Networking Concepts and Technology: A Designers Resource

A token ring network is a physically star-wired local area network that interconnects various devices such as personal computers and workstations into a logical ring configuration. The cabling system consists of wiring concentrators, connectors, and end stations.

The Sun token ring protocol conforms to the IEEE 802.5-1988 standard. Token ring refers to the media access control (MAC) portion of the link layer (DLC) as well as the entire physical layer (PHY). Access to the ring is controlled by a bit pattern, called a token, that circulates from station to station around the ring. Any station can use the ring. Capturing the token means that a station changes the token bit pattern so that it is no longer that of a token but that of a data frame. The sending station then sends its data within the information field of the frame. The frame also includes the destination address of the destination station. The frame is passed from station to station until it arrives at the proper destination. At the destination station, the frame is altered to indicate that the address was recognized and that the data was copied. The frame is then passed back to the original sending station, where the sending station checks to see that the destination station copied the data. If there is no more data to be sent, the sending station alters the frame's bit configuration so that it now functions as a free token available to another station on the ring.

If a station fails, it is physically switched out of the ring, dynamically. The ring is then automatically reconfigured. When the station has been repaired, the ring is again automatically reconfigured to include the added station.

Token Ring Interfaces

Sun supports two token ring drivers for its range of SPARC® platforms. This section describes the token ring interfaces in detail.

The SBus-based and the PCI token ring interfaces provide access to 4-Mbit/sec or 16-Mbit/sec token ring local area networks. SunTRI/S software supports the IEEE 802.5 standards for token ring networks.

The IEEE standard specifies the lower two layers of the OSI 7-layer model. The two layers are the Physical layer (Layer 1) and the Data Link layer (Layer 2). The Data Link layer is further divided into the Logical Link sublayer (LLC) and the Media Access Control (MAC) sublayar.

The token ring driver is a multi-threaded, loadable, clonable, STREAMS hardware driver that supports the connectionless Data Link Provider Interface, dlpi(7p), over a token ring controller. Multiple token ring controllers installed within the system are supported by the driver. SunTRI/S software can support different protocol architectures concurrently, via the SNAP encapsulation technique of RFC1042. From this SNAP encapsulation, high-level applications can communicate through their different protocols over the same SunTRI/S interface. Support also exists for adding different protocol packages (not included with SunTRI/S). These protocol packages include OSI and other protocols available directly from Sun or through third-party vendors. TCP/IP is implicit with the Solaris operating system.

The software driver also provides source routing, which enables the workstation to access multiple ring networks connected by source-route bridges. Locally administered addressing is also supported and aids in management of certain user-specific and vendor-specific network configurations.

Support for IBM LAN Manager is provided by the TMS380 MAC-level firmware that complies with the IEEE 802.5 standard.

Configuring the SunTRI/S Adapter with TCP/IP

The Sbus token ring driver is called tr and can be configured using ifconfig once you have established that the interface is physically present in the system and the device driver is installed. Refer to "Configuring the Network Host Files" on page 234. The rest of this section describes the configuration of individual parameters of the tr device that can be altered in the driver.conf file and global parameters that can be altered using /etc/system. TABLE 5-1 describes the tr.conf parameters.

Setting the Maximum Transmission Unit

Sun supports the IEEE 802.5 Token Ring Standard Maximum Transmission Unit (MTU) size of 17800 bytes. All hosts should use the same MTU size on any particular network. Additionally, if different types of IEEE 802 networks are connected by transparent link layer bridges, all hosts on all of these networks should use the same MTU size.

The maximum MTU sizes supported are 4472 for 4 Mbit/sec operation and 17800 for 16 Mbit/sec operation. These are the rates specified by the token ring chip set on the SunTRI/S adapter. TABLE 5-2 lists the MTU indices and their corresponding sizes.

The default value of the MTU index is 3 (4472 bytes).

Disabling Source Routing

Source routing is the method used within the token ring network architecture to route frames through a multiple-ring local area network. A route is a path taken by a frame as it travels through a network from the originating station to a destination station.

By default, source routing is enabled. To disable source routing, set the sr value in the tr.conf file to 0.

Disabling ARI/FCI Soft Error Reporting

In 1989, the Token Ring committee changed its recommendations on the use of the Address Recognized Indicator/Frame Copied Indicator (ARI/FCI). The old recommendation was to use the bits to confirm the receipt or delivery of frames. The new recommendation is to use the bits to report soft errors. This recommendation gave rise to issues in networks that had devices developed based on the old recommendation and in networks with devices developed since 1989 that did not adhere to the new recommendation.

