topic 7: lans & backbone networks - chapter 15: lan systems business data communications, 4e

Topic 7: LANs & Backbone Networks- Chapter 15: LAN Systems

Business Data Communications, 4e

Business Data Communications

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Ethernet Standards

Ethernet Cable Features

10Base-2 RG-58 coax (thin) 185m, 10Mbps10Base-5 RG-8 coax (thick) 500m, 10Mbps10Base-T Cat 3 UTP 100m, 10Mbps100Base-T4 Cat 3 UTP x 4 100m, 100Mbps100Base-TX Cat 5 UTP/STP 100m, 100Mbps100Base-FX Fiber optic 100m, 100Mbps


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Types of Ethernet

10BASE-T (10 Mbps) Uses a twisted-pair cable with maximum distance of 100

meters 100BASE-T (100Mbps)

Based on 10Base-T standard, 10 times faster, uses cat-5 UIP/STP cable. NIC is downward compatible to 10Base-T

Gigabit Ethernet Three new types of Ethernet. They can use Ethernet

traditional half-duplex approach, but most are configured to use full-duplex. Also they can run over fiber-optic cables.

1000Base-T Ethernet, sometimes is called 1 GbE. 10 GbE 40 GbE


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802.3 10BaseX Media Options


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High-Speed LANs

Why? Extraordinary growth in speed, power, and

storage capacity of PCs Increasing use of LANs as computing platforms

Examples Server farms Workgroups with “power” requirements High-speed backbones


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100Base-T Ethernet (IEEE 802.13) It gives a 100 Mbps data rate using the

standard Ethernet bus topology, data link packets and CSMA/CD media access protocol.

Three versions of 100Base-X differing 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) 100Base-T Ethernet can co-exist with 10Base-T

Ethernet.


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Fast Ethernet (100Mbps)

Easy to integrate with existing systems

Can use UTP (-TX) or fiber (-FX)Uses star-wired topology, using a

central multiport repeater (broadcast method)

If NICs support full-duplex mode, switched hub must be used


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100Base-T Ethernet (IEEE 802.13)

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.

Three versions of 100Base-X differing 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)


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802.3 100Base-T Options


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802.3 100BaseX Media Options


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Gigabit Ethernet

Still under development Retains CSMA/CD protocol and Ethernet

format, ensuring smooth upgrade path Uses optical fiber over short distances 1-Gbps switching hub provides

backbone connectivity May not be good for LAN (explain why)

and has been used in backbone networks for point-to-point connections.


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Gigabit Ethernet

1000BASE-LX: Long-wavelength, supports up to 550m (m-mode fiber) or 5km (single-mode fiber)

1000BASE-SX: Short-wavelength, supports up to 275 - 550 m(m-mode fiber)

1000BASE-CX: uses copper jumpers in a single room or equipment rack

1000BASE-T: uses 4 pairs of Cat-5 UTP


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Gigabit Ethernet Media Options


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Example 100-Mbps Ethernet Backbone Strategy


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Fibre Channel

combine the best features of channel and protocol-based technologies the simplicity and speed of channel

communications the flexibility and inter-connectivity that

characterize protocol-based network communications.

more like a traditional circuit-switched or packet-switched network, in contrast to the typical shared-medium LAN


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Fiber Channel Network

N_portF_port


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Fibre Channel Elements

Nodes The end systems Includes one or more N_ ports for

interconnection

Fabric Collection of switching elements between

systems Each element includes multiple F_ ports Responsible for buffering and for routing

frames between source and destination nodes


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Fibre Channel Goals

Full-duplex links with two fibers per link

Performance from 100 Mbps to 800 Mbps on a single link (200 Mbps to1600 Mbps per link)

Support for distances up to 10 km

Small connectors High-capacity utilization

with distance insensitivity

Greater connectivity than existing multidrop channels

Broad availability (i.e., standard components)

Support for multiple cost/performance levels, from small systems to supercomputers

Ability to carry multiple existing interface command sets for existing channel and network protocols


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*Fibre ChannelProtocol Architecture

FC-0 Physical Media: Includes optical fiber, coaxial cable, and shielded twisted pair, based on distance requirements

FC-1 Transmission Protocol: Defines the signal encoding scheme

FC-2 Framing Protocol: Defines topologies, frame format, flow/error control, and grouping of frames

FC-3 Common Services: Includes multicasting FC-4 Mapping: Defines the mapping of various

channel and network protocols to Fibre Channel


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Fibre Channel - Maximum Distance

800Mbps 400Mbps 200Mbps 100Mbps

SingleMode 10,000m 10,000m 10,000m 10,000m

M-mode 500m 1,000m 2,000m --

CoaxialCable 50m 71m 100m 100m

STP 28m 46m 57m 80m


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Wireless LANS

LAN extension Wireless network connected to a main wire-based

network

Cross-building interconnect Point-to-point link between networks in separate

buildings

Nomadic access Wireless link between a LAN hub and a mobile data

terminal

Ad hoc networks a peer-to-peer network (no centralized server) set up

temporarily to meet some immediate need.


