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Operating Systems
CIS 3718
Chapter 16
Chapter 16: Overview of Distributed Computing •
Networks
•
Networking Standards
•
OSI Reference Model
•
Media
•
OSI Network Management
•
OSI Testing
•
TCP/IP
5/2/01
CIS 3718 Operating Systems
1
CIS 3718
Introduction
Chapter 16
This chapter is primarily concerned how computer networks relate to operating systems.
It deals with network types, network communications and standards.
5/2/01
CIS 3718 Operating Systems
2
CIS 3718
What is OSI? / What is a Network? Chapter 16
Open Systems Interconnection (OSI) is a set of internationally recognized, non-proprietary standards for networking and for operating system involved in networking functions. What is a Network? Business View – a tool to achieve business goals; example: the fast and efficient sharing of information among relevant persons in a business Information Systems View – various pieces of interconnected hardware and software General View – the communications paths between computers 5/2/01
CIS 3718 Operating Systems
3
CIS 3718
Network Types
Chapter 16
The most basic type of network (around since the 60’s) is the remote access network. In this scheme, a central host computer has a number of dumb terminals (containing no processors) which are connected via cabling More typically, a network is thought of as various host computers which can provide various services to users. In this type of network, computers are connected via phone wire, coaxial cable, fiber optic cable, infrared light beams, radio waves, microwave links, satellite links, etc. Users on such systems are provided operating system services, such as file transfer, inter-user communication (e-mail, etc.) 5/2/01
CIS 3718 Operating Systems
4
CIS 3718
Network Types
Chapter 16
With the latter type of network, there are two basic ways to organize relationships between intelligent devices: •
Peer-to-Peer – the devices have the ability to negotiate the information exchange; the devices act as partners, or equal entities and have great flexibility; most OSI networks are peer-to-peer networks
•
Hierarchical – master/drone relationships, one device must seek the permission of the other for the potential information exchange (ex. IBM’s System Network Architecture (SNA), which is less flexible)
OSI is primarily intended as an intermediary for transfer of information among similar and dissimilar peer hosts. 5/2/01
CIS 3718 Operating Systems
5
CIS 3718
Networking Standards
Chapter 16
Advantages of having Networking Standards: Networking and Communications methods are widely known and accepted Permit economies of scale Permit lower costs in training Permit lower costs in interfaces Disadvantages: Not always the best technical solution Not always the most well known solution among managers and laymen 5/2/01
CIS 3718 Operating Systems
6
CIS 3718
International Standards Bodies
Chapter 16
Several international standards bodies are involved in networking standards, among them: ISO
International Standardization Organization (developed the OSI model)
CCITT
Consultative Committee for International Telephone and Telegraph
Some national standards committees: ANSI
American National Standards Institute
NIST
National Institute for Standards and Technology
Standards are also submitted to the above committees by other professional/technical organizations, such as IEEE (Institute for Electrical and Electronics Engineers). 5/2/01
CIS 3718 Operating Systems
7
Chapter 16 Network Architecture and OSI CIS 3718 The OSI reference model is an arbitrary hierarchical stratification (layering) of computer networking functions. The stratification consists of seven layers. There are various ways of implementing the protocols at any given layer. OSI is a CONCEPTUAL model. Protocols are prescriptive methods which delineate the communication that is to take place at a given layer. Several other well known and widely used reference models have NOT been recognized as standards, e.g., IBM’s SNA (also a layered approach), and the DoD developed protocols (which include TCP/IP – Transmission Control Protocol/Internet Protocol, SMTP – Simple Mail Transfer Protocol, FTP – File Transfer Protocol) are often used in UNIX and other environments. 5/2/01
CIS 3718 Operating Systems
8
CIS 3718
The OSI Reference Model
Chapter 16
The OSI reference model consists of seven layers, not including layer 8, the end user’s application, and layer 0 the physical transmission media.
8. O/S or User Application 7. Application Layer 2.
Presentation Layer
3.
Session Layer
4.
Transport Layer
5.
Network Layer
6.
