CCNA 1 and 2 Companion Guide, Revised (Cisco Networking Academy Program) part 38 ppt

1000BASE-T Goals for 1000BASE-T introduced as 802.3ab-1999 1000BASE-T Gigabit Ethernet over twisted-pair included these: ■ Capability to function over existing Category 5 copper cable pl

Bit patterns from the MAC sublayer are converted into symbols, with symbols

some-times controlling information (such as start frame, end frame, and medium idle

condi-tions) The entire frame is broken up into control symbols and data symbols (data code

groups) All of this extra complexity is necessary to achieve the tenfold increase in

net-work speed over Fast Ethernet For 1000BASE-T, the first part of the encoding uses a

technique called 8Bit-1Quinary quarter (8B1Q4); the second part of the encoding is

the actual line encoding specific to copper, called 4-dimensional 5 level pulse amplitude

modulation (4D-PAM5) The 8B1Q4 encoding followed by the 4D-PAM5 line

encod-ing provide the synchronization, bandwidth, and SNR characteristics needed to make

possible the four wire pairs (working in parallel) running full duplex on each wire pair

simultaneously For 1000BASE-X, 8-bit/10-bit (8B/10B) encoding (similar to the 4B/

5B concept) is used, followed by the simple NRZ line encoding of light on optical fiber

1000BASE-T

Goals for 1000BASE-T (introduced as 802.3ab-1999 1000BASE-T Gigabit Ethernet

over twisted-pair) included these:

■ Capability to function over existing Category 5 copper cable plants

■ Assurance that this cable would work by passing a Category 5e test, which

most cable can pass after a careful retermination

■ Applications such as building backbones, interswitch links, wiring closet

applica-tions, server farms, and high-end desktop workstations

■ Provision of 10x bandwidth of Fast Ethernet, which became very widely installed

by end users, helping to necessitate more speed upstream in the network

To achieve this speed running over Category 5e copper cable, 1000BASE-T needed

to use all four pairs of wires Category 5e cable reliably can carry up to 125 Mbps of

traffic Using sophisticated circuitry, full-duplex transmissions on the same wire pair

allow 250 Mbps per pair; multiplied by four wire pairs, this gives a total of 1000 Mbps

(1 Gbps) For some purposes, it is helpful to think of these four wire pairs as “lanes”

over which the data travels simultaneously (to be reassembled carefully at the receiver)

The timing, frame format, and transmission were described previously in Chapter 5

and are common to all versions of 1000-Mbps Ethernet considered here

1000BASE-T uses 8B1Q4 encoding with 4D-PAM5 line encoding on Cat 5e or better

UTP Achieving the 1-Gbps rate required use of all four pairs in full-duplex

simulta-neously This results in a permanent collision on the wire pairs, which is very different

from the first coaxial Ethernet systems The “permanent” collisions—transmission and

receipt of data happens in both directions on the same wire at the same time—results

in very complex voltage patterns But using sophisticated integrated circuits, which,

among other things, use a technique called echo cancellation, works well.

Despite the constant collision of the signals, the system is capable of operating through

a careful selection of voltage levels and use of Layer 1 forward error correction (FEC) Figure 6-17 shows the outbound (transmitting [Tx]) 1000BASE-T signal (the y-axis is voltage; the x-axis is the time taken from an oscilloscope—voltage is a “differential sig-nal” measured between two paired wires in one of the four pairs present in UTP cable)

Figure 6-17 Outbound (Tx) 1000BASE-T Signal

Figure 6-18 shows actually 1000BASE-T signal captured with a digital storage oscillo-scope after several meters of cable (the y-axis is voltage; the x-axis is time—voltage is

a “differential signal” measured between two paired wires in one of the four pairs present in UTP cable)

Figure 6-18 Actual 1000BASE-T Signal

It is quite remarkable that the signal can be recovered at all when it is revealed that during idle periods, there are nine voltage levels found on the cable, and during data transmission periods, there are 17 voltage levels on the cable Note the complex line encoding to begin with Then, in Figure 6-18, look at the actual signal on the wire with constant collisions, as well as attenuation effects and noise The signal looks analog The key here is that sophisticated circuitry is decoding all of this However, the system

is susceptible to cable problems, termination problems, and noise unless standards are followed Gigabit Ethernet works very well if the cabling, termination, and noise guidelines are followed

Table 6-8 summarizes the use of all four pairs in the UTP cable A, B, C, and D could

be considered “lanes” of data The data from the sending station carefully is divided into four parallel streams, encoded, transmitted and detected in parallel, and then reas-sembled into one received bit stream

