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Broadband Versus Narrowband

We frequently regard a broadband network as a "high speed connection" to the Internet run over Ethernet network interface cards (NICs). This is not a correct point of view. We must differentiate between broadband and narrowband networks in that broadband networks can be used for many different traffic characteristics, while narrowband networks are used for one. Broadband and narrowband networks have nothing to do with the capacity of asymmetrical digital subscribe line (ADSL) or cable modems. These are access points to a broadband network.

Narrowband technologies are Ethernet, Token Ring, FDDI, and certain types of WAN links. Narrowband technologies can be adapted to run over broadband technologies, but it is not possible to run broadband technologies over narrowband. Broadband technologies, on the other hand, are not limited to a single link protocol (like Ethernet) or to data communication only. Broadband networks use frame, or frame trains, and special methods to encapsulate and control the information sent through it. The information does not have to be computer related at all. For example, voice -over-IP is not a broadband technology because the audio is digitized and sent as IP packets, mostly over Ethernet, whereas on broadband, voice can be sent as a separate channel without encapsulating it into a computer communication protocol.

The three major types of broadband communication are:

  • Constant bit rate (time critical)—typically video streams

  • Available bit rate (in-order packet delivery)—typically phone systems

  • Unspecified bit rate (error-free)—typically data communications

Broadband networks can be adapted to form the physical layer for LAN technologies (broadband ISDN or ATM), or to run subsets of TCP/IP directly (such as PPP over SDH).

The three major groups of broadband technologies are:

  • Synchronous optical network (SONET, North America)

  • Synchronous digital hierarchy (SDH, Europe)

  • Broadband ISDN (ATM)

ATM can function by itself or run over SONET or SDH. The latter is more common.

What is a Metropolitan Area Network?

A MAN resembles a large corporate network where different LANs are connected through campus-type transfer networks into a core-type backbone. The difference is that the typical corporate network is often a narrowband network, while a MAN, often, at least partly, relies on broadband technology.

A MAN also spans a geographical area and can, from a LAN point of view, traverse long distances. In a corporate network, security is implemented at the edges, policies at the transfer nets, and the core is unrestricted.

In a MAN, the edges are often owned by subscribers to the MAN services, and are not under the MAN owner's direct control; whereas the core and transfer nets are under a very high degree of control.

MANs are often owned by telcos, major ISPs or government agencies, even though individual companies or corporations can build their own MAN-type networks. A MAN owner has an advantage if the MAN can deliver various types of services, not only data communications. To effectively use the available MAN bandwidth, MAN owners want to eliminate overhead as much as possible because bandwidth is, in the end, what generates a profit.

Principles for a Sun Ray Environment Over Broadband Networks

First, some seemingly prohibiting facts:

  • A Sun Ray appliance cannot connect directly to a broadband network.

  • A Sun Ray appliance cannot be connected to a pair of single mode fibers for long distance communication.

  • A Sun Ray appliance is a LAN-bound narrowband device, connecting only to 10 Mbps and 100 Mbps Ethernet networks over RJ45 connectors (twisted pair).

The solution is to connect the Sun Ray appliance to a broadband-capable switch. Such a switch is frequently called an edge device or proxy switch. The proxy switch can be equipped with one (or several) fiber interfaces, enabling long distance connections. The Sun Ray appliance can "talk" Ethernet to the proxy switch; the proxy switch then "talks" TCP/IP through the broadband network.

In the computer center, the Sun Ray server can be equipped with one or more broadband interface cards (BICs). Because we have control over the broadband network characteristics, we can set up channels through the network, connecting the proxy switch and the Sun Ray server. The proxy switch is configured with per-port VLANs, and the channels to the broadband interface are included in the VLAN group.

The Sun Ray appliance sees all traffic going to and from the Sun Ray server. The channel through the MAN can be disregarded because it can be configured in such a way that it does not add any significant amount of latency, is error-free, and delivers packets in the correct order. Other proxy switches can be set up elsewhere, and channels can be set up to these switches as well.

It is now irrelevant where the Sun Ray appliances are located geographically. They are all logically on the same LAN. Because we deal with per-port VLANs on the proxies, a proxy can be set up to contain several VLANs to different Sun Ray domains (residing on the same server or on different servers). Thus, one VLAN on a proxy can consist of one Ethernet port and one broadband channel, while the rest of the Ethernet ports plus another channel can be set up as a different VLAN.

FIGURE 3 illustrates a MAN that has a data center with four Sun Ray domains, geographically spread over the MAN into smaller or larger Sun Ray sites. This figure shows that although a Sun Ray backnet is a LAN, the LAN can be spread over a geographical area.

Figure 3FIGURE 3 Metropolitan Area Network

FIGURE 3 also shows that it is possible to have several different Sun Ray LANs separated from each other on the broadband-based MAN at the same time. There is no limitation to the number of LANs it is possible to have.

The Sun Ray Environment Using Broadband Technology


One of the major manufacturers of broadband ISDN and ATM equipment when this article was written, is Marconi (formerly Fore Systems). The following sections refer to Marconi equipment when describing LAN emulation hardware and BICs. Even though Sun Microsystems makes their own BICs, the Marconi BICs are more suitable to the Sun Ray environment over a broadband network. All work done with broadband technologies over ISDN, so far, has been done using Marconi equipment, even though talks with other vendors are held continuously.

Setting up, configuring, and maintaining broadband channels through a MAN is a complicated task, especially in large to very large networks. By superimposing broadband ISDN on top of SONET or SDH and using LAN emulation, the task can be simplified.

LAN emulation is easy to configure and maintain, and the necessary channels are automatically set up. Load sharing, redundancy, and failover are features built into the network and need not be configured separately. An error-free network is also automatically made available as well as in-order packet delivery.

On the server side, several BICs can be trunked together to form what can only be described as an interface conglomerate. Alternatively, they can be used as several separate interfaces. Useful BICs have bandwidths of either 155 Mbps (OC3) or 622 Mbps (OC12). One to four BICs can form one interface conglomerate, yielding a maximum total capacity per conglomerate of approximately 2.5 Gbps (OC48).

BICs, in an interface conglomerate, do not have to reside on the same bus inside the server, thus preventing bus overload. It is also possible to have several interface conglomerates on one server. One interface conglomerate can hold several emulated LAN interfaces. Each of these emulated LAN interfaces is perceived by the machine as an Ethernet interface and handled as such with, for instance, the ifconfig command. An emulated Ethernet interface can be used as a Sun Ray backnet.

The frontnet can be run over a narrowband interface (10/100/1000 Ethernet, FDDI, and so on) or over an emulated Ethernet interface on one of the interface conglomerates.

MASS Superimposed Over Narrowband Networks

If a CityNet is run over narrowband networks, it can still be used as a carrier with additional equipment such as dense wavelength division multiplexing - DWDM (preferably from Nortel Networks or Marconi because they provide ring-type DWDM equipment).

Standard fiber technology uses monochrome light bursts as an information carrier over the media. DWDM uses polychrome light so the fiber appears to be several fibers (one for each color). Each one of these virtual fibers has the same capacity as the original fiber. By introducing DWDM between the fiber media and the equipment using it, you have more fibers. When running the Sun Ray broadband networks over one color, the other narrowband traffic is not disturbed, provided that it runs over a different color.

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