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Network and Data Communication cha7-8


Chapter 07 Introduction to Communication Networks

Outline
7.1 7.2 7.3 7.4 7.5 Computer Networks Network Models Network Components Network Topology Types of Networks

7.1 Computer Networks
Transmission Link Transmitter Receiver

Destination Source

Figure 7.1 A data communication model
n Source:
- The source station can be a computer, and its function is to pass information to a transmitter.

n Transmitter
- The function of a transmitter is to accept information from the source and change the information such that it is compatible with the transmission link.

n Transmission Link
- The function of a transmission link is to carry information from a transmitter to a receiver. The transmission link can be conductor, fiber optic cable, or wireless media (air).

7.2 Network Models
n Three models are used, based on the type of network operation needed:
l l l

Peer-to-peer network (workgroup) Server based network Client/server network

Peer-to-Peer Model (Workgroup)
n No special station that holds shared files or a network operating system. n Each station can access the resources of the other stations in the network.

Figure 7.2 Peer-to-peer network model

File Server Model
n Server stores all the network’s shared files, applications such as word processor documents, compilers, database applications, and the network operating system (NOS). n NOS manages the operations of the network.

Client

Server

Figure 7.3 File server model with one server and three clients

Client/Server Model
n Clients submit tasks to the server, and server executes the client’s task and returns the results to the clients.

Server

Clients

Figure 7.4 Client /server model

7.3 Network Components
n The basic components of a computer network:
l l l

Network interface card (NIC) Transmission medium Network operating system (NOS)

7.4 Network Topology
n Topology of a network describes the way computers are connected together. n Common topologies include:
l l l l l l

Star Ring Bus Mesh Tree Hybrid

Star Topology
n All stations are connected to a central controller or hub.
Station 1 Station 2

HUB

Station 4

Station 3

Figure 7.5 Star topology

Ring Topology
n All the stations are connected in cascading order to make a ring.

Figure 7.6 Ring topology

Bus Topology
n A multi-point connection in which stations are connected to a single cable called a bus.

Figure 7.7 Bus topology

Mesh Topology
n Mesh topology can be full mesh topology (fully connected topology) or partial mesh topology. n In a full mesh topology, each station is directly connected to every other station in the network.

Figure 7.8 Full mesh topology

Mesh Topology (continued)
n In a partial mesh topology, some of the stations are connected to other stations, while other stations are connected only to those stations with which they exchange the most data.
(( )) (( )) (( ))

Internet Service Provider (( ))

(( ))

(( )) (( ))

(( )) (( )) (( )) (( )) (( ))

((

))

(( ))

(( ))

Figure 7.9 Partial mesh topology

Tree Topology
n Uses an active hub or repeater to connect stations together.
HUB

HUB

Figure 7.10 Tree topology

Hybrid Topology
n A combination of different topologies connected together by a backbone cable.

Bridge Backbone

Bridge

Bridge

HUB

Ring HUB

Figure 7.11 Hybrid topology

7.5 Types of Networks
n Distance between computers that are connected as a network determines the type of network.
l l l

Local Area Network (LAN) Metropolitan Area Network (MAN) Wide Area Network (WAN)

Local Area Network (LAN)
n Links computers and other data communication systems together within a small geographic area such as an office, department, or a single floor of a multi-story building.

Metropolitan Area Network (MAN)
n Connects multiple networks that are situated in different locations of a city or town.

Metropolitan

Figure 7.12 Metropolitan Area Network

Wide Area Network (WAN)
n Covers a large geographical area, such as an entire country or continent. n WANs may use leased lines from telephone companies, Public Switch Data Networks (PSDN), or satellite links. n The Internet is a collection of networks located all around the world that are connected by gateways
G G G G

Internet
G G

G: Gateway

Figure 7.13 Internet architecture

Chapter 08 Local Area Networks

Outline
8.1 Ethernet 8.2 Token Rings 8.3 FDDI 8.4 Fast Ethernet 8.5 100VG-ANYLAN 8.6 Switches and Bridges 8.7 Routers and Layer 3 Switches

8.1 ETHERNET
n Developed by the University of Hawaii (1968 - 1972) Invented by the Xerox Corporation in 1972, it has since been modified not only by Xerox but by Digital and Intel. n IEEE was assigned to develop a standard for Local Area Networks (LAN), calling it "802.” n Most widely used LANs n Uses CSMA/CD protocol n Minimum frame length must be at least 64 octets

n Ethernet, the least expensive LAN to implement, had the standards defined in 1984, called IEEE 802.3. n Uses the bus topology, but is logically a star topology

Figure 8.1 Ethernet bus topology

CSMA and CD used in Ethernet
CD CSMA Stop sending Send a jam to clear the network Yes Is the link being used No Wait for a random period of time Send a frame of the message Resend the frame Is the link being used by another station while I am sending a frame?

