This chapter describes the Nx Networks implementation of Synchronous Data Link Control Relay (SRLY). It includes the following sections:
About SDLC Relay
How SDLC Relay Works
Setting Up SDLC Relay
Sample SDLC Relay Configuration
About SDLC Relay
Like DLSw, SRLY is a method for consolidating SDLC traffic onto the corporate multiprotocol backbone.
Unlike DLSw, SDLC Relay does not terminate the SDLC data link to reduce the likelihood of session timeouts, and does nothing to help reduce congestion on the WAN link. What SRLY provides is a serviceable method for shipping HDLC-formatted frames across WAN links in situations when it is not possible to use data link switching (Nx Networks DLSw product).
For more information on Nx Networks DLSw product, see Using the DLSw Protocol.
How SDLC Relay Works
Despite its name, the SDLC Relay protocol (SRLY) is designed to handle other protocols besides SDLC. The protocol works by encapsulating SDLC or any bit-oriented protocol (HDLC, LAPB) in UDP packets, and transmitting them through the IP cloud on a point-to-point connection to another SRLY device.
These connections are established by matching SRLY traffic to specific ports and groups. During configuration, each group has a unique group number assigned, and exactly two ports: one SDLC primary port, and one SDLC secondary. Matching SRLY traffic to group numbers and ports ensures that attached end stations can only send packets to the end stations for which they are intended.
Once the router receives packets, it strips them of their UDP/IP header and transmits them to their destination address in their original protocol format.
Figure 10 SDLC Primary/Secondary Stations and Local/Remote Ports
Encapsulation in UDP/IP packets allows for SDLC frames to be handled via IP routing techniques. And since each SDLC frame is encapsulated unchanged, SRLY is transparent to sending and receiving stations. This transparency allows SRLY to support all SNA PU Types.
SDLC Primary and Secondary Stations
When configuring SRLY, you must connect a router's primary port to its primary end station, and connect its secondary port to its secondary end station. Within the primary-secondary communication process, the primary end station is responsible for initiating, scheduling, and terminating the session. The secondary station does not initiate communication, but responds to commands from its primary partner.
When running balanced protocols like LAP-B or HDLC, you can assign roles arbitrarily as long as one device is Primary, and its connected counterpart is Secondary.
When to Use SDLC Relay
Generally, you would use SRLY instead of DLSw when you need to exchange any bit-oriented protocol, such as LAPB, HDLC, or SDLC primary over the wide area, between SNA or non-SNA devices.
DLSw can be configured for Host 1 and end station C in Figure 11: other wide-area connections would have to be accomplished using SDLC Relay.
Figure 11 SDLC Relay Configurations
Setting Up SDLC Relay
Configuring SDLC Relay (SRLY) involves performing these steps on each of two routers.
Depending on the type of serial card that you are using, dual-port or quad-port, the SRLY interface may be either DTE or DCE. If you are using a dual-port, the SRLY interface is DTE. For DTE interfaces, you must use modems or modem eliminators between the primary and secondary devices and the router, if connecting to another DTE device (or, you can connect directly to a DCE device). The modem eliminator must be compatible with the interface, such as RS-232 or V.35. The interface may be DCE or DTE if you are using the quad-port and you are not using modem eliminators.
The serial line supports NRZ. The Quad Serial line supports NRZ and NRZI.
Sample SDLC Relay Configuration
Following is a complete SDLC Relay configuration. The example assumes that the router has not been configured for any other protocols or data links.
Context Diagram
The example is based on the information shown in Figure
12. The IP connection between the two routers is over PPP.
Configuring R1 for SDLC Relay requires all of the information shown. This information includes the following:
Group numbers for each group of SRLY ports
Interface numbers for each SRLY port
The internet addresses for each SRLY router
Figure 12 Context Diagram for SRLY Configuration
This example explains how to configure two routers for SRLY traffic. Router 1 (R1) is connected to a PU Type 2.0 node. Router 2 (R2) is connected to a front end processor (FEP).
Configuring SDLC Relay
On R1, set the data link of interface 2 to an SDLC Relay device. Use the set data-link command shown here.
