CCNA 1: Module 7 Ethernet Technologies
Overview
• The most successful LAN technology
– Easy to install
– Has evolved to meet changing needs
• Media
• Increased bandwidth (speed)
– Backward compatibility maintained as it has
evolved
7.1 10-Mbps and 100-Mbps Ethernet
7.1.1 10-Mbps Ethernet
• All implementations of 10-Mbps Ethernet
are considered “Legacy Ethernet”
• The four common features of Legacy
Ethernet are
– timing parameters
– frame format
– transmission process
– a basic design rule.
7.1 10-Mbps and 100-Mbps Ethernet
7.1.1 10-Mbps Ethernet Cont.
Parameter
Bit Time
Slot Time
Interframe Spacing
Collision Attempt Limit
Collision Backoff Limit
Collision Jam Size
Max. Untagged Frame Size
Minimum Frame size
Value
100ns
512 bit times
96 bit times
16
10
32
1518
512 Bits (64 octets)
7.1 10-Mbps and 100-Mbps Ethernet
7.1.1 10-Mbps Ethernet Cont.
• The Legacy Ethernet transmission process
– The Layer 2 frame data is converted from hex to binary.
– As the frame passes from the MAC sublayer to the physical layer,
further processes occur prior to the bits being placed from the
physical layer onto the medium.
– All 10 Mbps forms of Ethernet take octets received from the MAC
sublayer and perform a process called line encoding.
– Line encoding describes how the bits are actually signaled on
the wire.
7.1 10-Mbps and 100-Mbps Ethernet
7.1.1 10-Mbps Ethernet Cont.
• Manchester Encoding
– Up transition = 1
– Down transition = 0
7.1 10-Mbps and 100-Mbps Ethernet
7.1.2 10Base5 (LEGACY ETHERNET)
• The Original Ethernet (1980)
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Coaxial cable
Bus Topology
10 Mbps
Inexpensive and no configuration is needed
NIC’s difficult to find
500 meter segment length
Manchester encoding
CSMA/CD timings were developed using the constraints of the
coaxial medium (5-4-3-2-1 Rule).
– Only supported half-duplex
7.1 10-Mbps and 100-Mbps Ethernet
7.1.3 10Base2 (LEGACY ETHERNET)
• The 2nd Generation Ethernet (1985)
– Original Ethernet signaling was modified to be used over thinner
coaxial cable to make installation easier (Thinnet)
– Bus Topology
– 10 Mbps
– It has a low cost and a lack of need for hubs NIC’s difficult to find
– 185 meter segment length
– Manchester encoding
– Used the same timings as 10Base5 and subject to the 5-4-3-2-1
Rule.
– Only supported half-duplex
– 30 Stations Max. on each segment
7.1 10-Mbps and 100-Mbps Ethernet
7.1.4 10BaseT (LEGACY ETHERNET)
• 10BASE-T was introduced in 1990
• Used cheaper and easier to install Category 3 unshielded twisted
pair (UTP) copper cable (now Cat 5e is minimum)
• Star Topology with a hub (multiport repeater at the center)
• 100 meter length between station and hub
• Used the same timings as 10Base5 and subject to the 5-4-3-2-1
Rule.
• Originally 10BASE-T was a half-duplex protocol, but full-duplex
features were added later.
• Manchester encoding
7.1 10-Mbps and 100-Mbps Ethernet
7.1.5 10BaseT Wiring Architecture
• 10 Base T using Hubs
• Subject to the same timing constraints as 10Base5 and 10Base2
– Reason: delay and latency
• Delay – time it takes the signal to propagate down the wire
• Latency – time it takes a NIC to put the bits on the wire AND a repeating
device to regenerate the signal and place it on the wire.
• The best design is to use a hierarchical arrangement.
7.1 10-Mbps and 100-Mbps Ethernet
7.1.6 100 Mbps Ethernet (FAST ETHERNET)
•
Two types
– 100BaseTX (copper UTP media)
– 100BaseFX (multimode fiber optic cable media)
•
Three characteristics common to 100BASE-TX and 100BASE-FX are
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the timing parameters
the frame format
parts of the transmission process.
•
Star or Extended Star Topology with a hub or switch at the center
•
100 meter length between station and hub/switch
•
Uses a different timing than Legacy Ethernet
•
Same Frame format as Legacy Ethernet
• Two separate encoding steps are used by 100-Mbps Ethernet.
– The first part of the encoding uses a technique called 4B/5B
– The second part of the encoding is the actual line encoding specific to
copper or fiber.
7.1 10-Mbps and 100-Mbps Ethernet
7.1.6 100 Mbps Ethernet (FAST ETHERNET) Cont.
