LAN & WAN COM211 Communications and Networks CDA College Theodoros Christophides Email: [email protected][email protected]

LAN & WAN

COM211 Communications and NetworksCDA CollegeTheodoros ChristophidesEmail: [email protected]/site/info-com-technology-ll/

LAN

A local area network (LAN) is a computer network that interconnects computers in a limited area such as a home, school or office building. The characteristics of a LAN include high data-transfer rates, small geographic areas, and a single network administration.

Ethernet Fast Ethernet Gigabit Ethernet 10 Gig Ethernet WLAN

Media Access

Ethernet and Wi-Fi are both “multi-access” technologies They have a broadcast medium that is shared by many hosts Support of simultaneous transmissions which result in collisions

Media Access Control (MAC) protocol required Rules on how to share medium

The Data Link Layer is divided into two parts: MAC Media Access Control) Sublayer LLC (Logic Link Control) Sublayer

802.3

Carrier-sense multiple access with collision detection (CSMA/CD). CS = carrier sense MA = multiple accessCD = collision detection

Base Ethernet standard is 10 Mbps.100Mbps, 1Gbps, 10Gbps standards came

later

Ethernet CSMA/CD

CSMA/CD protocol is used for: Data that is transmitted in the form of packets. To sense the channel prior to packet transmission. Transmitting packets only if the channel is idle, else

defer the transmission until channel becomes idle. After packet transmission is started, the node monitors

its own transmission to see if the packet had a collision. If the packet is observed to be undergoing a collision,

the transmission is aborted and the packet is retransmitted after a random interval of time

MAC Address

Nodes are identified by their Ethernet Addresses (MAC Address or Hardware Address) which is a unique 6 Byte address.

MAC Address is represented in Hex Decimal format e.x. 00:05:6A:FE:20:AA

The first 3 bytes identify a vendor (prefix) and the last 3 bytes are unique for every host or device

Ethernet Frame Structure

Preamble: 7 bytes with pattern 10101010 followed by one byte with pattern

10101011 Used to synchronize receiver, sender clock rates

Addresses: 6 bytes, frame is received by all adapters on a LAN and dropped if address does not match

Length: 2 bytes, length of Data field CRC: 4 bytes generated using CR-32, checked at the

receiver, if an error is detected, the frame is dropped Data Payload: Maximum 1500 bytes, minimum 46 bytes

Ethernet

Physical Media :- 10 Base5 - Thick Co-axial Cable 10 Base2 - Thin Co-axial Cable 10 BaseT - UTP Cat 3/5 10 BaseFL - Multimode/Singlemode

Fiber

Maximum Segment Length 10 Base5 - 500 m with at most 4 repeaters 10 Base2 - 185 m with at most 4 repeaters 10 BaseT - 100 m with at most 4 hubs

WAN

Wide area network (WAN) is a network that covers a broad area. In general a WAN is considered any network that links across metropolitan, regional, or national boundaries. Organizations use WANs to transfer data among employees from remote locations, to help and support clients and suppliers from various geographical locations. WANs allows an organization to carry out its daily functions regardless of location.

WAN Technologies

Dial-up Leased Line ISDN X.25 Frame Relay ATM DSL Cable Modem VSAT

Dial-up

Uses the Plain Old Telephone System (POTS) Provides low cost need based access. Low bandwidth On the Customer End the Modem is connected to the

Telephone Line On the Service Provider End a Remote Access Server

(RAS) is connected to Telephone Lines RAS providea dialin connectivity, authentication and

metering. Achievable bandwidth depends on the line quality.

Dial-up

Leased Line

Used to provide point-to-point dedicated network connectivity. Analog leased line can provide maximum bandwidth of 9.6 Kbps. Digital leased lines can provide bandwidths :

64 Kbps, 2 Mbps (E1), 8 Mbps (E2), 34 Mbps (E3)

ISP Broadba

nd Internet Connecti

vity

ISPRouter

Interface Converter

LL ModemG.703

LLModem

V.35Router

ISP PREMISES CUSTOMER PREMISES

PSTN

ISDN

Another alternative to using analog telephones lines to establish a connection is ISDN.

