Media, LAN Technologies, and Network Topologies

Lecture 5

Introduction to Media

Network traffic must flow through some form of media, whether it is a cable, or is wireless.The most common forms of network media are twisted-pair, coaxial, and fiber-optic cable.

Twisted-Pair Cable

T-P cable is the most common of all of the media types in the average local area network (LAN) environment.Different categories of T-P cable exist. The different categories of cable specify the maximum data bandwidth that the cable can withstand.T-P comes in two forms, Unshielded (UTP) or Shielded (Plenum/STP).

Twisted-Pair Categories

Category Maximum Data Rate

Usual Application

CAT-1 < 1 Mbps POTS & ISDN

CAT-2 4 Mbps IBM Token Ring

CAT-3 16 Mbps Voice/Data -10baseT

Twisted-Pair Categories (cont.)

CAT-4 20 Mbps 16Mbps Token Ring Networks

CAT-5 100 Mbps 100baseT, 155Mb ATM

CAT-7(in progress)

1000 Mbps1000baseT, Gigabit Ethernet

Twisted-Pair (cont.)

Twisted-pair cable (CAT5 and up) consists of 4 separate pairs of wires, all wound separately.

Coaxial Cable

Coaxial cable (coax) is almost the same thing that carries your cable TV signal. Data coax is just held to a higher quality.Historical Tidbit: Coax cable, although not commonly seen nowadays, was how Ethernet was developed!

Coax (cont.)

The physical medium itself consists of an inner wire, surrounded by an insulator, which is also surrounded by a shield.

Coax Applications

Local Area Networks (LANs) Thinnet (10base2) –

200 meters Thicknet (10base5) –

500 meters Baseband

transmissions only

Wide Area Networks (WANs) T3/DS3/E3 Broadband

transmissions

Baseband v. Broadband

Baseband is where the medium only carries one signal on the line.Broadband carries multiple signals on a single line.

Fiber Optic Cable Fiber optic cable is where the future of LAN wiring exists.Fiber comes in two different types:

Multimode – a channelized fiber-optic circuit. Multiple carrier frequencies.

Singlemode – a “clear channel” circuit. One carrier frequency.

Fiber Applications

High-bandwidth voice transmission.“Backbone” applications.Very fast data transfer between network devices.

Other Media

CellularInfraredSatellite Geosynchronous Low Earth Orbit

Packet RadioMicrowave

LAN Topologies

There are three main types of LAN systems: Star Topology Ring Topology Bus Topology

Some topologies are actually hybrids of the above!

Star Topology

All computers connect to a centralized point.The central point is called the hub.

Ring Topology

One computer is connected to the two computers adjacent to it.In the traditional case, if a system is disconnected from the ring, the network fails.

Bus Topology

A bus topology consists of a single cable to which each network device attaches.Bus topology has the same problems as a ring topology.

LAN Technology Optionso Etherneto Fast Etherneto Gigabit Etherneto 10 Gig Ethernet

LAN Technologies

Ethernet

Ethernet design by Bob Metcalfe in 1976.The Ethernet specification details how devices are supposed to interact on the segment, distances between devices, and a whole other multitude of other things.Carrier Sense On Multi-Access Networks (CSMA) with Collision Detection (CD) was the most important part of the specification.

Ethernet

10 Base 5 (Thicknet) (Bus Topology)10 Base 2 (Thinnet) (Bus Topology)10 Base T (UTP) (Star/Tree Topology)10 Base FL (Fiber) (Star/Tree Topology)

LAN Technologies

CSMA on Ethernet

CSMA indicates that computers wait until the ether is free. In this case, no electrical signal denotes when the ether is “free.”

CSMA on Ethernet (cont.)

The “signal” is the carrier of the ether.The act of waiting for the opportunity to send on the ether is carrier sense.

Collision Detection

Since networks are not instantaneous, it is possible for two stations to check the ether, deem it time to send, and both send at the same time. This is called a collision.When a collision occurs, the sender immediately stops transmission, and waits some random length of time, and then begins transmission again.

