8228 Token Ring Network Multistation Access Unit (MAU)

 

Figure 5. The 8228-001

The 8228 - an unmanaged hub - has 8 token ring user ports which use the IBM Cabling System (ICS) connectors; a media filter can be used to attach an RJ-45 token ring cable to the 8228. The 8228 has no external power supply; all its power requirements are provided by the connecting token ring adapters themselves which cause relays inside the 8228 to operate when a connection is made. There are no indicator lights on the 8228, so there is no way to know whether or not any particular port is in use or not.

The 8228 also has ring-in and ring-out ports, which can be used to link to other 8228s to form a complete ring. Two 8228s can be connected using a single cable between one unit's RO port and the other unit's RI port; greater resilience will be provided for networks of two or more 8228s if all RI/RO ports are attached, with the RO port of the last 8228 being connected back to the RI port of the first 8228. Doing this will allow the ring to remain active and complete even if any one of the RI/RO cables should fail or be disconnected. If the 8228 is to be used on its own then it is not necessary to connect the ring-out port to the ring-in port to complete the ring.

In a ring formed solely of 8228s, the speed at which the ring operates (4 Mbps or 16 Mbps) is determined by the first device to connect to the ring. This sometimes causes problems when the first device is set to auto-sense the speed of the ring: because there is not yet any ring activity it is unable to determine which speed to use and is unable to connect. This sometimes requires pre-configuration of ring speed in one or more devices. Watch out, however, because if the ring is operating at one speed (say 16 Mbps) and a new device is pre-configured with the other speed (4 Mbps in this case), attaching the new device to the 8228 will cause the ring to break. No recovery is possible until the offending device is disconnected from the 8228. The only totally fool-proof mode of operation is one in which all connecting devices are pre-configured with the same ring speed.

Table 9. 8228 models and features

Model	Description
8228-001	IBM Token Ring Network Multistation Access Unit

8226 Token Ring RJ45 Connection

 

Figure 6. The 8226-001

The 8226 is essentially an RJ-45 version of the 8228; it requires an external power supply and is therefore capable of showing port activity using indicator LEDs. It is still an unmanaged hub, meaning that it cannot report errors or be configured across the network.

 

Figure 7. The 8226 indicator LEDs and ports

Although RJ-45 connectors can be used with the 8228 when appropriate converters are installed, the 8226 does offer one function not possible with the 8228: the capability to act as a splitter. In this mode, which is selected by the switch on the 8226, the 8226's ring-in port is connected to a normal user port in another hub (such as an 8228 or another 8226). The 8226 itself provides the power required to activate this link, which then makes the devices attached to the 8226 acting as a splitter appear as part of the ring provided by the upstream hub. This can be very useful if a small group of terminals requires to be connected to a ring when the hub for the ring is not immediately adjacent to the terminals; the use of the 8226 means that only a single cable needs to be run to the main hub instead of a cable from each workstation separately.

There is no such thing as a "16/4 switch" on the 8226: the speed of operation of the token ring is determined by the connecting network adapters themselves, just as for the 8228.

 

Figure 8. The 8226 using the splitter function

Table 10. 8226 models and features

Model	Description
8226-001	IBM Token Ring RJ45 Connection

8230 Controlled Access Unit (CAU)

 

Figure 9. The 8230 base unit

The 8230 Controlled Access Unit (CAU) - a managed hub - provides a base unit as shown in Figure 9 in which up to 5 Lobe Insertion Units (LIUs) can be fitted. In addition, up to three Lobe Attachment Modules (LAMs) can also be connected using connections on the rear of the 8230 base unit. A single 8230 can provide token ring hub ports for up to 92 devices, all of which connect to the same token ring.

If the 8230 is required to connect to another hub in the ring using ring-in and ring-out connections, an RI/RO LIU must be installed in slot 1, the right-most LIU slot in the base unit. Apart from this requirement, any type of LIU can be installed in any slot.

