inst eecs berkeley edu cs61c su05 CS61C Machine Structures Lecture 26 Disks Networks 2005 08 04 CS 61C L26 Disks Networks 1 Andy Carle A Carle Summer 2005 UCB Outlin e Buses Networks Disks CS 61C L26 Disks Networks 2 A Carle Summer 2005 UCB Buses in a PC connect a few devices 2002 Memory CPU bus FSB Memory PCI Interface Data rates P4 Memory 400 MHz 8 bytes 3 2 GB s peak PCI Internal Backplane I O bus Ethernet SCSI Interface Interface Bus shared medium of communication that can connect to many devices Hierarchy SCSI External I O bus PCI 100 MHz 8 bytes wide 0 8 GB s peak SCSI Ultra4 160 MHz Wide 2 bytes 0 3 GB s peak 1 to 15 disks CS 61C L26 Disks Networks 3 Ethernet Local Gigabit Area Ethernet Network 0 125 GB s peak A Carle Summer 2005 UCB Main components of Intel Chipset Pentium II III Northbridge Handles memory Graphics Southbridge I O PCI bus Disk controllers USB controlers Audio Serial I O Interrupt controller Timers CS 61C L26 Disks Networks 4 A Carle Summer 2005 UCB A Three Bus System backside cache Processor Memory Bus FSB Processor Backside Cache bus Memory Bus Adaptor L2 Cache Backplane Bus Adaptor Bus Adaptor I O Bus I O Bus A small number of backplane buses tap into the processor memory bus FSB bus is only used for processor memory traffic I O buses are connected to the backplane bus PCI Advantage load on the FSB is greatly reduced CS 61C L26 Disks Networks 5 A Carle Summer 2005 UCB What is DMA Direct Memory Access Typical I O devices must transfer large amounts of data to memory of processor Disk must transfer complete block Large packets from network Regions of frame buffer DMA gives external device ability to access memory directly much lower overhead than having processor request one word at a time Issue Cache coherence What if I O devices write data that is currently in processor Cache The processor may never see new data Flush cache on every I O operation expensive Solutions CS 61C L26 Disks Networks 6 A Carle Summer 2005 UCB Outlin e Buses Networks Disks CS 61C L26 Disks Networks 7 A Carle Summer 2005 UCB Why Networks Originally sharing I O devices between computers e g printers Then Communicating between computers e g file transfer protocol Then Communicating between people e g email Then Communicating between networks of computers p2p File sharing WWW CS 61C L26 Disks Networks 8 A Carle Summer 2005 UCB How Big is the Network 1999 30 Computers in 271 Soda 400 in inst cs berkeley edu 4 000 in eecs cs berkeley edu 50 000 in berkeley edu 5 000 000 in edu 46 000 000 in US com net edu mil us org 56 000 000 in the world Source Internet Software Consortium CS 61C L26 Disks Networks 9 A Carle Summer 2005 UCB Growth Rates 100 000 000 Internet Hosts 90 000 000 80 000 000 Ethernet Bandwidth 70 000 000 1983 3 mb s 60 000 000 1990 10 mb s 50 000 000 1997 100 mb s 1999 1000 mb s 2004 10 Gig E 40 000 000 30 000 000 20 000 000 10 000 000 0 Jan 93 Apr 95 Jun 97 Aug 99 Source Internet Software Consortium http www isc org CS 61C L26 Disks Networks 10 A Carle Summer 2005 UCB What makes networks work links connecting switches to each other and to computers or devices Computer switch switch network interface switch ability to name the components and to route packets of information messages from a source to a destination Layering protocols and encapsulation as means of abstraction 61C big idea CS 61C L26 Disks Networks 11 A Carle Summer 2005 UCB Typical Types of Networks Local Area Network Ethernet Inside a building Up to 1 km peak Data Rate 10 Mbits sec 100 Mbits sec 10Gbits sec 1 25 12 5 1250 MBytes s Run installed by network administrators Wide Area Network Across a continent 10km to 10000 km peak Data Rate 1 5 Mb s to 10000 Mb s Run installed by telecommunications companies Sprint UUNet MCI AT T Wireless Networks CS 61C L26 Disks Networks 12 A Carle Summer 2005 UCB ABCs of Networks 2 Computers Starting Point Send bits between 2 computers appln appln network interface device OS OS Queue First In First Out on each end Can send both ways Full Duplex Information sent called a message Note Messages also called packets CS 61C L26 Disks Networks 13 A Carle Summer 2005 UCB A Simple Example 2 Computers What is Message Format Similar idea to Instruction Format Fixed size Number bits Length 8 bit Data 32 x Length bits Header Trailer information to deliver message Payload data in message What can be in the data anything that you can represent as bits values chars commands addresses CS 61C L26 Disks Networks 14 A Carle Summer 2005 UCB Questions About Simple Example What if more than 2 computers want to communicate Need computer address field in packet to know which computer should receive it destination and to which computer it came from for reply source just like envelopes Dest Source Len Net ID Net ID CMD Address Data 8 bits 8 bits 8 bits 32xn bits Header Payload CS 61C L26 Disks Networks 15 A Carle Summer 2005 UCB ABCs many computers application application network interface device OS OS switches and routers interpret the header in order to deliver the packet source encodes and destination decodes content of the payload CS 61C L26 Disks Networks 16 A Carle Summer 2005 UCB Questions About Simple Example What if message is garbled in transit Add redundant information that is checked when message arrives to be sure it is OK 8 bit sum of other bytes called Check sum upon arrival compare check sum to sum of rest of information in message Checksum Net ID Net ID Len Header CMD Address Data Payload Trailer Math 55 talks about what a Check sum is CS 61C L26 Disks Networks 17 A Carle Summer 2005 UCB Questions About Simple Example What if message never arrives Receiver tells sender when it arrives ack ala registered mail sender retries if waits too long Don t discard message until get ACK for ACKnowledgment Also if check sum fails don t send ACK Checksum Net ID Net ID Len Header CS 61C L26 Disks Networks 18 ACK INFO CMD Address Data Payload Trailer A Carle Summer 2005 UCB Observations About Simple Example Simple questions such as those above lead to more complex procedures to send receive message and more complex message formats Protocol algorithm for properly sending and receiving messages packets CS 61C L26 Disks Networks 19 A Carle Summer 2005 UCB Software Protocol to Send and Receive SW Send steps 1 Application copies data to OS buffer 2 OS calculates checksum starts timer 3 OS sends data to network interface HW and says start SW Receive steps 3 OS copies data from network interface HW to OS
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