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Network Architectureand Performance
Computer Networksalishahid
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Network Architecture
Application programs
Process-to-process channels
Host-to-host connectivity
Hardw are
How is a layered architecture helpful inthe design of networks that meet the
goals we stated?
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Protocols, Layers, and Interfaces
Layer n Layer n
Layer n-1
Host A Host B
service interfacepeerinterface
Protocol: a communication
service that higher-level
objects use to exchange
messages.
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Protocol GraphHost 1 Host 2
File
application
Digital
library
application
Video
applicationFile
application
Digital
libraryapplication
Video
application
RRP: request/reply
protocol.
MSP: message
stream protocol.
HHP: host-to-host
protocol.
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ISO: International Standards Organization
OSI: Open Systems Interconnection
Physical
Presentation
Session
Transport
Network
Data link
Application
The ISO/OSI Reference ModelSource: Computer Networks, Andrew Tanenbaum
The protocolstack:
The idea behind the model: Break up the
design to make implementation simpler.
Each layer has a well-defined function.
Layers pass to one another only the
information that is relevant at each level.Communication happens only between
adjacent layers.
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The Layers in the ISO/OSI RF ModelPhysical: Transmit raw bits over the medium.
Data Link: Implements the abstraction of an error free medium
(handle losses, duplication, errors, flow control).
Network: Routing.
Transport: Break up data into chunks, send them down the protocol stack,
receive chunks, put them in the right order, pass them up.
Session: Establish connections between different users and different
hosts.
Presentation: Handle syntax and semantics of the info, such asencoding, encrypting.
Application: Protocols commonly needed by applications (cddb, http,
ftp, telnet, etc).
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Layer n-1
Layer n+1
Layer n
Communication Between Layers within a Host
SAP SAP
SAP SAP
SAPs (service access points)
Note: This is ISO terminology.
Its important to specifythe services offered
to higher layers in
the hierarchy. What
they are + how to
use them = interface.
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Encapsulationsender
data
AH data
PH data
SH data
TH data
NH data
DH DTdata
BITSPhysical
Presentation
Session
Transport
NetworkData link
Application
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Communication Between Layers
in Different Hosts
One or more nodes
within the network
End host
Application
Presentation
Session
Transport
Network
Data link
Physical
Network
Data link
Physical
Network
Data link
Physical
End host
Application
Presentation
Session
Transport
Network
Data link
Physical
One or more nodes within the network.
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7/26/2013 BEE-8B Computer Networks 10
The Layers in the TCP/IP Protocol SuiteSource: The TCP/IP Protocol Suite, Behrouz A. Forouzan
Physical
Data link
IP
ARP RARP
ICMP IGMP
Transport TCP UDP
Network
Session
Presentation
Application
FTP HTTP DNS NFS
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7/26/2013 BEE-8B Computer Networks 12
PerformanceBandwidth: number of bits per time unit.
We can talk about bandwidth at the physical level, but we can also talk
about logical process-to-process bandwidth.
Latency: time taken for a message to travel from one
end of the network to the other.Again, we can consider a single-link or an end-to-end channel.
1
(a)
1
(b)
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Latency
QueueTransmitnPropagatioLatency
a vaccumin/103.0
cableain/102.3
fiberain/102.0
lightofSpeed8
8
8
sm
sm
sm
Bandwidth/SizeTransmit
lightofSpeed/DistancenPropagatio
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Delay x Bandwidth
Bandwidth
Delay
This product is analogous to the volume of a pipe or thenumber of bits it holds. It corresponds to how many bits the
sender must transmit before the first bit arrives at the
receiver.
Delay may be thought of as one-way latency or round-trip
time (RTT) depending on the context.
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Throughput
imeTransfer t/sizeTransferThroughput
sizeTransferh1/BandwidtRTTimeTransfer t
(effective end-to-end throughput)
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Jitter
Network
Interpacket gap
Packet
source
Packet
sink
1234 1234
Jitter is a variation (somewhat random) of the latency from
packet to packet. Jitter is most often observed when packets
traverse multiple hops from source to destination.
Question: What is the cause of jitter?
