Supporting Group Mobility in Mission-Critical Wireless Networks for SIP-based Applications

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Supporting Group Mobility in Mission-Critical
Wireless Networks for SIP-based Applications

• Project LaTe

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Topics

• Background
• Session Initiation Protocol
• SigComp
• Group Mobility
• Hierarchical State Routing
• Group mobility models
• Predictive Address Reservation
• Simulation part
• Conclusions
• Final remarks future work

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Background project LaTe 1/3

• Langattomien teknologioiden käyttömahdollisuudet
  puolustusvoimien tietoliikenneverkoissa /
  Possibilities for wireless technologies in
  defence networks funded by the Finnish Defence
  Forces
• A joint research program of HUT Networking
  Laboratory, Communications Laboratory and the
  Finnish Defence Forces, commenced in 2003

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Background project LaTe 2/3

• Contemporary disaster relief operations rely
  heavily on real-time wireless communications
• these systems fall into category It Just Must
  Work
• the technology commonly used for these ends has
  had propensity to be expensive
• The rapid development of civilian communications
  technology has caused their prices to decline
  fast, making them an attractive alternative for
  the military-grade equipment
• remember the price discrimination a price
  charged from a governmental authority is N-fold
  compared to the price charged from a civilian
  party
• Project LaTe is an attempt to find ubiquitous,
  affordable and easily disposable wireless
  solutions to complement (and even completely
  substitute) the aging authority communications
  equipment currently in use
• Commercial Off-The-Shelf (COTS)

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Background project LaTe 3/3

• Netlab involvement (masters theses)
• 2003 Wireless LAN Security (Ahvenainen, Marko)
• 2004 Mobility management with Mobile IP version 6
  (Merger, Mikko)
• 2005 An Overview of Mobile IPv6 Home Agent
  Redundancy (Keränen, Heikki)
• 2006 Mobile IPv6 performance in 802.11 networks
• handover optimizations on the link and network
  layer (Hautala, Mikko)
• 2007 Analysis of Handoff Performance in Mobile
  WiMAX Networks (Mäkeläinen, Antti)
• 2007 Supporting Group Mobility in
  Mission-Critical Wireless Networks for SIP-based
  Applications (Repo, Marko)
• 2008

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Masters thesis the main themes

• Session Initiation Protocol (SIP)
• flexible, scalable and reliable signaling
  protocol
• inadequate in terms of bandwidth security
• good starting point for application-layer
  mobility
• Seamless handoffs during mobility
• VoIP data
• inter-domain mobility assumed
• scarce network bandwidth resources
• Group handoffs
• Group Mobility is a term originally coined in
  the world of ad-hoc networks
• assumes that network nodes exhibit group behavior
  (often realistic!)
• attempt to forecast the future need of network
  resources and minimize the required amount of
  signaling during handoff procedure

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Session Initiation Protocol 1/3

• Citing RFC3261, SIP is an application-layer
  control (signaling) protocol for creating,
  modifying, and terminating sessions with one or
  more participants
• Has undergone a lot of development during the
  last half a decade
• and still does (various interoperability forums
  and events held by SIP Community)
• and will do (3GPP NGN/IMS, IETF, Microsoft etc.)
• Has gained a significant foothold as a signaling
  protocol both in academia and private sector
  companies, competing with ITU-T H.323 mainly
  backed by the telecommunications industry

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Session Initiation Protocol 2/3

• Provides all needed primitives for establishing a
  connection between 2-N end points
• Transport independent
• UDP, TCP, SCTP,
• Supporting unicast and multicast
• Extremely scalable
• Intended as a subscriber signaling protocol, but
  functions virtually in every network core where
  the intelligence is located at the edges
• Intercompatible when required
• ITU-T H.323
• ISUP (SS7)
• Q.931 (ISDN)

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Session Initiation Protocol 3/3

• Issues
• UTF-8 ASCII format implies bandwidth inefficiency
• SIP was not designed for low-bandwidth wireless
  environment
• Attempts to alleviate the bandwidth issue have
  spawned mechanisms such as SigComp. Many problems
  and issues.
• Light-weight?
• Way no. SIP is already as complex as H.323. By
  the date, the SIP specifications contain
  thousands of pages
• Irony underneath the protocol design started
  from the need for a robust signaling mechanism
  characterized by simplicity and lightness
• Many open security questions
• signaling
• media
• Virtually no support for seamless mobility
• Cannot be handled with MIPv4/v6, due to the
  triangular routing phenomenon (too high latencies
  involved!)
• suitable for data connections with loose temporal
  requirements
• The real-time streams problematic (VoIP can
  withstand lt100ms latencies without degradation)

