Transcript Business Data Communications and Networking

Business Data
Communications and
Networking, 6th ed.
FitzGerald and Dennis
8-1
Copyright © 1999 John Wiley & Sons, Inc.
All rights reserved. Reproduction or translation of this work
beyond that permitted in Section 117 of the 1976 United
States Copyright Act without the express written
permission of the copyright owner is unlawful.
Request for further information should be addressed to the
Permissions Department, John Wiley & Sons, Inc.
The purchaser may make back-up copies for his/her own use
only and not for redistribution or resale.
The Publisher assumes no responsibility for errors,
omissions, or damages, caused by the use of these
programs or from the use of the information contained
herein.
8-2
Chapter 8
Backbone Networks
8-3
Objectives of Chapter 8
Understand ...
 the internetworking devices used in
backbone networks,
 several types of fast ethernet and fast token
ring,
 several types of switched ethernet and
switched token ring,
8-4
Objectives of Chapter 8
Become familiar with…
 FDDI,
 ATM and fiber channel,
 ways to improve backbone network
performance,
 key factors in selecting backbone networks.
8-5
INTRODUCTION
8-6
Introduction
The driving force behind enterprise networking
is the shift toward an information-based
business economy and the Internet.
Interconnecting the organization's diverse
networks is one way to meet this challenge.
A backbone network is a high speed network
that connects many networks in a single
company or government site. It may also be
called an enterprise network if it connects all
networks within a company.
8-7
Introduction
There are two approaches to providing high
speed networking.
• The simplest and most straightforward is to
simply “speed up” the technologies currently
used in local area networks.
(Fast Ethernet and Fast Token Ring)
• The second approach is to develop a new high
speed technology that provides a set of
dedicated point-to-point communications
circuits between computers.
(Switched Ethernet and Switched Token Ring)
8-8
BACKBONE NETWORK
COMPONENTS
8-9
Backbone Network
Components
There are two basic components to a
backbone network:
 The network cable - essentially the same as
used in LANs, except it is usually higher
quality to provide higher data rates.
 The hardware devices that connect other
networks to the backbone - special purpose
devices and computers that just transfer
messages from one network to another.
8-10
Backbone Network Devices
Physical Data Link Network
Layer
Layer Layer
Device
Operates at
Messages
Hub
Bridge
Physical
Data link
S/D
S/D
Same Same
Same Same
Switch
Data link
S/D
Same Same
Router
Network
S/D
S/D
Same
Brouter
Data link &
Network
Network
All transferred
Filtered using
data link layer add.
Switched using
data link layer add.
Routed using
network layer add.
Filtered & routed
S/D
S/D
Same
Routed using
network layer add.
S/D
S/D
S/D
Gateway
8-11
Hubs
Operating at the physical layer, hubs are very
simple devices that pass all traffic in both
directions between the LAN sections they
link.
They may connect different types of cable,
but use the same data link and network
protocol.
Strictly speaking, hubs are not considered
part of a backbone network, but are usually
repeaters or amplifiers.
8-12
Hubs
8-13
Bridges
Bridges operate at the data link layer. They
connect two LAN segments that use the
same data link and network protocol. They
may use the same or different types of
cables.
Bridges “learn” whether to forward packets,
and only forward those messages that
need to go to other network segments.
8-14
Bridges
8-15
Bridges
If a bridge receives a packet with a
destination address that is not in the
address table, it forwards the packet to all
networks or network segments except the
one on which it was received.
Bridges are a combination of both hardware
and software, typically a “black box” that
sits between the two networks, but can also
be a computer with two NICs and special
software.
8-16
Switches
Like bridges, switches operate at the data link
layer. Switches connect two or more
computers or network segments that use
the same data link and network protocol.
They may connect the same or different
types of cable.
8-17
Switches
8-18
Switches
Switches operate at the same layers as
bridges but differ from them in two ways:
• First, most switches enable all ports to be in
use simultaneously, making them faster than
bridges.
• Second, unlike bridges, switches don’t learn
addresses, and need to have addresses
defined.
