Cryptography Reference
In-Depth Information
Upper to Lower. The upper layers provide updated information to the necessary
lower layers via an interface. For example, if the application layer senses a delay
or loss of data, a direct notification to the data-link layer by the application layer
would help adapt its error correction mechanism. In addition, delay sensitive
packets could be treated with priority. As proposed in Larzon et al. (2002) lower-
to-upper information flow is treated as notifications (the lower layer notifies the
upper layer about the underlying network condition), whereas the upper-to-lower
information flow is treated as hints (upper layers provide hints to the lower layers
on the means to process application data).
Lower and Upper . In this case, both the upper and lower layers are at liberty to
transmit notifications about their current state and send queries to the other lay-
ers. During runtime, layers executing different tasks can collaborate with each
other on an iterative loop basis, resulting in a back and forth communication
between them. For example, a back and forth information flow between layers is
seen in a proposal to solve the multiple access problem for contention-based wire-
less ad-hoc networks using joint scheduling and suggesting a distributed power-
control algorithm for such networks (ElBatt and Ephremides 2004). In addition,
direct communication between layers at runtime could indicate the advantage of
making the variables at each layer visible to the other layers of the stack. How-
ever, one of the disadvantages of this approach would be in managing the shared
memory spaces between the layers when variables and internal states are shared
between different layers.
Integration of Adjacent Layers. The formation of a super-layer by combining two
or more adjacent layers would result in a new cross-layer design scheme. The
resulting layer would simply provide the union of the services that were provided
by the individual layers. For example, a collaborative design of the data-link and
physical layer would suffice to produce a super-layer. From a network security
perspective, a super-layer that combines network and data-link layer would help
prevent advanced Address Resolution Protocol (ARP) poisoning attacks.
Design Coupling without Interfaces. Coupling two or more layers during the
design phase would avoid creating extra interfaces at runtime that could result
in a new cross-layer design approach. However, in deployed networks, one of the
architectural challenges would be to integrate the coupled layer with already-
existing fixed layers.
• Vertical and Horizontal Calibration Across Layers:
Vertical calibration . Vertical calibration refers to the efficient utilization of
parameters across different layers of the vertical stack. The parameters set at
the application level could dictate terms to the lower layers and vice versa. For
example, the transport protocol (TCP or UDP) chosen at the transport layer
would assert reliable or unreliable communication and would directly affect the
layers below it. Consequently, the joint adjustment at different layers of the ver-
tical stack would result in a more holistic performance of the system than the
adjustment of individual parameters.
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