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Note The information in this chapter is applicable to the Catalyst 8540 MSR, Catalyst 8510 MSR, and LightStream 1010 ATM switch routers. For detailed configuration information, refer to the ATM Switch Router Software Configuration Guide and the ATM Switch Router Command Reference publication. |
The chapter includes the following sections:
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Note This chapter provides technical background and configuration overview information applicable to the Frame Relay port adapters for the ATM switch router. It does not provide general Frame Relay information. |
The difference between these two interworking functions is that network interworking provides a transport between two Frame Relay devices, while service interworking provides transparent interworking between ATM devices and Frame Relay devices without either being aware of the technology used at the other end.
The implementation of network interworking and service interworking is specified in procedures jointly agreed upon by the Frame Relay Forum and the ATM Forum (FRF.5 and FRF.8).
The network interworking function (network IWF) facilitates transport of Frame Relay user traffic and Frame Relay permanent virtual circuit (PVC) signaling traffic over ATM. Tunneling, multiprotocol encapsulation, and other higher layer procedures are handled just as they would be over leased lines. A network IWF application connects Frame Relay devices over an ATM backbone, as shown in Figure 12-1.
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Note In this chapter PVC is used interchangeably to mean permanent virtual circuit (in the context of Frame Relay) and permanent virtual connection (in the context of ATM). |
In the example shown in Figure 12-1, the ATM network could take the place of a leased line to connect the two Frame Relay networks. The network IWF is integrated into the channelized Frame Relay port adapter. This method of connecting Frame Relay networks can provide economic savings when compared to leased lines and offers the improved scalability of ATM at the core.
If a Frame Relay port is connected across an ATM network to an ATM device, network interworking requires that the ATM device recognize that it is connected to an interworking function, such as Frame Relay. The ATM device must then exercise the appropriate service-specific convergence sublayer (SSCS), in this case the Frame Relay SSCS (FR-SSCS).
The service interworking function (service IWF) provides a transport between two dissimilar devices, such as Frame Relay and ATM. Unlike network IWF, service IWF does not transport traffic transparently. Rather, it serves as a protocol converter and allows communication between dissimilar devices, as shown in Figure 12-2.
In the example in Figure 12-2, Frame Relay traffic is sent on a PVC through the Frame Relay network to the service IWF, which then maps Frame Relay frames to ATM cells on an ATM PVC. This process illustrates a chief advantage of service interworking: each location can use the technology best suited to its applications and needs.
The service IWF converts Frame Relay PVC address information such as the data-link connection identifier (DLCI) to the ATM VPI/VCI. Additionally, the forward explicit congestion notification (FECN) bit maps to the explicit forward congestion indication (EFCI) bit in the payload type identifier (PTI), and the discard eligible (DE) bit maps to the cell loss priority (CLP) bit of the ATM cell.
The channelized DS3 (CDS3) Frame Relay port adapter provides one physical port (45 Mbps). Each DS3 interface consists of 28 T1 lines multiplexed through a single T3 trunk. Each T1 line operates at 1.544 Mbps, which equates to 24 time slots (DS0 channels). A DS0 time slot provides 56 or 64 kbps of usable bandwidth. You can combine one or more DS0 time slots into a channel group to form a serial interface. A channel group provides n x 56 or 64 Kbps of usable bandwidth, where n is the number of time slots, from 1 to 24. You can configure a maximum of 127 serial interfaces, or channel groups, per port adapter.
Figure 12-3 illustrates how a T3 trunk demultiplexes into 28 T1 lines that provide single or multiple time slots mapped across the ATM network. These time slots are then multiplexed to form an outgoing T3 bit stream.
Step 2 Configure the T1 lines.
Step 3 Configure the channel group.
Step 2 Specify the clock distribution mode (default is loop-timed). For more information on clocking modes, see "Network Clock Synchronization."
Step 3 Specify the DS3 framing type (the default is M23).
