Cisco Knowledge Suite Cisco SystemsCisco Press

Cutting Edge
Core Reference
Guided Learning
Networking Architecture
Internet Protocols (IP)
Network Protocols
Transport and Application Protocols
Desktop Protocols
Security and Troubleshooting
Network Resources and Management
Integrated Services

Cabling the WAN


< Back Contents Next >

Assembling and Cabling Cisco Devices



Cabling the LAN



Cabling the WAN



Setting Up Console Connections to Cisco Devices






Review Questions

Save to MyCKS

Interconnecting Cisco Network Devices

From: Interconnecting Cisco Network Devices
Author: Stephen McQuerry
Publisher: Cisco Press (53)
More Information

Cabling the WAN

In order to connect our networks to other remote networks, it is sometimes necessary to utilize WAN services. WAN services provide different connection methods, and the cabling standards differ from those of LANs. It is therefore important to understand the types of cabling needed to connect to these services. Figure 2-10 illustrates the cabling in a typical WAN.

This section discusses the following topics:

Figure 2-10. WAN Cabling

WAN Physical Layer Implementations

Many physical implementations carry traffic across the WAN. Needs vary, depending on the distance of the equipment from the services, the speed, and the actual service itself. Figure 2-11 lists a subset of the physical implementations that support some of the more common WAN solutions today. The type of physical layer you will choose depends on the distance, speed, and what type of interface in which you need to connect.

Figure 2-11. WAN Physical Layer Implementations

Serial connections are used to support WAN services such as dedicated leased lines running Point-to-Point Protocol (PPP), High-Level Data Link Control (HDLC), or Frame Relay encapsulations at Layer 2. The speeds of the connections typically range from 56 Kbps to T1/E1 (1.544/2.048 Mbps). Other WAN services, such as ISDN, offer dial-on-demand connections or dial backup services. An ISDN BRI (Basic Rate Interface) is composed of two 64 Kbps Bearer channels for data, and one Delta channel at 16 Kbps used for signaling and other link-management tasks. PPP is typically used to carry data over the B channels. You will learn more about the data link operation, ISDN, and Frame Relay in Chapters 11, 12, and 13.

Differentiating Between WAN Serial Connections

Serial transmission is a method of data transmission in which bits of data are transmitted over a single channel. This one-at-a-time transmission contrasts with parallel data transmission, which passes several bits at a time. For long-distance communication, WANs use serial transmission. To carry the energy represented in bits, serial channels use a specific electromagnetic or optical frequency range.

Frequencies, described in terms of their cycles per second (or Hertz), function as a band or spectrum for communications—for example, the signals transmitted over voice-grade telephone lines up to 3 kHz (kilo, or thousand, Hertz). The size of this frequency is called bandwidth.

Several types of physical connections allow us to connect to serial WAN services. Depending on the physical implementation you choose, or the physical implementation imposed by your provider, you will need to select the correct serial cable type to use with your router. Figure 2-12 shows the different serial connector options available. Note that serial ports on most Cisco routers use a proprietary 60-pin connector. Therefore, the router-ends of most port adapter cables use a male 60-pin connector, while the network ends of the adapter cable must match the specific WAN service hardware.

Figure 2-12. WAN Serial Connection Options

Another way to express bandwidth is to specify the amount of data in bits per second (bps) that can be carried using two of the physical layer implementations shown in Figure 2-12. Table 2-5 compares the physical standards for WAN serial connection options.

Table 2-5. Comparison of Physical Standards

Data in bps

Distance (Meters) EIA/TIA-232

Distance (Meters) EIA/TIA-449



















T1 (1,544,000 bps)



Cabling Routers for Serial Connections

In addition to determining cable type, you will need to determine if you need data terminal equipment (DTE) or data circuit-terminating equipment (DCE) connectors for your equipment. The DTE is the endpoint of the user's device on the WAN link. The DCE is typically the point where responsibility for delivering data passes into the hands of the service provider.

As shown in Figure 2-13, if you are connecting directly to a service provider, or to a device that will perform signal clocking, the router is a DTE and needs a DTE serial cable. This is typically the case for routers.

Figure 2-13. DTE/DCE Connections

There are cases, however, where the router will need to be the DCE. For example, if you are performing a back-to-back router scenario in a test environment, one of the routers will be a DTE, and the other will be a DCE.

When you're cabling routers for serial connectivity, the routers will have either a fixed or modular port. The type of port being used will affect the syntax you use later to configure each interface.

Figure 2-14 shows an example of a router with fixed serial ports (interfaces). Each port is given a label of port type and port number, such as “serial 0.” To configure a fixed interface, you specify the interface using this convention.

Figure 2-14. Fixed Serial Ports on a 2500 Router

Other routers have modular ports. Figure 2-15 shows examples of routers with modular serial ports. Usually each port is given a label of port type, slot number (the location of the module), and port number. To configure a port on a modular card, you will be asked to specify the interface using this convention:

  • <port type> <slot number>/<port number>

An example would be serial 1/0.

Figure 2-15. Modular Serial Ports on a 1603 Router and a 3640 Router


Depending on the type of router you have, port designation convention might change. For example, some high-end routers such as a 7500 series device can have a virtual interface processor. Designation of these ports would also include the VIP slot:

<port type> <slot number>/<port adapter number>/<port number>

An example would be serial 1/0/0.


The 1603 router shown in Figure 2-15 has both fixed and modular serial interfaces. Even though the serial port shown is a modular interface, you configure it as though it were fixed, using a label of port type and port number, such as serial 0.

Cabling Routers for ISDN BRI Connections

With BRI, there are two types of interfaces that you can use—BRI S/T and BRI U. To determine which interface type you need, you must determine whether you or the service provider will provide an NT1 device.

An NT1 device is an intermediate device between the router and the service provider's ISDN switch (the cloud) that is used to connect four-wire subscriber wiring to the conventional two-wire local loop. NT1 refers to a network termination type 1 device. In North America, the NT1 is typically provided by the customer, while in the rest of the world, the service provider provides the NT1 device.

If you need to provide the NT1 device, you can use an ISDN BRI with a U interface; a U interface indicates that the NT1 device is built in. If you are using an external NT1 device, or if your service provider uses an NT1 device, the router needs an ISDN BRI S/T interface. Because routers can have multiple ISDN interface types, you need to determine which interface you need when you purchase the router. You can determine which type of ISDN connector the router has by looking at the port label. Figure 2-16 shows the different port types for the ISDN interface.

Figure 2-16. ISDN Port Types

To interconnect the ISDN BRI port to the service provider device, you will use a UTP category 5 straight-through cable.


It is important to insert a cable running from an ISDN BRI port only to an ISDN jack or an ISDN switch. ISDN BRI uses voltages that can seriously damage non-ISDN devices.


< Back Contents Next >

Save to MyCKS


Breaking News

One of the primary architects of OpenCable, Michael Adams, explains the key concepts of this initiative in his book OpenCable Architecture.

Expert Advice

Ralph Droms, Ph.D., author of The DHCP Handbook and chair of the IETF Dynamic Host Configuration Working Group, guides you to his top picks for reliable DHCP-related information.

Just Published

Residential Broadband, Second Edition
by George Abe

Introduces the topics surrounding high-speed networks to the home. It is written for anyone seeking a broad-based familiarity with the issues of residential broadband (RBB) including product developers, engineers, network designers, business people, professionals in legal and regulatory positions, and industry analysts.


From the Brains at InformIT


Contact Us


Copyright, Terms & Conditions


Privacy Policy


© Copyright 2000 InformIT. All rights reserved.