Yes

No

Keep sending this frame of the message while checking the link status

Figure 8.2 CSMA/CD

Media

n

Ethernet networks use one of three different media: 10Base2, 10Base5 or 10BaseT.

Figure 8.3 Network Interface Card (NIC)

10Base2 (ThinNet)
ThinNet or 10Base2

Data Rate
10Mbps Base-band

Max. Segment Length x 100m
200 meters

Figure 8.4 Components of ThinNet

10Base2 (ThinNet) (continued)
n n n

n n

n n

n

Uses thin coaxial cable with BNC connectors. Maximum length of one segment is 185 meters. Maximum length of a network cable is 925 meters using four repeaters. The transceiver is built into the NIC. The minimum distance between T-connectors is 0.5 meters. No more than 30 connections are allowed per segment. The first and the last device on each segment must be terminated with a 50-W resistor (BNC terminator) to prevent signal reflection on the cable. A T-connector must plug directly into the Ethernet device.

10Base5 (ThickNet)
ThickNet or 10 Base5

Data Rate
10Mbps

Type of Bandwidth
Base-band

Max. Segment Length x 100m
500 meters

Figure 8.5 Location of a transceiver for 10Base5 (ThickNet)

10Base5 (ThickNet) (continued)
n

n n n

n n

n

Occasionally used for network backbones, the transceiver, which transmits, receives, and detects collisions on the network, is a separate component attached to a coaxial cable. The maximum length of one segment is 500 meters. Devices are attached to the backbone via a transceiver. The maximum length of the Attachment Unit Interface cable (AUI) is 50 meters. The minimum distance between transceivers is 2.5 meters. No more than 100 transceivers are allowed in one segment of the network. Both ends of the segments must be terminated by 50-W resistor.

10BaseT

HUB / REPEATER

10 BASE-T
Data Rate
10 Mbps Baseband

T represents Twisted Pair
Twisted Pair

Figure 8.6 10 BaseT connection

10BaseT (continued)
n

n n n n

n

n

Uses UTP cable for transmission media and requires all stations be connected to a repeater or hub which accepts frames from one port and retransmit the frames to all the other ports. The maximum length of one segment is 100 meters. Transceiver for 10BaseT is built into the NIC. The cable used is 22 to 26 AWG category 4 or 5 UTP. Devices are connected to a 10BaseT HUB in a physical star topology (electrically a bus topology). Devices with standard AUI connectors may be attached to the HUB by using a 10BaseT transceiver. 10BaseT topology allows a maximum of four repeaters connected together giving a maximum diameter of 500m.

Mixed use of Ethernet to form a LAN
10BASE2 10BASE2

10BASE-T Hub

10BASE-T Hub

10BASE-T Hub 10BASE2

10BASE-T Hub

Figure 8.7 Mixed use of Ethernet

Fast Ethernet
n

Offers a data rate of 100 Mbps, the specifications for which are housed under IEEE 802.3u. An extension of the Ethernet standard, the goal of Fast Ethernet is to increase the bandwidth of Ethernet networks while using the same CSMA/CD transmission protocol. Allows users to connect an existing 10BaseT LAN to a 100BaseT LAN with switching devices

n

n

34

Gigabit Ethernet
n

n

n

n

Gigabit Ethernet is a new technology that transfers data at one gigabit per second, 10 times faster than Fast Ethernet. Technology compatible with Ethernet and Fast Ethernet. Gigabit Ethernet is often used for backbones in conjunction with gigabit switches. Gigabit Ethernet is used for the campus backbone by connecting gigabit switches together.

Gigabit Ethernet Standards
n

In 1995, the IEEE 802.3 committee formed the IEEE 802.3z Task Force to research Gigabit Ethernet.
- The IEEE 802.3z Task Force developed standards for Gigabit Ethernet.

n

In 1996, the Gigabit Ethernet Alliance was formed by more than 60 companies to support development of Gigabit Ethernet.

Characteristics of Gigabit Ethernet
n

n n n n

n

Used for linking Ethernet and Fast Ethernet Switches as well as interconnecting very high-speed servers, Gigabit Ethernet enables upgrade to networks while using the same operating systems and the same application software. Operates at 1000 Mbps (1 Gbps) Uses the IEEE 802.3 frame format and maximum frame size Supports full-duplex or half-duplex operation Uses CSMA/CD access method for half-duplex operation while supporting only one repeater per 200 meter collision domain Can use optical-fiber or copper wire for transmission media

