Managing Multivendor Networks 12

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aging Multivendor Networks -- Ch 12 -- High-Speed Networking

//F|/Books/book-121/ch12.htm[10/9/2012 9:25:38 PM]

Managing Multivendor Networks

- 12 -

High-Speed Networking

Asynchronous Transfer Mode (ATM) NetworkingATM ManagementSlow ATMATM and Frame Relay Internetworking

SNA Access to ATMATM Inverse MultiplexingQuantum Flow ControlLAN EmulationMultiple Protocols Over ATM (MPOA)

Frame RelaySwitched Multimegabit Data Service (SMDS)Fibre ChannelHigh-Performance Parallel Interface (HIPPI)Fast Ethernet

Asynchronous Transfer Mode (ATM) Networking

ynchronous transfer mode (ATM) technology lends itself to applications with high bandwidth requirements, such aideo and multimedia. ATM not only enables the network to ship huge amounts of data, it can also reduce use of therver. With an ATM configuration, a NetWare server, for example, no longer has to wait for an Ethernet transmisshat would otherwise cause data to get backed up in the cache.

ATM networks are built on a star topology, with a centrally located ATM switch and each desktop wired directly the switch. ATM is a high-bandwidth packet-switching and multiplexing mechanism. Network capacity is divided iells of a fixed size, which include header and information fields. These cells are allocated on demand. This high-peed protocol will ultimately bring many advantages to wide-area networking. However, the technology can be cond might require other parts of the network to be upgraded to handle the load. A server optimized for a 10Base-Tetwork will probably require upgrading to handle the increased amount of data flowing in from the clients. Besidehe servers, the clients might also need a hardware upgrade.

More than ever, computer networks are being pushed to their limits. Huge applications, increased end-user demandata, and high-demand applications such as videoconferencing and multimedia are creating a need for more bandwhan is often available on a traditional 10 Mbps LAN. ATM, unlike Ethernet and token ring, is a connection-orienteechnology. In an Ethernet LAN, the amount of bandwidth available to each user decreases as more people use theetwork. However, in an ATM network, the amount of bandwidth available to each connection remains constant.
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arlier implementations of ATM used fiber optic cable and optical transceivers, although commercial acceptance oATM depends on its effective deployment on a variety of media. ATM technology is rapidly moving towards theesktop level, and is now available over Category 5 unshielded twisted pair (UTP) and Type 1 shielded twisted pairSTP) cabling. UTP and STP are the most commonly used types of media in the typical LAN environment. Catego

UTP and Type 1 STP both support ATM transmissions up to the full 155 Mbps. Cable lengths can reach 100 meternd a maximum of two connections per 100 meters is allowed.

upport for Category 5 UTP copper wiring means that ATM can now be brought to the desktop in a manner that isransparent to end users. FORE System's (Warrendale, Pennsylvania) PC ATM product line recognizes the need to

ring ATM to the desktop, and includes driver support for NetWare, Windows NT, and the Macintosh OS. In additAN 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 tostablish internetworking between the ATM and Ethernet or token ring LAN.

A recent LAN emulation specification, suggested by the ATM Forum, enables ATM to be deployed in a LANnvironment without having to change the system software. In addition, the price is gradually decreasing on all frons competition increases and new vendors enter the market. However, before ATM is widely accepted, more telephervice providers must establish their ATM services, and ATM interfaces must be built into network operatingystems.

f ATM is brought to every desktop, every client gains the ability to send data at speeds of 25 Mbps-155 Mbps, ormore than 15 times the existing data rate of a standard Ethernet LAN. The ATM architecture itself, however, has nopper speed limit.

ATM technology is still young, expensive, and lacking in standards, and an end-to-end ATM network is still not aealistic possibility. It is used primarily to support more specific, highly demanding applications that a traditionaletwork would not be able to support. A network with only ordinary, run-of-the-mill needs and productivitypplications running, for example, some database programs, productivity apps such as word processing, spreadsheend 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.

