Transcript MakingNetworksWork - Computing Sciences

Making Networks Work
ITEC 370
George Vaughan
Franklin University
1
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.
2
TCP/IP and OSI Models
TCP/IP and OSI Models (OSI-Model, n.d.) and (Tomsho, 2007)
TCP/IP
Layers
Application
PDU
Data
OSI Layers
7 Application
6
5
Transport
Segments 4
Network
Packets
3
Link
Frames
2
Function
Network process to application,
Initiates or accepts a request to transfer
data
Presentation Adds formatting, display, and
encryption of information
Session
Adds communication session control
information, Login/Logout
Transport
Adds End-to-end connections and
reliability, re-sequencing, flow control
Network
Path determination and logical
addressing (IP), translates MAC
address to logical address
LLC
Data
Adds error checking and physical
Link
addressing (MAC & LLC)
Devices - Apps
Standards
Browsers,
servers,
Gateways
Gateways
HTTP, SNMP,
FTP, Telnet
DNS,
Gateways
Gateways
NetBIOS
Routers
IP, ICMP,
ARP, NetBEUI
Switches,
Bridges, NICs
802.3, 802.11,
FDDI
ASCII, MPEG
TCP, UDP
MAC
Bits
1 Physical
Media, signal and binary transmission, Hubs,
sends data as a bit stream
Repeaters
10Base-T, T1,
E1
3
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?
4
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
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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 1980)
• 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
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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’.
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Structure of the OSI Reference Model
Tomsho, Tittel, Johnson (2007)
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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’.
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Virtual Communication
Tomsho, Tittel, Johnson (2007)
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Stack Connection Over a Network
http://upload.wikimedia.org/wikipedia/en/3/3e/IP_stack_connections.png
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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).
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Layers and PDUs
Headers and Data at different OSI Layers (Tomsho, 2007)
Application,
Presentation,
Session layers
Application,
Presentation,
Session layer
Data

Transport
layer header
Transport Layer

(PDU = Segment)
Network Layer
(PDU = Packet)
Date Link
(PDU = Frame)
Transport
layer header

Network
layer
header
Data Link
layer
 header
Network
layer
header
Transport
layer header
Application,
Presentation,
Session layer
Data
Transport layer
data
Application,
Presentation,
Session layer
Data
Network layer Data
Application,
Presentation,
Session layer
Data
Link Layer Data
FCS
(Data
Link
Trailer)
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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
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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
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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
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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
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Transport Layer (continued)
Tomsho, Tittel, Johnson (2007)
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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
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Network Layer (continued)
Tomsho, Tittel, Johnson (2007)
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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
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Data Link Layer (continued)
Tomsho, Tittel, Johnson (2007)
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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
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Summary of the OSI Layers
Tomsho, Tittel, Johnson (2007)
24
TCP/IP and OSI Models
TCP/IP and OSI Models (OSI-Model, n.d.) and (Tomsho, 2007)
TCP/IP
Layers
Application
PDU
Data
OSI Layers
7 Application
6
5
Transport
Segments 4
Network
Packets
3
Link
Frames
2
Function
Network process to application,
Initiates or accepts a request to transfer
data
Presentation Adds formatting, display, and
encryption of information
Session
Adds communication session control
information, Login/Logout
Transport
Adds End-to-end connections and
reliability, re-sequencing, flow control
Network
Path determination and logical
addressing (IP), translates MAC
address to logical address
LLC
Data
Adds error checking and physical
Link
addressing (MAC & LLC)
Devices - Apps
Standards
Browsers,
servers,
Gateways
Gateways
HTTP, SNMP,
FTP, Telnet
DNS,
Gateways
Gateways
NetBIOS
Routers
IP, ICMP,
ARP, NetBEUI
Switches,
Bridges, NICs
802.3, 802.11,
FDDI
ASCII, MPEG
TCP, UDP
MAC
Bits
1 Physical
Media, signal and binary transmission, Hubs,
sends data as a bit stream
Repeaters
10Base-T, T1,
E1
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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 sublayers:
– Logical Link Control (LLC)
– Media Access Control (MAC)
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IEEE 802 Extensions to the OSI Reference Model
Tomsho, Tittel, Johnson (2007)
27
IEEE 802 Specifications
Tomsho, Tittel, Johnson (2007)
28
IEEE 802 Specifications (continued)
Tomsho, Tittel, Johnson (2007)
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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.
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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
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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
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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
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