The Cisco 766 LEDs

The Cisco 766 LEDs

These LEDs are read as follows:
RD The ready LED is illuminated when the router is operating normally. You can use it to verify
that a successful power-on self-test (POST) has been completed and that power is available
to the device.
NT1 For routers with an internal ISDN NT1, this LED displays the status of the ISDN connection.
When steady, the ISDN switch and the NT1 are synchronized; when it’s blinking, the
connection is attempting synchronization.
LINE The LINE LED indicates that framing between the router and the ISDN switch has
been established.
RD NT1 LINE
CH1 RXD TXD
LAN RXD TXD
PH1 PH2 CH2 RXD LAN
LAN This light indicates that the Ethernet interface on the router is active and that a frame has
been sent or received within the past 60 seconds. A link light on the back of the router denotes
a valid connection.
LAN RXD The LAN received LED blinks upon receipt of a frame on the Ethernet interface.
LAN TXD The LAN transmitted LED blinks when frames are sent from the router onto the
Ethernet link.
CH1 and CH2 These LEDs indicate the status of the two B channels on the ISDN BRI. They
illuminate steadily when the connection is established and blink during the negotiation process.
CH1 RXD and CH2 RXD These LEDs reflect the receipt of packets on their respective ISDN
BRI channels. Each packet generates a blink of the LED.
CH1 TXD and CH2 TXD These LEDs reflect the transmission of packets on the respective
ISDN BRI channel. Each packet generates a blink of the LED.
PH1 and PH2 For routers so equipped, these LEDs provide information regarding the use
of the POTS ports on the router. These ports can be used for telephone, fax, or analog
modem services.

NOTE:Remember the significance of each LED, including its color, for the exam. Thisinformation can be helpful in live troubleshooting as well.


Summary
As with most aspects of networking, the Physical layer provides the foundation for both LANbased
solutions and remote access ones. Remote access refers to the use of longer range solutions
than the 100-meter Ethernet solutions commonly found in local area networks (LANs).
Remote access technologies include dial-up lines, ISDN BRI and PRI technologies, leased lines,
Frame Relay, cable modem, and xDSL. Each of these solutions provides the designer with various
benefits and detriments, including availability, cost, and complexity. For example, dial-up lines
are widely available but are relatively expensive and of lower capacity than Frame Relay.
In addition to the physical circuits between remote locations, remote access solutions also
require the physical termination equipment. This customer premises equipment (CPE) includes
the router, a DSU/CSU where necessary, or a modem. ISDN also incorporates different types of
terminations that the administrator needs to keep in mind.
Routers for remote access solutions vary widely within the Cisco product line. The Cisco
800 series routers are well suited to small offices and home users, whereas the Cisco 3600XM/3700
platform affords more expansion capabilities and performance.
The Remote Access exam materials might continue to focus on the older Cisco 700 series
ISDN routers. Although these routers are no longer available, success on the Remote Access exam requires a high level of understanding of the platform and its characteristics. Specific
attention should be paid to the interface types of the model, in addition to the fact that the
700 series does not run an IOS image.
It’s also important to note that the materials in this chapter focus on the exam and the information
needed for the exam, rather than the solutions necessary in modern remote access solutions.
For example, the Remote Access exam fails to note ATM technologies, which are quite
common in many networks today. This failure should be of concern to the reader and warrants
further augmentation beyond the focus of this text.

Exam Essentials
Understand the ISDN terminations of the Cisco 700 series platforms. The Cisco 776 router
includes both the S/T and the U type ISDN interfaces, for example, whereas the other 700 series
platforms presented provide only the S/T interface. More information regarding these interfaces
is included in Chapter 26.
Know which remote access platforms are best suited to small offices and home offices. Cisco
recommends that users consider the Cisco 700, 800, 1000, and 1600 platforms for inexpensive
remote connectivity to small user populations.
Be familiar with the WAN connection types. Readers should be comfortable with Frame
Relay, ISDN, analog, leased-line, and X.25 connection options. As presented in this chapter,
analog connections are the most common. They are highly available, but the bandwidth provided
is quite limited and the costs associated with usage are quite high. X.25 is a reasonable
option, particularly outside of the United States, and it is well suited to poor line conditions.
Leased line and Frame Relay typically provide the highest bandwidth capabilities, with Frame
Relay adding the benefit of distance-insensitive pricing.
Know the differences between ISDN BRI and PRI technologies. ISDN BRI services operate
over a 144Kbps connection, divided into two 64Kbps channels (B, or bearer) and a single
16Kbps channel (D, or data). This is best used for the remote side of a remote access solution.
The ISDN PRI technology uses a T-1 or E-1 connection for transport and can provide 23 or 30
B channels, respectively.
Understand the differences between North American and European standards. The ISDN
Primary Rate Interface (PRI) in North America and Japan offers 23 B channels and one D channel
for a total interface rate of 1.544Mbps. ISDN PRI in Europe, Australia, and other parts of
the world provide 30 B channels plus one 64Kbps D channel.
Be familiar with the high-end router platforms for central office termination. Cisco recommends
a wide variety of platforms for aggregation points, including the AS5300 series, the Cisco
7000 series routers, and the smaller 3600 systems. Admittedly there is some inconsistency in
selecting these platforms; test takers would be advised to understand the platforms and select
the best answer for each question.
Understand the router platforms’ flexibility regarding configuration. Fixed-configuration
routers are limited with regard to future enhancements. These platforms include the 700 and
800 series. Modular routers—including the 1600, 2600XM, and 3600/3700 series—allow for
the addition or replacement of specific components, which can be used to add features without
the need for a forklift upgrade.