INTERNET-DRAFT G-S. Ahn, A. T. Cambell, S-B Lee, X. Zhang
Columbia University
October 1999
<draft-ietf-manet-insignia-01.txt>
Expires May 2000
INSIGNIA
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are working
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unlimited.
Abstract
This document specifies INSIGNIA, an in-band signaling system for
supporting quality of service (QOS) in mobile ad hoc networks. The
term `in-band signaling` refers to the fact that control information
is carried along with data in IP packets. We argue that in-band
signaling is more suitable than explicit out-of-band approaches
(e.g., RSVP) when supporting end-to-end quality of service in highly
dynamic environments such as mobile ad hoc networks where network
topology, node connectivity and end-to-end quality of service are
strongly time-varying. INSIGNIA is designed to support the delivery
of adaptive real-time services and includes fast
session/flow/microflow reservation, restoration and adaptation
algorithms between source/destination pairs. In this memo we discuss
how INSIGNIA fits into our broader vision of a wireless flow
management model for mobile ad hoc networks and how it interfaces to
the proposed MANET Working Group routing algorithm.
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Table of Contents
0. WHAT'S CHANGED .............................................. 2
1. INTRODUCTION ................................................ 3
1.1 TERMINOLOGY ............................................ 4
1.2 ASSUMPTIONS ............................................ 6
2. A WIRELESS FLOW MANAGEMENT MODEL FOR MOBILE AD HOC NETWORKING 6
2.1 PACKET FORWARDING MODULE ............................... 7
2.2 ROUTING MODULE ......................................... 7
2.3 INSIGNIA MODULE ........................................ 7
2.4 ADMISSION CONTROL MODULE ............................... 7
2.5 PACKET SCHEDULING MODULE ............................... 8
2.6 MEDIUM ACCESS CONTROLLER MODULE ........................ 8
3. INSIGNIA PROTOCOL ........................................... 8
3.1 INSIGNIA IP OPTIONS .................................... 8
3.2 RESERVATION MODE ....................................... 9
3.3 SERVICE TYPE ........................................... 10
3.4 PAYLOAD INDICATOR ...................................... 10
3.5 BANDWIDTH INDICATOR .................................... 10
3.6 BANDWIDTH REQUEST ...................................... 11
4. INSIGNIA OPERATIONS ......................................... 11
4.1 FLOW SETUP ............................................. 12
4.2 QOS REPORTING .......................................... 13
4.3 SOFT-STATE MANAGEMENT .................................. 14
4.4 FLOW RESTROATION ....................................... 15
4.5 ADAPTATION ............................................. 16
5. SECURITY ISSUES ............................................. 20
6. APPLICATION ................................................. 20
7. ACKNOWLEDGMENT .............................................. 20
8. REFERENCE ................................................... 20
9. AUTHOR'S ADDRESSES .......................................... 22
0. WHAT'S CHANGED
This memo has minor modifications from the previous draft, the
operation of protocol remains the same. For full detail on the
evaluation of INSIGNIA see [26].
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1. INTRODUCTION
The introduction of real-time audio, video and data services into
mobile ad hoc networks presents number of technical barriers that are
due to the time-varying nature of the network topology, node
connectivity and end-to-end quality of service (QOS). In such
networks, mobile nodes function as hosts and routers. As hosts they
represent source and destination nodes in the network while as
routers they represent intermediate nodes between a source and
destination providing store-and-forward services to neighboring
nodes. The wireless topology that interconnects mobile hosts/routers
can change rapidly in unpredictable ways or remain relatively static
over long periods of time. Another technical issue that needs to be
addressed is associated with the wireless link level performance.
Mobile ad hoc networks are bandwidth constrained and time-varying due
to radio link characteristics and impairments.
The end-to-end communications abstraction between two communicating
mobile hosts can be viewed as a complex channel. Due to node mobility
and wireless link impairments, user-to-user sessions may need to be
rerouted in the network while preserving the session connectivity and
quality. Network algorithms need to be strongly adaptive and
responsive to the time-varying and location dependent topological
changes, resource availability, quality of service degradation and
session connectivity.
In order to provide adaptive quality of service support for real-time
service in mobile ad hoc networks, 'flow-states' (i.e., reservation
states at nodes associated with flows or microflows) need to be
managed. A flow needs to be established, restored, adapted and
removed over the course of a user-to-user session in response to
time-varying topology, connectivity and end-to-end quality of service
conditions.
Since wireless and computational resources are limited in mobile ad
hoc networks, any signaling overhead needed for wireless flow
management must be kept to a bare minimum. Future signaling systems
should be capable of restoring reservations and associated flow-
states along a new path in response to topological changes with
minimum noticeable degradation at the user session level.
This memo provides an overview of wireless flow management model that
supports the delivery of adaptive real-time services in dynamic
mobile ad hoc networks. A key component of wireless flow management
is INSIGNIA, an in-band signaling system that supports fast flow
reservation, restoration and adaptation algorithms that are
specifically designed to deliver adaptive real-time services in
mobile ad hoc networking environments. INSIGNIA is designed to be
lightweight and highly responsive to changes in network topology,
node connectivity and end-to-end quality of service conditions. For
full detail on the evaluation of INSIGNIA, see [26].
