FIT3165 / FIT4165 COMPUTER NETWORKS
WEEK 11 – LAN OVERVIEW
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LAN Overview
LOCAL AREA NETWORK OVERVIEW
LAN Applications(1)
● Personal computer LANs
○ low cost of attachment to the network ( client/server apps etc..)
○ high-performance workstations ( 1 Gbps, 10 Gbps..)
● Backend networks
○ interconnecting large systems (High performance computing systems, Server farms, Data repositories, Backup systems and Large storage devices – SAN’s)
■ high data rate
■ high speed interface
■ distributed access
■ limited distance
LAN Applications(2)
● Storage area networks (SANs)
○ Backend networks
○ Separate network handling storage needs
○ Detaches storage tasks from specific servers
○ Six data storage systems categories that include
■ all-flash storage systems, data backup and disaster recovery software and services, backup hardware, hard disk/hybrid storage systems, SAN management tools, and server-based storage products.
○ Shared storage facility
■ eg. hard disks, Blue- D arrays
○ Accessed using a high-speed network ■ eg. Fibre Channel
○ Improved client-server storage access
○ Direct storage to storage communication for backup
LAN Applications(3)
● Six data storage systems categories that include
– Backup and recovery software, include cloud backup and recovery services, disaster
recovery, snapshot and replication, electronic vaulting and archivers.
– Data Backup hardware include tape libraries and drives, backup media, disk backup targets, virtual tape libraries, deduplication devices and gateway appliances for cloud backup.
– Storage and SAN management tools include storage resource management and SAN management software, performance monitoring, configuration management, provisioning and data reduction.
– Server-based storage include hyper-converged and software-defined storage systems that include storage and servers in one chassis; software that pools data to allow storage capacity across servers to work together under common management with storage services.
LAN Applications(4)
● Six data storage systems categories that include
– All-flash systems category include storage platforms that comes with all-flash storage and no hard disk drives; includes FC and iSCSI SAN, NAS, multi-protocol systems, converged/hyper-converged infrastructure products, Direct-attached storage (DAS), solid-state storage drives (SSD’s), disk controllers, caching appliances, storage virtualization appliances and cloud-integrated storage.
– Hybrid storage systems include hybrid flash arrays, Fibre Channel and iSCSI SAN, NAS, multiprotocol systems, converged/hyper-converged infrastructure products, DAS, hard disk drives, disk controllers, caching appliances, storage virtualization appliances and cloud-integrated storage.
Storage Area Networks
DAS, NAS AND SAN Structure
Direct Attached Storage (DAS) Network Attached Storage (NAS) Storage Area Network (SAN)
Network Attached Storage (NAS) Vs Storage Area Networks (SANs)
RAID – Redundant Array of Inexpensive Disks
LAN Applications(5)
● High speed office networks
○ Desktop image processing
○ High capacity local storage
● Backbone LANs
○ Interconnect low speed local LANs
○ Reliability
○ Capacity
Hierarchical Network Design
High-speed WAN routers can carry traffic across the enterprise WAN backbone, medium-speed routers can connect buildings at each campus, and switches can connect user devices and servers within buildings.
Building C-1
Enterprise WAN Backbone
Core Layer
Campus B Campus C
Campus C Backbone
Access Layer
Building C-2
Distribution Layer
LAN Architecture evolution
• Topologies
• Transmission medium • Network Layout
• Medium access control
LAN Topologies
Bus and Tree
• Characterized by the use of multipoint medium
• Transmission propagates throughout medium
• Heard by all stations
• Full duplex connection between station and tap
– allows for transmission and reception
• Need to regulate transmission
– to avoid collisions and channel hogging
• Terminator absorbs frames at end of medium
• The tree topology is a generalization of the bus topology
• Head-end connected to branching cables
tap (T-connector)
Frame Transmission on Bus LAN
Ring Topology
• A closed loop of repeaters joined by point to point links
• Receive data on one link & retransmit on another
– Links are unidirectional
– Stations attach to repeaters
• Data transmitted as frames
– Circulate past all stations
– Destination recognizes address and copies frame
– Frame circulates back to source where it is removed
• Medium access control determines when a station can insert frame
Frame Transmission Ring LAN
This figure illustrates how a frame continues to circulate until it returns to the source station, where the frame is removed
Star Topology
• Each station connects to central node
– Usually via two point to point links (UTP)
• Either central node will broadcast (Hub)
– Physical star, logical bus: frame broadcasting
– Transmission from a station is seen by all others
– Only one station can transmit at a time
– If two stations transmit at the same time we have a collision
• Or central node can act as frame switch
– Frame switching
– Non-broadcast, transmission is private between peers only
– Switch, using full-duplex cables, allows simultaneous transmissions, with no collisions (from Fast Ethernet up)
Star Topology with Hubs or Switches
• Frame Broadcast (hub)
– Frame retransmitted on all outgoing links
– Received by all
– Central node is then
referred to as a hub.
