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Networking Basic network components and layered architecture Internet and WWW basics IP, TCP, URL, HTTP Jean Walrand, Communication Networks, a first course, McGraw-Hill 1998 (2 nd edition). Types of computer networks: Point-to-point connection (link) between two computers

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networking
Networking
  • Basic network components and layered architecture
  • Internet and WWW basics
  • IP, TCP, URL, HTTP

Jean Walrand, Communication Networks, a first course, McGraw-Hill 1998 (2nd edition).

ECMM 6000, Fall 2004

slide2

Types of computer networks:

  • Point-to-point connection (link) between two computers
  • Store-and-forward transmission: packets
  • Datagram packet switching: destination address in packet
  • also, LAN, WAN, ATM (virtual circuit switching), wireless

e.g. PPP, SLIP

A

B

C

e.g. token ring

ECMM 6000, Fall 2004

slide8

Review of components

  • Hosts
    • Considered a “node” or “end point” in the network (client/server/printer)
    • Processes all levels of the protocol stack
  • Hubs
    • acts as an “extender” - similar in effect to taking all incoming lines and twisting the wires together
    • Does not do any processing - acts only at the physical layer
  • Bridges
    • attaches two physically identical LANs together, physical layer processing
    • forwards only traffic which is destined for “the other side”
  • Switches
    • depending on level of switch complexity, anywhere from a hub to a router
  • Routers
    • Processing at the Network layer
    • Route packets between networks with potentially different lower level protocol stacks (i.e., different physical and data link layers)
  • Gateways
    • Processes all levels of the protocol stack
    • Used to connect networks with different protocol stacks

ECMM 6000, Fall 2004

slide9

Layered communication model

Message received

Message sent

Layer n

Layer 2

Layer 1

Communication

Sender

Recipient

medium

Coulouris, Dollimore, Kindberg, Distributed Systems, Addison Wesley 2001 (3rd ed)

ECMM 6000, Fall 2004

slide10

ISO-OSI layer model

Open systems interconnection reference model

A

B

communication services

communication services, e.g. file transfer,

email, …

7.

7.

Application

local syntax, secure,

efficient connections

e.g. compression, security, format conversion

6.

6.

Presentation

connections

5.

5.

supervises connections between end systems

Session

delivery of messages

4.

4.

supervises end-to-end transmission

Transport

3.

3.

guides the packet from source to destinations

Network

implements packet delivery service between two

nodes on the same physical link

2.

2.

Data Link

1.

1.

Physical

Implements digital communication link that

delivers bits

ECMM 6000, Fall 2004

slide11

Layer

Description

Examples

Application

Protocols that are designed to meet the communication requirements of

FTP

HTTP,

,

SMTP,

specific applications, often defining the interface to a service.

CORBA IIOP

Presentation

Protocols at this level transmit data in a network representation that is

Secure Sockets

independent of the representations used in individual computers, which may

(

SSL),CORBA Data

differ. Encryption is also performed in this layer, if required.

Rep.

Session

At this level reliability and adaptation are performed, such as detection of

failures and automatic recovery.

Transport

This is the lowest level at which messages (rather than packets) are handled.

TCP,

UDP

Messages are addressed to communication ports attached to processes,

Protocols in this layer may be connection-oriented or connectionless.

Network

Transfers data packets between computers in a specific network. In a WAN

IP,

ATM virtual

or an internetwork this involves the generation of a route passing through

circuits

routers. In a single LAN no routing is required.

Data link

Responsible for transmission of packets between nodes that are directly

Ethernet MAC,

connected by a physical link. In a WAN transmission is between pairs of

ATM cell transfer,

routers or between routers and hosts. In a LAN it is between any pair of hosts.

PPP

Physical

The circuits and hardware that drive the network. It transmits sequences of

Ethernet base- band

binary data by analogue signalling, using amplitude or frequency modulation

signalling,

ISDN

of electrical signals (on cable circuits), light signals (on fibre optic circuits)

or other electromagnetic signals (on radio and microwave circuits).

