Design and Performance Study for a Mobility Management Mechanism (WMM) Using Location Cache for Wireless Mesh Networks

1
Design and Performance Study for a Mobility
Management Mechanism (WMM) Using Location Cache
for Wireless Mesh Networks

• Di-Wei Huang, Phone Lin, Senior Member, IEEE, and
  Chai-Hien Gan, Member, IEEE
• Presented By Mahmoud ElGammal

2
Wireless Mesh Networks Architecture

• Wireless Mesh Networks (WMNs) have emerged as one
  of the major technologies for 4G high speed
  mobile networks.
• WMN Components
• A mesh backhaul connects the WMN with the
  internet.
• Stationary Mesh access points (MAPs) (or Mesh
  Nodes, MNs) provide wireless network access
  service to mobile stations (MSs).

3
(No Transcript)
4
Mobility Management is Required!

• Proposed solution WMN Mobility Management
  Mechanism (WMM)
• The WMM adopts the location cache approach.
• MS location information is cached while routing
  the data for the MS.
• The goal is to minimize signaling and routing
  costs.

5
Existing Mobile Management Protocol Categories

• 1. The ad hoc routing protocol
• Adopted by mobile ad hoc networks (MANETs).
• A routing path from the source to the destination
  is established.
• User data is relayed hop by hop by MSs.
• Unlike MANETs, WMNs have a fixed infrastructure.
• Ad hoc routing schemes are not efficient for WMNs.

6
Existing Mobile Management Protocol Categories

• 2. The centralized-database MM protocol
• A centralized database is maintained to store MS
  location information.
• Usually adopted in cellular networks.
• Whenever an MS moves from one LA to another, the
  database is accessed to update the MS location
  information.
• When the size of an LA is small, high signaling
  cost is expected.
• Due to the diversity of WMNs (varying from
  several kilometers to at most hundreds meters),
  it may not be so efficient to directly apply the
  centralized database scheme for the MM protocol
  in WMNs.

7
Existing Mobile Management Protocol Categories

• 3. The mobile IP protocol
• The service area of an IP network is partitioned
  into a home network and foreign networks.
• Two network entities, home agent (HA) in the home
  network and foreign agent (FA) in the foreign
  network, are responsible to tunnel user data to
  MSs.
• Introduces signaling overhead to inform the HA of
  the MSs movement.
• Tunneling lengthens the routing path (the
  triangle routing problem).

8
WMN Mobility Management

• Association
• Delivering Data
• Location Management / Handoff Management

9
WMM Association

• When an MS enters the coverage are of a MAP, it
  performs the association procedure to establish a
  wireless access link to the MAP.
• This MAP is known as the Serving MAP (SMAP) of
  the MS.
• The wireless link between the MS and the MAP can
  be a direct link or a relay link via other MSs.

10
WMM Delivering Data

• Before delivering the user data to an MS, the
  SMAP of this MS must be identified.
• The user data is then sent to this SMAP through
  one or more MNs via the wireless mesh links.
• These MNs are known as the relaying MAPs (RMAPs).
• Since an MS may change the SMAP from time to
  time, MM is required for packet delivery to the
  moving MSs.
• Existing standards (such as IEEE 802.11 and IEEE
  802.16) for WMNs do not address the MM issue.

11
WMM Location Management / Handoff Management

• Location Management When an MS changes its SMAP,
  location management updates the SMAP information
  for the MS.
• Handoff Management During data transmission, if
  the MS changes from old SMAP to new SMAP, handoff
  management enables the old SMAP to forward user
  data to the new SMAP.

12
The WMM Mechanism

• MNs are assigned fixed IPs.
• MSs are assigned IPs manually or via DHCP, and
  are not required to change their IP addresses.
• An MN maintains two cache tables
• The routing table maintains the routing paths
  between the MN and other MNs.
• The proxy table maintains the MS location
  information.
• The MS location information is carried in the
  packet headers.

13
The WMM Mechanism

• When MNs route packets for an MS, the location
  information of the MS in proxy tables in the MNs
  are updated.
• MNs can correctly route the packets for MSs by
  referencing the proxy table and routing table.
• If the mesh backhaul does not cache MS location
  information when processing packet routing, a
  query procedure is executed to obtain the MS
  location information.

14
The WMM Mechanism

• The options field in the IP header is utilized to
  store the MS location information.
• The options field is filled or modified by MNs
  when they route the packets for an MS.
• The options field is divided into four subfields
• The ISS field (to store the IP address of the
  senders SMAP)
• The SST field (to store the senders serving time
  stamp)
• The IRS field (to store the IP address of the
  receivers SMAP)
• The RST field (to store the receivers serving
  time stamp)

15
WMM Procedures

1. Registration To register an MS to its SMAP.
2. Routing executed by MNs to route the packets for
   an MS.
3. Query executed by the mesh backhaul to obtain
   the IP address of the receiver's SMAP when it's
   unknown.

