2.5.6 Mobile Ad-hoc Networks (manet)

NOTE: This charter is a snapshot of the 39th IETF Meeting in Munich, Bavaria, Germany. It may now be out-of-date.


Joseph Macker <macker@itd.nrl.navy.mil>
Scott Corson <corson@isr.umd.edu>

Routing Area Director(s):

Joel Halpern <jhalpern@newbridge.com>

Routing Area Advisor:

Joel Halpern <jhalpern@newbridge.com>

Mailing Lists:

General Discussion: manet@itd.nrl.navy.mil
To Subscribe: majordomo@itd.nrl.navy.mil
In Body: subscribe manet

Description of Working Group:

A "mobile ad-hoc network" is an autonomous system of mobile routers (and associated hosts) connected by wireless links--the union of which form an arbitrary graph. The routers are free to move randomly and organize themselves arbitrarily; thus, the network's wireless topology may change rapidly and unpredictably. Such a network may operate in a standalone fashion, or may be connected to the larger Internet.

The focus of the working group will be to standardize an intra-domain unicast routing protocol which efficiently reacts to topological changes while maintaining effective routing. The goal is to support networks scaling up to hundreds of routers. If this proves successful, future work may include development of other protocols to support additional routing functionality.

The working group will examine the security issues around this protocol. They will consider the intended usage environments, and the threats that are (or are not) meaningful within that environment.

Goals and Milestones:

Jul 97


Post as an informational Internet-Drafts a discussion of mobile ad-hoc networking and issues.

Aug 97


Agenda bashing, discussion of charter and of mobile ad hoc networking draft.

Oct 97


Post Internet-Drafts for candidate protocols.

Dec 97


Discuss proposed protocols. Obtain early performance results for the protocols.

Apr 98


Obtain comparative performance results for the protocols. Implement the various protocols and test.

Aug 98


Reach consensus on a mobile, ad-hoc unicast routing protocol.

Dec 98


Document mobile ad-hoc routing protocol and submit to the IESG as a proposed standard, including security threat analysis.


No Request For Comments

Current Meeting Report

Minutes of Mobile Ad Hoc Networks (manet) Working Group Meeting

Meeting Secretary: Eric Guttman, Sun Microsystems
Minutes Editor: M. Scott Corson, University. of Maryland

Meeting convened by WG co-chair M. Scott Corson.
Co-chair Joe Macker (NRL) was absent due to a prior commitment, and Vince Park (NRL) filled in for Joe.


I. Presentation of a MANET Issues Draft (Scott Corson)
II. Presentation on the Architecture of the NTDR Network (Chip Elliott, BBN)
III. Presentation of AODV and Recent Results (Charlie Perkins, SUN)
IV. Presentation of DSR (Dave Johnson, CMU)
V. Continuing presentation of draft (Scott Corson)
VI. Discussion of draft, charter bashing and WG next steps (all)

(Editorial note: At the time of the meeting, the draft had not been posted to the I-D repository, but has been subsequently submitted and should be available soon.)

Dave Johnson (Mobicom program chair) made an announcement regarding Mobicom to be held in Budapest, Sept 26-30, and mentioned that their would be a panel discussion on MANETs moderated by Scott.

I. Presentation of a MANET Issues Draft (Scott Corson)

Presentation of draft entitled "Mobile Ad Hoc Networks: Routing Protocol Performance Issues and Evaluation Considerations" by M. Scott Corson and Joe Macker.

The draft gives a brief history of mobile packet radio, the relationship of this technology to other networking technologies in the context of hybrid communication networks, and a list of possible military and commercial applications. The draft then goes on to define a Mobile Ad hoc NETwork (MANET) as a set of mobile nodes (combined radios/routers) communicating with some form of wireless technology. The salient characteristics of MANETs are dynamic, randomly changing topologies, bandwidth-constrained links, potentially energy-constrained nodes (battery powered) and limited physical security (easy snooping).

