Network + LAN Technologies 1 of 3

Types of LANs: Intro to Ethernet

LAN standards specify signaling and cabling at the physical and data-link layers of the OSI model

IEEE divided the OSI data-link layer into two separate sublayers:

• Logical Link Control (LLC)
  • operates independently of the technology it is workin in
  • interfaces between the network layer above it and the MAC sublayer below it
  • involved int he encapsulation process – an LLC header on a packet instructs the data-link layer what to do with the packet.
• Medium Access Control (MAC)
  • uniquely idenifies multiple devices at the data-link layer
  • for a device to operate on a network it must have  a MAC address

Ethernet (IEEE 802.3 standard) features:

• baseband signaling
  • when a network signal uses all of the available signal frequencies (or the entire bandwidth) to transmit data
• Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
  • used in ethernet and wireless ethernet networks
  • listens to the signal (Carrier Sensing) – only transmits when line is free
  • Listens to see if a collision occurs (Collision Detection) – if so, both devices wait a random amount of time and resend the signal.
  • More than one stantion can be on the network at the same time (multiple access)

802.2 – defines LLC (data-link sublayer) only

802.3 – defines physical layer and MAC (data-link sublayer)

Steps in the CSMA/CD Process

1. Host wants to transmit
2. Is carrier sensed? (if yes > 1 if no >3)
3. Assemble Frame
4. Transmit Data Frame
5. If collision detected? (if yes > 9 if no > 6)
6. Keep transmitting
7. Is transmission done? (if yes > 8 if no > 6)
8. Transmission is complete – media is idle
9. Jam signal is broadcast if collision is detected
10. Attempts +1 (transmission attempt counter increates by one)
11. Attemps too many? (if yes > 12 if no > 13)
12. Too many attempts and transmission is aborted
13. a backoff algorithm calculates “t” (a random length of time that must pass before transmission is attempted)
14. host waits ‘t’ microseconds as calculated by the algorithm then returns to step 4 to try transmitting again.

4 Categories of Ehternet:

10Mbps -

• uses fiber, coax, or TP cables
  • 10Base5 – Coax – 10Mbps – 300 meters per segment
  • 10Base2 – Coax – 10Mbps – 185 meters per segment
  • 10BaseT – UTP – 10 Mbps – 100 meters per segment
  • 10BaseF – Fiber – 10Mbps – 500 – 2000 meters

100 Mbps -

• Uses Fiber, STP or UTP
  • 100BaseT – UTP – 100Mbps – 100 Meters per segment
  • 100BaseVG – UTP – 100Mbps – 213 Meters (Cat 5) or 100 Meters (Cat 3)
  • 100BasesT4 – UTP – 100Mbps  100 Meters per segment
    • uses 4 pairs of Cat 3, Cat 4 or Cat UTP
  • 100BaseTX – UTP – 100Mbps  100 Meters per segment
    • uses 2 pairs of Cat 5 UTP or Type 1 STP
  • 100BaseFX – Fiber – 100Mbps  2000 Meters per segment
  • FDDI (Fiber Distributed Data Interface) – Multimode Fiber – 100Mbps – 10 Km per segment

Gigabit Ethernet -

• uses Multimode  Fiber, UTP or copper Cables
• IEEE 802.3z and 802.3ab relate to Gigabit Ethernet using Fiber optic and TP cables
  • 1000BaseT – copper – 1Gbps – 100 meters per segment
  • 1000BaseTx – Cat 5 – 1Gbps – 100 meters per segment
  • 1000BaseCx – copper STP – 1Gbps – 25 meters
  • 1000BaseSx – multimode Fiber – 1Gbps – 550 meters
  • 1000BaseLx – multimode Fiber – 1Gbps – 550 meters

10 Gigabit -

• 802.3ae standard relates to 10 Gigabit Ethernet
  • 10GBaseCX4 – twin-axial copper cables – 10Gbps – 15 meters per segment
  • 10GBaseSR – FDDI-grade multimode fiber – 10Gbps – 300 meters
  • 10GBaseLX4 – FDDI-grade multimode fiber or single mode fiber – 10Gbps – 300 m or 10 km
  • 10GBaseLR – Single mode fiber – 10Gbps – 10 km
  • 10GBaseER – single mode fiber – 10Gbps – 40 km

Types of LANs: Token Ring and FDDI

802.5 – IEEE toekn ring standard (almost identical to IBM token ring standard)

Uses Star topology

all NIC are connected to a Multistation Access Unit (MAU or MSAU)

Token Ring Advantages:

• Performs Regeneration – reduces degradation because each data signal transmitted on the network is read and repeated by each of the devices on the network that it passes
• Performance “degrades w/ Grace” – as traffic increases the network gets slower because there is only one token. It does not crash. TR networks are very reliable
• Communicates with IBM mainframes – IBM mainframes are still used
• Reliable deterministic – able to calculate maximum amount of wait time
• Uses sophisticated priority system – allows “high-priority” nodes

Token Ring Management Mechanisms:

• Active Monitors – any station can be an active monitor. becomes the centralized source of timing information for other stations in the ring
• MAUs (Multistation Access Units or MSAUs) – in star topology MSUs see all connections on the network, can check devices for faults and remove faulted stations from the network.
• Beaconing - when a station detects a fault (for example a cable break) it sends out a beacon frame. The beacon frame defines the failure domain: the station reporting the failure, the nearest active upstream neighbor (NAUN) and everything inbetween. Activates autoreconfiguration – MSAUs can do this using electrical reconfiguration.

