Download Networking Basics - Undergraduate Research in Consumer

Introduction to Networking
Slides adapted from Larry Peterson
Outline
Applications and Features
Statistical Multiplexing
Inter-Process Communication
Network Architecture
Performance Metrics
Implementation Issues
Summer 2014
NSF/MU REU
1
Goal
• Network applications
– WWW, email
– File sharing, Napster, Facebook
– Streaming media, Skype, IPTV
• PPLive: http://www.pptv.com/
• YouTube: http://www.youtube.com/
• How does it work?
– Scalable connectivity
– Cost efficient resource sharing
– Support for common services
• Course objective:
– Understand some basic principles of computer network
Summer 2014
NSF/MU REU
2
1
What’s a Network: Key Features
•
Providing certain services
–
•
Shared resources
–
•
used by many users, often concurrently
Basic building blocks
–
–
•
transport goods, mail, information or data
nodes (active entities): process and transfer goods/data
links (passive medium): passive “carrier” of goods/data
Typically “multi-hop”
–
–
two “end points” cannot directly reach each other
need other nodes/entities to relay
Summer 2014
NSF/MU REU
3
What’s a Network: “Nuts and Bolts” View
router
•
•
network edge: millions of endsystem devices:
– pc’s workstations, servers
– PDA’s, phones, toasters
running network apps
network core: routers, switches
forwarding data
server
workstation
mobile
local net
regional net
– packets: packet switching
– calls: circuit switching
•
communication links
– fiber, copper, radio, …
Summer 2014
company
net
NSF/MU REU
4
2
Building Blocks
• Nodes: PC, special-purpose hardware…
– hosts
– switches (store-and-forward)
• Links: coax cable, optical fiber…
– point-to-point
(a)
– multiple access
(b)
Summer 2014
■■■
NSF/MU REU
5
Brief History of the Internet
• 70’s: started as a research project, 56 kbps, < 100
computers
• 80-83: ARPANET and MILNET split,
• 85-86: NSF builds NSFNET as backbone, links 6
Supercomputer centers, 1.5 Mbps, 10,000 computers
• 87-90: link regional networks, NSI (NASA), ESNet(DOE),
DARTnet, TWBNet (DARPA), 100,000 computers
• 90-92: NSFNET moves to 45 Mbps, 16 mid-level networks
• 94: NSF backbone dismantled, multiple private backbones
• Today: backbones run at >10 Gbps, >600 millions
computers in >190 countries
Summer 2014
NSF/MU REU
6
3
Sprint
Network
Seattle
Tacoma
Click here for
a closer look
at the Sprint
network on the
East Coast
Click here for a closer look at the
Sprint network in Washington state
Stockton
Cheyenne
San Jose
Click here for
a closer look
at the Sprint
network in
Northern
California
DS3
OC3
OC12
OC48
Legend
New York
Pennsauken
Relay
Wash. DC
Chicago
Kansas City
Roachdale
Anaheim
Atlanta
Pearl City in Hawaii is
a future network location
Fort Worth
Orlando
Summer 2014
NSF/MU REU
7
Addressing and Routing
• Address: byte-string that identifies a node
– usually unique
– What other properties?
• 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
Summer 2014
NSF/MU REU
8
4
Statistical Multiplexing
•
•
•
•
•
•
Used in Internet
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
■■■
Summer 2014
NSF/MU REU
9
Inter-Process Communication
• Turn host-to-host connectivity into process-to-process
communication (to support common services).
• Fill gap between what applications expect and what the
underlying technology provides.
