Chapter 2: Physical Layer Objectives: Transmission media and cabling LAN Physical Layer Ethernet WAN Technologies Network Devices

Guided Transmission Data Magnetic Media Twisted Pair Coaxial Cable Fiber Optics

Twisted Pair (a) Category 3 UTP. (b) Category 5 UTP.

Coaxial Cable A coaxial cable.

Fiber Cables (a) Side view of a single fiber. (b) End view of a sheath with three fibers.

Fiber Optics (a) Three examples of a light ray from inside a silica fiber impinging on the air/silica boundary at different angles. (b) Light trapped by total internal reflection.

Lightwave Transmission Convection currents can interfere with laser communication systems. A bidirectional system with two lasers is pictured here.

The Local Loop: Modems, ADSL, and Wireless The use of both analog and digital transmissions for a computer to computer call. Conversion is done by the modems and codecs.

Modems (a) A binary signal (c) Frequency modulation (b) Amplitude modulation (c) Frequency modulation (d) Phase modulation

Digital Subscriber Lines (3) A typical ADSL equipment configuration.

Wireless Communication Wireless networks use radio frequency (RF), laser, infrared (IR), or satellite/microwaves to carry signals from one computer to another without a permanent cable connection.

LAN Physical Layer Each media has advantages and disadvantages. Some of the advantage or disadvantage comparisons concern the following: Cable length Cost Ease of installation Susceptibility to interference

Ethernet in the Campus Ethernet technologies can be used in a campus network in several different ways:

Connection Media / UTP Implementation EIA/TIA specifies an RJ-45 connector for unshielded twisted-pair (UTP) cable. The letters RJ stand for registered jack, and the number 45 refers to a specific wiring sequence. The RJ-45 connector and jack are the most common

Attach the RJ-45

Straight-Through Cables Maintain the pin connection all the way through the cable. Wire connected to pin 1 is the same on both ends. Used to connect such devices as PCs or routers to other devices such as hubs or switches.

Crossover Cable Cross the critical pair to properly align, transmit, and receive signals on devices with like connections. Pin 1 connected to pin 3, pin 2 connected to pin 6. Used to connect similar devices: switch to switch, switch to hub, hub to hub, router to router, PC to PC.

Rollover Cables Setting Up Console Connections Maintain the pin connection all the way through the cable. The console port allows monitoring and configuration of a Cisco hub, switch, or router. Connect the devices using a rollover cable from the console port, on the router, to the serial port, on the terminal (workstation), Then Configure the terminal emulation application with the following common equipment (COM) port settings: 9600 bps, 8 data bits, no parity, 1 stop bit, and no flow control.

LAN Transmission Technologies Ethernet 10 Mbit/s Token Ring 4/16 Mbit/s Fast Ethernet 100 Mbit/s FDDI 100 Mbit/s Gigabit Ethernet 1 Gbit/s ATM 25 Mbit/s to 2.4 Gbit/s Only Ethernet versions are growing

Gigabit Ethernet Standards 1- IEEE 802.3z 2- IEEE 802.3ab Currently, there are two standards of Gigabit Ethernet technology, one is IEEE 802.3z, and the other one is IEEE 802.3ab. Figure-1 shows the functional elements of these two standards in Gigabit Ethernet technology. Fiber Cabling Specifications There are two physical layers use fiber optic as the transmission medium. 1000BASE-SX (‘S’ for Short wavelength) is targeted at lowest cost multimode fiber runs in horizontal and shorter backbone applications. 1000BASE-LX(‘L’ for Long wavelength) is targeted at longer multimode building fiber backbones and single-mode campus backbones. In figure-1, SMF stands for Single-Mode Fiber; while MMF stands for Multimode Fiber. 1000BASE-LX is specified use on either multimode or single-mode Fiber. when 1000BASE-LX uses single-mode fiber, it can cover 5km. Note that the distance Gigabit Ethernet can reach depends on the bandwidth (measured in MHz*km)—the greater the bandwidth of the fiber, the further the distance supported. Also, IEEE specifies minimum rather than maximum ranges, and under average operating conditions, the minimum specifies distance can be exceeded by a factor of three or four. However, most network managers are conservative when they design networks and use the IEEE specifications as the maximum distances. Both of 1000BASE-LX and 1000BASE-SX use 8B/10B physical coding sublayer (PCS). There is another specification using fiber optic, which is known as 1000BASE-LH(‘LH’ for Long Haul). It is not IEEE specification but multivendor specification; each vendor has a set of transceivers covering different distances. The minimum range of distance can be 1km-49km or 50km-100km depending on the wavelength. Copper Cabling Specifications There are two specification transmitting over copper cabling. 1000BASE-CX(‘C’ for Copper) defines transceivers or physical layer devices for shielded copper cabling. It is intended for short-haul copper connections (25 meters or less) within wiring closets. The advantage of 1000BASE-CX has is that it can be generated quickly and is inexpensive to implement. 1000BASE-T(‘T’ for Twisted pair), helps network managers boost their network performance in a simple, cost-effective way. It runs over four-pair category 5 unshielded twisted pair for distances up to 100 meters, enabling network managers to build networks with diameters of 200 meters Category 5 copper cabling is today the dominant horizontal/floor cabling, providing connectivity to both desktops and workgroup aggregators; and it is one of the major options for building risers/backbone cabling for connection of different floor wiring closets. 1000BASE-T is the most cost-effective high-speed networking technology available now.   1- Fiber Cabling Specifications 2- Copper Cabling Specifications