ATM takes all types of traffic, including data, voice, and video, and transforms it into 53-byte packets, which can th

ravel directly over a network via switching. This small packet size lends itself to real-time applications, such as vidn order to increase speed, the switches can route traffic through multiple paths. The link, however, will appear as aoint-to-point connection, or virtual circuit. Bandwidth is available on demand, and users do not need to bear thexpense of a dedicated line.

ecause of the lack of standards, various ATM switches are often incompatible. The ATM Forum has done aonsiderable amount of groundwork for defining ATM standards, however, and more vendors are starting to complnd offer complete ATM product lines. An ATM solution can be costly by the time the switching equipment is paior, workstations are upgraded, and training has been planned. (In the near future, however, it is likely that ATM wome to be accepted as a robust and complete backbone technology.)

he ATM Forum is a consortium of over 500 organizations. One of the first companies to release ATM products wore Systems, one of the ATM Forum's principal members. Fore released the first ATM adapter cards in 1991, the

ATM LAN switches in 1992, and remains the leader in this market. Fore approaches ATM with a four-tieredrchitecture, as follows:

Layer 1: ATM Transport Services. These services convert non-ATM traffic to ATM cells, allowing all types traffic to make use of ATM features.

Layer 2: VLAN (Virtual LAN) Services. A VLAN is a logical association of users with a common broadcastdomain. VLAN technology permits a network to be designed based on logical relationships, instead of physicconnections.


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Layer 3: Distributed Routing Services. Although VLANs eliminate a substantial amount of routing, some roumight still be required, such as establishing communications between different VLANs, or conversion betwedifferent MAC types (Ethernet to token ring).

Layer 4: Application Services. This layer makes the services in the above three layers available to existingapplications.

An ATM network can carry three types of traffic: constant bit rate (CBR),variable bit rate (VBR), and available biate (ABR). CBR accommodates voice and video, and requires the ATM network to act like a dedicated circuit and

rovide sustained bandwidth. VBR traffic is similar, except that the bandwidth requirement is not constant. ABR traoes not require a specified amount of bandwidth or delay parameters, and is useful for most common applicationsuch as e-mail or file transfer.

he ATM network uses three techniques to manage traffic. They are as follows:

Traffic shaping. This is performed at the user-network interface level and ensures that the traffic matches thenegotiated connection between the user and the network.

Traffic policing. This is performed by the ATM network and ensures that traffic on each connection is withinparameters negotiated at the establishment of the connection. An ATM switch uses a buffering technique calla "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.

Congestion control. This is still being defined by the ATM Forum.

More on Congestion ControlThe ATM Forum is still defining the congestion control technique of traffic management, although twoschemes 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 drawbacksof this method are that some cells can be lost and it requires a considerable amount of buffer space. Alink-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 commerciallyavailable. An integrated proposal, being considered by the ATM Forum, would establish a default end-to-end mechanism, with an optional link-by-link scheme.

or ATM to be widely accepted, however, switching systems must be capable of interoperating. The ATM Forum'srivate Network-to-Network Interface (PNNI) is a dynamic routing protocol that can be used to build a multivendo

ATM switching network. PNNI permits different vendors' switching hardware to interoperate and establish a switchirtual circuit (SVC) routing system. Under this model, several switches can work together and act like a single swNNI distributes information about network topology between switches, so that paths can be calculated. It alsorovides for alternate routing in the event of a linkage failure.

ATM Management

ATM networks, like traditional networks, need tools for analyzing and managing switches and connections. Howevhese types of tools are in short supply for ATM networks. As more software vendors respond to the demand, thevailability of ATM analysis tools will be another contributing factor to the widespread acceptance of ATM. (Aonsortium led by Fore Systems has created a solution to the lack of management tools for ATM networks. Foreroposes to extendRemote Monitoring, orRmon, to ATM networks, providing fault and performance monitoringervices on ATM networks.)

low ATM


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You might not need ATM if you don't have demanding applications like videoconferencing, but you might still wamore speed. AT&T Corp. is offering a new option, referred to as "slow ATM." The service runs at 1.5 Mbps, instea

f standard ATM's minimum of 45 Mbps. The ATM Forum is, however, working on a standard for 25 Mbps ATMither 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 Mbpservice, rather than moving immediately to high-speed ATM. The low-speed ATM network technology lets you mradually to high-speed ATM, as the need arises; this is an ideal solution for easing into ATM technology withoutaving to make a big commitment.

