Internet Draft Stephen Bush
Expires in June 1997 Sunil Jagannath
<draft-bush-ncp-config-00.txt> ITTC
January 16, 1997
Network Control Protocol for the Configuration of Mobile Wireless Beam-
formed GPS-Based Networks
Status of this Memo
This document is a submission by the Information and Telecommunica-
tions Technologies Center (ITTC) at the University of Kansas. Com-
ments should be submitted to sbush@tisl.ukans.edu.
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Abstract
The Network Control Protocol (NCP) facilitates the configuration and
rapid reconfiguration of mobile wireless beam-formed networks. It
controls the operation of a network of omni-directional packet radios
(orderwire) that overlays the mobile wireless network. Each network
element in this network uses Global Positioning System (GPS) informa-
tion to control a beamforming antenna subsystem which provides for
spatial reuse. The GPS information is shared among the network ele-
ments over the orderwire and an optimal topology for the beam-formed
links is determined.
Network Control Protocol Description
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Network Control Protocol Terminology
This section defines some of the terminology used in the Description
of the NCP operation.
o "AX.25"
Asynchronous X.25 Protocol (See [1]).
o "Callsign"
The packet radio callsign is assigned by the FCC and
identifies the packet radio operator.
o "Edge Switch" (ES)
A node which either resides within the wireless
network or at the edge of the fixed and
wireless network and which serves as a base station.
o "Global Positioning System" (GPS)
Satellite system which provides location and time.
o "Remote Node" (RN)
A host with the ability to connect via a beamforming
antenna to an edge switch (ES).
Network Control Protocol Operation
At the physical level we will be using the orderwire to exchange
position, time and link quality information and to setup the wireless
connections. The process of setting up the wireless connections
involves setting up links between ESs and between ESs and RNs.
The network will have one master ES, which will run a topology con-
figuration algorithm and distribute the resulting topology informa-
tion to all the connected ESs over point-to-point orderwire packet
radio links. The point-to-point link layer for the orderwire uses
AX.25 [1]. The master ES is initially the first active ES, and any
ES has the capability of playing the role of the master.
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The first ES to become active initially broadcasts its callsign and
start-up-time in a MYCALL packet, and listens for responses from any
other ESs. In this prototype system, the packet radio callsign is
assigned by the FCC and identifies the radio operator. Since it is
the first active ES, there would be no responses in a given time
period, say T. At the end of T seconds, the ES rebroadcasts its
MYCALL packet and waits another T seconds. At the end of 2T seconds,
if there are still no responses from other ESs, the ES assumes that
it is the first ES active and takes on the role of the master. If the
first two or more ESs start up within T seconds of each other, at the
end of the interval T, the ESs compare the start-up times in all the
received MYCALL packets and the ES with the oldest start-up time
becomes the master. In this system, accurate time stamps are provided
by the GPS.
Each successive ES that becomes active initially broadcasts its call-
sign in a MYCALL packet. The master on receipt of a MYCALL packet
extracts the callsign of the source, establishes a point-to-point
link to the new ES and sends it a NEWSWITCH packet. The new ES on
receipt of the NEWSWITCH packet over a point-to-point orderwire link,
obtains its position from its GPS receiver and sends its position to
the master as a SWITCHPOS packet over the point-to-point orderwire
link. On receipt of a SWITCHPOS packet, the master records the posi-
tion of the new ES in its switch position table, which is a table of
ES positions, and runs the topology configuration algorithm to deter-
mine the best possible interconnection of all the ESs. The master
then distributes the resulting information to all the ESs in the form
of a TOPOLOGY packet over the point-to-point orderwire links. Each ES
then uses this information to setup the inter-ES links as specified
by the topology algorithm. The master also distributes a copy of its
switch position table to all the ESs over the point-to-point order-
wire links, which they can use in configuring RNs as discussed below.
Also, the ES then uses the callsign information in the switch posi-
tion table to setup any additional point-to-point orderwire packet
radio links corresponding to the inter ES links required to exchange
any link quality information. Thus this scheme results in a point-to-
point star network of orderwire links with the master at the center
of the star and also point-to-point orderwire links between those ESs
that have a corresponding inter ES link.
In the event of failure of the master node which can be detected by
listening for the AX-25 messages generated on node failure, the
remaining ESs exchange MYCALL packets, elect a new master node, and
the network of ESs is reconfigured.