Figure 6-19 is a schematic representation of simultaneous full-duplex on four wire

pairs Station-to-station, switch-to-switch, and station-to-switch cabling connections

are the same as in Fast Ethernet

Figure 6-19 1000BASE-T Signal Transmission

Table 6-8 1000BASE-T Pinout

6 4

4

6

6 4

4

6

6 4

4

6

6 4

4 6

It is especially important to desktop, office, and wiring closet applications that there be interoperability among Gigabit, Fast, and 10BASE-T Ethernet This might seem to be a hopeless affair But upon close inspection, note that if the cabling installed in the walls tests out (as it often does or easily can be made to by retermination) at Category 5e and if all eight wires in the RJ-45 connectors and jacks are connected, the signal paths exists for Gigabit, Fast, and 10BASE-T Ethernet to interoperate Just as 10/100 devices emerged in Fast Ethernet, 10/100/1000 interfaces have been developed for interopera-bility By using the same frame format, compatible wiring paths, and clever interface engineering, it all works well

For historical reasons, CSMA/CD and half duplex are options on 1000BASE-T But the overwhelming use of 1000BASE-T is full duplex This is accomplished with sophis-ticated hybrid circuits that can act as Tx and Rx at the same time for the same wires Before communications can begin, the two link partners must determine which will source the master clock and which will use the data stream to recover the slave clock The master clock and slave clock are used as time markers for signal transmission This process usually is determined during autonegotiation, although it can be config-ured manually A number of other parameters also are determined in the same manner, including duplex type Autonegotiation usually determines that a multiport device (a switch or hub) should become the master clock The overall message here is that with the 1 nanosecond bit-times, 1 billion bps data transfer rate, and four wire pairs simul-taneously transmitting and receiving, synchronization is extremely important

When the topic of 1000BASE-X (1000BASE-SX and 1000BASE-LX) is presented, comparisons with 1000BASE-T architecture are included

1000BASE-SX and 1000BASE-LX

Gigabit Ethernet over fiber is one of the most recommended backbone technologies Its benefits are tremendous:

■ 1000-Mbps data transfer, which can aggregate groupings of widely deployed Fast Ethernet devices

■ Lack of any ground potential problems between floors or buildings

■ An explosion in 1000BASE-X device options

■ Excellent distance characteristics Gigabit Ethernet over fiber originally was introduced in the IEEE 802.3 supplement entitled “802.3z-1998 1000BASE-X Gigabit Ethernet.” The only application for which 1000BASE-SX and 1000BASE-LX has not caught on as rapidly is the office

desktop—1000BASE-TX is considered more “user-proof” in terms of day-to-day wear,

and 10-/100-/1000-Mbps copper interfaces are common

The timing, frame format, and transmission were described previously in Chapter 5

and are common to all versions of 1000-Mbps Ethernet considered here

1000BASE-X uses 8B/10B encoding converted to NRZ line encoding, with either

lower-cost short-wavelength 850 nm laser (or sometimes LED) sources and multimode

optical fiber (1000BASE-SX, S for short), or long-wavelength 1310 nm laser sources

and single-mode optical fiber (1000BASE-LX, L for long)

NRZ encoding relies on the signal level found in the timing window to determine the

binary value for that bit period Unlike most of the other encoding schemes described,

this encoding system is level-driven instead of edge-driven.

In the encoding example in Figure 6-20, one timing window is highlighted vertically

through all four waveform examples The top waveform is low across the timing

win-dow A low signal level represents a binary 0 A single 1 was introduced at the end of

the waveform to show the other signal level

Figure 6-20 NRZ Encoding Example

The second waveform is high across the timing window A high signal level represents

a binary 1 Again, a single 0 was introduced at the end of the waveform to show the

other signal level Instead of a repeating sequence of the same binary value in the third

waveform, there is an alternating binary sequence In this example, it is more obvious

that a low signal level indicates a binary 0 and a high signal indicates a binary 1

0

1

1

0

0

1

0

1

0

1

0

1

0

1

1

0

0 0 0 0

1 1 One Bit Period

The fourth waveform example is random data Three of these examples are good examples of why this encoding scheme has the potential to cause dc voltage drift on copper media The second example is changing levels each bit period and would not suffer from dc voltage drift It is very easy for a string of the same binary signal to cause a dc voltage bias on the cable, which has the potential of causing clocking errors

On fiber media, this is not an issue

The NRZ-encoded serialized bit stream is ready for transmission using pulsed light as specified for 1000BASE-SX or 1000BASE-LX Because of cycle time problems related

to turning the transmitter completely on and off each time, the light is pulsed using low and high power A logical 0 is represented by low power, and a logical 1 is repre-sented by high power