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1.1 TERMINOLOGY
Mobile Ad Hoc Networks:
Represent autonomous distributed systems that comprise a
number of mobile nodes connected by wireless links forming
arbitrary time-varying wireless network topologies [20].
Adaptive real-time flows:
This type of flow represents delay sensitive traffic,
e.g., voice and video which can sustain some loss. Real time
data flows are assumed to be somewhat loss tolerant and delay
sensitive. These types of flows typically require flow setup
procedures, resource reservation provided by INSIGNIA.
Microflows:
Micro flows represent short-lived flows, e.g. web style
client/server interactions that comprises a limited train of
data packets. These types of flows may require resource
assurances in the network and, therefore, typically require
some form of in-band support for fast resource allocation. We
use the terms session/flow and microflow interchangeably.
INSIGNIA has been designed to transparently support the
requirements of both flowsand microflows in mobile ad hoc
networks.
Flow Setup:
A Source initiates a flow set up by transmitting a request
packet with its minimum and maximum bandwidth requirements.
Intermediate mobiles receiving request packets, processes the
requests and forward them to the next appropriate mobile host.
A flow setup is complete when a source receives a QOS report
from its peer destination.
Restoration:
When a reserved flow is rerouted and its associated states
(e.g., reservation) are successfully created along the new
route. Three types of restoration (viz. `max to max`,
`max to min` and `min to max`) may be observed along the new
path.
Enhancement Layer (EL) Degradation:
When a reserved flow is rerouted and its EL restoration fails,
then a flow/sessions enhancement layer packets are degraded
to best effort service. In a such case, only base layer (BL)
packets are forwarded/received as reserved packets.
Flow Degradation:
When a reserved flow is rerouted and both EL and BL restoration
fails. No resource allocation or associated states are created
and all packets are treated as best effort after re-routing.
Adaptation:
When EL degradation persists for an unacceptable period, a
destination mobile notifies its source to drop the EL packets
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at the source host (scaling down). The destination can also
initiates an EL resource recovery (scaling up) procedure when a
monitored flow state at the destination indicate that
sufficient resources exist along the path to support a better
quality level.
Adaptation Policy:
Describes the bandwidth adaptation characteristics of a flow
and the actions to be taken based on the observed network
conditions experienced by a flow and its ability to adapt to
those conditions. The decision to trigger adaptation mechanisms
(i.e., scaling flows up/down)is based on application-specific
adaptation policy.
Adaptation Handler:
A module that stores the adaptation policy that interacts with
flow monitoring and QOS report modules.
Monitoring Module:
A module that keeps track of the incoming INSIGNIA flow state.
Typically the packet type, resource availability and QOS
are periodically monitored.
QOS reports:
These are periodic messages that are generated by destinations
to inform peer sources of reception state/status of adaptive
real-time flows. The periodicity depends on the sensitivity of
a flow. Best effort flows do not, typically, generate QOS
reports.
Soft-state management:
Each mobile host creates, stores and updates the state
information for each adaptive real-time flow and its
reservation status. This state information requires subsequent
packets to refresh the flow state otherwise the flow state is
considered old and automatically removed after a soft-state
interval.
Soft-state timer:
The soft-state timer value defines the holding time for real-
time reservation state for adaptive real-time flows/flows. If
the mobile soft-state is not refreshed within the soft-state
timer interval then the state is automatically removed. (Note
that the treatment of flows and microflows may differ in terms
of the setting of this state variable. Typically, flows would
call for extremely fast reservation and release that may be
more aggressive than the dynamics and timescales associated
with longer lived flows. This issue is under experimentation
and for further study.)
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1.2 ASSUMPTIONS
INSIGNIA assumes that link status sensing and access schemes are
provided by lower layer entities/protocols.
2. A WIRELESS FLOW MANAGEMENT MODEL FOR MOBILE AD HOC NETWORKING
The goal of wireless flow management is to support the delivery of
adaptive real-time services in mobile ad hoc hosts under time-
varying conditions. An adaptive service model allows packet audio,
video and real-time data applications to specify their maximum and
minimum bandwidth needs. INSIGNIA plays a central role in the
resources allocation and management between source and destination
mobiles. Based on availability of end-to-end resources, wireless
flow management attempts to provide assurances for the minimum or
maximum bandwidth needs depending of resource availability. In
addition to supporting adaptive real-time services the service
model also supports IP best-effort packet delivery.
