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MITP 413: Wireless Technologies Week 9

MITP 413: Wireless Technologies Week 9. Michael L. Honig Department of EECS Northwestern University. March 2008. Wireline Call Setup. Switch. wire pair. PSTN. Helen’s phone. network address. Bob’s phone. Information Flow. off hook. Wireline Call Setup. Switch. wire pair. PSTN.

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MITP 413: Wireless Technologies Week 9

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  1. MITP 413: Wireless TechnologiesWeek 9 Michael L. Honig Department of EECS Northwestern University March 2008

  2. Wireline Call Setup Switch wire pair PSTN Helen’s phone network address Bob’s phone Information Flow off hook

  3. Wireline Call Setup Switch wire pair PSTN Helen’s phone network address Bob’s phone Information Flow off hook dial tone

  4. Wireline Call Setup Switch wire pair PSTN Helen’s phone network address Bob’s phone Information Flow off hook dial tone keystrokes alert signal

  5. Wireline Call Setup Switch wire pair PSTN Helen’s phone network address Bob’s phone Information Flow off hook dial tone keystrokes alert signal ring indication off hook remove ring indication

  6. Wireline Call Setup Switch wire pair PSTN Helen’s phone network address Bob’s phone Information Flow off hook dial tone keystrokes alert signal ring indication off hook remove ring indication conversation

  7. 1. Call Request Cellular Call Setup

  8. Cellular Call Setup 1. Call Request 2. Send numbers to switch 3. Page Receiver 4. Request Channel

  9. Cellular Call Setup (cont.) 5. Switch assigns channels 6. Cellular conversation is set up

  10. Information Flow for Cellular Call

  11. Mobility Management • Location management • How to track mobile users? • Handoff management • How to change the wireless access point? • Uses wireline resources: • Uses wireless resources:

  12. Mobility Management • Location management • How to track mobile users? • Handoff management • How to change the wireless access point? • Uses wireline resources:database and signaling link capacity • Uses wireless resources:paging, registration

  13. Location Areas (LAs) LA-1 LA-2 LOCATION UPDATE NO LOCATION UPDATE Mobiles announce changes in LAs • Requires database updates

  14. Paging LA-1 LA-2 LOCATION UPDATE NO LOCATION UPDATE • Identifies cell of mobile user. • Mobile is paged within reported LA.

  15. Location Area Tradeoff • Small location areas: • Mobile users update frequently • Fewer wireless resources spent on paging • Large location areas: • Mobile users update infrequently • More wireless resources spent on paging • Can also implement dynamic update rules(e.g., depending on time since last update, distance traveled, mobility and call patterns)

  16. Common Channel Signaling • Provides control and management functions in the PSTN • Supervisory functions, addressing, and call information provisioning • CCS channel: • Conveys messages to initiate and terminate calls • Determines the status of some part of the network • Controls the amount of traffic allowed • Separated from data traffic (out-of-band signaling) • Signaling System (SS)7: CCS for the PSTN

  17. SS7 Network Components • Service Switching Point (SSP) • Telephone switch interconnected by SS7 links. • Can be a Central Office in the PSTN, or an MSC in a PCS/cellular network • Signal Transfer Point (STP) • A switch that relays SS7 messages between network switches and databases. • Relays message to appropriate signaling links (e.g., for database query) • Provided in matched pairs to reduce chances of failure. • Service Control Point (SCP) • Contains databases for providing enhanced services (e.g., an HLR or VLR) • Accepts and answers queries from an SSP • Connected to an SSP through an STP

  18. Interconnection Between a PCS Network and the PSTN SCP SCP STP STP ( HLR ) SCP: Service Control Point STP: Signal Transfer Point SSP: Service Switching Point SSP MSC Trunk PSTN PCN (PCS network)

  19. Location Databases HLR Local service area VLR Service provider footprint Home Location Register: Stores and manages all mobile Subscriptions for a specific operator Contains directory number, profile Information, current location, andvalidation period Visitor Location Register:Stores and manages subscription information for visiting subscribers.Directs calls to and from visiting subscribers. Both are accessed through the Mobile Switching Center (MSC).