• Frame Switching (switch)
– Incoming frame is buffered in the switch and retransmitted only on an outgoing
link to the destination station. – Central node is referred to
as a switch.
LAN Architecture evolution
The choice of topology depends on a variety of factors •Reliability
•Expandability
•Performance
•Needs considering in context of:
– wiring layout – access control
Bus LAN Transmission Media (1)
– Twisted Pair
> Early LANs used voice grade cable > Didn’t scale for fast LANs
> Not used in bus LANs now
– Baseband coaxial cable
> Uses digital signalling > Original Ethernet
Baseband coaxial cabling is still used in old existing Ethernet but not often in new installations ( also known as thin ethernet, thinnet or thick ethernet thicknet)
Bus LAN Transmission Media (2)
• 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
• Less convenient than star topology twisted pair
broadband coaxial still used in old existing Ethernet but not often in new installations ( also known as thin ethernet, thinnet or thick ethernet thicknet)
Ring and Star Usage
– Very high speed links over long distances
– Single link or repeater failure disables network
– Uses natural layout of wiring in building
– Best for short distances
– High data rates for small number of devices
– The star topology currently dominates the market.
Choice of Medium
Choice of transmission medium is determined by a number of factors and constrained by LAN topology
•Reliability
•Types of data supported •Environmental scope
Media Available
• Voice grade unshielded twisted pair (UTP)
– Cat 3 UTP cable for phones
– cheap but low data rates
• Shielded twisted pair / baseband coaxial
– more expensive, higher data rates
• Broadband coaxial cable
– even more expensive, higher data rate
• High performance UTP
– Cat 5, 5e, 6, 7 & 8 very high data rates, switched star topology
• Optical fibre
– security, high capacity, small size, highest cost
IEEE 802 Layers (1)
• Physical
– encoding/decoding of signals
– preamble generation/removal (synchronization)
– bit transmission/reception
– on transmission medium and topology
IEEE 802 Layers (2)
• Logical Link Control
– interface to higher levels
– flow and error control
• Medium Access Control
– on transmit, assemble data into frame
– on receive, disassemble frame
– govern access to transmission medium
– for the same LLC, there may be several MAC options
LAN Protocols in Context
LLC Services
• Mechanisms for addressing stations across the medium and controlling data exchange
• Format and operations are based on HDLC
1. Unacknowledged connectionless service
2. Connection-mode service
3. Acknowledged connectionless service
The IEEE 802 Reference Model
This architecture was developed by the IEEE 802 committee and has since then been adopted in the definition of LAN standards:
– IEEE 802.3 Ethernet MAC
– IEEE 802.5 Token Ring MAC
– IEEE 802.6 Metropolitan Area Networks – obsoleted
– IEEE 802.11 Wireless LAN – “Wi-Fi” – MAC
– IEEE 802.14 Cable modems – obsoleted
– IEEE 802.15 Wireless PAN
> IEEE 802.15.1 Bluetooth
> IEEE 802.15.4 ZigBee
– IEEE 802.16 Broadband Wireless Access – “WiMAX”
– IEEE 802.16e (Mobile) Broadband Wireless Access
MAC Frame Handling
● MAC layer receives data from LLC layer ● fields
○ MAC control
○ destination MAC address
○ source MAC address
● MAC layer detects errors and discards frames
● LLC optionally retransmits unsuccessful frames
Expanding Networks: Using Repeaters
● Repeaters can address signal attenuation.
● Operates purely at the physical layer.
● Any type of LAN segment has a defined maximum limit to the physical length of the segment and the number of stations that may be attached to it.
● Repeaters are used to connect segments of a LAN.
● Repeaters may use optical isolation to protect segments from power surge transients.
● Signals are simply digitally regenerated.
● But no error checking is performed.
