Subject: Concerns with proposed MANET routing protocols

From: [email-masked] (Mike Butler)
Date: Thu, 05 Feb 1998 09:43:58 -0500

Hi all.

We've been reviewing the MANET routing proposals with the military's
tactical networks in mind.  After considering the three proposed
algorithms, AODV, TORA, and ZRP, we have several concerns and a few
general questions.  
    
Our concerns are:
   1) There is an apparent reliance on reversible links
   2) The importance of load balancing seems to be overlooked
   3) There seems to be no exploitation of "advantaged" nodes
   4) An early quench of route discovery may hide the best route
   5) The routing objective function is unclear

The general questions are:
   6) What does the charter's "a unicast algorithm" statement mean?
   7) Has there been work in link-layer and network-layer coupling?
   
The following paragraphs will elaborate on each of these points.

----
1) There is an apparent reliance on reversible links.

    The proposed routing algorithms have an apparent reliance on
    bidirectional or reversible links.  There are a number of factors
    which will make wireless links unidirectional, among these are:

  - Differing radio capabilities.

    Radios within a network can have different transmit powers or
    receive sensitivities.  This is quite likely in a tactical
    environment where man-pack and vehicular radios exist.  Vehicular
    radios, being less unconstrained by size and weight, typically
    have 10dB greater transmit power than their man-pack counterparts.
    Unidirectional links are exceedingly likely in tactical networks.

  - Interference

    Even a network of identical radios will have unidirectional links.
    Interference, either by hostile jammers or by friendly "cosite"
    will reduce a nearby receiver's sensitivity.  Since it is only one
    receiver that is handicapped, unidirectional links may result.

  - Wide-area information broadcast

    There is an increasing emphasis, especially in tactical networks,
    on the wide-area broadcast of information. Satellite-based
    transmitters (GBS) are being used for the forward links while the
    the return links use alternative paths.  (The commercial sector
    display similar topologies in Direct-PC and some HFC
    configurations.) 

  - EMCON operations
    
    An extreme instance---applicable only in military networks---is when
    some not cannot transmit due to an impending threat (EMCON). In
    such a case, it may be necessary to have some other node provide a
    "likely" route in response to a route discovery request.
    (Obviously, an EMCON node can not participate in bidirectional
    communications, but it still needs to receive information.)

----
2) The importance of load balancing seems to be overlooked

    Another critically important issue in tactical networks will be
    load balancing.  Specifically, a node's purview will change with
    it's position.  A node in a particularly advantageous position
    (e.g., mountain top) will "see" much more of the network.  The
    current routing proposals seem to favor routing traffic through
    this advantaged node, thereby causing a bottleneck.  The result is
    that the introduction of an advantaged node can cripple the
    network.

    We expect that "advantaged nodes" will occur in most wireless
    topologies; a person on stage is likely to have a much better view
    of the wireless network throughout an auditorium.  Advantaged
    nodes will certainly be an issue in tactical networks.  In fact,
    there are efforts underway to introduce highly advantaged
    (air-borne) communications nodes into tactical networks.

    The approach to load balancing in a wireless network will likely
    differ from that used in wired networks.  In wired networks, load
    balancing is only beneficial when multi-homed hosts (multiple
    network segments) are present.  In the wireless environment, load
    balancing is a problem even if there is a single, flat network
    segment and no multi-homed hosts.

----
3) There seems to be no exploitation of "advantaged" nodes

    Although "advantaged" nodes are a liability for the currently
    proposed routing algorithms, we believe that other routing
    algorithms could use these nodes to great advantage.  For example,
    consider an airborne node with limited traffic handling capacity
    but purview of the entire terrestrial network.  Such a node could
    easily collect neighbor information from the terrestrial assets,
    construct a theater-wide routing picture, and broadcast a common
    routing picture. 

    Furthermore, a node need not be omniscient to assist routing
    decisions.  For example, if some advantaged node sees a superset
    of another sees, it has a decided advantage in finding and
    propagating routes.  Given radio's propagation phenomena, we
    expect that advantaged nodes will occur in every wireless network,
    even in flat, homogeneous networks.  A node on stage, in the
    center of a group, or near a doorway is likely to have a much
    wider view; it makes sense to exploit that in finding routes.