There was discussion of how this definition compared with commercial ad hoc technology--in particular, IEEE 802.11 and HIPERLAN. It was mentioned that in its present form, 802.11 essentially considered only single-hop operation (no routing), and that the MANET definition was much closer to the latest version of HIPERLAN which permits multi-hop operation using a substantially modified form of link-state routing.

The draft then defined the intent of the WG as "to aid in the development of a peer-to-peer mobile IP networking capability beyond the fixed network (supported by traditional IP) and the mobile one-hop fringe of the fixed network (supported by mobile IP) which may be standalone (autonomous operation) or connected to the larger net via gateway(s)."

A question was raised regarding the type of network management to be practiced in these networks. While not stated explicitly, the draft document implies that network management and control is to be completely distributed and automated.

II. Presentation on the Architecture of the NTDR Network (Chip Elliott, BBN)

Chip presented a brief on the architecture of the NTDR network--a wireless military network based on the Near-Term Digital Radio (NTDR)--which has a mobile, multi-hop topology with roughly 400-1,000 mobile nodes/routers. The 1,000-node network will be divided in three portions--interconnected with gateways--and some form of hierarchical, link-state routing will be employed. Numerous hosts may hang off each router on a given mobile platform, and the nodes may move at speeds up to 50 mph. The available radio bandwidth is somewhere between 0.5-1.0 Mbps. Current status: a 20-node network has been fielded and a 100-node demonstration is planned in the winter.

III. Presentation of AODV and Recent Results (Charlie Perkins, SUN)

A presentation of the Ad hoc, On-demand Distance Vector (AODV) Routing Protocol. AODV is a distance-vector routing technique which employs destination-oriented and sequenced update waves to remove the counting-to-infinity problem inherent in distributed Bellmann-Ford approaches without requiring the use of split-horizon/poison-reverse techniques. As the name suggests, routes are built *on demand* in response to source-initiated route requests. The update waves are carried in reply packets generated in response to the queries. Each update carries among other fields a tag--a pair <SEQ,HOP>--where SEQ is a sequence number and HOP is the hop count, and nodes are instructed to pay attention to the pair with the most recent sequence number received from the destination. Route requests also carry similar routing information so that reverse path set up back to the source occurs as the result of route requests. Also, requests need not propagate all the way to the destination, but may stop at some intermediate node that has a route to the destination. The protocol's properties include quick convergence, minimal latency for route request, loop-freedom, reduced BW utilization and triggered updates. The protocol also incorporates a hello protocol.

A question was raised as to whether multicast trees could be built directly using this technique. The answer was a cautious *maybe*, but it hadn't been thought about.

Some simulation results were presented, but the results are preliminary. General observations drawn from the results indicate that AODV's range of applicability should be when nodes stay within range long enough for the results obtained from a route request to be used.

IV. Presentation of DSR (Dave Johnson, CMU)

Dave presented "Dynamic Source Routing" (DSR), another demand-based routing protocol, but one which uses source routing as opposed to hop-by-hop routing. It consists of route discovery and route maintenance phases. Route maintenance is straightforward, and consists of passively monitoring the health of existing routes by listening to the ACKs of data packets transmitted to adjacent neighbors. The listening is either explicit through reception of a direct ACK, or implicit by monitoring adjacent neighbor's transmission activity while the receiver is in promiscuous mode. When a route is needed, route discovery is performed--a process which consists of a two or three-stage process. First, a source floods a query looking for the destination, or some intermediate node that has a path to the destination (as it travels, the query records the route it takes and grows in length). If neither is found, the source can query again later. If either is found (this node is generically referred to as the *replier*), a reply--carrying a full source route--is sent back towards the source. If the replier has a route to the source (this will always be true if one assumes unidirectional links), the reply is unicast; otherwise, it is piggybacked onto a query looking for the original source (the query is also recording the route back to the destination). When the source receives the route, it may begin sending data. If the reply was piggybacked, then the source also replies to the replier via unicast sending it the route by which the source may be reached. The protocol makes use of aggressive caching in that any node participating in the exchange may snoop on the routing information in the control packets to keep its cache up-to-date. Also, the protocol has no hello protocol (periodic link status messaging)--link health is monitored passively. It was mentioned that one way to view the protocol is as a multi-hop extension or generalization of ARP.

