Unit 2:
Network Hardware
Section 2: Standards
In this section you will learn about network standards used with Ethernet
based networks. The material in this section is based on chapter 5 of the
Network + Guide to Networks book.
At the end of this section you should be able to:
1.
2.
3.
4.
5.
Identify Physical and Switching Standards
Describe the Ethernet logical topology
Identify Ethernet Frames
Identify Ethernet Standards for Copper Cable
Identify Ethernet Standards for Fiber Cable
Physical Topologies
From the previous unit, you should be familiar with the Bus, Ring, and Star topologies described on
pages 195 – 199. While certain Fiber based networks are based on a Ring topology, most all Ethernet
network standards in use today are based on combinations of Star networks and Backbone networks.
As described on pages 201 and 202. Backbone networks are methods of connecting multiple Star based
network using switches and routers. Backbone networks can be either Serial or Distributed. Serial are
used in smaller simple networks that consist of only a few switches. Distributed backbones allow better
distribution of network services and can provide multiple paths for packets in the event of a cable or
device failure. Distributed backbones can be subdivided into Collapsed and Parallel backbone networks.
However, for the purposes of Network Plus certification it is not necessary to identify the differences
between Collapsed and Parallel backbones.
Switching technologies
Switching is the methods used to make connections between nodes for transmission of data. The book
describes 4 switching technologies on pages 205 – 207. You need to be aware of the differences
between these switching technologies.
Circuit Switching
Connection established prior to data transmission.
Used on conventional telephone voice networks
Message Switching
Data is sent as a single complete message or file, such as text message. Uses a store and transfer
the message where each device in the path receives the entire file, stores the files, and then
transfers the file to the next device in the path.
Packet Switching
Used in conventional networks.
Data file or message is broken down into fixed length packets and sent across the network. In
packet switched networks, packets may travel different paths to reach the destination. The
destination device reassembles the packets to create the file or message.
MPLS (Multiprotocol Label Switching)
Works at layer 2 (Network Layer) to combine multiple types of layer 3 (Network layer) protocols
to travel across both Ethernet and WAN connections. MPLS includes a “Shim” that is used to
prioritize and direct the packet along a pre-defined path.
The Shim is created by the Network layer MPLS protocol and acts as a layer between the
Network and Data Link (Layer 2.5) that directs the packet between network routers and
switches.
One of the benefits of MPLS is its ability to use packet switching over traditional circuit-switchd
(phone) networks. MPLS is also used in Voice Over IP (VOIP) networks to offer better Quality of
Service (QoS) needed to support voice calls. You will see MPLS again when we discuss VOIP
systems and QoS technologies.
Read pages 205 – 207 to help understand the differences between Circuit, Message, Packet, and MPLS
switching technologies.
Ethernet Standards
There are a number of Ethernet standards based on the type of cable or transmission system. Essentially
Ethernet can be divided into two major IEEE standards; IEEE802.3 for wired networks, and IEEE802.11
for wireless network. In this section we will look at the 802.3 standards.
Ethernet Logical Topology
While a physical topology describes the physical layout of a network or cable system, a logical topology
describes the way this network is used to transmit and receive data frames. Page 199 describes the two
major types of logical topologies:
In a logical ring topology a frame of data is transmitted from one device to the next in a circular
fashion until it returns to the sender. The sender can then verify that the frame was received
correctly or retransmit if necessary. Access to the network is manage using a free token system.
The token is a special frame that is passed from machine to machine. When a device needs to
transmit data, it waits for the token and then sends its data packet. When the data packet is
returned via the ring, the device then releases the token making the network available for the
next device to use. The token system prevents multiple devices from accessing the network at
the same time. While this topology was used in the early 90’s with IBM’s Token Ring LAN, today,
the ring logical topology is used only in certain WAN environments.
The logical bus topology is used by Ethernet networks. In a logical bus topology, a frame of data
is transmitted, or broadcast, across an entire network segment – being picked up by all devices
attached to that segment. The device whose MAC address is specified in the frame then
processes the data. To prevent multiple devices from transmitting data at the same time,
causing data collisions and corruption, the 802.3 standard uses the CSMA/CD (Carrier Sense
Multiple Access / Collision Detection) protocol.
Read pages 208 – 209 for a description of the CSMA/CD protocol. The Network + certification
objectives expect you to understand the way CSMA/CD works to better troubleshoot and
configure networks.
