Download ppt

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project

Document related concepts

Wake-on-LAN wikipedia , lookup

Piggybacking (Internet access) wikipedia , lookup

Low-voltage differential signaling wikipedia , lookup

CAN bus wikipedia , lookup

Asynchronous Transfer Mode wikipedia , lookup

IEEE 802.1aq wikipedia , lookup

Net bias wikipedia , lookup

Computer network wikipedia , lookup

Network tap wikipedia , lookup

Deep packet inspection wikipedia , lookup

Zero-configuration networking wikipedia , lookup

Internet protocol suite wikipedia , lookup

Cracking of wireless networks wikipedia , lookup

List of wireless community networks by region wikipedia , lookup

Airborne Networking wikipedia , lookup

Routing in delay-tolerant networking wikipedia , lookup

IEEE 1355 wikipedia , lookup

Recursive InterNetwork Architecture (RINA) wikipedia , lookup

UniPro protocol stack wikipedia , lookup

Transcript
Welcome to COS 461
Vivek Pai
Spring 2003
CS 461
1
Mechanics
• First time teaching 461
– But have been doing some level of networking for a
while…
• Same book as last year – Peterson/Davie
– Will also put others on reserve
• Syllabus on web site, but not updated
– General concepts the same
– Actual dates will differ
Spring 2003
CS 461
2
Assignment
• Read Chapter 1
• Send me an e-mail
– Name, year, phone #, preferred e-mail address
– Jpeg image of yourself
– Reason for taking the course
• Go to newsgroup pu.cs.461
Spring 2003
CS 461
3
But First, A Word From Slammer
Bank of America said 13,000 of its ATMs refused
to dispense cash. In South Korea, the country's
largest ISP, KT, said all almost all its customers
lost their connections during the attack. Chinese
computer users saw sites freeze and a dramatic
slowdown in download speeds, as the worm's
effects hit the Internet's nameservers--the
computers that translate Web addresses into
numerical Internet Protocol addresses. And all
this in just 376 bytes of code, meaning the entire
SQL Slammer worm code is about half the length
of this paragraph.
Spring 2003
CS 461
4
Introduction
Outline
Statistical Multiplexing
Inter-Process Communication
Network Architecture
Performance Metrics
Implementation Issues
Spring 2003
CS 461
5
Building Blocks
• Nodes: PC, special-purpose hardware…
– hosts
– switches
• Links: coax cable, optical fiber…
– point-to-point
– multiple access
Spring 2003
…
CS 461
6
Switched Networks
• A network can be defined recursively as...
– two or more nodes
connected by a link, or
Spring 2003
– two or more networks
connected by a node
CS 461
7
Strategies
• Circuit switching: carry bit streams
– original telephone network
• Packet switching: store-and-forward messages
– Internet
Spring 2003
CS 461
8
Addressing and Routing
• Address: byte-string that identifies a node
– usually unique
• Routing: process of forwarding messages to the
destination node based on its address
• Types of addresses
– unicast: node-specific
– broadcast: all nodes on the network
– multicast: some subset of nodes on the network
Spring 2003
CS 461
9
Multiplexing
• Time-Division Multiplexing (TDM)
• Frequency-Division Multiplexing (FDM)
L1
R1
L2
R2
L3
Spring 2003
Switch 1
Switch 2
CS 461
R3
10
Statistical Multiplexing
•
•
•
•
•
On-demand time-division
Schedule link on a per-packet basis
Packets from different sources interleaved on link
Buffer packets that are contending for the link
Buffer (queue) overflow is called congestion
…
Spring 2003
CS 461
11
Inter-Process Communication
• Turn host-to-host connectivity into process-to-process
communication.
• Fill gap between what applications expect and what the
underlying technology provides.
Host
Host
Application
Host
Channel
Application
Host
Host
Spring 2003
CS 461
12
IPC Abstractions
• Request/Reply
– distributed file systems
– digital libraries (web)
• Stream-Based
– video: sequence of frames
• 1/4 NTSC = 352x240 pixels
