CHAPTER-1
INTRODUCTION
1.1 GENERAL
INTRODUCTION
From its origin more than 25 years
ago, Ethernet has evolved to meet the increasing demands of packet-switched
networks. Due to its proven low implementation cost, its known reliability, and
relative simplicity of installation and maintenance, its popularity has grown
to the point that today nearly all traffic on the Internet originates or ends
with an Ethernet connection. Further, as the demand for ever-faster network speeds
has grown, Ethernet has been adapted to handle these higher speeds and the concomitant
surges in volume demand that accompany them. The One Gigabit Ethernet standard
is already being deployed in large numbers in both corporate and public data
networks, and has begun to move Ethernet from the realm of the local area network
out to encompass the metro area network. Meanwhile, an even faster 10 Gigabit
Ethernet standard is nearing completion. This latest standard is being driven
not only by the increase in normal data traffic but also by the proliferation
of new, bandwidth-intensive applications.
The
draft standard for 10 Gigabit Ethernet is significantly different in some
respects from earlier Ethernet standards, primarily in that it will only
function over optical fiber, and only operate in full-duplex mode, meaning that
collision detection protocols are unnecessary. Ethernet can now step up to 10
gigabits per second, however, it remains Ethernet, including the packet format,
and the current capabilities are easily transferable to the new draft
standard.In addition, 10 Gigabit Ethernet does not obsolete current investments
in network infrastructure. The task force heading the standards effort has
taken steps to ensure that 10 Gigabit Ethernet is interoperable with other
networking technologies such as SONET. The standard enables Ethernet packets to
travel across SONET links with very little inefficiency.Ethernet’s expansion
for use in metro area networks can now be expanded yet again onto wide area
networks, both in concert with SONET and also end-to-end Ethernet. With the
current balance of network traffic today heavily favoring packet-switched data
over voice, it is expected that the new 10 Gigabit Ethernet standard will help
to create a convergence between networks designed primarily for voice, and the
new data centric networks.
Ethernet is a family of frame-based computer networking
technologies for local area networks (LANs). The name comes
from the physical concept of the ether. It defines a number of wiring and
signaling standards for the Physical
Layer of the OSI networking model, through means of network
access at the Media Access Control protocol (a sub-layer
of Data Link Layer), and a common addressing
format.
Ethernet is standardized
as IEEE 802.3.
The combination of the twisted pair versions of Ethernet for
connecting end systems to the network, along with the fiber optic
versions for site backbones, is the most widespread wired LAN
technology. It has been in use from around 1980 to the present, largely
replacing competing LAN standards such as token ring,
FDDI, and ARCNET.
1.2 History
Ethernet
was developed at Xerox PARC between 1973 and 1975. In 1975, Xerox filed a patent
application listing Robert Metcalfe, David Boggs,
Chuck Thacker
and Butler Lampson as inventors, U.S. Patent 4,063,220
"Multipoint data communication system (with collision detection)". In
1976, after the system was deployed at PARC, Metcalfe and Boggs published a
seminal paper.
The experimental Ethernet
described in the 1976 paper ran at 3,000,000 bits per
second (3 Mbit/s) and had eight-bit destination and source address
fields, so the original Ethernet addresses were not the MAC addresses they are today. By software
convention, the 16 bits after the destination and source address fields
specified a "packet type", but, as the paper says, "different
protocols use disjoint sets of packet types". Thus the original packet
types could vary within each different protocol, rather than the packet type in
the current Ethernet standard which specifies the protocol being used.
Metcalfe left Xerox in
1979 to promote the use of personal
computers and local area networks (LANs), forming 3Com. He convinced DEC, Intel, and Xerox to work
together to promote Ethernet as a standard, the so-called "DIX"
standard, for "Digital/Intel/Xerox"; it specified the
10 megabits/second Ethernet, with 48-bit destination and source addresses
and a global 16-bit type field. The first standard draft was first published on
September 30, 1980 by the Institute of
Electrical and Electronics Engineers (IEEE). It competed with two
largely proprietary systems, Token Ring and Token Bus.
To get over delays of the finalization of the Ethernet "Carrier sense
multiple access with collision detection" (CSMA/CD) standard
due to the difficult decision processes in the "open" IEEE, and due
to the competitive Token Ring proposal strongly supported by IBM, support of CSMA/CD in
other standardization bodies (i.e. ECMA, IEC and ISO) was instrumental to
its success. The proprietary systems soon found themselves
buried under a tidal wave of Ethernet products. In the process, 3Com became a
major company. 3COM built the first 10 Mbit/s Ethernet adapter (1981). This was
followed quickly by DEC's Unibus to Ethernet adapter, which DEC sold and used internally
to build its own corporate network, reaching over 10,000 nodes by 1986, far and
away the largest then extant computer network in the world.