----
4) An early quench of route discovery may hide the best route

    We are concerned that the current routing algorithms seem to
    quench the route discovery as soon as a path is found.  The
    concern is that the "best" route might easily escape discovery if
    one packet along the "best" path is corrupted or lost.  Since
    wireless bit error rates are quite high (even for good links), it
    is not unlikely that a packet along a good link could be dropped.

----
5) The routing objective function is unclear

    Unlike wired links, there are a large number of objective
    functions which make sense when selecting routes in a wireless
    network.  Although it is not explicitly stated in the
    proposals, the tacit assumption seems to be that any
    route is acceptable and the shortest path is generally preferable.

    The "shortest path" route is frequently a poor choice in a
    wireless network.  A shortest path route through a wireless
    networks would tend to favor longer hops which would (1) require
    higher transmitter powers, (2) introduce higher bit-error rates,
    (3) make hidden nodes more likely, etc.  Furthermore, as mentioned
    above, blindly accepting the "first found" route may prevent the
    discovery of much better routes.

    Objective functions which make more sense for a wireless
    (particularly tactical) environment are (1) most reliable path
    (best link margin), (2) most stable path (least likely to change),
    (3) minimum total power path, (4) least congested path, (5)
    minimal spectral use, etc.  

    We believe that any of these five objective functions might be a
    superior choice to the shortest path or first-found routes in
    tactical wireless environments.  We also believe that route
    discovery could provide this with little additional overhead---a
    route's objective "cost" could be calculated as the route is
    discovered and the high "cost" routes could be selectively pruned.
    In short, we think that it is highly desirable to discover
    multiple routes and down-select based on some criteria, and
    first-found and shortest-path are unlikely to be provide a good
    selection criteria.

---- 
6) What does the charter's "a unicast algorithm" statement mean?

    According to the working group's charter, the intention is to
    select "a" unicast routing algorithm.  It seems highly unlikely
    that a single algorithm will work well for all network sizes,
    topologies, and rates of change.  Is the working group making some
    tacit assumptions about the networks of interest when they discuss
    "an algorithm?"  If so, would you please make those assumptions
    explicit.

----
7) Has there been work in link-layer and network-layer coupling?

    In "Mobile Ad hoc Networking (MANET): Routing Protocol Performance
    Issues and Evaluation Considerations" the authors pointed out the
    need for "interaction/interface with link-layer protocols".  At
    the link level there is a tremendously rich design space which
    trades-off power, bandwidth, latency, coding, bit error rates,
    etc.  It would seem that these can be readily exploited in routing
    through a wireless network, but none of the proposals addresses
    these issues explicitly.

    Has any work been done in this area?  Does the working group
    intend to explore this area at some future time?  Is there a tacit
    assumption that the proposed algorithms can be retrofitted with
    these link-layer embellishments?

----

Mike Butler  ([email-masked])
Tom Ferguson ([email-masked])

The MITRE Corp
202 Burlington Road
Bedford, MA 01730

---

From: "Vincent D. Park" <[email-masked]>
Date: Thu, 05 Feb 1998 17:57:31 -0500

Thanks for your input. I will try to address your comments individually. As a 
>    which will make wireless links unidirectional, among these are:

This is not exactly true for the TORA/IMEP. TORA as currently specified is
designed to operate on top of IMEP (a lower level protocol that provides
some basic functionality needed by TORA and potentially many other routing
algorithms). One of the functions provided by IMEP is a link-status sensing
capability (i.e. neighbor discovery and maintenance). IMEP's link-status
sensing mechanism has the capability to form a "logical" bidirectional link
between two nodes from the combination of two oppositely directed
unidirectional connections. This mechanism is described in detail in the
IMEP internet draft. The mechanism operates with only one-hop knowledge and
thus cannot for a logical link between two connected by multi-hop
unidirectional paths.  We have considered several possible extensions to
TORA to address this case; however, there is non-significant cost (in
control overhead, etc.) in forming logical links of this nature. This is
probably an area that requires additional research before standardization
(and thus is not included in the current drafts). Note: there is also a
separate working group on unidirectional link routing.

>    display similar topologies in Direct-PC and some HFC

This problem is somewhat orthogonal to the design of a dynamic *routing*
protocol. Although you could design a routing algorithm tailored for this
particular architecture, that would not be a good design approach: 1) not
all networks of interest have this architecture, and 2) dependence on the
satellite for routing could result in a non-robust multi-hop system. A more
appropriate way to incorporate a direct broadcast satellite is through the
use of proxy (as is done with Direct-PC), or through some other extension
that is tailored for the specific satellite system. 

