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Networks and Network ProgrammingJune 2, 2008
Networks and Network ProgrammingJune 2, 2008
TopicsTopics Client-server programming model Networks A programmer’s view of the Internet
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– 2 – CS213, S’08
Hardware Org of a Network HostHardware Org of a Network Host
mainmemory
I/O bridge
MI
ALU
register file
CPU chip
system bus memory bus
disk controller
graphicsadapter
USBcontroller
mousekeyboard monitor
disk
I/O bus
Expansion slots
networkadapter
network
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– 3 – CS213, S’08
A Client-Server Transaction A Client-Server Transaction
Clientprocess
Serverprocess
1. Client sends request
2. Server handlesrequest
3. Server sends response4. Client handles
response
Resource
Every network application is based on the client-server Every network application is based on the client-server model:model: A server process and one or more client processes Server manages some resource. Server provides service by manipulating resource for clients.
Note: clients and servers are processes running on hosts (can be the same or different hosts).
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– 4 – CS213, S’08
Computer Networks Computer Networks
A network is a hierarchical system of boxes and wires A network is a hierarchical system of boxes and wires organized by geographical proximityorganized by geographical proximity LAN (local area network) spans a building or campus.
Ethernet is most prominent example.
WAN (wide-area network) spans country or world.Typically high-speed point-to-point phone lines.
An An internetworkinternetwork ( (internetinternet) ) is an interconnected set of is an interconnected set of networks.networks. The Gobal IP Internet (uppercase “I”) is the most famous
example of an internet (lowercase “i”)
Let’s see how we would build an internet from the Let’s see how we would build an internet from the ground up.ground up.
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– 5 – CS213, S’08
Lowest Level: Ethernet SegmentLowest Level: Ethernet SegmentEthernet segment consists of a collection of Ethernet segment consists of a collection of hostshosts connected by wires (twisted pairs) to a connected by wires (twisted pairs) to a hubhub. .
Spans room or floor in a building.Spans room or floor in a building.
OperationOperation Each Ethernet adapter has a unique 48-bit address. Hosts send bits to any other host in chunks called frames. Hub copies each bit from each port to every other port.
Every host sees every bit.
host host host
hub100 Mb/s100 Mb/s
ports
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– 6 – CS213, S’08
Next Level: Bridged Ethernet SegmentNext Level: Bridged Ethernet Segment
Spans building or campus.Spans building or campus.
Bridges cleverly learn which hosts are reachable from which ports and then Bridges cleverly learn which hosts are reachable from which ports and then selectively copy frames from port to port.selectively copy frames from port to port.
host host host host host
hub hubbridge100 Mb/s 100 Mb/s
host host
hub 100 Mb/s 100 Mb/s
1 Gb/s
host host host
bridge
hosthost
hub
A B
C
X
Y
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– 7 – CS213, S’08
Conceptual View of LANsConceptual View of LANsFor simplicity, hubs, bridges, and wires are often shown as a collection of hosts attached to a single wire:For simplicity, hubs, bridges, and wires are often shown as a collection of hosts attached to a single wire:
host host host...
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– 8 – CS213, S’08
Next Level: internets Next Level: internets Multiple incompatible LANs can be physically connected by specialized Multiple incompatible LANs can be physically connected by specialized
computers called computers called routersrouters..
The connected networks are called an The connected networks are called an internetinternet..
host host host
LAN 1
... host host host
LAN 2
...
router router routerWAN WAN
LAN 1 and LAN 2 might be completely different, totally incompatible LANs (e.g., Ethernet and ATM)
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– 9 – CS213, S’08
The Notion of an internet ProtocolThe Notion of an internet Protocol
How is it possible to send bits across incompatible How is it possible to send bits across incompatible LANs and WANs?LANs and WANs?
Solution: Solution: protocol softwareprotocol software running on each host and running on each host and router smoothes out the differences between the router smoothes out the differences between the different networks.different networks.
Implements an Implements an internet protocolinternet protocol (i.e., set of rules) that (i.e., set of rules) that governs how hosts and routers should cooperate governs how hosts and routers should cooperate when they transfer data from network to network.when they transfer data from network to network.• TCP/IP is the protocol for the global IP Internet.