Gigabit Ethernet Components
Gigabit Ethernet NIC Switches that can handle 1Gbps Ethernet Gigabit Ethernet Repeater Transmission media able to handle 1Gbps

n n n n

Gigabit Ethernet Applications
n

n

n

Most organizations are currently using Fast Ethernet, easily upgradeable to a Gigabit Ethernet. Gigabit Ethernet is used for campuses or buildings that require greater data rate. Gigabit Ethernet applications are:
? ? ? Switch-to-switch connections Switch-to-server connections Repeater-to-switch connections Upgrading Fast Ethernet switches to Gigabit Ethernet switches and installing Gigabit NICs in high-speed servers Upgrading a switch to a server link with a data rate of 1000 Mbps

n

Some current applications:
? ?

n

n

Upgrading a Fast Ethernet backbone switch from 100 Mbps to 1000 Mbps Upgrading a switch to a switch link

Applications of the Gigabit Ethernet
1 Gbps connection (1) Server 1 Gbps connection (3) Fast Etherne t switch 100 Mbps connecti on Fast Ethernet switch 1 Gbps connection (2)

Gigabit Ethernet switch 1 Gbps connection (5)

100 Mbps connection (4) FDDI concentrat or 10 Mbps connecti on

Hub

Hub

Fast Ethernet switch

100 Mbps connecti on

10 Gigabit Ethernet
n

n

The IEEE 802.3ae task force is in charge of completing the standard for 10 Gigabit Ethernet (10 GbE). The 10 Gigabit Ethernet standard defines two different types of physical layers:
? ? LAN Physical Layer (LAN PHY) WAN physical Layer (WAN PHY) Connecting a server to a switch with 10GbE Connections between switches Connecting two campus networks Storage Network Architecture (SNA) Connecting multiple networks in one metropolitan area with 10 GbE would offer services such as distance learning, video conferencing, etc.

n

For LANs
? ?

n

For WAN
? ? ?

Characteristics of 10 Gigabit Ethernet
n

n n n n

Uses the IEEE 802.3 frame format with minimum and maximum IEEE 802.3 frame sizes Only supports a full-duplex connection Uses optical cable as a transmission medium Supports LAN and WAN Physical layers Can provide a direct connection to OC-192C SONET

8.2 TOKEN RINGS
n

n

The token ring was originally developed by IBM in the 1970s, especially designed to handle heavy data loads. Token ring networking was introduced in 1985, at a data rate of 4 Mbps. The IEEE 802.5 specification was hence modeled after the IBM token ring. A token ring network uses a wiring concentrator device called Multistation Access Unit (MAU).

n

n

Token

Figure 8.8 Token ring topology

Token Ring Operation
n

n

n

n

n

Within a token ring network, traffic passes through each station on the ring and repeats the information to the next station on the ring. The token is a three-byte frame circulating around the network that any station that wants to transmit information must possess. When a station does not have any information to transmit, it passes the token to the next station. If a station possesses the token and has information to transmit, it inserts information into the token and transmits frame on the ring. Each station checks the destination address of the frame and, if it matches, performs following:
q q

q

q

Node copies the frame into its buffer. Buffer sets the last two bits of the frame, informing the source that the frame was copied. Frame is retransmitted on the ring and circulates until it reaches the source, which removes the frame. Source releases token by changing token bit (T Bit) to 1.

Physical Connections
n

A ring station is called a Multistation Access Unit (MAU), and each computer is connected to the MAU. A MAU can accommodate up to eight stations.
q q

n

STP cable is used for 16-Mbps token ring network. UTP cable is used for 4-Mbps token ring network.

n

When a station is attached to the ring it performs the following:
q

q q

The station receives a frame from the ring and passes it to the next station. The station then removes its data from the ring. Each station repeats data on the ring, and when the data returns to the originating station, it is checked for errors.

Token Operations: Step 1

Token A frame to send A source station Token Ring

Token Operations: Step 2

A source station

A frame to send

Token is caught Token Ring

Token Operations: Step 3

A destination station A frame to send

A source station

Token Ring

Token Operations: Step 4
A destination station

A source station

A frame to send

Token Ring

Token Operations: Step 5

A destination station

A source station

Token Ring

Token Operations: Step 6

A destination station

A source station

Token Ring Token

Token Ring and Ethernet

Table 8.1 Comparison of Token Ring and Ethernet
Token Ring Priority Routing Information Field Frame Type Frame Size Performance Cable Speed Yes Yes IEEE 802.5 1 - 18000 bytes Deterministic UTP/STP/ Fiber/Coax 4, 16 Mbps Ethernet No No IEEE 802.3 64 - 1500 bytes Variable UTP/STP/ Fiber/Coax 10, 100,1000, 10000 Mbps

8.3 FDDI (Fiber Distributed Data Interface)
n

n

The Fiber Distributed Data Interface (FDDI) standard was developed by the ANSI X3T9.5 Standards Committee in 1980 and submitted to the ISO. The ISO then developed a new version of FDDI, compatible with the current ANSI standard.

