MANET S. Ruffino
Internet-Draft P. Stupar
Expires: August 15, 2005 TILAB
T. Clausen
LIX
S. Singh
SAMSUNG AIT
February 11, 2005
Connectivity Scenarios for MANET
draft-ruffino-conn-scenarios-00
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Copyright (C) The Internet Society (2005).
Abstract
This Internet Draft aims at describing a wide spread set of possible
connectivity scenarios involving mobile ad-hoc networks, in order to
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provide reference for standardization effort in this field. The
aspects considered for definition and classification of the scenarios
are number and characteristics of the gateways that connect MANET
nodes to external networks. Analysis will range from a scenario
where no connectivity is provided, i.e. an isolated MANET, to more
complex scenario where a MANET has multiple mobile Gateways.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1 Isolated MANET . . . . . . . . . . . . . . . . . . . . . . 6
3.2 MANET connected to an external network . . . . . . . . . . 6
3.2.1 Fixed Gateways . . . . . . . . . . . . . . . . . . . . 8
3.2.2 Mobile Gateways scenario . . . . . . . . . . . . . . . 9
3.3 MANET intermittently connected to external networks . . . 10
4. Roaming from a MANET to an Infrastructure Network . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 15
A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . . 17
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1. Introduction
MANET were initially designed to be employed in highly dynamic and
unpredicatable environments, characterized by high mobility of users
and terminals. MANETs are essentially autonomous, self-configuring,
self-healing networks, whose mobile nodes discover other nodes and
supported services in an automatic fashion. MANET routing protocols,
as studied in IETF, enable two generic MANET nodes to exchange data
traffic through multi-hop connections, if a 1-hop radio link between
them is not available. In this way, nodes can freely move within the
MANET: routing protocols dynamically react to movement and constantly
discover the optimal path according to a predifined metric, e.g.
number of hops. If an intermediary node, belonging to a path between
a source and a destination, fails, traffic is automatically re-routed
through an alternative path.
RFC2501 [1] defines a MANET and also introduces the possibility to
connect a MANET to an external network, by means of gateways. These
are devices equipped with two or more network interfaces: a MANET
interface and an interface typically connected to one or more
non-MANET networks. MANET nodes exchange traffic among themselves
using multi-hop paths and can reach outside hosts and the Internet by
means of the gateways. In this case the MANET acts as a "stub"
network, whose nodes route traffic originating and/or terminating
within the MANET itself.
Operators, Network and Service providers show increasing interest in
this type of network, as a consequence of the wide spread deployment
of low-cost radio technologies such as IEEE802.11a/b/g/h and the
increasing customer base. Initially, commercial MANETs are expected
to be deployed as an extension to the traditional infrastructure
networks, to realize the so-called hybrid networks.
An example of this networks are the Mesh Networks, used to extend the
coverage area of a public hot-spot or to realize large-scale low-cost
wireless coverage in urban areas. A further interesting application
and research field is represented by multi-hop cellular networks:
MANETs connected to cellular WAN networks. In this case MANETs can
be used to realize an extended wireless coverage in areas where
"traditional" cellular network is not available.
Many proposals and projects that introduce integration between MANET
and 3G+ networks exist: for example, see [2], [3], [4] and [5].
This Internet Draft aims at describing and analyzing connectivity
scenarios for MANET, to provide a reference for standardization
effort in this field. In fact, the scenarios described herein can be
used as a starting point for the design of solutions to technical
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problems, such as address autoconfiguration, gateway discovery,
Duplicate Address Detection and global prefixes management.
Analysis will range from a scenario where no connectivity is
provided, i.e. an isolated MANET, to more complex scenarios where a
MANET has multiple mobile Gateways. This document is structured in
the following way: in Section 2 a glossary for commonly used terms is
given; in Section 3 connectivity scenarios for a MANET are listed.