You can list the devices to confirm that an SDLC Relay device has been added.Config>set data srly 2
Config>list dev
Ifc 0 (Token Ring): CSR 6000000, vector 28
Ifc 1 (WAN PPP): CSR 81620, CSR2 80D00, vector 93
Ifc 2 (WAN SDLC Relay): CSR 81640, CSR2 80E00, vector 92
For RBX Series routers, you must also set the cable type.Config>network 2
SDLC relay interface user configuration
SRLY 2 Config>set clock internal
Must also SET SPEED for internal or mixed clocking
SLC Config>set speed
Internal Clock Speed [0]? 56000
After setting the line speed, clocking, and cable type, you can check the configuration with the list command.SRLY 2 Config>set cable rs-232 dce
SRLY 2 Config>list
Synchronous serial line interface configurationMaximum frame size in bytes = 2048
Encoding: NRZ
Idle State: Flag
Clocking: Internal
Cable type: RS-232 DCE
Internal Clock Speed: 56000
Transmit Delay Counter: 0
SLC Config>exit
As this example shows, the prompt for the SDLC Relay (SRLY) area is SDLC config>. Commands entered at this prompt only affect the SDLC Relay protocol. They have nothing to do with, and do not affect, SDLC data links or devices.Config>protocol sdlc
SDLC relay protocol user configuration
SDLC config>
Exit the SDLC Relay configuration procedure at any time by entering exit.
Assign a Group Number
First, assign a group number with the add group command. This number is assigned to the primary and secondary ports on the router you are configuring for SRLY. The group number you designate must be the same for each router.
Notice that the list group command shows that no ports have yet been configured for group 1.SDLC config>add group
Group number: [1]?
SDLC config>list group
Group number: [1]? 1SDLC Relay Configuration
Group Number Port Status Net SDLC Station IP Address
Number address(hex)
---------- ---------- ----- ----------- -----------
No ports configured for group 1
Notice that the list all command shows that a local secondary port is configured for group 1.SDLC config>add local
Group number: [1]?
Interface number: [0]? 2
(P)rimary or (S)econdary: [P]?
The (E) shown within the Port Status column stands for Enabled. By default, SRLY ports are enabled; SRLY ports must remain enabled in order to use the feature.SDLC config>list all
SDLC Relay Configuration
Group Number Port Status Net SDLC Station IP Address
Number address(hex)
---------- ---------- ----- ----------- -----------
1 (E) Local PRIMRY (E) 2
Add a Remote Port
Next add a remote port for group 1. This is the port that leads to the IP cloud. Each group must consist of a pair of ports, one primary, the other secondary. The remote port added here must be secondary since the local port attached to it is primary.
The IP address provided is that of the router on the other side of the IP cloud, R2.
SDLC config>add remote
Group number: [1]?
IP address of remote router: [0.0.0.0]? 10.2.50.30
(P)rimary or (S)econdary: [S]? p
SDLC config>list allSDLC Relay Configuration
Group Number Port Status Net SDLC Station IP Address
Number address(hex)
---------- ---------- ----- ----------- -----------
1 (E) Local PRMRY (E) 2 10.2.50.30
1 (E) Remote SCNDRY (E)
Set Data Link, Add Group, and Add Port
First, set up an SRLY data link for R2. Do this in the same manner as shown earlier for R1.
Next, add a group for R2, assigning the same group number (1, in this case) as that assigned on R1. Add a local port for the assigned group. This is the SRLY line you have already defined. In this case, the port type is secondary since a front end processor (FEP) (which, like a host, is always primary) is on the line.
SDLC config>add local
Group number: [1]?
Interface number: [0]?
(P)rimary or (S)econdary: [S]?
SDLC config>list allSDLC Relay Configuration
Group Number Port Status Net SDLC Station IP Address
Number address(hex)
---------- ---------- ----- ----------- -----------
1 (E) Local SCNDRY (E) 0 10.2.50.30
Since we are configuring R2, the IP address of the remote router belongs to R1. See Figure 12 for the addresses of R1 and R2, and their roles in the overall SRLY configuration.
SDLC config>add remote
Group number: [1]?
IP address of remote router: [0.0.0.0]? 10.1.50.7
(P)rimary or (S)econdary: [S]? pSDLC config>list all
SDLC Relay Configuration
Group Number Port Status Net SDLC Station IP Address
Number address(hex)
---------- ---------- ----- ----------- -----------
1 (E) Remote PRMRY (E) 10.1.50.7
1 (E) Local SCNDRY (E) 0