Overview of the T1 or E1 Interface Module

Table 1. Feature History

Feature Name

Release Information

Description

48-Port T1/E1 CEM Interface Module support in ASR-920-12SZ-IM

Cisco IOS XE Cupertino 17.8.1

The router supports the following features for the 48-Port T1/E1 Circuit Emulation (CEM) interface module:

  • Basic mode, and T1 or E1 controller required configurations

  • CEM clocking, ACR, and DCR

  • CEM pseudowires such as Structure-Agnostic TDM over Packet (SATOP) and Circuit Emulation over Packet-Switched Network (CESoPSN)

  • BERT, loopback, and alarms

  • Performance monitoring

The support for the interface module provides cost-effective delivery of CEM over a packet-based network (MPLS).

The T1 or E1 interface module delivers T1 or E1 connectivity on the router with the RSP3 module. The module can be software configured as either T1 mode or E1 mode per interface module The module provides physical connectivity using a single high-density connector and requires a breakout cable and patch panel for individual port connections.

The T1 or E1 interface module supports the following modes:

  • T1

  • E1


Note


Mixing T1 and E1 ports on the same interface module is not supported.


CEM configurations are supported on different modes on the interface module. The troubleshooting, monitoring, and redundancy features are supported on the module. The module can be clocked from a line or from an internal clock source. The table describes the configurations and features for the modes that are supported on the T1 or E1 interface module.

Table 2. Configurations on T1 or E1 Interface Module
T1 E1

Required Configurations

Mode

Yes

Yes

Internal/Line Clock Source

Yes

Yes

ACR/DCR Clock

Yes

Yes

CEM Configurations

Structure-Agnostic TDM over Packet (SATOP) (Framed/Unframed)

Yes

Yes

Circuit Emulation over Packet-Switched Network (CESoPSN)

Yes

Yes

Troubleshooting Features

Bit Error Rate Testing (BERT)

Yes

Yes

Loopback

Yes

Yes

Monitoring Features

Performance Monitoring

Yes

Yes

Restrictions for Configuring T1 or E1 Interfaces

  • You can configure CEM to support serial interface configuration.

  • The card can be configured either in the T1 or E1 mode. A combination of T1 and E1 ports is not supported.

Circuit Emulation

Circuit Emulation (CEM) is a technology that provides a protocol-independent transport over IP/MPLS networks. It enables proprietary or legacy applications to be carried transparently to the destination, similar to a leased line.

CEM provides a bridge between a Time-Division Multiplexing (TDM) network and a Multiprotocol Label Switching (MPLS) network. The router encapsulates the TDM data in the MPLS packets and sends the data over a CEM pseudowire to the remote Provider Edge (PE) router. As a result, CEM functions as a physical communication link across the packet network.

The router supports the pseudowire type that utilizes CEM transport: Structure-Agnostic TDM over Packet (SAToP) and Circuit Emulation Service over Packet-Switched Network (CESoPSN).

L2VPN over IP/MPLS is supported on the interface modules.


Note


We recommend that you configure the controller in the administratively up mode. Configuration under the administratively down mode is not recommended and it might cause configuration errors.



Note


The default behaviour of the CEM pseudowire is always UP irrespective of the controller alarms.


Overview of CEM Pseudowire

Pseudowires manage encapsulation, timing, order, and other operations in order to make it transparent to users. The pseudowire tunnel acts as an unshared link or circuit of the emulated service. CEM is a way to carry TDM circuits over packet switched network. CEM embeds the TDM circuits into packets, encapsulates them into an appropriate header, and then sends that through Packet Switched Network. The receiver side of CEM restores the TDM circuits from packets.

Configuring Pseudowire

Cisco Pseudowire Emulation Edge-to-Edge (PWE3) allows you to transport traffic by using traditional services such as T1/E1 over a packet-based backhaul technology such as MPLS or IP. A pseudowire (PW) consists of a connection between two provider edge (PE) chassis that connects two attachment circuits (ACs), such as T1/E1 or T3 /E3 links.