adaptive mobile
applications
^
+--------------------------------------------------------------+
| | |
| +---------------+ | +-----------------+ +-----------+ |
| | MANET routing | | | INSIGNIA |<--->| admission | |
| | protocol | | | | | control | |
| +---------------+ | +-----------------+ +-----------+ |
| | \ | | | | | |
| | \ | | | control | |
| --------- \ | | --------- | --------- |
| routing \ | | mobile | channel |
| table \ | | soft-state | state |
| --------- \ | | --------- | --------- |
| \ \ | signal / \ | packet / \ |
| \ \ v -ing / \ | drop / \ |
| \ +------------+ +-----------+ \ |
| +-----+ \| packet | | packet | +-----+ |
===>| MAC |===>| forwarding |======>| scheduling|====>| MAC |===>
| +-----+ +------------+ +-----------+ +-----+ |
|IP packet in data packets IP packet out|
+--------------------------------------------------------------+
Figure 1. Wireless Flow Management Model at a Mobile Host/Router
Realizing wireless flow management in mobile ad hoc networks presents
a number of technical challenges. First, flows and microflows should
be rapidly established without the penalty of a round trip delay and
with minimal overhead due to signaling. Second, active flows should
be maintained and restored in case of routing changes or link
failure. Wireless flow management should be capable of rapidly
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responding to dynamic topology changes by adapting and re-
establishing affected flows with minimal service disruption. Third,
flow-state set up during flow establishment should be automatically
removed when an application session terminates. Flow-state should
also be automatically removed at routers no longer on the new path
after re-routing has occurred due to topological changes. The main
modules of the wireless flow management model are illustrated in
Figure 1).
2.1 PACKET FORWARDING MODULE
The packet forwarding module [15] classifies incoming packets and
forwards them to the appropriate module (viz. MANET routing,
INSIGNIA, local applications, wireless packet scheduling modules).
Signaling messages are processed by INSIGNIA and data packets
delivered locally or forwarded to the packet scheduling module.
2.2 ROUTING MODULE
The routing module dynamically tracks changes in ad hoc network
topology making the routing table visible (via APIs) to all
intermediate packet forwarding module (e.g., INSIGNIA, packet
forwarding). Wireless flow management assumes the availability of
MANET routing protocol [2] (e.g. Temporally Ordered Routing Algorithm
(TORA) [1], Dynamic Source Routing [7], Zone Routing Protocol [5], Ad
Hoc On demand Distance Vector Routing Protocol [6]).
2.3 INSIGNIA MODULE
The INSIGNIA module establishes, restores, adapts and tears down
real-time flows. Flow restoration algorithms respond to dynamic route
changes due to mobility. Adaptation algorithms respond to changes in
available bandwidth. Based on an in-band signaling approach that
explicitly carries control information in the IP packet header, flows
can be rapidly established, restored, adapted and released in
response wireless impairments and topology changes. Because of this
dynamic environment, network state management is based on soft-state
[3], which is well suited to managing reservation flow-state in
mobile ad hoc networks.
2.4 ADMISSION CONTROL MODULE
The admission control module is responsible for allocating bandwidth
to flows based on the maximum/minimum bandwidth requested. Once
resources have been allocated they are periodically refreshed by a
mobile soft-state mechanism through the reception of data packets.
Admission control testing is based on the measured channel
capacity/utilization and requested bandwidth. To keep the protocol
simple and lightweight, new reservation requests do not affect
existing flow reservations. Rerouted or new flows may be degraded
ifresources are unavailable.
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2.5 PACKET SCHEDULING MODULE
The packet scheduling module responds to location dependent channel
conditions experienced in wireless networks [22]. The scheduling
mechanism is implementation and QOS model dependent. Currently, we
have implemented a simple Weighted Round-Robin (WRR) service
discipline which takes location dependent channel conditions into
account. It should be noted that a wide variety of scheduling
disciplines can be used to realize the packet scheduling module.
2.6 MEDIUM ACCESS CONTROLLER MODULE
The medium access controller module (possibly) provides quality of
service driven access to the shared wireless media for adaptive
real-time services and best-effort services. The wireless flow
management is designed to be transparent to any underlying media
access control protocols. However, the performance of the MANET is
strongly coupled to the provisioning of QOS support at the MAC layer.
Nevertheless, our approach is to investigate the performance of
INSIGNIA using both non QOS-capable and QOS-capable MACs.
3. INSIGNIA PROTOCOL
Mobile ad hoc signaling systems should be lightweight in terms of the
amount of bandwidth they consume and be capable of reacting to fast
network dynamics close to call/session and packet transmission time
scales. Future signaling systems should be highly responsive to flow
re-routing and be capable of re-establishing active reservations
along the new path with minimum disruption to on-going services.
In-band signaling systems are capable of operating close to packet
transmission time scales and are therefore well suited toward
managing fast time-scale dynamics found in mobile ad hoc
environments. In contrast, out-of-band signaling systems (e.g.
Internet's RSVP, ATM's UNI, etc.) are incapable of responding to such
fast time-scale dynamics. Based on an in-band approach, INSIGNIA is
designed to restore 'flow-state' (i.e., a reservation) in response to
topology changes within the interval of two consecutive IP packets
under ideal conditions.
3.1 IP OPTIONS
To establish an adaptive real-time flows, INSIGNIA uses a new IP
option to setup, restore and adapt resources between source-
destination pairs. When intermediate nodes receive packets with the
these IP options set they attempt to reserve, restore or adapt
resources forwarding date packets toward the destination.
By coding control information in the INSIGNIA IP option (in each IP
header), we support the notion of in-band control which we believe is
called for to support QOS in ad-hoc mobile networks. The INSIGNIA IP
option supports flow reservation, restoration and adaptation control.
