Network Topologies 5/11/10

Network Topologies

04/10/23 2

Objectives

• Describe the basic and hybrid LAN physical topologies, their uses, advantages, and disadvantages

• Describe a variety of enterprise-wide and WAN physical topologies, their uses, advantages, and disadvantages

• Compare the different types of switching used in data transmission

• Understand the transmission methods, or logical topologies, underlying Ethernet, Token Ring, LocalTalk, and FDDI networks

04/10/23 3

Simple Physical Topologies

• Physical topology– Physical layout of a network

• A Bus topology consists of a single cable—called a bus— connecting all nodes on a network without intervening connectivity devices

04/10/23 4

Advantages of Bus Topology

• Works well for small networks

• Relatively inexpensive to implement

• Easy to add to it

04/10/23 5

Disadvantages ofBus Topology

• Management costs can be high

• Potential for congestion with network traffic

04/10/23 6


• Ring topology– Each node is connected to the two nearest nodes so the entire

network forms a circle– One method for passing data on ring networks is token passing

• Active topology– Each workstation transmits data

04/10/23 7

Advantages of Ring Topology

• Easier to manage; easier to locate a defective node or cable problem

• Well-suited for transmitting signals over long distances on a LAN

• Handles high-volume network traffic

• Enables reliable communication

04/10/23 8

Disadvantages ofRing Topology

• Expensive

• Requires more cable and network equipment at the start

• Not used as widely as bus topology– Fewer equipment options– Fewer options for expansion to high-speed

communication

04/10/23 9


• Star topology– Every node on the network is connected through

a central device

04/10/23 10

Advantages of Star Topology

• Good option for modern networks

• Low startup costs

• Easy to manage

• Offers opportunities for expansion

• Most popular topology in use; wide variety of equipment available

04/10/23 11

Disadvantages ofStar Topology

• Hub is a single point of failure

• Requires more cable than the bus

04/10/23 12

Hybrid Physical Topologies

• Hybrid topology– Complex combination of the simple physical topologies

• Star-wired ring– Star-wired topologies use physical layout of a star in

conjunction with token ring-passing data transmission method

04/10/23 13


• Star-wired bus– In a star-wired bus topology, groups of workstations are

star-connected to hubs and then networked via a single bus

04/10/23 14


• Daisy-Chained– A Daisy chain is linked series of devices

04/10/23 15


• Hierarchical hybrid topology– Uses layers to separate devices by priority or function

04/10/23 16

Enterprise-Wide Topologies

• Enterprise– An entire organization

• Backbone networks– Serial backbone– Distributed backbone– Collapsed backbone– Parallel backbone

04/10/23 17


• Serial backbone– Two or more hubs connected to each other by a single cable

• Distributed backbone– Hubs connected to a series of central hubs or routers in a hierarchy

04/10/23 18


• Collapsed backbone– Uses a router or switch as the single central

connection point for multiple subnetworks

04/10/23 19


• Parallel Backbone– Collapsed backbone arrangement that consists of more than one

connection from central router or switch to each network segment

04/10/23 20


• Mesh networks– Routers are interconnected with other routers, with at least two

pathways connecting each router

04/10/23 21

Wide Area Network (WAN) Topologies

• Peer-to-peer topology– WAN with single interconnection points for each location– Dedicated circuits

• Continuous physical or logical connections between two access points that are leased from a communication provider

04/10/23 22


• Ring WAN topology– Each site is connected to two other sites so that entire

WAN forms a ring pattern

04/10/23 23


• Star WAN topology– Single site acts as the central connection point for several

other points

04/10/23 24


• Mesh WAN topology– Many directly interconnected locations forming a complex mesh

04/10/23 25

Logical Topologies

• Refers to the way in which data are transmitted between nodes

• Describes the way:– Data are packaged in frames

– Electrical pulses are sent over network’s physical media

• Logical topology may also be called network transport system

04/10/23 26

Switching

• Component of network’s logical topology that determines how connections are created between nodes– Circuit switching

• Connection is established between two network nodes before they begin transmitting data