The advantage of CSMA/CD
was that, unlike Token Ring and Token Bus, all nodes could "see" each
other directly. All "talkers" shared the same medium - a single coaxial cable
- however, this was also a limitation; with only one speaker at a time, packets
had to be of a minimum size to guarantee that the leading edge of the
propagating wave of the message got to all parts of the medium before the
transmitter could stop transmitting, thus guaranteeing that collisions
(two or more packets initiated within a window of time which forced them to
overlap) would be discovered. Minimum packet size and the physical medium's
total length were thus closely linked.
Through the first half of
the 1980s, Digital's ethernet implementation utilized a coaxial cable about the
diameter of a US nickel (5¢ coin) which became known as "thick wire
ethernet" when its successor, "thin wire ethernet" was introduced.
Thin-wire ethernet was in essence a high-quality version of the cable used on
closed-circuit television of the era. The emphasis was on making the physical
routing of cable easier, less costly, and, whenever possible, utilize existing
wiring. The observation that there was plenty of excess capacity in unused
"twisted pair" (sometimes "twisted copper") telephone
wiring already installed in commercial buildings provided another opportunity
to expand the installed base and thus twisted-pair ethernet was the next logical
development.
Twisted-pair Ethernet systems were
developed in the mid 1980s, beginning with StarLAN,
and become widely known with 10BASE-T. These systems replaced the
coaxial cable on which early Ethernets were deployed with a system of hubs
linked with unshielded twisted pair (UTP), ultimately replacing the
CSMA/CD scheme in favor of a switched full duplexsystem offering higher
performance.
1.3 General description
This is a combination
card that supports both coaxial-based using a 10BASE2
(BNC connector,
left) and twisted pair-based 10BASE-T,
using an RJ45
(8P8C modular
connector, right).
Figure 1.2: A 1990s network
interface card.
Ethernet was originally
based on the idea of computers communicating over a shared coaxial cable
acting as a broadcast transmission medium. The methods used show some
similarities to radio systems, although there are fundamental differences, such
as the fact that it is much easier to detect collisions in a cable broadcast
system than a radio broadcast. The common cable providing the communication
channel was likened to the ether
and it was from this reference that the name "Ethernet" was derived.
From this early and
comparatively simple concept, Ethernet evolved into the complex networking
technology that today underlies most LANs. The coaxial cable was replaced with
point-to-point links connected by Ethernet hubs
and/or switches to reduce installation costs, increase
reliability, and enable point-to-point management and troubleshooting. StarLAN
was the first step in the evolution of Ethernet from a coaxial cable bus to a
hub-managed, twisted-pair network. The advent of twisted-pair wiring
dramatically lowered installation costs relative to competing technologies,
including the older Ethernet technologies.
Above
the physical layer, Ethernet stations communicate by sending each other data
packets, blocks of data that are individually sent and delivered. As with other
IEEE 802
LANs, each Ethernet station is given a single 48-bit MAC address,
which is used to specify both the destination and the source of each data
packet. Network interface cards (NICs) or chips normally do not accept packets
addressed to other Ethernet stations. Adapters generally come programmed with a
globally unique address, but this can be overridden, either to avoid an address
change when an adapter is replaced, or to use locally administered addresses.Despite
the significant changes in Ethernet from a thick coaxial
cable bus running at 10 Mbit/s to point-to-point links running at 1
Gbit/s and beyond, all generations of Ethernet
(excluding early experimental versions) share the same frame formats (and hence
the same interface for higher layers), and can be readily interconnected.Due to
the ubiquity of Ethernet, the ever-decreasing cost of the hardware needed to
support it, and the reduced panel space needed by twisted pair
Ethernet, most manufacturers now build the functionality of an Ethernet card
directly into PC motherboards, eliminating the need for
installation of a separate network card.
CHAPTER-2
THEME: GIGABIT
ETHERNET
2.1 Ethernet
1.
Bridged Ethernet
2.
Switched Ethernet
3.
Fast Ethernet
4.
Gigabit Ethernet
Fig.2.1:Ethernet evolution through four generations
IEEE Project 802 (ETHERNET) has created a sublayer called Media Access Control (MAC) that defines the specific access
method for each LAN.
2.1.1 Bridged
Ethernet
The
first step in the Ethernet evolution was the division of a LAN by bridges.
Bridges have two effects on an Ethernet LAN: They raise the bandwidth and they
separate collision domains. In an
unbridged Ethernet network, the total capacity (10 Mbps) is shared among all
stations. The problem is if all the system want to transmit the data at same
time means the speed of the N/W will be decreased.A bridge divides the network
into two or more networks. Bandwidth-wise, each network is independent. For
example, a network with 12 stations is divided into two networks, each with 6
stations.
Now each network
has a capacity of 10 Mbps. The 10-Mbps capacity in each segment or subnet is now shared between 6 stations (actually 7
because the bridge acts as a station in each segment), not 12 stations.