ATM and Frame Relay Internetworking

he ATM Forum and the Frame Relay Forum have jointly established a new standard--the Frame relay to ATM PVPermanent Virtual Circuit) Service Internetworking Implementation Agreement--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 ATMwithout having to make an absolute choice between the two technologies. As a result, protocol conversion softwarennecessary. The ability to use a mixed model permits a company to use ATM at high-volume sites, while retainingrame relay at lower-volume sites such as branch offices, and enabling the two to communicate.

f you use frame relay, but want to upgrade to ATM as a central hub, a hybrid frame-relay/ATM internetworkingervice might do the trick. Protocols adopted by the Frame Relay Forum and ATM Forum facilitate the establishme

f such a hybrid network. Under the service, the carrier provides protocol translations that enable the ATM switch talk to the frame-relay switch. The system lets you bring ATM into an existing frame-relay network, instead of havo decide on deploying one or the other.

FUNI

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), aservice that performs a protocol conversion between frame relay and ATM. This service permits a networkmanager to use existing frame relay equipment, while gradually scaling up to ATM without having tomake changes to the existing frame relay network. FUNI is actually a low-speed, frame-based ATMsolution. 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 beextended to equipment on the customer premises, and it might be an attractive solution for sites with manydifferent applications needing low-speed connections into an ATM network.

NA Access to ATM

BM is also working to support ATM in LAN/WAN environments. Price is one major barrier to wide area ATM, bnother is the amount of work required to interface ATM with legacy networks. IBM's solution for joining ATM wis SNA/APPN installed base uses theHigh Performance Routing (HPR) feature to provide native access to wide-a

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 hat the native interface to ATM take place through the HPR feature. Under this model, mainframe SNA and APPNwould connect directly to ATM using either LAN emulation or Frame Relay emulation.

heAPPN/ATM Internetworking specification, submitted by IBM to the APPN Implementers Workshop, defines amethod for SNA users to migrate existing applications to ATM. The AIW is a consortium of vendors that includesBM, Cisco Systems, and 3Com. The specification maps IBM HPR class-of-service routing to ATM's Quality-of-ervice specification. The specification will permit APPN/HPR users to make use of APPN's class of service across

ATM net, without having to change existing APPC applications. The APPN class of service defines route security,ransmission priority and bandwidth between session partners. HPR is an APPN extension that provides the ability ypass failures and eliminate network congestion. The specification would permit users to deploy SNA class-of-


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ervice routines over an ATM net, without having to change existing applications. IBM's HPR/ATM proposal is paf its strategy of helping users migrate to switched network environments.

ATM Inverse Multiplexing

he ATM Forum is working on another way to ease the migration to IBM environments. Their Asynchronous TranMode inverse multiplexing (AIM) technique provides for a more cost-effective deployment of broadband ATM oveWAN, by allowing a manager to stay with their less expensive T-1 links as opposed to moving to a more costly T-onnection. T-3 runs at 45 Mbps, whereas a T-1 link runs at 1.544 Mbps. AIM establishes a high-speed connectionsing multiple, point-to-point T1 links that are managed collectively. The AIM specification permits ATM devices e linked with a single T-1 link; as the network requirements grow, additional links can be added, until volumeustifies the use of a T-3 link. AIM sends parallel streams across multiple T-1 lines and dynamically balances the cver all available links.

Quantum Flow Control

A consortium of vendors known as the Flow Control Consortium are proposing an alternative to ATM, making it evmore confusing for potential ATM users. The group, which includes Digital Equipment and ten other companies, sahat their Quantum Flow Control (QFC) specification complements the ATM Forum's Traffic Management Workin

Group's work on the Available Bit Rate (ABR) specification. QFC is designed to interoperate with the ATM andorum's Explicit Rate specification for ABR services.