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– 10 – CS213, S’08
What Does an internet Protocol Do? What Does an internet Protocol Do?
1. Provides a naming scheme1. Provides a naming scheme An internet protocol defines a uniform format for host
addresses. Each host (and router) is assigned at least one of these
internet addresses that uniquely identifies it.
2. Provides a delivery mechanism2. Provides a delivery mechanism An internet protocol defines a standard transfer unit (packet) Packet consists of header and payload
Header: contains info such as packet size, source and destination addresses.
Payload: contains data bits sent from source host.
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– 11 – CS213, S’08
Transferring Data Over an internetTransferring Data Over an internet
protocolsoftware
client
LAN1adapter
Host A
data
data PH FH1
data PH
data PH FH2
LAN1 LAN2
data
data PH
FH1
data PH FH2
(1)
(2)
(3)
(4) (5)
(6)
(7)
(8)
internet packet
LAN2 frame
protocolsoftware
LAN1adapter
LAN2adapter
Router
FH1
LAN1 frame
data PH FH2
protocolsoftware
server
LAN2adapter
Host B
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– 12 – CS213, S’08
Other Issues Other Issues
We are glossing over a number of important questions:We are glossing over a number of important questions: What if different networks have different maximum frame
sizes? (segmentation) How do routers know where to forward frames? How are routers informed when the network topology
changes? What if packets get lost?
These (and other) questions are addressed by the area These (and other) questions are addressed by the area of systems known as of systems known as computer networking.computer networking.
Topic of EECS340Topic of EECS340
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– 13 – CS213, S’08
Global IP Internet Global IP Internet
Most famous example of an internet.Most famous example of an internet.
Based on the TCP/IP protocol familyBased on the TCP/IP protocol family IP (Internet protocol)
Provides basic naming scheme and unreliable delivery capability of packets (datagrams) from host-to-host.
UDP (Unreliable Datagram Protocol)Uses IP to provide unreliable datagram delivery from process-
to-process. TCP (Transmission Control Protocol)
Uses IP to provide reliable byte streams from process-to-process over connections.
Accessed via a mix of Unix file I/O and functions from Accessed via a mix of Unix file I/O and functions from the the sockets interfacesockets interface..
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– 14 – CS213, S’08
Organization of an Internet Application Organization of an Internet Application
TCP/IP
Client
Networkadapter
Global IP Internet
TCP/IP
Server
Networkadapter
Internet client host Internet server host
Sockets interface(system calls)
Hardware interface(interrupts)
User code
Kernel code
Hardwareand firmware
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– 15 – CS213, S’08
Basic Internet Components Basic Internet Components
An An Internet backboneInternet backbone is a collection of routers is a collection of routers (nationwide or worldwide) connected by high-speed (nationwide or worldwide) connected by high-speed point-to-point networks.point-to-point networks.
A A Network Access Point Network Access Point (NAP)(NAP) is a router that is a router that connects multiple backbones (sometimes referred connects multiple backbones (sometimes referred to as to as peerspeers).).
Regional networksRegional networks are smaller backbones that cover are smaller backbones that cover smaller geographical areas (e.g., cities or states) smaller geographical areas (e.g., cities or states)
A A point of presence point of presence (POP)(POP) is a machine that is is a machine that is connected to the Internet.connected to the Internet.
Internet Service ProvidersInternet Service Providers (ISPs) provide dial-up or (ISPs) provide dial-up or direct access to POPs.direct access to POPs.
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– 16 – CS213, S’08
The Internet Circa 1993 The Internet Circa 1993
In 1993, the Internet was one backbone (NSFNET) that In 1993, the Internet was one backbone (NSFNET) that connected 13 sites via 45 Mbs T3 links.connected 13 sites via 45 Mbs T3 links. Merit (Univ of Mich), NCSA (Illinois), Cornell Theory Center,
Pittsburgh Supercomputing Center, San Diego Supercomputing Center, John von Neumann Center (Princeton), BARRNet (Palo Alto), MidNet (Lincoln, NE), WestNet (Salt Lake City), NorthwestNet (Seattle), SESQUINET (Rice), SURANET (Georgia Tech).
