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" frame-relay-inarp: Dynamically clears any IP-to-DLCI mappings created through the inverse
ARP function.
"
sh int type [number]: Displays DLCI and LMI information.
"
sh frame-relay lmi [type number]: Displays LMI statistics.
"
sh frame-relay map: Displays the current map entries.
" sh frame-relay pvc [type number [dlci]]: Displays the current PVC statistics.
"
sh frame-relay traffic: Display statistics about the Frame Relay traffic.
"
sh frame-relay route: Displays the static routes configured in a Cisco router.
"
sh frame-relay svc maplist: Displays all the SVCs under a specific map list.
PPP WAN Encapsulation
A serial port can also be configured to support a point-to-point protocol (PPP) interface. This configuration
enables the port to emulate PPP data encapsulation, which allows Cisco devices to communicate with
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non-Cisco devices across a WAN link. To ensure that devices from different vendors are interoperable, PPP
is considered a better tool, although more complex, than HDLC. PPP uses LCP (Link Control Protocol) to
negotiate basic line interoperability as well as a whole family of network control protocols for negotiating
individual Layer 3 protocols.
Remember To enable PPP encapsulation on a serial connection, the serial line must be configured to use PPP.
Then, the interface subcommand encapsulation ppp is used:
Router(config)# interface s0
Router(config-if)# encapsulation ppp
where s0 is the subinterface number being configured.
Here are a couple of URLs you may want to visit to learn more about Frame Relay and PPP protocols:
www.protocols.com/
www.rad.com/networks/tutorial.htm
Putting ISDN to Use
Instant Answer One of the best uses for ISDN PRI (Primary Rate Interface) services on a WAN (and one you
should know for the exam) is providing RAS (Remote Access Service) to your network. An ISDN PRI service
enables you to add 23 dialup access lines that can be used by remote workers to dial into the local network.
ISDN PRI makes this possible in two ways.
First, an ISDN PRI line can have separate phone numbers assigned to each of the 23 B- (bearer) channels.
Second, an ISDN PRI line can be terminated in an RJ-45 connector and directly connected to an ISDN PRI
interface on a Cisco 7000 series router. Together, these two features simplify the deployment of dialup RAS
connections by eliminating multiple phone lines, modems, and connecting cables.
Defining some ISDN basics
Several characteristics define and describe ISDN services, including the terminal type, reference points,
protocols, channelization, and the type of service (BRI versus PRI).
ISDN terminal types
Instant Answer Two types of terminals connect to an ISDN network:
" TE1: Terminal equipment type 1 complies with the ISDN standards.
"
TE2: Terminal equipment type 2 can be used only when a terminal adapter is applied because the
type existed before the ISDN standards were developed.
ISDN reference points
Instant Answer Four reference points designate logical interfaces within an ISDN configuration. Logical
interfaces are designated by the letters R, S, T, and U:
" Reference point R: Refers to the reference point between a non-ISDN device and a terminal adapter
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(TA).
"
Reference point S: Refers to the reference point between a user terminal and an NT2 device.
"
Reference point T: Refers to the reference point between an NT1 device and an NT2 device.
"
Reference point U: Refers to the reference point between an NT device and the line-termination
equipment on a providerÇs network.
ISDN protocols
Instant Answer There are three basic ISDN protocols, which are designated by the letters E, I, and Q in their
first letter:
" E Protocols support ISDN on the PSTN (Public Switched Telephone Network).
"
I Protocols define ISDN concepts, terminology, and services.
"
Q Protocols define signaling and switching.
Time-Saver Save yourself some grief and just memorize these bullets and those in the preceeding sections
(ÝISDN terminal typesÛ and ÝISDN reference pointsÛ). Trust us, you need to know this for the exam.
Identifying the ISDN twins: PRI and BRI
Remember ISDN service is defined to operate on a line that is comprised of multiple 64 Kbps B (bearer)
channels which carry payload (voice and data) and either a 16 Kbps or 64 Kbps D (data) channel that really
carries command signals. It may sound like the names assigned to the channels were switched somewhere
along the way, but they werenÇt. The bearer channel bears the payload and the data channel carries the data
about the payload. Remember this, because youÇre likely to be asked a question about this on the exam. There
are two flavors of ISDN service: Primary Rate Interface (PRI) and Basic Rate Interface (BRI), which we
cover in the next two sections.
Primary Rate Interface
Remember PRI service consists of 23 B channels and one D channel, all of which are 64 Kbps. This adds up
to 24 channels, the same number of channels available on a T1 circuit. What? You say that a T1 provides
1.544 Mbps of bandwidth and 24 times 64 Kbps only equals 1.536 Mbps? Where did the missing 8 Kbps go?
When a T1 line is channelized, 8 Kbps are lost to the channelization and cannot be used for either data or
control signaling.
Basic Rate Interface
Instant Answer BRI service consists of two B channels at 64 Kbps each and one D channel at 16 Kbps. This
adds up to a combined bandwidth of 144 Kbps (128 Kbps for the actual data and 16 Kbps used for control
signaling).
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Working with ISDN BRI on a Cisco Router [ Pobierz całość w formacie PDF ]