Deployment Considerations
A variety of specific deployment examples are provided in this paper (figures 3 to 6). General deployment considerations are discussed below.
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| Figure 3. Campus deployment. |
Corporate campus settings are characterized by a large number of users and multiple network segments, resulting in complex needs. Copper cabling (CAT 5) is likely to be in place within the data center, while fiber is typically used to connect buildings, to link segment switches to the data center, and to connect servers outside the enterprise. Gradual migration to Gigabit Ethernet will provide more bandwidth for high performance desktops, server connections, and switch-to-switch connections. Deployment steps include: For high-demand servers, replace 10/100 Mbps adapters with auto-negotiating 1000 Mbps fiber adapters. In the R&D department, replace 10/100 desktop adapters with Gigabit adapters and replace the 10/100 segment switch with a Layer 2 Gigabit switch such as the Intel® NetStructure™ 470T Switch. Install Gigabit uplinks from 10/100 switch stacks to the data center. Replace the 10/100 backbone switch with a high performance, Layer 3 Gigabit switch such as the Intel® NetStructure™ 480T Routing Switch. At this point, the legacy CAT 5 cabling within the data center and existing fiber cabling to segment switches will begin running at Gigabit speed.
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| Figure 4. Departmental deployment. |
At the department level, organizations may find that more bandwidth is needed for high performance workstations to run bandwidth-intensive applications such as engineering, design or medical imaging. The same department may also contain administrative workgroups where 10 Mbps or 100 Mbps performance is sufficient. A Gigabit solution can be deployed on the department's existing CAT 5 copper cabling as follows: Install a Layer 2 Gigabit departmental switch with direct connections to power user desktops. Create a high performance server connection by replacing the existing 10/100 server adapter with a Gigabit adapter. Boost bandwidth at the key aggregation point for administrative desktops by installing a Gigabit uplink from the 10/100 switch stack to the departmental Gigabit switch.
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| Figure 5. Deployment at an ISP. |
Due to the rapid growth experienced by service providers today, an ISP must look 3 to 5 years ahead for infrastructure planning. More and more customers are being added, along with more and more servers, and traffic must be parsed for a variety of different service levels. Confined spaces and short cabling distances often mean that an all-copper network is in place. A Gigabit solution can help ensure responsiveness by moving traffic quickly from the back end to the front end. Recommended steps include: Install Gigabit adapters in all mid-tier and back end servers. Install a Layer 2 Gigabit switch for linking these 1000 Mbps servers to the front end. For added reliability, install a Gigabit adapter and a 10/100 adapter in each back end server, with automatic fail-over to the 10/100.
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| Figure 6. Deploying in a growing organization |
In rapidly growing organizations, the demands of adding new 10/100 Mbps desktops will eventually outstrip network capacity, especially if users regularly need to move large files. With all desktop PCs running at 100 Mbps, users will experience slow response times and sluggish retrieval of files stored on the server. The following Gigabit solution can increase throughput to and from the server by a factor of 10 using the existing copper infrastructure. In addition, it will allow the organization to deploy new workgroups using copper or fiber cabling as required by distances or environmental factors. Deployment includes: Replacing 10/100 server adapters with Gigabit adapters. Installing Gigabit uplinks from existing or new 10/100 segment switches. Installing a Layer 3 Gigabit backbone switch linked to servers and segment switches.
Media Selection
Network managers deploying Gigabit Ethernet have a choice of media to match different situations. Factors influencing this choice include cabling distance, physical location and environmental effects.
For example:
- CAT 5 cable is the most common medium for horizontal cabling in ceilings and floors
- Fiber cable is the most common choice for connecting buildings in campus settings
- Either is used in the vertical risers that connect different floors within a building
As discussed previously, Gigabit Ethernet has now been approved for fiber optic cable in 550M and 5Km lengths, for short copper connections (intended for data centers but not supported by vendor products), and for Category 5 copper cable up to 100 meters. Additionally, through the use of vendor-specific Long-haul Gigabit Interface Connectors (LH GBICs) in switches, Gigabit connections can be established at lengths of up to 70Km.
Since fiber is more expensive than copper, it is often reserved for situations that require cabling distances greater than the 100-meter copper limit - for example, between buildings. Environmental factors can also make fiber the best choice even when long distances are not involved. Copper cable is susceptible to electromagnetic interference, which can corrupt files, while fiber optic cable is not. Thus, fiber can be used to bring Gigabit Ethernet from servers to high performance workstations even when these machines are located near elevators, fluorescent light fixtures or other sources of high external noise.
Many experts believe that fiber will continue to be the main infrastructure in risers due to the possibility of electromagnetic interference. In risers where environmental factors are not a problem, it is less expensive to use CAT 5 cabling.
Accessing legacy wiring in risers is difficult and therefore costly. Prior to the approval of Gigabit over copper, companies wanting to deploy Gigabit Ethernet often had to choose between replacing existing CAT 5 in risers, which was potentially cost-prohibitive, or delaying the move to high-speed networking. Today, this is no longer an issue. With 1000BASE-T, organizations can have the benefits of Gigabit performance without the expense of upgrading to fiber cabling.
Still another reason to choose fiber in some situations is the need for security. Fiber cable cannot be spliced except under clean-room conditions, making it nearly impossible for a hacker to tap into the cable at a work site and gain unauthorized access to information. This means fiber might be the best choice for intra-building uses where cabling runs must be left exposed.
Testing Existing Cable
Existing Category 5 cabling must meet certain transmission characteristics before it can be used for Gigabit Ethernet. Network managers need not be overly concerned, since it is estimated that only ten percent of existing CAT 5 installations will not meet the requirements. These installations would also not support 100BASE-TX Fast Ethernet.
Legacy cable destined for 1000BASE-T use should be tested for Far-end Crosstalk and Return Loss, and corrected if necessary. If the cabling link doesn't pass, the problem is most likely in the connectors or patch cable rather than the horizontal cable. ANSTI/TIA/EIA TSB-95 (1998) defines five relatively simple options for correcting performance.
Far-end Crosstalk and Return Loss were not specified in the 1995 cabling standards because they were not well understood at the time. It has since been determined that they can significantly affect 100BASE-TX and 1000BASE-T signals, even though they have negligible impact on 10BASE-T.
Return Loss
This parameter defines the amount of signal energy that is reflected back towards the transmitter due to impedance mismatches in the link, such as those caused by connectors. Category 5 systems installed prior to the completion of ANSI/TIA/EIA569-A in 1995 may contain connecting hardware that does not comply with the standard.
Far-end Crosstalk
This defines noise on a wire pair at the far end from the transmitter - that is, at the receiver. Crosstalk is caused by signals leaking from adjoining wire pairs. It is measured at each wire pair as Equal Level Far-end Crosstalk (ELFEXT), or as Power Sum ELFEXT (PSELFEXT) by adding up the total noise from all adjacent wire pairs.
New Installations
The Gigabit Ethernet Alliance suggests that network designers installing new cable might want to consider the new, enhanced Category 5 cable (CAT 5e) to gain extra signal margin. More detailed information on the enhanced cable, as well as test procedures for existing cable and sources of testing equipment, can be found by visiting the Gigabit Ethernet Alliance Web site at www.Gigabit-ethernet.org.