Connecting to the Internet involved connecting one of your Connecting to the Internet involved connecting one of your routers to a router at a backbone site, or to a regional network routers to a router at a backbone site, or to a regional network that was already connected to the backbone.that was already connected to the backbone.
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– 17 – CS213, S’08
NSFNET Internet Backbone NSFNET Internet Backbone
source: www.eef.org
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– 18 – CS213, S’08
Current NAP-Based Internet Architecture Current NAP-Based Internet Architecture
In the early 90’s, commercial outfits built their own high-speed In the early 90’s, commercial outfits built their own high-speed backbones, connecting to NSFNET, and selling access to their backbones, connecting to NSFNET, and selling access to their POPs to companies, ISPs, and individuals.POPs to companies, ISPs, and individuals.
In 1995, NSF decommissioned NSFNET, and fostered creation of In 1995, NSF decommissioned NSFNET, and fostered creation of a collection of NAPs to connect the commercial backbones.a collection of NAPs to connect the commercial backbones.
Currently in the US there are about 50 commercial backbones Currently in the US there are about 50 commercial backbones connected by ~12 NAPs (peering points).connected by ~12 NAPs (peering points).
Similar architecture worldwide connects national networks to the Similar architecture worldwide connects national networks to the Internet. Internet.
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– 19 – CS213, S’08
Internet Connection HierarchyInternet Connection Hierarchy
NAP NAP
Backbone BackboneBackboneBackbone
NAP
POP POP POP
Regional net
POPPOP POP
POPPOP
Small Business
Big BusinessISP
POP POP POP POP
Pgh employee
dialup
DC employee
POP
T3
T1
ISP (for individuals)
POP
dialupT1
Colocationsites
Private“peering”
agreementsbetween
two backbonecompanies
often bypassNAP
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– 20 – CS213, S’08
Network Access Points (NAPs)Network Access Points (NAPs)
Source: Boardwatch.com
Note: Peers in this context are commercial backbones..droh
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– 21 – CS213, S’08Source: Boardwatch.com
MCI/WorldCom/UUNET Global Backbone
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– 22 – CS213, S’08
A Programmer’s View of the InternetA Programmer’s View of the Internet
1. Hosts are mapped to a set of 32-bit 1. Hosts are mapped to a set of 32-bit IP addressesIP addresses.. 129.105.5.8
2. The set of IP addresses is mapped to a set of 2. The set of IP addresses is mapped to a set of identifiers called Internet identifiers called Internet domain namesdomain names.. 129.105.5.8 is mapped to eecs.northwestern.edu
3. A process on one Internet host can communicate 3. A process on one Internet host can communicate with a process on another Internet host over a with a process on another Internet host over a connectionconnection..
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– 23 – CS213, S’08
1. IP Addresses 1. IP Addresses
32-bit IP addresses are stored in an 32-bit IP addresses are stored in an IP address structIP address struct
Host byte order: either big- or little-endian order
Network byte order: Big-endian byte order
/* Internet address structure */struct in_addr { unsigned int s_addr; /* network byte order (big-endian) */};
Handy network byte-order conversion functions:htonl: convert long int from host to network byte order.htons: convert short int from host to network byte order.ntohl: convert long int from network to host byte order.ntohs: convert short int from network to host byte order.
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– 24 – CS213, S’08
Dotted Decimal Notation Dotted Decimal Notation
By convention, each byte in a 32-bit IP address is By convention, each byte in a 32-bit IP address is represented by its represented by its decimaldecimal value and separated by a value and separated by a periodperiod
IP address 0x8002C2F2 = 128.2.194.242
Functions for converting between binary IP addresses Functions for converting between binary IP addresses and dotted decimal strings:and dotted decimal strings: inet_aton: converts a dotted decimal string to an IP
address in network byte order. inet_ntoa: converts an IP address in network by order to
its corresponding dotted decimal string. “n” denotes network representation. “a” denotes application
representation.
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– 25 – CS213, S’08
IP Address quizIP Address quiz
Complete this table:Complete this table:
Hex addressHex address Dotted-decimal addressDotted-decimal address
0x00x0
0xFFFFFFFF0xFFFFFFFF
0x7F0000010x7F000001
205.188.160.121205.188.160.121
64.12.149.1364.12.149.13
205.188.146.23205.188.146.23