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SigComp

• Attempt to address the bandwidth issue by binary
  compressing text-based SIP messages
• May improve efficiency especially on
  low-bandwidth connections
• However, SigComp has some severe shortcomings
• consumes computing power for message processing
• requires a lot of memory for storing state
  information
• security issues (may subject to DoS attacks)
• problems with mobility
• After all, SigComp introduces another extra
  layer, and thus more complexity. So, well take a
  different approach.

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Group mobility 1/2

• The fundamental problem with SIP
• It was never intended for narrowband airlinks.
  The size of a single message with a payload can
  range anything between a few hundreds of bytes to
  many kilobytes.
• Ergo, even a modest number of moving nodes may
  generate a significant amount of SIP signaling
  traffic during connection hand-off.

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Group mobility 2/2

• We may try to eliminate the unnecessary signaling
  by dealing with groups instead of individual
  nodes.
• Introducing group handoffs.

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Another approach WiMAX MRS

• Creating an isolated cell using a mobile relay
  station (MRS), which gains the control of the
  moving mobile nodes.
• Suitable for public transportation vehicles
  (buses, trains, aeroplanes) where groups
  guaranteed to stay compact. Not suitable for
  loose or scattered groups (e.g. infantry).

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Hierarchical State Routing 1/3

• HSR A link state protocol
• a low-latency routing solution for applications
  requiring group mobility
• Applies hierarchical addressing to keep channel
  utilization efficient
• conservative on routing table sizes
• Unbundles the physical affinity from the logical
  partition representing different logical or
  functional levels where the nodes may reside
• The amount of signaling remains low, since there
  is no need for flooding
• even when the location of the corresponding node
  is not known

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Hierarchical State Routing 2/3
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Hierarchical State Routing 3/3

• Better in terms of complexity (fewer routing
  table entries) than traditional flat routing
  schemes
• Let N no. nodes, M no. hierarchy levels then
• Flat routing O(NM)
• HSR O(N X M).

Leads to better scalability

• The flip side of the coin constant need for
  updating databases
• increased complexity update latency
• dynamic cluster re-arrangement?

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Handoff delay components

• Link layer (L2) delay
• scanning, authentication and reassociation
• Movement detection (L3)
• Router Solicitation / Router Advertisement
• DHCP
• Duplicate Address Detection (DAD) is a major
  source of delay!
• Re-configuration delay
• SIP re-establishment delay
• RTT for re-INVITE and message processing, a major
  contributor
• Packet transmission time
• The time for first packet to be exchanged over
  the restored connection
• QoS AAA (optionally)
• Quality and security reservation introduce some
  latency when used

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PAR-SIP 1/4

• Predictive Address Reservation (PAR) is a
  mechanism attempting to alleviate incurred
  handoff latency by eliminating the most
  significant sources of delay Duplicate Address
  Detection (DAD) during DHCP and SIP connection
  re-establishment (re-INVITE)
• Allows approximate latencies of 60 ms, allowing
  possibly even better performance!
• Allocate L3 addresses and the session
  establishment proactively, so that the handoff
  process is almost seamless

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PAR-SIP 2/4

1. MN starts searching for a new AP/BS when the
   Signal-to-Noise falls below the Cell Search
   Threshold
2. MN consults its internal database and chooses a
   suitable target BS (TBS), then sends a
   reservation request to its serving BS (SBS)
3. SBS consults its neighboring BS table to see
   whether the MAC of the TBS belongs into the same
   (L3) domain or not
4. If so, the SBS initiates a normal L2 handoff
   (L2HO) procedure
5. If not, a network level (L3) handoff is needed.
   The SBS requests a new IP address from the TBS,
   which obtains it using DHCP and allocates
   resources proactively. Reservation reply
   containing procedure acknowledgments and a new IP
   address is sent to the MN

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PAR-SIP 3/4

• Subsequently, the MN sends a re-INVITE request to
  its corresponding node (CN), using its newly
  reserved IP address
• The CN opens a new session in parallel with the
  old session
• The packet exchange happens through both sessions
  (bi-casting) until the handoff procedure is
  completed
• for minimizing the amount of lost packets
• When the handoff is completed, the old session
  will be torn down. All traffic is now sent using
  the new session.