Step 4 Specify the cable length (the default is 224).
Step 5 Configure the Maintenance Data Link (MDL) message (the default is no message). MDL messages are only supported when the framing type is set for c-bit parity.
Step 2 Specify the T1 framing mode for the lines you are configuring (the default is ESF).
Step 3 Specify T1 yellow alarm detection, generation, or both for the lines you are configuring (the default is both).
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Note A time slot can be part of only one channel group. Additionally, all time slots within a channel group must be on the same T1 line. |
Configuring the T1 channel group requires the following steps:
Step 2 Create the channel group by specifying a channel group number, T1 line number, and the time slots that comprise the channel.
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Note You can group either contiguous or noncontiguous time slots on a T1 line. |
The channelized E1 (CE1) Frame Relay port adapter provides four physical ports. Each port supports up to 31 serial interfaces, also referred to as channel groups. The E1 line operates at
2.048 Mbps, which is equivalent to 31 time slots (DS0 channels). A time slot on an E1 provides 64 Kbps of usable bandwidth. You can combine one or more time slots into a channel group to form a serial interface. A channel group provides n x 64 Kbps of usable bandwidth, where n is the number of time slots, from 1 to 31. You can configure a maximum of 124 serial interfaces, or channel groups, per port adapter.
Figure 12-4 illustrates how an E1 trunk (with four ports) provides single or multiple time slots mapped across the ATM network. Multiple n x 64 circuits can be connected to a single port, using separate time slots.
To configure the CE1 Frame Relay port adapter, you will need the following information:
Step 2 Configure the channel group.
The following defaults are assigned to all CE1 Frame Relay port adapter interfaces:
Step 2 Specify the clock distribution mode (the default is loop-timed). For more information on clocking modes, see "Network Clock Synchronization."
Step 3 Specify the DS3 framing type (the default is CRC4).
Configuring the channel group requires the following steps:
Step 2 Create the channel group by specifying a channel group number and the time slots that comprise the channel.
For information on how to customize your Frame Relay to ATM connections, see the "LMI Configuration Overview" section and "Frame Relay to ATM Resource Management Configuration Overview" section.
Step 2 Enable IETF encapsulation on the interface.
Step 2 Specify the interface type.
When you specify DCE, the ATM switch router supports only network-side PVC status management procedures. When you specify NNI, the ATM switch router supports both user-side and network-side PVC status management procedures.
Configuring the LMI type requires the following steps:
Step 2 Specify a Frame Relay LMI type (Cisco is the default type).
Step 3 Exit configuration mode and save your running configuration to the startup configuration.
Configuring the keepalive interval requires the following steps:
Step 2 Specify a keepalive interface for the interface.
Step 2 Perform one or more of the following substeps:
a. Specify the number of keepalive exchanges to be completed before requesting a full status message.
b. Specify the error threshold for DCE and NNI interfaces.
c. Specify the error threshold for DTE and NNI interfaces.
d. Specify the monitored events count on DCE and NNI interfaces.
e. Specify the monitored event count on DTE and NNI interfaces.
f. Specify the polling verification timer on DCE and NNI interfaces.
For general information on ATM connection traffic table rows, see the "Connection Traffic Table" section in the "Traffic and Resource Management" chapter.
The Frame Relay traffic parameters (specified in the command used to create the row) are converted into equivalent ATM traffic parameters. Both parameters are stored internally and used for interworking virtual connections.
The formulas for Frame Relay to ATM traffic conversions are specified in the Broadband Inter-Carrier Interface (B-ICI) specification, V2.0, and use a frame size (n) of 250 bytes and a header size of 2 bytes. The traffic parameters are mapped between ATM and Frame Relay as follows:
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Note Peak information rate and committed information rate are expressed in bits per second. Committed burst size is expressed in bits. |
For PVCs, PVC connection traffic rows, or stable rows, are used to specify traffic parameters.
