SYST5030 /4030 Local Area Networks Industry leaders agreed about the potential of home networking, and they say that eventually every technological component of a home will be connected and will also incorporate Internet access.

SYST5030 /4030 Intro to Local Area Networks Why LANs? 1) Need to connect systems and equipment within a local environment 2) Diverse machines such as computers, printers, terminals, workstations, telephones, facsimiles must be able to communicate with each other. (Now, add home appliances too!) 3) Multiple users must be able to access common databases, exchange electronic mail, share programs and applications. 80% of the information generated within a local environment is used within that environment.

SYST5030 /4030 What is a Local Area Network? (source: Goldman)

SYST5030 /4030 Design Goals for LANs High Speed and bandwidth Reliable and Maintainable Low cost Compatibility/Standards Flexible and Extendible Simplicity Sample Parameters 1) Speed: Mbits per sec 2) Distance covered: 5 to 10 miles 3) Number of devices: 5 or 10, to several hundred.

SYST5030 /4030 How is a Local Area Network Implemented? (source: Goldman)

SYST5030 /4030 Key Design Elements of LANs Topology Control, Access and Allocation of network channel Transmission media

SYST5030 /4030 Topology LANs are based on simple structured topologies like Star Ring Bus The topology is also a means of implementing control strategy. Bus and Ring are the most common LAN topologies in organizations. The Star topology is more common in home networks.

SYST5030 /4030 All nodes joined to a central point Point to point lines connect central and outlying points.

SYST5030 /4030 Star Topology Control options (central node control): 1) Central control: optimal when bulk of communication is between central and outlying nodes. Otherwise, switching burden on center node is high. Other control possibilities: 1) control exercised by an outlying node. 2) distributed control. Other issues: Central node is a single point of network failure. If it goes down, entire network fails! Reliability -> may need redundant power supplies, dual busses, etc.

SYST5030 /4030 Nodes connected by point to point lines, form ring Messages travel around link in 1 direction. A node also serves as repeater. Control may be distributed or centralized.

SYST5030 /4030 Ring Topology Control Options: 1) Distributed control: each node can communicate directly with every other node under its own initiative. 2) Centralized control: One node in the ring controls access to and communications over channel. Problems 1) Failure of node or a component will cause network to fail (remedy: need to bypass failure points). 2) Link failure will also lead to breakdown. 3) Difficult to pre-wire building for ring network. 4) Failure of control node is disastrous (if central control).

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Bus Topology Similar to multi-drop line. Bi-directional flow of data. Nodes share single physical channel via cable taps or connectors. Easy to configure and expand in most physical locations. Appropriate with distributed control (central control is uncommon). Nodes play a passive role Resistant to single node failure.

SYST5030 /4030 Logical versus Physical Topology Physical Topology: refers to the physical layout of the LAN. Logical topology: refers to the logical arrangement in which the data flows through the LAN. e.g., it is possible to have: Physical topology = STAR, while the Logical topology = RING.

SYST5030 /4030 Channel control, allocation and access Control may be centralized or distributed Need allocation scheme to make most effective use of channel capacity Access techniques are means by which nodes gain use of common channel to transmit messages. WHERE control resides, WHO gets the channel, HOW MUCH channel capacity a node can have.

SYST5030 /4030 Channel Access and allocation 1) POLLING Centralized Polling (master queries each node in turn) Distributed Polling (e.g. Token Passing, Slotted Rings) 2) CONTENTION TECHNIQUES -- CSMA/CD (e.g. Ethernet) Carrier sense multiple access with collision detect For how long can a node use the channel? How many bytes can be transmitted at one time?

SYST5030 /4030 Token-Passing Access Methodology (source: Goldman)

SYST5030 /4030 Carrier Sense Multiple Access with Collision Detect (CSMA/CD) Each node listens for traffic on network and waits for line to become free. If two nodes transmit at the same time, a collision occurs. Upon detecting the collision, each node backs off and retransmits after a random amount of time. In case of successive collisions, nodes back off and wait for a still longer random interval of time. If line is free, a node can transmit at any time.

SYST5030 /4030 Transmission Media Twisted wire pair: + Low cost, easy to install, may already exist. - high error rate, noise, speed and distance limitations. Coaxial Cable + simple to install and tap, low maintenance - not secure, more expensive than twisted wire pair Fiber-optics cable + very secure, low weight and diameter, spans long distance - high cost, high skills required, expensive connection equipment.

SYST5030 /4030 LAN Performance Performance criteria: 1) Throughput versus load 2) Delay versus throughput Studies show that: 1) CSMA/CD deteriorates rapidly if load > 30 %. 2) Token-based methods perform better under high load and high throughput conditions. Token passing is better suited for the needs of a heavy-duty, high-load backbone environment. Token bus backbones can also span a longer distance than CSMA/CD backbones.