>    communications, but it still needs to receive information.)

Again a problem that is somewhat orthogonal to the design of the routing
protocol. The word "proxy" comes to mind again. This type of problem is
perhaps best addressed within the context of a specific network. The
solution can then address questions such as 1) Do all destinations require
this service or only some? 2) Are there particular advantaged nodes (such
as direct broadcast satellites) that should serve as the proxy?

>    that the introduction of an advantaged node can cripple the

While load balancing is an interesting topic, there are both advantages and
disadvantages. While theoretically one can achieve higher network
utilization and throughput, it can also cause variations in delay and out
of order delivery for packets from a given stream. If traffic is primarily
TCP, this can result in frequent retransmission and reduction in "goodput".
The engineering trade-offs of any approach should be thoroughly explored
before advocating its use.

Given the above disclaimers, I must disagree with your assertion that the
routing proposals favor routing through advantaged nodes. TORA is not a
shortest path routing algorithm. TORA forms a directed acyclic graph (DAG)
rooted at the destination (often resulting in multiple downstream paths to
the destination). The next-hop forwarding decision can be made any number
of ways. In fact, in our performance testing of TORA we used two different
forwarding mechanisms. One which favored the "lowest" neighbor (a technique
which approximates the shortest path) and one in which the next-hop was
selected at random from among the set of downstream neighbors (effectively
spreading the traffic load for a destination over the DAG). For any given
network, many other possibilities exist.

>    segment and no multi-homed hosts.

I think your terminology here is quite confusing. I don't agree that load
balancing is only beneficial in a wired network with multi-homed hosts. If
there are multiple paths through an internetwork to a given destination,
then load balancing could be of benefit. I believe the problem is much the
same in a wireless network. Remember we are working on routing at the IP
layer (not within a given subnetwork).

>    wider view; it makes sense to exploit that in finding routes.

Whether it is preferable to forward through advantaged nodes or not can
potentially be addressed by the metrics used by the routing protocol.
During the route creation process of TORA, nodes increment a value in the
"height" metric as routes are propagated out from the destination. From the
routing protocol perspective it is only important that the value be
increased. This can potentially be exploited to affect how the DAG is
formed or how next-hop routing decisions are made. Finally, routing or not
routing through "advantaged nodes" can also be looked at as a policy
decision (orthogonal to the routing algorithm).

>    is not unlikely that a packet along a good link could be dropped.

I don't see how this applies to TORA. TORA will often establish multiple
routes to a destination, and uses the redundant routes to limit reactions
to link failures. 

>    minimal spectral use, etc.  

My comment here is general and does not apply to TORA. You seem to
associate "shortest path" with lowest hop count. Although this is a common
metric for shortest path routing algorithms, it is not the only choice.
Most shortest-path routing algorithm need not perform the computation based
on hop count. However, there are lots of text books that describe the
instability problems that can occur when your routing metric is coupled to
the traffic load (i.e. least congested path).

>    first-found and shortest-path are unlikely to be provide a good

I agree that some link level information may be useful in making better
routing decisions. It is possible to incorporate some of this information
into the "height" metric used by TORA in forming its routing DAG. However,
remember that we a routing at the IP layer, and not designing for a
particular type of wireless technology. The TORA/IMEP protocol stack is
designed to operate over wireless fabric comprised of a heterogeneous mix
of wireless (and/or hardwired) technologies. In this type of environment it
becomes difficult to decide what link layer parameters may be useful and
how to compare them.

>    "an algorithm?"  If so, would you please make those assumptions

I agree that there is no one size fits all solution. However, I believe
there is potential a small set of algorithms. It is important to indicate
the routing environment (size, rate of change, average connectivity) that a
given algorithm is well-suited.

>    these link-layer embellishments?

Please see my comments to 5) above. I'll leave any comments about the
charter to one of the working group chairs.

There's no doubt that this is a complex problem. I hope these comments have
been helpful in someway.

-Vince

------------------------------------------------------
Vincent D. Park
Information Technology Division
Naval Research Laboratory
4555 Overlook Ave.
Washington, DC 20375-5000
------------------------------------------------------

---

From: Zygmunt Haas <[email-masked]>
Date: Fri, 6 Feb 1998 08:34:28 -0500 (EST)

Dear Mike,

On Thu, 5 Feb 1998, Mike Butler wrote:
...
>    5) The routing objective function is unclear
...
>    7) Has there been work in link-layer and network-layer coupling?