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Note PVC connection traffic rows cannot be deleted while in use by a connection. |
For SVCs, connection traffic rows, or transient rows, are used by the signaling software to obtain traffic parameters.
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Note SVC connection traffic rows cannot be deleted from the CLI or SNMP. They are automatically deleted when the connection is removed. |
To make the CTT management software more efficient, the CTT row-index space is split into two ranges, allocated by the CLI/SNMP and signaling. (See Table 12-1.)
| Allocated by | Row-Index Range |
|---|---|
CLI/SNMP | 1 through 1,073,741,823 |
Signaling | 1,073,741,824 through 2,147,483,647 |
Table 12-2 shows the parameters and values in the predefined CTT row.
| CTT Row-Index | CIR (bps1) | Bc (bits) | Be (bits) | PIR (bps) | Service Category | ATM Row-Index |
|---|---|---|---|---|---|---|
100 | 64000 | 32768 | 32768 | 64000 | VBR-nrt | 100 |
| 1Bits per second |
To create a Frame Relay to ATM CTT row, you specify the following information:
Step 2 Specify discard and marking thresholds for any of the supported service categories in the outbound direction.
Step 3 Specify the committed burst size for ABR/UBR soft virtual connections on the destination interface.
Step 4 Configure to accept or discard overflow traffic that exceeds the CIR for VBR circuits. This applies only to CDS3 interfaces.
Step 5 Specify the percentage of CIR overbooking to allow.
Step 2 Configure the T1 interface (or E1 interface) and channel group on the Frame Relay port adapter.
Step 3 Configure Frame Relay encapsulation and the Frame Relay LMI on the serial interface corresponding to the channel group configured in Step 2.
Step 4 Configure Frame Relay connection traffic table rows and related resource management functions.
These switching features can be turned off with the interface configuration commands.
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Note For more information about ATM connections, see "Virtual Connections." |
Table 12-3 lists the types of supported virtual connections.
| Connection | Point-to-Point | Point-to-Multipoint | Transit | Terminate |
|---|---|---|---|---|
Permanent virtual connection (PVC) | X | -- | X | X |
Soft permanent virtual connection (soft PVC) | X | -- | X | -- |
Figure 12-5 shows an example of a Frame Relay to ATM network interworking PVC between Frame Relay user A and ATM user D through an ATM network.
Configuring a Frame Relay to ATM network interworking PVC, such as the internal cross-connect in switch B or switch C in Figure 12-5, requires the following steps:
Step 2 Configure the PVC, specifying the following values:
You can optionally specify the row index for the receive and transmit rows in the CTT, if previously configured. You can also specify mapping of resource management parameters between Frame Relay and ATM.
Figure 12-6 shows an example of a Frame Relay to ATM service interworking PVC between Frame Relay user A and ATM user D through an ATM network.
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Note VPI and VCI values can change when traffic is relayed through the ATM network. |
Configuring a Frame Relay to ATM service interworking PVC, such as the internal cross-connect on switch B or switch C in Figure 12-6, requires the following steps:
Step 2 Configure the PVC, specifying the following values:
You can optionally specify the row index for the receive and transmit rows in the CTT, if previously configured. You can also specify mapping of resource management parameters between Frame Relay and ATM.
Figure 12-7 shows an example of transmit and terminating connections. Terminating connections connect to the CPU on the ATM switch router.
The internal cross-connect on switch B in Figure 12-7 is a PVC between serial interface 0/1/0:5, DLCI = 50 and the terminating connection on ATM interface 0, VPI = 0 and an unspecified VCI. Configuring this connection requires the following steps:
Step 2 Configure the PVC, specifying the following:
You can optionally specify the row index for the receive and transmit rows in the CTT, if previously configured. You can also specify mapping of resource management parameters between Frame Relay and ATM.
Frame Relay transit PVCs are used to establish a bidirectional facility to transfer Frame Relay traffic between two Frame Relay users. Figure 12-8 shows a Frame Relay transit PVC between Frame Relay users A and D.
Configuring a Frame Relay transit PVC, such as the one between the serial interfaces on switch B and switch C in Figure 12-8, requires the following steps:
Step 2 Configure the PVC, specifying the following values:
Each subsequent cross-connection and link must be configured until the virtual connection is terminated to create the entire VCC.
This section provides guidelines and an overview of configuring the following types of Frame Relay to ATM interworking soft PVC connections:
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Note Frame Relay interworking soft PVCs can only be configured from a Frame Relay interface. |
Configuring a Frame Relay interworking soft PVC requires the following steps:
Step 2 Determine the source (active) side of the soft PVC.
Step 3 Determine an available DLCI value on the source end of the soft PVC.
Step 4 Determine the destination (passive) side of the soft PVC.
Step 5 Determine the ATM address of the destination side of the soft PVC.
Step 6 If the destination side of the soft PVC is a Frame Relay interface, choose an available DLCI value. If the destination side of the soft PVC is an ATM interface, choose an available VPI/VCI value.
Step 7 Choose the interworking function type and the relevant interworking parameters (for example, de-bit/clp-bit mapping options).
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Note If the soft PVC terminates on a Frame Relay interface, the soft PVC can only be configured as a network interworking connection. If the soft PVC terminates on an ATM interface, the soft PVC can be configured either as a network interworking connection or a service interworking connection. |
Step 8 Configure the Frame Relay interworking soft PVC on the source side. See the following sections for configuration steps and examples.
Figure 12-9 shows a Frame Relay to Frame Relay network interworking soft PVC between
switch A and switch B.
Configuring a Frame Relay to Frame Relay network interworking soft PVC requires the following steps:
Step 2 Determine an available DLCI value for the serial interface on the source side.
Step 3 Determine the ATM address for the destination serial interface.
Step 4 Determine an available DLCI value for the destination serial interface.
Step 5 Enter interface configuration mode and select the serial interface (source) to configure.
Step 6 Configure the soft PVC, specifying the following values:
You can also specify the relevant interworking parameters, such as the Frame Relay to ATM traffic parameter mappings. You do not need to specify the interworking type; soft PVCs that originate and terminate on Frame Relay interfaces are configured as network interworking by default.
Figure 12-10 shows a Frame Relay to ATM service interworking soft PVC between switch A and switch B.
Configuring Frame Relay to ATM service interworking soft PVC requires the following steps:
Step 2 Determine an available DLCI value for the serial interface.
Step 3 Determine the ATM address on the destination interface.
Step 4 Determine available VPI and VCI values on the ATM interface.
Step 5 Enter interface configuration mode and select the serial interface to configure.
Step 6 Configure the soft PVC, specifying the following values:
You can also specify the relevant interworking parameters, such as the Frame Relay to ATM traffic parameter mappings.
The soft PVC route optimization feature is supported on Frame Relay interfaces. For a detailed explanation of the feature, see the "Route Optimization for Soft PVCs" section.
Soft PVC route optimization must be enabled and configured to determine the point at which a better route is found and the old route is reconfigured. Enabling and configuring a Frame Relay interface with route optimization requires the following steps:
Step 2 Enter interface configuration mode and select the serial interface to configure. You configure route optimization on the source end of a soft PVC only.
Step 3 Specify during what time of day and how often routes should be recomputed on this interface.
You can also manually trigger route optimization on a specific soft PVCC or PVPC.
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Note Route optimization for soft permanent virtual connections should not be configured with constant bit rate (CBR) connections. |
For more information, see the "Soft PVCs with Explicit Paths" section.
Respecifying Frame Relay to ATM interworking soft PVCs requires configuring the soft PVC with the redo-explicit feature and related parameters, such as the explicit path precedence and partial path.
Posted: Wed Sep 27 13:34:48 PDT 2000
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