CSMA/CD creates collision domains in which all computers on that network segment are subject
to collisions. In addition, within a collision domain, all packets or data frames are visible to all
devices attached to that segment. This may create a security issue, as data frames can be
intercepted by other devices. Collision devices can be separated using switches and routers as
shown below. Notice in this diagram that the computers on the top network segment are not
affected by the transmissions occurring on the lower segment. The two segments can be
connected together using a bridge, switch, or router. We will discuss using switches and routers
to work with collision and broadcast domains later in this section.
Ethernet Frames
Frames are Data Link layer packets that carry data across the LAN. As the physical layer works
with bits, it does not affect the type of framing used by the Data Link. Over the years changing
LAN technology combined with a variety of specialized vender networks created four different
Ethernet frame types as described on pages 215-216.
Ethernet_802.2 – Original frame type. No longer used on modern networks.
Ethernet_802.3 – Used by Novell company for proprietary networks
Ethernet_II (DIX) – Developed by DEC, Intel, and Xerox. Contains a type-field that allows
it to carry multiple protocols. Currently standard used by TCP/IP. Most commonly used
on Ethernet today.
Ethernet_SNAP – Similar to Ethernet_II, but has additional control fields that leave less
room for data. Sometimes used on Apple proprietary networks.
In order for two devices to communicate across the network, they must both use the same
frame type.
Ethernet frames can range in length from 64-bytes to 1518 bytes. 18 bytes are used for framing
and include 14 bytes for the header and 4-bytes for the FCS(used for error checking). Frames
must be a minimum of 46 data bytes in order for CSMA/CD to detect collisions. If you are
sending a message of less than 46 bytes, the Data Link layer will add “padding” bits to make the
data portion 46 bytes in length.
Ethernet Standards over Copper
The IEEE 802.3 standard describes how signals are transmitted at the physical level and affect the way in
which networks are configured and wired. In this section we will look at 4 major divisions of the
Ethernet standard as described on pages 210 – 212. These standards can all be express using the
##BASET designation. The ## represents the speed in Mbps (Million bits per second), the BASE stands
for Baseband (digital) signaling, and the “T” indicates Twisted pair copper cable. As described in Unit 2
Section 1, twisted pair copper cable can be classified by it Cat number (see page 99 in the book). Each of
the Ethernet standards have certain CAT cable requirement. Following are some notes regarding each of
these standards.
10Base-T
First twisted pair Ethernet standard.
Uses RJ-45 connectors.
Previous standards were coaxial based systems 10Base-5 (500 meter “thick” RG-8 coaxial
cable) and 10Base-2 (200 meter “thin” RG-58 coaxial cable)
Can work with CAT 3 or higher.
Uses 2 wire pairs (4-wires). One pair for transmit and one pair for receive. This makes it cabable
of full-duplex transmission.
100 Meter maximum cable length.
Uses 5-4-3 rule, which allows 5 segments separated by up to 4 hubs. This allows for a maximum
distance between devices of 500 meters. See figure on page 210 for good illustration of applying
the 5-4-3 rule.
100Base-T (Fast Ethernet)
Based on IEEE 802.3 u standard, also known as Fast Ethernet.
Uses 100 Mbps data transfer rate.
Requires CAT 5 or higher.
Uses RJ-45 connectors.
Because of faster response requirements, can have a maximum of 2 repeaters. This limits the
distance between devices to 300 meters as shown in the figure on page 211.
Uses same wire pairs as 10Base-T to achieve full-duplex.
When using full-duplex, can double effective bandwidth to 200 Mbps.
1000Base-T (Gigabit Ethernet)
Uses IEEE 802.3ab standard known as Gigabit Ethernet. The 1000Base-T standard includes both
copper and fiber. It is technically known as 1000Base-TX in copper based networks.
Requires CAT 5 cabling and RJ-45 connectors.
Standard uses all 4 wires to achieve the higher speeds and therefore operates in half-duplex.
Can have only one repeater limiting the maximum segment length between two devices is 200
meters.
While it uses a different bit encoding method than 100Base-T, the signals are compatible on the
same cable system.
Some network cards can be set to operate for 10, 100, or 1000 Base-T environments.
10GBase-T
Uses the latest IEEE 802.3an standard.
Requires CAT 6 or 7 cabling.
No repeaters are allowed – must use a Switch to connect devices. Maximum distance between
device and switch is 100 meters.
Used to connect servers to switch to improve access times.
Power over Ethernet (PoE)
As described on pages 217 and 218, the PoE standard (IEEE 802.3f) specifies how power can be
carried to a device using standard twisted pair cables.
Power runs over unused pairs.
Requires special connectivity devices such as switches and routers that meet the PoE standards.