I am glad that you have asked these questions, (which, by the way are
excellent points) as they should allow our MANET group to focus some of
the discussions of our work. I will try to address some of them. Please
note that my "bias" is towards the ZRP protocol, as I have been working
a lot on the protocol (similation and design issues) and, thus, I am the
most familiar with it. I am sure others will address your questions from
their point of view.

>     Unidirectional links are exceedingly likely in tactical networks.

There are a number of "issues" here. First, at least in narrowband
communication, there is a tradeoff between the data-rate and transmitted
power. You can have a link between two reasonably close nodes, although
the data-rate of this link may be *really* low. So, I prefer to call the
problem that you have stated as "asymmetrical" links, rather than
uni/bi-directional. Similar argument can be made for broadband
transmission. Furthermore, I want to point out that due to propagation
conditions and mobility, links are fluctuating in quality all the time. 
Thus, the inherent imbalance in transmission power of the man-mounted and
vehicle-mounted radios is not, by itself a new problem.

There are few ways that your question could be answer. The first one (and
this is a rather poor solution) is to declare a link between two
(adjacent) nodes as "up" *only* if both directions are "up."  This will
work, although will *unnecessarily* limit the connectivity in the network. 
Another approach is not to rely on, what is called in ZRP as, "accumulated 
route" for reverse routing of the discovered route back to the querying node 
(which is currently done by reversing the accumulated route). Rather, a 
separate route discovery from the destination, back to the source could take 
place, through which the found forward-accumulated-route could be returned. 
This involves some additional control traffic, but protects you against the 
asymmetrical link problem.

>     receiver that is handicapped, unidirectional links may result.

See above.

>     display similar topologies in Direct-PC and some HFC

Again, as long as a path from the source to the destination and a path
from the destination to the source exist - although they do not have to 
be "the same path," there is no problem in discovering and using these
paths.
 
>     communications, but it still needs to receive information.)

Such a "proxy" services are perfectly ok and there is nothing in ZRP which
prevents this from happening. Of course, there are a couple of "deeper"
problems here, for example, how does the "proxy" node knows that it is in
radio contact with the EMCON node. To know this, EMCON node needs to
convey something to the "proxy" node, so it needs to transmit. Although,
its transmission could be at much lower power, it still needs to transmit
and reach at least one neighbor (i.e., the proxy node). If the EMCON node
can transmit even to one close neighbor only, the ZRP protocol will
discover the route to it anyway. So, nearly "by definition" I am not sure
whether there is a problem here at all. 

>     segment and no multi-homed hosts.

Load balancing is being currently addressed in our ZRP work. And yes, this 
is a very important aspect. I will not describe our solution here, but to 
give you one possible direction, there has been work by Michael Pursley on
"Least Resistance Routing," which could be used in this context.

>     wider view; it makes sense to exploit that in finding routes.

This is a "reverse" problem that you have stated in 2). Yes, strategically
placed nodes have advantage. In fact, this advantage is already used by a
number of MANET protocols, including ZRP. I would not go as far as saying
that the "advantaged" nodes should be responsible for route determination
(the single-point-of-failure problem). However, these "advantaged" nodes
have more path passing through them already and thus can reply to a route
request query if they know the answer. So, again, this is to a large degree
already there. If you had something more extensive in mind, please
explain.

>     is not unlikely that a packet along a good link could be dropped.

No, not in ZRP. ZRP finds *all* the routes between the source and the
destination. The quenching process in ZRP is to ensure that you do not
unnecessarily discover the same route more than once and, thus, waste
network resources. However, all the routes are reported back to the
source.

Please note that there is a mechanism in ZRP (it was not described in the
Internet Draft, though), by which intermediate nodes can "get rid" of some
routes which are clearly inferior. This was created to reduce the amount
of control traffic and will not allow the best route to escape the
discovery process.

>     discovery of much better routes.

I agree that any routing protocol should be able to "evaluate" paths based
on realistic criteria and choose the "best" one. Again, I would like to
mention the work by Michael Pursley on "Least Resistance Routing."
Further, I would like to point out that there is no reason while routes
cannot be compared in ZRP, since ZRP returns all the routes back to the
querrying node.