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Wireless LANs (IEEE802.11)

Wireless LANs are growing very rapidly. Wireless LANs transmit data through the air (space) rather than through wire or cable.

New terms: WLAN (Wireless LAN) LAW (Local Area Wireless Network)

IEEE 802.11 standard is likely to be the dominant standard for wireless LAN

It is easy to connect wireless LANs to Ethernet. So, it is usually called wireless Ethernet


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Wireless LANs (IEEE802.11)

Topology. The same as traditional Ethernet. It is both a physical star and a logical bus.

A central wireless access point (AP) is a radio transceiver that plays the role of hub. The maximum range is 100-500 feet depending on interference

Wireless LANs use CSMA/CA (Carrier Sense Media Access with Collision Avoidance) similar to CSMA/CD by Ethernet. Two methods are simultaneously used:

Physical carrier sense method. Packets are sent using stop-and-wait ARQ. Receiver waits less time to send ACK than other computers waiting for available time slots.

Virtual carrier sense method. Using AP hidden node problem must be solved. It is optional.


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Hidden Node Problem

When one computer transmits packets, a computer in another side of AP may not detect the signal and send packets as well. This causes collision at AP.

So, AP is the only device that is able to communicate with both computers. To solve the problem, AP uses controlled access method instead of the contention based method. A computer wanting to send packets must send a request (RTS) to AP. If no other computer is using the circuit, AP will respond with a clear to transmit (CTS) specifying the amount of time for the circuit reserved for the computer.

All other computers hear the CTS and remain silent for the specified time period.


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Types of Wireless Ethernet

IEEE 802.11b. Two basic forms: Direct-sequence spread-spectrum (DSSS) Frequency-hopping spread-spectrum (FHSS)

IEEE 802.11a. Expected to run at 5 GHz. Not completely defined yet.

Other type of wireless LANs: Infrared wireless LAN. Less flexible because most require

direct line of sight between transmitters and receivers. The primary advantage: the reduction of wiring. The primary disadvantage: the low speed (1-4 Mbps).

Bluetooth. Provide seamless networking of devices in a very small area (up to 30 feet)

Small, cheap Called Piconet with no more than 8 devices


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IEEE 802.11b

Two basic forms: Direct-sequence spread-spectrum (DSSS), in 2.4 GHz

band. Transmits signals through a wide spectrum of radio frequencies simultaneously. The signal is divided into many different parts and sent on different frequencies. 1, 2, 5.5, 11 Mbps speeds. 20 Mbps version is in the way out.

Frequency-hopping spread-spectrum (FHSS). Uses the same band, but once each frequency in turn. Sender and received synchronize in a frequency. So, minimizes jamming an eavesdropping. 1 Mbps and 2 Mbps.

They are shared media implementation. As the number of devices increases the speed will be reduced.


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Infrared Wireless LANs


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Fiber Distributed Data Interface (FDDI)

Fiber Distributed Data Interface (FDDI) is a set of standards originally designed in the late 1980s, but has since made its way into backbone networks.

FDDI is a token-passing ring network that operates at 100 Mbps over two-counter-rotating fiber optic cable rings.


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Topology

The FDDI standard assumes a maximum of 1000 stations and a 200-kilometers (120 miles) path that requires a repeater every 2-kilometers. The second ring is for backup.

Single attachment stations (SAS) and dual-attachment 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.


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Topology


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Topology


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Media Access ControlThe FDDI-MAC scheme uses a variation of the

IEEE 802.5 token-passing standard.

Messages and the token are sent in different frames separately in a FDDI LAN. A computer can send data only when it captures the token.

When a computer on an FDDI network waiting for transmission receives the token, it holds the token and then transmits all messages that were attached to it. The computer then transmits whatever messages its wants before transmitting the token.

When receiver receives the data frame it simply copy the data frame leaving it to be absorbed by the sender.


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LAN

LAN

LAN

LAN

LAN

LAN

Access LayerDistributionLayerCore Layer

Figure 7-5 Backbone network design layers (FD)

Backbone NetworkArchitecture


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*Backbone Network Architectures

Routed backbone – using routers Advantage – clearly segment each part of the network Disadvantage – Delay, and more management

Bridged backbone – using bridges, not popular any more Advantages – cheaper, simpler Disadvantages – difficulties in management

Collapsed backbone –using switches, is most commonly used. Advantages - Better performance, Fewer network devices are

used Disadvantages – switch problem may fail whole network, more

cabling work Two types

Rack-based collapsed backbone Chassis-based collapsed backbone

Virtual LAN (VLAN)


