Chapter 5 Flashcards
Physical Topology
Physical topology is the physical layout of the media, nodes and devices on a network
Commonly used LAN topologies
Commonly used LAN topologies are the bus, ring and star
Bus Topology
Bus topology uses a single cable (the bus) connecting all network devices (without intervening connectivity devices
Bus topology is implemented with coaxial cable; therefore older technology
Transmissions go to all nodes connected to the bus; not just the sender and the receiver
If a second node attempts to transmit while another node is transmitting, the transmissions will collide causing both transmissions to fail therefore, a bus only supports one transmission at a time
backbone
A bus topology that connects multiple network segments
BNC Connectors
Physical component of bus topology
BNC Connectors at the end of each cable
T-connectors
Physical component of bus topology
T-connectors are required to connect network coaxial cables and NICs
Terminator
Physical component of bus topology
Terminator is required at the end of the bus to absorb the signals
signal bounce
Any opening in the bus (cut coax, disconnected BNC connector or missing terminator) will cause all transmissions to fail due to signal bounce
passive topology
Bus topology is a passive topology
A passive topology is a topology in which the devices simply pass the signals on to the next device without repeating (digital) or amplifying (analog) the transmission. Because of the passive nature of the bus, signal continues to get weaker (attenuate) as the signal moves along the bus.
maximum distance of transmission across a bus
Maximum distance of transmission across a bus is the total distance between the sending and receiving nodes
bus communication
Because the bus only contains a single channel, bus topology only supports half duplex communications
access method
The term access method when used in relation to network topologies refers to how a node determines whether or not it can transmit
access method for bus communications
Node (NIC) desiring to transmit tests the channel to see if there is any activity on the channel (is another node is transmitting)
If the node detects no activity, the node assumes that it is Ok to transmit
Problems:
Two or more nodes can (1) be listening at the same time, (2) detect no activity and (3) begin transmissions which would result in a collision of the signals and a failed transmission
Potential for this problem to occur increases as the bus
grows in terms of number of nodes and amount of network traffic
bus topology scalability
Low level of scalability (the ability of the network to grow) because:
Single transmission restriction
Higher potential for collisions
Difficult to trouble-shoot problems due to difficulty in identifying the location of the problem since a single failure causes the entire bus to fail
ring topology
Ring topology is configured so that every node is connected to the two nearest nodes creating a ring
Packets are passed clockwise around the ring
A node accepts the packets that are addressed to it and passes other packets to the next node on the ring
Twisted pair and fiber optic are most commonly used media
active topology
active topology
ring topology is an active topology
An active topology is a topology in which each node repeats or amplifies the signal back to full strength
Since each node in an active topology puts the signal back to full strength, maximum segment length applies to the distance between each node
access method for a ring topology
Access method for a ring is typically token passing (Token Ring network technology)
A packet called an access token is passed around the ring
Only one node (the node with the access token) can transmit at a time; therefore collisions (failures due to two devices transmitting at the same time) should not occur
access token
The access token is an indication to a node that it is Ok to transmit
ring topology tolerance
Failure of any device on the ring or any break in the ring will cause the entire ring to fail
This characteristic causes the ring topology to not be fault tolerant
Topology is difficult to trouble shoot because a failure anyplace on the ring will cause the entire ring to fail
ring topology scalability
ring Topology is not highly scalable because it only supports one transmission at a time
star topology
Star topology connects each node individually through a central device
connected through twister pair or fiber optics with RJ45 connectors, ethernet NIC’s, and hubs/switches
active topology:
Hubs and switches are active devices that repeat the signal
Maximum segment length applies to the distance between the hub/switch and the node
Easier to trouble-shoot:
Failure of a single node is probably due to connection with the node or failure of the node itself
Failure of all nodes is probably due to failure of the hub /switch
star topology fault tolerance
Fault tolerant due to separate channel for each device; but dependant on central device
star topology scalability
Scalable due to (1) separate channel for each node and (2) ability to support multiple communications if an appropriate switch is used
hybrid topologies
Hybrid topologies combine two or more simple topologies to form a complex network
Star wired bus
Star wired bus uses bus to connect multiple star segments
Extends the length of the network with minimal cabling
Allows for multiple communications if appropriate switches are used
Nodes on Switch A can be communicating with other nodes on Switch A at the same time that nodes on Switch B are communicating with other nodes on Switch B
Limited to a single communication across the backbone
hybrid topology
network backbone
A network backbone is the cabling that connects the hubs, switches and routers in a network