>     first-found and shortest-path are unlikely to be provide a good
  
I absolutely agree with you. Furthermore, the set of criteria may change
dynamically. I think that this would be a very good topic for the next
MANET discussion. 

>     "an algorithm?"  If so, would you please make those assumptions

Let me do some ZRP advertising here (thanks for your question (:-)). 
I do not see ZRP as "a" routing algorithm, but rather as a framework under
which a number of routing protocols could be used. For example, the
Intrazone (IARP) protocol that each node runs could be any protocol
(preferably proactive). The IARP allows to discover routes in a local
neighborhood, which is an important aspect due to traffic locatization. Of
course, the major reason for doing so is to "partition" the problem, so
that in a large network the amount of control traffic is *significantly*
reduced. The size of the partitioning is govern by a single parameter -
the Zone Radius, which can be dynamically changed.

Joe Macker termed the feature in the December MANET meeting as "having a 
knob" to adjust the behavior of the protocol based on the particular current 
network conditions. I like the "knob" analogy. 

Thus, to summarize, ZRP addresses exactly your question on two levels -
the underlying IARP protocol can be selected based on the network and its
conditions and the geographical scope on which this IARP protocol operates
is (dynamically) determined (by setting teh Zone Radius) by the current
operational conditions.

>     these link-layer embellishments?

We talked about this a bit in the last MANET meeting. In particular, the
issue of whether broadcasting (eavesdropping) could be assumed in the
design of the routing protocol was addressed. Yes, I agree that we need to
have much more detailed discussion about these issues.

Best regards,

Zygmunt.
==-=--=-=-=  
~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-
Prof. Zygmunt J. Haas             tel: +1-607-255-3454
Wireless Networks Laboratory
323 Frank Rhodes Hall             fax: +1-607-255-9072
School of Electrical Engineering  
Cornell University                e-mail: [email-masked]
Ithaca, N.Y. 14853                
U.S.A                             http://www.ee.cornell.edu/~haas/wnl.html
~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-

---

From: [email-masked] (Mike Butler)
Date: Fri, 06 Feb 1998 10:11:23 -0500

Hi Vince:

Thanks for your response; you clarified a number of things for me.
There are a couple points, however, that I think I must have
miscommunicated.  Let me try to clarify our concerns...

> One of the functions provided by IMEP is a link-status sensing
> capability (i.e. neighbor discovery and maintenance). IMEP's
> link-status sensing mechanism has the capability to form a "logical"
> bidirectional link between two nodes from the combination of two
> oppositely directed unidirectional connections. This mechanism is
> described in detail in the IMEP internet draft. The mechanism
> operates with only one-hop knowledge and thus cannot for a logical
> link between two connected by multi-hop unidirectional paths.

Our concern is the apparent common assumption that if I can hear you,
you can hear me.  This is frequently untrue in a wireless environment,
specifically a tactical one.  A "combination of two oppositely
directed unidirectional connections" still makes the same assumption,
it just recognizes that a full duplex link is really two reciprocal
simplex links.

I was unaware of the unidirectional link routing working group; I will
investigate that.

(We suspect that this WILL be a problem in tactical wireles networks.)

> before advocating its use.

I do not mean load balancing of the packets within a single stream.  I
mean, instead, that ALL streams will attempt to follow the SAME route.
As I understand them, the proposed routing algorithms do not consider
link capacity and loading when they choose a route.  Thus, an
"advantaged" node, which will be likely, will become a bottleneck.

> layer (not within a given subnetwork).

Perhaps I've miscommunicated.  Let me try again.

On a single wired broadcast segment there is no opportunity (or need)
for load balancing.  All hosts on that segment (wire) contend for and
gain access to the ENTIRE segment.  

In contrast, in a wireless a host contends for a (spatially limited)
PIECE of a network segment; even when all hosts are logically on the
same segment, some are prevented from hearing one another another by
propagation losses.  This is a spatial diversity (spectral reuse); it
has no equivalent in a wired network.

One (there are several) manifestation of spatial diversity has an
obvious impact on routing (and I do mean network-layer routing here,
e.g., IP).  In a wired broadcast medium (e.g., ethernet) there is
never a need to relay a packet out the same interface it arrived on.
This is clearly not be the case in wireless networks.  Ergo, the
entity that makes the routing decisions must behave differently in a
wireless environment than it does in a wired environment.