Simulation results for DSR were also presented, but these are also preliminary.

Dave was asked about the suitability of this scheme for supporting multicast, and the answer was that there was not enough information to draw any conclusion. However, there was concern within the group about the possibility of performing source routing for multicast due to scalability limitations.

V. Continuing Presentation of Draft (Scott Corson)

Resumed presentation of MANET issues draft...

The WG's near-term goal is the development of a *unicast routing protocol* to support traditional, connectionless IP datagram delivery in a MANET: integration with the greater Internet is--for the

The protocol may contain multiple routing *modes*, each appropriate for a given networking *context*, and a standard, distributed *mode discovery* protocol would be devised to allow nodes to dynamically join existing networks. A networking context is a collection of attributes including network size, rate of topological change, available bandwidth, radio and link characteristics, battery limitations, etc. which affect the functioning of a routing algorithm. Implicit in this approach is that routers be able to function as intermode gateways should two MANETs running differing modes merge, or should a router have multiple radios communicating with different neighbors running different routing modes. (Editorial note: A policy for dynamically switching modes on-the-fly is viewed as a research issue and is not being considered.) It was emphasized that while multiple modes may be permitted, there would have to be a clear and overwhelming need for more than one mode--a need demonstrated via comparative simulation. The intent is for the protocol to operate efficiently in any networking context or topology--ranging from small, quasi-static work groups to large, mobile networks. This may require more than one routing mode.

A discussion then ensued about whether the scope of the group's effort should be limited to purely *autonomous* operation (standalone with no integration with the larger Internet), *stub* operation (access to the greater Internet via a single gateway or multiple gateways), or *transit* operation (access to the Internet via multiple gateways permitting flow of exogenous Internet traffic *through* the MANET cloud). It was suggested that the transit mode of operation was significantly more difficult to implement as it required advertisement of IP reachability information between the gateways, and recommended only stub network operation. There was concern in the group that transit style operation would be too complex, and could also potentially congest the ad hoc network with exogenous traffic. Still, there was no attempt to reach consensus in the WG on this issue yet...people wanted to think about it a bit. There was a request for someone to author a draft on all the issues and trade-offs of stub vs. transit operation but, to date, no one has volunteered to do so.

There was a lengthy discussion regarding whether these wireless nodes (combined routers/radios) should have a unique IP address per interface (traditional IP practice) or simply one IP address per node (as assumed by many algorithms proposed for ad hoc routing). There are advantages and disadvantages to each approach, and the group consensus leaned towards staying with the traditional approach.

The question was also raised as to whether routing should be a layer 2 or layer 3 function? Numerous multi-hop wireless networks have implemented routing at the layer 2 subnet level with a mapping to IP only at the edges such as the NTDR network. The consensus of the working group was to implement routing as a layer 3 function. The MANET issues draft states that the rationale is much the same as the original Internet--to develop a homogeneous networking capability over a heterogeneous networking infrastructure. In this case, the infrastructure is wireless, rather than hardwired, with multiple platforms, radios and access technologies.

The question was then raised as to whether multicast routing should be addressed now, or deferred until later. The consensus was that the issue should be deferred and that the group should focus on unicast routing. However, it was recognized that for efficient operation, multicast routing could benefit significantly if tightly coupled to the unicast algorithm. Thus, suitability for supporting multicast (and QoS) should be part of the evaluation criteria when examining unicast protocols.

