ch12.htm

this describes managing multivendor networks

The ATM Forum's Private Network-to-Network Interface (PNNI) is a dynamic routing
protocol that can be used to build a multivendor ATM switching network. PNNI permits
different vendors' switching hardware to interoperate and establish a switched virtual
circuit (SVC) routing system. Under this model, several switches can work together
and act like a single switch. PNNI distributes information about network topology
between switches, so that paths can be calculated. It also provides for alternate
routing in the event of a linkage failure.
<H3><A NAME="Heading2"></A><FONT COLOR="#000077">ATM Management</FONT></H3>
<P>ATM networks, like traditional networks, need tools for analyzing and managing
switches and connections. However, these types of tools are in short supply for ATM
networks. As more software vendors respond to the demand, the availability of ATM
analysis tools will be another contributing factor to the widespread acceptance of
ATM. (A consortium led by Fore Systems has created a solution to the lack of management
tools for ATM networks. Fore proposes to extend <I>Remote Monitoring,</I> or <I>Rmon,</I>
to ATM networks, providing fault and performance monitoring services on ATM networks.)
<H3><A NAME="Heading3"></A><FONT COLOR="#000077">Slow ATM</FONT></H3>
<P>You might not need ATM if you don't have demanding applications like videoconferencing,
but you might still want more speed. AT&amp;T Corp. is offering a new option, referred
to as &quot;slow ATM.&quot; The service runs at 1.5 Mbps, instead of standard ATM's
minimum of 45 Mbps. The ATM Forum is, however, working on a standard for 25 Mbps
ATM. Either service would add extra speed over a standard network configuration,
while being less costly than standard ATM service. Many more low-end users could
be expected to move from 56 Kbps frame relay to the 1.5 Mbps service, rather than
moving immediately to high-speed ATM. The low-speed ATM network technology lets you
move gradually to high-speed ATM, as the need arises; this is an ideal solution for
easing into ATM technology without having to make a big commitment.
<H3><A NAME="Heading4"></A><FONT COLOR="#000077">ATM and Frame Relay Internetworking</FONT></H3>
<P>The ATM Forum and the Frame Relay Forum have jointly established a new standard--the
<I>Frame relay to ATM PVC (Permanent Virtual Circuit) Service Internetworking Implementation
Agreement</I>--to let users mix frame relay and ATM traffic on the same high-speed
network. This will permit frame-relay sites to move to higher-bandwidth ATM without
having to make an absolute choice between the two technologies. As a result, protocol
conversion software is unnecessary. The ability to use a mixed model permits a company
to use ATM at high-volume sites, while retaining frame relay at lower-volume sites
such as branch offices, and enabling the two to communicate.</P>
<P>If you use frame relay, but want to upgrade to ATM as a central hub, a hybrid
frame-relay/ATM internetworking service might do the trick. Protocols adopted by
the Frame Relay Forum and ATM Forum facilitate the establishment of such a hybrid
network. Under the service, the carrier provides protocol translations that enable
the ATM switch to talk to the frame-relay switch. The system lets you bring ATM into
an existing frame-relay network, instead of having to decide on deploying one or
the other.


<BLOCKQUOTE>
	<P>
<HR>
<FONT COLOR="#000077"><B>FUNI</B></FONT><BR>
	Frame relay to ATM internetworking provides for transparent linking of frame relay
	sites to ATM sites. One way to achieve this is through a new standard known as the
	Frame User Network Interface (FUNI), a service that performs a protocol conversion
	between frame relay and ATM. This service permits a network manager to use existing
	frame relay equipment, while gradually scaling up to ATM without having to make changes
	to the existing frame relay network. FUNI is actually a low-speed, frame-based ATM
	solution. The FUNI standard is still under development, while frame relay is widely
	available and fairly stable. The difference between FUNI and frame relay is that
	FUNI allows signaling and flow control to be extended to equipment on the customer
	premises, and it might be an attractive solution for sites with many different applications
	needing low-speed connections into an ATM network. 
<HR>


