ch12.htm

this describes managing multivendor networks

	part of international frame relay. 
<HR>


</BLOCKQUOTE>

<P>Frame relay technology is becoming much more attractive economically, and carriers
are getting intensely competitive. In many circumstances, frame relay is superior
to a private line for data networking scenarios. The carriers' pricing models should
be taken into account when considering a frame relay solution. Pricing schemes are
complex, and include port charges for physically connecting to the network, charges
per PVC (permanent virtual circuit), and charges for local access. Other charges
include <I>COC (central-office connection)</I> tariffs, which cover the cost of the
connection between local access service and the interexchange carrier.</P>
<P>The lack of switched virtual circuit (SVC) services has delayed the widespread
implementation of frame relay in the past. However, manufacturers and service providers
are starting to implement these services in earnest. The lack of SVC services caused
customers to instead rely on frame-relay PVCs. SVCs would permit a network manager
to establish a frame relay connection on demand, and replace the need for PVCs between
sites.</P>
<P>Software is starting to become available to integrate voice, fax, and data networks
over frame-relay. Products are available to enable a frame relay network to handle
all three types of traffic. This type of software would naturally give priority to
voice traffic, sending it at a Committed Information Rate--which reduces delays typically
associated with sending voice over frame relay.
<H2><A NAME="Heading11"></A><FONT COLOR="#000077">Switched Multimegabit Data Service
(SMDS)</FONT></H2>
<P><I>Switched Multimegabit Data Service (SMDS),</I> a connectionless service, can
be advantageous in some multivendor networks over ATM or frame relay technologies.
Network design under an SMDS architecture is actually quite simple. With frame relay,
on the other hand, you have to assign and configure PVCs (permanent virtual circuits)
between locations. ATM has similar complex design requirements. SMDS, on the other
hand, establishes any-to-any connectivity. Each location has its own E.164 address,
so all you have to do is assign it a port connection speed. After a site is hooked
up, it can communicate with any other site on the SMDS net.</P>
<P>SMDS is a scalable solution, and is capable of keeping pace with an increased
number of sites at a low incremental cost. SMDS port speeds are also scalable. In
addition, the ATM Forum and SMDS Interest Group have established a specification
for internetworking SMDS and ATM services. SMDS networks have a group addressing
feature, which can be used to create multiple virtual private networks that can be
easily modified as needed. However, it is limited to data only, and is not suited
for real-time multimedia as is ATM.
<H2><A NAME="Heading12"></A><FONT COLOR="#000077">Fibre Channel</FONT></H2>
<P>The ANSI <I>Fibre Channel</I> standard offers higher available bandwidth than
ATM, and more products supporting Fibre Channel are available in the marketplace.
Sun and HP both have workstations that support Fibre Channel networks. ATM was designed
as a cell-based, high-speed network architecture for data and voice traffic. Fibre
Channel, on the other hand, is a high-speed architecture for connecting network devices,
such as PCs and workstations, and high-speed hardware (such as hard drives) that
are usually connected directly to a system bus. The bus (channel) offers the combination
of high transmission speed with low overhead. The standard supports four speeds:
133 Mbps, 266 Mbps, 530 Mbps, and 1.06 Gbps. Fibre Channel NICs supporting these
speeds are currently available. ANSI has approved 2.134 Gbps and 4.25 Gbps Fibre
Channel specifications (although the technology for these rates have not yet been
made commercially available). Commercially available ATM products, on the other hand,
usually support only the middle of the ATM transmission rate range.</P>
<P>Switching in Fibre Channel networks is done by ports logging directly onto each
other, or to connecting devices (the &quot;fabric&quot;). Fibre Channel architecture
consists of five layers:

<UL>
	<LI><I>FC-0.</I> This is the physical layer, and includes the Open Fibre Control
	system. If a connection is broken, Open Fibre Control permits the receiving device
	to change over to a lower-level laser pulse.<BR>
	<BR>
	
	<LI><I>FC-1.</I> This is the transmission protocol layer,<BR>
	<BR>
	
	<LI><I>FC-2.</I> This is the Signaling Protocol layer. FC-2 defines three service
	classes: Class 1 is a dedicated connection, class 2 provides for shared bandwidth,
	and class 3 is the same as 2 except that it does not confirm frame delivery.<BR>
	<BR>
	