  20. MS Registration (IS-41) 1. MS turns on, registers with local (new) VLR. NEW VLR HLR OLD VLR 2 4 3 1 Morristown, NJ New York City, NY Los Angeles, CA

  21. MS Registration (IS-41) 1.MS turns on, registers with local (new) VLR 2. New VLR informs user’s HLR of new location. HLR sends an ack, which includes the MS’s profile, to the new VLR. NEW VLR HLR OLD VLR 2 4 3 1 Morristown, NJ New York City, NY Los Angeles, CA

  22. MS Registration (IS-41) 1.MS turns on, registers with local (new) VLR 2. New VLR informs user’s HLR of new location. HLR sends an ack, which includes the MS’s profile, to the new VLR. 3. The new VLR informs the MS of the successful registration. NEW VLR HLR OLD VLR 2 4 3 1 Morristown, NJ New York City, NY Los Angeles, CA

  23. MS Registration (IS-41) 1. MS turns on, registers with local (new) VLR 2. New VLR informs user’s HLR of new location. HLR sends an ack, which includes the MS’s profile, to the new VLR. 3. The new VLR informs the MS of the successful registration 4. After step 2, the HLR also sends a deregistration message to cancel the obsolete location record in the old VLR. NEW VLR HLR OLD VLR 2 4 3 1 Morristown, NJ New York City, NY Los Angeles, CA

  24. OLD VLR HLR 1 1 PSTN 2 2 MSC 1 3 3 Call Delivery (IS-41)

  25. OLD VLR HLR 1 1 PSTN 2 2 MSC 1 3 3 Call Delivery (IS-41) 1. Call is forwarded to a switch (SSP), which queries the HLR to find the current VLR of the MS.

  26. OLD VLR HLR 1 1 PSTN 2 2 MSC 1 3 3 Call Delivery (IS-41) 1. Call is forwarded to a switch (SSP), which queries the HLR to find the current VLR of the MS. The HLR queries the VLR associated with the MS to get an address.

  27. OLD VLR HLR 1 1 PSTN 2 2 MSC 1 3 3 Call Delivery (IS-41) 1. Call is forwarded to a switch (SSP), which queries the HLR to find the current VLR of the MS. The HLR queries the VLR associated with the MS to get an address. 2. The VLR returns the address to the SSP through the HLR.

  28. OLD VLR HLR 1 1 PSTN 2 2 MSC 1 3 3 Call Delivery (IS-41) 1. Call is forwarded to a switch (SSP), which queries the HLR to find the current VLR of the MS. The HLR queries the VLR associated with the MS to get an address. 2. The VLR returns the address to the SSP through the HLR. 3. A trunk (voice circuit) is set up from the originating switch to the MS through the visited MSC.

  29. Move Operation ( HLR ) MSC MSC MSC ( VLR ) ( VLR ) ( VLR ) SCP SCP SCP SCP SCP SCP SCP SCP Find Operation ( HLR ) MSC MSC MSC ( VLR ) ( VLR ) ( VLR ) Pointer Fowarding • Move operation (registration): Pointer is created from the old VLR to the new VLR. No HLR registration is required. • Find operation (call delivery): The pointer chain is traced to locate MS. Pointer from HLR moved to destination VLR.

  30. Mobile IP • Enables computers to maintain internet connectivity (TCP connections) while moving among internet attachments. • Applies to both mobile use and to nomadic use (e.g., with wired connections) • All connections are automatically maintained. • Nomadic use does not require mobile IP. • Forwards packets to new IP address via tunneling: • IP datagram is encapsulated inside a new IP datagram with a care-of-address (COA). • Some analogies with GSM mobility management: • HLR  “Home agent” • VLR  “Foreign agent”

  31. Mobile IP Scenario Mobile node A 1. Server X transmits IP datagram to mobile node A’s home address. 2. IP datagram is intercepted by home agent, and tunneled to A’s COA. 3. Foreign agent strips off outer IP header, encapsulates the original IP datagram in a network-level packet, and delivers the original datagram to A across the foreign network. 4. A sends IP traffic to X through router on foreign network (e.g., foreign agent). 5. IP datagram is delivered to X over internet. 3 Home network for A Foreign network 4 Internet or other topology of routers and links 2 Home agent Foreign agent 1 5 Server X

  32. Mobile IP: Basic Operations • Discovery:Identifies prospective Home Agents and Foreign Agents for mobile node (MN). • Registration:Authenticated procedure to inform the home agent of its COA. • Tunneling:Forwards IP datagrams from a home address to a COA.

  33. Discovery • Determines whether or not attachment point has changed (e.g., due to handoff). • MN continually listens for “advertisements” from foreign and home agents. • Eligible routers issue periodic broadcast messages. • Advertisements include: • IP address of router • If registration is required • The maximum lifetime of registration request • If router is busy • Nature of agent (home and/or foreign ) • Maximum allowable time of registration request • COAs supported • MN compares the network portion of IP address with its own home address. Mismatch implies that the MN is on a foreign network. • MN can solicit an agent advertisement (e.g., if timer has expired). • If no foreign agents are available, then MN may act as its own foreign agent by using a “co-located” COA.

  34. Registration • Message is sent to Home Agent to set up COA. • MN sends registration request to Foreign Agent. • Foreign agent relays request to MN’s Home Agent. • The HA accepts or denies the request and sends a registration reply to the FA. • The FA relays this reply to the MN. • The HA creates a mobility binding between the MN’s home address and the current COA. • Registration request message includes: • Request to retain old bindings (e.g., for handoff) • Request to receive broadcast datagrams in home network • If the mobile node is using a co-located COA • Lifetime of binding • IP addresses of the HA and FA (i.e., the COA), and the home address of the MN • Authentication extension for security.