Best effort and adaptive real-time services are supported by INSIGNIA
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and are indicated by the reservation mode and service type fields in
the IP options as illustrated in Figure 2. Flows are represented as
having a discrete base layer (BL) with a minimum bandwidth and an
enhancement layer, which requires the maximum bandwidth. This
characterization is commonly used for multi-resolution traffic (e.g.,
MPEG audio and video) and more generally for real-time data that has
discrete max-min requirements.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL |Type of Service| Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live | Protocol | Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options (Used for INSIGNIA IP Options) | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2a. IP Header
reservation payload bandwidth request
mode indicator
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
+-------+-----+-----+-------+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|REQ/RES|AS/BE|BL/EL|max/min| max_bandwidth | min_bandwidth |
+-------+-----+-----+-------+---------------+---------------+
service bandwidth
type indicator
|<----->|<--->|<--->|<----->|<----------------------------->|
1 bit 1 bit 1 bit 1 bit 16 bits
Figure 2b. INSIGNIA IP Options
3.2 RERSERVATION MODE
To establish an adaptive real-time flow, a source node sets the
request (REQ) bit in the IP option of a data packet to initiate a
reservation request. On reception of a REQ packet, the intermediate
nodes execute admission control and accept or deny the request. If
the request is accepted, resources are committed and subsequent
packets are scheduled accordingly. Otherwise, packets are treated as
best effort packets if resources are unavailable.
Packets that are received by nodes with their reservation mode set to
reserved (RES) indicate that the session has previously passed
admission control and resources have been reserved. In the case where
a RES packet is received and no resources have been allocated the
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admission controller immediately attempts to make a reservation. This
condition commonly occurs when reserved flows are rerouted during the
lifetime of an active session due to mobility of sources,
intermediate router nodes or destinations.
3.3 SERVICE TYPE
The interpretation of the service type, which indicates either a
adaptice service (AS) or best-effort (BE) packet, is dependent on the
reservation mode. A packet with the reservation mode set to REQ and
service type to AS is attempting to setup a real-time flow with the
bandwidth requirements of the flow specified in the bandwidth request
field. A packet with RES/AS set indicates that an end-to-end
reservation has previously been established. A RES/AS packet service
may be degraded to RES/BE service if the flow is rerouted along a new
path when insufficient resources were available on the new path.
A best effort packet sets the reservation mode to REQ as default and
the service type to BE requiring no resource reservation to be made
in the network. Reception of a RES/BE by a destination node indicates
an active adaptive real-time flow was degraded to BE due to
insufficient resource availability after rerouting to a new path.
3.4 PAYLOAD INDICATOR
The payload field indicates the type of packet being transported.
INSIGNIA supports two types of payload, i.e., base (BL) and
enhancement layers (EL). The semantics of the adaptive real-time
services are related to the payload type and resource availability.
Base and enhancement layers can be assured via distributed end-to-end
admission control and resource reservation. Maximum bandwidth
reservation is required to support both base and enhancement layers
of a flow whereas only minimum bandwidth reservation is required to
support the base layer. When a flow with minimum reservation receives
a EL packet in reserved mode (RES/AS) set, it indicates either the
reservations for EL has been restored at the bottleneck node or an
adaptation (scale-up) has been occurred.
3.5 BANDWIDTH INDICATOR
The bandwidth indicator represents the potential resource
availability for a flow/session along its current path between a
source and destination pair. In this respect the bandwidth indicator
represents the prospective resource availability to an application
which will change over time. This does not, however, represent an
actual resource reservation but the potential for one to succeed give
the current indication. The bandwidth indicator is carried in each
packet and can be therefore viewed as a dynamic state variable that
can be updated by any mobile host on the current path. Based on its
value it represents a good bandwidth hint that resources are
available along the current path to meet the flows minimum or maximum
needs. In this capacity the bandwidth indicator plays an important
role during the flow setup phase and, more importantly, during the
adaptation phase.
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During flow setup the bandwidth indicator represents the resource
availability along the chosen setup route. Reception of setup request
packets with the bandwidth indicator bit set to MAX indicates that
all nodes en-route have sufficient resources to support the maximum
bandwidth requested. In contrast, a packet with the bandwidth
indicator set to MIN implies that at least one of the intermediate
nodes (known as the bottlenecked mobile host) between the source and
destination has insufficient bandwidth resources to meet the maximum
needs (if specified); however, reception of a packet with the
bandwidth indicator set to MIN does indicate that all nodes can
support the minimum bandwidth requirement. In this case, only the
base layer reservation is acknowledged as having been successful
established via QOS reporting (see Section 4.2). QOS reporting
between the destination and source can be used to force the source to
'drop' enhancement layers. In this case the source would only forward
the BL packets toward the destination in reserved mode. Any
enhancement layer packets would be forwarded as best-effort packets.
This action has the benefit of releasing an 'partial reservations'
for the enhancement layer that may exist between a bottlenecked
mobile host and the destination. We will discuss the issue of
'partial reservations' (which may occur in all phases of INSIGNIA
operation)in the sections of flow setup, restoration and adaptation.
