The backbone style refers to the method in which the backbone interconnects the networks attached to it and also how that manages the means in i m sorry packets from one network move through the backbone to other networks.

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While there space an boundless number of means in which network developers can build backbone networks, there are really only three an essential architectures that deserve to be linked in various ways. This architectures space routed backbones (routers that move packets top top the basis of network great addresses), switched backbones (switches that move packets based upon data attach layer addresses), and also virtual LANs (switches that relocate packets with LANs that are developed virtually, not using physical location).

These architectures are mixed and also matched to construct sets of BNs. Prior to we talk about these architectures, we first must discuss the method in which network designers think around backbone designs and how to combine them; that is, the various layers the backbones the exist in most establishments today.

Backbone architecture Layers

Network designers often think about three distinct modern technology layers1 once they architecture BNs. The class closest to the users is the access layer, the technology used in the LANs attached come the BN as explained in the previous object (e.g., 100Base-T, wireless Ethernet) (Figure 8.5). Return the access layer is not part of the BN, the technologies provided in the LANs (or access layer) can have significant impacts on the style of the backbone.


Figure s.5 Backbone network design layers. LAN = regional area network

The circulation layer is the component of the backbone that connects the LANs together. This is the part of the backbone that contains the "TCP/IP gateways" described in following topic. It commonly runs transparent one building.

The core layer is the part of the backbone the connects the various BNs together, regularly from building to building. The main point layer is technologies provided in the campus network or the companies network. Some little organizations are not huge enough to have a core layer; your backbone spans just the circulation layer. Other organizations are big enough the they have a main point network in ~ several locations that room in turn connected by WANs.

In the sections the follow, we describe the three an easy BN architectures and also discuss in ~ which layer lock are often used. We emphasis on TCP/IP networks as soon as comparing this architectures. Us assume that you space comfortable through the product on TCP/IP in next topic; if you are not, you might want to go ago and testimonial the last section of the topic, licensed has been granted TCP/IP Example, prior to you proceed reading.

Switched Backbones

Switched backbones are more than likely the most common type of BN provided in the circulation layer (i.e., in ~ a building); most new building BNs designed now use switched backbones. They likewise are make their method into the main point layer together the campus backbone, but routed backbones still continue to be common.

Switched backbone networks use a star topology v one switch at that is center. Figure 8.6 mirrors a switched backbone connecting a series of LANs. There is a switch serving each LAN (access layer) i beg your pardon is associated to the backbone switch at the bottom the the number (distribution layer). This figure implies that the LAN switches space close to the computer systems in their LANs and farther native the backbone switch. Most institutions now use switched backbones in which every network gadgets for one part of the building are physically located in the exact same room, often in a rack the equipment.


Figure s.6 Switched backbone network design

This type of switched backbone is presented graphically in number 8.7. This has the advantage of placing all network equipment in one place for basic maintenance and also upgrade, however it does require an ext cable. In many cases, the price of the cable itself is only a small part of the in its entirety cost to install the network, for this reason the expense is significantly outweighed by the simplicity of maintenance and the versatility it provides for future upgrades.


Figure s.7 Rack-mounted switched backbone network design

The room comprise the rack the equipment is sometimes referred to as the main circulation facility (MDF) or centra! circulation facility (CDF). Number 8.8 reflects a photo of one MDF room at Indiana University. Figure 8.9 reflects the equipment diagram of this very same room. The cables from all computers and devices in the area offered by the MDF (often hundreds of cables) space run into the MDF room. When in the room, lock are linked into the miscellaneous devices. The devices in the rack are connected among themselves using really short cables called patch cables


Figure 8.8 one MDF through rack-mounted equipment. A layer-2 chassis switch with six 100Base-T modules (center the photo) associate to four 24-port 100Base-T switches. The chassis switch is connected to the campus backbone utilizing 1000Base-F end fiber-optic cable. The cables from every room are wired right into the behind of the patch dashboard (shown in ~ the peak of the photo), v the port on the front of the patch panel labeled to present which room is which. Patch cables affix the patch dashboard ports to the harbor on the switches

Switched Backbones at Indiana University


At Indiana university we commonly use switched backbones in our buildings. Number 8.10 mirrors a usual design. Each floor in the building has a set of switches and access points that serve the LANs on the floor. Each of these LANs and WLANs are associated into a move for the floor, thus creating a switched backbone on every floor. Typically, we use switched 100Base-T within each floor.

The switch creating the switched backbone on each floor is then linked into another switch in the basement, which offers a switched backbone because that the entire building. The building backbone is normally a greater speed network to run over fiber-optic cable (e.g., 100Base-F or 1 GbE). This switch, in turn, is associated into a high-speed router the leads come the campus backbone (a routed backbone design).

With rack-mounted equipment, the becomes straightforward to move computers from one LAN come another. In the switched backbone architecture as displayed in figure 8.6, because that example,all the computers in the same general physical ar are associated to the exact same switch and thus re-publishing the capacity of the switch. Back this frequently works well, the can reason problems if countless of the computer systems on the switch room high-traffic computers. Because that example, in figure 8.6, if all the busy computer systems on the network are located in the upper left area that the figure, the switch in this area may come to be a bottleneck.


Figure 8.9 MDF network diagram


Figure 8.10 Switched backbones at Indiana University

With an MDF, every cables run right into the MDF. If one switch becomes overloaded, the is simple to unplug the cables from several high-demand computers from the overloaded switch and also plug them into one or an ext less-busy switches. This properly spreads the traffic roughly the network much more efficiently and method that network capacity is no longer tied come the physical place of the computers; computers in the very same physical area can be connected into different network segments.

Sometimes a chassis switch is used rather of a rack. A chassis switch allows users come plug modules directly into the switch. Every module is a certain form of network device. One module could be a 16-port 100Base-T hub, an additional might be a router, whereas another might it is in a 4-port 100Base-T switch, and so on. The switch is designed to hold a certain variety of modules and also has a certain internal capacity, so that all the modules can be active at one time. For example, a switch with 5 10Base-T hubs, 2 10Base-T switches (with 8 port each), a 100Base-T move (with 4 ports), and a 100Base-T router would have to have an inner switching capacity of at least 710 Mbps (<5 x 10 Mbps> + <2 x 8 x 10 Mbps> + <4 x 100 Mbps> + 100 Mbps = 710 Mbps).

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The an essential advantage that chassis switches is their flexibility. That becomes simple to add new modules with extr ports together the LAN grows and to update the switch to use new technologies. Because that example, if you want to include gigabit Ethernet, you merely lay the cable and also insert the suitable module right into the chassis switch.