In a network
with a heavy load, each station theoretically is offered 10/6 Mbps instead of
10/12 Mbps, assuming that the traffic is not going through the bridge.
if we further
divide the network, we can gain more bandwidth for each segment. For ex, if we
use a four-port bridge, each station is now offered 10/3 Mbps, which is 4 times
more than an unbridged network.
Fig.2.2:Without bridging
Fig.2.3: With bridging
2.1.2 Switched
Ethernet
The
idea of a bridged LAN can be extended to a switched LAN. Instead of having two
to four
networks, why not have N networks, where N is the number of stations on the
LAN? In other words, if we can have a multiple-port bridge, why not have an
N-port One of the limitations of 10Base5 and 10Base2 is that communication is
half-duplex a station can either send or receive, but may not do both at the
same time. (10Base-T is always full-duplex);
The
next step in the evolution was to move from switched Ethernet to full-duplex
switched Ethernet. The full-duplex mode increases the capacity of each domain
from 10 to 20 Mbps. Below figure shows a
switched Ethernet in full-duplex mode. Note that instead of using one link
between the station and the switch, the configuration uses two links: one to
transmit and one to receive.
Fig2.4: Switched
Ethernet
Fig.2.5: Full Duplex Switched Ethernet
2.1.3 FAST
ETHERNET / IEEE 802.3u
Fast
Ethernet was designed to compete with LAN protocols such as FDDI or Fiber
Channel. IEEE created Fast Ethernet under the name 802.3u.
The goals of
Fast Ethernet can be summarized as follows:
1. Upgrade the
data rate to 100 Mbps.
2. Make it
compatible with Standard Ethernet.
3. Keep the same
48-bit address.
4. Keep the same
frame format.
5. Keep the same
minimum and maximum frame lengths.
2.1.4 GIGABIT
ETHERNET / IEEE 802.3z
The
goals of the Gigabit Ethernet design can
be summarized as follows:
1. Upgrade the
data rate to 1 Gbps.
2. Make it
compatible with Standard or Fast Ethernet.
3. Use the same
48-bit address.
4. Use the same
frame format.
5. Keep the same
minimum and maximum frame lengths.
6. To support
autonegotiation as defined in Fast Ethernet.
2.1.5 Ten-Gigabit
Ethernet
The
IEEE committee created Ten-Gigabit Ethernet and called it Standard 802.3ae.
The goals of the Ten-Gigabit Ethernet design can
be summarized as follows:
1. Upgrade the
data rate to 10 Gbps.
2. Make it
compatible with Standard, Fast, and Gigabit Ethernet.
3. Use the same
48-bit address.
4. Use the same
frame format.
5. Keep the same
minimum and maximum frame lengths.
6. Allow the
interconnection of existing LANs into a metropolitan area network (MAN)
or a wide area
network (WAN).
7. Make
Ethernet compatible with technologies such as Frame Relay and ATM.
2.2 GIGABIT
ETHERNET TECHNOLOGY
The Gigabit Ethernet Alliance was
established in order to promote standards-based Gigabit Ethernet technology and
to encourage the use and implementation of Gigabit Ethernet as a key networking
technology for connecting various computing, data and telecommunications
devices. The charter of the Gigabit Ethernet Alliance includes Supporting the Gigabit
Ethernet standards effort conducted in the IEEE 802.3 working group
Contributing resources to facilitate convergence and consensus on technical.
Promoting industry awareness, acceptance, and
advancement of the 10 Gigabit Ethernet standard. Accelerating the adoption and
usage of 10 Gigabit Ethernet products and services. Providing resources to
establish and demonstrate multi-vendor interoperability and generally encourage
and promote interoperability and interoperability events. Fostering
communications between suppliers and users of 10 Gigabit Ethernet technology
and products.
2.3
Gigabit Ethernet Alliance
The purpose of the Gigabit
Ethernet proposed standard is to extend the 802.3 protocols to an operating
speed of 10 Gbps and to expand the Ethernet application space to include WAN
links. This will provide for a significant increase in bandwidth while
maintaining maximum compatibility with the installed base of 802.3 interfaces,
previous investment in research and development, and principles of network
operation and management.
In order to be adopted as a
standard, the IEEE’s 802.3ae Task Force has established five criteria that the
new 10 Gigabit Ethernet P (proposed) standard must meet:
It must have broad market potential, supporting
a broad set of applications, with multiple vendors supporting it, and multiple
classes of customers.It must be compatible with other existing 802.3 protocol
standards, as well as with both Open Systems Interconnection (OSI) and Simple
Network Management Protocol (SNMP) management specifications.
It must be substantially different from other
802.3 standards, making it a unique solution for a problem rather than an
alternative solution.It must have demonstrated technical feasibility prior to
final ratification. It must be economically feasible for customers to deploy,
providing reasonable cost, including all installation and management costs, for
the expected performance increase.