Collision Detection (cont.)

A busy segment will always have collisions.Collisions do not damage the equipment, but it forces the two machines that caused the collision to wait, and therefore it slows down the network.Fewer machines on a segment, smaller segments, can improve the collision count.

Ethernet Addresso End nodes are identified by their Ethernet

Addresses (MAC Address or Hardware Address) which is a unique 6 Byte address.

o MAC Address is represented in Hexa Decimal format e.g 00:05:5D:FE:10:0A

o The first 3 bytes identify a vendor (also called prefix) and the last 3 bytes are unique for every host or device

Ethernet Addresso MAC address allocation administered by IEEEo manufacturer buys portion of MAC address space (to

assure uniqueness)o Analogy: (a) MAC address: like Social Security Number (b) IP address: like postal addresso IP hierarchical address NOT portable

o depends on IP network to which node is attached

Etherneto Physical Media

10 Base5 - Thick Co-axial Cable with Bus Topology 10 Base2 - Thin Co-axial Cable with Bus Topology 10 BaseT - UTP Cat 3/5 with Tree Topology 10 BaseFL - Multimode/Singlemode Fiber with Tree Topology

o Maximum Segment Length 10 Base5 - 500 m with at most 4 repeaters (Use Bridge to extend

the network) 10 Base2 - 185 m with at most 4 repeaters (Use Bridge to extend

the network) 10 BaseT - 100 m with at most 4 hubs (Use Switch to extend the

network)

AN Technologies

Fast Etherneto 100 Mbps bandwidtho Uses same CSMA/CD media access protocol

and packet format as in Ethernet.o 100BaseTX (UTP) and 100BaseFX (Fiber)

standards o Physical media :

100 BaseTX - UTP Cat 5e 100 BaseFX - Multimode / Singlemode Fiber

o Full Duplex/Half Duplex operations.

LAN Technologies

Fast Etherneto Provision for Auto-Negotiation of media speed:

10 Mbps or 100Mbps (popularly available for copper media only).

o Maximum Segment Length 100 Base TX - 100 m 100 Base FX - 2 Km (Multimode Fiber) 100 Base FX - 20 km (Singlemode

Fiber)

LAN Technologies

Gigabit Etherneto 1 Gbps bandwidth.o Uses same CSMA/CD media access protocol as in

Ethernet and is backward compatible (10/100/100 modules are available).

o 1000BaseT (UTP), 1000BaseSX (Multimode Fiber) and 1000BaseLX (Multimode/Singlemode Fiber) standards.

o Maximum Segment Length 1000 Base T - 100m (Cat 5e/6) 1000 Base SX - 275 m (Multimode Fiber) 1000 Base LX - 512 m (Multimode Fiber) 1000 Base LX - 20 Km (Singlemode Fiber) 1000 Base LH - 80 Km (Singlemode Fiber)

LAN Technologies

10 Gig Etherneto 10 Gbps bandwidth.

o Uses same CSMA/CD media access protocol as in Ethernet.

o Propositioned for Metro-Ethernet

o Maximum Segment Length 1000 Base-T - Not available 10GBase-LR - 10 Km (Singlemode Fiber) 10GBase-ER - 40 Km (Singlemode Fiber)

LAN Technologies

LocalTalk

LocalTalk is another form of a bus network.LocalTalk differs from Ethernet in a few ways: When a machine senses the segment is free, it

holds it until the frame transmission is over. All other machines know to wait for transmission to complete.

Bandwidth is quite small at ~230Kbps. That’s 2.3% of the earliest Ethernet specification!

IBM Token RingAccess mechanism is called token passing.Once the sent information makes a complete turn around the ring, the sender passes the token to the next machine.This is a strict-alternation scheme where all machines have the same chance to transmit information.

Fiber Distributed Data Interconnect (FDDI)