Subject: [manet-dlep-rg] DLEP and Vehicle/Aircraft Mounted Tactical Radios

From: "Cheng, Bow-Nan - 0665 - MITLL" <[email-masked]>
Date: Fri, 30 Aug 2013 16:04:20 -0400

Hi all,

Below are my inputs for vehicle/aircraft mounted tactical radios

DLEP considerations on some vehicle/aircraft mounted tactical radios. Format
is shameless taken from Rick who swiped from Teco

1. Scope

The information below applies to a subset of tactical radios that are larger
(mounted on vehicles/aircraft) and mobile. It's hard to get into details of
all the radios, but I'll try to provide what can be shared. There are: 1)
directional high capacity systems, 2) medium capacity omnidirectional
systems (Random-access-like MAC), and 3) medium capacity directional systems
(TDMA/Scheduled MAC). Some provide a multi-hop "subnet routing" (I.e. Mesh)
capability for multicast/broadcast and unicast traffic. Others are non-IP,
but there's some discussion to move to an IP stack.

2. Topology

As described earlier, most of the radios have subnet-routing protocols (I.e.
Sub-IP/non-IP MANET routing). The goal with these designs is to make the
interface look like one broadcast domain (I.e. Ethernet) even though it is
multiple RF hops. In many cases, the sub-IP routing occurs on the
ciphertext/"black" side of the network so there is no access to do
otherwise. In some of the systems, the topology is a full mesh, some are
point-to-point, and some are tandem networks (N1  N2  N3). To an external
router, the radio network is essentially 1 IP hop.

3. Interface to External Router

Because the MANET-type routing occurs at layer 2, the radios that support IP
typically interface with an external router by running something like OSPF
on the wired interface out of the radio, and a variant of OSPF optimized for
wireless networks on the interface into the wireless network. In some cases,
more advanced implementations will attempt to generate a link *cost*
associated with a neighbor (or multi hop neighbor) to inform the external
router of potential choices.

4. Interface to multi-hop subnet routing technology

The interface to the subnet routing process is usually taken care of with
API calls since its all on the same box.

5. Security Domains

Some of the radios include multiple security levels for encryption all in
one box. Multiple "red" networks all converge on a ciphertext/black core. In
some of these cases, DLEP will need to be run on the "red" side for each
security enclave. If there are 5 different security domains, then 5
instances of DLEP will need to be run. One of the requirements of the
current draft of DLEP is that MAC addresses of remote routers need to be
known prior to establishing a neighbor relationship. It has been suggested
that if the radio does not provide this feature, the DLEP client could
exchange it and cache this information when a link becomes available.
However, with multiple enclaves, subnet routing, this can become extremely
difficult and bandwidth consuming (think 30 node network "seeing" another 30
node network for the first time). Another issue is that multi-hop routes are
typically not exposed from "black" to the enclaves and limited link metrics
are available in the enclave. In some cases, nodes at a certain security
level (enclave) cannot know that other nodes exist even though they are
being routed through.

6. Link Technology

As mentioned by others before, some of the radios can adjust burst rate by
flow (I.e. Flow matching this IP src/dst, this DSCP value, etc. -- send out
transmit power X and rate Y, flow matching another criterion, send out
transmit power A rate B). Many of the technologies can be asymmetric (tx and
rx transmit rates and powers are different). Adaptive rate control is also
available and used to maintain a certain link quality (error rate).

Some of the radios use techniques like frequency hopping and spread spectrum
and depending on the technique used and what nodes are tuned to, different
groups of neighbors (1 RF hop) can receive and decode the message. Radios
can say "flow 1 goes with certain rate, power, and frequency hop pattern,
flow 2 does X, Y, Z". The implication here is that DLEP might or might not
need a way to handle all these variations on a theme in multicast.

Most tactical radios exchange neighbor information periodically and have a
good sense of neighbors or links being "up".

7. Metrics

Some metrics we've observed with these radios:
1. NUM_RX_FRAMES 
2. NUM_RX_MISSED_FRAMES
3. NUM_TX_FRAMES 
4. NUM_TX_DISCARDED_FRAMES
5. RX_DATARATE  Burst receive rate
6. TX_DATARATE  Burst transmit rate
7. DELAY_AVG 
8. DELAY_STD
9. DELAY_MAX 
10. SINR_AVG 
11. SINR_STD 
12. NOISE_FLOOR_AVG
13. NOISE_FLOOR_STD
14. BW_CONSUMPTION / LINK_UTILIZATION
15. BIT_ERROR_RATE / VITERBI_BIT_ERROR_RATE
16. QUEUE_DEPTH (per MAC queue)
17. QUEUE_TX_DELAY
18. NUM_HOPS  number of layer 2 hops
8. Flow Control

Because in tactical radios, the physical interface between radio and router
is typically Fast Ethernet (100Mbps), flow control is needed to ensure the
radio is not overrun. Several approaches have been taken: credit-based,
rate-based, and pause-frame based for a number of systems. All have their
advantages and disadvantages. Flow control can be maintained either: per
neighbor (generally directional/TDMA radios), per interface, or per QoS
level (can be per QoS, per neighbor as well). The main goal of doing flow
control on a per neighbor basis is to prevent blocking if MAC protocols have
transmission opportunities to specific neighbors.

9. Multiple Complex Queues at the Radio

Some of the radios we're working with have multiple complex queues that can
be mapped to different flow information. While the premise of any R2RI is to
shorten radio queues and queue packets at the router, these 10's-100's of
long complex queues at the radio can impact DLEP design.

10. Tight latency constraints

Many of these tactical radios have tight latency constraints, dropping older
packets in queue (vs. tail drop) when queues are being filled. Knowing the
latency guarantees of the link are important in these systems.

Would be happy to go into more detail on any of these points if needed.

-Bow-Nan