Title: Supporting Group Mobility in Mission-Critical Wireless Networks for SIP-based Applications
1Supporting Group Mobility in Mission-Critical
Wireless Networks for SIP-based Applications
2Topics
- Background
- Session Initiation Protocol
- SigComp
- Group Mobility
- Hierarchical State Routing
- Group mobility models
- Predictive Address Reservation
- Simulation part
- Conclusions
- Final remarks future work
3Background 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
4Background 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)
5Background 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
6Masters 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
7Session 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
8Session 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)
9Session 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)
10SigComp
- 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.
11Group 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.
12Group mobility 2/2
- We may try to eliminate the unnecessary signaling
by dealing with groups instead of individual
nodes. - Introducing group handoffs.
13Another 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).
14Hierarchical 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
15Hierarchical State Routing 2/3
16Hierarchical 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?
17Handoff 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
18PAR-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
19PAR-SIP 2/4
- MN starts searching for a new AP/BS when the
Signal-to-Noise falls below the Cell Search
Threshold - MN consults its internal database and chooses a
suitable target BS (TBS), then sends a
reservation request to its serving BS (SBS) - SBS consults its neighboring BS table to see
whether the MAC of the TBS belongs into the same
(L3) domain or not - If so, the SBS initiates a normal L2 handoff
(L2HO) procedure - 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
20PAR-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.
21PAR-SIP 4/4
22Group 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
23Column 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.
24Pursue 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
25Nomadic 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.
26Reference 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
27Simulation 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!
28Simulation part 2/3
29Simulation part 3/3
30Conclusions
- 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.
31Final 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
32The End