Power Tools 1993 November - Disc 2/Power Tools Plus (Disc 2 of 2)(November 1993)(HP).iso/hotlines/cnhl/porter/tech.txt

Text File | 1993-10-05 | 21KB | 349 lines

100VG-AnyLAN:
The Natural Evolution of Ethernet and Token Ring

Over the past ten years, dramatic changes have taken place in the office
computing environment.  Computers are faster.  Files are larger.  Networks are
more crowded.  Over the same period, however, the data transmission speed of
standard Ethernet and Token Ring local area networks has remained constant at
four, ten, or sixteen megabits per second (Mbit/s).  As a result, network
performance has become a critical bottleneck in a variety of key business
application areas.  Over the next few years, emerging applications will cause
even more strain on these existing networks.

By the end of 1993, Ethernet and Token Ring networks will share a combined
installed base of over 36 million users worldwide, according to industry
researcher International Data Corp.  Many of these users will be considering
alternatives to increase their network performance.

In the search for a successor to these two highly successful networking
standards, one alternative showing unique promise is 100VG-AnyLAN, a new 100-
Mbit/s local area network technology that combines the best of existing
Ethernet and Token Ring standards.  Announced by Hewlett-Packard and IBM,
100VG-AnyLAN is an extension of the 100Base-VG technology developed by Hewlett-
Packard and AT&T and recently endorsed by the IEEE 802 standards organization
as the foundation for a new IEEE 802.12 standard.

100VG-AnyLAN  is a new IEEE 802.12 technology for transmitting Ethernet and
Token Ring frame information at 100 Mbit/s.  100VG-AnyLAN combines increased
transmission speeds with a simple yet efficient media access control that
operates over Category 3, 4, or 5 unshielded twisted-pair (UTP), shielded
twisted-pair (STP), and optical fiber.  By supporting all of the network design
rules and topologies of 10Base-T as well as Token Ring, 100VG-AnyLAN allows
organizations to leverage their existing network and cable infrastructure.  In
addition, 100VG-AnyLAN can provide guaranteed bandwidth for emerging time-
sensitive applications such as multimedia.  Low costs and an easy migration
path from existing 10Base-T and Token Ring networks promise to make 100VG-
AnyLAN the best alternative for upgrading 10Base-T as well as Token Ring users
to 100-Mbit/s speeds (see Figure 1).


Figure 1.  100VG-AnyLAN: the natural evolution of Ethernet and Token Ring.

The Natural Evolution of Ethernet and Token Ring

100VG-AnyLAN brings together the best characteristics of both Ethernet and
Token Ring, combining the simple, fast network access familiar to Ethernet
users with the strong control and deterministic delay characteristics of Token
Ring networks.  In addition, by providing a single network hardware
infrastructure capable of supporting both Ethernet as well as Token Ring packet
frames, at ten times the bandwidth of existing Ethernet networks and more than
six times the bandwidth of the fastest Token Ring networks, 100VG-AnyLAN is
truly positioned as the logical successor to both Ethernet and Token Ring
technologies.

The key to 100VG-AnyLAN's powerful capabilities is its leverage of  the
physical star topology used in most modern networks.  Ethernet and Token Ring
were initially conceived and implemented as shared-media bus and ring
topologies, respectively. As a result, these technologies did not rely on any
central intelligence to coordinate network usage and manage advanced
capabilities such as security or guaranteed bandwidth.  Over the past five
years, however, as technologies matured, almost all 10Base-T and Token Ring
networks have come to be physically implemented using a star topology with a
central hub, or media attachment unit (MAU), and individual connections
radiating out to each connected node.

Taking advantage of this star topology, 100VG-AnyLAN places intelligence in the
hub to better manage network usage and improve network control.  This central
intelligence implements a powerful frame switching technique called Demand
Priority.  Using Demand Priority, 100VG-AnyLAN hubs arbitrate requests from
connected nodes for access to the network, building in a natural flow control
that allows 100VG-AnyLAN to minimize network latency, maximize network
throughput, and enable support for time-sensitive applications such as
multimedia.  The resulting network is simple in concept, yet delivers powerful
capabilities that expand on the best characteristics of its Ethernet and Token
Ring predecessors (see Figure 2).


Figure 2.  100VG-AnyLAN leverages the star topology of today's networks.

How Demand Priority Works

A simple 100VG-AnyLAN network consists of a central hub and a network of
individual connections radiating out to each connected node.  Using Demand
Priority, a node wishing to transmit a packet signals its request to the hub.
If the network is idle, the hub immediately acknowledges the request and the
node begins transmitting its packet to the hub.  As the packet arrives at the
hub, the hub decodes the destination address contained in the packet and
automatically switches the incoming packet to the outbound destination port
(see Figure 3).  If more than one request is received at the same time, the hub
uses a simple 'round robin' arbitration scheme to acknowledge each request in
turn, until all requests are serviced.