Framed Structure-Agnostic TDM over Packet (SAToP)

Framed Structure-Agnostic TDM over Packet (SAToP) is required to detect an incoming AIS alarm in the DS1 SAToP mode. An AIS alarm indicates a problem with the line that is upstream from the DS1 network element connected to the interface. Framed SAToP further helps in the detection of a packet drop.

In case of unframed mode of SAToP, data received from the Customer Edge (CE) device is transported ove the pseudowire. If the Provider Edge (PE) device receives a Loss of Frame (LOF) signal or Remote Alarm Indication (RAI) signal from a CE, the PE can only transmit the signal that is detected by the CE device. With the introduction of Framed SAToP, when the PE device receives the LOF or RAI signal, the PE device can detect the alarm for SAToP. Thus, the alarm can be detected earlier in the network. This helps in enhanced performance.


Note


Framing type should be maintained same in all routers end to end.


Difference between Framed and Unframed SAToP:

  1. For unframed SAToP, the incoming signal is transmitted to the far end. This signal is not analyzed by the PE device. Hence, no alarm is reported.

  2. For framed SAToP, the incoming signal is analyzed but is not terminated. If a LOF or RAI signal is detected, the remote PE detects the signals and transmits towards the remote CE.

Difference between Framed SAToP and CESoP:

Table 3. Behaviour Difference between Unframed SAToP, Framed SAToP, and CESoP on LOF Alarm
Modes

Alarm Detected at PE

Controller Status at PE

Alarm Detected at CE (Remote)

Framing Bits Generationat PE (Remote)

Framing Bits Terminated at PE (Remote)

Unframed SAToP

None

Up

LOF

No

No

Framed SAToP

LOF

Down (Data path remians up)

AIS12

Yes

No

CESOP

LOF

Down (Data path remians up)

AIS

Yes

Yes

1 AIS—Cisco IOS XE Amsterdam 17.3.1 to later releases
2 LOF—Support until Cisco IOS XE Amsterdam 17.2.1
Table 4. Behaviour Difference between Unframed SAToP, Framed SAToP, and CESoP on RDI Alarm
Modes

Alarm Detected at PE

Controller Status at PE

Alarm Detected at CE (Remote)

Framing Bits Generation at PE (Remote)

Framing Bits Terminated at PE (Remote)

Unframed SAToP

None

Up

RDI

No

No

Framed SAToP

RDI

Down (data path remains up)

RDI

No

No

CESOP

RDI

Down (data path remains up)

RDI

M-bit is set into control word

Yes

Table 5. Behaviour Difference between Unframed SAToP, Framed SAToP, and CESoP on AIS alarm

Modes

Alarm Detected at PE

Controller Status at PE

Alarm Detected at CE (Remote)

Framing Bits Generation at PE (Remote)

Framing Bits Terminated at PE (Remote)

Unframed SAToP

AIS

Down (data path remains up)

AIS

No

No

Framed SAToP

AIS

Down (data path remains up)

AIS

No

No

CESOP

AIS

Down (data path remains up)

AIS

L-bit is set into control word

Yes

Remote Loopback from CE to PE Detection:

Framed SAToP does not detect any loopback.

Loopback Detected at PE

Controller Status at PE (Remote)

Controller Status at CE (Remote)

Unframed SAToP

No

Not in Loopback

Loopback

Framed SAToP

No

Not in Loopback

Loopback

CESOP

Yes

Loopback

Not in loopback

Circuit Emulation Service over Packet-Switched Network

CESoPSN is a method for encapsulating structured (NxDS0) TDM signals as pseudowires over packet switching networks.

Restrictions for CESoPSN on T1 Interface

  • The maximum number of CEM interface supported is 192.

  • DS0 loopback is not supported on the T1 interface.

  • Alarm forwarding is not supported on the T1 interface.

  • Card protection is not supported on the T1 interface.