The 8230 itself has internal token ring ports which are used for management purposes, and since these ports connect to the same single token ring as the rest of the user devices they need to be configured with an appropriate ring speed (4 Mbps or 16 Mbps). This is done using the switch on the front of the 8230 base unit, and requires that all devices which connect to the 8230 are either configured for this same ring speed or are auto-sensing devices. Attempting to connect a device set with the wrong ring speed, however, will not affect other ports - the 8230 will simply refuse to allow it to connect.

The MAC addresses of the internal ports are shown on the front of the base unit itself. There are in fact three of them (PO, PI & S) and they are consecutively numbered in this order. The presence of three MAC addresses allows either the ring-in or ring-out port to wrap in the case of some kind of failure, allowing the ring to remain active even with a single physical break in a ring cable. This feature is known as "dual ring redundancy". Previous models of the 8230 required the addition of the "dual ring redundancy feature", feature #2029, but this feature is now supplied as part of the base 8230-013 or 8230-213.

User ports on the 8230 can either be "active" or "passive". Active ports provide re-timing and re-generation of the signal and allow longer cable lengths to be used. The only difference between the two base models of 8230 is that the 8230-213 supports active UTP ports in its LAMs; the 8230-013 only supports passive LAM ports.

LAM and LIU ports offer a variety of media formats: primarily RJ-45 and the IBM Cabling System (ICS). The RI/RO ports also offer the option of using fiber, which can be used to interconnect 8230s over long distances.

 

Figure 10. Layout of the front of the 8230 base unit

The 8230 LIU ports also offer a fan-out function. This allows up to 8 MAC addresses to be connected to a single LIU port, by using a connection to the ring-in port of another hub such as the 8228. No more than 8 user devices can be connected to a single LIU port in this manner.

 

Figure 11. Fan-out using LIU ports

Fan-out is not possible using LAM ports. The other option here is the use of a hub such as the 8226 which provides the splitter function. There is no 8-port restriction imposed by the 8230 on the number of workstations which can connect using the splitter function. It just happens in this example that the 8226 only has 8 ports.

 

Figure 12. Fan-out using LIU ports, splitter using LAM ports

Both 8230 models support a choice of remote management through either CMOL (Common Management Information Protocol over Logical Link Control) or SNMP (Simple Network Management Protocol).

Management in CMOL mode is supported LAN Network Manager (LNM) for OS/2. Diskettes with the CMOL and SNMP microcode currently ship with the product; the reason for this is that the 8230 hardware only supports one mode of management at a time and the management software needs to be reloaded to change from CMOL to SNMP operating mode or vice-versa. A planned future hardware change will allow both code loads to reside in the 8230 simultaneously, at which point it will no longer be necessary to ship diskettes containing microcode. LNM for OS/2 V2 provides full management of the Controlled Access Units, including time-of-day access control, password security for configuration changes, enabling/disabling of ports, and remote microcode update. LNM offers a graphical display of the hub with color-coded indications of port health. This view is available on the LNM local ring, on token rings bridged to LNM, or across a routed environment if the router supports the flows of LLC type 1.

SNMP management of the 8230 is provided IBM Lan Network Manager, which is part of IBM's Nways Manager for AIX, HP-UX or Windows NT operating systems. LNM provides full management of these concentrators, including time-of-day access control, enabling/disabling of ports, remote microcode update, and token ring segment utilization. LNM offers a graphical display of the concentrators with color-coded indications of port health.

