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| Title: | DEChub/HUBwatch/PROBEwatch CONFERENCE |
| Notice: | Firmware -2, Doc -3, Power -4, HW kits -5, firm load -6&7 |
| Moderator: | NETCAD::COLELLA DT |
|
| Created: | Wed Nov 13 1991 |
| Last Modified: | Fri Jun 06 1997 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 4455 |
| Total number of notes: | 16761 |
2340.0. "FDDI Configuration Guide" by DELNI::PIEPER () Fri Jun 02 1995 13:43
FDDI CONFIGURATION OPTIONS FOR THE DEChub 900MS BACKPLANE AND DEChub ONEs
This note is the replacement for note 1597, which dealt with the FDDI
configuration options for dual rings in DEChub 900 backplanes. This note
explains the changes included with the Wave 3 product release, which are:
- Support for tree connections in the backplane
- Support for dual homing of the hub in a treed configuration
- Support for the DECconcentrator 900TH
- Support for auto healing of both dual ring and tree connections
- Support for dual rings and trees in the DEChub ONEs
- Selection of FDDI network building blocks via setup port
- Support for cold swapping of FDDI modules
- Support for quick PC-trace recovery
- Defined token ordering of hub modules
This memo will detail the configuration capabilities that are supported in
DEChub FDDI modules with Wave 3. It is assumed that the reader knows basic
FDDI configuration rules and understands the differences between an A, B,
M, and S port. If these are not familiar, see Appendix A for a brief dis-
cussion of the important concepts. These DEChub configuration options will
be explained by using the DECconcentrator 900MX, DECconcentrator 900TH, the
PEswitch 900TX and the DECswitch 900EF.
BASIC FDDI RULES
First, realize that ANY FDDI connection between two adjacent stations is
actually two POINT to POINT connections no matter where the stations are in
the configuration (tree or dual ring). This is a basic fact for any vendor's
FDDI products, whether they are in a hub or not. The backplane of the DEC-
hub 900 is used to make these point to point connections between DECconcen-
trators, FDDI DECswitches or PEswitches in the hub. One backplane channel is
needed for each connection. Since two connections are required between any
two ports, TWO backplane channels are required for each connection between
any two ports on DECconcentrators, FDDI DECswitches, or PEswitches, regard-
less of the actual configuration.
The terminology used is, unfortunately, very ambiguous when it comes to
describing configurations. It is important to understand that dual rings
and trees are PHYSICAL descriptions of the network topology. In all cases,
the FDDI is a LOGICAL ring, i.e., a token passes from station to station in
the ring. The PHYSICAL implementation may be configured as a tree or a
dual ring, but in all cases a logical ring exists.
Technically, any type of configuration (dual ring, tree, or dual ring of
trees) could be supported in the DEChub 900 backplane. For ease of use,
only dual ring and tree configurations are supported. A user can build up
to FOUR independent FDDI networks across the hub backplane. Each FDDI net-
work can be either a dual ring or a tree, but not a mixture of both.
BASIC DUAL RING CONFIGURATIONS
DEChub FDDI modules can typically support front panel as well as backplane
FDDI ports. When configured in a dual ring, ports are assigned a RING
port type (A or B) via the Station Configuration screen of HUBwatch. The
dual attachment station (DAS) port configurations in Diagram #1 are all
possible with this soft assignment capability. Since individual modules
may support a subset of these configurations, each module will be detailed
in other sections.
Diagram #1: Possible DUAL RING Port Configurations
Front Panel Ports
A B A B
| | | |
+-+----------+ +------------+ +---------+-+ +-+--------+-+
| | | | | | | |
+----------+-+ +-+--------+-+ +-+---------+ +----------+-+
| | | |
B A B A
Backplane Ports
BASIC TREE CONFIGURATIONS
When connected in a tree configuration, front panel ports and backplane
ports are assigned a TREE port type (M or S) via the Station Configuration
screen of HUBwatch. The tree port configurations in Diagram #2 are all
possible with this soft assignment capability.
Diagram #2: Possible TREE Port Configurations
Front Panel Ports
S M S M A B
| | | | | |
+--------+ +------+-+ +-+---+-+ +-+------+ +-+----+-+
| | | | | | | | | |
+-+----+-+ +-+------+ +-------+ +------+-+ +-+------+
| | | | |
M S M S M
Backplane Ports
Note the fifth configuration with an M port in the backplane, and A and B
ports on the front panel. This configuration is only implemented in con-
centrators, and is used for connecting to a dual ring, or in a dual homed
configuration.
Another important point to note is that when the user accessible FDDI ports
are reconfigured as TREE ports, the A port always becomes an M port and the
B port always becomes an S port. This is true for either front panel ports
or MODPMD ports in a DEChub ONE-MX.
DECconcentrator 900MX
The DECconcentrator 900MX is actually an EIGHT port FDDI concentrator where
SIX ports are on the front panel and TWO ports attach to the DEChub 900 back-
plane or to the DEChub ONE-MX that supports MODPMDs.
As shown in Diagram #3, Port #1 on the front panel of the DECconcentrator
900MX can act as either an A or M port and Port #6 can act as either a B,
S or M port. The two backplane ports are also software configurable via
HUBwatch.
Diagram #3: DECconcentrator 900MX Port Configuration Capabilities
A,M B,S
+-----------------------------+
DEChub 900MS Backplane / DEChub ONE-MX /|
+-----------------------------+ |
A,M B,S / / +
| | / DECconcentrator / |/
+--+-----------+---+ / / +
| concentrator | +-----------------------------+ /
+-+---+-+-+-+----+-+ | | /
| | | | | | | A,M M M M M B,S,M |/
A,M M M M M B,S,M +-----------------------------+
Module Front Panel Module Front Panel
DECconcentrator 900TH
The DECconcentrator 900TH is a sixteen port FDDI concentrator where four-
teen ports are on the front panel and TWO ports attach to the DEChub 900
backplane or to the DEChub ONE-MX that supports MODPMDs. Twelve of the
front panel ports are fixed UTP connections. The two remaining ports can
be configured for either UTP, multimode fiber, or single mode fiber by the
addition of MODPMD modules.
As shown in Diagram #4, MODPMD Port #1 on the front panel of the DECconcen-
trator 900TH can act as either an A or M port and MODPMD Port #2 on the
front panel can act as either a B, S or M port. The two backplane ports
are also software configurable via HUBwatch so both dual ring and tree
connections can be supported.
Diagram #4: DECconcentrator 900TH Port Configuration Capabilities
A,M B,S
+-----------------------------+
DEChub 900MS Backplane / DEChub ONE-MX /|
+-----------------------------+ |
A,M B,S / / +
| | / DECconcentrator / |/
+--+----------+----+ / / +
| concentrator | +-----------------------------+ /
+-+-----+----+---+-+ | | /
| | |...| | A,M B,S,M M M .... M |/
A,M B,S,M M M +-----------------------------+
Module Front Panel Module Front Panel
DECswitch 900EF
The DECswitch 900EF (previously called the DECbridge 900MX) differs from
the DECconcentrator in that it supports only TWO FDDI ports (Port #1A and
Port #1B) that can be INDIVIDUALLY ASSIGNED to either the front panel or
the backplane. That means the DECswitch 900EF can have only two active
FDDI ports at any one time (two front panel ports, one front panel and one
backplane port, or two backplane ports). The port-type assignments are
"software-selectable" via HUBwatch or the set up port menu, where two front
panel ports, two backplane ports or a front panel port and a backplane port
can act as A and B ports or M and S ports.
Diagram #5: DECswitch 900EF Port Configuration Capabilities
A,M B,S
------------------------------+
DEChub 900MS Backplane / DEChub ONE-MX /|
+-----------------------------+ |
A,M B,S / / +
| | / DECswitch / |/
+-+---------+-+ / / +
| DECswitch | +-----------------------------+ /
+--+-------+--+ | | /
| | | A,M B,S |/
A,M B,S +-----------------------------+
Module Front Panel Module Front Panel
PEswitch 900TX
The PEswitch 900TX differs from the DECswitch 900EF in that it supports two
FDDI port connections to the DEChub backplane or DEChub ONE-MX ONLY. There
are NO front panel FDDI ports on the PEswitch 900TX. The port-type assign-
ments are also "software-selectable" allowing either A and B or M and S
connections at any time.