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PAR-SIP 4/4
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Group Mobility Models

• Mobility models are needed for system analysis
  and protocol during the design phase, but also
  for predicting the future availability of
  wireless resources
• Conventional models (Random Walk, Gauss-Markov)
  put the emphasis on individual entities
• In many cases, however, it makes sense to observe
  the movement and interaction characteristics for
  groups instead
• Group mobility is currently undergoing heavy
  research, mainly in the world of ad-hoc networks
• The future need of resources can be predicted
  with aid of group mobility models.
• logic when a MN belonging into a group performs
  handoff, it can be anticipated that that others
  will follow in a certain pattern
• the rest is about queuing theory and e-?ts

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Column Mobility Model
The most simple group mobility model. It is a
conventional model for representing e.g. field
operations involving searching activity. The
group consists of MNs associated with a line of
reference, which fully characterizes the group
behavior.
The participants also have a reference point on
the line, around which they may freely wander.
The movement of individual nodes does not have
effect on the location of group center.
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Pursue Mobility Model
Another simple model representing e.g. a chasing
scenario. A target node (TN) takes now the place
of the point of reference, which denotes the
group center.
At any time t, the scenario can be modeled
mathematically
Where MNi is place at any time t, A is an
acceleration vector of form F(TN MNi ), i.e.
position of the target node TN and the Mobile
Node i. RMi is a random motion displacement
vector for any node i, RM ltlt A
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Nomadic Community Model
Describes activity of wandering tribes, camping
for night. One may imagine that the point of
reference (RP) is the camp fire. The group
motion vector GM represents the movement of the
campfire (RP), and the mobile nodes are able to
wander around it randomly. The roaming distance
can be set as a parameter.
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Reference Point Group Mobility
RPGM is perhaps the most generally seen ad-hoc
mobility model. It can be considered of
generalization of all the presented. RPGM it is
also maybe the most commonly studied group
mobility model as it comes to the ad-hoc
mobility. Has been an inspiration for several
derivative models.
The location vector for each individual node i
can be written now
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Simulation part 1/3

• Carried out using network simulator ns-2
• several contributed modules needed
• Mobility enhancements (NIST HSNTG)
• A SIP module by Rui Prior
• C coding needed
• insufficient 802.11b model
• No way to model PAR
• Attempt to demonstrate the benefits obtainable by
  deploying GM-enhanced PAR-SIP with four plausible
  scenarios
• simulating VoIP (RTP) and data (TCP) traffic
• Indicators of interest total traffic, hand-off
  latency and packet loss during the hand-off
  process
• As of May 2007, work still in progress!

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Simulation part 2/3
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Simulation part 3/3
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Conclusions

• The main goal of this thesis minimizing
  signaling, minimizing handoff latency!
• SIP is the choice of the future, currently
  undergoing very rapid active development
• However, yet a far cry from all-around protocol
• There are many ways to mitigate the incurred
  handoff latency. Predictive Address Reservation
  (PAR) is one of them.
• Group mobility mechanisms aim at minimizing the
  unnecessary signaling during handoff, allowing
  better channel utilization in many scenarios,
  group handoffs (group handovers) are their
  realization.

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Final remarks future work

• 802.11x not necessarily the most realistic
  platform for such wide-area scenarios
• as it comes to uro, very alluring (comparing to
  WiMAX!)
• still undergoing evolution
• Vertical handovers? IEEE 802.21 (Media
  Independent Handover) on the verge of
  introduction
• How about voice and data taking different routes?
• hybrid MIP-SIP
• The research dealt solely with the most
  rudimentary transport level protocols, UDP and
  TCP
• how about more advanced protocols? DCCP? SCTP?
• Hybrid networks? The strict division into
  infrastructured and ad-hoc networks is likely to
  disappear in the future
• actually, this is happening already, slowly but
  steadily
• look at VIRVE/TETRA for instance, but also
  civilian applications (WPANs, Bluetooth, UWB, )
  although the scale is different

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The End

• Thank you!