Chapter 11 began with an introduction to WAN technologies, including how they map to the lowest three layers of the OSI model. Different WAN concepts and connectivity techniques were also introduced, including point-to-point, circuit-switched, and packet-switched connections. A look at different carrier lines and speeds compared the differences between the T and E carrier systems […]

There are a variety of commands available for the purpose of monitoring Frame Relay on Cisco routers. Some of the commands that you should be familiar with include:

show frame-relay lmi. This command provides detailed statistics on LMI traffic passed between a router and its local Frame Relay switch, as well the LMI type is use.
show […]

Having looked at both Frame Relay concepts and an example of the communication process, let’s take a look at configuring a Cisco router to use Frame Relay. Our network in this example is configured as illustrated in the figure below. Notice that the PVC between Chicago and Toronto is a point-to-point interface, while the PVCs […]

Now that you’ve taken a look at the key concepts associated with Frame Relay, let’s take a look at an example of how communication occurs across a Frame relay network. I am going to assume that the network is configured as shown in the figure below, and that Computer1 at the New Orleans location ultimately […]

Back in the CIR section of this chapter, you looked at how the discard eligibility (DE) bit is used to “mark” frames that are transmitted above the CIR on a Frame relay virtual circuit. Making certain frames discard-eligible provides a way to determine which frames should be discarded first if a Frame Relay switch is […]

Back in Chapter 7 you looked at the concept of subinterface. Subinterfaces allow you to configure a single physical interface in such a way that it can act as multiple interfaces, each of which can have different properties. When configuring Frame Relay on a router, each virtual circuit is usually assigned to its own serial […]

The Local Management Interface (LMI) is a set of extensions to the Frame Relay protocol that were designed to provide information about the status of Frame Relay networks, and extend the technology’s capabilities. LMI is primarily concerned with diagnostic functions. For example, LMI is used to send keepalive messages between a router and a Frame […]

In order for upper-layer data to be transmitted across a Frame Relay network, it obviously needs to be framed. Cisco routers support two different Frame Relay encapsulation types, known as Cisco and IETF. By default, a Cisco router will use Cisco encapsulation on Frame Relay interfaces, unless IETF is explicitly specified. IETF encapsulation is usually […]

In order to ensure that data reaches its proper destination through a packet-switched network, virtual circuits somehow need to be identified. On a Frame relay network, virtual circuits are identified using what are known as Data Link Connection Identifiers (DLCIs).
A DLCI is a 10-bit number that is stored in the header of a frame that […]

When a company provisions a leased line from a service provider, that link provides a fixed, dedicated amount of bandwidth. For example, a company might implement a dedicated 256 Kbps link between two locations. Things work a little bit differently in the world of Frame Relay. Instead of providing fixed bandwidth over a dedicated circuit, […]