CCDA Notes: Enterprise LAN Design (LAN Media)

Enterprise LAN Design

LAN Media

Ethernet Design Rules

Scalability Constraints for 802.3:

Specification
10BASE5 (Thicknet)

• Bus Topology
• 500 meter maximum segment length
• 100 maximum attachments per segment
• 2500 meters of five segments and four repeaters, of which only three segments can be populated as maximum collision domain

10BASE2 (Thinnet)

• Bus Topology
• 185 meter maximum segment length
• 30 maximum attachments per segment
• 2500 meters of five segments and four repeaters, of which only three segments can be populated as maximum collision domain

10BASET (Ethernet)

• Star Topology
• 100 meters from hub to station
• 2 maximum attachments per segment (hub and station or hub - hub)
• 2500 meters of five segments and four repeaters, of which only three segments can be populated as maximum collision domain

100BASET (Fast Ethernet)

• Star Topology
• 100 meters from hub to station
• 2 maximum attachments per segment (hub and station or hub - hub)
• Maximum collision domain is dependent on repeater technology but in general can only have two repeaters. Most networks use switches instead of repeaters

Main design rule for Ethernet is that the round-trip propagation delay in a single collision domain must not exceed 512-bit times in order for collision detection to work correctly. Maximum round-trip delay for 10MBPS Ethernet is 51.2 microseconds and 100MBPS Ethernet network is only 5.12 because its delay is .001 instead of .01

100-MBPS Fast Ethernet Design Rules

Uses CSMA/CD (Carrier Sense Multiple Access / Collision Detection) and UTP/fiber cabling. Speed/distance constraints are greater with Fast Ethernet because delays must be shorter to meet 512 bit rule (5.12 microseconds). Cabling specifications follow:

• 100BASE-TX
• 100BASE-T4
• 100BASE-FX

100BASE-TX Fast Ethernet

100BASE-TX requires no special cabling to support over 10-Mbps Ethernet. Uses Cat5 UTP wiring, RJ-45 connectors. Utilizes only two pairs of the four-pair UTP wiring. Punchdown blocks in wiring closet must be Cat5 certified if used. Uses 4B5B coding.

100BASE-T4 Fast Ethernet

100BASE-T4 not widely deployed, supports Cat3, Cat4 and Cat5 UTP. To support older wiring, three of four wiring pairs are utilized with the fourth being reserved for collision detection Since there is no separate transmit/receive pairs this cabling cannot run at full-duplex. Uses 8B6T coding.

100BASE-FX Fast Ethernet

100BASE-FX is a fiber cabling standard. Operates over two strands of multimode or single-mode fiber with media interface connectors (MIC), Stab and Twist (ST), or Stab and Click (SC) fiber connectors. Fiber can transmit over greater distances than copper. Uses 4B5B coding.

100BASE-T Repeaters

Fast Ethernet limited to two repeaters. General rule is that Fast Ethernet has maximum diameter of 205 meters with UTP cabling. Since switches are used instead of repeaters in modern networks, effective length of cabling is 100 meters between host and switch.

Gigabit Ethernet Design Rules

802.3z-1998 specifies Gigabit Ethernet over fiber and coax and introduces GMII (Gigabit Media-Independent Interface). 802.3ab-1999 specified operation of Gigabit Ethernet over Cat5 UTP. Both are rolled into latest revision 802.3-2002. GigEthernet still uses same framing methods, CSMA/CD and full-duplex communication. All GigEthernet uses 8B10B coding.

Scalability Constraints/Specifications for Gigabit Ethernet

1000BASE-T

• 100 meter maximum segment length
• Cat5, four-pair UTP media

1000Base-LX Long-Wavelength

• 62.5 micrometer wiring: 440 meter maximum segment length
• 50 micrometer wiring: 550 meter maximum segment length
• 9 micrometer (single-mode fiber): 5 kilometer maximum segment length
• Single/multi-mode fiber

1000BASE-SX Short Wavelength

• 62.5 micrometer wiring: 220 meter maximum segment length
• 50 micrometer wiring: 500 meter maximum segment length
• Multimode fiber media

1000BASE-CX Gigabit Over Coaxial

• 25 meters meter maximum segment length
• Used mainly for server connections
• Shielded balanced copper media

1000BASE-T Gigabit Over UTP

• Cat5, 4-pair UTP
• Maximum length 100 meters
• Five-level coding scheme
• 1 byte is sent over 4 pairs at 1250 MHZ

10Gigabit Ethernet Design Rules

802.ae supplement to 802.3 standard defines 10 Gigabit Ethernet. Defined for full-duplex operation over fiber, UTP and copper. Disallows usage of hubs/repeaters as they operate in half-duplex mode. Distances covered are consistent with MAN (Metropolitan Area Network) and WAN designs. Also includes data centers/server farms, corporate backbones.

10GE Media

10GBASE-SR

• Short-wavelength multimode fiber media using 66B encoding
• 300 meter maximum distance

10GBASE-SW

• Short-wavelength multimode fiber media using Wan Interface Sublayer (WIS)
• 300 meter maximum distance

10GBASE-LR

• Long-wavelength single-mode fiber using 66B encoding
• 10 kilometers maximum distance

10GBASE-LW

• Long-wavelength single-mode fiber using WIS
• 10 kilometers maximum distance

10GBASE-ER

• Extra-long wavelength single-mode fiber using 66B encoding
• 40 kilometers maximum distance

10GBASE-EW

• Extra-long wavelength single-mode fiber using WIS
• 40 kilometers maximum distance

10GBASE-LX4

• Division multiplexing to leverage SMF and MMF using 8B/10B encoding
• 10 kilometer maximum distance

10GBASE-CX4

• Four pairs of twinax copper
• 15 meters maximum distance

10GBASE-T

• Cat6a UTP
• 100 meter maximum distance

EtherChannel

Cisco Etherchannel allows method of increasing bandwidth/link redundancy by bundling like speeds, ie, FastEthernet, Gigabit and 10GE into single logical port load balancing across all physical links. Can be formed with up to eight compatibly configured ports, must have same speed, duplex and vlan

Comparing Campus Media

Copper/UTP

• Up to 10GBPS
• Up to 100 meters
• Inexpensive

Multimode Fiber

• Up to 10GBPS
• Up to 2 kilometers (FastEthernet)
• Up to 550 meters (GigabitEthernet)
• Up to 300 meters (10GigabitEthernet)
• Moderate cost

Single-mode Fiber

• Up to 10GBPS
• Up to 100 kilometers (FE)
• Up to 5 kilometers (GE)
• Up to 40 kilometers (10GE)
• Moderate to expensive cost

Wireless LAN

• Up to 300MBPS
• Up to 500 meters at 1MBPS
• Moderate cost