# Ethernet Connectivity Selection Tutorial

Chia sẻ: Dang Thach Quan Koliadang | Ngày: | Loại File: PDF | Số trang:4

0
51
lượt xem
4

## Ethernet Connectivity Selection Tutorial

Mô tả tài liệu

Category 5, 5e or 6? 110 punchdown, or RJ to RJ? T568A or T568B? Shielded or unshielded? Will I choose the right Ethernet patch panel for my application? Will this choice work with future applications? Am I getting the best overall value? With all the choices you face as you design your network and select equipment, including available Ethernet patch panels, it’s easy to become confused and frustrated. Ultimately your choice of Ethernet panels should fit the applications you plan to run. ADC wrote this short tutorial to guide you through these decisions, to make them as painless as possible...

Chủ đề:

Bình luận(0)

Lưu

## Nội dung Text: Ethernet Connectivity Selection Tutorial

1. Ethernet Connectivity Selection Tutorial Category 5, 5e or 6? 110 punchdown, or RJ to RJ? T568A or T568B? Shielded or unshielded? white paper Will I choose the right Ethernet patch panel for my application? Will this choice work with future applications? Am I getting the best overall value? With all the choices you face as you design your network and select equipment, including avail- able Ethernet patch panels, it’s easy to become confused and frustrated. Ultimately your choice of Ethernet panels should fit the applications you plan to run. ADC wrote this short tutorial to guide you through these decisions, to make them as painless as possible and offer you the best solution for your network. First, let’s ask a few key questions. Your answers will help guide you in the decision process. Next, we will briefly discuss each of the most popular options available so you can draw conclusions based on your network needs. Discovery Questions • What applications are you or do you plan to run on this network? 10/100Base-T? 1000Base-T? • What type of network are you designing? Data center? Data backbone? LAN? • Is the project a new network installation or addition to existing network? • Is the installation being built to expand existing capacity with current data capabilities or is it for new, faster data applications? Answers to these questions will guide you to a particular cable type, a particular data patch panel, and the means to terminate the cable into the patch panel — whether the terminations into the patch panel involve “punchdown” cable terminations, pre-made telco-type multi-pair cable ends, or standard RJ45 cable ends. The general guidelines for network transmission capabilities segment the data network; data cen- ter and data network backbone system applications require the highest level of transmission capa- bilities, while feeds to work areas generally require a bit less. However, all network connectivity should be designed with only the highest network engineering standards available. Category 5, 5e, and 6 Cabling The Telecommunications Industry Association (TIA) standards forming group consists of a variety of industry experts including connectivity and cable manufacturers, distributors, installers, and end customers. The TIA determines certain transmission characteristics that must be met to qualify a cable for certain network applications. Category 5 cabling is currently the most prevalent wiring in existing buildings. Electrical charac- teristics defined by the TIA specify near end cross-talk (NEXT), attenuation, and return loss to 100 MHz. The TIA Technical Services Bulletin (TSB) 95 recommends additional criteria for far end cross- talk (FEXT).
2. Category 5e is currently the minimum TIA recommended category of wiring for new installations. Electrical characteristics for NEXT, FEXT, attenuation, and return loss are specified to 100 MHz. NEXT performance is slightly better than category 5. Category 6 is gaining popularity for new installations. Electrical characteristics for NEXT, FEXT, atten- uation, and return loss are specified to 250 MHz. Improvements in all electrical parameters are part of the higher TIA Category 6 standard. Category 7 cabling is a developing standard as of this writing. The International Standards Organization (ISO) is leading the standardization efforts for this new individually-shielded, overall- shielded, 4-pair cable with transmission specifications referenced to 600MHz. The cable end interface will probably be something other than the familiar RJ45 connector, mainly to differentiate the Category 7 installation from existing lower-bandwidth infrastructure. So, which should you use? There is quite a bit of misleading information in the industry on this