Data Link Layer
7. Physical Layer 0. Physical Transmission Media 5/2/01
CIS 3718 Operating Systems
9
CIS 3718
The OSI Reference Model
Chapter 16
LAYER 7 – The APPLICATION Layer
The top layer of the OSI model Provides a set of interfaces for sending and receiving applications to gain access to and use network services, such as: networked file transfer, message handling and database query processing
5/2/01
CIS 3718 Operating Systems
10
CIS 3718
The OSI Reference Model
Chapter 16
LAYER 6 – The PRESENTATION Layer Manages data-format information for networked communications (the network’s translator) For outgoing messages, it converts data into a generic format for network transmission; for incoming messages, it converts data from the generic network format to a format that the receiving application can understand This layer is also responsible for certain protocol conversions, data encryption/decryption, or data compression/decompression A special software facility called a “redirector” operates at this layer to determine if a request is network related on not and forward network-related requests to an appropriate network resource 5/2/01
CIS 3718 Operating Systems
11
CIS 3718
The OSI Reference Model
Chapter 16
LAYER 5 – The SESSION Layer Enables two networked resources to hold ongoing communications (called a session) across a network Applications on either end of the session are able to ex hange data for the duration of the session This layer is: Responsible for initiating, maintaining and terminating sessions Responsible for security and access control to session information (via session participant identification) Responsible for synchronization services, and for checkpoint services 5/2/01
CIS 3718 Operating Systems
12
CIS 3718
The OSI Reference Model
Chapter 16
LAYER 4 – The TRANSPORT Layer Manages the transmission of data across a network Manages the flow of data between parties by segmenting long data streams into smaller data chunks (based on allowed “packet” size for a given transmission medium) Reassembles chunks into their original sequence at the receiving end Provides acknowledgements of successful transmissions and requests resends for packets which arrive with errors
5/2/01
CIS 3718 Operating Systems
13
CIS 3718
The OSI Reference Model
Chapter 16
LAYER 3 – The NETWORK Layer Handles addressing messages for delivery, as well as translating logical network addresses and names into their physical counterparts Responsible for deciding how to route transmissions between computers This layer also handles the decisions needed to get data from one point to the next point along a network path This layer also handles packet switching and network congestion control
5/2/01
CIS 3718 Operating Systems
14
CIS 3718
The OSI Reference Model
Chapter 16
LAYER 2 – The DATA LINK Layer Handles special data frames (packets) between the Network layer and the Physical layer At the receiving end, this layer packages raw data from the physical layer into data frames for delivery to the Network layer At the sending end this layer handles conversion of data into raw formats that can be handled by the Physical Layer
5/2/01
CIS 3718 Operating Systems
15
CIS 3718
The OSI Reference Model
Chapter 16
LAYER 1 – The PHYSICAL Layer Converts bits into electronic signals for outgoing messages Converts electronic signals into bits for incoming messages This layer manages the interface between the the computer and the network medium (coax, twisted pair, etc.) This layer tells the driver software for the MAU (media attachment unit, ex. network interface cards (NICs, modems, etc.)) what needs to be sent across the medium The bottom layer of the OSI model
5/2/01
CIS 3718 Operating Systems
16
CIS 3718
The OSI Reference Model
Chapter 16
A convenient aid for remembering the OSI layer names is to use the first letter of each word in the phrase: All People Seem To Need Data Processing
5/2/01
CIS 3718 Operating Systems
17
CIS 3718
The OSI Reference Model Sending Computer
User Application
6 Presentation
6 Presentation
5 Session
5 Session
Transmission Media
7 Application
3 Network
5/2/01
Receiving Computer
7 Application
4 Transport
Chapter 16 User Application
4 Transport 3 Network
2 Data Link
2 Data Link
1 Physical
1 Physical CIS 3718 Operating Systems
18
CIS 3718
TCP/IP
Chapter 16
Transmission Control Protocol/Internet Protocol (TCP/IP) is a DoD developed, widely accepted and used communications protocol. TCP/IP has only four layers, which roughly correspond to groups of the OSI model. The Internet, many internal business networks and some home networks used TCP/IP. The four layers in TCI/IP are: Application Layer Transport Layer Internet Layer Network Interface Layer 5/2/01
CIS 3718 Operating Systems
19
CIS 3718
TCP/IP
Chapter 16
TCP (Transmission Control Protocol) is the portion of TCP/IP that is responsible for reliable delivery of data TCP is a TRANSPORT protocol in the OSI and TCP/IP models
IP (Internet Protocol) is the portion of TCP/IP that provides addressing and routing information IP is a NETWORK protocol in the OSI model and an INTERNET protocol in the TCP/IP model
5/2/01
CIS 3718 Operating Systems
20
CIS 3718
Chapter 16
TCP/IP
Application
vs.