Host
Host
Application
Channel
Host
Application
Host
Summer 2014
Host
NSF/MU REU
10
5
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
Summer 2014
NSF/MU REU
11
Internet Architecture
• Defined by Internet Engineering Task Force (IETF)
• Hourglass Design
• Application vs Application Protocol (FTP, HTTP)
FTP
HTTP
NV
TFTP
UDP
TCP
IP
NET 1
Summer 2014
NET 2
NSF/MU REU
■■■
NET n
12
6
Layering: Logical Communication
E.g.: transport
•
•
•
•
•
take data from app
add addressing,
reliability check info
to form “datagram”
send datagram to peer
wait for peer to ack
receipt
analogy: post office
Summer 2014
data
application
transport
transport
network
link
physical
ack
application
transport
network
link
physical
network
link
physical
data
application
transport
network
link
physical
NSF/MU REU
data
application
transport
transport
network
link
physical
13
Layering: Physical Communication
data
application
transport
network
link
physical
application
transport
network
link
physical
Summer 2014
network
link
physical
application
transport
network
link
physical
NSF/MU REU
data
application
transport
network
link
physical
14
7
Performance Metrics
• Bandwidth (throughput)
– data transmitted per time unit
– link versus end-to-end (effective bandwidth)
– 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
Summer 2014
NSF/MU REU
15
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)
Summer 2014
NSF/MU REU
16
8
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)
Summer 2014
NSF/MU REU
17
Direct Link Networks
Point-to-Point Links
Shared Access Networks
FTP
Our goals:
understand principles behind data
link layer services:
HTTP
NSF/MU REU
TFTP
UDP
TCP
IP
NET1
Summer 2014
NV
NET
2
■■■
NETn
18
9
Point-to-Point Links
Slides adapted from Larry Peterson
Encoding
Framing
Error Detection
Sliding Window Algorithm
Summer 2014
NSF/MU REU
19
CRC Example
• Message M(x): x7+x4+x3+x1
• Multiply by X3
• C(x)=1101
11111001
1101 10011010000
1101
1001
…
101
10011010
10011010000
remainder
• Send 10011010101
Summer 2014
NSF/MU REU
20
10
Acknowledgements & Timeouts
Sender
Receiver
Fram
Sender
Receiver
Fram
e
e
ACK
ACK
Fram
e
Duplicated frame
ACK
(a)
(c)
Sender
Receiver
Fram
Sender
Receiver
Fram
e
e
ACK
Fram
Fram
e
e
Duplicated frame
ACK
ACK
(b)
(d)
include 1-bit sequence number
Summer 2014
NSF/MU REU
21
Sliding Window
• Allow multiple outstanding (un-ACKed) frames
• Upper bound on un-ACKed frames, called window
• How to determine the value of “window”?
Sender
Summer 2014
NSF/MU REU
Receiver
22
11
Timeline Diagram for Sliding Window
SWS=RWS=3 frames
Timeout= 2 RTT
Summer 2014
NSF/MU REU
23
Shared Access Networks
Slides adapted from Larry Peterson
Outline
Bus (Ethernet)
Wireless (802.11) (later)
Summer 2014
NSF/MU REU
24
12
Ethernet Overview
• History
–
–
–
–
developed by Xerox PARC in mid-1970s
roots in Aloha packet-radio network
standardized by Xerox, DEC, and Intel in 1978
similar to IEEE 802.3 standard
• Media access control (MAC)
– CSMA/CD
• carrier sense
• multiple access
• collision detection
• Frame 64
Format
Preamble
48
48
16
Dest
addr
Src
addr
Type
Summer 2014
32
Body
CRC
NSF/MU REU
25
Transmit Algorithm
• If line is idle…
– send immediately
– upper bound message size of 1500 bytes
• If line is busy…
– wait until idle and transmit immediately
– called 1-persistent (special case of p-persistent)
Summer 2014
NSF/MU REU
26
13
Algorithm (cont)
• If detect collision…
– Send jamming signal for 32 bits, then stop transmitting
frame
– delay and try again
• 1st time: delay 0 or 51.2us
• 2nd time: 0, 51.2, 102.4, 153.6us
• 3rd time: 0, 51.2, 102.4, …, or 7*51.2us
• nth time: k x 51.2us, for randomly selected
k=0..2n - 1
• give up after several tries (usually 16)
• exponential backoff
Summer 2014
NSF/MU REU
27
Switching and Forwarding
Slides adapted from Larry Peterson
Outline
Store-and-Forward Switches
Bridges and Extended LANs
FTP
HTTP
NV
TFTP
UDP
TCP
IP
NET1
Summer 2014
NSF/MU REU
NET
2
■■■
NETn
28
14
Scalable Networks
• Switch
– forwards packets from input port to output port
– port selected based on address in packet header
T3
T3
STS-1
Switch
Input
ports
T3
T3
STS-1
Output
ports
• Advantages
– cover large geographic area (tolerate latency)
– support large numbers of hosts (scalable bandwidth)
• Three approaches
Summer 2014
NSF/MU REU
29
Datagram Model
• There is no round trip delay waiting for connection setup; a
host can send data as soon as it is ready.
• Source host has no way of knowing if the network is
capable of delivering a packet or if the destination host is
even up.
• Since packets are treated independently, it is possible to
route around link and node failures.
• Since every packet must carry the full address of the
destination, the overhead per packet is higher than for the
connection-oriented model.