Diagram #6: PEswitch 900TX Port Configuration Capabilities
A,M B,S
------------------------------+
DEChub 900MS Backplane / DEChub ONE-MX /|
+-----------------------------+ |
A,M B,S / / +
| | / PEswitch / |/
+-+---------+-+ / / +
| PEswitch | +-----------------------------+ /
+-------------+ | | /
| |/
+-----------------------------+
ADDITIONAL INFORMATION ON THE USE OF M and S PORTS
1) In order to simplify the rules as much as possible, a decision was made
to allow an individual network to be configured as a dual ring or a tree.
This was required to prevent configurations that would automatically be
disconnected by the actions of the FDDI configuration rules, which operate
at the module level, independent of HUBwatch. The intent is to offer
choices which work, not ones that need additional rule checking beyond
what HUBwatch can provide. In hubs with multiple FDDI networks, some
of the networks can be configured as dual rings, others can be configured
as trees, but each individual network can be of only one type.
2) For concentrators, we now have the option of devices with one S port, and
up to 15 M ports. Such a device is known as a Single Attach Concentrator
(SAC) in FDDI terminology. This is a new device type in Digital's FDDI
product set.
3) The FDDI rules require that stations with M ports be called concentrators.
Consequently, when a switch is configured with M and S ports, it must report
itself as a concentrator in FDDI NIF and SIF frames, and in the FDDI and
SNMP MIBs. Therefore, HUBwatch, FDDI monitors, and FDDI Ring Maps will
announce the station type of a treed DECswitch 900EF or PEswitch 900TX as
a Single Attach Concentrator (SAC), rather than as a Single Attach Station
(SAS).
FDDI BUILDING BLOCKS
Since ANSI standard FDDI configuration rules are very complex and various
connections are defined as "legal" but result in limited use configurations
such as wrapped rings, a simple to use "building block" approach was adopted
for configuring FDDI in the backplane of the DEChub 900 and in the DEChub
ONE-MX. The network manager assigns a port type by selecting a "building
block". These building blocks are divided into two groups - RING and TREE.
There are a total of 9 building blocks; 4 are used for building dual rings,
and 5 are used for building trees. HUBwatch will only allow connections to
be made between building blocks of the same group, in order to minimize
annoying errors such as connections that break because of the standard's
preference for trees over dual rings.
RING BUILDING BLOCKS
The four RING building blocks, which are used to build dual rings,
are named as follows and shown in Diagram #7.
Trunk B: B port connects to the backplane or DEChub ONE-MX MODPMD,
A port out the front
Trunk AB: A and B ports connect to the backplane or MODPMDs on the
DEChub ONE-MX
Trunk A: A port connects to the backplane or DEChub ONE-MX MODPMD,
B port out the front
Stump Primary: A and B ports connect to the front panel
Diagram #7: RING Building Blocks
Front Panel ports
A B A B
| | | |
+-+-----+ +-------+ +-----+-+ +-+---+-+
| Trunk | | Trunk | | Trunk | | Stump |
| B | | A B | | A | |Primary|
+-----+-+ +-+---+-+ +-+-----+ +-------+
| | | |
B A B A
Backplane or DEChub ONE-MX MODPMD ports
TREE BUILDING BLOCKS
The five TREE building blocks are named as follows, and shown in Diagram #8:
Nonroot MS: M and S ports connect to the backplane or MODPMDs on the
DEChub ONE-MX
Nonroot M: M port connects to the backplane or DEChub ONE-MX MODPMD,
S port out the front
Nonroot SAC: M and S ports connect to the front panel
Nonroot S: S port connects to the backplane or DEChub ONE-MX MODPMD
and M port out the front
Root Primary: A and B out the front, M connected to backplane or
DEChub ONE-MX MODPMD
Diagram #8: TREE Building Blocks
Front Panel Ports
S M S M A B
| | | | | |
+--------+ +------+-+ +-+----+-+ +-+------+ +-+----+-+
| Nonroot| | Nonroot| | Nonroot| | Nonroot| | Root |
| MS | | M | | SAC | | S | | Primary|
+-+----+-+ +-+------+ +--------+ +------+-+ +-+------+
| | | | |
M S M S M
Backplane or DEChub ONE-MX MODPMD ports
DEFAULT CONFIGURATIONS
Modules in the DEChub 900
The default configuration for either the DECconcentrator 900MX, the DEC-
concentrator 900TH, or the DECswitch 900EF is that ALL front panel ports
are active and A and B ports are out the front. This means that NO
redirection to backplane ports or backplane connections are made between
FDDI modules unless the Network Manager chooses to do so. The Network
Manager will need to issue the appropriate HUBwatch commands to establish
FDDI networks across the backplane of the DEChub 900. While the default
for the PEswitch 900TX is to the backplane ports, no FDDI LAN connections
across the backplane are made by default. The Network Manager will need to
issue the appropriate HUBwatch commands to connect PEswitches to an FDDI
backplane LAN.
Modules in DEChub ONE / DEChub ONE-MX
The default configuration for either the DECconcentrator 900MX, the DEC-
concentrator 900TH, or the DECswitch 900EF is that ALL front panel ports
are active and A and B ports are out the front. This is true for either
the DEChub ONE (DEHUA) which supports one Ethernet connection or the DEChub
ONE-MX (DEF1H) which supports one Ethernet connection and up to two MODPMD
FDDI connections. The default configuration for the PEswitch 900TX is A
and B to the MODPMD ports of the DEChub ONE-MX. No FDDI connections are
available when the PEswitch 900 is used with the DEChub ONE.
A Network Manager who wishes to use the MODPMD ports of the DEChub ONE-MX
will need to issue the appropriate commands to enable the MODPMD ports,
using the building blocks previously described. This can be done either
via HUBwatch or the setup port of the DEChub ONE-MX.
Modules in a DEChub ONE or DEChub ONE-MX are required to perform two
additional tasks. The first is that they must remember their configuration
so that they wake up in the previously configured state following a power
failure. This memory applies if a module is moved to the same type of
DEChub ONE - as far as the module can tell, it is in the same environment
as when it was powered off.
The second task for a module in a DEChub ONE or DEChub ONE-MX is for it to
recognize a change of environment when moved between a DEChub 900, the
DEChub ONE-MX, or the DEChub ONE. When the change of environment is detected
the module assumes the default condition of A and B out the front panel,
except for the PESwitch 900 TX, which is A and B to the backplane or DEChub
ONE-MX MODPMD ports.
For example, if a DECswitch 900EF module which had been configured with
S and M ports on the back is moved from a DEChub ONE-MX to another DEChub
ONE-MX, the module will power up with the MODPMDs of the second DEChub ONE-MX
enabled as S and M ports. If the module is then moved to a DEChub ONE, it
will detect an environment change, and power up with the front panel A and B
ports enabled. If it is then moved back to a DEChub ONE-MX, it will detect
a new environment, and power up with the front panel ports enabled as A and
B ports.
Also, if a module is moved from a DEChub ONE-MX to another DEChub ONE-MX with
a different MODPMD configuration, the module will wake up believing that it
is still in the original DEChub ONE-MX, and will attempt to configure its
ports per the remembered configuration. It will not detect the change in
configuration of the MODPMDs.
FDDI AUTO HEALING
The auto healing features of the FDDI modules have been improved with
this Wave of firmware. New features include:
1) reconfiguration around modules determined to be "unavailable"
2) support for cold swapping of modules
3) indication of a change in the FDDI configuration of the hub via
dotted lines on the HUBwatch LAN Interconnect screen
When the HUB manager is upgraded, Auto Healing will be disabled by default.
Following the upgrade of the modules to the latest version of firmware, Auto
Healing can be enabled. It will then continue to be enabled unless it is
subsequently turned off by the network manager.
Previously, when a module was removed from the hub, the connections on
either side of it would first wrap, and then be joined together, once
the hub detected the removal of the module. If a module failed, the
connections would wrap, but the healing would never occur, unless the
module was physically removed from the hub chassis.
In this release, the ability to heal the connections becomes more important,
due to the addition of treed connections, which, by their nature, cannot
restore the ring by wrapping. Without the auto-healing feature, the loss of
a module results in the loss of all modules below that module in the tree.
Now, for both dual ring and tree configurations, if a module is physically
removed, or, is determined to be "unavailable", the hub will heal the broken
connection, thus restoring the network to operation. "Unavailable" is
defined as a condition in which the HUB's built in manager cannot communicate
with the module for longer than 3 seconds. Such a condition is indicated by
the word "Unavailable" in the lower line of the slot report in the LCD
display on the DEChub 900 front panel.