The bandwidth indicator is also utilized for restoring the
reservation for EL if previously degraded to best effort service. In
order to accomplish scaling up adaptation, the adaptation handler
resident at destination should monitors a flow's resource
availability (by monitoring the bandwidth indicator) and, based on
the adaptation policy, initiate a 'scale up' operation using a QOS
report.
3.6 BANDWIDTH REQUEST
The bandwidth request allows a source to specify its maximum (MAX)
and minimum (MIN) bandwidth requirements for adaptive real-time
service support. This assumes that the source has selected the AS
service type. A source may also simply specify a minimum or a maximum
bandwidth requirement. For adaptive real-time services the base layer
is supported by the MIN bandwidth whereas the MAX bandwidth supports
the delivery of the base and enhancement layers between a source and
destination pair.
4. INSIGNIA OPERATIONS
The IP option and operations support the delivery of adaptive real-
time services to mobile hosts. These operations collectively define
the foundation of the INSIGNIA system and include flow setup, flow
restoration, soft-state management, adaptation and QOS reporting.
Once a flow has been established between a source-destination pair,
QOS reports are used to inform the source of the progress of the
delivered packet quality at the destination. Node mobility may
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trigger topology changes. In this case the MANET routing protocol may
provide alternative or new path information to destination, in which
case, INSIGNIA would attempt to restore reservations at all nodes on
the new path through the restoration operation. Moreover, adaptation
may be triggered to adjust a flow to match resources availability
found on the new path. Managing the network state,while responding to
these network dynamics, is handleby a soft-state management mechanism
in INSIGNIA. In the following sections,each of the INSIGNIA
operations are outlined.
4.1 FLOW SETUP
To establish adaptive real-time flows, source nodes set the
appropriate fields in the IP option before forwarding 'reservation
request' packets toward destination mobile hosts. A reservation
request packet is characterized as having its reservation mode set to
REQ, service type set to AS, a valid payload (viz. BL or EL) and a
MAX/MIN bandwidth requirement.
Reservation packets traverse intermediate nodes executing admission
control modules, allocating resources and establishing flow-state at
all nodes between source-destination pairs. If any intermediate
mobile node lacks resources to support the requested flow setup, the
appropriate IP option field is changed to indicate this condition (or
state).
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
+---+----+-----+-------+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|REQ| AS |BL/EL|max/min| max_bandwidth | min_bandwidth |
+---+----+-----+-------+---------------+---------------+
Figure 3. INSIGNIA Packet Requesting MAX/MIN reservation
If an intermediate mobile receives a request packet and can only
support the minimum requirement then the flow request is degraded to
the minimum request at the bottleneck mobile node by resetting the
bandwidth indicator to MIN. Meanwhile the source continues to send
reservation requests packets until the destination informs it of the
status of flow establishment phase via QOS report (discussed in
Section 4.2). Subsequent reservation request packets do not execute
admission control but simply refresh existing soft-state reservation.
The establishment of an adaptive real-time flow is illustrated in
Figure 4. A source mobile host (M1) issues a flow setup by requesting
resource reservation. M2 performs admission control upon reception of
the request packet. Resources are allocated if available and the
request packet is forwarded to the next mobile (M3). This process is
repeated hop by hop until the request packet reaches the destination
mobile host (M6). The destination mobile node determines the resource
allocation status by checking the service type and current level of
service.
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When a reservation request is received at the destination node, the
INSIGNIA module checks the reservation status. The status of the flow
setup is determined by inspecting the bandwidth indication field. If
the bandwidth indicator is set to MAX then this implies that all
mobile hosts between the source destination have successfully
allocated resources to meet the base and enhancement layers bandwidth
requirements. On the other hand, a bandwidth indication set to MIN
indicates that only the base layer can be currently supported. In
this case, all reserved packets with a payload of EL received at the
destination have their service level flipped from AS to BE by the
bottleneck node. In such case, a partial reservation may exist
between the source and bottleneck mobile node. This partial
reservation can be viewed as a waste of resources between the source
and bottlenecked node (since they go unused) or, as a 'near
reservation' where all but the remaining nodes (between the
bottlenecked node and the destination) hold reservations. Holding on
to these reservations - in effect locking them in - is a 'hedge'
against completing the setup phase in the near future. The treatment
of 'partial reservations' is still under consideration. Currently,
the adaptation process allows the mobile host to clear partial
reservations using the adaptation process or leave them in place.
+----+ +----+
QOS_REPORT(2)| M9 |---| M8 |\QOS_REPORT(2)
+----+ /+----+ +----+ \ +----+
| M2 |/ / \| M7 |\QOS_REPORT(2)
REQ(1)/+----+\ / +----+ \+----+
+----+/ \ +----+/ +----+ | M6 |
| M1 | REQ(1)\| M3 |---| M4 |REQ(1) /+----+
+----+ +----+ +----+\ +----+/
REQ(1) \| M5 | REQ(1)
+----+
Figure 4. INSIGNIA Request Packet and QOS report
4.2 QOS REPORTING
QOS reports are used to inform the source of the status of received adaptive
real-time flows. Destination nodes actively monitor on-going flows inspecting
status information (e.g., bandwidth indication) and calculating QOS statistics
(viz. packet loss, delay, out-of-sequence delivery and throughput). QOS
reports are periodically sent to source host for the purpose of completing
flow establishment and managing adaptations. QOS reporting is application
dependent where the periodicity of reports is determined by the application's
sensitivity to the delivered QOS. Note that QOS reports do not have to travel
on the reverse path toward the source. Typically they will take an alternate
route through the ad hoc network as illustrated in Figure 4.