8-19
Switches
There are two types of switches:
Cut-through switches examine the destination
of the incoming packet and immediately
connect the port with the incoming message
to the correct outgoing port.
Store-and-forward switches copy the
incoming packet into memory before
processing the destination address.
8-20
Routers
Routers operate at the network layer.
Routers connect two or more LANs that use
the same or different data link protocols, but
the same network protocol.
Routers may be “black boxes,” computers
with several NICs, or special network
modules in computers.
In general they perform more processing on
each message than bridges and therefore
operate more slowly.
8-21
Routers
8-22
Routers
Routers choose the best route between
networks when there are several possible
routes between them.
Routers also only process messages
specifically addressed to it, unlike bridges.
Routers make no changes to the network
layer packet and user data it receives.
8-23
Brouters
Brouters are devices that combine the
functions of both bridges and routers.
These operate at both the data link and
network layers. A brouter connects both
same and different data link type network
LAN segments.
It is as fast as a bridge for same data link type
networks, but can also connect different
data link type networks.
8-24
Brouters
8-25
Gateways
Gateways operate at the network layer and
use network layer addresses in processing
messages.
Gateways connect two or more LANs that use
the same or different (usually different) data
link and network protocols. The may
connect the same or different kings of
cable.
Gateways process only those messages
explicitly addressed to them.
8-26
Gateways
Gateways translate one network protocol into
another, translate data formats, and open
sessions between application programs,
thus overcoming both hardware and
software incompatibilities.
A gateway may be a stand-alone
microcomputer with several NICs and
special software, a FEP connected to a
mainframe computer, or even a special
circuit card in the network server.
8-27
Gateways
One of the most common uses of gateways is
to enable LANs that use TCP/IP and
ethernet to communicate with IBM
mainframes that use SNA.
The gateway provides both the basic system
interconnection and the necessary
translation between the protocols in both
directions.
8-28
Gateways
8-29
A Caveat
The terminology used in the marketplace may differ
substantially. One vendor’s bridge may provide
the functions of a router.





Multiprotocol bridges - translate between different data link
layer protocols.
Multiprotocol routers -can understand several different
network layer protocols.
Protocol filtering bridges - multiprotocol bridges that forward
only packets of a certain type.
Encapsulating bridges - connect networks with different data
link protocols.
Layer-3 switches (IP switches) - can also switch messages
8-30
base on their network layer address.
The Opryland Network
8-31
SHARED MEDIA
TECHNOLOGIES
8-32
Shared Media Technologies
One approach to providing high speed
networks is to develop faster versions of the
same technology used in LANs.
The technologies operate by providing a high
speed circuit that is shared among all
computers on the LAN or backbone
network.
8-33
Fast Ethernet
The concept behind fast ethernet is simple:
take an ethernet LAN and make it run
faster.
There are several fundamentally different
approaches in the marketplace: Those that
refer to 100Mbps “Fast Ethernet” and
“faster” ethernet: gigabit ethernet and IsoENET.
8-34
100Base-X Ethernet
(IEEE 802.13)
100Base-X, (a.k.a. 100Base-T), is virtually
identical to 10Base-T (IEEE 802.3). It gives
a 100 Mbps data rate using the standard
ethernet bus topology, data link packets and
CSMA/CD media access protocol.
There are three versions of 100Base-X that
differ only at the physical layer:
• 100BaseTX uses cat 5 UTP
• 100BaseFX uses fiber optic cable
• 100BaseT4 uses 4 sets of cat 3 UTP (inverse
multiplexed)
8-35
100BaseVG (IEEE 802.12)
100Base-VG (a.k.a. 100VG-AnyLAN) is
considered part of the fast ethernet family
but is really not ethernet.
There are two differences between 100BaseVG and 100Base-X:
100Base-VG can send and receive both ethernet
and token ring packets.
100Base-VG does not use ethernet’s standard
CSMA/CD media access control. Instead it
uses demand priority access method (DPAM)
which is very similar to roll call polling
8-36
100Base-VG (IEEE 802.12)
In theory 100Base-VG should be faster than
100Base-T when network traffic becomes
heavy because controlled media access
techniques such as DPAM perform better
than contention-based approaches like
CSMA/CD.