Please note that some outages will not be detected, so healing cannot be
guaranteed to always correct the break in a tree, unless the module has
been physically removed.
In high availability situations where outages longer than 500 milliseconds
cannot be tolerated, DIGITAL recommends that a dual ring configuration be
implemented, since the dual ring will wrap and connectivity will be
maintained in all cases.
Before this Wave, the removal of an FDDI module caused the HUB to forget
what type of module was in the slot, what building blocks were used, and
also the position of the module in the hub's token flow. With this Wave,
the Hub will automatically restore the previous configuration, as long as
a module of the same type is inserted in the slot. This behavior occurs
whether the module is replaced with power applied to the hub (hot swapping),
or when the hub power is shut down (cold swapping). This makes repair of
a faulty module significantly less time consuming.
Finally, when an FDDI module is patched out of an FDDI configuration by
Auto Healing, the LAN Interconnect screen of HUBwatch will flag that module
with a dashed line connection instead of a solid line. This is not auto-
matically displayed, but will appear when the screen is refreshed. For
example, if a module has become unavailable and has been removed from the
ring by Auto Healing, the connections from the module to the LAN will be
dotted, indicating that a change of configuration has occurred.
********************* I M P O R T A N T *** N O T E ************************
If the Auto Healing function is enabled, HUBwatch will PREVENT the
user from adding or deleting FDDI connections, Ethernet connections,
Ethernet LANs or FDDI LANs via the LAN Interconnect screen. This
is designed to preserve the existing configuration until someone
can physically replace any failed modules. An error message will
be displayed informing the user that the requested action cannot
be taken, and will offer a list of alternatives. If the change
is still desired the user must first disable Auto Healing by
selecting "Disable" from the Auto Healing buttons on the LAN
Interconnect screen. This will delete the patched out connections.
Following the reconfiguration, Auto Healing can be reenabled. This
new configuration will then be shown on the screen.
********************* I M P O R T A N T *** N O T E ************************
EXAMPLE CONFIGURATIONS
FDDI trees and FDDI dual rings are supported across the backplane of the
DEChub 900MS. The dual ring configuration should be used across the back-
plane if dual ring connections are pulled to the hub since it has more robust
and quicker fault tolerance capabilities (ring wrapping plus auto-healing -
both are detailed later) than tree configurations. If an FDDI tree connection
is pulled to the DEChub, obviously a tree configuration should be built across
the backplane. The following diagrams attempt to demonstrate the various
types of FDDI configurations that are currently supported in the DEChub.
TREE CONFIGURATIONS
It is possible to build many types of tree configurations in the DEChub900
backplane. Trees can be contained within the backplane, they can connect
an individual tree in the hub to a higher level of a tree, or, they can
be used for interconnection of hubs. The following examples demonstrate
different supported tree configurations.
EXAMPLE 1: SELF CONTAINED TREE OF CONCENTRATORS IN BACKPLANE
In this example, a tree is constructed entirely within the backplane. The
backplane ports of the concentrator modules are enabled to be of type M and
S, and the front panel ports become M ports. The module in the highest slot
number will be the top of the tree, and its M port will connect to the S
port of the module with the second highest slot number, and so on down the
line. Two backplane channels are required per connection. For the example
shown, a total of four backplane channels are in use.
Diagram #9: DECconcentrator Tree Connections in backplane
Front Panel Ports
M M M M M M M M M M M M M M M M M M
| | | | | | | | | | | | | | | | | |
+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+
| CON #1 | | CON #2 | | CON #3 |
+-+---------+-+ +-+---------+-+ +-+---------+-+
| | | | | |
| +-------------+ +-------------+ |
M S M S M S
Backplane Ports
Diagram #10: Building Block Representation of Diagram #9 Configuration
+-------+ +-------+ +-------+
|Nonroot| |Nonroot| |Nonroot|
| MS | | MS | | MS |
+-+---+-+ +-+---+-+ +-+---+-+
| | | | | |
M S M S M S
EXAMPLE 2: SELF CONTAINED TREE OF SWITCHES AND CONCENTRATORS IN BACKPLANE
In this example, a tree is constructed entirely within the backplane, but
a mixture of device types is used. The backplane ports of the modules are
enabled to be of type M and S. The front panel ports of the concentrators
become M ports, and the front panel ports of the switches become unusable.
The module in the highest slot number will be the top of the tree, and its
M port will connect to the S port of the module with the second highest slot
number, and so on down the line. This example also uses a total of four
backplane channels.
Diagram #11: Tree Connections to an FDDI Network
Front Panel Ports
M M M M M M
| | | | | | | |
+-+-+-+-+-+-+-+ +-------------+ +---------+-+-+
|DECcon 900TH | |PEswitch 900 | |DECsw 900 EF |
+-+---------+-+ +-+---------+-+ +-+---------+-+
| | | | | |
| +-------------+ +-------------+ |
M S M S M S
Backplane Ports
Diagram #12: Building Block Representation of Diagram #11 Configuration
+-------+ +-------+ +-------+
|Nonroot| |Nonroot| |Nonroot|
| MS | | MS | | MS |
+-+---+-+ +-+---+-+ +-+---+-+
| | | | | |
M S M S M S
EXAMPLE 3: TREE CONNECTIONS TO AN EXTERNAL CONCENTRATOR
Trees within the hub can connect to a higher level concentrator by making
one of the modules have a front panel S port, and making all other modules
have M and S ports on the backplane. For example, a tree of PESwitch 900TX
modules can be connected to an external ring using either a DECSwitch 900EF
or one of the concentrators to make the external connection.
Diagram #13: Tree Connections to an FDDI Network
Front Panel Ports
S
|
+-------------+ +-------------+ +-----------+-+
|PEswitch 900 | |PEswitch 900 | |DECsw 900 EF |
+-+---------+-+ +-+---------+-+ +-+-----------+
| | | | |
| +-------------+ +-------------+
M S M S M
Backplane Ports
Diagram #14: Building Block Representation of Diagram #13 Configuration
S
|
+-------+ +-------+ +-----+-+
|Nonroot| |Nonroot| |Nonroot|
| MS | | MS | | M |
+-+---+-+ +-+---+-+ +-+-----+
| | | | |
M S M S M
EXAMPLE 4: DUAL HOMING AND CONNECTION TO AN EXTERNAL DUAL RING
In some cases it is desirable to connect the hub to an external dual ring,
and tree the modules within the backplane. In other cases, it is desirable
to have a redundant connection from the hub to higher level concentrators.
This second case is commonly referred to as dual homing. Either of these
configurations requires the use of a concentrator at the top of the tree.
Note, the modules connected via the hub backplane are single attach
modules; the dual homing pertains to the connection between the hub based
tree and the external concentrator.
Diagram #15: Dual Homed Connections to an FDDI Network
Front Panel Ports
A B
| M M M M |
| | | | | |
+-------------+ +-------------+ +-+-+-+-+-+-+-+
|Switch | |Switch | |Concentrator |
+-+---------+-+ +-+---------+-+ +-+-----------+
| | | | |
| +-------------+ +-------------+
M S M S M
Backplane Ports
Diagram #16: Building Block Representation of Diagram #15 Configuration
A B
| |
+-------+ +-------+ +-+-----+-+
|Nonroot| |Nonroot| | Root |
| MS | | MS | | Primary |
+-+---+-+ +-+---+-+ +-+-------+
| | | | |
M S M S M
EXAMPLE 5: TREE EXTENSION
In cases where it is desirable to tree together multiple hubs or hub modules
(e.g., when more than 8 modules are required in the same closet), it is
possible to configure an FDDI module with front panel connections (DECswitch
900EF or DECconcentrator) at the bottom of the tree to have an M port out
the front panel. This M port can be used to connect an external module or
an additional hub to the hub based tree.