sub- ject, the biggest myth being that Category 6 is required to run Gigabit Ethernet over copper (1000Base-T). Actually 1000Base-T was designed by the IEEE to run on Category 5. As long as the Category 5 is installed according to TIA-568-B standards and meets the testing criteria in TIA TSB 95, 1000Base-T will perform satisfactorily on Category 5. However, as of this writing, the TIA recommends Category 5e over Category 5 as the minimum cabling for new network infrastructure installations. When do I use Category 6? Does the application standard (i.e., Gigabit Ethernet, 10G, etc.) specify Category 6 as a minimal requirement? As of this writing, the TIA is making recommendations to the IEEE 802.3ae and the 10 Gigabit Ethernet Alliance, who are currently working on 10 Gigabit cabling systems, that any 10 Gigabit Ethernet designed to run on copper cabling use Category 6 because of its improvement in signal to noise. The good news is that Category 6 is backward compatible and will have no trouble running existing applications such as 10/100Base-T and 1000Base-T. Cable Type Summary The chart below summarizes the industry standard UTP cable types used in current networking instal- lations. In addition to the UTP cabling described above, you should understand the issues of cable shielding, and stranded versus solid cable. Category Test Frequency 10/100BaseT 1000BaseT Future Applications Relative Cost Cat 5 100 MHz Yes Yes No $Cat 5e 100 MHz Yes Yes Maybe$ Cat 6 250 MHz Yes Yes Yes $$Cat 7 600 MHz Yes Yes Yes$$ Shielded vs. Unshielded Twisted Pair Unshielded twisted pair (UTP) cabling provides immunity to electromagnetic interference (EMI) with the properties of the two conductors that make up a transmission pair being twisted together. When UTP cabling encounters electrical interference, the noise crossing the twisted pairs is cancelled by the twists in the cable (called “Common Mode Rejection”, a subject outside the scope of this paper). Standard Category 5, 5e and 6 cables contain four unshielded twisted pairs of conductors. For 10BASE-T and 100BASE-TX applications, only two pairs are used, one for the transmit circuit and one for receive circuit. For 1000BASE-T (Gigabit Ethernet) all four pairs are required. The term “shielded twisted pair” cabling can be misleading. There are actually two methods of shield- ing a twisted pair cable. Screened twisted pair cable (ScTP) provides an overall screen or metal foil around the four pairs of conductors, but each individual twisted pair is unshielded. Shielded Twisted 2
3. Pair cable (STP) has each individual pair shielded, plus an overall screen around the four individually shielded pairs. This makes a very expensive and hard to install cable - the legacy token ring IBM Type 1 cable and Category 7 are examples of STP cable. STP cable requires metal end connectors and metal jacks that bond the cable shield to earth ground to carry the interfering signals safely away from the signal conducting pairs – failure to connect the cable shield to earth ground results in the shield cou- pling the interfering noise to the conductors, providing very poor transmission performance. Most of the world uses UTP cabling, with some exceptions located in a few countries in Europe. Stranded vs. Solid Conductor Cable Stranded cable is flexible and often used for patch panel jumpers and work area connections. Stranded cabling is used for shorter patching applications for its flexible cable construction, but also exhibits higher attenuation due to the smaller diameter conductors, and as such should not be used for long, permanent installations. Solid conductor cable is used for the “horizontal” cable runs from the telecommunications room to the work area wall outlet. The typical gauge for Category 5e cable is 24 AWG. Category 6 is 23 AWG - the larger conductor diameter improves attenuation characteristics and signal-to-noise ratio versus the smaller conductor diameter of Category 5e. Wiring Schemes, T568A vs. T568B Wiring schemes also raise a variety of questions: Q: What’s the difference between T568A and T568B? A. The only difference is the positioning of the Green and Orange pairs of wires (see figure 1) Pair 2 Pair 3 Pair 3 Pair 1 Pair 4 Pair 2 Pair 1 Pair 4 T568A T568B Figure 1 Typical RJ45 cable ends, T568A vs. T568B Q: Is there a performance difference between T568A and T568B? A: No. Both wiring schemes have to meet the same performance criteria. Q: Why two schemes? A: The reason is outside of the scope of this paper but it is related to old telephone legacy issues. All you really need to know is that there are two schemes, and how to deal with them. 3