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The following are the main functional blocks implemented in the PR_EA Unit:
•
SDH–MAP
It provides to deassemble the SDH virtual containers (toward MPLS direction), removing the
SDH OverHead, and to assemble them toward SDH direction, thus "loading" and "unloading"
the packets to/from the SDH frames (refer to ITU–T rec. G.707); the packets are then switched
toward GFP or HDLC processing, according to the logical ports configurations.
•
HDLC
It provides: to deassemble (toward MPLS direction) the HDLC frames (High–Level Data Link
Control), removing the HDLC header; and to assemble them toward SDH direction; to
scrambler/descrambler the data; byte stuffing/destuffing. The HDLC frame format is reported
in Figure 117. page 237 (refer to rec. RFC 1662 and RFC 2615).
•
PPP
It provides to deassemble (toward MPLS direction) the PPP frames (Point–to–Point Protocol),
removing the PPP header, and to assemble them toward SDH direction; the PPP frame format
is reported in Figure 116. page 237 (refer to rec. RFC 1661).
The "Martini Encapsulation" can be configured for the MPLS packets (substitution of ethernet
"FCS" field with an error check value consistent with the entire labelled packet).
•
GFP
It provides to deassemble (toward MPLS direction) the GFP frames (Generic Framing
Procedure), removing the GFP header, and to assemble them toward SDH direction; the GFP
frame format is reported in para. 3.8, page 263 (refer to rec. ITU–T G7041). It supports
un–concatenated ethernet frames over unstructured VC4 payloads.
•
PUSH1
It provides to "push in" the first label to the ethernet packet, after having inspected the ethernet
header, identified the destination and the class of service. It classifies the packets by decoding
the 802.1p/q "User Priority" and "VLAN–Tag" fields. Depending on the type of decoded or
negotiated ethernet SLA (Service Level Agreement), the stream can be associated with one of
three types of QoS (Quality of Service): Best Effort bandwidth (BE–BW), or Min–BW with
regulated bursts, or Guaranted constant BW. The label format is reported in Figure 115. page
237 (refer to rec. RFC 3032).
•
POP1
It provides to "pop out" the label from the ethernet packet.
•
PREAMBLE
It provides to remove (toward MPLS direction) the "preamble" and "start–of–frame–delimiter"
fields from the ethernet MAC 802.3 header (Medium Access Control), and to re–insert them
toward ethernet direction. Moreover it decodes the "Tag" fields of the MAC client header: 802.1p
and 802.1q. The ethernet FCS value is calculated too. The MAC frame is illustrated in
Figure 118. page 238 and Figure 119. page 238 (refer also to rec. IEEE 802.3).
•
LOCAL PORT
This block represents a module that is mounted on the board and, according to the the module,
it distinguishes the type of unit.
The three possible types of module are:
4xFE: it contains 4 Fast Ethernet transceiver interfaces type 10/100Base–T, each
interface allowing a local connection to a LAN at auto–negotiable rates 10 or 100 Mb/s.
1xGbE: it contains 1 small–form Gigabit Ethernet optical transceiver, implementing the
optical/electric conversion and a full–duplex Gigabit Ethernet interface at 1.25 Gb/s, as
specified in IEEE–802.3.
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