In the case of flow establishment, reception of a reservation request packet
with the bandwidth indicator set to MAX (or MIN) indicates that the source's
maximum (minimum) reservation has been successfully made en-route. The
destination informs the source of this reservation status by setting the
bandwidth indicator field with MAX (MIN) in the QOS report, accordingly. The
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QOS report is a best effort data packet with a payload that comprises of a
adaptation commands and measured QOS information.
QOS reports are also used as part of on-going adaptation process that responds
to mobility and resources changes in the mobile ad hoc network. Periodic QOS
reports can be used to inform the source to 'drop' (e.g., drop all EL packets)
or 'scale-up' (i.e., transmit EL packets) based on available resources and the
adaptation policy of the application. These are the 'adaptation commands'.
4.2.1 QOS REPORT INTERVAL
Since each flow has different sensitivity to QOS, the periodicity of QOS
report for each flow should reflect this sensitivity. A flow that is sensitive
to service quality requires more frequent QOS report than one that is less
sensitive (i.e., more QOS control). A source relates the sensitivity of a flow
via setting the TTL value with relatively small value. The destination
utilizes the TTL value, requested bandwidth and the adaptation policy to
determine the flow's sensitivity to service quality. We are currently
investigating the migration of this function to the INSIGNIA IP options field.
4.2.2 QOS PACKET FORMAT
The role of the QOS report is to serve as a simple notification of the
satisfaction level perceived by the destination. The QOS report includes a
QOS. In fact, the QOS report of INSIGNIA has the same format as a best effort
INSIGNIA data packet. A QOS report has the reservation mode set to RES and
service type set to BE. The minimum bandwidth field is set to zeros and
maximum bandwidth is set to ones. By doing so, the QOS report can be
distinguished from the degraded RES packet. The various packet formats are
illustrated in Figure 8.
4.2.3 QOS REPORT DELIVERY
QOS reports should be delivered in a timely fashion. We propose to schedule
QOS reports before the transmission of best effort packets but without
affecting the performance of reserved flows. The IP option codepoint for QOS
reports, even though best effort in service type, set it a side from all
other best effort traffic for a 'better than best effort treatment' at
intermediate nodes.
4.3 SOFT-STATE MANAGEMENT
Maintaining the quality of service of real time flows in mobile ad hoc network
is one of the most challenging aspects that INSIGNIA addresses. Typically,
wireline networks requires little QOS or state management where the routes and
the reservations remain fixed for the duration of the session/flows. This
style of 'hard-state' connection oriented communications guarantees quality of
service for the duration of the holding time. However, these techniques are
not applicable/valid in mobile ad hoc networks where paths and reservations
need to dynamically respond to topology changes in a timely manner over
multiple time scales and network dynamics.
Based on the work by Clark [3], 'mobile soft-state' relies on the fact that
sources periodically send data messages along the existing path. If a data
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packet arrives at a mobile router and no reservation exists then admission
control and resource reservations are needed to establish soft-state
reservations. Subsequent reception of a data packet at a router is used to
refresh the soft-state reservation. Thus a mobile host receiving a data packet
for an existing reservation reconfirms the reservation over the next time
interval. The holding-time for a reservation is based on a soft-state timer
interval and not, as in the case of call setup, based on the session duration
holding time. If a new packet is not received within a soft-state timer
interval, resources are released and flow-states removed automatically without
any explicit tear-down messaging.
The soft-state approach is well suited for management of resources in dynamic
environment where the path and reservation associated with a flow may change
rapidly. The transmission of data packets is strongly coupled to maintenance
of flow-states, i.e., reservations. As the route changes in the network, new
reservations will be automatically restored by the restoration mechanism
provided that resources are available along the new path.
Another benefit of mobile soft-state is that resources allocated during flow
establishment are automatically removed when the path changes without any
explicit signaling interactions. In-band approaches are flexible and scalable
in dealing with a number of difficult mobile ad hoc network issues whereas
out-of-band signaling systems need to maintain source route information and
respond to topology changes by directly signaling 'affected mobiles' to
allocate or free radio resources. In some case, this is impossible to do when
using out-of-band signaling techniques if the 'affected router' is out of
radio contact from the signaling entity that is attempting to de-allocate
resources over the old path.
4.4 FLOW RESTORATION
Flows are often rerouted during the lifetime of sessions due to mobility in
mobile ad hoc networks. The goal of flow restoration is to re-establish
reservation as fast and efficiently as possible. Rerouting of an active flow
involves new admission control and resource reservations for nodes on the new
path. Restoration procedures also call for the removal of flow-state at nodes
along the old path. In an ideal case, the restoration of flows can be
accomplished within the duration of a few consecutive packets because of the
in-band nature of INSIGNIA's control.