Parameter
Bit Time
Slot Time
Interframe Spacing
Collision Attempt Limit
Collision Backoff Limit
Collision Jam Size
Max. Untagged Frame Size
Minimum Frame size
Value
10ns
512 bit times
96 bit times
16
10
32
1518
512 Bits (64 octets)
7.1 10-Mbps and 100-Mbps Ethernet
7.1.7 100BaseTX
• 1995 Standard adopted
• Uses Cat5 UTP
• 1997, Ethernet was expanded to include a full duplex capability that
allowed more than one PC on a network to transmit at the same
time.
• 100BASE-TX uses 4B/5B encoding, which is then scrambled and
converted to multi-level transmit-3 levels or MLT-3.
• TX can exchange 200 Mbps of traffic in full-duplex mode
7.1 10-Mbps and 100-Mbps Ethernet
7.1.7 100BaseTX Encoding
• 4B/5B encoding (Frame Encoding – shorthand)
– All data is encoded prior to transmission
• Encoding uses 4 of 5 group code known as 4B/5B
• Every 4 bit group (16 different combinations) is mapped onto a 5 bit code (symbol)
• 5B symbols for 4B data groups are chosen such that a maximum of 2 successive zeros
occur
• 5B symbols which are not used for data encoding are used as control symbols symbols such as 0001, 00010 ... are not used
• Multi-Level Transmit-3 levels or MLT-3 (actual physical transmission
on the wire.
– No transition = 0
– Any transition (up or down) = 1
7.1 10-Mbps and 100-Mbps Ethernet
7.1.8 100BaseFX
• Fiber was developed because it could be used in places
that were noisy AND/OR to overcome distance
limitations.
• 100BASE-FX was never adopted successfully. This was due to the
timely introduction of Gigabit Ethernet copper and fiber standards.
– Gigabit Ethernet standards are now the dominant technology for
• backbone installations
• high-speed cross-connects
• general infrastructure needs.
• The timing, frame format, and transmission are all common to both
versions of 100 Mbps Fast Ethernet.
7.1 10-Mbps and 100-Mbps Ethernet
7.1.9 100Mbps Architecture
• Fast Ethernet links generally consist of a connection between a
station and a hub or switch.
• Design is similar to 10 Mbps Ethernet
• Unlike 10 Mbps Ethernet, No allowance for additional delay
• Hierarchical design is best
• Class 1 repeater
– Any repeater that changes between one Ethernet implementation and
another
– Introduces 140 bit times of latency
7.2 Gigabit and 10 Gigabit Ethernet
7.2.1 1000 Mbps Ethernet
• 1000Base-X (802.3z)
– 1Gbps full-duplex over optical fiber
• 1000BASE-TX, 1000BASE-SX, and 1000BASE-LX use the same
timing parameters
• The Gigabit Ethernet frame has the same format as is used for 10
and 100-Mbps Ethernet.
•
The differences between standard Ethernet, Fast Ethernet and Gigabit
Ethernet occur at the physical layer.
•
Since the bits are introduced on the medium for a shorter duration and more
often, timing is critical.
•
Gigabit Ethernet to use two separate encoding steps.
– 8B/10B (similar to 4B/5B)
– Non-Return to Zero line encoding
7.2 Gigabit and 10 Gigabit Ethernet
7.2.1 1000 Mbps Ethernet Cont.
Parameter
Bit Time
Slot Time
Interframe Spacing
Collision Attempt Limit
Collision Backoff Limit
Collision Jam Size
Max. Untagged Frame Size
Minimum Frame size
Burst Limit
Value
.1ns
4096 bit times
96 bit times
16
10
32
1518
512 Bits (64 octets)
65,536 bits
7.2 Gigabit and 10 Gigabit Ethernet
7.2.2 1000BaseT
• was developed to provide additional bandwidth to help alleviate
these bottlenecks
• provided more "speed" for applications such as
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intra-building backbones
inter-switch links
server farms
other wiring closet applications
connections for high-end workstations.
• One of the most important attributes of the 1000BASE-T standard is
that it be interoperable with 10BASE-T and 100BASE-TX.
7.2 Gigabit and 10 Gigabit Ethernet
7.2.2 1000BaseT Cont.
• Uses all four pairs to transmit data
– Each pair can transmit up to 125 Mbps in half-duplex (250 Mbps in full
duplex)
– Four pair multiplied by 250 Mbps equals 1000 Mbps
– Required complex circuitry to allow full duplex on the same wire pair
• The data from the sending station is carefully divided into four
parallel streams, encoded, transmitted and detected in parallel, and
then reassembled into one received bit stream.