Diagram #17: Tree Connections to an FDDI Network
S
Front Panel Ports |
+----------------------------------------+-----+
| DEChub 900 | |
+-------------+ | |
|S | |M | |
+-----------+-+ | +-+-----------+ +-----------+-+ |
|FDDI Module | | | DECswitch | | DECswitch | |
+-+-----------+ | +-----------+-+ +-+---------+-+ |
| | | | |
M | +-------------+ |
| S M |
External +----------------------------------------------+
Module Backplane Ports
Diagram #18: Building Block Representation of Diagram #17 Configuration
S M S
| | |
+-----+-+ +-+-----+ +-----+-+
|Nonroot| |Nonroot| |Nonroot|
| M | | S | | M |
+-+-----+ +-----+-+ +-+---+-+
| | |
M S M
FAULT TOLERANCE IN TREES
If a concentrator or bridge/switch in a tree fails, the FDDI ring will be
broken, and the stations below the break will be isolated from the rest of
the network. Two mechanisms then come into play. If the module is detected
as being "unavailable", Auto Healing will detect the condition and
reconnect the two neighboring modules in the DEChub via the backplane,
thereby healing the ring. If the module is physically removed, HUB
Management will detect the removal and reconnect the two neighboring FDDI
modules via the backplane, thereby healing the ring. This is a distinct
advantage that FDDI modules in a DEChub have over individual non-hub-based
FDDI products.
DUAL RING CONFIGURATIONS
EXAMPLE 1: DUAL RING CONCENTRATORS WITH CONNECTION TO EXTERNAL DUAL RING
In the Diagram #19 configuration, all the concentrators connect directly to
the dual ring. Concentrator #3 has a front panel port act as the external
B-port connection to the dual ring, and one of its backplane ports act as
the A-port. With Concentrator #2, both backplane ports are used as the A/B
connections to the dual ring. Concentrator #1 has the B-port connection to
the dual ring via the backplane and the dual ring exits via a front panel
port that is acting as an A-port.
Diagram #19: DECconcentrator Dual Ring Connections to an FDDI Network
Front Panel Ports
A B
| M M M M M M M M M M M M M M M M |
| | | | | | | | | | | | | | | | | |
+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+
| CON #1 | | CON #2 | | CON #3 |
+-----------+-+ +-+---------+-+ +-+-----------+
| | | |
+-------------+ +-------------+
B A B A
Backplane Ports
Diagram #20: Building Block Representation of Diagram #19 Configuration
A B
| |
+-+-----+ +-------+ +-----+-+
| Trunk | | Trunk | | Trunk |
| B | | A B | | A |
+-----+-+ +-+---+-+ +-+-----+
| | | |
B A B A
EXAMPLE 2: DUAL RING SWITCHES WITH CONNECTION TO EXTERNAL DUAL RING
DECswitch 900EFs can be dual-ringed just like DECconcentrator 900MXs;
Diagram #21 shows that configuration. Switch #3 has the B-port assigned to
one front panel port and the A port assigned to a backplane port. Switch #2
has the A and B ports assigned to the backplane ports only (front panel ports
are not active nor usable). Switch #1 has the B-port assigned to a backplane
port while the A-port is assigned to a front panel port.
Diagram #21: Dual Ring Connections for DECswitch 900EFs
Front Panel Ports
A B
| |
+---+---------+ +-------------+ +---------+---+
| SWITCH #1 | | SWITCH #2 | | SWITCH #3 |
+-+---------+-+ +-+---------+-+ +-+---------+-+
| | | |
+-------------+ +-------------+
B A B A
Backplane Ports
Diagram #22: Building Block Representation of Diagram #21 Configuration
A B
| |
+-+-----+ +-------+ +-----+-+
| Trunk | | Trunk | | Trunk |
| B | | A B | | A |
+-----+-+ +-+---+-+ +-+-----+
| | | |
B A B A
Obviously, a fourth option is available, which is to assign both A and B to
the front panel ports (the Stump Primary building block), which would allow
a single DECswitch 900EF or DECconcentrator in a DEChub 900 to connect up
to an external FDDI backbone network.
EXAMPLE 3: PESWITCH CONNECTIONS TO AN EXTERNAL DUAL RING
One option for PEswitch 900TXs is to configure them in a dual ring, but
remember that there are NO front panel FDDI connections on a PEswitch 900
Therefore dual ring connections to a PEswitch 900TX require that FDDI be
brought INTO the DEChub backplane via a DECswitch 900EF or a DECconcentrator,
and OUT of the DEChub backplane via a DECswitch 900EF or a DECconcentrator.
In other words, TWO DECswitch or DECconcentrator modules are needed for
dual ring connections of PEswitch 900TXs to an external FDDI network.
Diagram #23: Dual Ring Connections for PEswitch 900TX
Front Panel Ports
A B
| M M M M M |
| | | | | | |
+---+---------+ +-------------+ +-+-+-+-+-+-+-+
| DECSWITCH | | PESWITCH | |CONCENTRATOR |
+-+---------+-+ +-+---------+-+ +-+---------+-+
| | | |
+-------------+ +-------------+
B A B A
Backplane Ports
Diagram #24: Building Block Representation of Diagram #23 Configuration
A B
| |
+-+-----+ +-------+ +-----+-+
| Trunk | | Trunk | | Trunk |
| B | | A B | | A |
+-----+-+ +-+---+-+ +-+-----+
| | | |
B A B A
EXAMPLE 4: SELF CONTAINED DUAL RING ON BACKPLANE
To create a DUAL RING that is completely contained in the DEChub 900 back-
plane, you need to connect all the backplane ports of the FDDI modules
together.
Diagram #25: Self-Contained Dual Ring in the Backplane
Front Panel Ports
M M M M M M
| | | | | |
+-+-+-+-+-+-+-+ +-------------+ +-------------+
| CON #1 | | PESWITCH #1 | | PESWITCH #2 |
+-+---------+-+ +-+---------+-+ +-+---------+-+
| | | | | |
| +-------------+ +-------------+ |
| B A B A |
+---------------------------------------------------------+
A Backplane Ports B
NOTE: You can create a self-contained dual ring in the DEChub backplane
with PEswitches by themselves, or PEswitches and DECconcentrators and
DECswitches, since there is NO EXTERNAL connection to an FDDI DUAL RING
required. Note that the DECconcentrator in Diagram #25 is providing M
port tree connections to externally-treed FDDI stations (bridges,
concentrators or end user stations with S, A or B ports), and is NOT
connected to an external M port (NOT treed off an external concentra-
tor's M port).
MULTIPLE RINGS
Just repeat configuration #19 (the ring) twice and don't interconnect them.
You can support FDDI concentrators or FDDI switches (note that the DECswitch
900EF is a power hungry module, so all eight slots cannot be populated with
DECswitch 900EFs) in all eight slots of the DEChub 900, and interconnect them
across the backplane into a single FDDI network, or into a maximum of four
independent FDDI networks.
FAULT TOLERANCE in DUAL RINGS
When a concentrator or switch in a dual ring is removed (hot swapped), the
FDDI ring will wrap per the FDDI standard. If the removed module has both
the A and B ports connected to the DEChub backplane, then the DEChub Manage-
ment will detect the removal and reconnect the two neighboring FDDI stations
in the DEChub via the backplane thereby "un-wrapping" the ring. If a module
is detected as being "unavailable", the HUB manager will also patch around
the module (as long as AUTO HEALING has been enabled). This is a distinct
advantage that FDDI modules in a DEChub have over individual non-hub-based
FDDI products.
NOTE: Ring wrap occurs much faster than "backplane healing", so it will
always occur first and then the DEChub management will reconnect
the DAS stations via the backplane and the dual ring will "un-wrap".
NOTE: Fault recovery (unwrapping of the dual ring in the DEChub backplane)
is supported in all FDDI DEChub modules.
Looking at Diagram #26, if Concentrator #1 is hot swapped, Concentrator #2
and Switch #1 can continue communicating with each other and all other FDDI
stations on the DAS backbone, since Concentrator #2 will wrap the FDDI
dual ring. If Concentrator #2 fails, Concentrator #1 and Switch #1 will
wrap the dual ring and communications can continue. Within seconds of this
particular ring wrap where Concentrator #2 has become "unavailable", Hub
Management will automatically reconnect Switch #1 to Concentrator #1 and the
dual ring will unwrap. If, at a later time, another concentrator of the same
type is inserted in the same slot that held Concentrator #2, the replacement
concentrator will be reinserted into the ring via the Auto Healing feature.
Diagram #26: Ring Configuration
Front Panel Ports
B A
M M M M M | M M M M M M |
| | | | | | | | | | | | |
+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+ +---------+---+
| CON #1 | | CON #2 | | SWITCH #1 |
+-+---------+-+ +-+---------+-+ +-+---------+-+
| | | |
+-------------+ +-------------+
A B A B
Backplane Ports
TOKEN ORDERING OF TREES OR DUAL RINGS
A new feature for Wave 3 is the introduction of a defined token order
for FDDI dual rings or trees in the hub. The token flow, defined as the
order in which the token visits the MACs, is essentially from slot 1
towards slot 8, whether the backplane network is a dual ring or a tree.