16
WMM The Registration Procedure

• Suppose that MS1 moves from its SMAP MAP1 to
  another MAP, MAP2
• Step 1 MS1 sends a registration request message,
  REREQ(MS1s IP Address, Previous SMAPs IP
  Address, Selected SMAPs IP Address) to MAP2.
• Step 2a Upon receipt of REREQ at t1, MAP2
  updates/creates MS1's entry in the proxy cache
  (Im MS1s IP Address, Is MAP2s IP Address,
  Ts t1).
• Step 2b MAP2 sends an update request message,
  UREQ(MS1s IP Address, Selected SMAPs IP
  Address, t1), to MAP1.
• Step 2c Upon receipt of UREQ, MAP1 updates the
  entry for MS1 in its proxy table (Im MS1s IP
  Address, Is MAP2s IP Address, Ts to t1).
• Step 3a MAP1 responds to MAP2 by an update
  response message, URSP.
• Step 3b MAP2 sends a registration response
  message, RERSP, to MS1, indicating the completion
  of the registration request.

17
WMM The Registration Procedure

• MS1s location information is kept in the proxy
  tables of both MAP1 and MAP2.
• The location management for MS1 is done at MAP1
  and MAP2.
• MNs with obsolete MS1s location information
  (that is, Is field for MS1 stores MAP1s IP
  address), the packets are first routed to MAP1,
  and then MAP1 retrieves its proxy table to
  forward the packets to MAP2.
• This mechanism is loop free.

18
WMM The Routing Procedure

• Consists of two parts Location Information
  Synchronization, and Packet Routing.
• 1. Location Information Synchronization
• the MS location information in the proxy table of
  the MN and that carried in the IP header of the
  packets are updated to the latest MS location
  information.
• Suppose that MS1 (sender) is sending IP packets
  to MS2 (receiver), where MAP3 is one of the MNs
  along the routing path

19
(No Transcript)
20
WMM The Routing Procedure

• 2. Packet Routing

21
WMM The Query Procedure

• Step 1 The mesh backhaul broadcasts a route
  request message, RREQ(MS2s IP Address), to all
  MAPs, then expects to receive a route response
  message, RRES, before a timer Tq expires.
• Step 2 Upon receipt of the RREQ message, MS2s
  SMAP replies by a route response message, RRES(IP
  Address of MS2s SMAP, MS2s Serving time stamp),
  to the mesh backhaul.
• Step 3 If the RRES message is received before Tq
  expires, the mesh backhaul updates MS2s location
  information carried in the IP header and that in
  the proxy table. After the query procedure, MAP3
  can route the packet. Otherwise (that is, Tq
  expires), the mesh backhaul discards the packet.
• The query procedure requires flooding signaling
  messages to all MNs in the WMN, which is a
  high-cost operation.

22
WMM Analytical Model

• WMN traffic is classified into Internet and
  intranet sessions.
• Suppose that MS0 enters the WMN at time t0.
• Let x be the time period between t0 and the time
  when MS0 initiates the first Internet session.
• Suppose that when MS0 enters the WMN, there are
  another N identical MSs.
• Each MS initiates intranet sessions towards MS0
  with probability ?.
• Let N' (0 lt N' lt N) be the number of MSs (that
  initiate intranet sessions toward MS0). Without
  loss of generality, we assume that the N' MSs are
  MS1, MS2, ..., MSN.
• Let yk be the time period between t0 and the time
  when MSk (1 lt k lt N') initiates the first
  intranet session toward MS0.

23
WMM Analytical Model

• MS0 initiates the first Internet session at to
  x, where the mesh backhaul creates an entry to
  store MS0s location information. After to x,
  if there are packets to be routed to MS0, these
  packets can be correctly routed to MS0 without
  invoking the query procedure.

• At least one MSi (1 lt i lt N') initiates the
  first intranet session towards MS0 at t0 yi
  before MS0 initiates the first Internet session
  at t0 x. At t0 yi, if any of the MNs along
  the routing path between MSis SMAP, and the mesh
  backhaul stores MS0s location information, then
  the query procedure is not invoked during the
  packet transmission for the intranet session from
  MSi to MS0.

24
WMM Analytical Model

• A probability that case (a) occurs.
• B probability that case (b) occurs.
• The analysis of B is too complicated, so we will
  calculate an upper bound for Pq.
• x follows a Poisson distribution with rate ?.
• yi follows a Poisson distribution with rate ?.

25
(No Transcript)
26
WMM Analytical Model
With yk being exponentially distributed with mean
1/?
27
WMM Experiments

• The WMN is modeled as a regular hexagonal
  topology.
• Each hexagon represents the coverage area of a
  MAP.
• The WMN consists of 61 MNs (1 mesh backhaul and
  60 MAPs) and 1,000 MSs (N 1,000).
• The mesh backhaul is located at the center of the
  WMN.
• The movement of an MS follows a 2D random walk
  model, where an MS resides in a MAPs coverage
  area for a period of time and then moves to one
  of its neighboring MAPs with the a probability of
  1/6.

28
WMM Experiments
29
WMM Comparisons

• Cu Location Update cost (the average number of
  MNs and MSs that exchange signaling messages for
  location update operation -- executed when an MS
  changes its SMAP.)
• Ct Location Tracking cost (the average number of
  MNs and MSs that exchange signaling messages for
  location tracking operation -- executed when a
  session is initiated toward an MS.)
• Cr Routing cost (the average number of MNs or
  MSs that route a packet to a destination MS.)
• M The number of MNs in the WMN.
• N The number of MSs in the WMN.
• R The average number of MNs in the routing path
  between two MSs or between an MS and a
  centralized node (for example, a centralized
  database or an HA.)
• r The average number of sessions initiated
  toward an MS in the WMN.
• ns The average number of sessions between any
  two MSs, MS0 and MS1, within a time period where
  MS0 and MS1 do not change their SMAP.

30
WMM Comparisons