	<LI><I>FC-3</I>. This layer defines common services.<BR>
	<BR>
	
	<LI>FC-4. This layer includes the Upper Layer Protocols (network and channel protocols).
</UL>

<H2><A NAME="Heading13"></A><FONT COLOR="#000077">High-Performance Parallel Interface
(HIPPI)</FONT></H2>
<P>Fibre channel is meant to be the successor to <I>HIPPI (high performance parallel
interface),</I> which was developed to connect heterogeneous supercomputers with
IBM mainframes. Like HIPPI, the primary application for fibre channel has been clustering,
or joining processors together in a point-to-point link for parallel processing.
It can also be used to link the processor to a storage array. The advantage of frame
relay over HIPPI is that processors can be located several kilometers apart, whereas
HIPPI had a much shorter maximum distance (at least during its earlier incarnation).
Fibre channel is not currently used as a LAN backbone technology (although it is
being proposed for that purpose).</P>
<P>Is Fast Ethernet still not fast enough? Although 100Base-T, ATM, and other fast
networking technologies are probably more than most people need. Some areas, such
as scientific visualization, fluid dynamics, structural analysis, and even cinematic
special effects, require a gigabit-per-second throughput. HIPPI, a connection-oriented,
circuit-switched transport mechanism, offers an incredible data rate of up to 1.6
Gbps. Originally designed in the late 1980s as a supercomputer technology, the latest
incarnation of this ANSI standard is now applied to workstation clusters and internetworks.
Although it is limited to a distance of 50 meters in a point-to-point connection
over copper wire, it can reach 300 meters over multimode fiber, and up to 10 kilometers
over single-mode fiber. In addition, the original specification has been extended
to allow the 50 meter copper wire connection to be extended to 200 meters by cascading
multiple switches.</P>
<P>Much has been done to extend the capabilities of HIPPI below the supercomputer
level; it can now be applied to an Ethernet internetwork or workstation cluster.
HIPPI works well with most LAN and WAN technologies, including all varieties of Ethernet,
FDDI, ATM, Fibre Channel, and standard TCP/IP protocols. It is capable of linking
workstations and other hosts, and connecting workstations to storage systems at very
high speeds. While HIPPI offers greater potential than other high-speed technologies
such as ATM, HIPPI can coexist well with an ATM network, combining ATM's wide-area
possibilities with the super high speed throughput of HIPPI over the local area.
(HIPPI-ATM interfaces are still under development by the ANSI committee and HIPPI
Networking Forum. Such a connection would encapsulate HIPPI data, send it over the
ATM network, and then rebuild it at the other end.)
<H2><A NAME="Heading14"></A><FONT COLOR="#000077">Fast Ethernet</FONT></H2>
<P>The <I>Fast Ethernet</I> specification provides ten times as much bandwidth as
a traditional 10Base-T network. Some consider the technology to be overkill, especially
for smaller networks running standard productivity applications. Very few corporate
users even use more than a few Mbps of bandwidth, and do well with their existing
Ethernets. However, there are cases in which 100Base-T and other fast networking
scenarios are practical and economical. Fast Ethernet networks might prove invaluable
to professionals in the fields of engineering, CAD, and multimedia. Using Fast Ethernet
as a backbone in a client/server network might make sense, especially if a high number
of clients want to access the backbone network.</P>
<P>100BaseT is an extension of the IEEE's official 802.3 Ethernet standard. The 100Base-T
network interface cards are fairly easy to install and widely available, and use
standard two-pair UTP wiring (category 3, 4 or 5). Chances are, you already have
category 3 or 4 wiring in the walls, which makes upgrading to 100BaseT fairly economical.
There are actually three physical layers to the 100Base-T specification:

<UL>
	<LI><I>100Base-TX.</I> The most common layer, 100Base-TX is full-duplex capable but
	supports only category 5. Most Fast Ethernet products target category 5 installations
	only.<BR>
	<BR>
	