2.4 Gigabit Ethernet Standard
Under
the International Standards Organization’s Open Systems Interconnection (OSI)
model, Ethernet is fundamentally a Layer 2 protocol. 10 Gigabit Ethernet uses
the IEEE 802.3 Ethernet Media Access Control (MAC) protocol, the IEEE 802.3
Ethernet frame format, and the minimum and maximum IEEE 802.3 frame size. Just
as 1000BASE-X and 1000BASE-T (Gigabit Ethernet) remained true to the Ethernet
model, 10 Gigabit Ethernet continues the natural evolution of Ethernet in speed
and distance. Since it is a full-duplex only and fiber-only technology, it does
not need the carrier-sensing multiple-access with collision detection (CSMA/CD)
protocol that defines slower, half-duplex Ethernet technologies. In every other
respect, 10 Gigabit Ethernet remains true to the original Ethernet model.
An
Ethernet PHYsical layer device (PHY), which corresponds to Layer 1 of the OSI
model, connects the media (optical or copper) to the MAC layer, which
corresponds to OSI Layer 2. Ethernet architecture further divides the PHY
(Layer 1) into a Physical Media Dependent (PMD) and a Physical Coding Sublayer
(PCS). Optical transceivers, for example, are PMDs. The PCS is made up of
coding (e.g., 64/66b) and a serializer or multiplexing functions.
The
802.3ae specification defines two PHY types: the LAN PHY and the WAN PHY
(discussed below). The WAN PHY has an extended feature set added onto the
functions of a LAN PHY. These PHYs are solely distinguished by the PCS. There
will also be a number of PMD types.
Fig. 2.6:The
architectural components of the 802.3ae standard
2.5 Gigabit Ethernet in the Marketplace
The accelerating growth of worldwide network traffic is
forcing service providers, enterprise network managers and architects to look
to ever higher-speed network technologies in order to solve the bandwidth
demand crunch. Today, these administrators typically use Ethernet as their
backbone technology. Although networks face many different issues, Gigabit
Ethernet meets several key criteria for efficient and effective high-speed
networks: Easy, straightforward migration to higher performance levels without disruption,
Lower cost of ownership vs. current alternative technologies – including both acquisition
and support costs Familiar management tools and common skills base .Ability to
support new applications and data types Flexibility in network design. Multiple
vendor sourcing and proven interoperability. Managers of enterprise and service
provider networks have to make many choices when they design networks. They
have multiple media, technologies, and interfaces to choose from to build
campus and metro connections: Ethernet (100, 1000,and 10,000 Mbps), OC-12 (622
Mbps) and OC-48 (2.488 Gbps), SONET or equivalent SDH network, packet over
SONET/SDH (POS), and the newly authorized IEEE 802 Task Force (802.17) titled
Resilient Packet Ring.Network topological design and operation has been
transformed by the advent of intelligent Gigabit Ethernet multi-layer switches.
In LANs, core network technology is rapidly shifting to Gigabit Ethernet and
there is a growing trend towards Gigabit Ethernet networks that can operate
over metropolitan area distances. The next step for enterprise and service
provider networks is the combination of multi-gigabit bandwidth with
intelligent services, leading to scaled, intelligent, multi-gigabit networks
with backbone and server connections ranging up to 10 Gbps.
In
response to market trends, Gigabit Ethernet is currently being deployed over
tens of kilometers in private networks. With 10 Gigabit Ethernet, the industry
has developed a way to not only increase the speed of Ethernet to 10 Gbps but
also to extend its operating distance and interconnectivity. In the future,
network managers will be able to use 10 Gigabit Ethernet as a cornerstone for
network architectures that encompass LANs, MANs and WANs using Ethernet as the
end-to-end, Layer 2 transport method.
Ethernet
bandwidth can then be scaled from 10 Mbps to 10 Gbps – a ratio of 1 to 1000 —
without compromising intelligent network services such as Layer 3 routing and
layer 4 to layer 7 intelligence, including quality of service (QoS), class of
service (CoS), caching, server load balancing, security, and policy based
networking capabilities. Because of the uniform nature of Ethernet across all
environments when IEEE 802.3ae is deployed, these services can be delivered at
line rates over the network and supported over all network physical
infrastructures in the LAN, MAN, and WAN. At that point, convergence of voice
and data networks, both running over Ethernet, becomes a very real option. And,
as TCP/IP incorporates enhanced services and features, such as packetized voice
and video, the underlying Ethernet can also carry these services without
modification.As we have seen with previous versions of Ethernet, the cost for
10 Gbps communications has the potential to drop significantly with the
development of new technologies. In contrast to 10 Gbps telecommunications
lasers, the 10 Gigabit Ethernet short links — less than 40km over single-mode
(SM) fiber — will be capable of using lower cost, uncooled optics and, in some
cases, vertical cavity surface emitting lasers (VCSEL), which have the
potential to lower PMD costs. In addition, the industry is supported by an
aggressive merchant chip market that provides highly integrated silicon
solutions. Finally, the Ethernet market tends to spawn highly competitive
start-ups with each new generation of technology to compete with established
Ethernet vendors.
