Transcript Determination of the topology of high survival HF radio

DETERMINATION OF THE
TOPOLOGY OF HIGH
SURVIVAL HF RADIO
COMMUNICATION
NETWORK
Andrea Abrardo.
Outline
1. Communications requirements
2. The physical topology of connections
envisaged in the SWING project
3. Higher layer requirements
4. Identification of MAC techniques and
possible scenarios
5. Comparisons
6. Looking forward
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SWING Final Meeting | CNIT - Pisa, Italy
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Communications requirements
• ECIs send data only to their home CGAs (ECIs to ECIs
communication is not required, not even within the same
area).
• More than one ECI belonging to the same area, i.e.,
connected to the same CGA, may transmit at same time.
• Communication between different CGAs must be
permitted.
• The major part of network traffic is confined within each
area, i.e., ECIs to CGAs communications.
• Accordingly, the probability of concurrent transmissions of
ECIs (either belonging to the same area or not) is greater
than that of CGAs.
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SWING Final Meeting | CNIT - Pisa, Italy
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HYBRID TREE/MESH TOPOLOGY
The choice of the topology has a direct impact on the
design of higher layer protocols, and vice versa.
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SWING Final Meeting | CNIT - Pisa, Italy
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Higher layers requirements
• SWING requirements involving higher layer
operations
– Most of the times end-to-end communications are
confined to single-hop communications, i.e., from ECIs to
CGAs or among CGAs (MAC layer aspects)
• Considering these premises we provided:
– MAC requirements
– Identification of possible MAC techniques suitable for the
SWING system
– MAC protocols comparison
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SWING Final Meeting | CNIT - Pisa, Italy
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MAC requirements
• Contention-based MAC protocols such as IEEE
802.11 provide fast and efficient channel access in
presence of light traffic.
• Contention-free protocols such as IEEE 802.4 (token
bus) achieve high efficiency under heavy loads, and
provide bounded access time as well.
• One of the factors that influence the
performance of MAC protocols for HF networks is
the link turnaround time, i.e., the time it takes for a
node to process a received packet and to send back
a response.
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SWING Final Meeting | CNIT - Pisa, Italy
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Identification of possible MAC techniques: Token Passing
• Token passing is a contention-free protocol where
the nodes agree that only the node that currently
holds a token is allowed to transmit.
• The HF Token Protocol (HFTP) is a token bus
protocol, so each node can (nominally) send data
directly to any or all other nodes (broadcast
channel).
• Token passing is attractive for use in surface-wave
naval high-frequency (HF) radio networks due to its
potential for high throughput, fairness, and
bounded access time.
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SWING Final Meeting | CNIT - Pisa, Italy
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Identification of possible MAC techniques: Distributed
Coordination for High Frequency (DCHF)
• DCHF is a contention-based scheme based on the
popular wireless MAC protocol IEEE 802.11 DCF.
• The main characteristics of DCHF are the lack of
synchronization requirement and the possibility left
to the nodes to join or leave the network, without
any management overhead.
• DCHF uses only "virtual carrier sensing“
implemented through the exchange of RTS and CTS
packets.
13/12/2013
SWING Final Meeting | CNIT - Pisa, Italy
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Possible scenarios
Considering the general comms requirements, and the
characteristics of the two MAC schemes we propose 3 different
solutions based on 3 different scenarios:
1.
2.
3.
Token passing scenario: in this solution the logical ring is passed among all
the nodes of the SWING network (both among ECIs and among CGAs).
Contention based scenario: all nodes belonging to SWING network apply
DCHF MAC technique; every transmitting node senses the channel and then
establishes a connection with the receiver.
Mixed scenario: in this case, we have a contention free access technique
(i.e., HFTP) for inter-area communications, i.e., between ECIs and their home
CGA, while for the global network (communication between CGAs) we
consider a contention based access technique (i.e. DCHF).
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SWING Final Meeting | CNIT - Pisa, Italy
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Token Passing scenario
This solution allows every radio
terminal to transmits its data
without incurring in collisions.
In case of heavy traffic, this procedure
helps regulating the access to the
channel avoiding collisions.
On the other hand, for light traffic (i.e.
only one ECI want to transmit to the
respective CGA) this solution
introduces a strong management
overhead, which severely degrades
the system performance.
Do not recommended in presence of
long turnaround times (due to long
interleavers).
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SWING Final Meeting | CNIT - Pisa, Italy
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Contention based Scenario
Suitable for light traffic (no
collisions).
In presence of long turn
around times it is
necessary to avoid
RTS/CTS: this is possible if
each node lies in the
interference region of
each other (channel
sensing is sufficient to
avoid collisions).
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SWING Final Meeting | CNIT - Pisa, Italy
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Mixed Scenario
Whenever an ECI have to transmit a
packet to its home CGA, it waits for the
reception of the token that is
continuously exchanged within the logical
ring composed by one CGA and its
connected ECIs.
When a CGA receives the token, it starts
the contention based procedure to submit
a pending packet towards another CGA.
In case no pending packet is present, the
token is released, otherwise it is kept until
packet transmission.
Such a solution could efficiently manage the tradeoff between
access time and system throughput.
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SWING Final Meeting | CNIT - Pisa, Italy
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Comparisons (Simulations)
Simulated scenario
Comparisons
Behavior of MAC techniques
with turnaround of 1 s.
Top: average latency per
packet in DCHF (red) and
HFTP (blue);
Down: channel utilization in
DCHF (red) and HFTP (blue).
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SWING Final Meeting | CNIT - Pisa, Italy
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Comparisons (Simulations)
Comparisons
Throughput versus turn around: saturation traffic analysis.
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SWING Final Meeting | CNIT - Pisa, Italy
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Looking forward
• Include MAC protocols in the SWING system.
• Network layer issues:
– In the present SWING scenario, network functionality
can be regulated as a transparent bridge, without the
need of additional overhead due to IP addresses.
– However, scaling to larger networks with more
complex topologies needs the introduction of routing
algorithms.
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SWING Final Meeting | CNIT - Pisa, Italy
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