Local Area Network (LAN)

LAN About 80% of the data traffic originated within the business Advantages of LAN Timely access to data for customer service and product development Centralized management of shared applications Economic and cost saving due to sharing resources Separating network nodes Sharing the resources

LAN Components Network nodes – an addressable entity where a communication line interfaces (e.g., a server with multiple MAC to work as multiple nodes) NIC – Network interface card which connects to the physical medium of LAN interface Transmission system – a wired or wireless medium to carry actual data/connection Software and data – protocol data unit (PDU) handling control, packaging and addressing as per standard User interface – a interface to receive user input to initiate, manage and terminate the communication Operating system – serves the user requirement for data, file or resources

LAN characteristics Four key characteristics of a LAN Type of transmission Medium Transmission technique Network accessing Network topology

LAN transmission media Bandwidth requirement How much do you need per client? How much do you need per server? Application specific, peak/off-pick load, up gradation/commissioning/relocation Cost and easy of connection Wired or wireless Bandwidth Easy up gradation/relocation Interference and noise sensitivity Type of business (office or power plant) Security Encryption

LAN transport techniques and standards Broadband Cable TV – through FDM different channels carry analog and digital information A set-top-box is used to extract information on a particular channel frequency band from a multichannel coaxial cable Baseband A single channel digital system carrying packets of frames of data Ethernet Token ring FDDI/CDDI – later replaced by 1Gbps Ethernet

LAN standards Characteristics Ethernet Token Ring FDDI Standard IEEE 802.3 IEEE 802.5 IEEE 802.6 Logical topology Bus Ring Physical topology Bus, star Ring, star Dual ring, dual bus Media Coax, UTP, STP, fiber Coax, UTP, STP Fiber Transmission mode Baseband BW 10Mbps, 100Mbps, 1Gbps, 10Gbps 4Mbps, 16Mbps, 100Mbps, 1Gbps 100Mbps Media access Nondeterministic Deterministic Control CSMA/CD, CSMA/CA Token passing

LAN access method: Token Passing Used in token ring and FDDI MSAU- Multistation access unit The process A token is inserted into the ring Token circulates around the ring Grab the token to send data and release when finished Token hold time - a timer for sender to finish and release token Receiver grab the data, send acknowledgement Sender get notified and generates a new token Pros and cons Deterministic – maximum delay can be estimated Unidirectional ring - wait for the token Broken ring – needs to reinitiate the ring

LAN access method: CSMA/CD Carrier sense multiple access/ collision detection (CSMA/CD) Nondeterministic Needs to scan the network for collision Process Listen If clear, send the data If collide, produce a jam signal and stop sending Wait random amount of time and retransmit If collide again, back off, wait and try again If frequent collision, break the LAN into sub segments

LAN topologies Common topologies are Tree Bus Ring Star All transmission must pass through head end Transmission and reception may use different frequencies Translation from transmit to receive frequency is called re-modulation Bus Each station is connected to the trunk or backbone A terminator is used to absorb the free signal and clear the cable Ring Nodes are connected to a unbroken loop Each node receives and boosts the signal and sends to the next node Star All stations are connected to the central hub Easy of by passing, fault isolation and centralized resource management

LAN interconnection: Hubs Hubs are used to expand the network Easy of connectivity and suitable for centralized monitoring Commonly known as concentrator or multi-station access unit (MSAU) Intelligent hub – can accommodate Ethernet, token ring or FDDI Active Regenerates and retransmits data Requires electrical power to run and can serve 8-12 nodes Passive Do not regenerate, signals just pass through the point Requires no electrical power to run

LAN interconnection: LAN switches To meet the demand for increased bandwidth Each port offers a dedicated channel with high speed connectivity full duplex mode provides great scalability to the backbone network

LAN interconnection: VLANs Does not restrict to a limited geographical location A single switch serving multiple LAN allowing users to share the same broadcast domain Restricts the broadcast and collision within each virtual LAN Managed and controlled by software application

LAN interconnection: Bridges Used for connecting network segments To avoid traffic bottleneck and to control the traffic flow Cannot translate between Layer 2 protocols (e.g., Ethernet, FDDI) Faster and less expensive, but subject to broadcast storm Functions include Learning Builds a MAC address table that controls the access of each NIC to the shared transmission media Only determines whether a destination is within a network segment Packet transfer Filter, ignore or forward packets Using STP (Spanning Tree Protocol) Provides a loop-free topology to ensure that no two alternate routes are active simultaneously

What would have happened?

