Lan.ppt u522z

LAN is a datacomm system allowing a number of independent devices to communicate directly with each other, within a moderately sized geographic area over a physical communications channel. • A LAN usually connects servers, workstations, printers, and mass storage devices, enabling s to share the resources. • Most local area networks are built with relatively inexpensive hardware such as Ethernet cables, network adapters, and hubs.

LAN APPLICATIONS: • Personal computer LANs – low cost – limited data rate • Back end networks – Interconnecting large systems (mainframes and large storage devices). • high data rate • high speed interface • distributed access • limited distance • limited number of devices

LAN ACCESS PROTOCOLS : 1. Ethernet 2. Token ring 3. FDDI (Fiber Distributed Data Interface)

LAN TOPOLOGIES: 1. BUS

2. RING

3. STAR

4. TREE

BUS TOPOLOGY • Used with multipoint medium • Allows for transmission and reception •Avoids collisions and hogging. • Terminator absorbs frames at end of medium.

RING TOPOLOGY • A closed loop of repeaters ed by point to point links • Receive data on one link & retransmit on another – links unidirectional – stations attach to repeaters • Media access control determines when a station can insert frame

STAR TOPOLOGY • Each station connects to central node – usually via two point to point links. • Either central node can broadcast – only one station can transmit at a time. • central node can act as frame switch

TREE TOPOLOGY • Used with multipoint medium • Heard by all stations • Full duplex connection between station and tap • Need to regulate transmission • Tree is a generalization of bus

HARDWARE COMPONENTS of a local area network… A local area network is made of computers linked by a set of software and hardware elements. The hardware elements used for connecting computers to one another are: The network card: This is a card connected to the computer's motherboard, which interfaces with the physical medium, meaning the physical lines over which the information travels The socket: This is the element used to mechanically connect the network card with the physical medium. The physical connection medium: The main physical media used in local area networks are: •Coaxial cable •Twisted pair •Fiber optics

LAN’s TRANSMISSION MEDIA… Twisted pair Voice grade unshielded twisted pair (UTP) – Cat 3 phone, cheap, low data rates Shielded twisted pair – more expensive, higher data rates.

Coaxial cable Baseband coaxial cable – uses digital signaling – original Ethernet Broadband coaxial cable – as in cable TV systems – analog signals at radio frequencies – expensive, hard to install & maintain. Optical fiber – security, high capacity, small size, high cost

DEVICES USED FOR CONNECTIVITY…

LAN PROTOCOL ARCHITECHTURE…

LAN PROTOCOLS IN CONTEXT…

MAC FRAME FORMAT…

• MAC layer detects errors and discards frames

Connection of Two LANs

Why High Speed LANs? How’s the weather in Seattle, Mar?

• Speed and power of PCs has risen – Graphics-intensive applications & GUIs. • LANs are essential for client/server computing

[email protected] Ethernet

• Now have requirements for – centralized server farms

Network

Ethernet (CSMA/CD) • Developed by – Xerox - original Ethernet – IEEE 802.3 • Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

Tokenring

MSN Messenger

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Large LAN Organization Diagram :

SUMMARY •LAN is a computer network covering a small physical area, like a home, office, or small group of buildings, such as a school, or an airport. • LAN usually links computers (or resources such as printers) using a wired transmission medium (most frequently twisted pairs or coaxial cables). • Logical topologies  1. Ethernet 2.Token Ring (10mbps,100mbps) (16mbps)

3. FDDI (100mbps)

• Carrier Sense Multiple Access with Collision Detection (CSMA/CD) • Packets routed based on physical address (MAC). • Ethernet technologies – CSMA/CD media access – 10Mbps Ethernet – 100Mbps Ethernet – 1Gbps Ethernet – 10Gbps Ethernet