• (352 x 240 x 24)/8=247.5KB
• 30 fps = 7500KBps = 60Mbps
– video applications
• on-demand video
• video conferencing
Spring 2003
CS 461
13
What Goes Wrong in the Network?
• Bit-level errors (electrical interference)
• Packet-level errors (congestion)
• Link and node failures
• Packets are delayed
• Packets are deliver out-of-order
• Third parties eavesdrop
Spring 2003
CS 461
14
Layering
• Use abstractions to hide complexity
• Abstraction naturally lead to layering
• Alternative abstractions at each layer
Application programs
Request/reply Message stream
channel
channel
Host-to-host connectivity
Hardware
Spring 2003
CS 461
15
Protocols
• Building blocks of a network architecture
• Each protocol object has two different interfaces
– service interface: operations on this protocol
– peer-to-peer interface: messages exchanged with peer
• Term “protocol” is overloaded
– specification of peer-to-peer interface
– module that implements this interface
Spring 2003
CS 461
16
Interfaces
Host 1
High-level
object
Protocol
Spring 2003
Host 2
Service
interface
Peer-to-peer
interface
CS 461
High-level
object
Protocol
17
Protocol Machinery
• Protocol Graph
– most peer-to-peer communication is indirect
– peer-to-peer is direct only at hardware level
Host 2
Host 1
Digital
Video
File
library
application application application
RRP
Digital
Video
File
library
application application application
MSP
RRP
HHP
Spring 2003
MSP
HHP
CS 461
18
Machinery (cont)
• Multiplexing and Demultiplexing (demux key)
• Encapsulation (header/body)
Host 1
Host 2
Application
program
Application
program
Data
Data
RRP
RRP
RRP Data
RRP Data
HHP
HHP
HHP RRP Data
Spring 2003
CS 461
19
Internet Architecture
• Defined by Internet Engineering Task Force (IETF)
• Hourglass Design
• Application vs Application Protocol (FTP, HTTP)
FTP
HTTP
NV
TFTP
UDP
TCP
IP
NET1
Spring 2003
NET2
CS 461
…
NETn
20
ISO Architecture
End host
End host
Application
Application
Presentation
Presentation
Session
Session
Transport
Transport
Network
Network
Network
Network
Data link
Data link
Data link
Data link
Physical
Physical
Physical
Physical
One or more nodes
within the network
Spring 2003
CS 461
21
Performance Metrics
• Bandwidth (throughput)
– data transmitted per time unit
– link versus end-to-end
– notation
• KB = 210 bytes
• Mbps = 106 bits per second
• Latency (delay)
– time to send message from point A to point B
– one-way versus round-trip time (RTT)
– components
Latency = Propagation + Transmit + Queue
Propagation = Distance / c
Transmit = Size / Bandwidth
Spring 2003
CS 461
22
Bandwidth versus Latency
• Relative importance
– 1-byte: 1ms vs 100ms dominates 1Mbps vs 100Mbps
– 25MB: 1Mbps vs 100Mbps dominates 1ms vs 100ms
• Infinite bandwidth
– RTT dominates
• Throughput = TransferSize / TransferTime
• TransferTime = RTT + 1/Bandwidth x TransferSize
– 1-MB file to 1-Gbps link as 1-KB packet to 1-Mbps link
Spring 2003
CS 461
23
Delay x Bandwidth Product
• Amount of data “in flight” or “in the pipe”
• Usually relative to RTT
• Example: 100ms x 45Mbps = 560KB
Delay
Bandw idth
Spring 2003
CS 461
24
Socket API
• Creating a socket
int socket(int domain, int type, int protocol)
• domain = PF_INET, PF_UNIX
• type = SOCK_STREAM, SOCK_DGRAM,
SOCK_RAW
• Passive Open (on server)
int bind(int socket, struct sockaddr *addr, int addr_len)
int listen(int socket, int backlog)
int accept(int socket, struct sockaddr *addr, int addr_len)
Spring 2003
CS 461
25
Sockets (cont)
• Active Open (on client)
int connect(int socket, struct sockaddr *addr,
int addr_len)
• Sending/Receiving Messages
int send(int socket, char *msg, int mlen, int flags)
int recv(int socket, char *buf, int blen, int flags)
Spring 2003
CS 461
26
Protocol-to-Protocol Interface
• Configure multiple layers
– static versus extensible
• Process Model
– avoid context switches
• Buffer Model
– avoid data copies
Spring 2003
CS 461
27