LAN Emulation

AN Emulation (LANE) defines how existing applications can run unaltered on the ATM internetwork, and how thATM internetwork itself can communicate with Ethernet, token ring, and FDDI LANs. LANE, a specification of thATM Forum, is an internetworking strategy that permits an ATM node to establish connections to theMedia AccesControl (MAC) protocol section on the Data Link Layer. This capability permits most major LAN protocols to runver an ATM network, without having to modify the LAN applications. LANE does this through three distinctechniques: data encapsulation, address resolution, and multicast group management.

ach end station in the ATM network possesses a LANE driver, which establishes the IEEE 802 MAC Layer interhe driver will translate the MAC-layer addresses to ATM addresses through the LANE Server's Address Resolutioervice. Furthermore, the MAC layer interface is transparent to high-level protocols, such as IP and IPX. It is throu

his mechanism that a point-to-point ATM switched virtual circuit (SVC) connection is established and data can thee transmitted to other LANE end nodes.

Multiple LANs can be emulated on a single ATM network, allowing for the creation ofvirtual LANs (VLANs). AANE driver located on an access device, such as a router or hub, functions as a proxy for multiple end stationsonnected to the device.

ANE offers advantages over a traditional LAN bridge environment, which is not scalable enough to support a larg

nternetwork. In addition, the LANE model supports dynamic configuration, making it unnecessary to define physiconnections and allowing a host to be physically relocated, while remaining with the same VLAN.

ecause existing 802 frame types are used in the LANE environment, an ATM adapter can appear to an end stationn Ethernet or Token Ring card. Consequently, any protocol that runs on Ethernet or token ring can also run on the

ATM network.

he ATM Forum'sLAN Emulation Over ATM 1.0 specification describes how an end station communicates with thATM network. The specification consists of two parts: theLAN Emulation Client (LEC) andLAN Emulation Servic

he latter includes theLAN Emulation Server (LES), Broadcast and Unknown Server (BUS), andLAN EmulationConfiguration Server (LECS). The ATM Forum has gone out of its way to demonstrate the computer industry's affi


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or bizarre acronyms, by collectively referring to this mechanism as theLAN Emulation User-to-Network InterfaceLUNI).

Despite the strange name, LUNI (pronounced "looney") goes a long way toward providing multivendor compatibilihrough the LUNI specification, vendors can easily establish interoperability between their various end stations.

ach ATM LAN end station has a unique MAC-layer address, as do standard 802 LAN end stations. When one ATnd station is transmitting data to another ATM end station, the first station will look for the second station's MACddress. After the first station has discovered the second station's ATM address, any existing LANE connection

etween the two can be used. If there is no existing connection, the first station will initiate a connection using ATMignaling.

f an end station on an ATM LAN wishes to connect with an end station on an Ethernet LAN, a few more steps arenvolved. Suppose John sits in front of a workstation on an ATM LAN and wants to send the results of the Worlderies to Dan, whose machine is connected to an Ethernet LAN. This is where the LAN Emulation Services (LES)ome into play. John's machine will send an address request message to the LES which sends the request to a routehe Ethernet LAN. The router acts as a proxy LEC for the end stations on the Ethernet LAN, and stores all theddresses of all the Ethernet stations, including that of Dan's machine. When the address request is sent to the Etheouter, it is then broadcast to all of the end stations on the Ethernet LAN. Dan's machine will eventually receive theequest and respond to the router, which then uses its own ATM address to make the connection.

ypically, connectionless LANs use bridges or routers to add additional end stations to the internetwork. ATM, on ther hand, is connection-oriented, and data sent between devices on an ATM network is seen only by the destinatitation. An ATM network can use two types of connections: a permanent virtual circuit (PVC) or a switched virtuaircuit (SVC). The PVC is manually configured, where the SVC is dynamically created by the ATM switch.

Also, the ATM network uses a different address structure from the connectionless LAN. LANE takes care of the PVnd SVC connections transparently, using an address resolution procedure to bridge the different addressing schemnd enable the two to be connected. Products such as Fore Systems' ForeThought 4.0 include ATM Forum LANE oftware, which establishes a seamless connection between the ATM and Ethernet LAN.

