Transcript ECE 4400:427/527 - Computer Networks Spring 2012

ECE 4400:427/527 - Computer Networks
Spring 2017
Dr. Nghi Tran
Department of Electrical & Computer Engineering
Lecture 3: Network Architectures
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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Some Discussions
• We know that there are substantial requirements for
NETWORK DESIGN
• General, cost-effective, fair, robust connectivity
among large computers/users
• Should be manageable by humans of varying levels
of skills
• Network designers have developed general blueprints
referred to as NETWORK ARCHITECTURES to deal with
complexity
• Guide the design and implementation of networks
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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Outline
• In this lecture, we introduce some central ideas
common to all network architecture
• Layering
• Protocols
• We also consider two most widely referenced
architectures:
• The OSI -7 –layer
• Internet architecture
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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Layering
• Communication network is so complex
• Contain many pieces: hosts, switching
devices, channels, etc
• How we can manage complexity?
• Using divide and conquer approach: Idea
of Layering
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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Example of Air Travel
Travelling contain a series of steps
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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Layering of Air Travel
ticket (purchase)
ticket (complain)
ticket
baggage (check)
baggage (claim
baggage
gates (load)
gates (unload)
gate
runway (takeoff)
runway (land)
takeoff/landing
airplane routing
airplane routing
airplane routing
airplane routing
departure
airport
airplane routing
intermediate air-traffic
control centers
arrival
airport
Layers: each layer implements a service
– via its own internal-layer actions
– relying on services provided by layer below
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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Why Layering?
Dealing with complex systems:
•
Explicit structure allows identification,
relationship of complex system’s pieces
• Layered reference model for discussion
•
Modularization eases maintenance, updating of
system
• change of implementation of layer’s service
transparent to rest of system
• e.g., change in gate procedure doesn’t affect rest of
system
•
Layering considered harmful?
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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Layering Abstraction
Layer: A set of functionalities encapsulated in an object that can be
used by other network components
Why layering? Think complexity and common services
Layers consist of protocols
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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Protocols
• Protocol defines the interfaces between the layers in
the same system and with the layers of peer system
• Building blocks of a network architecture
• Each protocol object has two different interfaces
– service interface: operations on this protocol
– peer-to-peer interface: messages exchanged with peer
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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Protocols
Protocols in each layer have
Service interface with upper layer/lower layers
Peer-to-peer interface with host on same layer
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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Hierarchical Layer Structure
Layering implies the use of a layer hierarchy
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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OSI 7-Layer Model
• First formal way defined
to connect computers
• One or more protocols
implement the
functionality assigned to a
given layer
• Acts like a reference
model rather than a realworld protocol graph
• First three layers are
implemented in all
network nodes
The OSI 7-layer Model
OSI – Open Systems Interconnection
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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Description of Layer
• Physical Layer
– Handles the transmission of raw bits over a communication link
• Data Link Layer
– Collects a stream of bits into a larger aggregate called a frame
– Network adaptor along with device driver in OS implement the
protocol in this layer
– Frames are actually delivered to hosts
• Network Layer
– Handles routing among nodes within a packet-switched network
– Unit of data exchanged between nodes in this layer is called a packet
The lower three layers are implemented on all network nodes
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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Description of Layer
• Transport Layer
– Implements a process-to-process channel
– Unit of data exchanges in this layer is called a message
• Session Layer
– Provides a name space that is used to tie together the potentially
different transport streams that are part of a single application, e.g.,
synchronization
• Presentation Layer
– Concerned about the format of data exchanged between peers, e.g.,
encryption, compression
• Application Layer
– Standardize common type of exchanges
The transport layer and the higher layers typically run only on end-hosts
and not on the intermediate switches and routers
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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The Internet Architecture
•
Application: supporting network
applications
• FTP, SMTP, HTTP
•
Transport: process data transfer
• TCP, UDP
•
Network: routing of datagrams from
source to destination
Transport
Network
Link
• IP, routing protocols
•
Application
Link: data transfer between neighboring
network elements
Physical
• Ethernet, 802.111 (WiFi), PPP
•
Physical: bits “on the wire”
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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Internet Architecture vs OSI
•
•
•
Presentation: allow applications to
interpret meaning of data, e.g.,
encryption, compression, machinespecific conventions
Session: synchronization, checkpointing,
recovery of data exchange
Internet stack “missing” these layers!
• These services, if needed, must
be implemented in application
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Application
Presentation
Session
Transport
Network
Link
Physical
Computer Networks
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The Internet: Protocol Encapsulation
source
message
segment
M
Ht
M
datagram Hn Ht
M
frame Hl Hn Ht
M
application
transport
network
link
physical
Hl Hn Ht
M
link
physical
Hl H n H t
M
switch
destination
M
Ht
M
Hn Ht
Hl Hn Ht
M
M
application
transport
network
link
physical
Dr. Nghi Tran (ECE-University of Akron)
Hn Ht
Hl Hn Ht
M
M
network
link
physical
Hn Ht
Hl Hn Ht
M
M
router
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Protocol Encapsulation: Example
A in Office 1 sends to B in Office 2 a memo
• Memo: Application-layer message
• Memo needs to placed on an interoffice envelope and A
needs to write an address:
• Envelope: Transport-layer segment, with header is
A’s address
• Envelope headed to sending office mailroom and placed
in a postal envelope; suited for public postal service:
Datagram
• Sending to receiving office mailroom: De-encapsulation
begins. B will finally get the memo.
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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The Internet: Alternative View
FTP
HTTP
TFTP
TCP
DNS
UDP
IP
Net 1
Ethernet
Net 1
FDDI
FTP: File Transfer Protocol
HTTP: Hypertext Transport Protocol
TFTP: Trivial File Transfer Protocol
FDDI: Fiber Distributed Data Interface
Dr. Nghi Tran (ECE-University of Akron)
TCP: Transmission Control Protocol
UDP: User Datagram Protocol
IP: Internet Protocol
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The Internet: Alternative View
• Subnetwork: Involve sublayers
• Internet Protocol: Support the interconnection of
multiple networking technologies into a single, logical
internetwork
• TCP/UDP: Two main protocols of third layer
– TCP: provide a reliable byte-stream channel
– UDP: provide an unreliable datagram delivery channel
– Sometimes called end-to-end protocols
• Application
We will step by step go through those layers/protocols
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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TCP vs. UDP
Source: Skullbox.net
• TCP: most commonly used protocol on the Internet
• UDP:
• Important data?
• For streaming audio and video; UDP packets in Denial of
Service (DoS); also implemented in trojan horse viruses
etc.
Again, we will step by step go through all these
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527
Computer Networks
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