Table 11. 8230 models and features

Model / feature	Part number	Description
8230-013		IBM Controlled Access Unit
8230-213		IBM Controlled Access Unit
#2011	73G2011	ICS 2-port LIU
#2009	73G2009	UTP 4-port LIU
#2008	73G2008	UTP 3-port LIU
#6738	13H6738	Shielded RJ-45 LAM (passive)
#5501	53F5501	ICS LAM
#6748	13H6748	Shielded UTP LAM (active - model 213 only)
#7737	59G7737	ICS RI/RO
#2007	73G2007	Shielded RJ-45 RI/RO
#2010	73G2010	Optical fiber RI/RO
#7751	59G7751	Combination ICS/fiber RI/RO
#7754	59G7754	Combination fiber/ICS RI/RO

8239 Token Ring Stackable Hub

 

Figure 13. A fully-configured 8239-001

The 8239 Token Ring Stackable Hub - a managed hub - provides a logical concentration of a single management point for several token ring segments. Unlike the 8230, in which all devices connecting to a single managed unit are connected to the same token ring segment, a stack of 8239s can provide up to 8 separate token ring segments from a single management point.

The primary building block of this hub offering is the Model 1. It is a fully functional concentrator or hub, with the additional capability of providing Ring-In/Ring-Out (RI/RO) connections to expand the LAN segment, stack management functions, and network management functions. The Model 2 is a fully functional hub that can be used as a stand-alone hub or as an expansion hub to increase the number of device attachments in the stack. For example, the 8239-002 will isolate beaconing token ring ports and will show the error using its status LEDs but will not be able to communicate this problem to a network management station if there is no 8239-001 on the same ring segment.

An optional 16-port Expansion Feature for both models and, for Model 1 only, RJ-45 copper or ST fiber RI/RO modules complete the offering. The RI/RO modules would only be used to connect to another hub such as the 8228 or 8230. Fan-out to devices such as the 8226 or 8228 is also supported; more than 8 ports may be provided through the fan-out device but only the first 8 are reported for network management purposes using RMON.

A single stack of 8239 units is constructed by interconnecting the 8239 units through the stack-in and stack-out ports. Standard Category 5 UTP cables are required for this.

All hubs in the stack are manageable from a single point using out-of-band access, available on both models, or in-band access via the Model 1. A Model 1 is required for network management functions. Information is accessed either through the terminal interface or an SNMP-compatible application. The 8239 is supported by IBM's Nways Workgroup Manager for Windows NT, Nways Manager for AIX and Nways Manager for HP-UX. The 8239 offers many or more of the same network management features as multifunction switching hubs but at a much lower price per port. Management functions include the ability to identify which port in the stack is being used by a particular MAC address and the ability to configure ports so that only specific MAC addresses can use them.

In the 8239 stack, segmentation is provided at the hub level, by wrapping a given hub in or out of the default single segment. This isolates the data path of one or more hubs from the data paths of the other hubs in the stack. This segmentation does not extend to segmenting ports in a single hub: all ports in the hub, including additional ports if the optional feature card is installed, are treated as a single entity or hub when segmenting a ring. Every hub in a stack must be assigned to a segment; the factory default has all hubs assigned to a single segment. If, for example, a stack consisted of four hubs (any combination of models), it could be segmented into a maximum of four segments. If a stack consisted of the maximum eight hubs, from one to eight segments could be created. Hubs in the same segment must be adjacent to each other in ring order when you connect them with the intra-stack cables. Management of the stack is maintained because the control path of the stack is not affected when the data path is altered because of segmentation. If network management functions, like Ring-In/Ring-Out or RMON, are important for a particular segment, that segment must consist of at least one Model 1.

The 8239 offers an impressive array of network management functions as well as stack management capability. Functions like Ring-In/Ring-Out, RMON, 802.5, Surrogate MIB for media management, etc. are all programmed into the Model 1. Accordingly, a Model 1 must be included in each segment where this activity is required.

 

Figure 14. 8239 stack with three segments

As an example of segmentation, Figure 14 shows a single stack containing three segments and six hubs; each segment can be managed because an 8239-001 is included in each.

Table 12. 8239 models and features

Model / feature	Part number	Description
8239-001	08L3033	IBM Token Ring Stackable Hub
8239-002	08L3034	IBM Token Ring Stackable Hub
#3035	08L3035	16-port Expansion Feature
#3036	08L3036	RJ-45 Copper RI/RO (Model -001 only)
#3037	08L3037	Optical fiber RI/RO (Model -001 only)