Back to back T1 connection

Answered Question
May 21st, 2008

I am trying to simulate a t1 connection between 2 routers (both 2600 non xm with 12.2 ios), I have 2 serial t1 csu/dsu interface. I connected those using a cross over t1 cable. I assigned ip addresses and encapsulation ppp on both interface, layer 1 & 2 is up, i can ping both the interfaces. Now my question is i did not provide any clocking (both the interface shows up as serial interfaces, not t1 controller interface and did not accept clock source internal command in the router interface) but the t1 connection seems to be working. any info will be appreciated.

thankx

Correct Answer by miller811 about 8 years 9 months ago

T1 Configuration Commands

service-module t1 clock source

Syntax

service-module t1 clock source {line | internal}Description

The service-module t1 clock source command configures the T1 CSU/DSU module to accept the source of clock from the line (or network, in telco terminology) or to generate clocking internally. This command configures the CSU/DSU module, not the Cisco 2524-2525 interface to the CSU/DSU. The 2524-2525 interface is clocked from the CSU/DSU in either setting.

In most applications, the CSU/DSU should be configured with the clock source line. For back-to-back configurations, one CSU/DSU should be configured with clock source internal and the other with clock source line.

Application

This command applies to the T1 CSU/DSU.

Default

lineExample

interface serial 0

service-module t1 clock source lineservice-module t1 data-coding

Syntax

service-module t1 data-coding {normal | inverted}Description

The service-module t1 data-coding command determines whether the user data is inverted by the CSU/DSU. Data inversion makes every one bit in the data stream into a zero and every zero bit into a one. Data inversion is used with bit-oriented protocols like HDLC, PPP, and LAPB to ensure density on a T1 line with Alternate Mark Inversion (AMI) encoding. These bit-oriented protocols perform zero insertions after every five "one" bits in the data stream. This has the effect of ensuring at least one zero in every eight bits. If the data stream is then inverted, it ensures at least one out of every eight bits is a one.

This command cannot be used if the timeslots speed is set to 56.

Application

This command applies to the T1 CSU/DSU. It is the preferred method to ensure density on an AMI line.

Default

normalExample

interface serial 0

service-module t1 linecode ami

service-module t1 data-coding invertedservice-module t1 timeslots

Syntax

service-module t1 timeslots {all | } [speed 56 | 64]Description

The service-module t1 timeslots command configures which timeslots (DS-0s) are used in fractional T1 operation. It also configures the amount of bandwidth available to the router in each timeslot. In order to use the entire T1 line, set timeslots to all.

For fractional T1, the timeslots are configured as 1-4, 6, 7-10, for example.

When the speed is set to 56, the CSU/DSU takes one out of every eight bits of bandwidth and makes it a one bit. This is not the preferred method of ensuring ones density because of this loss of bandwidth. The preferred methods of ensuring density are service-module t1 linecode b8zs and service-module t1 data-coding inverted .

Application

This command applies to the T1 CSU/DSU.

Default

all

speed 64Example

interface serial 0

service-module t1 timeslots 1-10service-module t1 fdl

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Correct Answer
miller811 Thu, 05/22/2008 - 19:14

T1 Configuration Commands

service-module t1 clock source

Syntax

service-module t1 clock source {line | internal}Description

The service-module t1 clock source command configures the T1 CSU/DSU module to accept the source of clock from the line (or network, in telco terminology) or to generate clocking internally. This command configures the CSU/DSU module, not the Cisco 2524-2525 interface to the CSU/DSU. The 2524-2525 interface is clocked from the CSU/DSU in either setting.

In most applications, the CSU/DSU should be configured with the clock source line. For back-to-back configurations, one CSU/DSU should be configured with clock source internal and the other with clock source line.

Application

This command applies to the T1 CSU/DSU.

Default

lineExample

interface serial 0

service-module t1 clock source lineservice-module t1 data-coding

Syntax

service-module t1 data-coding {normal | inverted}Description

The service-module t1 data-coding command determines whether the user data is inverted by the CSU/DSU. Data inversion makes every one bit in the data stream into a zero and every zero bit into a one. Data inversion is used with bit-oriented protocols like HDLC, PPP, and LAPB to ensure density on a T1 line with Alternate Mark Inversion (AMI) encoding. These bit-oriented protocols perform zero insertions after every five "one" bits in the data stream. This has the effect of ensuring at least one zero in every eight bits. If the data stream is then inverted, it ensures at least one out of every eight bits is a one.

This command cannot be used if the timeslots speed is set to 56.

Application

This command applies to the T1 CSU/DSU. It is the preferred method to ensure density on an AMI line.

Default

normalExample

interface serial 0

service-module t1 linecode ami

service-module t1 data-coding invertedservice-module t1 timeslots

Syntax

service-module t1 timeslots {all | } [speed 56 | 64]Description

The service-module t1 timeslots command configures which timeslots (DS-0s) are used in fractional T1 operation. It also configures the amount of bandwidth available to the router in each timeslot. In order to use the entire T1 line, set timeslots to all.

For fractional T1, the timeslots are configured as 1-4, 6, 7-10, for example.

When the speed is set to 56, the CSU/DSU takes one out of every eight bits of bandwidth and makes it a one bit. This is not the preferred method of ensuring ones density because of this loss of bandwidth. The preferred methods of ensuring density are service-module t1 linecode b8zs and service-module t1 data-coding inverted .

Application

This command applies to the T1 CSU/DSU.

Default

all

speed 64Example

interface serial 0

service-module t1 timeslots 1-10service-module t1 fdl

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