If there are multiple FDDI networks, each network independently orders
the token flow from lowest slot to highest slot, as closely as is allowed
by the FDDI rules. This algorithm was designed to ensure that repaired
modules return to the same token order that had been assigned prior to
the occurrence of a module fault. It also matches the power shedding
algorithm (which sheds modules from slot 1 towards slot 8). The following
examples illustrate the concept.
Please refer to Diagram #27 for the following discussion. Suppose a hub is
configured as a dual ring, with FDDI modules in slots 1,2,3,4,6, and 8.
Assume further that the front panel A port is found on the module in slot 4,
and the B port on the module in slot 8. So the token, which is flowing
on the primary ring, enters the hub at slot 4 and exits from slot 8.
A ringmap will show the order of token flow, based on the ordering of the
MACs in the ring. In this case, HUBwatch will configure the backplane so
that the token enters the A port of slot 4, encounters the MAC for slot 4,
and the next MAC it sees is in slot 1. The token flows, in order, through
the MACs in slots 1,2,3, 6, and finally slot 8. In this case a ringmap
would record the token order as 4>1>2>3>6>8. Note that, in order to
accomplish this ordering, the built-in DEChub management has automatically
connected the B port of Slot 4 to the A port of Slot 1, and so on for the
other modules, so that the token flows in the correct order.
Diagram #27: Token Flow through Dual Ringed DEChub 900 modules
@ = location of MAC
secondary <............<........... ...<.......<
: :
primary >----------->--------+ : : +---->----->
| : : |
v ^ : ^
A| : : |B
+----+ +-+-:+ +-:-+-+
| A| | | :| | : @ |
| +--+-------<-----------+@+ :| | : | |
| | .|...........>.......|...:| | : | |
| | :| |B | | v | |
| | :| +----+ | : ^ |
| | :| +---+ +---+ +---+ | : | |
| | .| | | | | | | | : | |
| | :| |A B| |A B| |A B| |A: | |
| | :|...|...|...|...|.....<..........|...|.....|.: | |
| | | | | | | | | | | |
| +-@+->-+--@+---+--@+----------->----+--@+-->--+---+ |
| B| | | | | | | | |
+----+ +---+ +---+ +---+ +-----+
Slot 1 2 3 4 5 6 7 8
Token Order on Ring MAP = 4>1>2>3>6>8
Refer to Diagram #28 for the following discussion. Suppose the same
modules are to be configured as a tree. The modules are in slots 1,2,3,
4,6, and 8, and the front panel S port is found on the module in slot
4. So the token enters and exits the hub at slot 4.
A ringmap will show the order of token flow, based on the ordering of the
MACs in the ring. FDDI rules require that a station's MAC be located
immediately prior to the port where the token exits the station. So in
this case, the token enters the S port of slot 4 and the token flows, in
order, through the MACs in slots 1,2,3,6,8 and finally slot 4. The physical
connection to do this requires that the S port of slot 8 connect to the M
port of slot 4. In this case a ringmap would record the token order as
1>2>3>6>8>4.
Diagram #28: Token Flow through Treed DEChub 900 modules
@ = location of MAC
to ring <-----------<----------+
from ring >----------->--------+ |
| |
v ^
S| |
+----+ +---+ +---+ +-+-+-+ +-----+
| | | | | | | | @ | |S |
| | | | | | | | +-+-----<-----------+@--+ |
| | | | | | | +---+----------->-----+-+ | |
| | | | | | | M| | | | |
| | | | | | | | +----+ | v ^ |
| | | | | | +-----+ | | | | | |
| +--+---+---+---+---+------<---------+----+-----+-+ | |
| | | | | | | | | | | |
| +-@+---+--@+---+--@+------>---------+---@+-----+---+ |
| S| |M S| |M S| |M S| |M |
+----+ +---+ +---+ +----+ +-----+
Slot 1 2 3 4 5 6 7 8
Token Order on Ring MAP = 1>2>3>6>8>4
QUICK PC TRACE OPTION FOR CONCENTRATORS
A Quick PC Trace option is supported for all DEChub FDDI concentrator modules.
As defined by the FDDI standard, a PC Trace is a method for recovering from a
stuck beacon condition. All stations that are in the fault domain perform
some level of hardware diagnostic test before attempting to re-enter the FDDI
network. Normally, concentrator modules run their full set of hardware diag-
nostics. This will take approximately one minute, but gives the highest level
of assurance that any hardware failure would be found. In order to decrease
the recovery time following a trace, the quick PC Trace option has been added.
When this option is enabled, only a subset of the hardware diagnostics is run
whenever a PC-trace occurs. The reduced set of diagnostic tests completes in
approximately 10 seconds. This feature can be enabled and disabled only from
the configuration screen of the module's setup port.
Note: The DECswitch 900EF and the PEswitch 900TX do not have this optional
feature since they normally recover from PC Traces very rapidly (less
than 10 seconds). This is due to the fact that these products are FDDI
end stations and have a much smaller set of FDDI-specific diagnostics
to run than an FDDI concentrator.
SUMMARY OF IMPORTANT CONFIGURATION FEATURES
This section is a short review of the FDDI configuration features for
the DEChub FDDI modules:
o ALL DEChub FDDI modules now support dual ring connections (A and B ports)
and tree connections (M and S ports) across the DEChub 900 backplane,
or out the front panel of individual modules in a DEChub 900.
o ALL DEChub FDDI modules now support dual ring connections (A and B ports)
and tree connections (M and S ports) when configured standalone in either
a DEChub ONE or a DEChub ONE-MX. (Note, PEswitch 900TX requires DEChub
ONE-MX with appropriate MODPMDs for standalone FDDI connections.)
o Multiple independent FDDI networks (trees and/or dual rings) can be
supported across the backplane of the DEChub 900.
o An automatic healing capability to patch around failed modules is
supported for both trees and dual rings across the backplane of the
DEChub 900.
o A Quick PC Trace capability has been added to concentrators, to minimize
the time it takes to return to operation following a PC Trace. This
option is selectable from the module setup screens, whether the module
is installed in a DEChub 900, a DEChub ONE, or a DEChub ONE-MX.
o DEChub 900s can participate in a dual ring of trees topology as either part
of the dual ring or as part of the tree; however, a dual ring of trees
topology is not supported across the backplane (see Diagram #29). A dual
ring of trees can be constructed by first building a dual ring, then a tree,
and connecting them together with a cable on the front panel (see Diagram
#30). Note though, that while they will all be in one network, HUBwatch
will need to manipulate the connections as though they are in unconnected
LANs.
Diagram #29: ILLEGAL Dual Ring of Trees Topology
Front Panel Ports
A B
| |
+-+----------+ +----------+-+ +-----------+ +------------+
| | | | | | | |
+-+--------+-+ +-+--------+-+ +-+-------+-+ +-+--------+-+
| | | | | | |
+----------+ +----------+ +----------+ M
B A M S M S
Backplane Ports
Diagram #30: LEGAL Dual Ring of Trees Topology
Front Panel Ports
A B M S
| | +----------+
| | | |
+-+----------+ +-+--------+-+ +-+---------+ +------------+
| | | | | | | |
+-+--------+-+ +-+--------+-+ +-+-------+-+ +-+--------+-+
| | | | |
+----------+ +----------+ M
B A M S
Backplane Ports
o Dual-homing to multiple FDDI modules in a DEChub 900 can be supported two
ways:
1) Each module can be individually dual-homed via its front panel
ports (assuming the module has front panel ports)
2) One concentrator module can be dual-homed and the other FDDI
modules can be treed off of that concentrator
o Additional DEChubs or standalone FDDI modules can be "chained" off of ANY
DEChub FDDI module (including switches) configured as a tree building
block. Previously, only concentrators had this capability.
o Attempting to build a self-contained dual ring configuration in the DEChub
with eight FDDI modules will NOT work. This is due to the fact that
there are 14 backplane channels that can be used for FDDI connections and
16 channels would be required to interconnect 8 modules in a hub-contained
dual ring. Note that this configuration can be accomplished with 14 back-
plane channels AND one cable between two devices' front panel ports.
o Attempting to build a self-contained tree configuration in the DEChub
with eight FDDI modules WILL work. This configuration can be built
because it requires only 14 backplane channels.
o While the FDDI defaults on the DECswitch 900EF and the DECconcentrator
900MX and DECconcentrator 900TH are to the front panel ports, and not the
backplane ports, the FDDI default for the PEswitch 900TX is to the
backplane. This is because there are NO front panel FDDI ports on a
PEswitch 900TX. Many people overlook this when considering default
configurations.
o FDDI modules installed in a DEChub ONE-MX can configure their FDDI ports
either with HUBwatch, or via an FDDI port configuration menu on the
DEChub ONE-MX setup port.
