Page 716 - 5G Basics - Core Network Aspects

2 Transport aspects

prevent upper layer overflow. By setting the value of the RX Enable primitive to RXoff, the NT's L2+
functional block indicates to the FTU-R that it is not ready to receive data packets. In this case the FTU-R
shall set the RX DTU Enable (see clause 8.1.2) to RXoff and the PMS-TC receiver in the FTU-R
(see Figure 9-1) may respond with NACKs to any received downstream normal DTU when its buffer is full.
By setting the value of the RX Enable primitive to RXon, the NT's L2+ functional block indicates to the FTU-R
that it is ready to receive data packets.
NOTE – The NT's L2+ functional block setting the value of the RX Enable primitive to RXoff across the γR reference
point is expected to be used only when operating in a group with Ethernet-based multi-pair bonding (see G.998.2) in
order to facilitate delay equalization of the lines in the bonded group in the event of retransmissions.
The FTU management entity (FME) controls the TPS-TC using primitives that are conveyed via the
TPS-TC_MGMT interface; the same interface is used to retrieve relevant management primitives from the
TPS-TC.
The TPS-TC also facilitates transport of eoc. The eoc packets containing one or more eoc messages are
transferred transparently (except when non-correctable errors occur in the line) between the
TPS-TC_MGMT interfaces of peer FTUs. The eoc messages assigned for transmission (eoc commands and
responses), formatted as defined in clause 11.2.2.2, are encapsulated in eoc packets and submitted to the
TPS-TC_MGMT interface by the FME in the order determined by their priority.
The NTR and ToD primitives submitted to the FME interfaces of the peer FTU are communicated using eoc
messages defined in clauses 11.2.2.7 to 11.2.2.9. The DRA related primitives are defined in clause 8.1.1 and
communicated using RMC messages defined in clause 9.6.4 and eoc messages defined in clause 11.2.2.17.
The transmitted eoc packets are multiplexed with the incoming data packets with ordering as described in
clause 8.2.2, encapsulated in DTUs, and transferred to the TPS-TC of the peer FTU. For de-multiplexing of
the eoc packets at the receive side, each eoc packet encapsulated in a DTU carries a flag that distinguishes
it from data packets (see clause 8.3). The eoc packets recovered from the received DTUs are submitted to
the FME via the TPS-TC_MGMT interface.
When both eoc packets and data packets are available, the eoc packets shall have strict priority over data
packets. The maximum size of an eoc packet (see clause 11.2.2.1) and the number of eoc packets
transmitted per second is limited to avoid potential reduction of QoS; this limit is determined by the eoc
message format (see clause 8.1.3) and the maximum number of eoc bytes allowed per logical frame period.
The maximum number of eoc bytes per upstream logical frame period and per downstream logical frame
period shall meet the requirements presented in Table 6-1.
8.1.1 γ reference point

The γ reference point is defined in the data plane between the FTU and the L2+ functional block. The order
in which the data packets are mapped into DTUs is specified in clause 8.2.2; this order is determined by the
L2+ media access control mechanism, which is beyond the scope of this Recommendation. The data
packets shall be passed from the TPS-TC to the L2+ functional block in the order that they were transmitted
from the peer FTU.

The interface at the γ reference point is logical and is defined through primitives. The primitives at the γ
reference point depend on the type of TPS-TC. For a packet-based TPS-TC (PTM-TC), the unit of data is a
packet, which is a sequence of bytes. The content of the packet is application specific. The primitives that
control the flow of data packets across the γ reference point are summarized in Table 8-1. The TX primitives
in Table 8-1 control packet transfer from the upper layers to TPS-TC, while RX primitives control packet
transfer from the TPS-TC to upper layers.

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