Figure 3:  Demand Priority hubs switch packets to their destination.

In a Demand Priority network, since much of the intelligence is concentrated in
the hub rather than distributed out to each node, management functions can be
implemented inexpensively and their costs shared across all connected users.
At the adapter, Demand Priority's relatively simple request/acknowledge
handshaking and minimal management requirements greatly simplify adapter
design.  The combination of simple adapter functions with centralized
intelligence makes Demand Priority very cost-effective to implement, despite
its speed.

Improved Network Security.  In a Demand Priority network, data packets are
directed only to their intended destination port.  Since no other station on
the network sees the data packet, its source, or its destination, this frame
switching technique provides a level of Link Privacy or security that is not
provided today by existing Ethernet, Token Ring, or FDDI networks.  For network
diagnostic purposes, network administrators can activate individual hub ports
to monitor all traffic passing through the hub.

Deterministic Latency -- Minimizing Network Delay.  Since stations do not
transmit their packets until they receive an acknowledgment from the hub,
Demand Priority networks have a natural flow control that avoids packet
collisions and allows prioritization of network traffic.  By avoiding packet
collisions, Demand Priority eliminates the network overhead consumed by packet
collisions and recovery and substantially increases usable network throughput.
In doing so, Demand Priority simplifies network operation and improves network
characteristics such as latency.

Because the round-robin arbitration scheme used by Demand Priority is
completely deterministic, the maximum latency or network delay seen by a packet
of information is deterministic as well.  This deterministic latency
characteristic is similar to that of Token Ring networks.

The maximum delay seen by a packet of information is calculated by multiplying
the maximum packet interval by the number of stations that might simultaneously
request transmission.  For 1514-byte Ethernet packets at 100 Mbit/s, the
maximum packet interval is 120 microseconds.  On a 100VG-AnyLAN network with 10
active users, for example, the worst-case delay for any station to transmit a
packet of information would be no more than 1.2 milliseconds.  Best-case
latencies would be one-tenth that amount.  In comparison, on a completely idle
Ethernet network, the best-case delay for completion of a packet transmission
is 1.2 milliseconds, while worst-case delays could exceed a second or more if
the network is busy or if packet collisions occur.

Compared to Token Ring-based networks such as 16-Mbit/s Token Ring or 100
Mbit/s FDDI, the round-robin arbitration scheme of Demand Priority hubs
effectively collapses the token-passing process into the operation of the hub
itself, eliminating token-rotation delays and reducing latency for stations on
an otherwise idle network.  In addition, Demand Priority relaxes the limits on
the number of stations in a single ring or subnet.  Unlike traditional Token
Ring environments, the latency experienced by individual stations on a Demand
Priority network is unaffected by the number of idle stations connected to the
network.

Guaranteed Bandwidth -- Critical  for Multimedia.  The ability to guarantee
continuous, uninterrupted bandwidth is one of the critical requirements for
efficient network support of time-sensitive applications such as multimedia.
By prioritizing network traffic and taking advantage of the natural flow
control inherent in Demand Priority networks, 100VG-AnyLAN is able to guarantee
bandwidth to specific applications regardless of other traffic on the network.

To minimize delays experienced by time-sensitive applications, Demand Priority
networks have the ability to recognize high-priority as well as normal-priority
transmission requests.  By acknowledging high-priority requests before normal-
priority requests, Demand Priority hubs allow high-priority data to be
transmitted with minimal delay, without regard to the level of normal-priority
requests.  Using this approach, a time-sensitive application can be assured no
more than a specific maximum delay before its packet will be transmitted to its
destination, dependent only on the number of other applications transmitting at
high priority.  In this way, 100VG-AnyLAN can effectively guarantee bandwidth
to high-priority applications.  The minimum guaranteed bandwidth to an
application is simply the inverse of the maximum delay or latency experienced
by its individual packets.  To ensure that normal-priority data traffic is not
blocked by high-priority requests, the Demand Priority protocol incorporates
natural safeguards to guarantee that all traffic, regardless of priority,
eventually gets transmitted.

Increased Bandwidth over Existing Cabling

Demand Priority operates at 100 Mbit/s over 4-pair Category 3, 4, or 5
unshielded twisted-pair  (UTP) cable, over 2-pair shielded twisted-pair (STP or
IBM Type 1) cable, and over single-mode or multimode fiber-optic cable.  This
offers a ten-fold increase in bandwidth over existing 10Base-T networks, and a
six-fold increase over existing high-speed Token Ring networks, using the same
cable infrastructure.  With such broad cable support, 100VG-AnyLAN is likely to
operate over much of the 10Base-T and Token Ring cable installed today.