• Uses 8B/10B frame encoding
• 4D-PAM5 line encoding
– 9 voltages states in idle
– 17 voltage states during transmission
7.2 Gigabit and 10 Gigabit Ethernet
7.2.3 1000Base-SX and -LX
• The IEEE 802.3 standard recommends that Gigabit Ethernet over
fiber be the preferred backbone technology.
• The timing, frame format, and transmission are common to all
versions of 1000 Mbps
• The 8B/ 10B scheme is used for optical fiber and shielded copper
media
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Pulse Amplitude Modulation is used for UTP
Both use NRZ line encoding
1000BaseSX
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Uses Short Wavelenth (850nm laser OR LED)
Multimode
Shorter distances
Lower cost
7.2 Gigabit and 10 Gigabit Ethernet
7.2.3 1000Base-SX and –LX Cont.
• 100BaseLX
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Uses Longer Wavelenth (1310nm laser)
Single mode OR Multimode
Longer distances (up to 5000m)
Higher cost
• The Media Access Control method treats the link as point-to-point.
• Since separate fibers are used for transmitting (Tx) and receiving
(Rx) the connection is inherently full duplex.
• Gigabit Ethernet permits only a single repeater between two stations.
7.2 Gigabit and 10 Gigabit Ethernet
7.2.4 Gigabit Ethernet Architecture
• The distance limitations of full-duplex links are only limited by the
medium, and not the round-trip delay
• Most Gigabit Ethernet is switched
• Daisy-chaining, star, and extended star topologies are all allowed.
• The issue then becomes one of logical topology and data flow, not
timing or distance limitations.
• Modification of the architecture rules is strongly discouraged for
1000BASE-T.
• At 100 meters, 1000BASE-T is operating close to the edge of the
ability of the hardware to recover the transmitted signal.
7.2 Gigabit and 10 Gigabit Ethernet
7.2.5 10 Gigabit Ethernet
• IEEE 802.3ae was adapted to include 10 Gbps full-duplex
transmission over fiber optic cable.
• With the frame format and other Ethernet Layer 2 specifications
compatible with previous standards, 10GbE can provide increased
bandwidth needs that are interoperable with existing network
infrastructure.
• A major conceptual change for Ethernet is emerging with 10GbE.
– No longer is Ethernet considered a LAN technology
– Up to 40km
7.2 Gigabit and 10 Gigabit Ethernet
7.2.5 10 Gigabit Ethernet Cont.
• How does 10GbE compare to other varieties of
Ethernet?
– Frame format is the same, allowing interoperability between all varieties of
legacy, fast, gigabit, and 10 Gigabit, with no reframing or protocol
conversions.
– Bit time is now 0.1 nanoseconds. All other time variables scale accordingly.
– Since only full-duplex fiber connections are used, CSMA/CD is not
necessary
– The IEEE 802.3 sublayers within OSI Layers 1 and 2 are mostly preserved,
with a few additions to accommodate 40 km fiber links and interoperability
with SONET/SDH technologies.
– Flexible, efficient, reliable, relatively low cost end-to-end Ethernet networks
become possible.
– TCP/IP can run over LANs, MANs, and WANs with one Layer 2 Transport
method.
7.2 Gigabit and 10 Gigabit Ethernet
7.2.6 10 Gigabit Ethernet Architecture
•
The shorter bit time duration because of increased speed requires special
considerations
– For 10 GbE transmissions, each data bit duration is 0.1 nanosecond.
– This means there would be 1,000 GbE data bits in the same bit time as one data bit
in a 10-Mbps Ethernet data stream!
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Complex serial bit streams are used for all versions of 10GbE except for
10GBASE-LX4, which uses Wide Wavelength Division Multiplex (WWDM) to
multiplex four bit simultaneous bit streams as four wavelengths of light
launched into the fiber at one time.
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As with 10 Mbps, 100 Mbps and 1000 Mbps versions, it is possible to modify
some of the architecture rules slightly.
– Possible architecture adjustments are related to signal loss and distortion along the
medium.
– Due to dispersion of the signal and other issues the light pulse becomes undecipherable
beyond certain distances.
7.2 Gigabit and 10 Gigabit Ethernet
7.2.7 Future of Ethernet
• 40, 100, and 160 Gbps standards
• Copper and wireless media have certain physical and practical
limitations on the highest frequency signals that can be transmitted.
• The bandwidth limitations on optical fiber are extremely large and are
not yet being threatened.
– In fiber systems, it is the electronics technology (such as emitters and
detectors) and fiber manufacturing processes that most limit the speed.
• Qos – Quality of Service Telephony