Table of Contents

Chapter 1 POS Interface Configuration. 1-1

1.1 Overview. 1-1

1.1.1 SONET/SDH. 1-1

1.1.2 POS. 1-1

1.2 Configuring a POS Interface. 1-1

1.3 Displaying and Maintaining POS Interfaces. 1-3

1.4 POS Interface Configuration Example. 1-3

1.4.1 Network Requirements. 1-3

1.4.2 Network Diagram.. 1-4

1.4.3 Configuration procedure. 1-4

1.5 Troubleshooting POS Interfaces. 1-4

 

Chapter 1  POS Interface Configuration

When configuring a POS interface, go to these sections for information you are interested in:

l           Overview

l           Configuring a POS Interface

l           Displaying and Maintaining POS Interfaces

l           POS Interface Configuration Example

l           Troubleshooting POS Interfaces

1.1  Overview

1.1.1  SONET/SDH

Synchronous optical network (SONET), a synchronous transmission system defined by ANSI, is an international standard transmission protocol. It adopts optical transmission.

Synchronous digital hierarchy (SDH) was defined by CCITT (today’s ITU-T). It uses synchronous multiplexing and flexible mapping to add/drop low-speed tributary signals from SDH signals directly, without using multiple multiplexing/demultiplexing devices, thus reducing signal loss and investment in devices.

1.1.2  POS

Packet over SONET/SDH (POS) is a technology popular in WAN and MAN. POS maps length-variable packets directly to SONET synchronous payloads and uses the SONET physical layer transmission standard. It offers high-speed, reliable, and point-to-point data connectivity. It can support packet-switched data such as IP packets.

The POS interface on your device supports PPP, Frame Relay, and HDLC at the data link layer and IP at the network layer. The rate of POS interfaces may be different depending on your device. The rate can be STM-1 (155 Mbps), STM-4c (622 Mbps), and STM-16c/STM-16 (2.5 Gbps), each four times the immediate lower level.

1.2  Configuring a POS Interface

Before you configure the link layer and network layer protocols on a POS interface, you must configure its physical parameters. In addition, to have the interface participate in backup, configure the backup parameters; to set up firewall on the interface, configure packet-filtering rules.

Follow these steps to configure a POS interface:

To do...	Use the command...	Remarks
Enter system view	system-view	––
Enter POS interface view	interface pos interface-number	Required
Set the clock mode	clock { master | slave }	Optional The default is slave.
Set the CRC length	crc { 16 | 32 }	Optional The default is 32 bits.
Set the loopback mode	loopback { local | remote }	Optional Disabled by default
Configure the overhead byte	flag { c2 | { j0 | j1 } { sdh | sonet } } flag-value	Optional By default, SDH framing applies. The default is hexadecimal 16 for C2. In SDH framing, the defaults are 15 0x0 for both J0 and J1. In SONET framing, the defaults are 0x01 for J0 and 62 0x0 for J1.
Set the framing format	frame-format { sdh | sonet }	Optional The default is SDH.
Configure scrambling	scramble	Optional Enabled by default.
Set the link protocol type	link-protocol ppp	Optional The default is PPP.
Set the PPP negotiation timeout time	ppp timer negotiate seconds	Optional The default is 3 seconds.
Set the interval to send keepalive packets	timer hold seconds	Optional The default is 10 seconds.
Set the interface MTU	mtu size	Optional The default is 1,500 bytes.
Set the SD/SF threshold for the interface	threshold { sd | sf } value	Optional The SD threshold defaults to 10e-6. The SF threshold defaults to 10e-3.
Shut down the POS interface	shutdown	Optional POS interfaces are enabled by default.

 

 

1.3  Displaying and Maintaining POS Interfaces

To do...	Use the command...	Remarks
Display the information of a POS interface	display interface pos [ interface-number ]	Available in any view
Display the IP-related information of a POS interface	display ip interface pos interface-number
Display the IPv6-related information of a POS interface	display ipv6 interface pos interface-number

 

1.4  POS Interface Configuration Example

1.4.1  Network Requirements

Use a pair of optic fibers (respectively for receiving and sending data) to connect the POS interfaces on Switch A and Switch B.

Encapsulate the interfaces with PPP.

1.4.2  Network Diagram

Figure 1-1 Network diagram for connecting two POS interfaces through fiber

1.4.3  Configuration procedure

1)         Configure Switch A

# Configure interface POS 1/1/1, setting all its physical parameters to the defaults.

<SwitchA> system-view

System View: return to User View with Ctrl+Z

[SwitchA] interface pos 1/1/1

[SwitchA-Pos1/1/1] ip address 10.110.1.10 255.255.255.0

[SwitchA-Pos1/1/1] link-protocol ppp

[SwitchA-Pos1/1/1] mtu 1500

[SwitchA-Pos1/1/1] shutdown

[SwitchA-Pos1/1/1] undo shutdown

2)         Configure Switch B

# Configure interface POS 4/1/1.

<SwitchB> system-view

System View: return to User View with Ctrl+Z

[SwitchB] interface pos 4/1/1

# Set the clock mode to master and other physical parameters to the defaults.

[SwitchB-Pos4/1/1] clock master

[SwitchB-Pos4/1/1] ip address 10.110.1.11 255.255.255.0

[SwitchB-Pos4/1/1] link-protocol ppp

[SwitchB-Pos4/1/1] mtu 1500

[SwitchB-Pos4/1/1] shutdown

[SwitchB-Pos4/1/1] undo shutdown

You can check the interface connectivity between the POS interfaces with the display interface pos command and test network connectivity with the ping command.

1.5  Troubleshooting POS Interfaces

Symptom 1:

The physical state of the POS interface is down.

Solution:

l           Check that the transmitting and receiving fibers-optic are correctly connected to the POS interface. If you connect the two ends of a fiber-optic to the transmitting end and the receiving end of the same POS interface, you can see the message “loopback detected” on the screen when executing the display interface command even if you have not enabled loopback.

l           If your switch is connected to another switch directly, check that the clock mode of the local POS interface is opposite to that on the connected POS interface.

Symptom 2: The physical layer is up but the link layer is down.

Solution:

Check that:

l           The configurations of clock, scrambling and other physical interfaces are consistent on the two sides.

l           The same link layer protocol is configured on two sides.

l           Both ends are assigned IP addresses.

Symptom 3:

A great amount of IP packets are dropped.

Solution:

Check that:

l           The correct clock mode is configured on the POS interface. If not, enormous amount of CRC errors can be generated.

l           Check that the MTU configuration is appropriate.