Diagram #31: Valid FDDI Configurations for DEChub FDDI Modules
A B A B A B
+---------------+ +----------------+ +----------------------+
+---+DECswitch 900EF+------+ PEswitch 900TX +-----+DECconcentrator 900MX +---+
| +-+ in DEChub ONE +------+in DEChub ONE-MX+-----+or 900TH in DEChub ONE+-+ |
| | +---------------+ +----------------+ +----------------------+ | |
| | | |
| |<-----Dual Ring | |
| | | |
| | B A B A| |
| | +---------------+ +----------------------+ | |
| +----------+ DEChub 900MS +--------------------+DECconcentrator 900MX +-+ |
+------------+ with multiple +--------------------+or 900TH in DEChub ONE+---+
| FDDI modules | +---+-+-------+-+------+
+--+-+-----+-+--+ M| | M| |
M| | M| +--------------------+ | | | |
| | +--------------------+ | | | | |
| | | | | | | |
Dual | | | | | | | |
Homing | | +-------------------------------+ | | |
| | | +-------------------------------+ | |
| | | | | | +----------+ |
A| | B| | A| | B| +----------+
+--+-+---+-+-+ +--+-+-----+-+--+
| Any | | DEChub 900MS |
| Standalone | | with multiple |
|Concentrator| | FDDI modules |
+-----+-+----+ +--+-+------+-+-+
M| | M| | M| |
| +--------------+ +-----+ | | +-----+
+--------------+ | | +-----+ +-----+ |
A| | | |B S | |
+--+-+--+-+-----+ +----+-+-----+
| DEChub 900 | | Any |
| with multiple | | Standalone |
| FDDI modules | | FDDI module|
+-+-+-------+-+-+ +------------+
M| | M| |
| | | |
+-------+ | | +----+
| +-------+ +----+ |
| | | |
S| | S| |
+--------+-+-+ +--+-+----------+
| Any | | DEChub 900MS |
| Standalone | | with multiple |
| FDDI Module| | FDDI modules |
+------------+ +---------------+
Appendix A - FDDI Basics
OVERVIEW
Fiber Distributed Data Interface (FDDI) is a set of ANSI/ISO standards for
a 100 Mbps token passing ring which uses Multimode fiber, Single mode fiber,
Unshielded Twisted Pair, Screened/Shielded Twisted Pair or any combination
of the four as the transmission medium. The most basic FDDI network is
constructed of two independent rings, referred to as the "dual ring". The
dual ring connects to each FDDI station in the network. Each ring can span
a total distance of up to 100 km, making for an allowable distance of up to
200 km (2 x 100 Km/ring) for the FDDI dual ring. As many as 500 stations may
be attached to the dual ring; a typical configuration will usually have no
more than 200 stations.
Diagram A1: FDDI Dual Ring
+---------+ +---------+ +---------+
+-----+ FDDI +-------------+ FDDI +-------------+ FDDI +------+
| +---+ Station +-------------+ Station +-------------+ Station +----+ |
| | +---------+ +---------+ +---------+ | |
| | | |
| |<----- Dual Ring (200 km total distance) | |
| | | |
| | +---------+ +---------+ +---------+ | |
| +---+ FDDI +-------------+ FDDI +-------------+ FDDI +----+ |
+-----+ Station +-------------+ Station +-------------+ Station +------+
+---------+ +---------+ +---------+
All FDDI networks operate as logical token rings, in which the right to
transmit is granted by the possession of a token. There is one token per
ring, and it is passed from station to station, according to a set of rules
known as the "timed token protocol". A station which wishes to transmit on
the ring first "captures" the token. It then transmits frames for a period
of time determined by the timed token rules, and then "releases" the token
immediately after completing its transmission. A transmitting station is
also responsible for removing the frames it transmitted from the ring, once
they have circled the ring and returned to the station. This process is
called "frame stripping".
STATION TYPES
FDDI networks are constructed using two types of devices, referred to as
"Stations" or "Concentrators". Stations are of two types: Dual Attach
Stations (DAS) and Single Attach Stations (SAS). Dual Attach Stations
attach directly to the dual ring. Single Attach stations connect to the
ring via a Concentrator, which can be of two types: Dual Attach
Concentrators (DAC) which attach directly to the dual ring and Single
Attach Concentrators (SAC) which attach to the ring through other
concentrators.
Diagram A2: FDDI Station Types
|< Phys Connection >|
| |
| |
+---------+ +---------+ Phys Link +---------+
+-----+ DAS +------+ DAS +---------------------+ DAS +-----+
| +---+(station)+------+(station)+---------------------+(station)+---+ |
| | +---------+ +---------+ Phys Link +---------+ | |
| | | |
| | | |
| | | |
| | |< Phys Conn >| |< Phys Conn >| | |
| | +---------+ +---------+ +---------+ | |
| +---+ DAS +-------------+ DAC +-------------+ DAC +----+ |
+-----+(station)+-------------+ (con) +-------------+ (con) +------+
+---------+ ^ +--++-----+ +---++----+
| || ||
Dual Ring || ||
+--++-----+ +---++----+
| SAS | | SAC |
|(station)| | (con) |
+---------+ +---++----+ ---
|| ^
con = concentrator Tree -----> || Phys
|| Conn
|| v
+---++----+ ---
| SAS |
|(station)|
+---------+
All devices, whether single attach or dual attach, connect to each other
via a full duplex connection known as a "physical connection". Each
physical connection is comprised of two "physical links" (one fiber per
physical link). Single Attach Stations and Single Attach Concentrators
connect to a concentrator, or another station, via one physical connection.
Dual Attach Stations and Dual Attach Concentrators connect to each other via
two physical connections.
MEDIA TYPES and SUPPORTABLE DISTANCES
FDDI allows links to be built from four different media types. Important
characteristics of these media types are:
Multimode fiber: 62.5/125 micron graded index fiber. The power budget for
these links is 11 dB. The maximum distance for a link is 2 km.
Singlemode fiber: 8 to 10 micron fiber. The power budget for these links is
22 dB. The maximum distance for a link is 60 km.
Unshielded twisted pair: Category 5 100 ohm UTP cable. The maximum distance
for a link is 100 meters.
Screened twisted pair: Category 5 100 ohm screened cable. The maximum
distance for a link is 100 meters.
Shielded twisted pair: 150 ohm Shielded Twisted pair, equivalent to
IBM Type 1 cable. The maximum distance for a link is 100 meters.
STATION CONFIGURATIONS
Stations and Concentrators are identified by the types of "ports" that they
use to attach to other stations. There are four port types, referred to as
A, B, M and S. ALL concentrators, whether SAC or DAC, are identifiable by
the presence of "M" ports, to which other stations or concentrators can
attach. If the concentrator also has an S port, it is a SAC; if it has A
and B ports it is a DAC. A Single Attach Station has an "S" port for
connection to a concentrator M port. Dual Attach Stations have A and B
ports for attachment to other stations in the dual ring, or to concentrator
M ports.
The FDDI rules require that a station's MAC be physically located
immediately prior to the port where the token exits the station. For Dual
Attach devices that means that the MAC will be immediately ahead of the B
port; for Single Attach devices it will be immediately ahead of the S port.