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Layer-2Switch

ClientComputer

ClientComputer

ClientComputer

ClientComputer

ClientComputer

ClientComputer

10/100 Ethernet

1000Base-T

Layer-3 Switch

Router to WAN

Router to Internet

Server

1GbE on fiber

1GbE on fiber 1GbE

on fiber

Figure 7-11 Central Parking’s collapsed backbone (FD)

Layer-2Switch

ClientComputer

ClientComputer

ClientComputer

ClientComputer

ClientComputer

ClientComputer

10/100 Ethernet

1000Base-TServer

Server

Server

10/100 Ethernet


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*Virtual LAN (VLAN)

A new type of LAN backbone network architecture by intelligent high-speed switches. VLAN is configured using software not hardware. Single-switch VLAN – VLAN inside a switch Multiswitch VLAN – VLAN using several

switches.

VLAN is normally faster than traditional LANs, and provide better opportunity to manage data flows


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VLAN switch

ClientComputer

ClientComputer

ClientComputer

ClientComputer

ClientComputer

ClientComputer

10/100 Ethernet

1000Base-T

VLAN switch

VLAN switch

VLAN switch

VLAN switch

VLAN switch

VLAN switch

VLAN switch

VLAN switch

VLAN switch

VLAN switch

VLAN switch

VLAN switch

VLAN switchVLAN switch

VLAN switch

VLAN switch

1GbE on fiber

1GbE on fiber

1GbE on fiber

1GbE on fiber

Figure 7-14 IONA VLAN network (FD)


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How is a packet transmitted through the Internet?

An IP address tells the destination Transmission is done one hop after another

actually at data link layer This is just like you bought a flight ticket from

Lubbock to New York. The ticket package indicates New York is your destination (IP address). However, you may have three coupons for three flights that connect your route via two more cities between: Dallas and Chicago. Each coupon indicates your arriving airport (destination data link layer address), e.g. DFW, CHI and JFK.


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A TCP/IP Example


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How TCP/IP Works

How a client access a web server in the same subnet with a known address?

How a client access a web server in a different subnet with a known address?

How a client access a web server in the same subnet with an unknown address?


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*NetBIOS vs. NetBEUI

NetBIOS has 18 commands for PC connections.

NetBEUI adds 8 more and is used as a transport protocol. It is faster and more efficient than NetBIOS

When NetBEUI is in use, NETBIOS becomes API that invokes NetBeui.

They can support a LAN with less than 200 PCs.


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*Windows Network Model

Layer 7

Layer 6

Layer 5

Layer 4

Layer 3

Layer 2Layer 1

Physical layer

Data link layer

Network layer: IP

Transport layer:TCP, UDP

Application layer:

FTP, TELNET, HTTP, etc.

Internet Model Windows Network Model

I/O Named Pipes Mail Server

Environment Subsystem

NetBIOS (Redirector)

TDI WINSOCK

802.2 802.3 802.4 802.5

NDIS 3.0NDIS Environment

and Drivers

NetBEUI TCP/IP

Provider Interface

NDIS: Network Driver Interface Specification


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*NDIS

NDIS (Network Driver Interface Specification) is a Windows specification for how communication protocol programs (such as TCP/IP) and network device drivers should communicate with each other.


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*NetBIOS

NetBIOS (Network Basic Input/Output System)

Created by IBM for its early PC Network, was adopted by Microsoft, and has since become a de facto industry standard.

A program that allows applications on different computers to communicate within a local area network (LAN).

Used in Ethernet, token ring, and Windows NT networks.


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*NetBEUI

NetBEUI (NetBIOS Extended User Interface)

Developed by IBM for its LAN Manager product and has been adopted by Microsoft for its Windows NT, LAN Manager, and Windows for Workgroups products.

A new, extended version of NetBIOS, the program that lets computers communicate within a local area network.

Formalizes the frame format (or arrangement of information in a data transmission) that was not specified as part of NetBIOS.


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*NetBIOS over TCP/IP NetBIOS over TCP/IP runs over the TCP/IP, so that

you can share drives and printers over the Internet. In the "Network" configuration window in Windows

95, there is no option for NetBIOS over TCP/IP, but a "NetBEUI" entry, with which Microsoft actually means NetBIOS over NetBEUI.

With the installation of TCP/IP protocol, Windows automatically installs the "NetBIOS over TCP/IP”.

If you do want the TCP/IP protocol, but not "NetBIOS over TCP/IP" (because of security problem), you should uncheck "Files and Printer Sharing" in the Bindings tab of the TCP/IP entry in Network Configuration.


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Data transmission using TCP/IP and Ethernet

Ethernetpacket header

IPpacket

TCPpacket

HTTPpacket

User DataEthernet

packet trailer

IP address

Data link layer address

topic 7: lans & backbone networks - chapter 15: lan systems business data communications, 4e

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