FDDI Technology
n

n

n

FDDI is a high-speed LAN that employs a ring topology providing a data rate of 100 Mbps. FDDI uses two rings, and thus is termed a dual-ring topology. It is similar to IEEE 802.5 token ring, but differs in the use of optical fiber for transmission media.
- The main advantage of using fiber optics over copper wiring is security, because there is no electrical signal on the media to tap.

n n

FDDI uses two rings, one primary and one secondary. Traffic travels through the rings in opposite directions.
- The primary ring is used for data transmission. - The secondary ring is used for backup in the case of primary breakdown.

FDDI Technology (continued)
n

FDDI allows up to 1000 stations to be connected with a maximum ring circumference of 200 km.

A :FDDI station

Figure 8.9 FDDI data traffic flow

FDDI Layered Architecture
n

n

FDDI uses token passing as an access method, so any station that wants to transfer information must hold the token. The length of time a station holds the token is called synchronous allocation time (SAT) and is variable for each station. The time allocated for each station is achieved by station management. A new layer is added to the OSI model called Station Management.
Logical Link Control

n

Media Access Control

MAC

n

Station Management

Physical Layer protocol

SMT

Physical medium Dependent (PMD)

Figure 8.10 FDDI layered architecture

Components of FDDI
n

The components of FDDI are fiber-optic cable, concentrator (rings), and the stations connected to the concentrator, as seen in Figure 8.11.
SAS

SAS

S

S

M

M

Concentrator

A

B Primary Ring

B

Secondary Ring A

A

B

DAS

DAS

Figure 8.11 Components of an FDDI network

Components of FDDI (continued)
n

There are two types of stations used in FDDI:
- Dual attachment station (DAS) or Class A: attached to both rings, and has two ports to connect to the ring, one of which is connected to the primary ring and other to the secondary ring (Figure 13.4) - Single attachment station (SAS) or Class B: attaches only to the primary ring
Primary

Port A

Secondary

Secondary

Port B

Primary

Figure 8.12 Dual attachment station

FDDI Fault Tolerance
n

n n

n

n

Fault tolerance is defined as the ability to respond to unexpected hardware and software failures and continue to provide service. FDDI uses two fiber-optic rings. Traffic on these rings travels in opposite directions, so these dual rings in an FDDI network provide the fault tolerance for the FDDI. If the primary ring fails, FDDI uses the secondary ring as backup. If both rings are damaged, the dual ring automatically "wraps" (the primary ring connects to the secondary ring) and changes the ring to a single ring.

FDDI Fault Tolerance (continued)

A

B

A Cable breakdown
Primary Ring

B Primary Ring

B A Secondary Ring B A

A

B
B

A B

A

Secondary Ring

B

A

Figure 8.13: FDDI wrapping

Figure 8.14: FDDI wrapped ring

FDDI Fault Tolerance (continued)
n

n

n

If the cable breaks down in two places, FDDI wraps into multiple rings. If a station on a dual ring fails or is powered down, the dual ring will wrap into a single ring. If two stations on the ring fail, the failure will cause ring segmentation. An optical bypass switch is used to avoid segmentations of the ring by eliminating the failed stations.

n

Figure 8.15 FDDI ring and bypass switch

FDDI Backbone
n

Often used for LAN backbones in campuses and corporations having several buildings in one location. Despite this, FDDI is one of the most expensive network backbones, so most network designers rely on a 100-Mbps Ethernet backbone rather than FDDI. Advantages of 100-Mbps Ethernet over FDDI:
- A Fast Ethernet NIC is less expensive than an FDDI NIC. - Fast Ethernet can use UTP as a transmission media, which is less expensive than fiber-optic cable.

n

n

FDDI Ring as Backbone for LAN

Ethernet Hub FDDI Concentrat or

tenrehtE

FDDI Ring

MAU Supercomputer Switched Hub

: a FDDI station

8.4 100VG-ANYLAN
n Designed to solve inefficient CSMA/CD protocol by proposing priority demand scheme:
l l

Normal Priority

n Uses round-robin polling n 100 Mbps n Uses hierarchical structure of up to three levels

100VG-AnyLAN Hierarchical Structure

Hub 100VGAnyLAN Hub 1 2 UP

100VGAnyLAN Hub 1 2

UP

Level 1

3 . . . .8 100VGAnyLAN Hub Hub 1 2 UP

Level 2

3 . . . .8

3 . . . .8

Hub 100VGAnyLAN Hub 1 2 UP

Hub Hub 100VGAnyLAN Hub 1 2 UP 100VGAnyLAN Hub 1 2

Level 3 UP

3 . . . .8

3 . . . .8

3 . . . .8


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