OSI 7 Application 6 Presentation 5 Session
Transport
4 Transport
Internet
3 Network
Network Interface
2 Data Link 1 Physical
5/2/01
CIS 3718 Operating Systems
21
CIS 3718
Operating Systems
Chapter 16
End of Chapter 16
5/2/01
CIS 3718 Operating Systems
22
CIS 3718
Seek Optimization: SSFT
Review
Shortest Seek Time First (SSFT) – the request closest to the request currently being serviced is serviced next Assume: While 12 is being serviced, 11 enters the queue.
Shortest Seek 7 4 2 1 12 11 15 19 -bi-directional queue reordering new - proximity SRQ 15 2 7 12 4 19 1 11
5/2/01
1 2 4
7
11 12
15 19
Arm position at start: CYL 8 CIS 3718 Operating Systems
23
CIS 3718
Review
Seek Optimization: SCAN
SCAN – SSFT with directional preferences – elevator algorithm Assume: While 12 is being serviced, 10, 18 and 4 enter the queue.
SRQ 7 2 12 3 10 18 4
SCAN 12 18 10 7 4 3 2 --
2 3
4
Current Direction of bi-directional sweep queue reordering new – if in direction of current sweep 5/2/01
CIS 3718 Operating Systems
7
10
12
14
18
CYL 8 24
CIS 3718
Seek Optimization: N-Step SCAN
Review
N-Step SCAN – SCAN with newly arriving requests ignored Assume: While 13 is being serviced, 17, 4 and 7 enter the queue.
SRQ 13 11 20 17 4 7
N-Step SCAN 11 13 20 17 7 4 --
2 3 4
Current Direction of sweep 5/2/01
7
CYL 8
CIS 3718 Operating Systems
11
13
17
20
bi-directional queue reordering new – on next direction change 25
CIS 3718
Review
Seek Optimization: C-SCAN
C-SCAN – a unidirectional scan; newly arriving requests ignored Assume: While 11 is being serviced, 16, 3 and 7 enter the queue.
SRQ 13 11 20 16 3 7
C-SCAN 11 13 20 3 7 16 --
2
3
4
uni-directional queue reordering new – wait for next sweep 5/2/01
7
11
13
16
20
CYL 8 Direction of sweep CIS 3718 Operating Systems
26
CIS 3718
Operating Systems
Review
End of Problem Review
5/2/01
CIS 3718 Operating Systems
27
CIS 3718
Chapter 16
Chapter 16: Overview of Distributed Computing •
Networks
•
Networking Standards
•
OSI Reference Model
•
Media
•
OSI Network Management
•
OSI Testing
•
TCP/IP
5/2/01
CIS 3718 Operating Systems
1
CIS 3718
Introduction
Chapter 16
This chapter is primarily concerned how computer networks relate to operating systems.
It deals with network types, network communications and standards.