2.6 Interoperability Demos
One of the keys to Ethernet’s success is the widespread
interoperability between vendors. In keeping with its mission to provide
resources to establish and demonstrate multi-vendor interoperability of 10
Gigabit Ethernet products, the 10 GEA hosted the world’s largest 10 Gigabit
Ethernet Interoperability Network in May, 2002. The live, multi-vendor network
was on display at the NetWorld+Interop trade show in Las Vegas, Nevada. The
network will also be on display at SuperComm, June 4-7, 2002in Atlanta
Georgia.Comprised of products from 23 vendors, the network included a
comprehensive range of products: systems, test equipment, components and
cabling. The end-to-end 10GbE network was over 200 kilometers long and
showcased five of the seven PMD port types specified in the IEEE 802.3ae draft:
10GBASE-LR, 10GBASE-ER, 10GBASE-SR 10GBASE-LW and 10GBASE-LX4.The network
boasted 10 network hops, 18 10 GbE links, and represented all aspects of the
technology; WAN, MAN and LAN.As part of the demonstration 12 companies showed
chip-to-chip communication over the IEEE 802.3ae XAUI interface.The collection
of products and technologies illustrate years of industry collaboration and
signal to the market that 10 Gigabit Ethernet is ready to be deployed and
implemented into networks around the world.
Fig. 2.7:world’s largest 10 Giggabit Ethernet interperability Demonstration
2.7 Applications
for 10 Gigabit Ethernet
2.7.1 Ten Gigabit Ethernet in the Metro
Vendors and users generally agree that Ethernet is
inexpensive, well understood, widely deployed and backwards compatible from
Gigabit switched down to 10 Megabit shared. Today a packet can leave a server
on a short-haul optic Gigabit Ethernet port, move cross-country via a DWDM
(dense wave division multiplexing) network, and find its way down to a PC
attached to a “thin coax” BNC (Bayonet Neill Concelman) connector, all without
any re-framing or protocol conversion. Ethernet is literally everywhere, and 10
Gigabit Ethernet maintains this seamless migration in functionality.
Gigabit
Ethernet is already being deployed as a backbone technology for dark fiber
metropolitan networks. With appropriate 10 Gigabit Ethernet interfaces, optical
transceivers and single mode fiber, service providers will be able to build
links reaching40km or more. (See Figure 2.8)
Fig.2.8:Ten Gigabit Ethernet use in MAN
2.7.2 Gigabit Ethernet in Local
Area Networks
Ethernet
technology is already the most deployed technology for high performance LAN
environments. With the extension of 10 Gigabit Ethernet into the family of
Ethernet technologies, the LAN now can reach farther and support upcoming
bandwidth hungry applications. Similar to Gigabit Ethernet technology, the 10
Gigabit proposed standard supports both single mode and multi-mode fiber
mediums. However in 10 Gigabit Ethernet, the distance for single-mode fiber has
expanded from the 5km that Gigabit Ethernet supports to 40km in 10 Gigabit
Ethernet.
The
advantage for the support of longer distances is that it gives companies who manage
their own LAN environments the option of extending their data centers to more
cost-effective locations up to 40km away from their campuses. This also allows
them to support multiple campus locations within that 40km range. Within data
centers, switch-to-switch applications, as well as switch to server
applications, can also be deployed over a more cost effective multi-mode fiber
medium to create 10 Gigabit Ethernet backbones that support the continuous
growth of bandwidth hungry applications. (Fig2.9)
Fig2.9: 10 Gigabit Ethernet useExpanded LAN environment
With 10 Gigabit backbones
installed, companies will have the capability to begin providing Gigabit
Ethernet service to workstations and, eventually, to the desktop in order to
support applications such as streaming video, medical imaging, centralized
applications, and high-end graphics. 10 Gigabit Ethernet will also provide
lower network latency due to the speed of the link and over-provisioning
bandwidth to compensate for the bursty nature of data in enterprise
applications.
