSC anchor MSC  new MSCs add on to end PSTN MSC of MSC chain as mobile MSC moves to new MSC MSC  optional path minimization step to shorten multi-MSC chain (b) after handoff 23 Mobility: G S M versus Mobile IP GSM element Comment on GSM element Mobile IP element Home system Network to which mobile user’s permanent Home phone number belongs network Gateway Mobile Home MSC: point of contact to obtain routable Home agent Switching Center, or address of mobile user. HLR: database in “home MSC”. home system containing permanent phone Home Location number, profile information, current location of Register (HLR) mobile user, subscription information Visited System Network other than home system where Visited mobile user is currently residing network Visited Mobile Visited MSC: responsible for setting up calls Foreign agent services Switching to/from mobile nodes in cells associated with Center. MSC. VLR: temporary database entry in Visitor Location visited system, containing subscription Record (VLR) information for each visiting mobile user Mobile Station Routable address for telephone call segment Care-of- Roaming Number between home MSC and visited MSC, visible address (MSRN), or “roaming to neither the mobile nor the correspondent. number” 24  Wireless, mobility: impact on higher layer protocols logically, impact should be minimal … – best effort service model remains unchanged – TCP and UDP can (and do) run over wireless, mobile … but performance-wise: – packet loss/delay due to bit-errors (discarded packets, delays for link-layer retransmissions), and handoff – TCP interprets loss as congestion, will decrease congestion window un-necessarily – delay impairments for real-time traffic – limited bandwidth of wireless links 25 Thanks for attentions These slides are adapted from Computer Networking: A Top Down Approach Jim Kurose, Keith Ross Addison- Wesley March 2012 26