LAN interconnection: Routers To expand smaller networks into a larger one or to segment larger network into smaller ones Limits broadcast storm by Reading network addresses and forwarding the packet to target or destination address Acting as a traffic filtering, isolation and forwarding Can make linking and rerouting decisions Selection depends on cost, speed, priority and so on Often applied as firewalls to separate network segments Functions Learning Filtering Routing and switching Adapting to network conditions

Wide Area Network (WAN)

WAN A group of computers connected over long distances by communication link Circuit switched Leased line ISDN Packet switched X.25 Frame relay ATM IP

Circuit switched network: Leased Line Connectivity options Telco Network Leased Line (DLC) Services Installation and maintenance IP number allocation Domain Name Service (DNS) Usage Reporting Static & Dynamic Routing Protocol 24x7 Support Connection type Single point Multipoint

Leased line: Single point A dedicated connection between two nodes Challenges Cost per mile Not economic for network expansion or relocation CSU – Channel services equipment DSU – Data services equipment

Leased line: Multipoint A shared communication link to reduce mileage cost Shared link is Cost effective But increases control and services overhead CSU – Channel services equipment DSU – Data services equipment

Leased line: Connectivity Digital Data services (DDS) - 56Kbps or 64Kbps T, E or J carrier SDH/SONET Dark fiber

Leased line: DDS A lease line at either 56Kbps or 64Kbps serviced by a T, E or J carrier backbone Uses RS232 or V.35 for physical connectivity between DTE and DCE The access line from DCE connects to the digital circuit switch which is known as DDS hub DDS hub or DSU converts the binary data to line coding and synchronization A one for positive voltage A zero for negative voltage If >15zeros, network may loose synchronization Hence, DSU performs bipolar variation by alternating one as positive or negative voltages A switched DDS can support 56, 64, 384 or 1536 Kbps Switched 56 – 56Kbps full duplex dial up connection for serial interface V.35 – High speed serial interface between DTE and DCE Data set - A digital device connecting V.35 to 56Kbps access link of Telecom company

Leased line: T, E or J carrier Connectivity between cities are supported by both p2p and multipoint leased lines It requires a single backbone to replace all the different infrastructures A private network to replace existing Dynamic bandwidth Dynamic routing

Leased line: Private network backbone Dynamic routing Static and dynamic bandwidth

Leased line: SDH/SONET and Dark fiber An infrastructure based on fiber optics High speed digital access of multimedia and visualization requiring high bandwidth applications for enterprises OC-1 (51 Mbps) OC-3 (155 Mbps) . OC- 192 (10 Gbps) Customers of SDH/SONET are airports, universities, large government agencies Dark fiber Requires equipment to activate fiber at customer premises Possible to get extra bps or wavelength out of fiber Reduce costs for bandwidth

Circuit switched network: ISDN An alternate to leased lines that support both voiced and non-voiced services Reduces overhead costs for individual aces to circuit-switched, leased-line or packet- switched network Requires – Digital local exchange and software SS7 (signaling system 7) network CPE (customer premises equipment)

Circuit switched network: N-ISDN 2 interfaces Basic rate interface (BRI) Primarily for residential services and small businesses offered by Telcos Can be configured as 1B, 2B, 1B+D or 2B+D An ISDN modem at customer premises can be of 2B for 128kbps access to ISP Primary rate interface (PRI) Primarily used for business applications A key data application is LAN/WAN integration

Circuit switched network: ISDN applications Internet Access – Other than DSL or broadband availability, N-ISDN can provide speed Remote access – Teleworkers or telecommuters can access to corporate resources LAN/WAN connections – Multiple LANS across a WAN can be connected over N-ISDN High capacity access – Increased capacity access for file transfer, graphics, video and multimedia Private-line backup – N-ISDN can be a backup for DDS services recovery period BRI 0B+D packet data – One 16Kbps can be shared by 8 devices. 0B+D can support 9.6kbps low speed terminals such as credit card readers and automatic teller machines ISDN DSL (IDSL) – Full duplex dedicated data services only. Operates either at 1B or 2B (64kbps or 128kbps)

Packet switched network Designed to support burst data traffic Longer connection of low volume data May include statistical multiplexing Packet formats may vary depending on Number of bits/packet Sensitivity to delay/loss Addressing rules for forwarding to destination 2 types of network Connection oriented (X.25, Frame relay, ATM) Only one packet is required to set up the connection between source to destination. Rest of the packets are routed to the established connection Error detection and corrections are handled by destination devices Connectionless (X.25, IP) Each packet carries source and destination route information Sensitive to delay for real-time applications as each packet is subjective to inspection for routing and error control

Packet switched network: X.25 X.25 evolved to support Low volume and bursty nature of data shared among multiple users High integrity against high error rate of analog transmission Delay due to error control at each transmission nodes Small packet size (128 bytes or 256 bytes) to support retransmission for error control PSE – Packet switching equipment PAD – Packet assembler/disassembler