8-37
100Base-VG (IEEE 802.12)
When traffic is heavy, the throughput of
ethernet drops to about 50 % because of
the collisions that occur. For larger packets
this is also true for 100Base-T. For small
packets of 1K or less, 100Bast-T operates
at almost 100 Mbps. For large packets,
throughput drops to about 50Mbps.
100Base-VG operates at close to 100Mbps
regardless.
8-38
Gigabit Ethernet (IEEE802.3z)
Similar to 100Base-X, 1000Base-X is a set of
standards that provide 1 Gbps. One
problem with 1000Base-X is that using the
standard CSMA/CD media access control
on a shared network may cause problems.
For this reason, gigabit ethernet may remain
primarily a backbone technology for use
only in point-to-point full duplex data
communications links.
8-39
Gigabit Ethernet (IEEE802.3z)
Four versions of 1000Base-X are now in use,
and they differ only at the physical layer by
using different media:
•
•
•
•
1000Base-LX - fiber cable running up to 440m.
1000Base-SX - fiber cable running up to 260m.
1000Base-T - 4 pairs of cat 5 UTP up to 100m.
1000Base-CX 1 pair cat 5 UPT up to 24m.
8-40
Iso-ENET (IEEE 802.9A)
Iso-ENET (Isochronous ethernet) is standard
10BaseT ethernet with an additional 6.144
Mbps circuit placed on top. The two circuits
are carried on the same physical UTP, but
are completely separate to prevent
interference.
Several vendors have developed desktop
videoconferencing application software that
uses iso-ENET with several more
multimedia products under development.
8-41
Fast Ethernet at GMAC
8-42
Fast Token Ring
Fast token ring (a.k.a. High Speed Token
Ring (HSTR)) is similar in concept to fast
ethernet. Fast token ring uses the standard
token ring topology, protocols, and media
access control, but runs at 100Mbps,and
will run on cat 5 cable or fiber optic.
Sales of token ring have declined in recent
years as more and more networks have
switched to ethernet, which remains
cheaper.
8-43
Fiber Distributed Data
Interface (FDDI)
Fiber Distributed Data Interface (FDDI) is a
set of standards originally designed in the
late 1980s for use in MANs (ANSI X3T9.5),
but has since made its way into backbone
networks.
FDDI is a token-passing ring network that
operates at 100 Mbps over two-counterrotating fiber optic cable rings.
8-44
Topology
The FDDI standard assumes a maximum of
1000 stations and a 200k path that requires
a repeater every 2k. The second ring is for
backup.
Single attachment stations (SAS) and dualattachment stations (DAS) are both
computer that can connect to one or both of
the rings, respectively.
If the cable in the FDDI ring is broken, the
ring can still operate in a limited fashion.
8-45
Topology
8-46
Topology
8-47
Media Access Control
The FDDI-MAC scheme uses a variation of
the IEEE 802.5 token-passing standard
used for token-ring networks with two types
of tokens: free tokens and busy tokens.
When a computer on an FDDI network
receives the token with a message
attached, it first removes the token from the
ring, and then transmits all messages that
were attached to it. The computer then
transmits whatever messages its wants
8-48
before transmitting the token.
Types of FDDI
There are two additional types of FDDI:
• FDDI-C - FDDI on copper (or CDDI) uses the
same topology and MAC as FDDI but uses two
pairs of cat 5 STP or UTP.
• FDDI-II - uses time division multiplexing to
break up the available 100Mbps into 17
separate channels, one channel at 768 Kbps
(the token passing data circuit), and 16 wide
band channels at 6.144 Mbps each, which can
be used for the transmission of voice and/or
video.
8-49
SWITCHED MEDIA
TECHNOLOGIES
8-50
Switched Media Technologies
Over the past few years, there has been a
major change in the way we think about LANs
and backbone networks. LANs have
traditionally used multipoint circuits, and
WANs have traditionally used point-to-point
circuits.
As the shared circuits in LANs and BNs have
become overloaded with traffic, networks are
starting to use switched point-to-point circuits
rather than shared multipoint circuits.