FDDI – combines fault tolerance of Token Ring with high-speed cababilities of Fiber Optic. Opperate at 100Mbps

Supports real-time allocation of network bandwith

• Synchronous: used for Voice and Video – allocated to stations that need continuous transmission capability
• Asynchronous: The bandwitch left after the synchronous allocation is allocated to the asynchronous traffic. And 8 level priority scheme is used – higher level priority stations can lock out other lower-level stations

FDDI  use a dual-righ architecture that is counter rotating. The secondary ring is used when the primary ring fails.

Stations on a FDDI network

SAS (Single Attached Stations): attached to only one ring

DAS (Dual Attached Stations): attached to both rings

Types of LANs: Wireless Transmission

1. Spread Spectrum: the frequency of the transmitted signal is deliberately varied over a range or frequencies causing the signal to become noise-like and harder to intercept

-much more resistant to interference vs. conventional narrowband wireless signals.

802.11 – spread spectrum standard for IEEE

DSSS (Direct Sequence Spread Spectrum)

• Chipping: Uses a spreading code, called a PN (pseudorandom noise code) a sequence of chips or bit of information. Each “0″ or “1″ bit in the signal is represented by the code sequences so the signal is represented by a long code instead of the signal itself
• Signal Modification: the encoded representation of teh signal then modulates the carrier signal – spreading it over the range of reequencies being used (bandwidth)
  • There is a peak in the signal’s power at the main boradcast fequency and on the either side of this peack there are gradulally dissipating peakes called “side lobes”.
  • The width and number of side lobes depends on hte spreading code used and the signal itself.

FHSS (Frequency Hopping Spread Spectrum)

• Frequency Hopping: most widely used – if intercepted it is only for a moment before the frequency hops again.
• Signal Modulation:
  • Step 1: signal modulates the frequency of the carrier wave – results in a regular narrowband signal
  • Step 2: Spredding code is applied to modulate the carrier wave causing it to hop between frequencies – the spreading code provides a list of frequencies for the wave to hop to as well as the length of time is should stay at each frequency

2. Bluetooth - short range radio technology that operates on the 2.4 GHz ISM (Industrial Scientific Medical) band.

Uses:

• Automatic Synchronization: allows automatic communication between devices such as cellphone and computers
• Internet Bridge: Allows cellphone or modem to act as a wireless modem to dial up to the internet or receive data calls
• Bluetooth Headset: cellphone headset.

Bluetooth Integrated Security Features:

• Challenge-Response authentication
• Encryption
• session key generation (session keys can be changed at any time during a connection)

Two bluetooth ranges:

10 Meters at 1 mW (milliWatt)

100 Meters at 100 mW (milliwatts)

Not suitable for LAN or WAN applications – not desinged to carry heavy traffic loads.

3. Infrared (IR) – a form of electromagnetic (EM) radiation that operates at an extremely high frequency.

- in the EM spectrum IR is located between microwaves and visible light – the most useful band is the band just below visible light

LED IR has a Typical range of 3 M

Diffuse IR emits beams in an arc – the beams can bounce off obstructions and find at least one path tot he reciving device. Diffuse IR has a range of 270 square meters

IR Lasers can travel 5 km – suceptable to interference from other light sources and requires a filter at recieving end.

Types of LANs: Wireless LANs

802.11 standard uses

DSSS in noisy environments at 1 Mbps

FHSS in less noisy environments at 2 Mbps

802.11 uses CSMA/CA

802.11 a – 54 Mbps, 5 GHz, 25 – 75 ft.

802.11 b – 11 Mbps, 2.4 GHz, 100 – 150 ft.

802.11 g – 54 Mbps, 2.4 GHz, 100 – 150 ft.

Devices on a wireless network are either basestations or clietents. (Basestations are commonly called access points)

Basestations are required to provide: association, distribution, integration and reassociation services to clients on the wireless network.

Wireless LAN modes:

• Ad hoc: no basestaions – all clients can access each other and communicate directly. All nodes have equal rights and responsibilities. Separate networks may coexists on the same frequencey using different SSIDs (Service Set Identifiers)
• Infrastructure: basestation is used – clients only communicate with basestation and do not directly communicate with each other. Multiple basesations can be used to broaden the coverage area.

3 Main Components in a Wireless LAN:

1. Wireless NICs: All devices or nodes need a NIC. A wireless NIC has a fixed or internal antenna.
2. Access Points: Used to connect existing wired or wireless networks or to extend the range or a wireless network. Uses an omnidirectional antenna, a wired NIC, and bridging software (forwards data between the LAN and the wireless nodes)
3. Wireless Bridges: Used to connect two LANs. Use unlicensed Spread Spectrum Radio Frequency (RF) or Lazer IR.

Wireless Topologies:

Bus: all nodes are within point-to-point coverage and they communicate with each other forming a BSS (Basic Service Set.) No access point is needed.

Star: Allow nodes to communicate beyond BSS to ESS (Extended Service Set). Use access points to extend network coverage by 400% creating and ESA (Extended Service Area.)

Factors that affect performance:

Interference: Caused when a signal, other than the desired signal, is transmitted on the same or nearyby frequency.

Surrounding Environment: Walls, Concrete floos, electrical equipment, building structural elements, and natrual obstructions (trees, mountains, etc…) negatively affect performance by obstructing wireless signals.

Types of Antennae used: Can Omnidirectional or Point to Point.

Noise: the less noisy the conditions the better the performance of the wireless LAN