Figure 5.1 Features of 100VG-AnyLAN
These notes are divided into hyperlinked sections
Introduction
Medium Access Control
Cabling Options
Cabling Alternatives
Demand
Priority Medium Access Control
Managing 100VG-AnyLAN
Migrating to 100VG-AnyLAN
100VG-AnyLAN Summary
Note concerning take-up
100VG-AnyLAN was created by Hewlett Packard and was intended to provide a 100 Mbit/sec network solution that would function over existing UTP and STP cabling. Another intention was to provide a network that could use either Ethernet or Token Ring frames, thus keeping compatibility with existing software applications, bridges and routers.
A new MAC function was provided to give rapid network access under light loads, like Ethernet and lose the inefficiencies caused by collisions in Ethernet yet provide high efficiency under heavy loads like token passing.
A further intention was to allow differing priorities to be assigned to different types of network traffic. This would allow isochronous (voice, video, multimedia) needs to be met. (more)
100VG-AnyLAN uses Cat-3 and Cat-5 voice grade cabling. The data rate is 100 Mbit/sec and the MAC is either Ethernet or Token Ring frames. The 100VG-AnyLAN hub is the intelligent controller of the network with stations (nodes) star wired to the hubs. Many cabling options are supported, UTP, STP and fibre. Large tree-wired networks can be built up using up to 3 hub levels. 100VG-AnyLAN bridges can connect segments using 802.3 and 802.5 frames.
The hubs themselves are intelligent repeaters. All incoming frames are repeated out of the 'up' port. Other ports are individually configured to either normal or monitor mode.
· Normal mode is where only frames addressed to
the attached node are output
· Monitor mode is where all incoming frames are
output.
Figure 5.1 Features of 100VG-AnyLAN
The hubs provide many other functions to the attached nodes. The MAC is managed by the hub with access control performed by demand priority. The hubs can be configured to use either 802.3 or 802.5 frames, but they cannot be mixed within a segment.
100VG-AnyLAN supports the use of several different cabling options as summarised in table 5.1 below.
Table 5.1 Cabling Option
supported by 100VG-AnyLAN
The standard connector is the RJ-45 with Cat-3 UTP using all four pairs and STP or Cat-5 UTP using pairs 1 and 3, see fig 5.2 for details of connection.
Figure 5.2 Cabling connections
for RJ-45
Demand Priority Medium Access Control
MAC is deterministic for all users i.e. it depends on previous events and the state of the system. It allows fast access for high-priority traffic and is based on round-robin polling by the hubs. A node that wishes to transmit a frame must firstly send a request to the hub. These requests can be either normal or high priority. Each hub cyclically scans its ports for requests, a fast process. A list is made of normal and high priority requests. The hub grants port requests in the order that they were received. Each node may transmit one frame per request. The high priority list is serviced before the low priority list. For guaranteed access, any pending normal priority requests are promoted to high priority after a wait time of around 300 ms.
A large tree network will have several levels of hubs
branching out from one root hub, see fig 5.1. Upper level hubs know of
the existence of lower level hubs by port training. Lower level hubs issue
transmission requests to higher-level hubs via the 'up' port to the higher-level
hub. When a hub's request is granted, network access control is passed
to that hub. The controlling hub now services its port requests as described
above. After the ports have transmitted one frame each, control is passed
back to the upper-level hub.
Figure 5.3 The Operation
of Demand Priority MAC
100 VG-AnyLAN has two modes – normal and monitor. The monitor mode is only used for traffic analysis.
The manager can set the hubs to normal mode where only those frames that have been addressed to the attached node will be output to that particular node. Normal or high priority can only be set on a per-port basis and this will remain so until applications are written to support automatic-priority assignments. 100VG-AnyLAN products were expected to be compatible with existing manufacturers platforms and vendors' products would offer SNMP agents and MIBs that have been adapted from Ethernet, offered as optional add-on modules or boards. There still remains much work to be done to add management capabilities that are unique to 100VG-AnyLAN.
The steps involved with migration to 100VG-AnyLAN are summarised below.
1. Using traffic analysis and user feedback, identify
the workgroup(s) that could benefit from the features of 100VG-AnyLAN i.e.
100 Mbit/sec data rate, security, priority transmissions.
2. Install new 100VG NICs and drivers into workstations
and PCs. This must be done overnight to avoid losing the network during
changeover. In existing
10 BASE-T LANs the NICs must be tested using the Ethernet option.
3. Replace the 10 BASE-T or Token Ring hub with 100VG
for that particular workgroup. 100VG-to-legacy bridges will be needed to
connect to the existing network.
4. Add 100VG hubs as required observing the following
rules:
- Three levels of hubs is the practical maximum
- The maximum delay-limited distance between nodes and the root hub is 6000m, reduced by 1100m for each hub between the node and the root hub
- There is no limit on the number of users but HP recommends less than 250 nodes per subnetwork.
100VG-AnyLAN was a totally new LAN technology that required intelligent hubs, new NICs and drivers. The existing UTP/ STP cabling should accommodate 100VG-AnyLAN. The existing legacy Ethernet or Token Ring applications should be employable. Low-speed isochronous traffic could be accommodated using priorities but applications would need to be updated to access this service. Security was enhanced by hub-filtering when ports were set to normal mode. This means that nodes would only receive the frames that have been addressed to them.
Market forces dictated that this network was not installed in any great number and 100VG-AnyLAN never really took off. It is only found now in legacy installations.
(c)MMClements 2000
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