Diagram A3: FDDI Port Types
+---------+ +---------+ +---------+
+-----+ DAS +----->-------+ DAS +------>------+ DAS +------+
| |A B| |A B| |A B| |
| +---+ +-------------+ +-------------+ +----+ |
| | +---------+ +---------+ +---------+ | |
| | | |
| | | |
| | | |
| | | |
| | +---------+ +---------+ +---------+ | |
| +---+ DAS +-------------+ DAC +-------------+ DAC +----+ |
| |B A| |B A| |B A| |
+-----+ +------<------+ M +------<------+ M +------+
+---------+ +--++-----+ +---++----+
|| ||
|| ||
|| ||
+--++-----+ +---++----+
| S | | S |
| | | |
| SAS | | SAC |
+---------+ | |
| M |
+---++----+
||
||
+---++----+
| S |
| |
| SAS |
+---------+
PHYSICAL TOPOLOGIES
Although all FDDI networks are logical rings, they may be constructed
using various physical topolgies. There are three types of topologies:
1) Dual Rings
2) Trees
3) Dual Ring of Trees
Dual Ring topologies are constructed solely of Dual Attach Stations. The
A port of one station connects to the B port of the next station, forming a
physical connection between the two stations. This can be repeated until
up to 500 stations are included in the dual ring. Remember that there are
two physical links per physical connection, so when a ring is formed, there
are two operating links between each station. This allows for two
independent rings to be formed; these rings are referred to as the primary
ring and the secondary ring. The Primary ring enters the station on the A
port, and exits on the B port. The Secondary ring enters the station on the
B port and exits on the A port.
In general, all data traffic between stations is carried on the primary ring,
and the secondary ring is idle during this time. The FDDI standards actually
allow both rings to be used for carrying data traffic, but in practice this
is rarely done. The common practice is to use the secondary ring as a backup
for the primary ring.
A benefit of having dual rings is that, in case of a failure, the secondary
ring can be used as a backup ring to the primary ring. If a station detects
that one of its A or B ports has failed, it "wraps" the primary and secondary
rings together, thus restoring operation to the other stations in the ring.
Wrapping occurs very quickly, usually in well under a half a second.
FDDI also allows the construction of tree configurations, which start with a
standalone concentrator at the "top" of the tree. Stations or other
concentrators connect to this concentrator, and "branch out" from the top of
the tree. The distinguishing feature of a tree is the connection to an M
port. Single attach stations (S ports) typically connect to a concentrator,
but Dual Attach Stations (A and B ports) can also connect to the M ports.
A major advantage of the use of trees built with concentrators is the ability
of the concentrator to electronically disconnect stations from the ring in
case of failure, or, by management command.
The third, and most common, FDDI configuration is referred to as the Dual
Ring of Trees. This is a very robust topology, which is a hybrid of the Dual
Ring and Tree topologies. Dual Attach Concentrators and Dual Attach Stations
attach together in a dual ring, with treed stations connected to the
concentrators' M ports. The concentrator connects stations attached to
these M ports into the token flow of the primary ring.
Diagram A4: FDDI Topologies
Primary Ring
|
+---------+ +---------+ v +---------+
+-----+ DAS +----->-------+ DAS +-------------+ DAS +------+
| |A B| |A B| |A B| |
| +---+ +-----<-------+ +-------------+ +----+ |
| | +---------+ +---------+ ^ +---------+ | |
| | | | |
| |<--------Dual Ring Secondary Ring | |
| | | |
| | +---------+ +---------+ +---------+ | |
| +---+ DAS +-------------+ DAC +-------------+ DAC +----+ |
+-----+B A+------<------+B A+------<------+B A+------+
+---------+ +--++-----+ +---++----+
M|| M||
|| ||
S|| S||<-----Tree
Dual Ring of Trees +--++-----+ +---++----+
Configuration Example | SAS | | SAC |
+---------+ +---++----+
M||
Stations in the tree are ||
connected to the primary ring ||
S||
+---++----+
| SAS |
+---------+
STATION STATES
The internal configuration of the paths within a station is described by
something called the "station state". Stations can be in one of two states:
"thru or "wrapped". DAS or DAC stations in an unwrapped dual ring will be
in the "thru" state. If a station detects that it should wrap the rings
together, that station will be in the "wrap" state. Only two DAS or DAC can
be wrapped in a properly wrapped dual ring; this fact is used to locate the
points of failure if a ring wraps unexpectedly.
When wrapping, a station can adjust its internal configuration in a number
of ways, called out by the FDDI standard. Each of these configurations has
a different name, and a station is required to use that name when telling
management about its internal configuration. All Digital SAS and SAC
devices will report wrap_S in their station state reports. All Digital DAS
and DAC products will report c_wrap_A or c_wrap_B in their station state
reports. This means "concatenated wrap A" or "concatenated wrap B". For
example, C_wrap_A means that the B port is not active, the station has
wrapped the ring, and the A port is the active port.
Diagram A5: Wrapped FDDI Ring
+-----------+ +---------+ +---------+
+-----+ DAS +-+-------------+ DAS +-------------+ DAS +------+
| | FDDI | | | FDDI | | FDDI | |
| +---+ Station +-+-------------+ Station +-------------+ Station +----+ |
| | +-----------+ \ +---------+ +---------+ | |
/ / \ | |
<--- Break Wrapped | |
/ / in Cable Stations | |
| | / | |
| | +-----------+ / +---------+ +---------+ | |
| +---+ DAS +-+-----------+ DAS +-------------+ DAS +------+ |
| | FDDI | | | FDDI | | FDDI | |
+-----+ Station +-+-----------+ Station +-------------+ Station +--------+
+-----------+ +---------+ +---------+
CONNECTION RULES
One of the most confusing parts of FDDI is the operation of the FDDI
connection rules. These rules are necessary in order to prevent the
formation of non-useful topologies that can disrupt communication among
stations in the ring, and also to make sure that the ring will always
converge to a pre-defined topology. For example in Diagram A6, if the A
port of DAC#1 is connected to the B port of DAC#2, and then the B port of
DAC#1 is connected to an M port of DAC#3, the B port of DAC#1 will make the
connection to the M port of DAC#3, and the A port will break its connection
to DAC#2. This behavior is referred to as "taking the tree connection over
the ring connection". This particular rule ensures that the same tree
topology always is formed, independent of the order in which the physical
connections are made.
Diagram A6: FDDI Connection Rules
+---------+ +---------+ +---------+
+-----+ DAS +----->-------+ DAS +------>------+ DAS +------+
| +---+ +-------------+ +-------------+ +----+ |
| | +---------+ +---------+ +---------+ | |
| | | |
| |<--------Dual Ring | |
| | | |
| | +---------+ +---------+ +---------+ | |
| +---+ DAS +-------------+ DAC +-------------+ DAC #3 +----+ |
+-----+ +------<------+ +------<------+ M +------+
+---------+ +--++-----+ +---+-+---+
| |
S ^ V <-----Tree
+----------+ +---+-+----+
| DAC #2 | | | | |
| +------------+ +-+ |
| B+------------+A DAC #1 |
+----------+ ^ +----------+
|
Rejected Dual Ring Connection
FDDI rings are formed by the completion of physical connections between
pairs of ports. In order to form the connection, the ports signal various
parameters necessary for the successful completion of the connection.
When a port attempts to form a connection with another port, it indicates
both its own port type, and whether it wishes to form a connection with
the port type that it sees at the other end. One type of connection, the
M-M connection, is always rejected. Other types, such as A-A and B-B are
undesirable, but will be formed if the connection rules of one of the
stations allows the connection. For example, if a Digital FDDI product
attempts to form an A-A connection with another Digital FDDI product the
connection will not be made, because both ports signal that they do not
wish to connect to a remote A port. If the connection was made to a non-DEC
station, and that station's A port signaled that it wanted to take the
connection to the Digital A port, the Digital station would honor the
request, per the ANSI standard's rules for connection of ports. The
result, however, would be that the stations would be connected together,
but one stations's MAC would be in the primary ring, and the other station's
MAC would be in the secondary ring. Since the rings are isolated in the
non-wrapped case, the stations are unable to talk to one another, even
though their ports have formed a valid physical connection.
The following table summarizes the FDDI connection rules. The word "peer"
means connections in a dual ring. Tree preference means that when offered
the opportunity to form a tree and a dual ring simultaneously, the station
will form the tree, and disconnect the peer, if it was already connected.
For example, the last line of the table indicates that when the A port of a
station or concentrator connects to the M port of a concentrator, the A to
M connection is taken, a tree is formed, and the Station State will be
concatenated_wrap_A (c_wrap_A). Any existing B to A connection will be
disconnected, and, any new B to A will not be made.
