Communication Networks Lecture Week 3 Local Area Network

Local Area Networks (LANs) Owned by organizations for inter-networking in- house systems Cover limited geographical area: Department Building Cluster of buildings Higher data transmission capacity than WANs CC2009NI - Communication Networks, Saroj S. Regmi

LAN Applications Personal computer LANs Back end networks 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 CC2009NI - Communication Networks, Saroj S. Regmi

LAN Applications Storage Area Networks (SANs) Separate network handling storage needs Detaches storage task from specific servers Shared storage facility across high speed networks Hard disks, tape libraries, CD arrays Improved client-server storage access Direct storage to storage communication for backup High speed office networks Desktop image processing High capacity local storage Backbone LANs Interconnect low speed local LANs Reliability Capacity Cost CC2009NI - Communication Networks, Saroj S. Regmi

Typical Large LAN Organization Thousands to tens of thousands of devices Desktop systems links 10Mbps to 100Mbps Into layer 2 switch Wireless LAN connectivity available for mobile users Layer 3 switches at local network’s core From local backbone Interconnect at 1 Gbps Connect to layer 2 switches at 100 Mbps to 1 Gbps Servers connect directly to layer 2 or layer 3 switches at 1 Gbps Lower cost software based routers provide WAN connection Separate LAN subnetworks (circles in diagram) MAC broadcast frame to own subnetwork CC2009NI - Communication Networks, Saroj S. Regmi

LAN Topology The connection configuration Different configuration Bus Token Ring Star CC2009NI - Communication Networks, Saroj S. Regmi

Bus LANs Central cable, to which all devices are attached through a hardware interface (a transceiver) Transmission from a device travels along the bus in both directions Can be picked up by any other device attached At end of bus, terminators absorb, remove the signal CC2009NI - Communication Networks, Saroj S. Regmi

CSMA/CD Carrier Sense Multiple Access with Collision Detection Originally created by Xerox as the propriety, baseband Ethernet standard Simple, easily implemented algorithm Bus LANs are based on CSMA/CD algorithm CC2009NI - Communication Networks, Saroj S. Regmi

CSMA/CD Algorithm IF ready to signal AND no traffic on the bus, THEN transmit IF traffic on bus, WAIT until it ceases; THEN transmit immediately IF a collision detected on the bus, STOP transmission immediately afterwards WAIT a random period of time GOTO 1 CC2009NI - Communication Networks, Saroj S. Regmi

Frame Transmission on Bus LAN CC2009NI - Communication Networks, Saroj S. Regmi

Token Ring LANs Devices attached to a closed loop (ring) through a set of repeaters. A token (electronic signal) circulates around the ring continuously in one direction only; either clockwise or anti-clockwise A station wishing to transmit: Grabs the token Marks it as “busy” Fills it with data (now a frame) Adds address of receiving station Frames move around the ring until it reaches destination Token ring LAN is based on Fiber Distributed Data Interface (FDDI) algorithm CC2009NI - Communication Networks, Saroj S. Regmi

Star LAN Each station attached to a central node Central node acts either as: A broadcaster: Incoming frame transmitted on all outgoing lines A switching device: incoming frames switched to one outgoing line CC2009NI - Communication Networks, Saroj S. Regmi

Choice of Topology Depends on: Needs considering in context of: Performance Reliability Scalability (expandability) Needs considering in context of: Medium Wiring layout Access control Bus Ring Star Popular, versatile Higher speed, scalability up to some point Only suitable for small configurations and depends on integrity of central switch CC2009NI - Communication Networks, Saroj S. Regmi

LAN Transmission Media Distinction between baseband and broadband signaling Baseband: Uses digital signal Used on bus networks Consume entire bandwidth of cable Signal weakens (attenuates) quickly so repeaters used to boost signals Broadband: Uses analog signal Digital signal modulated into analog waveform Attenuation less of a problem, hence greater data transmission speed possible CC2009NI - Communication Networks, Saroj S. Regmi

LAN Transmission Medium Twisted pair cable Coaxial cable (thin coax) Optical fiber Wireless CC2009NI - Communication Networks, Saroj S. Regmi

LAN Transmission Media Twisted pair Early LANs used voice grade cables Didn’t scale for fast LANs Not used in bus LANs now Very easy to use with star topology Baseband coaxial cable Uses digital signaling Original Ethernet Not often used in new installations Broadband Coaxial cable As in cable TV systems Analog signals at radio frequencies Expensive, hard to install and maintain No longer used in LANs Optical fiber Expensive taps Better alternatives available Not used in bus LANs CC2009NI - Communication Networks, Saroj S. Regmi

LAN Standards Initial standards for communication on a LAN produced by IEEE Institute of Electrical & Electronics Engineers IEEE 802 family IEEE 802.11 for wireless LAN Adopted by American National Standard Institute (ANSI) and International Organization for Standardization (ISO) CC2009NI - Communication Networks, Saroj S. Regmi

LAN Standards Standard defined as a 3-layer protocol hierarchy: Logical Link Control (LLC) Medium Access Control (MAC) Physical Layer LLC MAC Physical Layer CC2009NI - Communication Networks, Saroj S. Regmi

Logical Link Control Upper sub-layer of data link layer Deals with addressing, data link control Independent of the topology, transmission medium, MAC techniques Specifies mechanism for controlling data exchange between users: Connectionless service (i.e. datagram) Connection-mode service (i.e. virtual circuit, with some flow and error control) CC2009NI - Communication Networks, Saroj S. Regmi

