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CSC 535Communication Networking I
Chapter 2Layered Architectures
Dr. Cheer-Sun Yang
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Protocol StacksTypically, communications is achieved via the
cooperation of software and hardwareCommunication software and hardware are
grouped into manageable sets called layersWe use the term network architecture to refer
to a set of protocols that specify how every layer is to function
A reference model, called a protocol stack, is used for understanding various networking protocols and their relations
OSI (7 layers) vs. TCP/IP (5 layers)
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Examples of Layering-Web BrowsingA client/server model A server process waits for incoming
requests by listening to a port.A client process makes requests as
desired.The server program usually is executed in
the background and is referred to as a daemon. For example, httpd refers to the server daemon for HTTP
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The user clicks on a link to indicate which document is to be retrieved.
The browser must determine the address that contains the document. It does this by sending a query to its local name server.
Once the address is known the browser establishes a connection to the specified machine, usually a TCP connection. In order for the connection to be successful, the specified machine must be ready to accept TCP connections.
The browser runs a client version of HTTP, which issues a request specifying both the name of the document and the possible document formats it can handle.
The machine that contains the requested document runs a server version of HTTP. It reacts to the HTTP request by sending an HTTP response which contains the desired document in the appropriate format.
The TCP connection is then closed and the user may view the document.
1.
2.
3.
4.
5.
6.
Figure 1.4 - Introduces topic
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HTTPserver
HTTPclient
Request
Response
Figure 2.1
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HTTPserver
HTTPclient
TCP TCP
GET 80, #
#, 80 STATUS
Port 80
Ephemeral
Port #
Figure 2.2
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The OSI Reference ModelA layer model defined by the ISO as an effort
to develop a seven-layer reference model for open system interconnection (OSI).
Each layer performs a subset of the required communication functions
Each layer relies on the next lower layer to perform more primitive functions
Each layer provides services to the next higher layer
Changes in one layer should not require changes in other layers
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How do layers work together?A concept called data encapsulation is
applied.In each layer, the smallest unit of data is
called a Protocol Data Unit (PDU). Each PDU contains a header, which contains protocol control information, and usually user information in the form of a service data unit (SDU).
“Conversations” occur between peer entities on different hosts.
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nentity
n-PDUs
nentity
Figure 2.3
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n+1entity
n-SAP
n+1entity
n-SAP
n entity n entity
n-SDU
n-SDU
n-SDU
H
H n-SDU
n-PDU
Figure 2.4
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OSI as Framework for Standardization
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Layer Specific Standards
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n-SDU
n-PDU n-PDU n-PDU
n-SDU
n-PDU n-PDU n-PDU
Segmentation Reassembly
n-PDU
n-SDU
n-PDU
Blocking Unblocking
n-SDUn-SDUn-SDUn-SDUn-SDU
(a)
(b)
Figure 2.5
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OSI Layers (1)Physical
Physical interface between devicesMechanicalElectricalFunctionalProcedural
Data Link Means of activating, maintaining and
deactivating a reliable link Error detection and control Higher layers may assume error free
transmission
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OSI Layers (2)Network
Transport of information Higher layers do not need to know about underlying
technology Not needed on direct links
Transport Exchange of data between end systems Error free In sequence No losses No duplicates Quality of service
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OSI Layers (3)Session
Control of dialogues between applications Dialogue discipline Grouping Recovery
Presentation Data formats and coding Data compression Encryption
Application Means for applications to access OSI environment
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Use of a Relay
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ApplicationLayer
PresentationLayer
SessionLayer
TransportLayer
NetworkLayer
Data LinkLayer
PhysicalLayer
ApplicationLayer
PresentationLayer
SessionLayer
TransportLayer
NetworkLayer
Data LinkLayer
PhysicalLayer
NetworkLayer
Electrical and/or Optical Signals
Application A Application B
Data LinkLayer
PhysicalLayer
NetworkLayer
Data LinkLayer
PhysicalLayer
Communication Network
Figure 2.6
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G
G
G
G
G
net 1
net 2
net 3
net 4
net 5
G = gateway/router
G
Figure 2.8
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The OSI Environment
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C
PS
PS
C
PSPS
C
C
C
PS = packet switch
C = computer
Figure 2.7
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ApplicationLayer
PresentationLayer
SessionLayer
TransportLayer
NetworkLayer
Data LinkLayer
PhysicalLayer
ApplicationLayer
PresentationLayer
SessionLayer
TransportLayer
NetworkLayer
Data LinkLayer
PhysicalLayer
Application A Application Bdata
data
data
data
data
data
data
ah
ph
sh
th
nh
dh
bits
dt
Figure 2.9
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TCP/IP Protocol SuiteDominant commercial protocol
architectureSpecified and extensively used before OSIDeveloped by research funded US
Department of DefenseUsed by the Internet
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ApplicationLayer
TransportLayer
InternetLayer
NetworkInterface
ApplicationLayer
TransportLayer
InternetLayer
NetworkInterface
(a) (b)
Figure 2.10
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TCP/IP Protocol Architecture(1)Application Layer
Communication between processes or applications
End to end or transport layer (TCP/UDP/…) End to end transfer of data May include reliability mechanism (TCP) Hides detail of underlying network
Internet Layer (IP) Routing of data
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TCP/IP Protocol Architecture(2)Network Layer
Logical interface between end system and network
Physical Layer Transmission medium Signal rate and encoding
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Application
Transport
Internet
Network Interface
Application
Transport
Internet
Network Interface
Internet
Network Interface
Network 1 Network 2
Machine A Machine B
Router/Gateway
Figure 2.11
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HTTP SMTP RTP
TCP UDP
IP
Network
Interface 1
Network
Interface 3
Network
Interface 2
DNS
Figure 2.12
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Some Protocols in TCP/IP Suite
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Net Interface
IP
TCP
HTTP
Net Interface
IP
Net Interface
IP
TCP
HTTP
Ethernet PPP
Router
router
(1,1)
s
(1,2)
w
(2,1)
(1,3) r
(2,2)
PPP
Ethernet
(a)
(b)
Server PC
Figure 2.13
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IP Header
Header containssource and destination physical addresses; network protocol type
Frame Check Sequence
Ethernet Header
Figure 2.14
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PDUs in TCP/IP
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HTTP Request
TCP Header
Header contains source and destination port numbers
Header contains source and destination IP addresses; transport protocol type
IP Header
Header contains source and destination physical addresses; network protocol type
Frame Check Sequence
Ethernet Header
Figure 2.15
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Required ReadingSections 2.1, 2.2, 2.3Section 2.4 is for next semesterCheck RFC 2068: go to my homepage and
click on “browsing RFCs”