Expanding Networks: Using Bridges
● Connect similar LANs
● Operate at the data link layer (L2)
● Identical physical / link layer protocols
● Minimal processing (Fast)
● Can map between MAC formats
● Perform error checking
● Reasons for use
○ Reliability (partition, fault isolation)
○ Performance (small broadcast domains)
○ Security (physical traffic management)
○ Geography (physical separation)
Bridge Function
• A bridge receives and buffers the frames from a segment.
• A bridge will forward frames only if
– they are error-free and
– are addressed to the other segment in the LAN.
Connection of Two LANs using bridge
Interconnecting LANs: Bus, Hubs and Switches
● Bus: shared medium
● Frame Broadcast (hub)
○ frame retransmitted on all outgoing links ○ received by all stations
○ central node is then referred to as a hub.
● Frame Switching (switch)
○ incoming frame is buffered in the central node and retransmitted on an outgoing link to the destination station.
○ The central node is referred to as a (Layer 2) switch.
Types of Layer 2 Switches
● Store-and-forward switch
○ accepts frame on input line, buffers briefly, routes to destination port ○ see delay between sender and receiver
○ better integrity
● Cut-through switch
○ use destination address at beginning of frame
○ switch begins repeating frame onto output line as soon as destination address recognized
○ highest possible throughput
○ risk of propagating bad frames
Layer 2 Switch vs Bridge
● Layer 2 switch can be viewed as full-duplex hub
● Incorporates logic to function as multiport bridge
● Differences between switches & bridges:
○ bridge frame handling done in software
○ switch performs frame forwarding in hardware
○ bridge analyzes and forwards one frame at a time
○ switch can handle multiple frames at a time
○ bridgeusesstore-and-forwardoperation
○ switch can have cut-through operation
● Hence bridge have suffered commercially
Layer 2 Switch Problems
• Large, flat networks will suffer from broadcast overload
– frames are not broadcast at all times (as in hubs), unless the MAC broadcast address (all bits are 1s) is used
– MAC broadcasts necessary in some situations, e.g., ARP (address resolution protocol, sender knows destination’s IP address but seeks unknown MAC address)
– broadcast frames are delivered to all devices connected by layer 2 switches and/or bridges
– broadcast frames can create big overhead
– broadcast storm from malfunctioning devices
• Current standards lack provision for multiple links
– limits performance & reliability
Expanding Networks: Routers
Break up flat networks into separate networks
Connect two LANs that may not share common medium access control.
Operates at Layer 3 (OSI Network Layer)
Hardware with embedded software:
1. Hardware — can be network server/special device
2. Software – Network Operating System (NOS) and routing protocol
Main functions:
1. Determine a route that a packet will take to reach its destination.
2. Choose the best route, or balance load across routes between the networks when there are several possible routes.
3. Filter traffic by segment.
4. May include firewall functions to isolate traffic by type, destination or direction.
Layer 3 Switches
• Routers do all IP-level processing in software
– High-speed LANs and high-performance layer 2 switches pump millions of packets per second.
– But routers handle well over a million packets per second.
• Solution: layer 3 switches
– implement packet-forwarding logic of router in hardware
• Layer 3 switches are of two categories
– Packet by Packet (like a router does, but faster)
– Flow based
> identifies flows of IP packets with same source and destination
> by observing traffic or using a flow label in packet header (IPv6) > a predefined (optimized) route is used for identified flows
• Connect two or more LANs that use completely different protocols, e.g., IP vs. AppleTalk or IPX.
• Interpret and translates one network protocol into another, translates data formats.
• May consist of software, dedicated hardware, or a combination of both.
• Example: gateways are typically used to connect IBM mainframes that use SNA (System Network Architecture) to LANs that use TCP/IP and Ethernet.
• Disambiguation: the term “default gateway” is typically used to designate an outgoing router or gateway to exit one’s network.
Typical Building – Floor LAN Organization Diagram
Typical Large LAN Organization Diagram
Network Components:
• Network Interface Cards
• Connectors
• Transmission Media
• Server(s)
• Intermediary devices:
– Core Switches
– Core Routers
– Workgroup Switches
Not in diagram:
Repeaters, Bridges, Gateways
● So far we have discussed
○ LAN Overview
○ LAN Applications
○ Evolution of LAN Architecture
○ Devices and example designs
● Next week
○ High Speed LANs
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