Networking Fundamentals Fiber-OpticCable
Application (Layer 7) • This layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other networksoftware services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.
Presentation (Layer 6) • This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer. • Mostly useless
Session (Layer 5) • This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination. • Mostly useless.
Transport (Layer 4) • This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer. • Layer 4 data units are also called packets, but when you're talking about specific protocols, like TCP, they're "segments" or "datagrams" in UDP. This layer is responsible for getting the entire message, so it must keep track of fragmentation, out-of-order packets, and other perils. Layer 4 provides end-to-end management of communication. Some protocols, like TCP, do a very good job of making sure the communication is reliable. Some don't really care if a few packets are lost--UDP is the prime example.
Network (Layer 3) • This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing. • IP is part of layer 3, along with some routing protocols, and ARP (Address Resolution Protocol). Everything about routing is handled in layer 3. Addressing and routing is the main goal of this layer.
Data Link (Layer 2) • At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls framesynchronization, flow control and error checking. • Ethernet, among other protocols,lives on Layer 2. • MAC address, switches, or network cards
Physical (Layer 1) • This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.
Characteristics of Fiber-Optic Cable • Security • Immunity to Electromagnetic Interference • Weight and Size • Safety • Bandwidth • Corrosion and Water Resistance • Greater Distances
Security No “Vampire” taps hard to eaves-drop I don’t think it’s impossible – just expensive and requires specialized equipment and know-how Immune to EMP
Immunity to Electromagnetic Interference Immune to EMP Motors and Generators do not cause interference HAM/CB Garage Door Normal Computer Hair Dryer
Weight and Size Lighter than copper (1/10) Smaller diameter than copper (10/1)
Safety No current means no sparks Light transmission safer (and cheaper) than work lamps in some hazardous environments
Bandwidth Compared to copper: higher frequency means greater bandwidth no impedance limitations no inductive reactance (at high frequencies copper can lose conduction)
Corrosion and Water Resistance Glass and plastic do not rust or corrode easily No tarnish or verdigris (oxidation/rust)
Greater Distances Copper networks segments mostly limited to 100 meters or less. fiber-optic can support distances over 20 kilometers. FDDI applications can be 200 km (124 mi).
The Nature of Light light energy waves - electromagnetic electromagnetic waves need no carrier (can travel through a vacuum) unlike sound waves instead of frequency wavelength visible light roughly 400 - 800 nm nano meter is meter/billion fiber-optic commonly use 850nm - 1550nm
Construction glass or plastic core serves as medium for light waves cladding surrounds the core traps light in the core buffer physically protects core/cladding water proofing may be added oil or water resistant sheath coversall loose tube gel filled greater protection tight buffer less space more fragile
Transmission Attenuation can be through scattering, dispersion, Fresnel reflection, or extrinsic loss due to bends splices and connectors Scattering due to impurities in the core, cumulative over distance. Glass is better than plastic. Dispersion distortion from cladding reflection. primary limiter on distance Fresnel reflection occurs at connectors
Specifications Multimode fiber optic cable - large core diameter Single-mode fiber optic cable - small core diameter - matched to wavelength to control dispersion - allows greater distances Micrometers - um - meter/million Cable identified as core/cladding multimode eg 50/125 65.5/125single-mode eg 8.3/125
Fiber-OpticCable 802.3 Standards
802.3 Standards • Gigabit Ethernet 1000Base___ • 10 Gigabit Ethernet 10GBase___ • 10GBaseW 10GBase___W W=WAN W=Wavelength
Gigabit Ethernet IEEE 802.3z 1000BaseSX - multimode fiber 1000BaseLX – single (5km) or multimode fiber (550m) 1000BaseCX - copper core 25m
10 Gigabit Ethernet IEEE 802.3ae fiber only 10GBaseSR (short range) 26m-82m 10GBaseLR (long range) 10km single-mode 10GBaseER (extended range) 40km single-mode
10GBaseW Wide area networks and SONET 10GBaseSW Short Wavelength (850nm)connect dist.= 33m 10GBaseLW Long Wavelength (1310nm) connect dist.= 10km 10GBaseEW Extended Wavelength (1550nm) connect dist.= 40km (25mi)
FDDI • Fiber Distributed Data Interference • 40km • 100Mbps • Backbone for MAN or WAN • Structured as dual rings (primary, secondary) • Fault tolerant – two ways • Rings transmit in opposite directions • Token ring
Fiber-Optic Cable Connectors Proprietary designs abound SC ST FC LC and MTRJ are most common ST round insert like BNC (push and twist) SC square plug FC screw threads like coaxial connector LC new small single or duplex dev. by LucentTechnologies (formerly Bell Labs) MTRJ - another small duplex design See page 135
Fiber-OpticCable Installation and Troubleshooting
Installation and Troubleshooting • Installing Connectors • Making a Fusion Splice • Using Fiber-Optic Cable Meters • not usually prepared in the field • requires expertise to apply, certifications (BICSI, FOA, Nortel Networks, Beldon ) • cleaved not cut
Installing Connectors Design/measure prior to installation/supply Splicing difficulties include dirt and alignment Glass cores must be cleaved carefully Plastic cores must be cut carefully
Making a Fusion Splice Fusion Splicetwo ends melted/welded/fused together Mechanical splicingends clamped with gel to mitigate Fresnel effects
Using Fiber-Optic Cable Meters Power meter and light source OTDR optical time Domain Reflectometer can locate faults (distance to) rent don’t buy