In this section particular attention is paid to the connection of a
MANET with other external networks, by means of one or more fixed
(Section 3.2.1) or mobile wireless gateways (Section 3.2.2). In
Section 4 the roaming of a node from a Infrastractured wireless LAN
to an ad-hoc network is considered.
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2. Terminology
Node
An IPv4/IPv6 device which is a MANET element: it runs a MANET
routing protocol and exchanges data with other nodes within a
MANET and with hosts located within external networks. A node has
at least one physical interface connecting it to the MANET.
Gateway
A node equipped with at least two interfaces, one of which
connects it to an external network, i.e. non-MANET, and can be
wired or wireless.
Host
An IPv4/IPv6 terminal/computer, external to the MANET. Host is
defined here as only "External" to differentiate it from the nodes
of the MANET.
Wireless Interface (or MANET interface)
The physical network interface that connects a node to the MANET.
Radio Interface (or Cellular Interface)
The physical network interface that can connect a gateway to an
external Wireless Wide Area Network, owned and administered by an
operator.
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3. Scenarios
In this section, we describe the typical connectivity scenarios of a
MANET. This section is structured as follows: first, the case of an
isolated MANET is examined, where no gateways exist. Then, various
scenarios of a connected MANET are given, classified by the
characteristics and the number of gateways, which can be fixed and/or
mobile. In the end, the case of an intermittently connected MANET is
analyzed.
3.1 Isolated MANET
An isolated MANET is a network that is autonomously set-up among
wireless mobile nodes localized in the same geographical area. Nodes
activate Layer 2 radio links, by which they can exchange traffic with
their neighbors, and run an ad-hoc routing protocol, which enables
multi-hop data forwarding through intermediate nodes. Routing
protocol constantly discovers routes between nodes, in a proactive
([13], [15]) or reactive fashion ([14], [16]): this enables each node
to route traffic to all other nodes within the MANET also during
movements.
In this type of MANET there is no connection to an external network:
all traffic is generated by MANET nodes and addressed to MANET nodes.
Typical applications of this scenario are temporary networks, that
must be set-up in areas where neither wireless coverage nor
infrastructure exist. Examples can be emergency networks used for
disaster recovery, battlefield applications, electronic surveillance.
Other examples can be found in occasional work meetings, where
networks are set-up to enable file sharing among co-workers.
3.2 MANET connected to an external network
In this scenario a MANET is connected to an external network by means
of one or more gateways (Figure 1). A generic MANET node can
exchange data traffic with every other node through multi-hop paths
and communicate with hosts located in the external network, routing
its uplink traffic towards a gateway. Such gateway, in turn, will
receive return traffic from the host and will route it to the source
node.
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H1
|
+---------------+
| Internet |**
+---------------+ *
* * *
* * *
GW1** * GW3
| +--GW2-------+
| | |
---N1--------+ |
/ \ |
N4 \ N2
N3-----/
Figure 1: MANET interconnected to an external network
Gateways play a critical role here. If the number of nodes in the
MANET increases, gateways can become bottlenecks, as they route an
increasing and possibily huge amount of traffic. This also depends
on the available bandwidth on the uplink interface. Moreover,
gateways can be equipped with a number of additional features. For
example, they could participate to the external routing protocol, in
order to announce internal routes to external routers and hosts,
possibly performing some kind of aggregation. They can act as
enforcement points for security purposes: they can control access to
external networks and, following a common practice, they can enforce
Ingress Filtering on MANET generated traffic. Finally they can also
provide services like DNS to MANET nodes.
This scenario can be expanded, depending on the characteristics of
the network interface connecting gateways to the external network: it
can be either wired or wireless, which can, in turn, be of a
different type with respect to the MANET interface. In the first
case Gateways are fixed, while in the second case they can also be
mobile, as the other MANET nodes.