2.7.3 10 Gigabit Ethernet in the
Storage Area Network
Additionally, 10 Gigabit Ethernet
will provide infrastructure for both network-attached storage (NAS) and storage
area networks (SAN). Prior to the introduction of 10 Gigabit Ethernet, some
industry observers maintained that Ethernet lacked sufficient horsepower to get
the job done. Ethernet, they said, just doesn’t have what it takes to move
“dump truck loads worth of data.” 10 Gigabit Ethernet, can now offer equivalent
or superior data carrying capacity at similar latencies to many other storage
networking technologies including 1 or 2 Gigabit Fiber Channel, Ultra160 or 320
SCSI, ATM OC-3, OC-12 & OC-192,and HIPPI (High Performance Parallel
Interface). While Gigabit Ethernet storage servers, tape libraries and compute
servers are already available, users should look for early availability of 10
Gigabit Ethernet end-point devices in the second half of 2001.There are numerous
applications for Gigabit Ethernet in storage networks today, which will
seamlessly extend to 10 Gigabit Ethernet as it becomes available. (See Figure
2.10) These include:
·
Business
continuance/disaster recovery
·
Remote backup
·
Storage on demand
·
Streaming media
Fig2.10:Ten Gigabit Ethernet in the Storage
Area Network
2.7.4 Ten Gigabit Ethernet in Wide Area Networks
Gigabit
Ethernet will enable Internet service providers (ISP) and network service
providers (N SPs) to create very highspeed links at a very low cost, between
co-located, carrier-class switches and routers and optical equipment that is
directly attached to the SONET/SDH cloud. 10 Gigabit Ethernet with the WAN PHY
will also allow the construction of WANs that connect geographically dispersed
LANs between campuses or POPs (points of presence) over existing SONET/SDH/TDM
networks. 10 Gigabit Ethernet links between a service provider’s switch and a
DWDM (dense wave division multiplexing) device or LTE (line termination
equipment) might in fact be very short — less than 300 meters. (See Figure 2.11.)
Fig.2.11:Ten Gigabit
Ethernet in Wide Area Networks
2.8 The 10
Gigabit Ethernet Technology 10GbE Chip Interfaces
Among the many technical innovations of the 10 Gigabit
Ethernet Task Force is an interface called the XAUI (10 Gigabit Attachment Unit
Interface). It is a MAC-PHY interface, serving as an alternative to the XGMII
(10 Gigabit Media Independent Interface). XAUI is a low pin-count differential
interfaces that enables lower design costs for system vendors.The XAUI is
designed as an interface extender for XGMII, the 10 Gigabit Media Independent
Interface. The XGMII is a 74 signal wide interface (32-bit data paths for each
of transmit and receive) that may be used to attach the Ethernet MAC to its
PHY. The XAUI may be used in place of, or to extend, the XGMII in chip-to-chip
applications typical of most Ethernet MAC to PHY interconnects. (See Figure
2.12)
The
XAUI is a low pin count, self-clocked serial bus that is directly evolved from
the Gigabit Ethernet 1000BASE-X PHY. The XAUI interface speed is 2.5 times that
of 1000BASE-X. By arranging four serial lanes, the 4-bit XAUI interface
supports the ten-times data throughput required by 10 Gigabit Ethernet.
. 
Fig 2.12:Functions as an extender interface between the Mac and PCS
2.9 Physical Media Dependent (PMDS)
XAUI The IEEE 802.3ae Task Force
has developed a draft standard that provides a physical layer that supports
link distances for fiber optic media.To meet these distance objectives, four
PMDs were selected. The task force selected a 1310 nanometer serial PMD to meet
its 2km and 10km single-mode fiber (SMF) objectives. It also selected a 1550 nm
serial solution to meet (or exceed) its 40km SMF objective. Support of the 40km
PMD is an acknowledgement that Gigabit Ethernet is already being successfully
deployed in metropolitan and private, long distance applications. An 850
nanometer PMD was specified to achieve a 65-meter objectiveover multimode fiber
using serial 850 nm transceivers.
Additionally, the task
force selected two versions of the wide wave division multiplexing (WWDM) PMD,
a 1310 nanometer version over single-mode fiber to travel a distance of 10km
and a 1310 nanometer PMD to meet its 300-meter-over-installedmultimode- fiber
objective.The LAN PHY and the WAN PHY will operate over common PMDs and, therefore,
will support the same distances. These PHYs are distinguished solely by the
Physical Encoding Sublayer (PCS). The 10 Gigabit LAN PHY is intended to support
existing Gigabit Ethernet applications at ten times the bandwidth with the most
cost-effective solution. Over time, it is expected that the LAN PHY will be
used in pure optical switching environments extending over all WAN distances.
However, for compatibility with the existing WAN network, the 10 Gigabit
Ethernet WAN PHY supports connections to existing and future installations of
SONET/SDH (Synchronous Optical Network/ Synchronous Digital Hierarchy)
circuit-switched telephony access equipment.
The WAN
PHY differs from the LAN PHY by including a simplified SONET/SDH framer in the
WAN Interface Sublayer (WIS). Because the line rate of SONET OC-192/ SDH STM-64
is within a few percent of 10 Gbps, it is relatively simple to implement a MAC
that can operate with a LAN PHY at 10 Gbps or with a WAN PHY payload rate of
approximately 9.29 Gbps. (See Figure 9.). Appendix III provides a more in depth
look at the WAN PHY.
Fig.2.13:Conceptual diagram of PHY’s And PMD’s
2.10 Standardization
Notwithstanding its technical merits,
timely standardization was instrumental to the success of Ethernet. It required
well-coordinated and partly competitive activities in several standardization
bodies such as the IEEE, ECMA, IEC, and finally ISO.
In February 1980 IEEE started a project,
IEEE 802 for the standardization of Local Area Networks (LAN).
