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<META NAME="Author" Content="Steph Mineart">
<TITLE>Managing Multivendor Networks -- Ch 12 -- High-Speed Networking</TITLE>
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<FONT COLOR="#000077">Managing Multivendor Networks</FONT></H1>
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<H1><FONT COLOR="#000077">- 12 -<BR>
High-Speed Networking</FONT></H1>
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<UL>
<LI><A HREF="#Heading1">Asynchronous Transfer Mode (ATM) Networking</A>
<UL>
<LI><A HREF="#Heading2">ATM Management</A>
<LI><A HREF="#Heading3">Slow ATM</A>
<LI><A HREF="#Heading4">ATM and Frame Relay Internetworking</A>
<LI><A HREF="#Heading5">SNA Access to ATM</A>
<LI><A HREF="#Heading6">ATM Inverse Multiplexing</A>
<LI><A HREF="#Heading7">Quantum Flow Control</A>
<LI><A HREF="#Heading8">LAN Emulation</A>
<LI><A HREF="#Heading9">Multiple Protocols Over ATM (MPOA)</A>
</UL>
<LI><A HREF="#Heading10">Frame Relay</A>
<LI><A HREF="#Heading11">Switched Multimegabit Data Service (SMDS)</A>
<LI><A HREF="#Heading12">Fibre Channel</A>
<LI><A HREF="#Heading13">High-Performance Parallel Interface (HIPPI)</A>
<LI><A HREF="#Heading14">Fast Ethernet</A>
</UL>
<P>
<HR SIZE="4">
</P>
<H2><A NAME="Heading1"></A><FONT COLOR="#000077">Asynchronous Transfer Mode (ATM)
Networking</FONT></H2>
<P>synchronous transfer mode (ATM) technology lends itself to applications with high
bandwidth requirements, such as video and multimedia. ATM not only enables the network
to ship huge amounts of data, it can also reduce use of the server. With an ATM configuration,
a NetWare server, for example, no longer has to wait for an Ethernet transmission
that would otherwise cause data to get backed up in the cache.</P>
<P>ATM networks are built on a star topology, with a centrally located ATM switch
and each desktop wired directly to the switch. ATM is a high-bandwidth packet-switching
and multiplexing mechanism. Network capacity is divided into cells of a fixed size,
which include header and information fields. These cells are allocated on demand.
This high-speed protocol will ultimately bring many advantages to wide-area networking.
However, the technology can be costly and might require other parts of the network
to be upgraded to handle the load. A server optimized for a 10Base-T network will
probably require upgrading to handle the increased amount of data flowing in from
the clients. Besides the servers, the clients might also need a hardware upgrade.</P>
<P>More than ever, computer networks are being pushed to their limits. Huge applications,
increased end-user demand for data, and high-demand applications such as videoconferencing
and multimedia are creating a need for more bandwidth than is often available on
a traditional 10 Mbps LAN. ATM, unlike Ethernet and token ring, is a connection-oriented
technology. In an Ethernet LAN, the amount of bandwidth available to each user decreases
as more people use the network. However, in an ATM network, the amount of bandwidth
available to each connection remains constant.</P>
<P>Earlier implementations of ATM used fiber optic cable and optical transceivers,
although commercial acceptance of ATM depends on its effective deployment on a variety
of media. ATM technology is rapidly moving towards the desktop level, and is now
available over Category 5 unshielded twisted pair (UTP) and Type 1 shielded twisted
pair (STP) cabling. UTP and STP are the most commonly used types of media in the
typical LAN environment. Category 5 UTP and Type 1 STP both support ATM transmissions
up to the full 155 Mbps. Cable lengths can reach 100 meters, and a maximum of two
connections per 100 meters is allowed.</P>
<P>Support for Category 5 UTP copper wiring means that ATM can now be brought to
the desktop in a manner that is transparent to end users. FORE System's (Warrendale,
Pennsylvania) PC ATM product line recognizes the need to bring ATM to the desktop,
and includes driver support for NetWare, Windows NT, and the Macintosh OS. In addition,
LAN Emulation techniques will permit existing applications running over NetWare,
Windows, DECnet, TCP/IP, MacTCP, and AppleTalk to run unchanged over an ATM network.
LAN Emulation also provides the means to establish internetworking between the ATM
and Ethernet or token ring LAN.</P>
<P>A recent LAN emulation specification, suggested by the ATM Forum, enables ATM
to be deployed in a LAN environment without having to change the system software.