  35. Tunneling • Home Agent “steals” identity of MN • Example: R3 is the HA for a host H attached to a foreign network • R3 informs IP layer in LAN Z that datagrams destined for H’s address should be sent to R3 • R2 and D (connected to LAN Z) insert address of R3 at the MAC-level for all packets transmitted to H. LAN X B A R1 INTERNET LAN Y C R2 R3 LAN Z D

  36. IP-within-IP Encapsulation IP version number, and other header fields -------------------------------------------------------- Tunnel source IP address (HA) -------------------------------------------------------- COA (for FA) __________________________________ IP version number and other header fields -------------------------------------------------------- Original source IP address --------------------------------------------------------- Home IP address of MN --------------------------------------------------------- TCP and rest of packet

  37. Issues • “Triangle routing” may be inefficient. • Handoff during registration. • Old data is dropped by old FA, retransmitted, and re-tunneled. • Other possibilities: • Smooth handoff: old FA tunnels to new FA • Old FA may tunnel back to HA • Packets from MN may have to be tunneled through the HA. • Foreign network may have a firewall • Called “Reverse tunneling”

  38. Handoff Decision • Depends on RSS, time to execute handoff, hysteresis, and dwell (duration of RSS) • Proprietary methods • Handoff may also be initiated for balancing traffic. • 1G (AMPS): Network Controlled Handoff (NCHO) • Handoff is based on measurements at BS, supervised by MSC. • 2G, GPRS: Mobile Assisted Handoff (MAHO) • Handoff relies on measurements at mobile • Enables faster handoff • Mobile data, WLANs (802.11): Mobile Controlled Handoff (MCHO) • Handoff controlled by mobile

  39. Soft Handoff (CDMA) ”Make before break” DURING AFTER BEFORE MSC MSC MSC BSC BSC BSC BSC BSC BSC Hard Handoff (TDMA) MSC MSC MSC BSC BSC BSC BSC BSC BSC

  40. Generic Handoff Procedure (3) Home database 1. Decision is made to handoff. 2. MS registers with the “new” visiting database. 3. New visited database requests subscriber profile from home database. 4. Home database responds with authentication of mobile. New up/downlink channels are assigned (circuit-switched). The two databases are updated with new location. 5. Home database sends a message to the old visited database to flush or redirect packets sent to or associated with MS. 6. Old database flushes/redirects packets, removes MS from its list. (4) Anchor point (5) Old visiting database (6) Old New New visiting database (1) (2)

  41. Handoff in 802.11: BSS Transition Distribution System (DS) BSS BSS Transition Basic Service Area 1 • Mobile station (MS) moves to a different BSS within the same Extended Service Set (ESS) • MS sends dissociate message to AP 1. • Need not be received. • MS sends re-associate message to AP 2. • AP 1 notified about change of location via wired network. Basic Service Area 2

  42. Handoff in 802.11

  43. Handoff in GSM Mobile Station (MS) Base Station Subsystem (BSS) Network and Switching Subsystem (NSS) • Internal handoff: between BTSs controlled by the same BSS. • External handoff: between BSSs controlled by the same MSC. • Mobile monitors the RSS for channels in adjacent cell, reports to MSC. • BTS also monitors RSS from mobile. VLR MS BSC AuC BTS HLR MS OMC BTS BSC MSC EIR MS A Um Abis Interface to other networks PSTN etc. BTS Radio interface

  44. Measurement report Handoff required Handoff request Handoff request ACK Handoff command Handoff command Handoff Handoff complete Handoff complete Clear command Clear complete MS BSS1 MSC BSS2 Handoff Information Flow

  45. BS1 BS1 BS2 BS2 Base Stations Base Stations PSTN PSTN MSCA MSCB MSCA MSCB Trunk Trunk After the handoff Before the handoff Intersystem Handoff Anchor MSC 1. MSC A requests MSC B to set up voice channel with BS2. 2. MS synchronizes to BS2. 3. MSC A connects the call path (trunk) to MSC B.

  46. MSCA MSCB X Handoff forward MSCB MSCC MSCA X Handoff through 3rd switch Forward/Backward Handoffs MSCA X MSCB X Handoff backward MSCB X X MSCC MSCA X Path minimization

  47. Handoff Issues • Intersystem handoffs • cellular (e.g., GPRS)  802.11 WLAN • 802.11  802.16 (WMAN) • Appropriate metrics? • Performance in mobile data networks • Different metrics than for voice (e.g., outage, average number of handoffs) • Throughput, maintaining QoS • Latency generally not an issue • Can retransmit

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