8-51
Switched Ethernet
The concept behind switched ethernet - and
all switched media technologies - is simple;
replace the LAN hub with a switch. Each
computer now has its own dedicated pointto-point circuit.
Switched ethernet dramatically improves LAN
performance. However, since much of the
network traffic is to and from the server, the
circuit to the server is often the network
bottleneck.
8-52
Switched Ethernet
8-53
Switched Ethernet
One obvious solution is to increase the number
of connections from the server to the switch
so that traffic now can reach the server on
several circuits.
Other solutions include:
• Full Duplex Ethernet (full duplex over traditional
10Base-T).
• 10/100 Switched Ethernet (combines 10Base-T
and 100Base-T). This is often used to provide 10
Mbps to the clients and 100 Mbps to the server.
8-54
Full Duplex Ethernet
8-55
Switched Ethernet
8-56
Switched Token Ring
Switched Token Ring is similar to switched
ethernet,in that a token ring switch replaces the
token ring hub, providing a series of point-topoint connections from the computers to the
switch instead of the traditional shared circuit.
The network has a star topology instead of a ring,
and no token.
Dedicated token ring (DTR) (or full duplex token
ring)is similar to full duplex ethernet, with a full
duplex connection to the switch providing a 32
Mbps data rate.
8-57
Switched FDDI
Switched FDDI is similar to switched ethernet,
in that a FDDI switch replaces the FDDI
hub, providing a series of point-to-point
connections from the computers to the
switch instead of the traditional shared
circuit. The network has a star topology
instead of a ring, and no token.
It does use the FDDI packet format and is
fully compatible with other FDDI hardware.
8-58
Asynchronous Transfer Mode
(ATM)
Asynchronous Transfer Mode (ATM) (a.k.a.
cell relay) is a technology originally
designed for use in wide area networks that
is now often used in backbone networks.
ATM backbone switches typically provide
point-to-point full duplex circuits at 155
Mbps (total of 310 Mbps).
8-59
Asynchronous Transfer Mode
(ATM)
ATM is a switched network but differs from
switched ethernet and switched token ring
in four ways:
1. ATM uses fixed-length packets of 53 bytes.
2. ATM provides no error correction on the user
data.
3. ATM uses a very different type of addressing
from traditional data link layer protocols such as
ethernet or token ring.
4. ATM prioritizes transmissions based on
Quality of Service (QoS).
8-60
Addressing & Forwarding with
ATM Virtual Circuits
8-61
Asynchronous Transfer Mode
(ATM)
Asynchronous Transfer Mode (ATM) is
connection-oriented so all packets travel in
order through the virtual circuit. A virtual
circuit can either be a:
 Permanent Virtual Circuit (PVC) - defined
when the network is established or
modified.
 Switched Virtual Circuit (SVC) - defined
temporarily for one transmission and
deleted with the transmission is completed.
8-62
ATM and Traditional LANs
ATM uses a very different type of protocol
than traditional LANs. It has a small 53byte fixed length packet and is connectionoriented.Ethernet and token ring use larger
variable length packets and are typically
connectionless.
Translation must be done to enable the LAN
packets to flow over the ATM backbones.
There are two approaches LAN
encapsulation (LANE) and Multiprotocol
over ATM (MPOA).
8-63
LAN Encapsulation (LANE)
8-64
ATM and Traditional LANs
Translating from ethernet or token ring into
ATM is not simple.
First the ethernet address must be translated
into an ATM virtual circuit identifier for the
circuit that leads from the edge switch to the
edge switch nearest the destination.
Once the virtual circuit address for the
destination data link layer address has been
found, it can be used to transmit the packet
through the ATM backbone.
8-65
ATM and Traditional LANs
Once the virtual circuit is ready, the LAN
packet is broken into the series of ATM
cells, and transmitted over the ATM
backbone using the ATM virtual circuit
identifier.
Unfortunately this process can cause quite a
delay (a reduction of 40 to 50 %).
Multiprotocol over ATM (MPOA) is an
extension to LANE.