ATM LAN emulation mitigates much of the complexity of the ATM network, but is only an interim approach on th

oad to full-scale ATM. Through emulation technology, a shared-media LAN, such as Ethernet and Token Ring, co-exist with ATM. This permits a company to retain their original investments, while implementing a gradual

migration to ATM.

Multiple Protocols Over ATM (MPOA)

MPOA, an extension of the LAN emulation concept, is used to map network layer addresses--such as IP or IPX--tATM. Under an MPOA scenario, routing protocols such as IP can use theATM Quality of Service (QoS) features, he ultimate goal of allowing a LAN to work over ATM without having to migrate the LAN to native ATM. As witAN emulation, MPOA creates an ATM SVC (switched virtual circuit) whenever a data relationship is establishedreating a virtual router of sorts. This permits network managers to create virtual subnetworks that go beyond route

oundaries regardless of physical locations. The MPOA architecture is compatible with all routing protocols capablarrying addresses used by ATM, and is compatible with ATM's P-NNI specification.

here are three components to the MPOA architecture:

Edge devices. These intelligent switches forward packets between legacy LAN segments and the ATMinfrastructure.

ATM-attached hosts. Adapter cards that implement MPOA and enable the ATM-attached hosts to communicwith each other and with legacy LANs connected by an edge device.


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Route server. This is actually a virtual server, not a physical device. It permits the network-layer subnetworkbe mapped to ATM.

Frame Relay

Frame relay switching is a type of packet switching that uses small packets. It also requires less"rror checking thanther packet switching mechanisms; instead, it relies more on end user devices, such as routers or front-end processo provide error correction. Frame relay is similar to X.25 in that it is a bandwidth-on-demand technology. It

stablishes a pool of bandwidth which is made available to multiple data sessions sharing a common virtual circuit.

he Frame Relay Implementors Forum, a consortium that includes Cisco Systems, Digital Equipment, Northernelecom, and StrataCom, has established a common specification for frame relay connections. The specification isased on the ANSI frame relay standard and includes an extension that establishes a local management interface.

n the past, frame relay networking technology was used only in large WAN environments, although it is coming tosed as a tool to carry multiple types of traffic, including data, fax and even SNA traffic. It is less costly than aedicated private line solution, and extremely fast. Frame relay offers a number of benefits. SNA over frame relaydds savings by enabling users to eliminate private lines typically used to support critical applications. A high-speerame relay network will let users transmit data at a rate of 1.544 Mbps.

Voice Support and NNI

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 bigmoney on international calls.

However, Network-to-Network Interfaces (NNI) have not yet been sufficiently developed. NNIs are usedto let carriers interconnect their separate networks, and are an essential part of international frame relay.

rame relay technology is becoming much more attractive economically, and carriers are getting intensely competitn 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, andnclude port charges for physically connecting to the network, charges per PVC (permanent virtual circuit), andharges for local access. Other charges include COC (central-office connection) tariffs, which cover the cost of theonnection between local access service and the interexchange carrier.

he lack of switched virtual circuit (SVC) services has delayed the widespread implementation of frame relay in theast. However, manufacturers and service providers are starting to implement these services in earnest. The lack ofVC services caused customers to instead rely on frame-relay PVCs. SVCs would permit a network manager tostablish a frame relay connection on demand, and replace the need for PVCs between sites.

oftware is starting to become available to integrate voice, fax, and data networks over frame-relay. Products are

vailable to enable a frame relay network to handle all three types of traffic. This type of software would naturally riority to voice traffic, sending it at a Committed Information Rate--which reduces delays typically associated withending voice over frame relay.

Switched Multimegabit Data Service (SMDS)

witched Multimegabit Data Service (SMDS), a connectionless service, can be advantageous in some multivendoretworks over ATM or frame relay technologies. Network design under an SMDS architecture is actually quite sim

With frame relay, on the other hand, you have to assign and configure PVCs (permanent virtual circuits) betweenocations. ATM has similar complex design requirements. SMDS, on the other hand, establishes any-to-anyonnectivity. Each location has its own E.164 address, so all you have to do is assign it a port connection speed. Af


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site is hooked up, it can communicate with any other site on the SMDS net.