SYST5030 /4030 Performance of CSMA/CD and Token Passing Network load Delay CSMA/CD Token Passing stations 30

SYST5030 /4030 ETHERNET Very popular and widely used LAN Developed in 1980 at Xerox Ethernet specification was issued to encourage standardized approach to LAN design Specification defines the physical and data link layer characteristics

SYST5030 /4030 Ethernet Physical Layer Topology: Bus Medium: Shielded coaxial cable Data rate: 10 Mbits per sec. Maximum separation of nodes: 2800 meters (1.7 miles) Maximum number of nodes: Data link layer Access control protocol: CSMA/CD Allocation: Packet length from 64 to 1518 bytes

SYST5030 /4030 Ethernet features High speed and Bandwidth (broadcast feature: packets travel in both directions) Reliable and maintainable (shared passive bus, no central controller, no routing software required, no modems, comprehensive system diagnostics) Compatibility and low cost Flexible and extendible Simplicity

SYST5030 /4030 Ethernet Media Interfaces (Source: Goldman)

SYST5030 /4030 Ethernet specifications (part of standard ) Thick coaxial cable (or 10 Base 5) : 10 Mbps, baseband, 500 meters, maximum distance of 500 meters between nodes. Thin coaxial cable (or 10 Base 2): 10 Mbps, baseband, maximum distance of 200 meters. 10 Base-T: 10 Mbps over unshielded twisted wire pair (UTP) 10 Base-F: 10 Mbps over fiber

SYST5030 /4030 Preamble 8 Octets Destination Address 6 Octets Source Address 6 Octets Length 2 Octets Data Unit 46 to 1500 bytes Frame Check (CRC) 4 Octets The overall frame length varies from 64 to 1518 Octets Ethernet Frame Layout

SYST5030 /4030 Simple Ethernet with a Printer Attached (Source: ITP Publishers) Local Area Network Configurations

SYST5030 /4030 Adding a Segment by Adding a Repeater (Source: ITP Publishers)

SYST5030 /4030 Building Multiple Segments from a Single Repeater (Source: ITP Publishers)

SYST5030 /4030 Multiple Floor Network Model (Source: ITP Publishers)

SYST5030 /4030 The Local Area Network Technology Architecture (source: Goldman)

SYST5030 /4030 Features of Network Operating Systems (NOS) Configuration management Print server support File server support Electronic mail/broadcast Network name service/directory service Accounting management Network management NetWare 4.1, Windows NT are NOS examples. The NOS software is installed on server and client.

SYST5030 /4030 Functions of physical layer Physical layer “Listening” to make sure channel is clear Physically encoding and decoding data received from data link layer Transmitting data Detecting collisions

SYST5030 /4030 Functions of Data Link layer Data Link Layer (2 Sublayers: Logical link control + Media access control) 1) Interface with the network layer above. 2) Encapsulating data into Ethernet packet. 3) Manage media access. These functions are handled by the Ethernet controller card. This card is also called the network interface card (NIC)

SYST5030 /4030 FDDI Network Architecture and Technology (source: Goldman) Fiber Distributed Data Interface

SYST5030 /4030 FDDI Protocol Maximum of 1000 stations. 120 mile path with repeaters every 1.25 miles. Timed-token rotation protocol (variation of token-ring) Uses two rings called primary ring and secondary ring. The rings rotate in opposite directions. Data usually travels on one ring. Second ring normally serves as backup path. Dual attachment stations (DAS) connect to both rings. Single attachment stations (SAS) connect to one ring. 100 Mbps data rate.

SYST5030 /4030 FDDI Token Ring and Data Frame Layouts

SYST5030 /4030 Applications of the FDDI Network Architecture: Backbone (source: Goldman)

SYST5030 /4030 FAST ETHERNET Operates at 100 Mbps Two competing technologies have emerged: BaseT (supported by 3COM, Intel, DEC, etc.) VG-AnyLAN (supported by HP, IBM, etc.) Issues: Maintaining compatibility with existing 10BaseT and Ethernet networks Compatibility of existing wiring and connectors. GIGABIT ETHERNET is another newer technology

SYST5030 / BaseT Network Architecture Implementation (source: Goldman)

SYST5030 /4030 IEEE 802.3, IEEE 802.5, and 100VG-AnyLAN Architectures (source: Goldman)

SYST5030 /4030 Wireless LANs — Increasingly becoming more popular. — Still evolving. Basic Idea: Access points connected to a wired LAN Adapters in the mobile unit. Speeds: 2 Mbps to 11 Mbps ( & b) 22 Mbps (802.11g) 54 Mbps (802.11a) Typical coverage area: 100 to 300 feet. Issues: Need to develop protocols that conserve battery power. Need ability to move from one cell to another (“roaming”) Increase speed.

SYST5030 /4030 Wireless LANs

SYST5030 /4030 Wireless Networks Source: ITP Publishing

SYST5030 /4030 Wireless LAN Technologies Radio LANs: Use narrowband microwave frequencies. Spread Spectrum LANs: Use a combination of frequencies. Infrared LANs: Use infrared frequencies. Limitation: This is a line of sight medium. Key Technologies

SYST5030 /4030 Summary LAN technology is a very important networking technology found in all organizations. Ethernet has become a world-wide standard. Most organizations are upgrading their LANs from 10 to 100 Mbps.