Daily Archives: July 21, 2013

DMARC / Network Interface Devices

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The demarcation point (DMARC) is the point at which the public switched telephone network (PSTN)ends and connects with the customer’s on-premises wiring (called Inside Wire or IW.)  Don’t confuse this with a NIU, it’s the same but different.

For residential locations you might have started off with an old Western Electric Company (WECO) lightning protector:

Lightning Protector

Used around 1915. The phone company line from the pole connected at the top binding posts marked “L” for “Line”, the house wiring connected to “I” for “Inside” and G for Ground. In later years the Bell System added copper straps that bypassed the fuses… unsure why.

The Western Electric Type 58A Protector, circa 1900, protects against lightning and other high voltages.

The Western Electric Type 58A Protector, circa 1900, protects against lightning and other high voltages.

 

After that they went to the carbon and porcelain blocks which were much smaller:

The carbon and porcelain block! In the presence of high voltage, the carbon blocks under the pressure of the spring would be moved to earth after the restraining glue melted. The whole thing had to be replaced.

The carbon and porcelain block! In the presence of high voltage, the carbon blocks under the pressure of the spring would be moved to earth after the restraining glue melted. The whole thing had to be replaced.

In the 1980s, Ma Bell started using a gas-filled protector. In the presence of high voltage, the gas ionizes and provides a path to earth (ground). When the voltage is removed, the protector returns to its normal state. Not a one shot deal like the older carbon ones.

 They got fancy with mounts  & attached them to the side of your house:

Use before the advent of Network Interfaces.

Use before the advent of Network Interfaces.

Then we come to the modern Network Interface Device, Telephone Network Interface, NID, NI, dmarc:

Modern NID

 

NID with Telco access opened.

NID with Telco access opened.

Check out http://catalog.corning.com/CableSystems/en-US/catalog/CategoryBrowser.aspx?cid=network_interface_devices_nids_web

 

What about businesses?  Do they just have 66 of these on the wall, one for each line?

Don’t be crazy,  they use a 66 block / M-Block / B-Block as a type of punchdown block to terminate the line.

Introduced in 1962, the term "66 block" simply reflects its Western Electric model number.

Introduced in 1962, the term “66 block” simply reflects its Western Electric model number.

They could also have a 110 block:

110 style blocks allow a much higher density of terminations in a given space than older style termination blocks

110 style blocks allow a much higher density of terminations in a given space than older style termination blocks.

 

 

http://pre-wire.tripod.com/interfaces_and_protectors.html

http://www.aflglobal.com/Products/Copper-Apparatus/Demarcation.aspx

DSU/CSU WIC LEDs

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A Data Service Unit/Channel Service Unit (DSU/CSU) WAN Interface Card ( WIC) these days is usually a blade on a router.  In the past, these were separate.  The CSU originated at AT&T as an interface to their non-switched digital data system. The DSU provides an interface to the data terminal equipment (DTE) using a standard (EIA/CCITT) interface. It also provides testing capabilities.  They evolved from standalone hardware, to shelf type systems and are now just a blade or Wan Interfacde Card (WIC) in a router.

Internal CSU/DSU WIC

Internal CSU/DSU WIC

 

External CSU/DSU Universal Shelf

External CSU/DSU Universal Shelf

 

External CSU/DSU

External CSU/DSU

 

The functions of the LEDs

WIC-1DSU-56K4 Front Panel DSU/CSU WIC to a 56/64-kbps Services Wall Jack RJ48S

LED Description
TD Data is being transmitted to the DTE interface.
RD Data is being received from the DTE interface.
LP Internal DSU/CSU is in loopback mode.
AL One of these alarm conditions is present: no receive signal, loss of frame signal from the remote station, or out of service signal from the remote station. This LED is off during normal operation.
CD Internal DSU/CSU in the WIC is communicating with another DSU/CSU. This LED is on during normal operation
WIC-1DSU-T1 Front Panel

Push this button to place the WIC into loopback mode. The service provider can send a signal to test the connection from your site to the central office switch. Push this button again to turn off loopback mode.

DSU/CSU WIC to a 56/64-kbps Services Wall Jack RJ48S

 

There are many manufactures, each with their own ideas of abbreviations so TD, TX, or TXD all mean you’re transmitting data. You may not have every LED but in general…

 

Power, PWR Power
ERR, ER Error indicator
AL, ALARM Critical alarm indicator
Loop, LP Diagnostic loopback indicator
SYNC, RS DTE sync indicator (Receive signa from telco)
 TD, TX, or TXD Transmit data
 RD, RX, or RXD Receive data
 CTS Clear to send (per flow control)
 CLOS Carrier loss of signal
 RLOS Receiver loss of signal

What you could see

Scenario Power Err Alarm Loop Sync TD RD CTS CLOS RLOS Description
1 flash flash Normal – up and passing traffic
2 Loopback mode detected from telco or configured in CPE
3 flash flash flash Circuit is experiencing errors, but still passing traffic.
4 CSU detects a total disconnect. Circuit disconnected/no cable.
5 Carrier loss of signal. Possible timing, switch misconfiguration, or circuit degradation
6 Receiver loss of signal. Possible timing, switch misconfiguration
11 No Power

See Also:

DataSMART-558 DataSMART_558 DataSmart_500_Series

http://www.cisco.com/en/US/products/hw/modules/ps3129/products_tech_note09186a00800b1501.shtml

http://www.cisco.com/en/US/products/hw/routers/ps233/products_tech_note09186a0080093c56.shtml

http://www.hypersurf.com/blog/t1-line/how-to-connect-a-business-t1-line/