Summer 2014
NSF/MU REU
30
15
Bridges: Traffic Isolation
• Bridge installation breaks LAN into LAN segments
• bridges filter packets:
– same-LAN-segment frames not usually forwarded onto
other LAN segments
– when frame is to be forwarded, uses CSMA/CD to
access segment
– segments become separate collision domains
collision
domain
collision
domain
bridge
LAN segment
= hub
= host
LAN segment
Extended LAN
Summer 2014
NSF/MU REU
31
Learning Bridges
• Do not forward when unnecessary
– based on MAC dest address
• Maintain forwarding table
A
B
C
Port 1
Bridge
Port 2
X
Y
Z
Host
A
B
C
X
Y
Z
Port
1
1
1
2
2
2
• Plug-and-play, self-learning
– bridges do not need to be configured
– learn table entries based on MAC source address
• Always forward broadcast frames
Summer 2014
NSF/MU REU
32
16
Internetworking
Slides adapted from Larry Peterson
Outline
FTP
Best Effort Service Model
Global Addressing Scheme
HTTP
NV
TFTP
UDP
TCP
IP
NET1
Summer 2014
NET
2
■■■
NETn
NSF/MU REU
1
The Internet Network layer
Host, router network layer functions:
Transport layer: TCP, UDP
Network
layer
IP protocol
•addressing conventions
•datagram format
•packet handling conventions
Routing protocols
•path selection
•RIP, OSPF, BGP
forwarding
table
ICMP protocol
•error reporting
•router “signaling”
Link layer
physical layer
Summer 2014
NSF/MU REU
2
1
Service Model
• Connectionless (datagram-based)
• Best-effort delivery (unreliable service)
–
–
–
–
packets are lost
packets are delivered out of order
duplicate copies of a packet are delivered
packets can be delayed for a long time
• Datagram format
0
4
Version
8
16
31
Length
Ident
TTL
19
TOS
HLen
Flags
Offset
Protocol
Checksum
SourceAddr
DestinationAddr
Pad
(variable)
Options (variable)
Data
Summer 2014
NSF/MU REU
3
Global Addresses
• IP address: 32-bit identifier for host, router interface
• Properties
– globally unique
– hierarchical: network + host
“class-full” addressing:
class
• Dot Notation
– 10.3.2.4
– 128.96.33.81
– 192.12.69.77
(a)
7
0
24
Network
Host
14
(b)
1
0
1
1
16
Network
Host
21
(c)
Summer 2014
NSF/MU REU
0
Network
8
Host
4
2
Datagram Forwarding
• Strategy
–
–
–
–
–
–
every datagram contains destination’s address
if connected to destination network, then forward to host
if not directly connected, then forward to some router
forwarding table maps network number into next hop
each host has a default router
each router maintains a forwarding table
• Example (R2)
Summer 2014
Network Number
1
2
3
4
Next Hop
R3
R1
interface 1
interface 0
NSF/MU REU
5
Routing
Slides adapted from Larry Peterson and Rose
Outline
FTP
Algorithms
Scalability
HTTP
TFTP
UDP
TCP
IP
NET1
Summer 2014
NV
NSF/MU REU
NET
2
■■■
NETn
6
3
Overview
• Forwarding vs Routing
– forwarding: to select an output port based on
destination address and routing table
– routing: process by which routing table is built
• Network as a Graph
A
4
2
1
B
C
6
1
3
9
E
F
1
D
• Problem: Find lowest cost path between two nodes
• Factors
– static: topology
– dynamic: load
Summer 2014
NSF/MU REU
7
Routing Algorithm Classification
Global or decentralized information?