– Message switching• Establishes connection between two devices, transfers

information to second device, and then breaks connection

– Packet switching• Breaks data into packets before they are transmitted

04/10/23 27

Ethernet

• Carrier Sense Multiple Access with Collision Detection (CSMA/CD)– The access method used in Ethernet

– Collision• In Ethernet networks, the interference of one network node’s

data transmission with another network node’s data transmission

– Jamming• Part of CSMA/CD in which, upon detection of collision,

station issues special 32-bit sequence to indicate to all nodes on Ethernet segment that its previously transmitted frame has suffered a collision and should be considered faulty

04/10/23 28

Ethernet

CSMA/CD process

04/10/23 29

Ethernet

• On an Ethernet network, an individual network segment is known as a collision domain– Portion of network in which collisions will occur if

two nodes transmit data at same time

• Data propagation delay– Length of time data take to travel from one point

on the segment to another point

04/10/23 30

Ethernet

• Demand priority– Method for data transmission used by 100BaseVG Ethernet networks– Demand priority requires an intelligent hub

CSMA/CD versus demand priority

04/10/23 31

Ethernet

• Traditional Ethernet LANs, called shared Ethernet, supply fixed amount of bandwidth that must be shared by all devices on a segment

• Switch– Device that can separate network segments into

smaller segments, with each segment being independent of the others and supporting its own traffic

• Switched Ethernet– Newer Ethernet model that enables multiple nodes to

simultaneously transmit and receive data over logical network segments

04/10/23 32

Ethernet

A switched Ethernet network

04/10/23 33

Ethernet

• Gigabit Ethernet– 1 Gigabit Ethernet

• Ethernet standard for networks that achieve 1-Gbps maximum throughput

– 10 Gigabit Ethernet• Standard currently being defined by IEEE 802.3ae

committee• Will allow 10-Gbps throughput• Will include full-duplexing and multimode fiber

requirements

04/10/23 34

Design Considerations for Ethernet Networks

• Cabling

• Connectivity devices

• Number of stations

• Speed

• Scalability

• Topology

04/10/23 35

LocalTalk

• Logical topology designed by Apple Computer, Inc.

• Uses a transmission method called Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA)

• A teleconnector is a transceiver used on a LocalTalk network

• Macintosh version of TCP/IP is called MacTCP

04/10/23 36

Token Ring

• Token Ring networks use the token passing routine and a star-ring hybrid physical topology

• The 100-Mbps Token Ring standard is known as High-Speed Token Ring (HSTR)

• On a Token Ring network, one workstation, called the active monitor, acts as the controller for token passing

04/10/23 37

Token Ring

• Multistation Access Unit (MAU)– Regenerates signals

Interconnected Token Ring MAUs

04/10/23 38

Token Ring

• Control Access Unit (CAU)– Connectivity device used on a Token Ring

network

• Lobe Attachment Module (LAM)– Device that attaches to a CAU to expand the

capacity of that device

04/10/23 39

Token Ring

• Token Ring networks with STP cabling may use a type 1 IBM connector

• A DB-9 connector is another type of connector found on STP Token Ring networks

Type 1 IBM and DB-9 Token Ring connectors

04/10/23 40

Token Ring

• Media filter– Device that enables two types of cables or connectors to be linked

• Token Ring media filter– Enables DB-9 cable and type 1 IBM cable to be connected

A Token Ring media filter

04/10/23 41

Design Considerations for Token Ring Networks

• Cabling

• Connectivity devices

• Number of stations

• Speed

• Scalability

• Topology

04/10/23 42

Fiber Distributed Data Interface (FDDI)

• Logical topology whose standard was originally specified by ANSI in mid-1980s and later refined by ISO

04/10/23 43

Asynchronous Transfer Mode (ATM)

• Logical topology that relies on a fixed packet size to achieve data transfer rates up to 9953 Mbps

• The fixed packet in ATM is called a cell• A unique aspect of ATM technology is that it

relies on virtual circuits

04/10/23 44

Asynchronous Transfer Mode (ATM)

• ATM uses circuit switching, which allows ATM to guarantee a specific quality of service (QOS)

• ATM technology can be integrated with Ethernet or Token Ring networks through the use of LAN Emulation (LANE)

Documents

Network Topologies 5/11/10