</BLOCKQUOTE>

<H3><A NAME="Heading5"></A><FONT COLOR="#000077">SNA Access to ATM</FONT></H3>
<P>IBM is also working to support ATM in LAN/WAN environments. Price is one major
barrier to wide area ATM, but another is the amount of work required to interface
ATM with legacy networks. IBM's solution for joining ATM with its SNA/APPN installed
base uses the <I>High Performance Routing (HPR)</I> feature to provide native access
to wide-area ATM networks for SNA/APPN. SNA is well suited for interfacing with ATM
because of its service features. However, SNA routing is less suited to high-speed
networking. HPR overcomes these limitations. IBM's proposal is that the native interface
to ATM take place through the HPR feature. Under this model, mainframe SNA and APPN
would connect directly to ATM using either LAN emulation or Frame Relay emulation.</P>
<P>The <I>APPN/ATM Internetworking specification,</I> submitted by IBM to the APPN
Implementers Workshop, defines a method for SNA users to migrate existing applications
to ATM. The AIW is a consortium of vendors that includes IBM, Cisco Systems, and
3Com. The specification maps IBM HPR class-of-service routing to ATM's Quality-of-Service
specification. The specification will permit APPN/HPR users to make use of APPN's
class of service across an ATM net, without having to change existing APPC applications.
The APPN class of service defines route security, transmission priority and bandwidth
between session partners. HPR is an APPN extension that provides the ability to bypass
failures and eliminate network congestion. The specification would permit users to
deploy SNA class-of-service routines over an ATM net, without having to change existing
applications. IBM's HPR/ATM proposal is part of its strategy of helping users migrate
to switched network environments.
<H3><A NAME="Heading6"></A><FONT COLOR="#000077">ATM Inverse Multiplexing</FONT></H3>
<P>The ATM Forum is working on another way to ease the migration to IBM environments.
Their <I>Asynchronous Transfer Mode inverse multiplexing (AIM)</I> technique provides
for a more cost-effective deployment of broadband ATM over a WAN, by allowing a manager
to stay with their less expensive T-1 links as opposed to moving to a more costly
T-3 connection. T-3 runs at 45 Mbps, whereas a T-1 link runs at 1.544 Mbps. AIM establishes
a high-speed connection using multiple, point-to-point T1 links that are managed
collectively. The AIM specification permits ATM devices to be linked with a single
T-1 link; as the network requirements grow, additional links can be added, until
volume justifies the use of a T-3 link. AIM sends parallel streams across multiple
T-1 lines and dynamically balances the cells over all available links.
<H3><A NAME="Heading7"></A><FONT COLOR="#000077">Quantum Flow Control</FONT></H3>
<P>A consortium of vendors known as the Flow Control Consortium are proposing an
alternative to ATM, making it even more confusing for potential ATM users. The group,
which includes Digital Equipment and ten other companies, says that their <I>Quantum
Flow Control (QFC)</I> specification complements the ATM Forum's Traffic Management
Working Group's work on the Available Bit Rate (ABR) specification. QFC is designed
to interoperate with the ATM and Forum's Explicit Rate specification for ABR services.
<H3><A NAME="Heading8"></A><FONT COLOR="#000077">LAN Emulation</FONT></H3>
<P><I>LAN Emulation (LANE)</I> defines how existing applications can run unaltered
on the ATM internetwork, and how the ATM internetwork itself can communicate with
Ethernet, token ring, and FDDI LANs. LANE, a specification of the ATM Forum, is an
internetworking strategy that permits an ATM node to establish connections to the
<I>Media Access Control (MAC)</I> protocol section on the Data Link Layer. This capability
permits most major LAN protocols to run over an ATM network, without having to modify
the LAN applications. LANE does this through three distinct techniques: data encapsulation,
address resolution, and multicast group management.</P>
<P>Each end station in the ATM network possesses a LANE driver, which establishes
the IEEE 802 MAC Layer interface. The driver will translate the MAC-layer addresses
to ATM addresses through the LANE Server's Address Resolution Service. Furthermore,
the MAC layer interface is transparent to high-level protocols, such as IP and IPX.
It is through this mechanism that a point-to-point ATM switched virtual circuit (SVC)
connection is established and data can then be transmitted to other LANE end nodes.</P>
<P>Multiple LANs can be emulated on a single ATM network, allowing for the creation
of <I>virtual LANs (VLANs).</I> A LANE driver located on an access device, such as
a router or hub, functions as a proxy for multiple end stations connected to the
device.</P>
<P>LANE offers advantages over a traditional LAN bridge environment, which is not
scalable enough to support a large internetwork. In addition, the LANE model supports
dynamic configuration, making it unnecessary to define physical connections and allowing
a host to be physically relocated, while remaining with the same VLAN.</P>
<P>Because existing 802 frame types are used in the LANE environment, an ATM adapter
can appear to an end station as an Ethernet or Token Ring card. Consequently, any
protocol that runs on Ethernet or token ring can also run on the ATM network.</P>
<P>The ATM Forum's <I>LAN Emulation Over ATM 1.0</I> specification describes how
an end station communicates with the ATM network. The specification consists of two
parts: the <I>LAN Emulation Client (LEC)</I> and <I>LAN Emulation Services.</I> The
latter includes the <I>LAN Emulation Server (LES), Broadcast and Unknown Server (BUS),</I>
and <I>LAN Emulation Configuration Server (LECS).</I> The ATM Forum has gone out
of its way to demonstrate the computer industry's affinity for bizarre acronyms,
by collectively referring to this mechanism as the <I>LAN Emulation User-to-Network
Interface</I> (LUNI).</P>
<P>Despite the strange name, LUNI (pronounced &quot;looney&quot;) goes a long way
toward providing multivendor compatibility. Through the LUNI specification, vendors
can easily establish interoperability between their various end stations.</P>
<P>Each ATM LAN end station has a unique MAC-layer address, as do standard 802 LAN
end stations. When one ATM end station is transmitting data to another ATM end station,
the first station will look for the second station's MAC address. After the first
station has discovered the second station's ATM address, any existing LANE connection
between the two can be used. If there is no existing connection, the first station
will initiate a connection using ATM signaling.</P>
<P>If an end station on an ATM LAN wishes to connect with an end station on an Ethernet
LAN, a few more steps are involved. Suppose John sits in front of a workstation on
an ATM LAN and wants to send the results of the World Series to Dan, whose machine
is connected to an Ethernet LAN. This is where the LAN Emulation Services (LES) come
into play. John's machine will send an address request message to the LES which sends
the request to a router on the Ethernet LAN. The router acts as a proxy LEC for the
end stations on the Ethernet LAN, and stores all the addresses of all the Ethernet
stations, including that of Dan's machine. When the address request is sent to the
Ethernet router, it is then broadcast to all of the end stations on the Ethernet
LAN. Dan's machine will eventually receive the request and respond to the router,
which then uses its own ATM address to make the connection.</P>
<P>Typically, connectionless LANs use bridges or routers to add additional end stations
to the internetwork. ATM, on the other hand, is connection-oriented, and data sent
between devices on an ATM network is seen only by the destination station. An ATM
network can use two types of connections: a <I>permanent virtual circuit (PVC)</I>
or a <I>switched virtual circuit (SVC).</I> The PVC is manually configured, where
the SVC is dynamically created by the ATM switch.</P>
<P>Also, the ATM network uses a different address structure from the connectionless
LAN. LANE takes care of the PVC and SVC connections transparently, using an address
resolution procedure to bridge the different addressing schemes and enable the two
to be connected. Products such as Fore Systems' ForeThought 4.0 include ATM Forum
LANE 1.0 software, which establishes a seamless connection between the ATM and Ethernet
LAN.</P>
<P>ATM LAN emulation mitigates much of the complexity of the ATM network, but is
only an interim approach on the road to full-scale ATM. Through emulation technology,
a shared-media LAN, such as Ethernet and Token Ring, can co-exist with ATM. This
permits a company to retain their original investments, while implementing a gradual
migration to ATM.
<H3><A NAME="Heading9"></A><FONT COLOR="#000077">Multiple Protocols Over ATM (MPOA)</FONT></H3>
<P>MPOA, an extension of the LAN emulation concept, is used to map network layer
addresses--such as IP or IPX--to ATM. Under an MPOA scenario, routing protocols such
as IP can use the <I>ATM Quality of Service (QoS)</I> features, with the ultimate
goal of allowing a LAN to work over ATM without having to migrate the LAN to native
ATM. As with LAN emulation, MPOA creates an ATM SVC (switched virtual circuit) whenever
a data relationship is established, creating a virtual router of sorts. This permits
network managers to create virtual subnetworks that go beyond routed boundaries regardless
of physical locations. The MPOA architecture is compatible with all routing protocols
capable of carrying addresses used by ATM, and is compatible with ATM's P-NNI specification.</P>
<P>There are three components to the MPOA architecture:

<UL>
	<LI><I>Edge devices.</I> These intelligent switches forward packets between legacy
	LAN segments and the ATM infrastructure.<BR>
	<BR>
	
	<LI><I>ATM-attached hosts.</I> Adapter cards that implement MPOA and enable the ATM-attached
	hosts to communicate with each other and with legacy LANs connected by an edge device.<BR>
	<BR>
	
	<LI><I>Route server.</I> This is actually a virtual server, not a physical device.
	It permits the network-layer subnetworks to be mapped to ATM.
</UL>

<H2><A NAME="Heading10"></A><FONT COLOR="#000077">Frame Relay</FONT></H2>
<P><I>Frame relay</I> switching is a type of packet switching that uses small packets.
It also requires less&quot;&#180;rror checking than other packet switching mechanisms;
instead, it relies more on end user devices, such as routers or front-end processors,
to provide error correction. Frame relay is similar to X.25 in that it is a bandwidth-on-demand
technology. It establishes a pool of bandwidth which is made available to multiple
data sessions sharing a common virtual circuit.</P>
<P>The <I>Frame Relay Implementors Forum,</I> a consortium that includes Cisco Systems,
Digital Equipment, Northern Telecom, and StrataCom, has established a common specification
for frame relay connections. The specification is based on the ANSI frame relay standard
and includes an extension that establishes a local management interface.</P>
<P>In the past, frame relay networking technology was used only in large WAN environments,
although it is coming to be used as a tool to carry multiple types of traffic, including
data, fax and even SNA traffic. It is less costly than a dedicated private line solution,
and extremely fast. Frame relay offers a number of benefits. SNA over frame relay
adds savings by enabling users to eliminate private lines typically used to support
critical applications. A high-speed frame relay network will let users transmit data
at a rate of 1.544 Mbps.


<BLOCKQUOTE>
	<P>
<HR>
<FONT COLOR="#000077"><B>Voice Support and NNI</B></FONT><BR>
	Although it does not currently support voice transmission, the potential of voice
	support is tantalizing. Frame relay voice support would let you make voice calls
	on the frame relay net, potentially saving big money on international calls. </P>
	<P>However, Network-to-Network Interfaces (NNI) have not yet been sufficiently developed.
	NNIs are used to let carriers interconnect their separate networks, and are an essential