Moreover, a MANET can have only one gateway (fixed or mobile) or can
have multiple gateways (fixed or mobile). Other than guaranteeing a
high degree of reliability and fault tolerance to the entire MANET,
the presence of multiple gateways enables load balancing among the
gateways themselves. This can be very useful especially when the
external network is a low-throughput cellular WAN, such as GPRS/EDGE,
in order not to overload a single gateway with traffic potentially
generated by many nodes at the same time. Single traffic flows of
multiple nodes or many flows of a single node can be routed through
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different gateways, consequently implying an improvement of the
overall performances of the MANET.
Gateways can also be equipped with additional resources in order to
grant better fault tolerance to the entire MANET: additional energy
resources, more processing power, more volatile and non-volatile
memory. This is especially true in case of fixed gateways, that can
be directly powered and directly operated.
The following sections detail usage scenarios for fixed and mobile
gateways.
3.2.1 Fixed Gateways
In this scenario, gateways are deployed in predefined positions
planned by the network operator. Each gateway is connected to the
external network by means of a wired or wireless interface.
Mesh networks and networks used for environmental surveillance can be
categorized under this scenario.
o Mesh Networks: these are probably the most widespread ad-hoc
networks. In a Mesh Network, user terminals (nodes) exchange
traffic between them directly through a layer-2 radio link and
using other nodes or fixed wireless devices as intermediate
relays. A Mesh Network is typically connected to an external
infrastructure network by means of fixed wired Access Points,
which act as gateways and typically connect the Mesh to an
external infrastructure network.
Mesh Networks can be further classified depending on the kind of
devices which form the mesh itself. In fact, in some deployments,
the mesh is realized only among the wireless Access Points, which
are devices endowed with two wireless interfaces: the first
interface forms the mesh with other peer access points,
participating to a routing protocol, the second interface provides
local connectivity to nodes, which cannot set-up a network
themselves, as they don't run any routing protocol. In another
case the mesh is realized among all the nodes, which have to run a
routing protocol.
Applications of this networks are Internet public access
(browsing, email etc.) by mobile users from outdoor areas,
wireless coverage of corporate building to give employees access
to shared data and commonly used services (email, Intranet
browswing). These solutions can bring to savings on cabling and
maintenance costs.
o Surveillance networks: several wireless nodes endowed with sensors
of various kinds are spread over high enviromental risk areas
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(e.g. fires in wooden areas). They communicate through multi-hop
connections and run a routing protocol. When an emergency
situation arises, data collected by sensors are transmitted from
the collecting nodes upwards one or more gateways (which can have
both a wired or wireless interface) and conveyed to a manned
monitoring station.
Topologies of this kind of network are typically static, as the
nodes are installed in fixed positions within the monitored areas.
Moreover, these networks are characterized by multiple constant
low-throughput data flows going from the sensors to the gateways.
3.2.2 Mobile Gateways scenario
In this scenario, the gateway's radio interface, connecting the MANET
to the external network, can be a cellular WAN interface (GSM, GPRS,
EDGE, UMTS), a broadband wireless MAN (WMAN) interface (e.g.
802.16x, 802.20) or a WLAN interface (802.11a/b/g/h/j). In each of
these cases, gateways can forward uplink traffic outside the MANET
only if located within the transmission/reception range of one or
more Base Stations or Access points. Gateways not only can move
freely within the coverage area, but they can also move outside this
area. In such case, the gateway can't forward uplink traffic
destined to external hosts anymore, nor downlink traffic destined to
internal nodes.
In this outlined scenario, the MANET can be seen as a coverage
extension of the radio infrastractured network to which the gateways
are connected. The primary benefit of such extension is that local
communication between two nodes is performed without using any
cellular radio resource, e.g. radio channels. Another benefit is
the possibility to grant network access also to those terminals that
are not equipped with a cellular radio interface (e.g. access
sharing). The implication of this business model on security,
accounting and rewarding aspects are out of the scope of this draft,
neverthless must be carefully investigated.
