Making Networks Work

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23 Οκτ 2013 (πριν από 3 χρόνια και 11 μήνες)

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1

Making Networks Work

ITEC 370

George Vaughan

Franklin University

2

Sources for Slides


Material in these slides comes primarily
from course text, Guide to Networking
Essentials,Tomsho, Tittel, Johnson (2007).


Other sources are cited in line and listed in
reference section.

3

TCP/IP and OSI Models

4

The Network Communication
Problem


The problem of Network Communication is quite
complex:


What medium should be used?


What voltage level, light level or wave amplitude
represents a 1 versus 0?


What should be used for addressing the recipient?


How should the data be encoded?


How should errors be handled?


What path to choose?

5

Networking Models


There are many issues to be worked out when
attempting to establish digital communication.


Just like programming, we decompose a difficult
task into smaller (yet easier) tasks


2 dominate networking models are used to
decompose the problem networking:


OSI: Open Systems Interconnection (OSI) networking
suite


IEEE 802: family of standards


6

OSI and IEEE 802


Tomsho, Tittel, Johnson (2007)



The IEEE defined a set of LAN standards to ensure network
interface and cabling compatibility


Project 802
(inception on February (
2
) of 19
80
)


Concentrates on standards that describe a network’s
physical elements


NICs, cables, connectors, signaling technologies, media
access control, and the like


OSI model was not standardized until 1983

1984


IEEE 802 standards predate the model


Both were developed in collaboration and are compatible with
one another

7

OSI Reference Model


OSI model divides the problem into
7different levels of complexity


called
layers.


Each layer ‘n’ is only concerned with how
to communicate to its neighbor layers,
‘n+1’ and ‘n
-
1’.


Layer ‘n’ could care less about layers ‘n+2’
and ‘n
-
2’.

8

Structure of the OSI Reference Model

Tomsho, Tittel, Johnson (2007)


9

OSI Layers


OSI defines the interface between layers.


Each layer ‘n’ provides services to layer
‘n+1’.


Communicating devices must have
compatible protocol stacks.


Layer ‘n’ in device ‘A’ has a virtual
connection to layer ‘n’ in device ‘B’.

10

Virtual Communication


Tomsho, Tittel, Johnson (2007)


11

Stack Connection Over a Network

http://upload.wikimedia.org/wikipedia/en/3/3e/IP_stack_connections.png

12

Protocol Data Units (PDU)


Each layer operates on a set of data called the
PDU.


The PDU in layer ‘n’ is not the same as the PDU
in layer ‘n+1’


(PDU ‘n’) = (Header ‘n’) + (PDU ‘n+1’)


The process of adding a header is called
encapsulation.


Similar to putting a letter in an envelope (the
envelope is like a header


it wraps the data).


13

Layers and PDUs

14

Application Layer


Tomsho, Tittel, Johnson (2007)



Layer 7; PDU: data


Set of interfaces to access networked services


E.g., networked file transfer, message handling,
and database query processing


Handles network access, moving data from sender to
receiver, and error recovery for applications


Components usually have a client and a server part


E.g., HTTP, Client for Microsoft Networks, NFS


Possible problems: missing/misconfigured client or
server SW, incompatible or obsolete commands used
to communicate between client and server

15

Presentation Layer


Tomsho, Tittel, Johnson (2007)



Layer 6


Data
-
formatting info for network communications


Handles: protocol conversion, character set issues,
encryption/ decryption, and graphics commands


May compress data


A
redirector

operates at this layer


Intercepts requests for service from the computer;
those that can’t be handled locally are redirected to
a networked resource that can handle the request


Usually built into the Application layer component


E.g., FTP, HTTP

16

Session Layer


Tomsho, Tittel, Johnson (2007)



Layer 5


Permits two parties to hold ongoing sessions


Handles session setup, data or message exchanges,
and teardown when the session ends


Monitors session identification so that only designated
parties can participate


Monitors security services for access control


Examples: name lookup and user logon and logoff


E.g., DNS name resolution, FTP’s logon/logoff


End
-
to
-
end task synchronization services


Manages mechanics of any ongoing conversation

17

Transport Layer


Tomsho, Tittel, Johnson (2007)



Layer 4; PDU: segment


Manages end
-
to
-
end transfer of data


Segments long data streams into chunks


Resequences chunks into original data on receipt


Includes error checks to ensure error
-
free delivery


Handles
flow control


E.g., TCP (TCP/IP) and SPX (from IPX/SPX)


Layer 4 problems include a corrupt protocol stack and
segments that are too large for the medium between
the source and destination networks


The latter forces Network layer to fragment
segments, which causes performance degradation

