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Power line communication technologies in smart grids Chapter 4 151

FIG. 4.12 A MAC frame structure example for ITU-T Rec. G.9904. (From Narrowband orthog-
onal frequency division multiplexing power line communication transceivers for PRIME networks,
ITU-T Rec. G.9904, October 2012. [Online] Available: http://www.itu.int/rec/T-REC-G.9904
(Fig. 8-7), with permission.)

contention period (SCP) or contention-free period (CFP). Devices need to
demand for allocation from base node in the CFP period. The base node either
approves or rejects the request according to the channel status. In the SCP
period, there is no an agreement requirement. Nonetheless, devices should con-
sider the timing limits of the SCP period. Typically, a MAC frame consists of
one or more beacons, one SCP and one or no CFP.
The ARQ is optionally provided in MAC layer of the standard in order to
accomplish a safe data transmission. Furthermore, the standard supports two
types of security operations. While the first profile security is performed in
the upper layers, the second one is achieved by using 128 bit Advanced Encryp-
tion Standard (AES) encryption.

4.4.3.3 Convergence layers
The CL provides an adaptation layer between upper protocol layers and MAC
layer. The main function of the CL is the acquiring traffic from upper supported
layers and summarizing them to the SDUs. The CL is composed of two sub-
layers that are Common Part Convergence Sublayer (CPCS) and Service Spe-
cific Convergence Sublayer (SSCS). While the CPCS supports many general
services, the SSCS supports certain services. The standard defines four SSCS
that are Internet Protocol version 4 (IPv4), IPv6, IEC 61334-4-32 and NULL
SSCS. The IEC 61334-4-32 is the most widely used SSCS method for the
AMI applications. The most important service of CPCS is the segmentation
and reassembly (SAR).

4.4.4 The IEEE 1901.2 standard
The IEEE Standards Association confirmed IEEE P1901.2 standard in 2013
[84]. The IEEE P1901.2 standard describes the PHY and MAC layers for
HDR NB-PLC systems working on the frequencies below 500 kHz. This stan-
dard is generally depending on the ITU-T Rec. G.9903 (G3-PLC). In addition,
this standard contains several annexes where a channel model is suggested in
Annex D, and an EMC measurement method with specific limits is presented
in Annex E.