	<LI><I>100Base-T4.</I> This is a four-pair system for category 3, 4, or 5 UTP cabling.
	100Base-T4 can be more difficult to install and maintain because it requires four
	pairs of wiring, and there are fewer products available.<BR>
	<BR>
	
	<LI><I>100Base-FX.</I> This is a multi-mode, two-strand fiber system. Use of fiber
	optic cable yields a maximum distance of 2 kilometers.
</UL>

<P>All three types of systems can be interconnected through a hub.</P>
<P>Hybrid 10/100 Mbps network interface cards (NICs) can run $100 more than straight
10 Mbps cards, (although prices are likely to come down when the market for Fast
Ethernet matures). These hybrid cards are usually software-configurable and capable
of running at either speed. They can also include an auto-negotiation feature, which
is a technique used by the card to communicate with the hub to automatically determine
the environment. It will automatically sense whether it is 10 Mbps, 100 Mbps, half-duplex,
or full-duplex. Some Fast Ethernet products might permit cables for both 10BaseT
and 100BaseT networks to be directed to a single hub.</P>
<P>Despite advancements in 100Base-T, 10Base-T is still the most widely used network
infrastructure, typically implemented in a star configuration with a central hub.
However, as demand for data increases and applications grow in size, high-speed LANs
are gradually becoming more important. Technology such as Fast Ethernet can provide
the faster response times that impatient end users need, as well as the additional
bandwidth that is required by high-end applications.</P>
<P>The Fast Ethernet standard has become the predominant standard for high-performance
networking. Like 10Base-T, 100Base-T is based on the Media Access Control (MAC) protocol
section of the Data Link (Layer 2) section of the OSI model. As a result, 100Base-T
can be easily integrated into an existing 10Base-T network and run over existing
cabling. Because many vendors now support 100Base-T with new products, including
hubs, routers, bridges and interface cards, Fast Ethernet networks enjoy a high level
of multivendor support. Adding 100Base-T to an existing 10Base-T network can be a
gradual process and is often largely determined by existing cabling. As new stations
are added to the network, dual-speed 10/100 adapters can be installed in anticipation
of full migration.</P>
<P>Data can move between 10Base-T and 100Base-T stations without protocol translation
because Fast Ethernet retains the same protocol as plain Ethernet--<I>Carrier Sense
Multiple Access Collision Detection (CSMA/CD).</I> A simple bridge will carry out
this movement between 10Base-T and 100base-T. Migration from 10Base-T to 100Base-T
is quite simple, because of the high level of compatibility and because it is based
on the same technology and protocols. Most 100Base-T NICs are actually 10/100 cards
and can run at either 10 or 100 Mbps. Many cards are auto-sensing and will automatically
detect whether it is connected to a 10Base-T or 100Base-T hub.</P>
<P>An alternative to 100Base-T is <I>100VG-AnyLAN.</I> This 100VG technology eliminates
packet collisions and provides for more efficient use of network bandwidth. The 100VG
also provides some facilities for prioritizing time-sensitive traffic. Despite these
technical advantages, many network professionals still prefer 100Base-T simply because
it is more familiar--it uses many of the same access mechanisms found on standard
10Base-T nets. However, being based on the same mechanisms means that 100Base-T is
not suitable for time-sensitive or real-time applications, such as videoconferencing.


<BLOCKQUOTE>
	<P>
<HR>
<FONT COLOR="#000077"><B>Gigabit Ethernet</B></FONT><BR>
	Gigabit Ethernet is the next step in the evolution of Ethernet. This wondrously fast
	gigabit-per-second Ethernet technology is still a long way off, and is currently
	little more than vaporous talk coming out of standards committees. However, this
	promising technology is likely to be less expensive than ATM and more scalable, not
	to mention less expensive to deploy because the costs normally associated with frame
	conversion are absent. The IEEE 802.3 working group studying Gigabit Ethernet might,
	if all goes well, have a specification by 1998. Under the group's initial design,
	Gigabit Ethernet would retain 100Base-T's frame size and CSMA/CD scheme, but would
	use the physical layer of the Fibre Channel architecture as underlying transport
	mechanism. 
<HR>
<FONT COLOR="#000077"></FONT></P>

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