The ari parameter in the tr.conf file can be used to set ARI/FCI soft error reporting. By default, the ARI/FCI soft error reporting parameter is enabled. If you have an older network device, you might need to disable ARI/FCI error reporting by setting the ari parameter to 1.

Configuring the Operating Mode

The SunTRI/S adapter supports both classic and Dedicated Token Ring (DTR) modes of operation. You can use the mode command to set the operating mode.

By default, the adapter is set to classic mode (half duplex). If the mode is set to DTR, the adapter will come up in full duplex mode. If the mode is set to auto, the adapter will automatically choose between classic and DTR mode, depending on the capabilities of the switch or media access unit (MAU).

Resource Configuration Parameter Tuning

The SunTRI/S driver is shipped with 64 2-kilobyte buffers for receiving and transmitting packets. This configuration should be adequate under normal situations. However, the token ring interface throughput can be sluggish under heavy load and may even lock up for an indefinite time. This is especially true under NFS-related operations.

This problem can be resolved by increasing the number of buffers available in the driver. The tunable parameter tr_nbufs can be set in the file /etc/system. Add this line in the file if it does not already exist:

# set tr:tr_nbufs=<xxx>

xxx is the number of 2-kilobyte buffers desired. You should not see a value less than the default value of 64. Proper setting of this parameter requires "tuning." Numbers between 400 and 500 should be reasonable for medium load. You must reboot the system after you have updated the /etc/system file for the changes to take effect.

Configuring the SunTRI/P Adapter with TCP/IP

The PCI Bus token ring driver is called trp and can be configured using ifconfig once you have established that the interface is physically present in the system and the device driver is installed. Refer to "Configuring the Network Host Files" on page 234. The rest of this section describes the configuration of individual parameters of the trp device that can be altered in the driver.conf file and global parameters that can be altered using /etc/system.

Setting the Maximum Transmission Unit

Sun supports the IEEE 802.5 Token Ring Standard Maximum Transmission Unit (MTU) size of 17800 bytes.

Configuring the Ring Speed

The ring speed is the number of megabits per second (Mbit/sec) at which the adapter transmits and receives data. The SunTRI/P software sets the ring speed to auto-detect by default. When the workstation enters the token ring,it will automatically detect the speed at which the ring is running and set itself to that ring speed. If your workstation is the first workstation on the token ring, the ring speed is set by the hub. However, if your workstation is the first workstation on the token ring and the token ring has no active hubs, you must set the ring speed manually. Additional workstations that join the token ring will set their ring speed automatically.

You can set the ring speed using the trpinstance_ring_speed parameter in the trp.conf file. The trpinstance_ring_speed parameter can be set for each interface. For example, setting the trp0_ring_speed parameter affects the trp0 adapter.

This parameter can be changed to the following settings.

To change the value of the ring speed on trp0 to 4 Mbit/sec and the ring speed on trp1 to 16 Mbit/sec, change the following settings in the trp.conf file:

trp0_ring_speed = 4 trp1_ring_speed = 16

Configuring the Locally Administered Address

The Locally Administered Address (LAA) is part of the token ring standard specification. You might need to use an LAA for some protocols, such as DECNET or SNA. To use an LAA, create a file with execute permission in the /etc/rcS.d directory, such as /etc/rcS.d/S20trLAA, with the ifconfig trinstance ether XX:XX:XX:XX:XX:XX command. The adapter instance is represented by trinstance and the LAA for that adapter is used in place of XX:XX:XX:XX:XX:XX.

# /sbin/sh case "$1" in 'start') echo "Configuring Token Ring LAA..." /sbin/ifconfig trX ether XX:XX:XX:XX:XX:XX ;; 'stop') echo "Stop of Token Ring LAA is not implemented." ;; *) echo "Usage: $0 { start | stop }" ;; esac

For example, to use an LAA of 04:00:ab:cd:11:12 on the tr0 interface, use the following command within the /etc/rcS.d/S20trLAA file:

# /sbin/ifconfig tr0 ether 04:00:ab:cd:11:12

The least significant bit of the most significant byte of the address used in the above command should never be 1. That bit is individual/group bit and used by multicasting. For example, the address 09:00:ab:cd:11:12 would be invalid and would cause unexpected networking problems.