A more advanced scenario can be realized when most of the nodes are
also equipped with two heterogeneous interfaces. In this case
gateways can be "occasional": they can be nodes that, after setting
up the connection towards the external network, whenever located
within its coverage area, can start forwarding other nodes' outbound
packets. In this kind of scenario, gateways can be "special" nodes
endowed with additional features, but they can also be ordinary MANET
nodes, such as mobile phones and PDAs. In this last case, gateways
are characterized by low computational power and limited energy
resources. Although the MANET can again exploit benefits given by
multiple gateways, additional issues arise: in fact, gateways are not
under operators control anymore. It's possible that the owner of the
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gateway establishes abruplty to turn his terminal off or to tear down
the connection towards the cellular network, in order to save battery
life. Thus, the number and the position of gateways are higly
dynamic and this can cause frequent re-routing of uplink data flows.
o Automotive scenario: a MANET is set up by a group of vehicles.
One or more of these may become a mobile gateway after connecting
to the Wireless LAN of a petrol station or setting up an UMTS
connection and, therefore, may be used by the other vehicles of
the MANET to exchange traffic with the external hosts.
3.3 MANET intermittently connected to external networks
Gateways in a MANET, especially if mobile and equipped with a radio
interface, may not be permanently connected to the external network.
MANETs of this kind have the characteristics of both MANET described
in Section 3.1 (while not connected) and of the ones described in
Section 3.2 (while connected).
Most of the nodes belonging to a MANET of this kind shall exploit the
connection temporally set up to an external network to communicate
with hosts they can't reach while the MANET is isolated. As a
consequence, such MANETs may experience a burst of exchanged traffic
while connected to the external network. The amount and the
distribution of such traffic depends on how long the MANET can be
connected to an external network.
o Train network: a MANET built in a train, which is connected while
stopped at the station and disconnected otherwise. In particular,
if the MANET is set up by some passengers, it may happen that
while the train is stopped at the station, some of the nodes may
become gateways. For example, the station area may be covered by
a wireless technology and some nodes equipped with a non-MANET
interface of the same technology may therefore set up a connection
to the external network. In this case, most of the users may use
the gateways to connect to their mail server, download and
eventually send their e-mails: the MANET they belong to may
therefore experience a burst of traffic exchanged with the
external network.
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4. Roaming from a MANET to an Infrastructure Network
A mobile node, connected e.g. to a IEEE 802.11 network
(infrastructure mode), can roam to a nearby IEEE 802.11 (ad-hoc mode)
MANET. This situation can be very commonly experienced by a mobile
node, during its movement, even not voluntarily. It is worth noting
that such roaming doesn't involve only layer-2 operations. It is
indeed likely that the procedures used within IEEE 802.11 network,
e.g. for address configuration or duplicate address detection, are
different from those used in a MANET. This is mainly due to the fact
that a MANET is characterized by multi-hop paths while in a WLAN all
hosts are connected to the same link.
There can be also situation where the destination MANET uses a
different radio technology for multi-hop links. This scenario, not
addressed in this document, brings added difficulties, because radio
interface should be dynamically switched to use a different Layer 1
and 2 technology.
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5. Security Considerations
This document raises no security issue.
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6. IANA Considerations
This document has no actions for IANA.
7. References
[1] Corson, S. and J. Macker, "Mobile ad hoc networking (MANET):
Routing protocol performance issues and evaluation
considerations", RFC 2501, January 1999.
[2] Siebert, M., "On Ad Hoc Networks in the 4G Integration
Process", Med-Hoc 2004 , June 2004.
[3] "Ambient Networks", http://www.ambient-networks.org .
[4] "Daidalos", http://www.ist-daidalos.org .
[5] "World Wireless Research Forum",
http://www.wireless-world-research.org .
[6] Wakikawa, R., Malinen, J., Perkins, C., Nilsson, A. and A.
Tuominen, "Global connectivity for IPv6 Mobile Ad Hoc
Networks", I-D draft-wakikawa-manet-globalv6-03.txt, October
2003.