Table A.1 - FDDI Connection Rules and Station States
Port A Port B Peer/Tree Station State
------ ------ -------- --------------
M Tree c_wrap_A
M Tree c_wrap_B
M M Tree c_wrap_B (dual homed)
B Peer c_wrap_A
A Peer c_wrap_B
B A Peer thru
A Peer c_wrap_A
B Peer c_wrap_B
S Peer c_wrap_A
S Peer c_wrap_B
S S Peer thru
S M Tree c_wrap_B (tree preference)
M S Tree c_wrap_A (tree preference)
S A Peer thru
B S Peer thru
B M Tree c_wrap_B (tree preference)
M A Tree c_wrap_A (tree preference)
RING OPERATION
An FDDI ring operates according to the rules of the "timed token protocol".
The operation of the ring can be divided into two parts - intialization of
the ring, and steady state operation. A very short description of these
operations is presented below.
FDDI initializes the ring by a process known as the "claim token process",
which is invoked each time any station enters or leaves the ring, or a
failure of the normal ring operation is detected. The purpose of this
process is to set the operational timers for the ring, and to choose the
station which will create the token. All stations send a special frame,
known as a "claim frame", which contains a "bid" for the length of time that
that station is willing to wait between receipt of tokens. The station
that wins the bidding is the station whose bid indicates that it needs the
token the most often. The outcome of the claim process is that all stations
agree to abide by this time, which is known as T_Negotiated (T_Neg).
Typical values for T_Neg are in the range of 5-10 ms, with 8 ms being a
common choice.
Varying the value of T_Neg can dramatically change the utilization and the
latency of a very busy FDDI ring, but has little to no effect on the
utilization or latency of a lightly loaded ring. It is strongly recommended
that the value of T_Neg not be changed from the manufacturer's default.
If a ring fails to complete the claim process within a certain time, the ring
enters the "beacon process". This process causes special frames known as
"beacon frames" to be sent around the ring in an attempt to isolate the
location of the fault. If beacons are seen, it is an indication of a serious
problem with the operation of the ring.
In the steady state, the token circulates around the ring. The time for a
token to circle once around the ring without being used by anyone is known as
the "token latency". Stations that wish to transmit must capture the token,
and can transmit as long as allowed by the token holding rules. All stations
keep a timer called the "valid transmission timer" (TVX) which they use for
timing valid activity on the ring. If, for some reason, a token gets "lost",
this timer will expire, and stations will enter the claim process, so that a
new token is created.
During the steady state, stations in the ring exchange frames which tell
each other about their adjacent stations. This information is communicated
via SMT frames, which are sent at a rate of approximately 1 every 10 to 30
seconds. Using these frames, stations determine their "upstream" and
"downstream" neighbors. Station 2 is said to be downstream of Station 1
if Station 2 receives the token after it was received by Station 1.
Appendix B - LEDs on FDDI modules
FDDI modules for the DEChub 900 family have a number of LEDs that reflect
the state of the FDDI connections. These will be detailed for each module.
Note that these LEDs apply to the DEChub family of FDDI modules, and may
be different from the LED codes used on other Digital FDDI products.
DECconcentrator 900 MX and 900TH
The LED next to the # symbol indicates that the module is in the ring, has
formed a connection to another module, and LLC traffic can be exchanged
(specifically, Ring_Op is true, and a duplicate address has not been
detected by this module). Please note, before this release, this LED
was lit even when no connection was formed.
The LED next to the PHY symbol on a MODPMD module indicates the state of
the connection for that port. These options also apply for the 12 UTP port
status LEDs of the DECconcentrator 900TH. Options are:
Off Available for connection
Solid Green Connection is Active
Blinking Green Management disabled, or broken
Solid Amber Link Confidence Test Failure
Blinking Amber Topology Rule Violation
Blinking Green/Amber Dual Homed connection
The other LED on a MODPMD module indicates the status of the MODPMD module,
or the FDDI port type. Options are:
Off M port
Solid Green S port
Blinking Green A or B port
Solid Amber MODPMD fault
Blinking Amber No meaning
Blinking Green/Amber No meaning
DECSwitch 900EF and PESwitch 900TX
The LED next to the # symbol for port 1 indicates the state of forwarding
for the FDDI port of the switch. Options are:
Off Bridging to/from FDDI not active
Solid Green Bridging to/from FDDI is active
Blinking Green Switch is learning on the FDDI port or
FDDI port is in the backup state
The LED next to the arrow symbol indicates activity on the FDDI port. A
green flashing LED means the front panel FDDI ports are in use. An amber
flashing LED means that the rear panel ports are in use. The amber color
will appear as long as one port is assigned to the backplane.
The LED next to the PHY symbol on the front panel indicates the state of
the connection for that port. Note: Since the FDDI ports of the 900EF can
be steered to either the front or back panel, this LED is operational when
a connection to the port is formed either via the front panel, or on the
backplane. Also, the lights on the MODPMD modules used with the switches
will be lit, independent of whether the front panel or MODPMD ports are in
use. Options for the front panel LED are:
Off Available for connection
Solid Green Connection is Active
Blinking Green Management disabled, or broken
Solid Amber Link Confidence Test Failure
Blinking Amber Topology Rule Violation
Blinking Green/Amber Dual Homed connection
The LED next to the PHY symbol on a MODPMD module indicates the state of
the connection for that port. The following options apply for MODPMD
modules used with either the DECswitch 900 EF or the PEswitch 900 TX.
Off Available for connection
Solid Green Connection is Active
Blinking Green Management disabled, or broken
Solid Amber Link Confidence Test Failure
Blinking Amber Topology Rule Violation
Blinking Green/Amber Dual Homed connection
The other LED on a MODPMD module indicates the status of the MODPMD module,
or the FDDI port type. Options are:
Off M port
Solid Green S port
Blinking Green A or B port
Solid Amber MODPMD fault
Blinking Amber No meaning
Blinking Green/Amber No meaning
Appendix C - References
The following are suggested readings for those wishing to learn more about
the operation of FDDI networks.
"A Primer on FDDI" - published by Digital, this book is a very simple
introduction to the operation of FDDI. It is, unfortunately, now out of
print, but old copies can sometimes be found. A different version of this
book is available from Digital Press, under the title "FDDI, An Introduction",
ISBN Number 1-55558-093-9, order number EY-J840E-DP
"FDDI Handbook" by Raj Jain. This is a very readable and very recent book on
all of the details of FDDI. It is published by Addison-Wesley, ISBN number
0-201-56376-2
Official FDDI Standards - The actual standards are available from the ANSI
Sales office in New York, N.Y.
Media Access Control (MAC) X3.139-1987
Physical Layer Protocol (PHY) X3.148-1988
Physical Layer Medium Dependent (PMD) {multimode fiber PMD} X3.166-1990
Station Management (SMT) X3.229-1994
Single Mode Fiber PMD (SMF-PMD) X3.184-1993
Twisted Pair PMD (TP-PMD) X3.263-199? (AWAITING PUBLICATION)
Unofficial versions of some of these documents can be gotten by anonymous
ftp from fddi.lbl.gov
| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 2340.1 | Copy Location | DELNI::BUZZELL | | Mon Jun 05 1995 09:21 | 10 |
|
This guide is also available at
NAC::NIPG:[HUB.PRESENT]FDDICONF.TXT
It will also be turned into a word document so that it can
be printed and given to customers. As soon as it is ready it will
be in the location above as FDDICONF.DOC.
|
| 2340.2 | Digital Confidential or not? | CMOTEC::CHOI | Shaking and Moving | Tue Jun 13 1995 14:41 | 9 |
| Ed,
I printed out the FDDICONF.PS and it has Digital Confidential on it.
Since it appears to have much the same content (if less detail) as
FDDICONF.TXT, should the "Digital Confidential" be removed if it is OK
to send to customers?
Clinton
|
| 2340.3 | Don't use it | DELNI::BUZZELL | | Wed Jun 14 1995 14:18 | 9 |
|
You should not provide the .ps. There are significant differences
in the naming conventions and representations. The .ps is the old
information and I have deleted it. The .doc refrenced above is being
worked and should be ready next week. Until that time the .txt should
be used.
|
| 2340.4 | Is it ready yet? | MAASUP::PORAMBO | | Mon Aug 28 1995 13:44 | 6 |
|
I have been waiting for the .DOC version of the FDDI Configuration
document. What , if anything, can be provided to the customer at this
time?
Bob
|
| 2340.5 | There Again | CONSLT::BUZZELL | | Mon Aug 28 1995 16:07 | 6 |
|
The .doc version should be accessible in the directory noted
in .2 NAC::NIPG:[HUB.PRESENT]FDDICONF.DOC.
|