MDS is a scalable solution, and is capable of keeping pace with an increased number of sites at a low incrementaost. SMDS port speeds are also scalable. In addition, the ATM Forum and SMDS Interest Group have established pecification for internetworking SMDS and ATM services. SMDS networks have a group addressing feature, whican be used to create multiple virtual private networks that can be easily modified as needed. However, it is limitedata only, and is not suited for real-time multimedia as is ATM.

Fibre Channelhe ANSI Fibre Channel standard offers higher available bandwidth than ATM, and more products supporting Fib

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 th

ther hand, is a high-speed architecture for connecting network devices, such as PCs and workstations, and high-spardware (such as hard drives) that are usually connected directly to a system bus. The bus (channel) offers theombination of high transmission speed with low overhead. The standard supports four speeds: 133 Mbps, 266 Mbp30 Mbps, and 1.06 Gbps. Fibre Channel NICs supporting these speeds are currently available. ANSI has approved.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 themiddle of the ATM transmission rate range.

witching in Fibre Channel networks is done by ports logging directly onto each other, or to connecting devices (thfabric"). Fibre Channel architecture consists of five layers:

FC-0. This is the physical layer, and includes the Open Fibre Control system. If a connection is broken, OpenFibre Control permits the receiving device to change over to a lower-level laser pulse.

FC-1. This is the transmission protocol layer,

FC-2. This is the Signaling Protocol layer. FC-2 defines three service classes: Class 1 is a dedicated connecticlass 2 provides for shared bandwidth, and class 3 is the same as 2 except that it does not confirm frame

delivery.

FC-3. This layer defines common services.

FC-4. This layer includes the Upper Layer Protocols (network and channel protocols).

High-Performance Parallel Interface (HIPPI)

ibre channel is meant to be the successor toHIPPI (high performance parallel interface), which was developed toonnect heterogeneous supercomputers with IBM mainframes. Like HIPPI, the primary application for fibre channas been clustering, or joining processors together in a point-to-point link for parallel processing. It can also be use

nk the processor to a storage array. The advantage of frame relay over HIPPI is that processors can be located sevilometers apart, whereas HIPPI had a much shorter maximum distance (at least during its earlier incarnation). Fibrhannel is not currently used as a LAN backbone technology (although it is being proposed for that purpose).

s Fast Ethernet still not fast enough? Although 100Base-T, ATM, and other fast networking technologies are probmore than most people need. Some areas, such as scientific visualization, fluid dynamics, structural analysis, and evinematic special effects, require a gigabit-per-second throughput. HIPPI, a connection-oriented, circuit-switchedransport mechanism, offers an incredible data rate of up to 1.6 Gbps. Originally designed in the late 1980s as aupercomputer technology, the latest incarnation of this ANSI standard is now applied to workstation clusters andnternetworks. Although it is limited to a distance of 50 meters in a point-to-point connection over copper wire, it ceach 300 meters over multimode fiber, and up to 10 kilometers over single-mode fiber. In addition, the original


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pecification has been extended to allow the 50 meter copper wire connection to be extended to 200 meters byascading multiple switches.

Much has been done to extend the capabilities of HIPPI below the supercomputer level; it can now be applied to athernet internetwork or workstation cluster. HIPPI works well with most LAN and WAN technologies, including arieties of Ethernet, FDDI, ATM, Fibre Channel, and standard TCP/IP protocols. It is capable of linking workstatind other hosts, and connecting workstations to storage systems at very high speeds. While HIPPI offers greaterotential than other high-speed technologies such as ATM, HIPPI can coexist well with an ATM network, combini

ATM's wide-area possibilities with the super high speed throughput of HIPPI over the local area. (HIPPI-ATM

nterfaces are still under development by the ANSI committee and HIPPI Networking Forum. Such a connectionwould encapsulate HIPPI data, send it over the ATM network, and then rebuild it at the other end.)