Table 6-9 shows the amazingly simple interface-to-interface interconnection for Gigabit Ethernet over fiber SC fiber-optic connectors most commonly are used

Figure 6-21 shows the interface-to-interface connection for 1000BASE-SX Short-wavelength laser (or sometimes LED) sources typically are used with multimode optical fiber

Figure 6-21 1000BASE-SX Fiber Interface-to-Interface Connection

Figure 6-22 shows the interface-to-interface connection for 1000BASE-LX Laser sources typically are used with single-mode fiber to achieve distances of up to 5000m

Table 6-9 Interface-to-Interface Interconnection for Gigabit Ethernet

Fiber Interface A (NIC, Switch Port, É)

Multimode Fiber (MMF)

Sc or MTRJ Connector

Tx LED Rx Detector

Multimode Fiber (MMF)

Rx

LED Tx Detector

Fiber Interface B (NIC, Switch Port, É) Fiber Cable

1000Base-SX

Figure 6-22 1000BASE-LX Interface-to-Interface Connection

The MAC method used treats the link as point-to-point, and fiber is intrinsically full

duplex because separate Tx and Rx fibers Gigabit Ethernet permits a single repeater

between two stations

Gigabit Ethernet Architecture

Any device that adapts between different Ethernet speeds, such as between 100 Mbps

and 1000 Mbps, is an OSI Layer 2 bridge It is not possible to adapt between speeds

and still be a repeater

Full-duplex links can be substantially longer that what is shown in Tables 6-9 and 6-10

because they are limited only by the medium, not by the round-trip delay Gigabit

Ether-net architecture is overwhelmingly station-to-station, station-to-switch, switch-to-switch,

and switch-to-router connections running at full duplex 1000BASE-SX is specified for

multimode fiber 1000BASE-LX is specified for multimode and single-mode fiber

Tables 6-10 and 6-11 show distance limitations for 1000BASE-SX and 1000BASE-LX

Because most Gigabit Ethernet is switched, these are the practical limits between devices

Daisy-chaining, star, and extended star topologies all are allowed The issue then

becomes one of logical topology and data flow, not timing or distance limitations

Table 6-10 Maximum 1000BASE-SX Cable Distances

Medium

The maximum 1000BASE-SX cable distances at 805 nm (minimum overfilled launch).

Fiber Interface A (NIC, Switch Port, …)

Multimode Fiber (MMF)

Sc or MTRJ Connector Tx

Laser

Rx

Detector

Single-Mode Fiber

Rx

Laser Tx Detector

Fiber Interface B (NIC, Switch Port, …) Fiber Cable

1000BASE-LX

A 1000BASE-T UTP cable is about the same as a 10BASE-T and 100BASE-TX cable, except that link performance must meet the higher-quality Category 5e or ISO Class D (2000) requirements

As with 10-Mbps and 100-Mbps versions, it is possible to modify some of the architec-ture rules slightly; however, there is virtually no allowance for additional delay in half duplex Modification of the architecture rules strongly is discouraged for 1000BASE-T

At 100m, 1000BASE-T is operating close to the edge of the hardware’s capability to recover the transmitted signal Any cabling problems or environmental noise could render an otherwise-compliant cable inoperable even at distances that are within the specification Refer to the technical timing descriptions in the current 802.3 standard and the technical information about your hardware performance before attempting any adjustments to the architecture rules

Links operating in full-duplex links might be longer that what is indicated in Table 6-12 because they are limited only by the capability of the medium to deliver a robust enough signal to decode the signaling; they are not limited by the round-trip delay It is extremely rare to find Gigabit Ethernet operating in half duplex Half duplex is undesirable because the signaling scheme is inherently full duplex, and forcing half-duplex communications rules onto a full-duplex signaling system is not a wise use of resources Operating under half-duplex rules requires adherence to slot time round-trip delay limitations that reduce the effective cable lengths, and there is also a substantial increase in overhead introduced by the carrier extension Furthermore, very few Gigabit repeaters are in service, which means that the link is probably between a station and an OSI Layer 2 bridge, or between two bridges, so the collision domain would end at the bridge anyway

It is recommended that all links between a station and a switch be configured for auto-negotiation, to permit the highest common performance configuration to be established without risking misconfiguration of the link, and to avoid accidental misconfiguration

of the other required parameters for proper Gigabit Ethernet operation

Table 6-11 Maximum 1000BASE-LX Cable Distances

The maximum 1000BASE-LX cable distances at 805 nm (minimum overfilled launch).