Backbones are usually capable of more throughput than the cabling that connects workstations due to the need to handle more traffic
serial backbone
A serial backbone consists of two or more devices (switches, hubs or routers) connected to each with a single cable
Allows the network to extended more efficiently than a single star network that requires every node to be connected to the central connectivity device
Switches, hubs and other devices connected via a serial backbone are active devices resulting in resulting in longer segment distances
There are technical limitations to how many devices you can connect in this manner (to be discussed later)
daisy chain
Connecting devices in this manner (one to the next to the next) is known as a daisy chain
distributed backbone
A distributed backbone consists of multiple levels of connectivity devices
Allows for simple expansion (through the addition of connectivity devices) but there are limitations to how many levels of devices can be on a distributed backbone
A distributed backbone can incorporate routers and possibly WAN connections to connect multiple phyiscal networks into a single logical LAN
parallel backbone
A parallel backbone provides fault tolerance through multiple connections between the connectivity devices
ethernet
Ethernet is, by far, the most popular network technology for implementing physical connections
Ethernet is implemented at the Physical and Datalink layers of the OSI model
Ethernet consists of multiple variations (wired Ethernet is compatible with but not the same as wireless Ethernets)
Wired Ethernet uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD) as its access method
Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
Collisions are a normal and expected characteristic of CSMA/CD
Higher level of collisions decrease throughput
Risk of collisions increases as the network grows and / or network traffic increases since the potential exists for more nodes to be transmitting
collision domain
Collision domain is the segment of a network in which collisions will occur if two or more nodes transmit simultaneously
When using hubs, the collision domain includes all nodes attached to the hub because the hub sends the transmission to all nodes
When using switches, the collision domain is limited to the nodes that are involved in the transmission
shared ethernet
Traditional Ethernet (Shared Ethernet) utilizes a hub that broadcasts to all connected nodes
All nodes are in the same collision domain
Only a single transmission can occur at any point in time
switched ethernet
Switched Ethernet isolates the transmission to the destination node
Only sending and receiving node are in the same collision domain
Can potentially support multiple simultaneous transmissions
More secure than Shared Ethernet since transmission does not go to all nodes
When two nodes on the same switch are communicating with each other, the collision domain is simply those two nodes
IEEE
IEEE establishes the standards for wired Ethernet
ethernet standards designations
Ethernet standards are designated in the following format:
10Base-T
First - maximum capacity in Mbps
Second - baseband
Third - twisted Pair
10Base-T
Older Ethernet standard that replaced coax cables
Uses two twisted pairs for full duplex communications
Requires CAT 3 or higher cable
Supports star topology
100 meter maximum segment length (between two devices)
5-4-3 rule determines the maximum size of the network
5-4-3 rule
Between two communicating devices there can be no more than:
5 network segments
4 repeating devices
3 populated segments (segment with nodes)
100Base-T (Fast Ethernet)
Currently popular technology with 100 Mbps capacity
Uses two twisted pairs for full duplex communications
Requires CAT 5 or higher cable
Supports star topology
100 meter maximum segment length (between two devices)
Maximum transmission distance is three segments with two repeating devices
1000Base-T (Gigabit Ethernet)
Supports high speed applications with 1 Gbps capacity
Uses four twisted pairs for full duplex communications
Requires CAT 5 or higher cable
Supports star topology with a single repeater
100 meter maximum segment length (between two devices)
1000BaseT and 100BaseT can coexist on the same network
10GBase-T
New standard with 10 Gbps capacity
Requires CAT 6 or Cat 7cable
Supports star topology
100 meter maximum segment length (between two devices)
Slowest component rule
a network transmission is only as fast as the slowest component
100Base-FX
Uses two strands of multimode fiber
100 Mbps in half duplex or full duplex transmission
Star topology with repeaters in a bus topology
Maximum segment length of 412 meters for half duplex and 2,000 meters for full duplex
Can coexist with Fast Ethernet (with appropriate connectivity devices) and is therefore considered a form of Fast Ethernet
1000Base-LX
1 Gbps using single mode or multimode fiber
Maximum distance can be extended with a single repeater
Maximum segment length of 550 meters with multimode and 5,000 meters with single mode
Due to longer distances, excellent choice for backbones (ex. connecting buildings)
1000Base-LX
Similar to 1000Base-LX except that it only supports multimode fiber and has a maximum segment length of 550 meters which can be extended with one repeater
Suited to shorter applications such as connecting a data center or entrance point with a telecommunications closet
10GBase-xx
10 Gbps transmission for a star topology
Standards differ in term of cable requirements and maximum distances
Ethernet PoE (Power over Ethernet)
Ethernet PoE (Power over Ethernet) is a new standard for providing power to devices via the Ethernet connection
Intended to support devices that do no have access to conventional power sources
