CCNA 1: Module 7 Ethernet Technologies

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.


7.1.1 10-Mbps Ethernet Cont.

Parameter Value

Bit Time 100ns

Slot Time 512 bit times

Interframe Spacing 96 bit times

Collision Attempt Limit 16

Collision Backoff Limit 10

Collision Jam Size 32

Max. Untagged Frame Size 1518

Minimum Frame size 512 Bits (64 octets)

• 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.



• Manchester Encoding– Up transition = 1– Down transition = 0



• The Original Ethernet (1980)– 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


7.1.2 10Base5 (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


7.1.3 10Base2 (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


7.1.4 10BaseT (LEGACY ETHERNET)

• 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.


7.1.5 10BaseT Wiring Architecture

• Two types– 100BaseTX (copper UTP media)– 100BaseFX (multimode fiber optic cable media)

• Three characteristics common to 100BASE-TX and 100BASE-FX are – 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.


7.1.6 100 Mbps Ethernet (FAST ETHERNET)


7.1.6 100 Mbps Ethernet (FAST ETHERNET) Cont.

Parameter Value

Bit Time 10ns








• 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


7.1.7 100BaseTX

• 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


7.1.7 100BaseTX Encoding

• 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.


7.1.8 100BaseFX

• 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


7.1.9 100Mbps Architecture

• 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


7.2.1 1000 Mbps Ethernet Cont.

Parameter Value

Bit Time .1ns








Burst Limit 65,536 bits

• was developed to provide additional bandwidth to help alleviate these bottlenecks

• provided more "speed" for applications such as– 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.


7.2.2 1000BaseT

• 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


7.2.2 1000BaseT Cont.

• 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

• Pulse Amplitude Modulation is used for UTP

• Both use NRZ line encoding

• 1000BaseSX– Uses Short Wavelenth (850nm laser OR LED)– Multimode– Shorter distances– Lower cost


7.2.3 1000Base-SX and -LX

• 100BaseLX– 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.


7.2.3 1000Base-SX and –LX Cont.

• 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.


7.2.4 Gigabit Ethernet Architecture

• 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


7.2.5 10 Gigabit Ethernet

• 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.


7.2.5 10 Gigabit Ethernet Cont.

• 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!

• 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.

• 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.


7.2.6 10 Gigabit Ethernet Architecture

• 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


7.2.7 Future of Ethernet

Documents

CCNA 1: Module 7 Ethernet Technologies