The "DIX-group" with Gary
Robinson (DEC), Phil Arst (Intel) and Bob Printis (Xerox) submitted the
so-called "Blue Book" CSMA/CD specification as a candidate for the
LAN specification. Since IEEE membership is open to all professionals including
students, the group received countless comments on this brand-new technology.In
addition to CSMA/CD, Token Ring (supported by IBM) and Token Bus (selected and
henceforward supported by General Motors) were also considered as
candidates for a LAN standard. Due to the goal of IEEE 802 to forward only one
standard and due to the strong company support for all three designs, the
necessary agreement on a LAN standard was significantly delayed.
In the Ethernet camp, it put at risk
the market introduction of the Xerox Star workstation
and 3Com's Ethernet LAN products. With such business implications in mind, David Liddle
(General Manager, Xerox Office Systems) and Metcalfe (3Com) strongly supported
a proposal of Fritz Röscheisen (Siemens Private Networks) for an alliance in the emerging
office communication market, including Siemens' support for the international
standardization of Ethernet (April 10, 1981). Ingrid Fromm, Siemens
representative to IEEE 802 quickly achieved broader support for Ethernet beyond
IEEE by the establishment of a competing Task Group "Local Networks"
within the European standards body ECMA TC24. As early as March 1982 ECMA TC24
with its corporate members reached agreement on a standard for CSMA/CD based on
the IEEE 802 draft. The speedy action taken by ECMA decisively contributed to
the conciliation of opinions within IEEE and approval of IEEE 802.3 CSMA/CD by
the end of 1982.Approval of Ethernet on the international level was achieved by
a similar, cross-partisan action with Fromm as liaison
officer working to integrate IEC TC83 and ISO TC97SC6, and the
ISO/IEEE 802/3 standard was approved in 1984.
2.11 CSMA/CD shared medium Ethernet
Ethernet originally used a shared coaxial cable
(the shared medium) winding around a building or campus to every attached
machine. A scheme known as carrier sense
multiple access with collision detection (CSMA/CD) governed the way
the computers shared the channel. This scheme was simpler than the competing token ring
or token bus
technologies. When a computer wanted to send some information, it used the
following algorithm:
1.
Frame ready for transmission.
2.
Is medium idle? If not, wait until it becomes ready and
wait the interframe gap period (9.6 µs in 10 Mbit/s
Ethernet).
3.
Start transmitting.
4.
Did a collision occur? If so, go to collision detected
procedure.
5.
Reset retransmission counters and end frame
transmission.
This
can be likened to what happens at a dinner party, where all the guests talk to
each other through a common medium (the air). Before speaking, each guest
politely waits for the current speaker to finish. If two guests start speaking
at the same time, both stop and wait for short, random periods of time (in
Ethernet, this time is generally measured in microseconds). The hope is that by
each choosing a random period of time, both guests will not choose the same
time to try to speak again, thus avoiding another collision. Exponentially increasing back-off times
(determined using the truncated binary exponential backoff
algorithm) are used when there is more than one failed attempt to transmit.
Computers were connected to an Attachment Unit Interface (AUI) transceiver,
which was in turn connected to the cable (later with thin Ethernet
the transceiver was integrated into the network adapter). While a simple
passive wire was highly reliable for small Ethernets, it was not reliable for
large extended networks, where damage to the wire in a single place, or a
single bad connector, could make the whole Ethernet segment unusable.
Multipoint systems are also prone to very strange failure modes when an
electrical discontinuity reflects the signal in such a manner that some nodes
would work properly while others work slowly because of excessive retries or
not at all (see standing wave for an explanation of why); these
could be much more painful to diagnose than a complete failure of the segment.
Debugging such failures often involved several people crawling around wiggling
connectors while others watched the displays of computers running a ping command and
shouted out reports as performance changed.
Since all communications happen on the
same wire, any information sent by one computer is received by all, even if
that information is intended for just one destination. The network interface
card interrupts the CPU only when applicable packets are
received: the card ignores information not addressed to it unless it is put
into "promiscuous mode". This "one speaks,
all listen" property is a security weakness of shared-medium Ethernet,
since a node on an Ethernet network can eavesdrop on all traffic on the wire if
it so chooses. Use of a single cable also means that the bandwidth is shared,
so that network traffic can slow to a crawl when, for example, the network and
nodes restart after a power failure.
2.12 Repeaters
and hubs
For signal degradation and timing
reasons, coaxial Ethernet segments had a restricted size which
depended on the medium used. For example, 10BASE5 coax cables had a maximum
length of 500 meters (1,640 ft). Also, as was the case with most other
high-speed buses, Ethernet segments had to be terminated with a resistor
at each end. For coaxial-cable-based Ethernet, each end of the cable had a 50 ohm
(Ω) resistor attached. Typically this resistor was built into a male BNC
or N connector
and attached to the last device on the bus, or, if vampire taps
were in use, to the end of the cable just past the last device. If termination
was not done, or if there was a break in the cable, the AC signal on the bus was reflected, rather than
dissipated, when it reached the end. This reflected signal was
indistinguishable from a collision, and so no communication would be able to
take place.