Unshielded Twisted-Pair (UTP) Cable.  To transmit 100 Mbit/s of data over
unshielded twisted-pair cable, 100VG-AnyLAN uses a technology called Quartet
Coding.  Using Quartet Coding, the data being transmitted is split into four
parallel streams, with one stream directed down each pair of the four-pair UTP
cable.  On each pair of wires, an efficient 5B6B NRZ encoding scheme is used to
transmit two bits of information per cycle.  In this way, Quartet Coding allows
100 Mbit/s worth of data to be sent across a 4-pair UTP cable while keeping
individual signal frequencies at no more than 15 MHz, well below U.S. FCC and
International CISPR-mandated limits.  This approach permits 100VG-AnyLAN to
operate over existing Category 3, 4, or 5 UTP cabling systems without any
changes in connectors, cross-connects, and cable distances (see Figure 4).


Figure 4.  Quartet Coding: 100 Mbit/s over 4-pair UTP.

Shielded Twisted-Pair (STP) Cable.  To transmit 100 Mbit/s data over shielded
twisted-pair cable (a 2-pair STP media such as IBM Type 1 cable), 100VG-AnyLAN
transmits the data in two parallel streams.  This approach takes advantage of
the comparably higher level of shielding provided by STP to transmit at higher
frequencies, achieving 100 Mbit/s of overall transmission speed using only two
pairs of wire (see Figure 5).  The frequencies are well within guidelines
specified in the IBM Cabling System specification, to permit use of existing
connectors and cable plant.


Figure 5.  Quartet Coding: 100 Mbit/s over 2-pair STP.

Fiber-Optic Media.  Many Ethernet and Token Ring networks take advantage of the
distance and electrical isolation characteristics of fiber-optic media,
particularly in building or campus backbone networks, or in high-noise or other
specialized desktop environments.  100VG-AnyLAN supports multimode fiber optic
links of up to 2 kilometers between devices, ensuring that any Ethernet or
Token Ring topology containing fiber-optic links can be duplicated at 100
Mbit/s using 100VG-AnyLAN components. 100VG-AnyLAN transmits the data packet
over a single fiber strand, using a second strand for receiving incoming
signals from the hub.  (see Figure 6).


Figure 6.  Quartet Coding: 100 Mbit/s over fiber optics.

100VG-AnyLAN Topologies

The network design rules and allowable topologies for 100VG-AnyLAN are a
superset of those supported by 10Base-T and Token Ring.  This means any 10Base-
T or Token Ring topology composed of twisted-pair and fiber media can be
duplicated using 100VG-AnyLAN components, without changing network topology or
design.

Like 10Base-T, multiple 100VG-AnyLAN hubs can be cascaded within a single
subnet to extend the topology without requiring additional bridges or other
components (see Figure 7).  In a cascaded 100VG-AnyLAN configuration, the
Demand Priority protocol allows hubs to  automatically recognize whether they
are connected to a higher-level hub.  When a lower-level hub receives a packet
request from a connected node, it forwards the request to the next-higher-level
hub before acknowledging the requesting node.  The top-level hub arbitrates
this request along with other packet requests from other nodes or hubs.  When
the top-level hub acknowledges each request in turn, the acknowledgment
cascades down to the lower-level hub, which then acknowledges each of its own
pending requests before relinquishing control back to the higher-level hub.  As
the lower-level hub passes the acknowledgment to the requesting node, the node
then transmits its packet with an assurance of uncontested transmission
throughout all the connected hubs in the subnet.  In this way, the Demand
Priority arbitration scheme is extended across multiple hubs with no loss of
fairness or efficiency.  As in 10Base-T, an 100VG-AnyLAN network can also be
segmented using bridges or switches to allow simultaneous packet transmissions
on separate subnets, further increasing the bandwidth available to individual
nodes or servers.


Figure 7.  100VG-AnyLAN duplicates any 10Base-T or Token Ring topology.


Compatible with Existing Ethernet and Token Ring Networks

100VG-AnyLAN is uniquely able to provide an upgrade path for both Ethernet and
Token Ring networks since it accommodates both Ethernet and Token Ring frames.
Because the operation of the Demand Priority protocol is relatively independent
of a specific frame format, Demand Priority networks can transmit Token Ring
frames as easily as they handle Ethernet frames.