Can be used with 10BaseT, 100BaseTX, 1000BaseT, and 10GBase-T
Ethernet Standards over Fiber
Fiber standards use similar designations as copper. In Fiber, the last two characters may be used to
specify the wavelength. Long wavelengths such as used in LX standards can go longer distances than
short wavelengths specified in the SX standard. Single-mode fiber systems provide higher speeds and
longer distance than multi-mode fiber. You should read the Ethernet fiber standards described on pages
212-215. Following are some notes regarding each of these standards.
100Base-FX
Uses Baseband (digital) fiber signaling described in 100Base-T standard (IEEE 802.3u) and is easy
to integrate into existing 100Base-T copper systems by using a repeater or media converter.
Requires Multi-mode cable.
Uses standard Star topology with one repeater.
Can use half or full duplex
Segment length up to 412 meters with half duplex and 2000 meters with full duplex.
May use almost any fiber connector such as SC, ST, LC or MT-RJ connectors.
1000Base-LX
Uses IEEE 802.3z standard
Uses long wavelengths of 1300 nm
Single or multi-mode fiber
Longest reach of any 1 GB Ethernet technology – up to 5000 meters on single-mode fiber (550
meters on multi-mode fiber)
1000Base-SX
Uses Multi-mode fiber and short wave lengths of 850 nm.
Less expensive to install than 1000Base-LX
From 275 – 550 meters depending on Model bandwidth
10GBase Standards
Uses IEEE 802.3ae standard
The L stands for long reach (Longer wave length) and the S for short reach (shorter wave lenth).
The W specifies a signal encoding that is designed work across SO-NET WANS that uses a highly
reliable fiber ring.
10GBase-SR and 10GBase-SW
Shortest segment length of 10GBase fiber standards
Uses Multi-mode fiber and 850 nm signals. The segment length depends on the fiber
cable
50-micron fiber = 300 meters
62.5-micron fiber = 66 meters
10GBase-S is intended to work with fiber segments on LANs
10GBase-LR and 10GBase-LW
Uses SMF cable and 1310 nm wave length to obtain longer distance.
Intended for MAN and WAN applications.
10GBase-ER and 10GBase-EW
The E stands for Extended range.
EW has the longest range of all 10GBase standards - nearly 25 miles.
Uses SMF cable with 1550 nm wavelength.
Page 215 contains a nice figure showing all the Copper and Fiber Ethernet standars. You may want to
mark this page for reference.
Unit 2 Section 2 Questions (See chapter 5 in textbook)
2. Which of the following topologies is susceptible to signal bounce?
Page 195
3. What type of topology is required for use with a 100Base-TX network?
Page 211
4. Your school’s network has outgrown its designated telco rooms, so you decide to house a
few routers in an old janitor’s closet temporarily. However, since the closet has no power
outlets, you will have to supply the routers power over the network. If you’re lucky, your
LAN already uses which of the following Ethernet standards that will allow you to do that?
Page 211-212
5. What is the minimum cabling standard required for 10GBase-T Ethernet?
Page 212
6. Which of the following is a potential problem with daisy-chaining hubs on a 100Base-T
network?
Page 210
8. You are part of a team of engineers who work for an ISP that connects large data centers,
telephone companies, and their customers throughout California and Oregon. Management
has decided that the company can make large profits by promising the utmost QoS to certain
high-profile customers. Which of the following switching methods will best guarantee the
promised QoS?
Page 207
9. What happens in CSMA/CD when a node detects that its data has suffered a collision?
Page 208
10. Why are Ethernet_II frames preferred over Ethernet_802.3 frames on contemporary
LANs?
Page 217
11. What is the purpose of padding in an Ethernet frame?
Page 216
12. You are designing a 100Base-T network to connect groups of workstations in two
different offices in your building. The offices are approximately 250 meters apart. If you only
use repeating devices to connect the workstation groups, how many hubs will you need?
Page 211
13. On a 10Base-T network, which of the following best describes how the wires of a UTP
cable are used to transmit and receive information?
Page 210
14. What technique is used to achieve 1-Gbps throughput over a Cat 5 cable?
Page 211
15. Which of the following Ethernet standards is specially encoded for transmission over
WANs using SONET technology?
Page 214
16. Which two of the following might cause excessive data collisions on an Ethernet
network?
Page 208 implies it
17. In which of the following examples do the workstations necessarily share a collision
domain?
Page 208
18. What are the minimum and maximum sizes for an Ethernet frame?
Page 216
20. Which of the following is the type of 10-Gigabit Ethernet that can carry signals the
farthest, nearly 25 miles?
Page 215