Fast Ethernet

he Fast Ethernetspecification provides ten times as much bandwidth as a traditional 10Base-T network. Someonsider 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. Fa

thernet networks might prove invaluable to professionals in the fields of engineering, CAD, and multimedia. Usinast Ethernet as a backbone in a client/server network might make sense, especially if a high number of clients waccess the backbone network.

00BaseT is an extension of the IEEE's official 802.3 Ethernet standard. The 100Base-T network interface cards arairly easy to install and widely available, and use standard two-pair UTP wiring (category 3, 4 or 5). Chances are,lready have category 3 or 4 wiring in the walls, which makes upgrading to 100BaseT fairly economical. There arectually three physical layers to the 100Base-T specification:

100Base-TX. The most common layer, 100Base-TX is full-duplex capable but supports only category 5. MosFast Ethernet products target category 5 installations only.

100Base-T4. This is a four-pair system for category 3, 4, or 5 UTP cabling. 100Base-T4 can be more difficu

install and maintain because it requires four pairs of wiring, and there are fewer products available.

100Base-FX. This is a multi-mode, two-strand fiber system. Use of fiber optic cable yields a maximum distaof 2 kilometers.

All three types of systems can be interconnected through a hub.

Hybrid 10/100 Mbps network interface cards (NICs) can run $100 more than straight 10 Mbps cards, (although pricre likely to come down when the market for Fast Ethernet matures). These hybrid cards are usually software-onfigurable and capable of running at either speed. They can also include an auto-negotiation feature, which is aechnique used by the card to communicate with the hub to automatically determine the environment. It willutomatically sense whether it is 10 Mbps, 100 Mbps, half-duplex, or full-duplex. Some Fast Ethernet products mi

ermit cables for both 10BaseT and 100BaseT networks to be directed to a single hub.

Despite advancements in 100Base-T, 10Base-T is still the most widely used network infrastructure, typicallymplemented in a star configuration with a central hub. However, as demand for data increases and applications gron size, high-speed LANs are gradually becoming more important. Technology such as Fast Ethernet can provide thaster response times that impatient end users need, as well as the additional bandwidth that is required by high-endpplications.

he Fast Ethernet standard has become the predominant standard for high-performance networking. Like 10Base-T00Base-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 existin


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abling. Because many vendors now support 100Base-T with new products, including hubs, routers, bridges andnterface cards, Fast Ethernet networks enjoy a high level of multivendor support. Adding 100Base-T to an existing0Base-T network can be a gradual process and is often largely determined by existing cabling. As new stations aredded to the network, dual-speed 10/100 adapters can be installed in anticipation of full migration.

Data can move between 10Base-T and 100Base-T stations without protocol translation because Fast Ethernet retainhe same protocol as plain Ethernet--Carrier Sense Multiple Access Collision Detection (CSMA/CD). A simple brid

will carry out this movement between 10Base-T and 100base-T. Migration from 10Base-T to 100Base-T is quiteimple, because of the high level of compatibility and because it is based on the same technology and protocols. M

00Base-T NICs are actually 10/100 cards and can run at either 10 or 100 Mbps. Many cards are auto-sensing and utomatically detect whether it is connected to a 10Base-T or 100Base-T hub.

An alternative to 100Base-T is 100VG-AnyLAN. This 100VG technology eliminates packet collisions and providesmore efficient use of network bandwidth. The 100VG also provides some facilities for prioritizing time-sensitiveraffic. 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 basn the same mechanisms means that 100Base-T is not suitable for time-sensitive or real-time applications, such asideoconferencing.

Gigabit Ethernet

Gigabit Ethernet is the next step in the evolution of Ethernet. This wondrously fast gigabit-per-secondEthernet technology is still a long way off, and is currently little more than vaporous talk coming out ofstandards committees. However, this promising technology is likely to be less expensive than ATM andmore scalable, not to mention less expensive to deploy because the costs normally associated with frameconversion 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'sframe size and CSMA/CD scheme, but would use the physical layer of the Fibre Channel architecture asunderlying transport mechanism.

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Managing Multivendor Networks 12

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