Nortel Networks 8000 - Manual (Page 67)

4 POS and CPOS interface configuration
Nortel Secure Router 8000 Series
Configuration -WAN Access
CQ NOTE
The SDH has a variety of overhead bytes. This section describes only a few of them that are used in the
CPOS configuration.
• SOH
SOH consists of RSOH and MSOH.
The payload of STM-N frame has the Overhead byte and Path Overhead (POH), which
monitors low speed tributary signals.
The J0 (regeneration section trace message) is included in RSOH. It is used to send the
Section Access Point Identifier repeatedly. Based on this, the receiving end ensures that
it is continuously connected to the transmission end. This byte can be any character in
the networks of the same carrier. The J0 at the network border of two carriers should be
matched at the receiving and transmission ends. Carriers can detect and locate the fault
in advance through J0 and quicken network recovery.
• Path overhead
Section overhead monitors the section layer, and path overhead monitors the path layer.
Path overhead is divided into higher order Path Overhead and lower order Path
Overhead.
The higher order overhead performs monitoring on channels of VC-4/VC-3.
The J1 (higher order VC-N path trace byte) is included in higher order path overhead.
Similar to j0, it is used to send higher order path access point identifier repeatedly. Based
on this, the channel ensures that it is connected with the specified transmission end (this
channel is in continuous connection state). The J1 at the receiving and transmission ends
should be matched.
The C2 (path signal label byte) is also included in higher order path overhead. The C2 is
used to indicate the multiplex structure of VC frame and the property of information
payload. The property includes whether the channel is loaded and the type of service
loaded and their mapping mode. The C2 at the receiving and transmission ends should
match.
4.1.3 POS
The Packet over SONET/SDH (POS) is a transmission technology applied in the MAN and
WAN. The POS supports the packet data such as IP packets. The POS can map packets of
variable length directly into the payload of SONET. The POS uses the physical layer
transmission standard of SONET. This offers a high speed, reliable, and P2P data connection.
The POS uses SONET as the physical layer protocol and uses PPP as the link control of the
data link layer. The POS encapsulates the IP packet service in the High-level Data Link
Control (HDLC) frame and runs the IP packet service at the network layer.
The SR8000 provides a single rate of POS interface, that is, STM-1 (155Mbit/s).
The HIC high-speed POS interface cards supported by SR8000 are as follows:
• 1-port unchannelized POS/155M optical interface module (RT-HIC-1POS)
• 2-port unchannelized POS/155M optical interface module (RT-HIC-2POS)
• 4-port unchannelized POS/155M optical interface module (RT-HIC-4POS)
4.1.4 CPOS
The CPOS interface refers to the channelized POS interface.
4-6 Nortel Networks Inc. Issue 5.3 (30 March 2009)