A greater length could be obtained by
an Ethernet repeater,
which took the signal from one Ethernet cable and repeated it onto another
cable. If a collision was detected, the repeater transmitted a jam signal
onto all ports to ensure collision detection. Repeaters could be used to
connect segments such that there were up to five Ethernet segments between any
two hosts, three of which could have attached devices. Repeaters could detect
an improperly terminated link from the continuous collisions and stop
forwarding data from it. Hence they alleviated the problem of cable breakages:
when an Ethernet coax segment broke, while all devices on that segment were
unable to communicate, repeaters allowed the other segments to continue working
- although depending on which segment was broken and the layout of the network
the partitioning that resulted may have made other segments unable to reach
important servers and thus effectively useless.
People recognized the advantages of
cabling in a star topology, primarily that only faults at
the star point will result in a badly partitioned network, and network vendors began
creating repeaters having multiple ports, thus
reducing the number of repeaters required at the star point. Multiport Ethernet
repeaters became known as "Ethernet hubs".
Network vendors such as DEC and SynOptics sold hubs that connected many 10BASE2
thin coaxial segments. There were also "multi-port transceivers" or
"fan-outs". These could be connected to each other and/or a coax
backbone. A well-known early example was DEC's DELNI. These devices
allowed multiple hosts with AUI connections to share a single transceiver. They
also allowed creation of a small standalone Ethernet segment without using a
coaxial cable. Ethernet on unshielded twisted-pair cables
(UTP), beginning with Star LAN and continuing with 10BASE-T,
was designed for point-to-point links only and all termination was built into
the device. This changed hubs from a specialist device used at the center of
large networks to a device that every twisted pair-based network with more than
two machines had to use. The tree structure that resulted from this made
Ethernet networks more reliable by preventing faults with (but not deliberate
misbehavior of) one peer or its associated cable from affecting other devices
on the network, although a failure of a hub or an inter-hub link could still
affect lots of users. Also, since twisted pair Ethernet is point-to-point and
terminated inside the hardware, the total empty panel space required around a
port is much reduced, making it easier to design hubs with lots of ports and to
integrate Ethernet onto computer motherboards.
Despite the physical star topology,
hubbed Ethernet networks still use half-duplex and CSMA/CD, with only minimal
activity by the hub, primarily the Collision Enforcement signal, in dealing
with packet collisions. Every packet is sent to every port on the hub, so
bandwidth and security problems aren't addressed. The total throughput of the
hub is limited to that of a single link and all links must operate at the same speed.
Collisions reduce throughput by their very nature. In the worst case, when
there are lots of hosts with long cables that attempt to transmit many short
frames, excessive collisions can reduce throughput dramatically. However, a Xerox report in 1980
summarized the results of having 20 fast nodes attempting to transmit packets
of various sizes as quickly as possible on the same Ethernet segment. The results showed that, even for the
smallest Ethernet frames (64B), 90% throughput on the LAN was the norm. This is
in comparison with token passing LANs (token ring, token bus), all
of which suffer throughput degradation as each new node comes into the LAN, due
to token waits.This report was controversial, as modeling showed that
collision-based networks became unstable under loads as low as 40% of nominal
capacity. Many early researchers failed to understand the subtleties of the
CSMA/CD protocol and how important it was to get the details right, and were
really modeling somewhat different networks (usually not as good as real
Ethernet).
CHAPTER-3
Conclusion
As
the Internet transforms longstanding business models and global economies,
Ethernet has withstood the test of time to become the most widely adopted
networking technology in the world. Much of the world’s data transfer begins
and ends with an Ethernet connection. Today, we are in the midst of an Ethernet
renaissance spurred on by surging E-Business and the demand for low cost IP
services that have opened the door to questioning traditional networking dogma.
Service providers are looking for higher capacity solutions that simplify and
reduce the total cost of network connectivity, thus permitting profitable
service differentiation, while maintaining very high levels of
reliability.Enter 10 Gigabit Ethernet. Ethernet is no longer designed only for
the LAN. 10 Gigabit Ethernet is the natural evolution of the well-established
IEEE 802.3 standard in speed and distance. It extends Ethernet’s proven value
set and economics to metropolitan and wide area networks by providing:An
Ethernet-optimized infrastructure build out is taking place. The metro area is
currently the focus of intense network development to deliver optical Ethernet
services. 10 Gigabit Ethernet is on the roadmaps of most switch, router and
metro optical system vendors to enable.
REFERENCES
1.http://www.10gea.org
2.http://standards.ieee.org/resources/glance.html
3.IEEE 802
LAN/MAN Standards Committee
4.IEEE 802.3
CSMA/CD (ETHERNET)
5.IEEE
P802.3ae 10Gb/s Ethernet Task Force
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