When planning the installation of LAN cabling, there are four physical areas to consider:
• Work area
• Telecommunications room, also known as the distribution facility
• Backbone cabling, also known as vertical cabling
• Distribution cabling, also known as horizontal cabling
Total Cable Length
For UTP installations, the ANSI/TIA/EIA-568-B standard specifies that the total combined length of cable spanning three of the areas listed above, excluding the backbone cable, is limited to a maximum distance of 100 meters per channel. This standard also specifies maximum backbone distances, ranging from 90m for UTP to 3000m for single mode fiber cable, based on application and media type.
Work Areas
The work areas are the locations devoted to the end devices used by individual users. Each work area has a minimum of two jacks that can be used to connect an individual device to the network. We use patch cables to connect individual devices to these wall jacks. Allowed patch cable length depends on the horizontal cable and telecommunication room cable lengths. Recall that the maximum length for these three area can not exceed 100m. The EIA/TIA standard specifies that the UTP patch cords used to connect devices to the wall jacks must meet or exceed the performance requirements in ANSI/TIA/EIA-568-B.
Straight-through cable is the most common patch cable used in the work area. This type of cable is used to connect end devices, such as computers, to a network. When a hub or switch is placed in the work area, a crossover cable is typically used to connect the device to the wall jack.
Telecommunications Room
The telecommunications room is where connections to intermediary devices take place. These rooms contain the intermediary devices - hubs, switches, routers, and data service units (DSUs) - that tie the network together. These devices provide the transitions between the backbone cabling and the horizontal cabling.
Inside the telecommunications room, patch cords make connections between the patch panels, where the horizontal cables terminate, and the intermediary devices. Patch cables also interconnect these intermediary devices.
The Electronics Industry Alliance/Telecommunications Industry Association (EIA/TIA) standards specify two different types of UTP patch cables. One type is a patch cord, with a length of up to 5 meters, which is used to interconnect equipment and patch panels in the telecommunications room. Another type of patch cable can be up to 5 meters in length and is used to connect devices to a termination point on the wall.
Horizontal Cabling
Horizontal cabling refers to the cables connecting the telecommunication rooms with the work areas. The maximum length for a cable from a termination point in the telecommunication room to the termination at the work area outlet must not exceed 90 meters. This 90 meter maximum horizontal cabling distance is referred to as the permanent link because it is installed in the building structure. The horizontal media runs from a patch panel in the telecommunications room to a wall jack in each work area. Connections to the devices are made with patch cables.
Backbone Cabling
Backbone cabling refers to the cabling used to connect the telecommunication rooms to the equipment rooms, where the servers are often located. Backbone cabling also interconnects multiple telecommunications rooms throughout the facility. These cables are sometimes routed outside the building to the WAN connection or ISP.
Backbones, or vertical cabling, are used for aggregated traffic, such as traffic to and from the Internet and access to corporate resources at a remote location. A large portion of the traffic from the various work areas will use the backbone cabling to access resources outside the area or facility. Therefore, backbones typically require high bandwidth media such as fiber-optic cabling.
Electromagnetic Interference/Radio Frequency Interference
Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI) must be taken into consideration when choosing a media type for a LAN. EMI/RFI in an industrial environment can significantly impact data communications if the wrong cable is used.
Interference can be produced by electrical machines, lightning, and other communications devices, including computers and radio equipment.
As an example, consider an installation where devices in two separate buildings are interconnected. The media used to interconnect these buildings will be exposed to the possibility of lightning strikes. Additionally, there maybe a great distance between these two buildings. For this installation, fiber cable is the best choice.
Wireless is the medium most susceptible to RFI. Before using wireless technology, potential sources of interference must be identified and, if possible, minimized.
Making LAN Connections
Straight-through UTP Cables
A straight-through cable has connectors on each end that are terminated the same in accordance with either the T568A or T568B standards.
Identifying the cable standard used allows you to determine if you have the right cable for the job. More importantly, it is a common practice to use the same color codes throughout the LAN for consistency in documentation.