Global:
• all routers have complete topology, link cost info
• “link state” algorithms
Decentralized:
• router knows physically-connected neighbors, link costs to
neighbors
• iterative process of computation, exchange of info with
neighbors
• “distance vector” algorithms
Summer 2014
NSF/MU REU
8
4
Dijkstra’s Algorithm
1 Initialization:
2 N = {A}
3 for all nodes v
4
if v adjacent to A
5
then D(v) = c(A,v)
6
else D(v) = infinity
7
8 Loop
9 find w not in N such that D(w) is a minimum
10 add w to N
11 update D(v) for all v adjacent to w and not in N:
12
D(v) = min( D(v), D(w) + c(w,v) )
13 /* new cost to v is either old cost to v or known
14 shortest path cost to w plus cost from w to v */
15 until all nodes in N
Summer 2014
NSF/MU REU
9
Dijkstra’s algorithm: example
Step
0
1
2
3
4
5
start N
A
AD
ADE
ADEB
ADEBC
ADEBCF
D(B),p(B) D(C),p(C) D(D),p(D) D(E),p(E) D(F),p(F)
2,A
1,A
5,A
infinity
infinity
2,A
4,D
2,D
infinity
2,A
3,E
4,E
3,E
4,E
4,E
5
2
A
2
1
Summer 2014
B
D
3
C
3
1
5
F
1
E
NSF/MU REU
2
10
5
Route Propagation
• Know a smarter router
–
–
–
–
hosts know local router
local routers know site routers
site routers know core router
core routers know everything
• Autonomous System (AS)
– corresponds to an administrative domain
– examples: University, company, backbone network
– assign each AS a 16-bit number
• Two-level route propagation hierarchy
– interior gateway protocol (each AS selects its own)
– exterior gateway protocol (Internet-wide standard)
Summer 2014
NSF/MU REU
11
Inter-AS routing in the Internet: BGP
R4
R5
R3
BGP
AS1
AS2
(RIP intra-AS
routing)
(OSPF
intra-AS
routing)
BGP
R1
R2
AS3
(OSPF intra-AS
routing)
Figure 4.5.2-new2: BGP use for inter-domain routing
Adapted from Rose
Summer 2014
NSF/MU REU
12
6
Reliable Byte-Stream (TCP)
Slides adapted from Larry Peterson
Outline
Connection Establishment/Termination
Sliding Window Revisited
FTP HTTP
Flow Control
Adaptive Timeout
TCP
NV
TFTP
UDP
IP
NET1
Summer 2014
NET
2
■■■
NSF/MU REU
NETn
13
Simple Demultiplexor (UDP)
•
•
•
•
Unreliable and unordered datagram service
Adds multiplexing: (port, host) pair
No flow control
Endpoints identified by ports
– Use well-known port
• Header format
0
16
31
SrcPort
DstPort
Length
Checksum
Data
Summer 2014
NSF/MU REU
14
7
TCP Overview
• Connection-oriented
• Byte-stream
• Full duplex
• Flow control: keep sender
from overrunning receiver
• Congestion control: keep
sender from overrunning
network
– app writes bytes
– TCP sends segments
– app reads bytes
Application process
Application process
Write
bytes
Read
bytes
TCP
TCP
Send buffer
Receive buffer
Segment
Summer 2014
Segment
■■■
Segment
Transmit
segments
NSF/MU
REU
15
Segment Format
0
10
4
16
31
SrcPort
DstPort
SequenceNum
Acknowledgment
HdrLen
0
Flags
AdvertisedWindow
Checksum
UrgPtr
Options (variable)
Data
Summer 2014
NSF/MU REU
16
8
Sliding Window Revisited
Sending application
Receiving application
TCP
TCP
LastByteWritten
LastByteAcked
LastByteRead
LastByteSent
NextByteExpected
(a)
• Sending side
• Receiving side
– LastByteAcked < =
LastByteSent
– LastByteSent < =
LastByteWritten
– buffer bytes between
LastByteAcked and
LastByteWritten
Summer 2014
LastByteRcvd
(b)
– LastByteRead <
NextByteExpected
– NextByteExpected < =
LastByteRcvd +1
– buffer bytes between
NextByteRead and
LastByteRcvd
NSF/MU REU
17
Congestion Control
Slides adapted from Larry Peterson
Outline
Queuing Discipline
Reacting to Congestion
Avoiding Congestion
FTP
HTTP
NV
TFTP
UDP
TCP
IP
NET1
NET
2
■■■
NETn
Resource allocation?
Summer 2014
NSF/MU REU
18
9
Issues
• Two sides of the same coin
– pre-allocate resources so as to avoid congestion
– control congestion if (and when) it occurs
Source
1
10-M
bp
s Et
hern
et
Router
1.5-Mbps T1 link
Source
2
ps
-Mb
100
I
FDD
Destination
Bottleneck router
• Two points of implementation
– hosts at the edges of the network (transport protocol)
– routers inside the network (queuing discipline)
• Underlying service model
– best-effort (assume for now)
– multiple qualities of service (not to be covered)
Summer 2014
NSF/MU REU
19
Queuing Discipline
• First-In-First-Out (FIFO)
– does not discriminate between traffic sources
• Fair Queuing (FQ)
– explicitly segregates traffic based on flows
– ensures no flow captures more than its share of capacity
– variation: weighted fair queuing (WFQ)
• Problem?