Speed is one advantage ISDN has over telephone line connections.

ISDN network is a switched digital network consisting of ISDN Switches.

Each node in the network is identified by hierarchical ISDN address which is of 15 digits.

ISDN user accesses network through a set of standard interfaces provided by ISDN User Interfaces.

ISDN Two types of user access are defined

Basic Access - Consists of two 64Kbps user channels (B channel) and one 16Kbps signally channel (D channel) providing service at 144 Kbps.

Primary access - Consists of thirty 64Kbps user channels (B channels) and a 64 Kbps signally channel (D channel) providing service at 2.048Mbps (One 64 Kbps channel is used for Framing and Synchronization).

BasicInformation 128 Kbps(Voice & Data)

Signaling 16Kbps

PrimaryInformation 1920 KbpsVoice & Data

Signaling 64 Kbps

X.25

Packet switched Network consisting of X.25 switches.

X.25 is a connection oriented protocol (Virtual Circuits).

End nodes are identified by an X .25 address. Typical bandwidth offered is 2.4/9.6 kbps. IP networks interface with X .25 through IP- X.25

routers.

Frame Relay

Designed to be more efficient than X.25 Developed before ATM Call control carried in separate logical connection No hop by hop error or flow control End to end flow and error control (if used) are done by

higher layer Single user data frame sent from source to destination

and ACK (from higher layer) sent back Two type of Virtual Circuits defined

Permanent virtual circuits (PVCs) Switched virtual circuits (SVCs)

ATM

Small fixed size packets of 53 bytes, called cells, are used for transferring information.

Each cell has 5 bytes of header and 48 bytes of payload for user information.

Connection oriented protocol. A virtual Circuit is established between the

communicating nodes before data transfer takes place. Can be seamlessly used in LANs and WANs. Almost unlimited scalability. Provides quality of service guaranties.

Digital Subscriber Line (DSL)

Digital Subscriber Line (DSL) uses the Ordinary Telephone line and is an always-on technology. This means there is no need to dial up each time to connect to the Internet.

Because DSL is highly dependent upon noise levels, a subscriber cannot be any more than 5.5 kilometers (2-3 miles) from the DSL Exchange

Service can be symmetric, in which downstream and upstream speeds are identical, or asymmetric in which downstream speed is faster than upstream speed.

DSL comes in several varieties: Asymmetric DSL (ADSL) High Data Rate DSL (HDSL) Symmetric DSL (SDSL) Very High Data Rate DSL (VDSL)

Cable Modems

1. Cable modems connect a computer to the cable company network through the same coaxial cabling that feeds cable TV (CATV) signals to a television set.

2. Use Cable Modem at Home End and CMTS (Cable Modem Termination System) at Head End.

3. Characteristics: 1. Shared bandwidth technology 2. 10 Mbps to 30 Mbps downstream 3. 128Kbps-3 Mbps upstream 4. Maximum Distance from provider to customer site: 30 miles

VSAT

Very Small Aperture Terminal (VSAT) provide communication between two nodes through a powerful Earth station called a Hub.

If two terminals want to communicate, they send their messages to the satellite, which sends it to the Hub and the Hub then broadcasts the message through the satellite.

Typical Bandwidth offered is 9.6/19.2/32/64/128/256/512 Kbps.

Operating modes are TDM/TDMA, SCPC PAMA & DAMA

VSAT

Each satellite sends and receives over two bands Uplink: From the earth to the satellite Downlink: From the satellite to the earth

Satellite frequency bands Band Downlink Uplink C 3.7-4.2 GHz 5.925-6.425 GHz Ku 11.7-12.2 GHz 14-14.5 GHz Ku-band based networks, are used primarily in Europe and North America

and utilize the smaller sizes of VSAT antennas. C-band, used extensively in Asia, Africa and Latin America, require larger

antenna.