18

Transport Layer (continued)


Tomsho, Tittel, Johnson (2007)


19

Network Layer


Tomsho, Tittel, Johnson (2007)



Layer 3; PDU: packet


Handles addressing messages for delivery


Translates logical addresses into physical addresses


Determines how to route transmissions from sender
to receiver (
routing

process)


Traffic cop for network activity and handles routing
and
access control

(during routing process)


E.g., IP (from TCP/IP) and IPX (from SPX/IPX)


Possible problems: incorrect IP addresses or subnet
masks, incorrect router configuration, and router
operation errors

20

Network Layer (continued)


Tomsho, Tittel, Johnson (2007)


21

Data Link Layer


Tomsho, Tittel, Johnson (2007)



Layer 2; PDU: frame (has header and trailer (FCS))


Sends PDUs from/to Network to/from Physical layer


FCS contains
Cyclical Redundancy Check (CRC)


It’s the responsibility of the upper layers (e.g.,
Layer 4) to retransmit data discarded due to errors


Header contains source/destination MAC addresses


Destination address is of final destination or
intermediate device (e.g., router)


The SW component at this layer is the NIC driver


HW components include NIC and switches


Possible problems: collisions, invalid frames, trying to
use incompatible network architectures

22

Data Link Layer (continued)


Tomsho, Tittel, Johnson (2007)


23

Physical Layer


Tomsho, Tittel, Johnson (2007)



Layer 1


Converts bits into signals and vice versa


Signals generated depend on the medium


Details for creating network connection are specified


Governs the type of connector used


Regulates the transmission technique


Handles intricacies of transmitting bits


Specifies
encoding

mechanism


Tries guarantee that received bits match pattern sent


Problems: improper media termination, EMI, faulty or
misconfigured NICs and hubs

24

Summary of the OSI Layers


Tomsho, Tittel, Johnson (2007)


25

TCP/IP and OSI Models

26

IEEE 802 Standards


Wikipedia (n.d.)


Defines many types of protocols and
services.


Maps to the Layers 1 and 2 in the OSI
Reference Model.


Divides Layer 2 (Link Layer) into two sub
-
layers:


Logical Link Control (LLC)


Media Access Control (MAC)

27

IEEE 802 Extensions to the OSI Reference Model


Tomsho, Tittel, Johnson (2007)


28

IEEE 802 Specifications


Tomsho, Tittel, Johnson (2007)


29

IEEE 802 Specifications (continued)


Tomsho, Tittel, Johnson (2007)


30

Protocols and Protocol Suites


A protocol is a set of rules to manage the
communication task of one or more layers.


Many protocols only apply to a single layer:



IP (Internet Protocol) applies to the network layer
(layer 3)


TCP (Transmission Control Protocol) applies to the
transport layer (layer 4).


A collection of protocols that work together to
support multiple layers is called a protocol suite.


TPC/IP is not a protocol


it is a protocol suite.


TCP/IP dominates and is replacing other
protocol suites.

31

Protocol Stack


Software that implements a protocol suite is
called a protocol stack.


A protocol stack is composed of software
elements, each element mapping to one (or
more) OSI layers.


Examples:


TCP/IP (Linux, Unix, Windows, Novell Netware 5.0
and later)


IPX/SPX (Novell Netware 4.x and earlier)


NetBEUI (IBM developed for PC


no longer
supported in Windows).


AppleTalk


originally developed for Macs

32

Data Frame Types


Unicast Frames


Only one destination.


NICs see all frames on shared medium.


NICS only forward unicast frames to Network layer that match NICs
MAC address.


Multicast Frames (Odom, 2006)


Frames that are sent to a range of MAC addresses (typically 0100.5E or
0100.5F)


Cheap switches treat multicast frames just like broadcast frames.


More expensive switches can detect which ports want multicast frames
and which do not.


Often used for audio and video conferences.


Broadcast Frames


Sent to all devices in LAN.


Sent to MAC address FFFF.FFFF.FFFF

33

References


Tomsho, Tittel, Johnson (2007).
Guide to Networking
Essentials.

Boston: Thompson Course Technology.

Odom, Knott (2006).
Networking Basics: CCNA 1
Companion Guide
. Indianapolis: Cisco Press

Wikipedia (n.d.).

OSI Model
. Retrieved 09/12/2006 from
http://en.wikipedia.org/wiki/OSI_Model

IEEE 802
. Retrieved 01/21/2007

http://en.wikipedia.org/wiki/IEEE_802

Wilson, G. (2001)
OSI Model Layers
. Retrieved 09/23/2006
from
http://www.geocities.com/SiliconValley/Monitor/3131/ne/o
simodel.html