Use straight-through cables for the following connections:
• Switch to a router Ethernet port
• Computer to switch
• Computer to hub
Crossover UTP Cables
For two devices to communicate through a cable that is directly connected between the two, the transmit terminal of one device needs to be connected to the receive terminal of the other device.
To achieve this type of connection with a UTP cable, one end must be terminated as EIA/TIA T568A pinout, and the other end terminated with T568B pinout.
To summarize, crossover cables directly connect the following devices on a LAN:
• Switch to switch
• Switch to hub
• Hub to hub
• Router to router Ethernet port connection
• Computer to computer
• Computer to a router Ethernet port
MDI/MDIX Selection
Many devices allow the UTP Ethernet port to be set to MDI or MDIX. This can be done in one of three ways, depending on the features of the device:
1. On some devices, ports may have a mechanism that electrically swaps the transmit and receive pairs. The port can be changed from MDI to MDIX by engaging the mechanism.
2. As part of the configuration, some devices allow for selecting whether a port functions as MDI or as MDIX.
3. Many newer devices have an automatic crossover feature. This feature allows the device to detect the required cable type and configures the interfaces accordingly. On some devices, this auto-detection is performed by default. Other devices require an interface configuration command for enabling MDIX auto-detection.
Making WAN Connections
By definition, WAN links can span extremely long distances. These distances can range across the globe as they provide the communication links that we use to manage e-mail accounts, view web pages, or conduct a teleconference session with a client.
Wide area connections between networks take a number of forms, including:
• Telephone line RJ11 connectors for dialup or Digital Subscriber Line (DSL) connections
• 60 pin Serial connections
The first cable type has a male DB-60 connector on the Cisco end and a male Winchester connector on the network end. The second type is a more compact version of this cable and has a Smart Serial connector on the Cisco device end. It is necessary to be able to identify the two different types in order to connect successfully to the router.
Data Communications Equipment and Data Terminal Equipment
The following terms describe the types of devices that maintain the link between a sending and a receiving device:
Data Communications Equipment (DCE) - A device that supplies the clocking services to another device. Typically, this device is at the WAN access provider end of the link.
Data Terminal Equipment (DTE) - A device that receives clocking services from another device and adjusts accordingly. Typically, this device is at the WAN customer or user end of the link.
The V35 compliant cables are available in DTE and DCE versions. To create a point-to-point serial connection between two routers, join together a DTE and DCE cable. Each cable comes with a connector that mates with its complementary type. These connectors are configured so that you cannot join two DCE or two DTE cables together by mistake.
Making the Device Management Connection
A terminal emulator is a software program that allows one computer to access the functions on another device. It allows a person to use the display and keyboard on one computer to operate another device, as if the keyboard and display were directly connected to the other device. The cable connection between the computer running the terminal emulation program and the device is often made via the serial interface.
To connect to a router or switch for device management using terminal emulation, follow these steps:
Step 1:
Connect a computer to the console port using the console cable supplied by Cisco. The console cable, supplied with each router and switch, has a DB-9 connector on one end and an RJ-45 connector on the other end. (Older Cisco devices came supplied with an RJ-45 to DB-9 adapter. This adapter is used with a rollover cable that has an RJ-45 connector at each end.)
Many newer computers do not have an EIA/TIA 232 serial interface. If your computer has only a USB interface, use a USB-to-serial conversion cable to access the console port. Connect the conversion cable to a USB port on the computer and then connect the console cable or RJ-45 to DB-9 adapter to this cable.
Step 2:
With the devices directly connected via cable, configure a terminal emulator with the proper settings. The exact instructions for configuring a terminal emulator will depend on the particular emulator. For the purpose of this course, we will usually use HyperTerminal because most varieties of Windows have it. This program can be found under All Programs > Accessories > Communications. Select HyperTerminal.
Open HyperTerminal, confirm the chosen serial port number, and then configure the port with these settings:
• Bits per second: 9600 bps
• Data bits: 8
• Parity: None
• Stop bits: 1
• Flow control: None
Step 3:
Log in to the router using the terminal emulator software. If all settings and cable connections are done properly, you can access the router by pressing the Enter key on the keyboard.
