protocol layering chapter 11: protocol layering. d.e.comer. “internetworking with tcp/ip:...
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Protocol Layering
Chapter 11: Protocol Layering.D.E.Comer. “Internetworking with TCP/IP: Principles, Protocols and Architecture”, Vol. 1, Prentice Hall, 2000
Presented by Wuilbert Jaramillo
2CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Outline
Part 1– Network problems, protocol and layering concepts– Need for protocols and layering
Part 2 – ISO/OSI and TCP/IP models– Comparison– Common points– Final remarks
3CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Outline Part 1
Existing problems in communication networks Protocol -definition The need for protocols Set of protocols: Layering What is Layering? Why Layering?
4CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Outline Part 2
Example: ISO/OSI 7-layer model TCP/IP 5 layer reference model ISO/OSI vs. TCP/IP Common points in layering Summary
5CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Existing Problems in Communication Networks
Hardware failure– Hosts, routers
Network congestion– Networks have finite capacity
Packet delay Data corruption
– Electric, magnetic interferences– HW failure
Data duplication
6CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Complexity of networks
Networks are complex !!!Networks are complex !!! Parts of a network:
– Hosts– Routers– Media– Applications– Hardware– Software– Different OS– Different protocols
Is there a Solution? Is there a Solution?
Organize all the elements under a same agreement
Better yet, use a divide and conquer approach
Result: the concept of a communications protocol
7CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Outline Part 1
Existing problems in communication networks Protocol -definitionProtocol -definition The need for protocols Set of protocols: Layering What is Layering? Why Layering?
8CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Some definitions for Protocol
an original draft, minute, or record of a document or transaction
a code prescribing strict adherence to correct etiquette and precedence (as in diplomatic exchange and in the military services)
a set of conventions governing the treatment and especially the formatting of data in an electronic communications system
9CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Protocol
Agreement about communication Specifies
– Format of messages– Meaning of messages– Rules for exchange– Procedures for handling problems
Protocols allow to specify or understand communication without knowing the details of a particular hardware
10CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Outline Part 1
Existing problems in communication networks Protocol -definition The need for protocolsThe need for protocols Set of protocols: Layering What is Layering? Why Layering?
11CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Need for Protocols
Hardware is low level Many problems can occur
– Bits corrupted or destroyed– Entire packet lost– Packet duplicated– Packets delivered out of order
12CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Need for Protocols(continued)
Need mechanisms to distinguish among – Multiple computers on a network– Multiple applications on a computer– Multiple copies of a single application on a computer– Different Operating Systems (OS)
13CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Outline Part 1
Existing problems in communication networks Protocol -definition The need for protocols Set of protocols: LayeringSet of protocols: Layering What is Layering? Why Layering?
14CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Set of Protocols
Work together Each protocol solves part of a communication
problem Known as
– Protocol suite– Protocol family
Designed in layers
15CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Plan for Protocol Design
Intended for protocol designers Divides protocols into layers Each layer is devoted to one sub-problem
16CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Outline Part 1
Existing problems in communication networks Protocol -definition The need for protocols Set of protocols: Layering What is Layering? Why Layering?
17CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
What is layering?
A technique to organize a network system into a succession of logically distinct entities, such that the service provided by one entity is solely based on the service provided by the previous entity.
18CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Conceptual Layers of Protocol Software
Layer n
…
Layer 2
Layer 1
Layer n
…
Layer 2
Layer 1
Sender Receiver
Network
The modules of Protocol SW are on each machine stacked vertically into layers
19CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Conceptual/Realistic view
High Level
Protocol Layer
Internet
Protocol Layer
Network
Interface Layer
Conceptual Layers Software Organization
Protocol 1Protocol 2
Protocol 3
Interface 1Interface 2
Interface3
IP Module
20CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Example: Internet Protocol Layers
Five layers– Application: supporting
network applications ftp, smtp, http
– Transport: host-host data transfer
tcp, udp– Network: routing of a
datagram from source to destination
ip,routing protocols– Link: data transfer between
neighboring network elements ppp, ethernet
– Physical: bits “on the wire”
Application
Transport
Network
Link
Physical
21CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Protocol Layering and Data
Application
Transport
Network
Link
Physical
M
MH
MHH
MHHH
Message
Segment
Datagram
Frame
22CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Layers and packet headers
Each layer – Appends header to outgoing packet– Removes header from incoming packet
Receiver uses header as demultiplexing key– Sender Multiplexes among several layers
MHHH
23CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Outline Part 1
Existing problems in communication networks Protocol -definition The need for protocols Set of protocols: Layering What is Layering? Why Layering?
24CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Why layering?
Dealing with complex systems:– Explicit structure allows identification of complex
system’s pieces– Modularization eases developing, maintenance,
updating of system Change of implementation of layer’s service transparent to
rest of system
25CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Example: No layering
TelnetFTP
HTTP
Coaxial cable
Fiber optic
Packet radio
Application
TransmissionMedia
No layering: each new application hast to be re-implemented for every network technology!
26CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Example: now with Layers
TelnetFTP
HTTP
Coaxial cableFiber optic
Packet radio
Application
Transport& Network
TransmissionMedia
Solution: introduce an intermediate layer that provides a common abstraction for various network technologies
27CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Outline Part 2
ISO/OSI 7-layer modelISO/OSI 7-layer model TCP/IP 5 layer reference model ISO/OSI vs. TCP/IP Common points in layering Summary
28CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
ISO 7 layer model
Based on early work done by the International Organization for Standardization (ISO)
Reference Model of Open System Interconnection (OSI)
Contains 7 conceptual layers OSI: conceptually define service, interface,
protocol
29CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
OSI Model concepts***
Service –says what a layer does Interface –says how to access the service Protocol –says how the service is implemented
– A set of rules and formats that govern the communications between two peers
30CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
ISO/OSI Reference Model
Seven Layers– Lower three layers are hop-by-hop– Next four layers are end-to-end
Application
Presentation
Session
Transport
Network
Datalink
Physical
Application
Presentation
Session
Transport
Network
Datalink
Physical
Network
Datalink
Physical
Physical Medium
31CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
ISO Layers
Layer 1: Physical (underlying hardware) Layer 2: Data Link (hardware frame definitions) Layer 3: Network (packet forwarding, routing) Layer 4: Transport (reliability, end-to-end) Layer 5: Session (login and passwords, session and
connection coordination) Layer 6: Presentation (data representation) Layer 7: Application (individual application program)
32CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
ISO Graphical View
Layer 7 Application Message Passing
Layer 6 Presentation Encoding
Layer 5 SessionAuthentication &
Encryption
Layer 4 TransportStreams & Segments
Layer 3 Network Datagrams
Layer 2 Data Link Frames & Packets
Layer 1Physical
Hardware Signaling & Wiring
33CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
X.25 and its relation to the ISO model
Best known and most widely used– Established as a recommendation of the ITU– Specially popular en Europe
Operates much like a telephone system– Consists of complex packet switches– Hosts attach to one of the packet switches
34CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
X.25 and its relation to the ISO model
35CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Outline Part 2
ISO/OSI 7-layer model TCP/IP 5 layer reference modelTCP/IP 5 layer reference model ISO/OSI vs. TCP/IP Common points in layering Summary
36CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
TCP/IP History
It originated from research– Developed by the Department of Defense (DOD)– Network of networks
Network of lowest bidders– The Army puts a bid on a computer and DEC wins
the bid– The Air Force puts out a bid and IBM wins– The Navy bid is won by Unisys
37CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
The TCP/IP 5-Layer Reference Model
Physical
Conceptual Layer Objects PassedBetween Layers
Application
Transport
Internet
Network Interface
Messages or Streams
Transport Protocol Packets
IP Datagrams
Network-Specific Frames
38CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
TCP/IP Layer Description
Layer 5: Application– Used for communicating among applications
Layer 4: Transport– Provides reliable delivery of data
Layer 3: Internet– Defines uniform format of packets forwarded across networks of
different technologies and rules for forwarding packets in routers Layer 2: Network
– Defines formats for carrying packets in hardware frames Layer 1: Physical
39CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
TCP/IP practical overview
Physical
Application
Transport
Internet
Network Interface
Telnet, FTP, e-mail, etc.
TCP, UDP
IP, ICMP, IGMP
device driver and interface card
40CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Two hosts running FTP
41CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Two networks connected with a router
42CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Mail with TCP/IP
43CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
A general background on TCP/IP
44CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Outline Part 2
ISO/OSI 7-layer model TCP/IP 5 layer reference model ISO/OSI vs. TCP/IP Common points in layering Summary
45CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Layers in both ISO and TCP/IP
Physical
Application
Transport
Internet
Network Interface
Physical
Application
Presentation
Network
Datalink
Session
Transport
47CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Differences between ISO and TCP/IP
Reliability Locus of Authority and control
48CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Reliability
ISO/X.25– Connection Oriented– Complex protocols
guarantee error free transport on every layer
– Retransmission of corrupted packages
– Flow control on every layer
TCP/IP– Connection less– Reliability is an end-to-end
problem– Freedom on handling
corrupted packets– Flow control on transport
layer
49CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Locus of Authority and Control
ISO/X.25– Network layer is service to
transport layer– Network handles routing,
flow control, acknowledgements internally
– Complex independent systems working for simple hosts
TCP/IP– Host participates in
network protocols– Host participates in e.g.
routing, flow control– Simple package delivery
system with intelligent hosts
50CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Outline Part 2
ISO/OSI 7-layer model TCP/IP 5 layer reference model ISO/OSI vs. TCP/IP Common points in layeringCommon points in layering Summary
51CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Protocol layering principle
Layered protocols are designed so that layer N at the destination receives exactly the same object sent by layer N at the source
52CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Protocol layering
Application
Transport
Internet
Network Interface
Host A Host B
Application
Transport
Internet
Network Interface
Physical net
Identicalmessage
Identicalpacket
Identicaldatagram
IdenticalFrame
53CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Protocol Layering with a router
54CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Layering in the presence of Network substructure
Transport
Internet
Network
Interface
Intranet
Software OrganizationConceptual Layers
Protocol 1Protocol 2
Protocol 3
Interface 1Interface 2
Interface3
IP Module
Point-To-Point(Intranet)
55CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Multiplexing and Demultiplexing
IP ModuleARP Module
RARP Module
Demultiplexing Based on Frame type
Frame arrives
56CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
More Demultiplexing
ICMP ProtocolUDP Protocol
TCP Protocol
IP Module
Datagram arrives
57CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Outline Part 2
ISO/OSI 7-layer model TCP/IP 5 layer reference model ISO/OSI vs. TCP/IP Common points in layering Summary
58CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003
Summary
Advantages– Breaks down complex
problem into more manageable components
– Implementation details of one layer are abstracted away from other layers
Disadvantages– Information hiding,
inefficient implementations– Can introduce overhead– Could lead to inefficiency
59CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003