This chapter covers the following topics:
Dedicated Local Access Configuration
Switched Local Access Configuration
Local Exchange Carrier (LEC) Central Office (CO) Configuration
Access to a network service provider's (NSP) services requires a physical connection (
is a cable that is attached to the ground between two end-points -for example, a telephone line between telephone poles. Landlines can be
is a permanent connection terminating (from the customer's perspective) at either the local exchange carrier's (LEC) or Interexchange Carrier's (IXC) central office (CO). Examples of dedicated access circuits are DS0, DS1/DS3, or OC-x. Switched access is not a permanent connection, requiring the customer/end-
Plain old telephone service (POTS) - the telephone system we know and use today. POTS runs across the public switched telephone network (PSTN).
Integrated services digital network ( ISDN ) , an international communications standard for sending voice, video, and data over digital telephone lines or normal telephone wires. ISDN is available in two offerings: Basic Rate Interface (BRI) at 144 Kbps (2B + D) and PRI at 1536 Kbps (23B + D). The B(earer) channels are 64 Kbps and carry the signal (voice/data), and the D(ata) channel carries the signaling: 16 Kbps for BRI, and 64 Kbps for PRI.
Two forms of dedicated local access exist, based on the network-side termination point:
. LEC dedicated access terminates at the customer site and the LEC CO, and IXC dedicated access terminates at the customer site and the IXC CO (passing through the LEC CO). Each configuration provides certain advantages, depending on the customer's networking requirements (for example, local dial-tone, IntraLATA data service, or InterLATA data services). Regardless of where the local loop terminates (LEC or IXC), the local loop can be
Local Access and Transport Area
(LATA) is a U.S.
connection is made between two telephone companies within the same region. An
connection is established between two local exchange
Provisions guiding the use of LATAs are outlined in the Telecommunications Act of 1996.
Figure 6-1 illustrates local access terminating at the LEC CO.
This configuration is implemented when any one (or more) of the following customer communications requirements are needed:
Local dial-tone (voice services)
IntraLATA data services
Any LEC-provided services, such as LEC-provided Internet access
Multiple IXC data services
Figure 6-2 illustrates local access terminating at an IXC CO.
This configuration is implemented when any one or more of the following customer communications requirements are needed:
Long distance (LD) dial-tone (voice service)
InterLATA data services
Any other IXC-provided services, such as IXC-provided Internet access
Note that in both configurations (Figures 6-1 and 6-2), the facilities between the LEC CO and the customer site are referred to as the
, or the
. These terms are
Whether the local access terminates at the LEC or IXC CO, a network interface unit (NIU), also referred to as a network termination unit (NTU), is required at the customer premise to terminate the other end of the access circuit. Figure 6-3 illustrates the placement of the NIU or NTU.
A modular jack is required for customers to connect their communications equipment to the NIU, in
Technical Note: Loopback Testing
Loopback testing is a means by which a circuit can be
There are three types of loopback testing:
Often the customer's communications equipment is in another space, separated from the NIU. In these instances, the demarc is extended from the NIU to the desired termination point. If this distance exceeds the maximum distance limitations for the cabling used, one or more repeaters can be installed to extend the signal reach.
This extended demarc can be installed by the customer or the LEC and can take the form of patch panels,
Although an extended demarc can be ordered from the LEC, often the end customer will perform this extension in-house.
Punch-down blocks, also known as
, were the predecessors to distribution frame patch panels. A 66-block is a punch-down block with type 66 connectors; hence the
Figure 6-4 illustrates a 66-block.
In this figure, columns 1 and 2 are connected, as are columns 3 and 4. These column pairs (1/2 and 3/4) are often prewired. Each of the four
Bridge clips are little metal clips used to wire "straight through," for example, to connect columns 2 and 3. If it is necessary to crosswire a circuit, you cannot use bridging clips to connect a wire from column 2 in one row to column 3 in a different row; in that case, the connection must be wired. This arrangement has made 66-blocks very popular in telephone and network cable management.
Figure 6-5 illustrates what a 66-block installation would look like at a customer premise.
Figure 6-6 illustrates a complete dedicated circuit termination at the customer premise, with a 66-block used to extend the demarc from the NIU to the CSU/DSU.