– Packet length variation
Flow 1
– Needs virtually bit-by-bit round-robin.
Flow 2
Round-robin
service
Flow 3
Flow 4
Summer 2014
NSF/MU REU
20
10
TCP Congestion Control:
Additive Increase/Multiplicative
Decrease (AIMD)
• Objective: adjust to changes in the available capacity
• New state variable per connection: CongestionWindow
– limits how much data source has in transit
MaxWin = MIN(CongestionWindow,
AdvertisedWindow)
EffWin = MaxWin - (LastByteSent LastByteAcked)
• Idea:
– increase CongestionWindow when congestion goes down
– decrease CongestionWindow when congestion goes up
Summer 2014
NSF/MU REU
21
AIMD (cont)
Source
Destination
• Algorithm
– increment CongestionWindow by
one packet per RTT (linear increase)
– divide CongestionWindow by two
whenever a timeout occurs
(multiplicative decrease)
Summer 2014
NSF/MU REU
22
11
AIMD (cont)
• Trace: typical sawtooth behavior
CongestionWindow
70
60
50
40
30
20
10
1.0
2.0
3.0
Summer 2014
4.0
5.0
6.0
Time (seconds)
7.0
8.0
9.0
NSF/MU REU
10.0
23
Congestion Avoidance
• TCP’s strategy
– control congestion once it happens
– repeatedly increase load in an effort to find the point at which
congestion occurs, and then back off
• Alternative strategy
– predict when congestion is about to happen
– reduce rate before packets start being discarded
– call this congestion avoidance, instead of congestion control
• Two possibilities
– router-centric: DECbit and RED Gateways
– host-centric: TCP Vegas
Summer 2014
NSF/MU REU
24
12
Random Early Detection (RED)
• Notification is implicit
– just drop the packet (TCP will timeout)
– could make explicit by marking the packet
• Early random drop
– rather than wait for queue to become full, drop each
arriving packet with some drop probability whenever
the queue length exceeds some drop level
Summer 2014
NSF/MU REU
25
Application Layer
Slides adapted from Kurose and Ross, Chapter 2
Computer Networking: A Top Down Approach Featuring the
Internet, 3rd edition.
Jim Kurose, Keith Ross
Addison-Wesley, July 2005.
FTP
HTTP
NV
TFTP
UDP
TCP
IP
NET1
Summer 2014
NSF/MU REU
NET
2
■■■
NETn
26
13
Outline
• Content distribution
• Principles of app layer
protocols
– clients and servers
– Network Web caching
– Content distribution networks
– P2P file sharing
• Web and HTTP
• Electronic Mail
– SMTP, POP3, IMAP
Summer 2014
NSF/MU REU
27
Security
Slides adapted from Larry Peterson
Outline
Encryption Algorithms
Authentication Protocols
Message Integrity Protocols
Key Distribution
Firewalls
Summer 2014
NSF/MU REU
28
14
History
•
•
•
•
•
•
•
•
•
Telephone (1876, Alexander Graham Bell, AT&T )
Radio,TV (early 20th century)
Digital revolution (second half of the 20th century)
ARPAnet/early Internet (1969)
Personal Computer (late 1970s, IBM, Apples, Intel, Microsoft)
Cell phone (late 1970s)
WWW/Internet (mid 90s)
Laptop/PDA/smartphone/iPod/iPhone/iPad (1990s-2014)
Plenty of new opportunities
–
–
–
–
–
•
Qualcomm, Yahoo, eBay, Amazon, Google !
Skype (free Internet telephony company, using peer-to-peer networking)
PPLive: http://www.pplive.com/en/index.html
YouTube: http://www.youtube.com/, Netflix
Facebook, Twitter
what is now/next?
– Convergence of computers, telecom and consumer electronics
• Huge market
– Apple changed its name in 2007
– Social networking, Cloud & Big Data
– Internet of Things
Summer 2014
NSF/MU REU Site
29
The Beautiful Web
4.0
3.0
2.0
1.0
30
15
References
•
•
•
Peterson and Davie, Computer Networks: A Systems Approach (4th
edition), Morgan Kaufmann, ISBN-10: 0123705487 ISBN-13: 9780123705488.
J. F. Kurose and K. W. Ross, Computer Networking: a Top-town
Approach Featuring the Internet, Addison-Wesley, ISBN: 0-32122735-2.
A. S. Tanenbaum, Computer Networks, Prentice Hall, ISBN: 0-13066102-3.
Summer 2014
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17