Discussion then drifted to the group's charter and its listing of milestones. There was strong consensus within the group that the existing charter's schedule is still too aggressive, and that reaching consensus on one or more MANET modes by August '98 is highly improbable. A rough time scale expansion estimate of 50% was suggested, moving the target date for consensus back to March '99.

Presentation of the draft continued, listing MANET protocol design considerations and idiosyncrasies and how these need to be considered in the evaluation of proposed MANET routing modes:

· Scarce BW
· Rapid topology changes
· Limited physical security
· Unidirectional links
· Nodes may need to sleep

A listing of potentially desirable qualitative characteristics for a MANET routing mode was given:

· Distributed operation (required)
· Loop-free operation (recommended)
· Demand-based operation (recommended) for non-uniform traffic patterns
· Support for unidirectional links (recommended)
· Secure operation (recommended)
· Sleep period accommodation (recommended)

When writing drafts describing proposed modes, authors should indicate whether or not their proposals incorporate these characteristics. In general, it was requested and emphasized that authors include qualitative listings of the strengths and weaknesses of their proposals so that a broad assessment and classification of the protocols in terms of suitability for various networking contexts can be made.

Following such assessments, appropriate simulation-based quantitative studies will be made to determine a mode's:

· Data routing performance--that is, the *goodness* of data routing measured via throughput and delay or other metrics (the *external* view of how well a routing mode performs its function).
· Routing efficiency--that is, for a given level of data routing performance, how *efficient* is a routing protocol--measured in terms of network resource consumption (bandwidth, memory, processing, energy)-in delivering this level of performance (the *internal* view of how well a routing mode performs its function).

In MANETs, routing efficiency is paramount as certain network resources--namely bandwidth and power--may be very scarce, yet are utilized by the protocol in performing its function.

The discussion on protocol evaluation moved to simulation, and to what level of detail would be necessary to have an accurate and realistic performance evaluation. There was much contention here within the group covering issues such as:

· How accurately to model a radio channel?
· Need we consider terrain/environmental models?
· Do we need to model a multiple access protocol in the simulation?
· Does the choice of a multiple access protocol favor one mode over another?
· Do we need to use a common simulation tool?
· What sorts of mobility models are appropriate? If brownian motion is no good, what's any better?
· How does the choice of a mobility model affect relative protocol performance etc.?

The discussion was contentious and consensus was no where in sight when the discussion had to be curtailed due to time constraints. During the discussion, people continued to talk past each other due to the lack of a common frame of reference (a set of commonly accepted definitions for the terms being used in this context). Thus, the need for a *MANET lexicon* became apparent, and it was agreed to begin drafting one as an Informational RFC to aid group communication. What came out of the discussion was general agreement as to the need for a common simulation tool so that models can be shared and simulation results mutually verified. The two leading candidates are Maisie and NS as they are freely available. There was general agreement to take the discussion to the list.

VI. Action Items

The following is a condensation of *action items* identified during the meeting:

· Drafts of proposed routing modes are due by the end of October. These should be highly detailed documents, fully specifying the proposed mode's operation with its advantages and limitations.
· Add to MANET issues draft requirement of suitability for future multicast and QoS support for routing modes
· Add to MANET issues draft section dealing with the pros and cons of stub versus transit operation
· Fix MANET issues draft--remove usage of term subnet (too much historical baggage) and clarify the intended meaning
· Add to MANET charter a list of what we will NOT do--that is, we will not consider transit operation in the near term, if ever
· Modify MANET charter milestones, pushing back the date for consensus until March 1998.
· Create MANET Lexicon document (Charlie Perkins to draft)
· Fully define the meaning of performance comparison for routing modes (take to list)
· Come to agreement on simulation framework (take to list)
· No hyphen in *Ad hoc*, only a space ;-)

There is an open call for drafts on the following topics:

· Mode discovery protocol
· Intermode gateway framework protocol


Dynamic Source Routing in Ad Hoc Wireless Networks
Ad Hoc On-Demand Distance Vector Routing

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