1. Communication Networks
Lecture Week 3
Local Area Network

2. 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

3. 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

4. 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

5. 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

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

7. 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

8. 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

9. 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

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

11. 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

12. 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

13. 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

14. 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

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

16. 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

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

18. 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

19. 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

20. 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

21. 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

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

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

24. 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

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

26. 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

27. 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

28. 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

29. 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

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

31. 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

32. 10 Mbps Specifications (Ethernet)
CC2009NI - Communication Networks, Saroj S. Regmi

33. 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

34. 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

35. 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

36. 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

37. 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

38. 10 Gbps Ethernet Advantages
CC2009NI - Communication Networks, Saroj S. Regmi

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

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