ECMM 6000, Fall 2004

slide12

What is a protocol

`A protocol is a set of rules governing message interchanges which occur between a number of computers in a distributed system; each of these messages implement functions of the system. A protocol is also used to establish a connection and allow entities to exchange data about themselves, for example the operating system they are using and the format of the data that they intend passing; this is known as a handshake. ‘

D. Ince

ECMM 6000, Fall 2004

slide14

Application message

port

TCP header

TCP

IP header

Ethernet header

IP

Ethernet frame

ECMM 6000, Fall 2004

slide15

IP Header

ECMM 6000, Fall 2004

slide16

Around 4 billion IP addresses

ECMM 6000, Fall 2004

slide17

Transport layer protocols

  • TCP (Transmission Control Protocol):
    • connection-oriented
    • Reliable packet delivery in sequence
  • UDP (User Datagram Protocol):
    • connectionless (datagram)
    • Unreliable packet delivery
    • Packets may arrive out of sequence or duplicated
    • Less overhead
    • Simply adds port addressing to IP
    • Checksum is optional
  • Internet Control Message Protocol
    • Used by the nodes in the internet to implement IP

ECMM 6000, Fall 2004

slide18

TCP and UDP Header

ECMM 6000, Fall 2004

the internet around 1990
The Internet around 1990

Jean Walrand, Communication Networks, a first course, McGraw-Hill 1998 (2nd edition).

The first three chapters give you a nice overview of the working of networks and the Internet.

ECMM 6000, Fall 2004

mci backbone
MCI backbone

Retrieved from: http://global.mci.com/about/network/maps/?flash=1&theme=/, Sept 5/2003

See this site also for interesting network statistics (e.g. latencies)

ECMM 6000, Fall 2004

internet network architecture

ISP

ISP

ISP

ISP

NAP

NAP

ISP

ISP

NAP

NAP

ISP

Backbone

ISP

ISP

ISP

Network Service Provider

Internet Service Provider

Private Networks / hosts

Internet network architecture

Adapted from Electronic Commerce: A Managerial Perspective. Turban, Lee, King and Chung, 2000. Pg. 385

ECMM 6000, Fall 2004

how big is the internet today
How big is the Internet today?
  • 171,638,297 connected computers (Jan 2003)“Source: Internet Software Consortium (http://www.isc.org/)”
  • 605.60 million people online Worldwide (Sep 2002)
    • Canada & USA 182.67 million
    • Europe 190.91 million
    • Asia/Pacific 187.24 million
    • Latin America 33.35 million
    • Africa 6.31 million
    • Middle East 5.12 million

Source: Nua Internet Surveys; retrieved from: http://www.nua.ie/surveys/how_many_online/ Sept. 5/2003

ECMM 6000, Fall 2004

slide24

b.atr.go.jp

a.cs.dal.ca

ECMM 6000, Fall 2004

slide25

URL: A Global Address

  • Scheme
  • Server name
  • Path
  • File

http://www.cs.dal.ca/cs1200/week1/x.html

ECMM 6000, Fall 2004

slide26

b.atr.go.jp

a.cs.dal.ca

123.777.19.6

168.12.13.3

ECMM 6000, Fall 2004

slide27

Routing and congestion control

  • Send information of nodes and links to each node of the network. This might include some physical properties such as maximal size of packets, typical time delays, …
  • Build map of network
  • Use routing algorithm to build routing tables

for example: OSPF (Open Shortest Path First)

if every router uses the same algorithm and maps they build consistent tables

  • Hierarchical Routing:

`use local map to get to the highway, use highway map to get to your

destination town, use local map to get to your friends house’.

More sophisticated routing on `highway’ (BGP, Border Gateway Protocol)

How is congestion controlled?

ECMM 6000, Fall 2004

slide28

How is congestion controlled?

Flow control  TCP

Destination publishes maximal acceptable window size in reply message

Source destination discovers congestion from unusually long delay times of response

 additive increase, multiplicative decrease

ECMM 6000, Fall 2004

slide29

Application layer:Programming example in Java

The JAVA Socket class Socket oldSock = new Socket("penny.open.ac.uk", 1048); remote computer penny in the domain open.ac.uk with communication occurring via port 1048. InputStream

ECMM 6000, Fall 2004

slide30

Packet filtering firewalls

  • Packet filtering firewalls decide whether or not to forward packets based on their source and destination IP addresses and port numbers
  • Rules dictate whether or not packets should be forwarded
  • Typically once a connection through the firewall has been established, further packets are passed without scrutiny
  • Processes up to the network layer of the protocol stack (one notable exception is for FTP, which requires some application-level support)
  • Can perform IP Masquerading

ECMM 6000, Fall 2004

slide31

Proxy-based firewalls

  • Proxy-based firewalls operate at the application layer of the protocol stack
  • Every type of application for which a connection through the firewall is requested requires that a proxy server be running on the firewall for that specific application, or the request will be denied
  • Allows for logging of events at the application layer, much more detailed logging than a packet-filtering firewall allows
  • Requires that client machines inside the firewall be configured on an application by application basis to use the proxied services of the firewall

ECMM 6000, Fall 2004