When 100VG-AnyLAN is used to upgrade portions of an existing 10Base-T Ethernet
network, a speed-matching bridge is all that is needed to connect the 10Base-T
and 100VG-AnyLAN subnets.  The bridge buffers the higher-speed packets as they
enter the slower-speed network.  Since the same Ethernet packet format can be
used on both the 10Base-T and 100VG-AnyLAN subnets, no packet translation or
other processing is required.

In a similar fashion, when portions of an existing Token Ring network are
upgraded to 100VG-AnyLAN, a speed-matching bridge is all that is needed to
connect the two subnets.  The same Token Ring packet format can be used on both
the Token Ring and 100VG-AnyLAN subnets.

The true integration capabilities of 100VG-AnyLAN show at their best when
100VG-AnyLAN is used to upgrade a mixed Token Ring and Ethernet environment.
Existing Token Ring and Ethernet subnets can be upgraded to 100VG-AnyLAN
individually, sharing a common network hardware infrastructure.  Individual
stations can continue to operate using their native packet format, while
transmitting information at 100 Mbit/s.  Servers and other resources can be
configured to accept and respond to packets in either Ethernet or Token Ring
format, or a router can be used to translate Ethernet and Token Ring frames for
communication between the two independent subnets.

Connecting individual 100VG-AnyLAN subnets to an FDDI backbone or other
backbone or wide area resource is also relatively straightforward, using
encapsulating bridges or routers to attach each 100VG-AnyLAN subnet to the FDDI
ring.

Migrating to 100VG-AnyLAN -- Simplest Path to High Performance

Migrating to 100VG-AnyLAN from 10Base-T or Token Ring network is a simple, two-
step process.  First, the network administrator identifies clients and servers
to be upgraded, and replaces the LAN adapter in each workstation with a 100VG-
AnyLAN adapter.  No new cabling needs to be installed.  The same RJ-45
connector and unshielded twisted-pair cabling, or the same IBM Data Connector
and Type 1 STP cabling used for the 10Base-T or Token Ring network would be
used when operating at 100 Mbit/s with 100VG-AnyLAN.

The second step is installing a 100VG-AnyLAN hub in the wiring closet, in
parallel with the existing 10Base-T or Token Ring module.  Individual
workstations can be migrated from the existing low-speed subnet to the new
100VG-AnyLAN subnet by simply disconnecting the station's cabling connector
from the 10Base-T or Token Ring hub port, and reconnecting it to the 100VG-
AnyLAN hub port.

No other changes are necessary in the wiring closet or cabling infrastructure.
Individual stations or entire workgroups can be upgraded to 100VG-AnyLAN,
depending on user requirements.  No changes are required for network operating
systems, software applications, or network management software.  100VG-AnyLAN
components can be managed just as easily using an SNMP network management
environment such as HP OpenView or IBM NetView, for example, as are 10Base-T
and Token Ring products today.

Broad Industry Support for 100VG-AnyLAN

As organizations plan their evolution to higher-speed networks, they can be
assured that a full complement of interoperable, standards-based 100VG-AnyLAN
products will be available from a variety of vendors.  Earlier this year, the
IEEE 802 standards organization, home of the successful 802.3 Ethernet and
802.5 Token Ring standards, chartered a new 802.12 committee to draft
specifications for Demand Priority as a new 100-Mbit/s network standard.   Over
30 vendors supported the proposal and expressed interest in participating in
the standards effort.   Many of these vendors have publicly stated their
commitment to work together with HP and IBM to ensure that their Demand
Priority-based products work together, even before IEEE standards efforts have
been completed.  These vendors include leading semiconductor vendors, PC
adapter and hub vendors, router vendors, and all three of the leading network
operating system vendors.

For existing 10Base-T and Token Ring users, the standards committee's actions
recognize the compelling opportunity 100VG-AnyLAN offers as an upgrade to
existing networks, and signify that 100VG-AnyLAN will be a technology they can
rely on for their growing network performance needs in the year ahead.  The
committee's actions also recognize the unique contributions offered by HP's
Demand Priority and Quartet Coding technologies and open the door for these
technology standards to evolve and embrace new functionality and even higher
data rates in the future.

100VG-AnyLAN:  The Natural Evolution of Ethernet and Token Ring

100VG-AnyLAN represents an attractive networking alternative for organizations
looking to migrate to higher-speed solutions.   Bringing together the best
characteristics of existing Ethernet and Token Ring networks, 100VG-AnyLAN
offers six- to ten-fold increases in network performance while preserving
investments in software, network topologies and cabling.  The low costs
implicit in 100VG-AnyLAN and its easy migration path from existing Ethernet and
Token Ring networks promise to make 100VG-AnyLAN the best alternative for
upgrading Ethernet as well as Token Ring users to 100-Mbit/s speeds.