Media Access Control Defines how devices gain access to the transmission medium Two main techniques: Bus LAN (Carrier Sense Multiple Access with Collision Detection) Token ringing LAN (Fiber Distributed Data Interface) CC2009NI - Communication Networks, Saroj S. Regmi

Media Access Control Assembly of data into frame with address and error detection fields Disassembly of frame Address recognition Error detection Govern access to transmission medium Not found in traditional layer 2 data link control For the same LLC, several MAC options may be available CC2009NI - Communication Networks, Saroj S. Regmi

Physical Layer Defines the characteristics for different transmission media options for each MAC e.g. For IEEE 802.3 (CSMA/CD): Baseband coaxial cable Shielded twisted pair Optical fiber For IEEE 802.5 (Token Ring): CC2009NI - Communication Networks, Saroj S. Regmi

Physical Layer 802 Layers - Physical Encoding/ decoding Preamble generation/ removal Bit transmission/ reception Transmission medium and topology CC2009NI - Communication Networks, Saroj S. Regmi

Hubs Active central elements of star layout Each station connected to hub by two lines Transmit and receive Hubs act as repeater When single station transmits, hub repeats signal on outgoing line to each station Line consists of two unshielded twisted pairs Limited to about 100 m Optical fiber may be used for longer distances (500 m max.) Physically star, logically bus Transmission from any station received by all other stations If two stations transmit at the same time, collision CC2009NI - Communication Networks, Saroj S. Regmi

LAN Protocols in Context CC2009NI - Communication Networks, Saroj S. Regmi

Layer 2 Switches Central hub acts as switch Incoming frame from particular station switched to appropriate output line Unused lines can switch other traffic More than one station transmitting at a time Multiplying capacity of LAN CC2009NI - Communication Networks, Saroj S. Regmi

Layer 2 Switch Benefits No change to attached devices to convert bus LAN or hub LAN to switched LAN. For Ethernet LAN, each device uses Ethernet MAC protocol Device has dedicated capacity equal to original LAN Assuming switch has sufficient capacity to keep up with all devices Layer 2 switch scales easily Additional devices attached to switch by increasing capacity of layer2 CC2009NI - Communication Networks, Saroj S. Regmi

Router Problems Routers do all IP-level processing in software High speed LANs and high performance layer 2 switches pump millions of packets per second Software based router only able to handle well under a million packets per second Solution: Layer 3 switches Implement packet forwarding logic of router in hardware Two categories Packet by packet Flow based CC2009NI - Communication Networks, Saroj S. Regmi

High-speed LANs Extensions made to older LAN standards to get higher data transmission speeds: Fast Ethernet – 100 Mbps for Bus networks Gigabit Ethernet – 1 Gbps FDDI – 100 Mbps for Token Rings ATM LANs CC2009NI - Communication Networks, Saroj S. Regmi

Ethernet (CSMA/CD) Carrier Sense Multiple Access with Collision Detection Xerox – Ethernet IEEE 802.3 CC2009NI - Communication Networks, Saroj S. Regmi

IEEE 802.3 Medium Access Control Random Access Stations access medium randomly Contention Stations content on time on Medium CC2009NI - Communication Networks, Saroj S. Regmi

10 Mbps Specifications (Ethernet) CC2009NI - Communication Networks, Saroj S. Regmi

100 Mbps Fast Ethernet Use IEEE 802.3 MAC protocol and frame format 100 BASE-X use physical medium specifications from FDDI Two physical links between nodes Transmission and reception 100BASE-TX use STP or Cat.5 UTP May require new cable 100BASE-FX uses optical fiber 100BASE-T4 can use Cat.3, voice grade UTP Uses four twisted pair lines between nodes Data transmission uses three pairs in one direction at a time Star-wire topology Similar to 10BASE-t CC2009NI - Communication Networks, Saroj S. Regmi

Gigabit Ethernet Configuration Gigabit Ethernet – Differences: Carrier Extension At least 4096 bit-times long (512 for 10/100) Frame bursting Not needed if using a switched hub to provide dedicated media access CC2009NI - Communication Networks, Saroj S. Regmi

Gigabit Ethernet - Physical 1000Base-SX Short wavelength, multimode fiber 1000Base-LX Long wavelength, multi or single mode fiber 1000Base-CX Copper jumpers < 25 m, shielded twisted pairs 1000Base-T 4 pairs, Cat. 5 UTP Signaling – 8B/10B CC2009NI - Communication Networks, Saroj S. Regmi

10Gbps Ethernet Uses High speed, local backbone interconnection between large-capacity switches Server farm Campus wide connectivity Enables Internet Service Providers (ISPs) and Network Service Providers (NSPs) to create very high speed links at very low cost Allow construction of (MANs) and WANs Connect geographically dispersed LANs between campuses or points of presence (PoPs) Ethernet competes with ATM and other WAN technologies 10 Gbps Ethernet provides substantial value over ATM CC2009NI - Communication Networks, Saroj S. Regmi

10 Gbps Ethernet Advantages No expensive, bandwidth consuming conversion between Ethernet packets and ATM cells Network is Ethernet, end to end IP and Ethernet together offer QoS and traffic policing approach ATM Advanced traffic engineering technologies available to users and providers Variety of standard optical interfaces (wavelengths and link distances) specified for 10 Gb Ethernet Optimizing operation and cost for LAN, MAN or WAN CC2009NI - Communication Networks, Saroj S. Regmi

10 Gbps Ethernet Advantages CC2009NI - Communication Networks, Saroj S. Regmi

Fiber Channel Applications CC2009NI - Communication Networks, Saroj S. Regmi

Thank You!! CC2009NI - Communication Networks, Saroj S. Regmi