In addition, the price is gradually decreasing on all fronts as competition increases
and new vendors enter the market. However, before ATM is widely accepted, more telephone
service providers must establish their ATM services, and ATM interfaces must be built
into network operating systems.</P>
<P>If ATM is brought to every desktop, every client gains the ability to send data
at speeds of 25 Mbps-155 Mbps, or more than 15 times the existing data rate of a
standard Ethernet LAN. The ATM architecture itself, however, has no upper speed limit.</P>
<P>ATM technology is still young, expensive, and lacking in standards, and an end-to-end
ATM network is still not a realistic possibility. It is used primarily to support
more specific, highly demanding applications that a traditional network would not
be able to support. A network with only ordinary, run-of-the-mill needs and productivity
applications running, for example, some database programs, productivity apps such
as word processing, spreadsheets, and e-mail, can run on a standard 10Base-T network
for quite some time without slowing down. Implementing an ATM network for these ordinary
tasks is like driving to the corner supermarket in an Indy 500 racecar.</P>
<P>ATM takes all types of traffic, including data, voice, and video, and transforms
it into 53-byte packets, which can then travel directly over a network via switching.
This small packet size lends itself to real-time applications, such as video. In
order to increase speed, the switches can route traffic through multiple paths. The
link, however, will appear as a point-to-point connection, or virtual circuit. Bandwidth
is available on demand, and users do not need to bear the expense of a dedicated
line.</P>
<P>Because of the lack of standards, various ATM switches are often incompatible.
The ATM Forum has done a considerable amount of groundwork for defining ATM standards,
however, and more vendors are starting to comply and offer complete ATM product lines.
An ATM solution can be costly by the time the switching equipment is paid for, workstations
are upgraded, and training has been planned. (In the near future, however, it is
likely that ATM will come to be accepted as a robust and complete backbone technology.)</P>
<P>The ATM Forum is a consortium of over 500 organizations. One of the first companies
to release ATM products was Fore Systems, one of the ATM Forum's principal members.
Fore released the first ATM adapter cards in 1991, the first ATM LAN switches in
1992, and remains the leader in this market. Fore approaches ATM with a four-tiered
architecture, as follows:
<UL>
<LI><I>Layer 1: ATM Transport Services.</I> These services convert non-ATM traffic
to ATM cells, allowing all types of traffic to make use of ATM features.<BR>
<BR>
<LI><I>Layer 2: VLAN (Virtual LAN) Services.</I> A VLAN is a logical association
of users with a common broadcast domain. VLAN technology permits a network to be
designed based on logical relationships, instead of physical connections.<BR>
<BR>
<LI><I>Layer 3: Distributed Routing Services.</I> Although VLANs eliminate a substantial
amount of routing, some routing might still be required, such as establishing communications
between different VLANs, or conversion between different MAC types (Ethernet to token
ring).<BR>
<BR>
<LI><I>Layer 4: Application Services.</I> This layer makes the services in the above
three layers available to existing applications.
</UL>
<P>An ATM network can carry three types of traffic: <I>constant bit rate (CBR),</I>
<I>variable bit rate (VBR),</I> and <I>available bit rate (ABR).</I> CBR accommodates
voice and video, and requires the ATM network to act like a dedicated circuit and
provide sustained bandwidth. VBR traffic is similar, except that the bandwidth requirement
is not constant. ABR traffic does not require a specified amount of bandwidth or
delay parameters, and is useful for most common applications such as e-mail or file
transfer.</P>
<P>The ATM network uses three techniques to manage traffic. They are as follows:
<UL>
<LI><I>Traffic shaping.</I> This is performed at the user-network interface level
and ensures that the traffic matches the negotiated connection between the user and
the network.<BR>
<BR>
<LI><I>Traffic policing.</I> This is performed by the ATM network and ensures that
traffic on each connection is within the parameters negotiated at the establishment
of the connection. An ATM switch uses a buffering technique called a "leaky
bucket" in order to police traffic. In the leaky bucket system, traffic flows
(leaks) out of a buffer ( bucket) at a constant rate, regardless of how fast the
traffic flows into the buffer.<BR>
<BR>
<LI><I>Congestion control.</I> This is still being defined by the ATM Forum.
</UL>
<BLOCKQUOTE>
<P>
<HR>
<FONT COLOR="#000077"><B>More on Congestion Control</B></FONT><BR>
The ATM Forum is still defining the congestion control technique of traffic management,
although two schemes have been proposed to control traffic flow, based on either
an end-to-end, or link-by-link basis. End-to-end schemes control the transmission
rate where the LAN meets the ATM device. The drawbacks of this method are that some
cells can be lost and it requires a considerable amount of buffer space. A link-by-link
flow control mechanism can support more users and uses less buffer space. This too,
has its drawbacks: it is more expensive and equipment to implement link-by-link control
is not commercially available. An integrated proposal, being considered by the ATM
Forum, would establish a default end-to-end mechanism, with an optional link-by-link
scheme.
<HR>
</BLOCKQUOTE>
<P>For ATM to be widely accepted, however, switching systems must be capable of interoperating.
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