[7] Cha, H., Park, J. and H. Kim, "Extended Support for Global
Connectivity for IPv6 Mobile Ad Hoc Networks", October 2003.
[8] Jeong, J., Park, J., Kim, H. and D. Kim, "Ad Hoc IP Address
Autoconfiguration",
I-D draft-jeong-adhoc-ip-addr-autoconf-02.txt, February 2004.
[9] Perkins, C., Malinen, J., Wakikawa, R. and E. Belding-Royer,
"IP Address Autoconfiguration for Ad Hoc Networks",
I-D draft-perkins-manet-autoconf-01.txt, November 2001.
[10] Singh, S., Kim, JH., Choi, YG., Kang, KL. and YS. Roh, "Mobile
multi-gateway support for IPv6 mobile ad hoc networks",
I-D draft-singh-manet-mmg-00.txt, June 2004.
[11] Paakkonen, P., Rantonen, M. and J. Latvakoski, "IPv6 addressing
in a heterogeneous MANET-network",
I-D draft-paakkonen-addressing-htr-manet-00.txt, December 2003.
[12] Jelger, C., Noel, T. and A. Frey, "Gateway and address
autoconfiguration for IPv6 adhoc networks",
I-D draft-jelger-manet-gateway-autoconf-v6-02.txt, April 2004.
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[13] Clausen, T. and P. Jacquet, "Optimized link state routing
protocol", RFC 3626, October 2003.
[14] Perkins, C., Belding-Royer, E. and S. Das, "Ad hoc On-Demand
Distance Vector (AODV) Routing", RFC 3561, July 2003.
[15] Ogier, R., Templin, F. and M. Lewis, "Topology Dissemination
Based on Reverse-Path Forwarding (TBRPF)", RFC 3684, February
2004.
[16] Johnson, D., Maltz, D. and Y. Hu, "The Dynamic Source Routing
Protocol for Mobile Ad Hoc Networks (DSR)",
I-D draft-ietf-manet-dsr-10.txt, July 2004.
[17] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
[18] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
[19] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[20] Aboba, B., "Dynamic Configuration of Link-Local IPv4
Addresses",
Internet-Draft draft-ietf-zeroconf-ipv4-linklocal-17, July
2004.
[21] Johnson, D., Perkins, C. and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
[22] Sun, Y. and E. Belding-Royer, "A study of dynamic addressing
techniques in mobile ad hod networks", I-D Wireless
communication and mobile computing, May 2004.
[23] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998.
[24] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host
Configuration Protocol (DHCP) version 6", RFC 3633, December
2003.
[25] Engelstad, P., T°nnesen, A., Hafslund, A. and G. Egeland,
"Internet Connectivity for Multi-Homed Proactive Ad Hoc
Networks", First IEEE International Conference on Sensor and Ad
hoc Communications and Networks , October 2004.
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Authors' Addresses
Simone Ruffino
Telecom Italia LAB
Via G.Reiss Romoli 274
Torino 10148
Italy
Phone: +39 011 228 7566
Email: simone.ruffino@telecomitalia.it
Patrick Stupar
Telecom Italia LAB
Via G.Reiss Romoli 274
Torino 10148
Italy
Phone: +39 011 228 5727
Email: patrick.stupar@telecomitalia.it
Thomas Heide Clausen
Laboratoire d'informatique
Ecole Polytechnique
Palaiseau Cedex 91128
France
Phone: +33 1 6933 2867
Email: thomas.clausen@polytechnique.fr
Shubhranshu Singh
SAMSUNG Advanced Institute of Technology - i-Networking Laboratory
San 14-1, Nongseo-ri, Giheung-eup
Yongin-si, Gyeonggi-do 449-712
Korea
Phone: +82 31 280 9569
Email: shubhranshu@samsung.com
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Appendix A. Acknowledgments
The authors would like to thank Ivano Guardini for his valuable
comments.
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