Each RN that becomes active obtains its position from its GPS
receiver and broadcasts its position as a USER_POS packet over the
orderwire network. This packet is received by all the nearby ESs.
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Each candidate ES then computes the distance between the RN and all
the candidate ESs which is possible since each ES has the positions
of all the other ESs from the switch position table. An initial guess
at the best ES to handle the RN is the closest ES. This ES then feeds
the new RN's position information along with the positions of all its
other connected RNs to a beamforming algorithm that returns the
steering angles for each of the beams on the ES so that all the RNs
can be configured. If the beamforming algorithm determines that a
beam and TDMA time slot are available to support the new RN, the ES
steers its beams so that all its connected RNs and the new RN are
configured. It also records the new RN's position in its user posi-
tion table which contains positions of connected RNs, establishes a
point-to-point orderwire link to the new RN and sends it a HANDOFF
packet with link setup information indicating that the RN is con-
nected to it. If the new RN cannot be accommodated, the ES sends it a
HANDOFF packet with the callsign of the next closest ES, to which the
RN sends another USER_POS packet over a point-to-point orderwire
link. This ES then uses the beamform algorithm to determine if it can
handle the RN.
This scheme uses feedback from the beamforming algorithm together
with the distance information to configure the RN. It should be noted
that the underlying AX.25 protocol [3] provides error free transmis-
sions over point-to-point orderwire links. Also the point-to-point
orderwire link can be established from either end and the handshake
mechanism for setting up such a link is handled by AX.25. If the RN
does not receive a HANDOFF packet within a given time it uses a retry
mechanism to ensure successful broadcast of its USER_POS packet.
A point-to-point orderwire link is retained as long as a RN is con-
nected to a particular ES and a corresponding high-speed link exists
between them to enable exchange of link quality information. The link
can be torn down when the mobile RN migrates to another ES in case of
a hand-off. Thus at the end of this network configuration process,
three overlaid networks are setup, namely, an orderwire network, an
RN to ES network and an inter-ES network. The orderwire network has
links between the master ES and every other active ES in a star con-
figuration, links between ESs connected by inter-ES links as well as
links between RNs and the ESs to which they are connected. Raw pipes
for the user data links between RNs and appropriate ESs as well as
for the user data links between ESs are also set up.
Finally, see [2] and [3] for the definition of managed objects for
the NCP and Virtual Network Configuration (VNC).
Network Control Protocol Packet Types
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The network control protocol uses the following packet types shown
below.
-----------------------------------------------------------------------
|MYCALL | Callsign, Boot-Time |
-----------------------------------------------------------------------
|NEWSWITCH | empty packet |
-----------------------------------------------------------------------
|SWITCHPOS | GPS Time, GPS Position |
-----------------------------------------------------------------------
|TOPOLOGY | Callsign and Position of each node with inter-connections |
-----------------------------------------------------------------------
|USER_POS | Callsign, GPS Time, GPS Position |
-----------------------------------------------------------------------
|HANDOFF | Frequency, Time Slot, ES GPS Position |
-----------------------------------------------------------------------
The MYCALL packet contains the ES identifier (packet radio Callsign)
and the time it powered-up.
The NEWSWITCH packet is an empty packet which serves as an acknowl-
edgment and completes the handshake between the ES and RN.
The SWITCHPOS packet contains the current ES time and location.
The TOPOLOGY packet contains packet radio callsigns and positions of
all nodes and the beamformed links to be established between them.
The USER_POS packet contains the callsign, current time, and position
of an RN.
The HANDOFF packet contains the frequency, time slot, and ES posi-
tion. It is sent by an ES to a RN indicating handoff to this ES.
Security Considerations
All orderwire packets are DES encrypted.
References
[1] AX.25 Amateur Packet Radio Link-Layer Protocol, IEEE October
(1984).
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[2] The Definition of Managed Objects for the Configuration of Mobile
Wireless Beamformed GPS-Based Networks, draft-bush-rdrn-
mib-00.txt,
Stephen F. Bush, Sunil Jagannath.
[3] The Definition of Managed Objects for Virtual Network Configura-
tion,
draft-bush-vnc-mib-00.txt, Stephen F. Bush, Sunil Jagannath.
Author's Address
Stephen F. Bush
Sunil Jagannath
Information and Telecommunications Technologies Center (ITTC)
University of Kansas
Lawrence, Kansas 66045
Phone: (913) 864-7761
EMail: sbush@tisl.ukans.edu
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