8-66
ATM to the Desktop
ATM-25 is a low speed version of ATM which
provides point-to-point full duplex circuits at
25.6 Mbps in each direction. It is an
adaptation of token ring that runs over cat 3
cable and can even use token ring
hardware if modified.
ATM-51 is another version designed for the
desktop allowing 51.84 Mbps from
computers to the switch.
8-67
ATM to the Desktop
Both of these ATMs appear to be good
choices for desktop connections when ATM
backbone networks are used. However,
industry has been very slow to accept either
and have instead moved to fast ethernet
which is both cheaper and faster.
8-68
ATM at
Carnival Cruise Lines
headquarters
8-69
Fiber Channel
Fiber channel is relatively new networking
technology, although it has been used
inside computer and disk storage devices
for several years.
Fiber channel was originally designed to
provide high speed transmission over fiber
optic cable. The maximum data rate is
1.062 Gbps up to 10 k with higher rates
under development.
8-70
Fiber Channel
Fiber channel is a switched technology like
ATM, and like ATM, all circuits are full
duplex and provide several classes of
service.
Fiber channel uses variable length data link
layer packets with a minimum of 2048 bytes
of user data in each, and performs routing
error control using CRC-32.
8-71
Fiber Channel Topologies
8-72
IMPROVING BACKBONE
PERFORMANCE
8-73
Improving Backbone
Performance
Improving the performance of backbone
networks is similar to improving LAN
performance. First find the bottleneck, then
solve it, or move it somewhere else.
You can improve performance by improving
the computers and other devices in the
network, by upgrading the circuits between
computers, and by changing the demand
placed on the network.
8-74
Improving Backbone
Performance
Increase Computer and Device Performance
• Change to a more appropriate routing protocol
(either a static or dynamic)
• Reduce translation between different protocols
Increase Circuit Capacity
• Upgrade to a faster circuit
• Add circuits
Reduce Network Demand
• Change user behavior
• Reduce broadcast messages
8-75
Improving Computer and
Device Performance
The primary functions of computers and
devices in backbone networks are routing
and protocol translations. They can be
improved with a faster routing protocol.
Static routing is faster than dynamic, but can
impair circuit performance in high traffic
situations.
Many of the newer backbone technologies
have standards that are not fully developed.
8-76
Improving Computer and
Device Performance
FDDI and ATM require the translation or
encapsulation of ethernet and token ring
packets before they can flow through the
backbone.
Translating protocols typically requires more
processing than encapsulation, so
encapsulation can improve performance if
the backbone devices are the bottleneck.
Most backbone devices are store and forward
devices.
8-77
Improving Circuit Capacity
If network circuits are the bottleneck there are
several options:
 Increase overall circuit capacity.
 Add additional circuits alongside heavily
used ones.
 Replace shared circuit backbones with a
switched circuit backbone.
If the circuit to the server is the problem:
 Replace the ethernet hub with a switch and
change one NIC on the server.
8-78
Reducing Network Demand
 Restrict
applications that use a lot of
network capacity, like video-conferencing,
imaging, or multimedia.
 Reduce the number of broadcast LAN
messages on non-switched LANs.
 Filter broadcast LAN messages so they do
not exit their native LAN.
8-79
SELECTING A BACKBONE
NETWORK
8-80
Selecting a Backbone
Network
5 important factors to consider:
 Throughput - for light traffic all are similar,
for heavy, large packet traffic, 100BaseT is
worse.
 Network cost
 Type of application - All backbones are
equally appropriate for most data apps. For
voice and video, ATM is better, due to its
small fixed-length packets.
8-81
Backbone Selection Checklist
 Throughput
 Cost
 Type
of application
 Ease of network management
 Compatibility with current and future
technologies
8-82
Selecting a Backbone
Network
 Ease
of Management - Newer technologies
are harder to manage than older (FDDI).
 Compatibility with current and future
technologies
• Ethernet LANs are compatible with fast and
switched ethernet etc.
• It is believed that switched technologies will
replace shared multipoint circuit LANs, in the
future.
8-83
Survey of Fortune 1000
Network Managers
8-84
Facilities
map,
Next Day
Air
8-85
End of Chapter 8
8-86