WAN Technologies A Wide Area Network (WAN) is a data communications network that covers a relatively broad geographic area and often uses transmission facilities provided by common carriers, such as telephone companies. A WAN is an interconnection of LANs. A WAN functions at the lower three layers of the OSI model.

WAN Physical Layer The speed of these connections ranges from 2400 bits per second (bps) to T1 service at 1.544 megabits per second (Mbps) and E1 service at 2.048 Mbps. ISDN offers dial-on-demand connections or dial backup services. With the increasing demand for residential broadband high-speed services, Digital Subscriber Line (DSL) and cable modem connections are becoming more popular.

WAN Backbones T1 (DS1) 1.54 Mbit/s North America E1 2.04 Mbit/s CCITT OC1 51.84 Mbit/s Sonet fiber OC3 155.52 Mbit/s Sonet fiber OC96 4.976 Gbit/s Sonet fiber OC192 10 Gbit/s Sonet fiber OC768 40 Gbit/s Sonet fiber A backbone is a larger transmission line that carries data gathered from smaller lines that interconnect with it. At the local level, a backbone is a line or set of lines that local area networks connect to for a wide area network connection or within a local area network to span distances efficiently (for example, between buildings). On the Internet or other wide area network, a backbone is a set of paths that local or regional networks connect to for long-distance interconnection. The connection points are known as network nodes or telecommunication data switching exchanges (DSEs).

Network Devices Layer 1 network devices: Repeaters, Hubs Layer 2 network devices: Bridges, Switches, modems, NICs Layer 3 network devices: Repeaters, Hubs

Repeaters: Layer 1

Repeaters A repeater solves the problem of too many nodes and not enough cable; cleans, amplifies, and resends a signal that is weakened by long cable length.

Hubs: Layer 1

Hubs Regenerate and repeat signals Used as network concentration points Multiport repeater Becoming obsolete

Hubs

Bridges: Layer 2

Bridges filter traffic by looking at MAC addresses. Designed to create two or more LAN segments, each of which is a separate collision domain

A Switch is a Multiport Bridge Switches: Layer 2 A Switch is a Multiport Bridge

LAN Switches Switches Combine the connectivity of a hub with the traffic regulation of a bridge on each port

Core and Layer3 Switches

NICs in the OSI Model

Host Connectivity When selecting a NIC, consider the following: Network architecture Operating system Media type Data transfer speed Available bus types

NICs ISA (Industry Standard Architecture) EISA (Extended ISA) Bus architectures ISA (Industry Standard Architecture) EISA (Extended ISA) PCI (Peripheral Component Interconnect) MCA (Micro Channel Architecture) PCMCIA (Personal Computer Memory Card International Association)

Routers and Serial Connections Routers are used to connect LANs to WANs Determine whether DTE or DCE connectors are required. The DTE is the endpoint of the user’s device on the WAN link. The DCE is the point where responsibility for delivering data passes into the hands of the service provider. When cabling routers for serial connectivity, the routers will either have fixed or modular ports.

Routers and DSL Connections The Cisco 827 ADSL router has one Asymmetric Digital Subscriber Line (ADSL) interface. To connect an ADSL line to the ADSL port on a router, do the following: Connect the phone cable to the ADSL port on the router. Connect the other end of the phone cable to the phone jack.