2-8 Packet-Over-SONET Interfaces

Packet-Over-SONET is available on POSIP and POSPA router interfaces.
POS provides an OC-3 155.520 Mbps interface that is compatible with SONET and Synchronous Digital Hierarchy (SDH) networks.
Dynamic Packet Transport (DPT) provides IP-over-SONET on an OC-12c SRP interface.
SRP interfaces provide fault tolerance by maintaining a topology map of all nodes on the ring. Topology discovery packets accumulate the MAC addresses of each node on the ring.
Automatic Protection Switching (APS) provides switchover of POS circuits, usually in a telco environment. Two SONET connections are required, both configured for APS.

Configuration

Select and configure one of the Packet-Over-SONET interfaces described in the following sections (OC-3, DPT OC-12c, APS on POS).

Configuring an OC-3 POS Interface

Select the interface:
```
(global) interface pos slot/number
```
(Optional) Select framing:
```
(interface) pos framing-sdh
```
By default, the POS interface uses SONET STS-3c framing. The framing-sdh keyword enables SDH STM-1 framing instead.
(Optional) Set the clock source:
```
(interface) clock source
```
By default, the transmit clock is derived from the recovered receive clock. The clock source command enables the internal clock as the transmit clock.
(Optional) Enable payload scrambling:
```
(interface) pos scramble-atm
```
If necessary, payload scrambling can be enabled to provide the proper bit transition density. Scrambling must be enabled on both ends of the POS connection.
(Optional) Enable loopback tests:
```
(interface) loop internal
```
-OR-
```
(interface) loop line
```
For POS testing, the interface can be looped internally (internal) or looped at the remote POS interface (line).

Configuring a DPT OC-12c POS Interface

Select the interface:
```
(global) interface srp slot/number
```
(Optional) Set the topology update timer:
```
(interface) srp topology-timer seconds
```
Topology discovery packets are sent out at intervals of seconds (1 to 600; the default is 10 seconds).
(Optional) Configure Intelligent Protection Switching (IPS).
1. Set the wait-to-restore request timer:
```
(interface) srp ips wtr-timer seconds
```
  The WTR timer can be set in seconds (10 to 600; the default is 60 seconds). This timer reduces ring oscillations by keeping a wrap condition in place for seconds after a wrap is removed.
2. Set the IPS message timer:
```
(interface) srp ips timer seconds [a | b]
```
  The frequency of IPS requests is set to an interval of seconds (1 to 60; the default is 1 second). The timer can be applied to either side of the ring if desired.
3. Initiate a ring wrap:
```
(interface) srp ips request {forced-switch | manual-switch} {a | b}
```
  A wrap condition is inserted on the ring. The forced-switch option causes the wrap to remain in effect until it is removed. The manual-switch option causes a wrap, but neither the command nor the wrap condition persists across a reload. The a keyword specifies a wrap on side A (the outer ring receive fiber), and b wraps on side B (the inner ring receive fiber).

Configuring APS on POS Interfaces

Select the working and protect interfaces.
1. Identify the working interface:
```
(global) interface pos slot/number



(interface) aps working circuit
```
  The working interface is used until a failure or a condition occurs to switch over to the protect interface. The circuit field is an arbitrary circuit number that links the working and protect interfaces.
2. Identify the protect interface:
```
(global) interface pos slot/number



(interface) aps protect circuit protect-ip-address
```
  The protect interface is identified and associated with the working interface that has the same arbitrary circuit number. The protect-ip-address field gives the IP address of the router with the working interface.
(Optional) Configure authentication:
```
(interface) aps authenticate string
```
Packets on the out-of-band POS channel are accepted if the authentication string (up to eight characters) matches string. Authentication must be configured on both working and protect interfaces.
(Optional) Set the APS timers:
```
(interface) aps timers hello hold
```
A POS interface sends a hello packet every hello seconds (the default is 1 second). If a hello packet is not received before the hold interval expires (the default is 3 seconds), the interface is declared down.
(Optional) Group APS interfaces:
```
(interface) aps group group-number
```
If more than one working and protect interface is used, the interfaces can be grouped. Each interface must be assigned to an arbitrary group-number (the default is 0).
(Optional) Configure APS switchover.
1. Lock out an interface:
```
(interface) aps lockout circuit
```
  A protect interface can be locked out to prevent it from being used. The circuit number must be given to identify the working/protect pair.
2. Manually switch to a protect interface:
```
(interface) aps manual circuit
```
  Normally, switchover to a protect circuit is automatic, based on interface or peer failure. However, a circuit can be manually switched from a working interface to a protect interface for the circuit number.
3. Automatically revert after a switchover:
```
(interface) aps revert minutes
```
  By default, the protect circuit must be manually switched back to the working circuit as soon as the working circuit is available. If desired, the switch back to a restored working circuit can be automatic, after minutes have elapsed.

Example

A router is configured with two PoS interfaces. The first interface is the working APS interface, and the second is the protect interface. The router exchanges APS control packets with itself to determine whether the working interface is down. The router also has a Dynamic Packet Transport OC-12 SRP interface that has an IP address configured.

interface pos 4/0

       description PoS OC-3 connection #1

       ip address 192.168.57.1 255.255.255.0

       aps working 1

interface pos 5/0

       description PoS OC-3 connection #2

       ip address 192.168.58.1 255.255.255.0

       aps protect 1 192.168.57.1

interface srp 5/0

       description DPT OC-12c connection

       ip address 10.1.1.1 255.255.255.0

< Free Open Study >

Posts Related to 2-8 Packet-Over-SONET Interfaces

2-7 Synchronous Serial Interfaces
< Free Open Study > Synchronous serial interfaces transport data and a clock signal across an end-to- end connection. Serial interfaces include High-Speed Serial ...
3-2 ISDN
< Free Open Study > Primary Rate Interface (PRI) has 23 B (bearer) channels and one D (data) channel in North America and Japan, ...
2-11 ATM Interfaces
< Free Open Study > ATM interfaces use a default MTU of 4470 bytes, a maximum of 2048 virtual circuits (VCs), and 1024 Virtual ...
CCIE Security Lab Exam Topics (blueprint) v3.0
Please review the Lab Exam Overview for general information about the CCIE Security lab exam. This lab exam blueprint v3.0 is a detailed outline of ...
1-4 System Time
< Free Open Study > System time is maintained by the IOS software. When a router is initialized, the system time is set from ...
4-1 Transparent Bridging
< Free Open Study > Not all network protocols can be routed, so it is sometimes necessary to bridge these protocols. Cisco routers support ...
2-3 Token Ring Interfaces
< Free Open Study > Token Ring networks can operate at either 4 Mbps or 16 Mbps. A token is passed around a ring ...
2-2 FDDI Interfaces
< Free Open Study > FDDI supports 100 Mbps data transfer rates using a token-passing scheme. A dual counter-rotating fiber-optic ring makes up an ...
1-3 Cisco Discovery Protocol (CDP)
< Free Open Study > Cisco Discovery Protocol allows for dynamic discovery of directly connected Cisco devices across SNAP-supported media. CDP runs on all ...
EIGRP Neighbor Relationships
< Free Open Study > Unlike IGRP, EIGRP must establish neighbor relationships before updates are sent out. When an EIGRP process is configured on the ...