Table 6-12 shows the speed case for half-duplex operation But because most Gigabit

Ethernet is switched, it is subject to link-by-link rules shown previously in Tables 6-10

and 6-11

10-Gbps Versions of Ethernet

Most recently, in 2002, IEEE 802.3ae was adapted This standard specifies 10-Gbps

full-duplex transmission over fiber-optic cable Taken as a whole, the similarities

between 802.3ae and 802.3 (the original Ethernet) and all of the other varieties of

Ethernet are remarkable Metcalfe’s original design has evolved, but it is still very

apparent in the modern Ethernet Recently, 10-Gb Ethernet (10GbE) has emerged as

the latest example of the extensibility of the Ethernet system Usable for LANs,

storage-area networks (SANs), metropolitan-storage-area networks (MANs), and WANs, 10GbE offers

exciting new networking possibilities What is 10GbE, and why should it be used?

Legacy Ethernet, Fast Ethernet, and Gigabit Ethernet now dominate the LAN market

The next step in the evolution of Ethernet is to move to 10-Gb Ethernet (10GbE,

oper-ating at 10,000,000,000 bps) By maintaining the frame format and other Ethernet

Layer 2 specifications, increasing bandwidth needs can be accommodated with the

low-cost, easily implementable, and easily interoperable 10GbE 10GbE runs only over

optical fiber media End-to-end Ethernet networks become possible

Because of massive growth in Internet- and intranet-based traffic, and the rapidly

increas-ing use of Gigabit Ethernet, even higher bandwidth interconnections are needed Internet

service providers (ISPs) and network service providers (NSPs) can use 10GbE to create

high-speed, low-cost, easily interoperable connections between colocated carrier switches

and routers Points of presence (POPs), intranet server farms comprised of Gigabit

Ethernet servers, digital video studios, SANs, and backbones already are envisaged

applications

Perhaps most significantly, a major conceptual change comes with 10GbE Ethernet

traditionally is thought of as a LAN technology But 10GbE physical layer standards

allow both an extension in distance (to 40 km over single-mode fiber) and compatibility

Table 6-12 Architecture Configuration Cable Distances for Half-Duplex Operation

Architecture 1000BASE-T 1000BASE-SX/LX

1000BASE-SX/LX and 1000BASE-T

110m 1000BASE-SX/LX

with Synchronous Optical Network (SONET)/Synchronous Digital Hierarchy (SDH) networks Operation at a 40 km distance makes 10GbE a viable MAN technology Compatibility with SONET/SDH networks operating up to OC-192 speeds (9.584640 Gps) makes 10GbE a viable WAN technology 10GbE also might com-pete with Asynchronous Transfer Mode (ATM) for certain applications

The following summarizes how 10GbE compares to other varieties of Ethernet:

■ Frame format is the same, allowing interoperability among all varieties of legacy, Fast, Gigabit, and 10-Gb Ethernet, with no reframing or protocol conversions

■ Bit-time now at 0.1 nanoseconds All other time variables scale accordingly

■ No need for CSMA/CD because only full-duplex fiber connections are used

■ IEEE 802.3 sublayers within OSI Layers 1 and 2 that are mostly preserved, with

a few additions to accommodate 40-km fiber links and interoperability with SONET/SDH technologies

■ Possibility of flexible, efficient, reliable, relatively low cost end-to-end Ethernet networks

■ Capability to run TCP/IP over LANs, MANs, and WANs with one Layer 2 trans-port method

The basic standard governing CSMA/CD is IEEE 802.3 An IEEE 802.3 supplement, entitled 802.3ae, governs the 10GBASE family As is typical for new technologies, a variety of implementations are being considered, including these:

■ 10GBASE-SR—Intended for short distances over already-installed multimode

fiber, supports a range between 26 m and 82 m

■ 10GBASE-LX4—Useswavelength-division multiplexing (WDM) Supports 240 m

to 300 m over already-installed multimode fiber, and 10 km over single-mode fiber

■ 10GBASE-LR and 10GBASE-ER—Supports 10 km and 40 km over single-mode

fiber

OC-192/STM SONET/SDH WAN equipment

The IEEE 802.3ae task force and the 10-Gb Ethernet Alliance (10 GEA) are working

to standardize these emerging technologies

10-Gb Ethernet (IEEE 802.3ae) was standardized in June 2002 It is a full-duplex protocol that uses only fiber-optic fiber as a transmission medium The maximum transmission distances depend on the type of fiber being used When using single-mode fiber as the transmission medium, the maximum transmission distance is 40 km (25 miles) Some discussions between IEEE members suggest the possibility of standards for 40-Gbps, 80-Gbps, and even 100-Gbps Ethernet Given the history of Ethernet, there is no reason