COMPUTER NETWORK LECTURE NOTES-- High-Speed LANs

COMPUTER NETWORK LECTURE NOTES-- High-Speed LANs

Emergence of High-Speed LANs

l2 Significant trends

–Computing power of PCs continues to grow rapidly

–Network computing

lExamples of requirements

–Centralized server farms

–Power workgroups

–High-speed local backbone

Classical Ethernet

lBus topology LAN

l10 Mbps

lCSMA/CD medium access control protocol

l2 problems:

–A transmission from any station can be received by all stations

–How to regulate transmission

 

 

Solution to First Problem

lData transmitted in blocks called frames:

–User data

–Frame header containing unique address of destination station

 

CSMA/CD

Carrier Sense Multiple Access/ Carrier Detection

 

lIf the medium is idle, transmit.

lIf the medium is busy, continue to listen until the channel is idle, then transmit immediately.

lIf a collision is detected during transmission, immediately cease transmitting.

lAfter a collision, wait a random amount of time, then attempt to transmit again (repeat from step 1).

 

 

 

 

Medium Options at 10Mbps

l<data rate> <signaling method> <max length>

l10Base5

–10 Mbps

–50-ohm coaxial cable bus

–Maximum segment length 500 meters

l10Base-T

–Twisted pair, maximum length 100 meters

–Star topology (hub or multipoint repeater at central point)

 

 

Hubs and Switches

Hub

lTransmission from a station received by central hub and retransmitted on all outgoing lines

lOnly one transmission at a time

 

Layer 2 Switch

lIncoming frame switched to one outgoing line

lMany transmissions at same time

 

 

Bridge

l  Frame handling done in software

l  Analyze and forward one frame at a time

l  Store-and-forward

 

Layer 2 Switch

l  Frame handling done in hardware

l  Multiple data paths and can handle multiple frames at a time

l  Can do cut-through

Layer 2 Switches

lFlat address space

lBroadcast storm

lOnly one path between any 2 devices

 

lSolution 1: subnetworks connected by routers

lSolution 2: layer 3 switching, packet-forwarding logic in hardware

Benefits of 10 Gbps Ethernet over ATM

lNo expensive, bandwidth consuming conversion between Ethernet packets and ATM cells

lNetwork is Ethernet, end to end

lIP plus Ethernet offers QoS and traffic policing capabilities approach that of ATM

lWide variety of standard optical interfaces for 10 Gbps Ethernet

Fibre Channel

l2 methods of communication with processor:

–I/O channel

–Network communications

lFibre channel combines both

–Simplicity and speed of channel communications

–Flexibility and interconnectivity of network communications

 

 

 

 

 

 

 

 

 

 

I/O channel

lHardware based, high-speed, short distance

lDirect point-to-point or multipoint communications link

lData type qualifiers for routing payload

lLink-level constructs for individual I/O operations

lProtocol specific specifications to support e.g. SCSI

Fibre Channel Network-Oriented Facilities

lFull multiplexing between multiple destinations

lPeer-to-peer connectivity between any pair of ports

lInternetworking with other connection technologies

Fibre Channel Requirements

lFull duplex links with 2 fibres/link

l100 Mbps – 800 Mbps

lDistances up to 10 km

lSmall connectors

lhigh-capacity

lGreater connectivity than existing multidrop channels

lBroad availability

lSupport for multiple cost/performance levels

lSupport for multiple existing interface command sets

Fibre Channel Protocol Architecture

lFC-0 Physical Media

lFC-1 Transmission Protocol

lFC-2 Framing Protocol

lFC-3 Common Services

lFC-4 Mapping