Additionally, because of spatial diversity, it suddenly makes sense to
consider load balancing on a "single segment" network where all hosts
have a single interface and a single IP address.  This wouldn't happen
in a wired network.

> potentially be addressed by the metrics used by the routing protocol.

I was not talking about whether traffic should be routed through
advantaged nodes or not.  I am suggesting that "advantaged" nodes
should play a more central role in choosing routes than the less
advantaged nodes.  (Whether or not they handle any traffic is an
independent issue.)

As an extreme (but intuitive) example, an airborne node could collect
and broadcast a complete routing picture for the entire theater, and
it could simultaneously handle none of that packet traffic.

-mb

---

From: "Vincent D. Park" <[email-masked]>
Date: Fri, 06 Feb 1998 15:52:07 -0500

Thanks for the elaboration; however, I believe I understood most of your
concerns the first time. In some cases I simply disagree with you, while in
others, I think our differences are influenced by our individual
preconceived notions of a wireless networking infrastructure/architecture.
See my comments below.

>(We suspect that this WILL be a problem in tactical wireles networks.)

Here I understand your concern perfectly. My first point is that there will
be an additional penalty (in control overhead, adaptability ...) to make
use a unidirectional link between two nodes (A to C in Fig. 1), when
bidirectional connectivity requires the use of multiple hops (intermediate
hop through B in Fig. 1). There is a trade-off here between cost and
benefit of adding the functionality to use unidirectional links. Although
it can be done, it is by no means clear that this is worth doing.

      ------------>                     UHF radio
    A <------------ B               --------------->
     |             |^              A                C
     |             ||               <---------------
     |             ||                   VHF radio
     |             v|
     -------------> C

         Fig. 1                           Fig. 2

As far as the functionality that IMEP adds, I think I haven't made myself
clear. Additionally, I think you may be limiting your focus to a mobile
node that has only one interface. In the case where nodes may have multiple
wireless interface (potentially of different technologies), IMEP can
establish logical links that are comprised of oppositely directed
unidirectional connections over the different interfaces (Fig. 2). This is
not something that is currently done by routing algorithms used in wired
networking environments. While this is not as general of a solution to the
unidirectional link problem, the cost of doing this is not as high.

>"advantaged" node, which will be likely, will become a bottleneck.

Even with shortest-path routing (SPR), packets intended for different
destinations may follow different paths through the network. However, SPR
does have a tendency to concentrate traffic along certain "good" paths.
TORA does not do SPR and need not suffer from the traffic concentration
problem. As TORA often provides multiple paths for a given destination,
there is an opportunity to cause packets for the same destination to take
different paths through the network. However, my earlier remark about
packet ordering ... needs to be considered in this case. Although examples
where load balancing improves performance can be constructed, it will be
difficult to show that load balancing is beneficial in general.

In this remark and in your previous message, you appear to be advocating
routing based on loading. I hope you are aware of the history with this
type of routing metric (route flapping, instability).

>have a single interface and a single IP address.  This wouldn't happen

There is a can of worms here that has been opened before. What you are
pointing out here is nothing that hasn't been discussed at length many
times before. My only point is that it has little (or no) effect on the
theoretical or mathematical aspects of load balancing. The diffenence is
simply one of the conceptual view of the network, and there are many
different ways to view a wireless network conceptually.

>it could simultaneously handle none of that packet traffic.

Thanks for the reminder. This is a point a forgot to comment on the first
time around. Here you imply a benefit to a somwhat more centralized routing
scheme, as opposed to a distributed routing scheme. I, for one, feel that
routing in a mobile network (especially a military network) should be as
distributed as possible. Centralized routing schemes lack robustness.
Secondly, you suggest the use of topological broadcast, as in link-state
routing. I believe this type of routing to be inappropriate for the size
and rates of change I envision in military tactical networks (perhaps you
have a different vision). Despite my reservations, if you have a proposal
please submit it for consideration.

-Vince

--------------------------------
Vincent D. Park
Information Technology Division
Naval Research Laboratory
4555 Overlook Ave.
Washington, DC 20375-5000
--------------------------------

---

From: Zygmunt Haas <[email-masked]>
Date: Fri, 6 Feb 1998 17:17:03 -0500 (EST)

On Fri, 6 Feb 1998, Mike Butler wrote: