Configuring Synchronous Data Link Control Connectivity

This chapter describes how to provide Synchronous Data Link Control (SDLC) connectivity over local and wide area networks, how the SDLC works on the router, and gives guidelines for operating and managing your SDLC configuration.

For conceptual information, see "How SDLC Conversion Works" later in this chapter. For information about the parameters in the SDLC Service, see the SDLC Service Parameters chapter in Reference for Enterprise OS Software.

On the NETBuilder II system, SDLC is supported only on the HSS 3-Port modules.

This section describes various SDLC connections. For configuration procedures, see "Configuring the Router for SDLC" later in this chapter.

Figure 226 shows an SDLC point-to-point configuration where remote PU2 devices use SDLC to connect to an SDLC- or token ring-attached host front end processor (FEP) through the WAN. In this configuration, the SNA and SDLC data is passed through the bridge/router using data link switching (DLSw).

Figure 226 SDLC Point-to-Point Configuration

A multipoint configuration may consist of several remote SDLC devices using SDLC connections to a 3Com bridge/router to reduce the number of independent (SDLC and other) links required by the site. In this configuration, the SDLC data is passed through the bridge/router using DLSw. As shown in Figure 227, a remote site may be configured as an SDLC primary node talking to 3x74 cluster controllers and other SDLC secondary devices (486x).

Figure 227 SDLC Multipoint Configuration

The SDLC connectivity of the NETBuilder II bridge/router also allows an SDLC-attached device to communicate with a local LAN-attached device or with a front-end processor (FEP) through Frame Relay (see Figure 228).

Figure 228 SDLC Connectivity through a LAN and Frame Relay

This section describes how to configure the bridge/router for SDLC. After you complete the procedures in this section, proceed to "Configuring the CU Devices on the Link" later in this chapter.

Prerequisites

Before beginning this procedure, complete the following tasks:

• Log on to the system with Network Manager privilege.

• Set up the non-SDLC ports and paths of your bridge/router according to the Configuring Basic Ports and Paths chapter and the Configuring Advanced Ports and Paths chapter. For the token ring bridge see the Configuring Source Route Bridging chapter.

• Set up the ports for SDLC as described later in this guide. Ports being used for SDLC must have a one-to-one port-to-path mapping.

• Set up the LLC2 data link interface as described in the Configuring the LLC2 Data Link Interface chapter.

  SDLC is affected by parameter settings in other services. For more information, see "Configuring LLC2 with Other Services" in the Configuring the LLC2 Data Link Interface chapter.

• Configure IP and obtain the IP addresses of the local bridge/router and DLSw peers.

• Obtain the SNA device address and the Virtual Telecommunications Access Method (VTAM) address so you can match the addresses of the devices you are configuring.

• Allocate a media access control (MAC) and Service Access Point (SAP) configuration to represent the attached SDLC device.

To configure SDLC, perform the procedures in the following section on bridge/router A (see Figure 229), which has the attached SDLC devices.

Figure 229 Configuring the Router for SDLC

Configuring the SDLC Port and Path Attributes

To configure the port attributes for SDLC, follow these steps:

1 .   For the port running SDLC, set the OWNer parameter using:

SETDefault !<port> -PORT OWNer = SDLC

2 .   Set the communication mode (using the PATH Service DUplex parameter) and the transmission encoding method (using the PATH Service ENCoding parameter) for the path assigned to the SDLC port.

For example, if the attached device requires half-duplex communication and nonreturn to zero (NRZ) encoding, use:

SETDefault !<path> -PATH DUplex = Half

SETDefault !<path> -PATH ENCoding = NRZ

SETDefault !<path> -PATH TxIdle = Mark

Make sure the parameter settings match the configuration of the device and that you configure the TxIdle parameter as shown. The Mark setting allows half-duplex operation to occur by setting up the system to receive the second half of the transmission without aborting.

3 .   Make sure the LineType and clocking parameters in the PATH Service are set correctly.

For a back-to-back or a null modem connection you must use external clocking. The NETBuilder II bridge/router does not provide an internal clock source. The LineType must be Leased and clocking must be External. Set the LineType and clocking parameters using:

SETDefault !<path> -PATH LineType = Leased

SETDefault !<path> -PATH Clock = External

Changes to these parameters do not take effect until you enable the ports and paths.

4 .   Disable Link Access Procedure, Balanced (LAPB) on the selected path using:

SETDefault !<path> -LAPB CONTrol = Disable

Because of the SDLC configuration, the port-to-path correlation must be mapped on a one-to-one basis. LAPB cannot be enabled when the port owner is SDLC.

If SDLC devices attached to the bridge/router need to communicate with LAN (LLC2) devices attached to the same bridge/router, the bridge/router must be set up to support LLC2 connections. You also must set up DLSw to perform internal switching. If this has not already been done, see the Configuring Data Link Switching for SNA and NetBIOS Networks chapter.

If you want your NETBuilder II bridge/router to connect the SDLC devices to a LAN, the LLC2 ports must be configured as described for DLSw in the Configuring Data Link Switching for SNA and NetBIOS Networks chapter.

Configuring the SDLC Protocol Characteristics

To configure SDLC for communication with the connected devices, follow these steps:

1 .   Define the control units (CUs) attached to the port.

Assign a name to the CU using this port using:

ADD !<port> -SDLC PortCU <CU name>

Assigning the CU to the port sets up the SDLC configuration of the port, which allows you to view and modify the port parameter settings. The CU name you assign has only local significance. CU names must be unique and can be no longer than 8 alphanumeric characters. A name longer than 8 characters is rejected and a warning message appears. However, maintaining name consistency between the NETBuilder II bridge/router and network control point (NCP) configurations may simplify configuration management. CU names must be unique within the bridge/router.

The SDLC parameters for a port are inaccessible. They cannot be viewed or modified until at least one CU is assigned to the port with the Port CU parameter.

2 .   Configure whether the port will act in a primary or secondary role in the connection.

In SDLC, a primary station controls the operation of other secondary stations. The role of the port applies to the port and all of the CUs configured on the port. The role must be set according to the CUs attached to the port, if the role of the CU is secondary, set the port as primary.

For example, to attach a CU device that is secondary, set the port as primary on the bridge/router using:

SETDefault !<port> -SDLC PROle = Primary

All SDLC ports that are attached to a primary (a host) should be set as secondary. All SDLC ports that are attached to a secondary CU (a 3174 downstream physical unit) should be set as primary.

3 .   Display the current parameter settings using:

SHow !<port> -SDLC PCONFig

4 .   Define whether the port operates in half- or full-duplex mode with the connected device.

To configure a port on the bridge/router for half-duplex operation, use:

SETDefault !<port> -SDLC PDatmode = Half

The port can be set for half-duplex (two-way alternating) or full-duplex (two-way simultaneous) communication to match the configuration of the SDLC devices on this port.

5 .   Set the maximum amount of data contained in a single frame (basic transmission unit (BTU) size) using:

SETDefault !<port> -SDLC PMaxData = 521

The value of this parameter should match the host.

6 .   Set the frame numbering method used by the CUs attached to this port using:

SETDefault !<port> -SDLC PMODulo = 128

The setting of this parameter must match the CU on this port.

To configure the timing of the port, which affects how the port waits and responds to communication with the CUs attached to this port, follow these steps:

1 .   Set the number of times the bridge/router attempts to complete a protocol exchange with an SDLC connected device before considering that device as having failed using:

SETDefault !<port> -SDLC PT1Retry = 3

2 .   Set the no-response time-out waiting period for the port using:

SETDefault !<port> -SDLC PT1Timer = 400

This parameter is used on primary ports only. If the CU does not send a response to a poll or a message from the SDLC port before this timer expires, the transmission is retried until the retry count set in the previous step runs out. At this point, the bridge/router will terminate (disconnect) the SDLC connection and attempt to contact the CU again for a new connection.

3 .   Set the delay between attempts to connect the network data link (LLC2) partner for CUs whose mode is set to originate using:

SETDefault !<port> -SDLC PRetryTimer = 20

After you have completed this procedure, proceed to the next section to configure the link stations (CUs) attached to the bridge/router.

This section describes how to configure the SDLC connection for the CU devices the bridge/router has configured on each SDLC port.

Prerequisites

Before beginning this procedure, complete the following steps:

• Configure the SDLC port parameters as described in the previous procedure.

• Obtain the MAC/SAP address pair for the CU. This includes the local MAC/SAP values used to represent this SDLC device in the LLC2 network environment and the remote MAC/SAP values, if the CUMOde parameter is set to Originate, which indicate the CUs partner (LLC2) device.

To configure the link for the CU, follow these steps:

1 .   Define the type of CU you are configuring by entering:

SETDefault !LS22 -SDLC CUType = T1

This command specifies the CU named LS22 which is a type PU1 or T1 device.

2 .   Set the CU device identification if required using:

SETDefault !<CU name> -SDLC CUXId = 0179097C

SETDefault !<CU name> -SDLC CUXidDefined = Yes

This step is optional and depends upon the configuration of the attached CU and the requirements of the network partner device.

The CUXId is only required if the PRole parameter is set to primary and the PU type is set to type 2.0 or type 1 and the attached (secondary) CU will not respond to an exchange identification (XID) poll. The CUXidDefined parameter must also be set to enable use of the defined CUXId value.

See the SDLC Service Parameters chapter in Reference for Enterprise OS Software for further information about the CUXId parameter.

3 .   Configure the poll address of the secondary CU using:

SETDefault !<CU name> -SDLC CUAddr = C2

If the bridge/router is configured as primary, the CU address must match the PU. If the bridge/router is set as secondary, the CU address must match the host configuration.

4 .   Configure the local MAC address for the CU using:

SETDefault !<CU name> -SDLC CULocalMac = %50004080C940

This value is the MAC address used within the LLC2/DLSw environment to communicate with the CU. LLC2 frames intended for this CU must use this value as the destination MAC address. When the NETBuilder II bridge/router sends LLC2/DLSw frames on behalf of this CU, this value is used as the source MAC address. The MAC addresses in this parameter are in noncanonical format.

Two CUs may not use the same CULocalMac and CULocalSap combination.

5 .   Configure the local SAP used by the CU using:

SETDefault !<CU name> -SDLC CULocalSap = 08

This value is the LLC2 SAP used for this CU in the LLC2/DLSw environment. LLC2 frames intended for this CU must use this value as the destination SAP. When the NETBuilder II bridge/router sends LLC2/DLSw frames on behalf of this CU, this value is used as the source SAP.

6 .   Set the maximum number of frames that may be transmitted before waiting for a response using:

SETDefault !<port> -SDLC CUMaxOut = 4

7 .   Set up the operating mode for the CU by entering:

SETDefault !<CU name> -SDLC CUMOde = Originate

The mode determines whether the bridge/router initiates sessions in the LLC2/DLSw environment on behalf of this CU, or whether the bridge/router simply responds to sessions initiated by other stations. The exact sequence of connection events also depends on the PRole parameter.

When CUMOde is set to Originate, the bridge/router initiates an LLC2 connection as soon as it has contacted the SDLC station; that is, when it has received an XID or set normal response mode (SNRM) (if PRole is secondary) or a response to an XID or SNRM (if PRole is Primary).

When CUMOde is set to Answer, the bridge/router will not initiate LLC2 sessions, but responds to LLC2 connection attempts by trying to establish contact with the SDLC station, sending XID or SNRM if PRole is Primary, and responding to XID or SNRM if PRole is secondary.

8 .   Configure the remote MAC address for the CU using:

SETDefault !<CU name> -SDLC CURemoteMac = %60003070C940

When CUMOde is Originate, the bridge/router uses this value as the desti- nation MAC address when initiating an LLC2 connection on behalf of this CU.

9 .   Configure the remote SAP used by the CU using:

SETDefault !<CU name> -SDLC CURemoteSap = 08

When CUMOde is Originate, the bridge/router uses this value as the destination LSAP when initiating an LLC2 connection on behalf of this CU.

10 .   Enable SDLC for the port.

For example, to connect a CU to a bridge/router, enable the SDLC Protocol using:

SETDefault !<port> -SDLC PCOntrol = Enable

11 .   Check that there is a one-to-one port-to-path mapping by displaying the PORT Service PAths parameter by entering:

SHow !1 -PORT PAths

12 .   Enable the CU using:

SETDefault !<CU name> -SDLC CUCONTrol = Enabled

Both the port and the CU must be enabled for an SDLC link to operate. The port and the CU may be enabled in any order. Be sure you have enabled the CONTrol parameter in the PORT Service and PATH Service.

After you have configured SDLC, you can display SDLC port and CU configuration information. You can also add or delete CUs assigned to a port. Deleting all CUs assigned to a port also deletes the SDLC configuration of the port.

To display all of the SDLC port parameters configured for the specified port and the CU configuration for all CUs assigned to that port, enter:

SHow -SDLC PCONFig

To display the SDLC configuration for a specific port, for example port 1, enter:

SHow !1 -SDLC PCONFig

Display the value of all CU-related parameters for each CU by entering:

SHow !* -SDLC CUCONFig

To display a specific CU, use:

SHow !<CU name> -SDLC CUCONFig

You can display a log of SDLC activity by entering:

SHow -SDLC SdlcLOG

The log displays a history of the most recent 256 log entries including the following actions:

• Control unit activation or deactivation

• Control unit failure

If SDLC devices attached to the bridge/router need to communicate with a FEP attached directly to the bridge/router through Frame Relay, the bridge/router must be set up to support the mapping of LLC2 traffic to Frame Relay. If you have not already configured Frame Relay, perform the procedures in the Configuring Wide Area Networking Using Frame Relay chapter.

You can configure Advanced Peer-to-Peer Networking (APPN) traffic to run over SDLC. To configure the bridge/router network node to run over SDLC, you first configure the SDLC port and path attributes between the network node and the partner node using the procedures in this chapter. You then configure the APPN network node following the procedures in the Configuring APPN Intermediate Session Routing chapter; the procedures are similar to configuring APPN over other data link control (DLC) types, except that you do the following tasks:

• When setting the -APPN PortDef parameter for APPN ports, set the DLC type to SDLC and optionally, set the DatMode and ROle values.

• Configure adjacent link stations using the -APPN SdlcAdjLinkSta parameter and configure Dependent LU Requestor (DLUr) link stations using the -APPN SdlcDlurLinkSta parameter.

For information about these APPN Service parameters, see the APPN Service Parameters chapter in Reference for Enterprise OS Software.

Figure 230 shows a configuration in which APPN traffic is being sent over SDLC connections. The NETBuilder II bridge/router acting as a network node is shown sending APPN over SDLC connections to a peer NETBuilder II network node, to a network control program (NCP), and to a 3174 PU2.0 type node. The network node is also serving as a DLUr for the VTAM Dependent LU server (DLUs).

Figure 230 APPN Traffic over SDLC

You can send either APPN ISR traffic or APPN HPR traffic over SDLC connections. For information about configuring APPN Intermediate Session Routing (ISR) over SDLC, follow the procedures in the Configuring APPN Intermediate Session Routing chapter. For information about configuring APPN High Performance Routing (HPR), see the APPN High Performance Routing chapter.

SDLC devices generally are referred to as physical units (PUs), control units (CUs), and linkstations. CU is used in parameter descriptions and names. The term PU is used in some examples and general discussion and when referring to device type. The term link station may also be used to see the device type. Except for parameter names or specific device types, these terms may be used interchangeably.

SDLC connectivity allows SDLC devices to communicate with local or remote non-SDLC (LLC2, Frame Relay devices, or other remote SDLC devices, using an SDLC connection to your bridge/router. SDLC polling and response occur locally between the SDLC device and the NETBuilder II bridge/router; the SNA data stream is tunneled through the network using the DLSw protocol. Figure 231 shows a typical SDLC/DLSw configuration.

Figure 231 SDLC/DLSw Configuration

The NETBuilder II bridge/router provides SDLC connectivity by mapping the SDLC device to a "virtual" LLC2 device, or an LLC2 device to an SDLC device. Other systems in the network communicate with this LLC2 device, for example, through DLSw. The bridge/router passes the data to and from the SDLC device.

In addition to the configuration information required to communicate with the SDLC device, the bridge/router must be given the LLC2 information used to communicate with non-SDLC devices, for example, MAC and SAP values.

Operating the bridge/router with SDLC is accomplished by mapping (or conversion) of SDLC connections into LLC2 connections. This section describes the key aspects of this mapping, how the configuration parameters relate to (and affect) the mapping behavior, and illustrates the configuration for common applications.

Both SDLC and LLC2 are reliable data link protocols. They provide sequenced, acknowledged, and retransmitted delivery of data frames, and include special frames for session initiation and termination. Although similar, SDLC and LLC2 operate in different environments using different modes. Because of this different frame sequences are used for session initiation, and different addressing schemes are used in each service.

Data Link Switch is a protocol (defined by RFC 1434) used to link LLC2 sessions together across an internetworked reliable transport protocol. The protocol definition for DLSw includes addressing schemes and session startup sequences that readily correspond to LLC2 addressing and session startup.

To link SDLC sessions with LLC2 or DLSw sessions, the bridge/router must handle two major functions: address mapping and session initiation.

Address Mapping

In an LLC2 (LAN) or DLSw environment, addressing consists of MAC/SAP pairs. Each station has a MAC (LAN) address; every frame sent from one station (A) to another station (B) contains both a source and a destination MAC address to distinguish the sending and receiving stations on the shared-access medium. Each LLC2 frame also contains a source and destination LLC2 SAP (LSAP). A pair of LAN stations may have multiple sessions between them; the LSAP values are used to distinguish between frames belonging to different sessions.

In an SDLC environment, each frame carries only a single address value; the identifier of the secondary station that is to receive, or that sent, this frame.

To allow stations in an LLC2 environment to communicate with an attached SDLC station, the bridge/router maps a set of LLC2 (LAN) addresses to each CU. This address mapping is configured using the CULocalMac, CURemoteMac, CULocalSap, and CURemoteSap parameters in the SDLC Service. The bridge/router appears as a LAN-based CU mapped to the SDLC CU, which uses the CULocalMac and CULocalSap to communicate with other LAN stations. Figure 232 shows various types of address mapping for SDLC.

In the LLC2 or DLSw environment, the CUs supported by the bridge/router appear to be attached to the LAN: Frames can be sent to them using the MAC/SAP values assigned as CULocalMac and CULocalSap. Frames sent by the bridge/router on behalf of the CU use the CULocalMac and CULocalSap values as the source address values.

If the bridge/router is initiating an LLC2 session on behalf of a CU (see "Session Initiation" next), it must know which LLC2 station to send the connection request to. This destination is determined by the CURemoteMac and CURemoteSap parameter values. These values are used as the destination for LLC2 frames when the bridge/router initiates such sessions.

Figure 232 SDLC Address Mapping

Session Initiation

In addition to address mapping, the SDLC configuration determines how the bridge/router initiates SDLC and LLC2/DLSw connections. The CUMOde parameter for the specific CU, in conjunction with the SDLC role of the port (the PROle parameter) determines the system's behavior as follows:

• In an SDLC environment, datalink connections are initiated by the bridge/router acting as the primary station. The primary station controls the operation of other secondary stations. When acting as an SDLC secondary station, the bridge/router accepts connections only. Use the CUMode parameter to configure the bridge/router to either originate a network connection request or answer a connection request from the network.

• In an LLC2 or DLSw environment, either of the two systems involved in a session may initiate the datalink connection. The CUMode parameter also determines whether and when the NETBuilder II bridge/router initiates LLC2 or DLSw connections.

When CUMOde is set to Originate, the bridge/router initiates datalink connections in the LLC2/DLSw environment. Contact is achieved by sending an XID or SNRM and receiving a response. When the bridge/router is secondary, contact is achieved by receiving an XID or SNRM from the primary station. However, if the bridge/router is a secondary station in Originate mode, it will not respond until it has completed the LLC2/DLSw connection.

When the CUMOde is set to Answer, the bridge/router will only accept datalink connections from the LLC2/DLSw environment. When a connection request is received, the bridge/router attempts to set up the corresponding SDLC connection before accepting the LLC2/DLSw connection. When you set up the SDLC connection, an XID or SNRM is sent if the bridge/router is acting as a primary station; if the bridge/router is acting as a secondary station, an XID or SNRM response is made.