When a mobile moves out of radio contact and loses connectivity, the
forwarding router mobile interacts with the routing module and forwards
subsequent packets via the new route. (Note that if the routing table does not
have an alternative route toward the destination then the performance of the
restoration process is tightly coupled to the performance of the
proactive/reactive MANET routing protocol that is operational. This issue is
for further study. In [25], however, we implemented INSIGNIA in a mid size ad
hoc network using TORA [1] as the routing protocol and discuss performance
issues there).
The mobile hosts on a new path receive rerouted packets and inspect their flow
state tables. If a reservation does not exist for the rerouted flow then the
INSIGNIA module invokes admission control and tries to allocate
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resources. Note that, if the reserved packets are routed back on to the
existing path then the old states are likely to be still valid; hence, the
states and reservations are simply refreshed, minimizing any service
disruption due to re-rerouting.
Network dynamics may also trigger rerouting with service degradation. When a
reserved flow is rerouted to a node where resources are unavailable, the flow
is degraded to best effort service. Subsequent downstream nodes receiving
these degraded packets make no attempt to attempt to allocate resources or
refresh existing soft-state associated with the flow. This results in the
automatic removal of any reservation state. In time the reservation may be
restored if resources free up at the bottleneck mobile node or because of the
subsequent rerouting allowing the complete restoration of the flow
quality. The worst case scenario is that the flow will remain degraded for the
duration of the session holding time.
The enhancement layer of a reserved flow with maximum reservation may get
degraded during flow restoration if the nodes along the new path can only
support the minimum bandwidth requirement. If the degradation of enhancement
layer packets persist, it may cause service disruptions and may trigger the
destination mobile to invoke an adaptation procedure that force the source
node to drop the EL packets. Adaptation details are provided in the following
section.
4.5 ADAPTATION
Reception quality of a flow is monitored and based on an application-specific
adaptation policy, actions may be taken to adapt the flow to observed network
conditions. Actions taken are conditional on the adaptation-policy resident at
the destination node, e.g., adaptation policy may chose to maintain the
service level under degraded conditions or scale-down flows to their base
layers in respond to degraded conditions. Other policy could scale-up flows
whenever resources become available. The application is free to program its
own adaptation policy that is executed by INSIGNIA through interaction between
the destination and source nodes. Details about the adaptation policy API are
described in [19].
The adaptation process includes the following adaptation actions:
(1) 'EL degradation' is a network driven action that forwards the
EL packets as best effort packets due to lack of resources;
(2) 'Drop enhancement layer' is a destination mobile driven action
which requests a source to drop its enhancement layers. This
happens when the EL degradation persists beyond an acceptable
period; and
(3) 'Scale-up', which requests a source to send its base and/or
enhancement layers in reserved mode. This event occurs when
a flow has only minimum reservation and the destination
learns (through the bandwidth indicator) that the route
can accommodate the maximum resource requirement.
The EL degradation is a network driven action whereas the others two actions
are driven by an adaptation handler resident at the destination mobile
host. Typically, the EL degradation can be observed after rerouting of an
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adaptive real-time flow. In such an event the EL packets are degraded and
forwarded as best effort packets whereas BL packets are forwarded in reserved
mode. Note that preference is given to base layers over enhancement layers in
the event that reserved packets have to be degraded to best effort. If the EL
degradation persists, a `drop` command may be issued by the adaptation handler
at the destination mobile host according to the adaptation policy. The
decision to drop the EL packets is facilitated by monitoring the incoming
packets. The destination mobile can readily detect the degraded RES packets by
reading the IP option fields (where the degraded packets have the format of
Figure 5d). Figure 5 illustrates the different modes of INSIGNIA packets.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
+---+----+-----+-----+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|REQ| BE |BL/EL| max | max_bandwidth | min_bandwidth |
+---+----+-----+-----+---------------+---------------+
Figure 5a. A Best Effort Packet
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
+---+----+-----+-----+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|REQ| AS |BL/EL| max | max_bandwidth | min_bandwidth |
+---+----+-----+-----+---------------+---------------+
Figure 5b. A Request Packet (EL or BL)
+---+----+-----+-------+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RES| AS |BL/EL|max/min| max_bandwidth | min_bandwidth |
+---+----+-----+-------+---------------+---------------+
Figure 5c. Typical Reserved (RES) Packet (EL or BL)
+---+----+-----+-----+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RES| BE |BL/EL| max | max_bandwidth | min_bandwidth |
+---+----+-----+-----+---------------+---------------+
Figure 5d. A Degraded RES Packet (EL or BL)
+---+----+----+-------+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RES| BE | BL |max/min|1 1 1 1 1 1 1 1|0 0 0 0 0 0 0 0|
+---+----+----+-------+---------------+---------------+
|<----------->| |<----- unique format --------->|
a QOS report
* max/min indicates the accepted service level
Figure 5e. Format of a QOS report
exist between a source and bottleneck mobile freeing up resources for other
adaptive real-time flows to utilize. It also removes degraded enhancement
layer packets from the network which in turn benefits the normal best effort
service flows.
