1. 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

2. 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

3. 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

4. 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

5. Example of Air Travel Travelling contain a series of steps
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527

6. intermediate air-traffic
Layering of Air Travel
ticket (purchase)
baggage (check)
gates (load)
runway (takeoff)
airplane routing
departure
airport
arrival
intermediate air-traffic
control centers
ticket (complain)
baggage (claim
gates (unload)
runway (land)
ticket
baggage
gate
takeoff/landing
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

7. 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

8. 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

9. 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

10. 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

11. Hierarchical Layer Structure
Layering implies the use of a layer hierarchy
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527

12. OSI – Open Systems Interconnection
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 real-world 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

13. Description of Layer Physical Layer Data Link Layer Network 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

14. Description of Layer Transport Layer Session Layer Presentation 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

15. The Internet Architecture
Application: supporting network applications
FTP, SMTP, HTTP
Transport: process data transfer
TCP, UDP
Network: routing of datagrams from source to destination
IP, routing protocols
Link: data transfer between neighboring network elements
Ethernet, (WiFi), PPP
Physical: bits “on the wire”
Application
Transport
Network
Link
Physical
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527

16. Internet Architecture vs OSI
Presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions
Session: synchronization, checkpointing, recovery of data exchange
Internet stack “missing” these layers!
These services, if needed, must be implemented in application
Application
Presentation
Session
Transport
Network
Link
Physical
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527

17. The Internet: Protocol Encapsulation
source
message M
application
transport
network
link
physical
segment Ht M Ht
datagram Ht Hn M Hn
frame Ht Hn Hl M
link
physical Ht Hn Hl M Ht Hn Hl M
switch
destination
network
link
physical Ht Hn M Ht Hn M M
application
transport
network
link
physical Ht Hn Hl M Ht Hn Hl M Ht M Ht Hn M
router Ht Hn Hl M
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527

18. 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

19. The Internet: Alternative View
FTP
HTTP
TFTP
DNS
TCP
UDP IP
Net 1
Net 1
Ethernet
FDDI
FTP: File Transfer Protocol
HTTP: Hypertext Transport Protocol
TFTP: Trivial File Transfer Protocol
FDDI: Fiber Distributed Data Interface
TCP: Transmission Control Protocol
UDP: User Datagram Protocol
IP: Internet Protocol
Dr. Nghi Tran (ECE-University of Akron)
ECE 4400:427/527

20. 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

21. TCP vs. UDP TCP: most commonly used protocol on the Internet 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