INSIGNIA is also equipped with capability to restore the reservation needed
for enhancement layers.This process takes advantage of network and session
dynamics allowing existing sessions to take advantages of resources released
due to re-routing (e.g., resources released along an old path) or session
termination. These events may allow other mobile nodes to take advantage of
released resources by scaling up. The bandwidth indicator plays a key role in
bandwidth needs of the particular session/flow.
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Typically, the scale-up process is invoked when the destination observes
sufficient resource have become available along the existing path restore the
reservation of an enhancement layer. The decision to scale up is determined by
the adaptation policy.
The following example scenario shows an example of a set of states (marked
[1] through [7]) observed at the destination illustrating a flow adaptation
scenario:
Adaptation Procedures :
[1] Incoming Packets at time t1 with maximum resource allocation
+---+----+----+-----+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RES| AS | BL | max | max_bandwidth | min_bandwidth |
+---+----+----+-----+---------------+---------------+
+---+----+----+-----+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RES| AS | EL | max | max_bandwidth | min_bandwidth |
+---+----+----+-----+---------------+---------------+
.
.
.
[2] EL packets are degraded due to lack of resources at an
intermediate mobile node at time t2 and now packet formats become
+---+----+----+-----+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RES| AS | BL | min | max_bandwidth | min_bandwidth |
+---+----+----+-----+---------------+---------------+
+---+----+----+-----+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RES| BE | EL | min | max_bandwidth | min_bandwidth |
+---+----+----+-----+---------------+---------------+
* Note that EL packet is degraded to a best effort packet
.
.
.
[3] If the degraded EL packets are determined to be not useful for
destination mobile host, an EL drop command is issued via QOS
report. Upon reception of the QOS report the source transmits only
BL packets in reserved mode and do not transmit any EL packets.
+---+----+----+-----+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RES| AS | BL | min | max_bandwidth | min_bandwidth |
+---+----+----+-----+---------------+---------------+
* EL packets are not transmitted/received
.
.
.
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[4] Constant resource availability is detected through the bandwidth
indicator at t4 where the received packets indicating the resource
availability have the following format.
+---+----+----+-----+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RES| AS | BL | max | max_bandwidth | min_bandwidth |
+---+----+----+-----+---------------+---------------+
* Currently no EL packets are received.
* Destination learns from the bandwidth indicator bit (set to max)
that the current route has the resources available to restore the
EL packet flow.
.
.
.
[5] Through the next QOS report destination informs the source to
reinitiate the transmission on EL in RES mode. If the recovery
(scale up) is successful, destination receives the following
packets.
+---+----+----+-----+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RES| AS | BL | max | max_bandwidth | min_bandwidth |
+---+----+----+-----+---------------+---------------+
+---+----+----+-----+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RES| BE | EL | max | max_bandwidth | min_bandwidth |
+---+----+----+-----+---------------+---------------+
.
.
.
[6] If scale up attempt fails at any mobile node on the route,
destination receives degraded EL packets.
+---+----+----+-----+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RES| AS | BL | min | max_bandwidth | min_bandwidth |
+---+----+----+-----+---------------+---------------+
+---+----+----+-----+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|RES| BE | EL | min | max_bandwidth | min_bandwidth |
+---+----+----+-----+---------------+---------------+
[7] If the EL degradation persist after step [6], another drop EL
command is issued via following QOS report.
The decision to drop/scale up is entirely up to the application-specific
adaptation policy residing at destination mobile. For example a video flow may
be sensitive to delays and delivery of constantly changing bandwidth so once
enhancement layer packets are dropped, it requires stable resource
availability of resources before a scale up decision is made. In the case of
real-time data, there may not be any drop command and the application may want
to closely follow the dynamics of resource availability. In such case the
adaptation policy is quite different from that of a video flow example.
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5. SECURITY ISSUES
The MANET computing environment is very different from the ordinary computing
environment. In many cases, mobile computers will be connected to the network
via wireless links. Such links are particularly vulnerable to passive
eavesdropping, active replay attacks, and other active attacks. A stringent
authentication and registration processes are required to avoid any malicious
users. Currently, INSIGNIA does not specify any special security measures.
6. APPLICATIONS
INSIGNIA can be used as signaling support for small (pico-cell) and large
scale mobile networks. Flows and microflows can be supported. Voice, video and
real-time data applications can be supported using the INSIGNIA adaptive
real-time service. In addition, INSIGNIA networks support traditional best
effort services.
7. ACKNOWLEDGMENT
The work is supported in part by the Army Research Office (ARO) under award
DAAD19-99-1-0287 and with support from COMET Group industrial sponsors.
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9. AUTHORS' ADDRESSES
Seoung-Bum Lee (Managing Author), Gahng-Seop Ahn, Andrew T. Campbell,
Xiawei Zhang
Department of Electrical Engineering, Columbia University
Rm. 801 Schapiro Research Building
530 W. 120th Street, New York, N.Y. 10027
phone: (212) 854 3109
fax : (212) 316 9068 (COMET Group)
email: [sbl, ahngang, campbell, xzhang]@comet.columbia.edu
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