5/2/01
CIS 3718 Operating Systems
2
CIS 3718
What is OSI? / What is a Network? Chapter 16
Open Systems Interconnection (OSI) is a set of internationally recognized, non-proprietary standards for networking and for operating system involved in networking functions. What is a Network? Business View – a tool to achieve business goals; example: the fast and efficient sharing of information among relevant persons in a business Information Systems View – various pieces of interconnected hardware and software General View – the communications paths between computers 5/2/01
CIS 3718 Operating Systems
3
CIS 3718
Network Types
Chapter 16
The most basic type of network (around since the 60’s) is the remote access network. In this scheme, a central host computer has a number of dumb terminals (containing no processors) which are connected via cabling More typically, a network is thought of as various host computers which can provide various services to users. In this type of network, computers are connected via phone wire, coaxial cable, fiber optic cable, infrared light beams, radio waves, microwave links, satellite links, etc. Users on such systems are provided operating system services, such as file transfer, inter-user communication (e-mail, etc.) 5/2/01
CIS 3718 Operating Systems
4
CIS 3718
Network Types
Chapter 16
With the latter type of network, there are two basic ways to organize relationships between intelligent devices: •
Peer-to-Peer – the devices have the ability to negotiate the information exchange; the devices act as partners, or equal entities and have great flexibility; most OSI networks are peer-to-peer networks
•
Hierarchical – master/drone relationships, one device must seek the permission of the other for the potential information exchange (ex. IBM’s System Network Architecture (SNA), which is less flexible)
OSI is primarily intended as an intermediary for transfer of information among similar and dissimilar peer hosts. 5/2/01
CIS 3718 Operating Systems
5
CIS 3718
Networking Standards
Chapter 16
Advantages of having Networking Standards: Networking and Communications methods are widely known and accepted Permit economies of scale Permit lower costs in training Permit lower costs in interfaces Disadvantages: Not always the best technical solution Not always the most well known solution among managers and laymen 5/2/01
CIS 3718 Operating Systems
6
CIS 3718
International Standards Bodies
Chapter 16
Several international standards bodies are involved in networking standards, among them: ISO
International Standardization Organization (developed the OSI model)
CCITT
Consultative Committee for International Telephone and Telegraph
Some national standards committees: ANSI
American National Standards Institute
NIST
National Institute for Standards and Technology
Standards are also submitted to the above committees by other professional/technical organizations, such as IEEE (Institute for Electrical and Electronics Engineers). 5/2/01
CIS 3718 Operating Systems
7
Chapter 16 Network Architecture and OSI CIS 3718 The OSI reference model is an arbitrary hierarchical stratification (layering) of computer networking functions. The stratification consists of seven layers. There are various ways of implementing the protocols at any given layer. OSI is a CONCEPTUAL model. Protocols are prescriptive methods which delineate the communication that is to take place at a given layer. Several other well known and widely used reference models have NOT been recognized as standards, e.g., IBM’s SNA (also a layered approach), and the DoD developed protocols (which include TCP/IP – Transmission Control Protocol/Internet Protocol, SMTP – Simple Mail Transfer Protocol, FTP – File Transfer Protocol) are often used in UNIX and other environments. 5/2/01
CIS 3718 Operating Systems
8
CIS 3718
The OSI Reference Model
Chapter 16
The OSI reference model consists of seven layers, not including layer 8, the end user’s application, and layer 0 the physical transmission media.
8. O/S or User Application 7. Application Layer 2.
Presentation Layer
3.
Session Layer
4.
Transport Layer
5.
Network Layer
6.
Data Link Layer
7. Physical Layer 0. Physical Transmission Media 5/2/01
CIS 3718 Operating Systems
9
CIS 3718
The OSI Reference Model
Chapter 16
LAYER 7 – The APPLICATION Layer
The top layer of the OSI model Provides a set of interfaces for sending and receiving applications to gain access to and use network services, such as: networked file transfer, message handling and database query processing
5/2/01
CIS 3718 Operating Systems
10
CIS 3718
The OSI Reference Model
Chapter 16
LAYER 6 – The PRESENTATION Layer Manages data-format information for networked communications (the network’s translator) For outgoing messages, it converts data into a generic format for network transmission; for incoming messages, it converts data from the generic network format to a format that the receiving application can understand This layer is also responsible for certain protocol conversions, data encryption/decryption, or data compression/decompression A special software facility called a “redirector” operates at this layer to determine if a request is network related on not and forward network-related requests to an appropriate network resource 5/2/01
CIS 3718 Operating Systems
11
CIS 3718
The OSI Reference Model
Chapter 16
LAYER 5 – The SESSION Layer Enables two networked resources to hold ongoing communications (called a session) across a network Applications on either end of the session are able to ex hange data for the duration of the session This layer is: Responsible for initiating, maintaining and terminating sessions Responsible for security and access control to session information (via session participant identification) Responsible for synchronization services, and for checkpoint services 5/2/01
CIS 3718 Operating Systems
12
CIS 3718
The OSI Reference Model
Chapter 16
LAYER 4 – The TRANSPORT Layer Manages the transmission of data across a network Manages the flow of data between parties by segmenting long data streams into smaller data chunks (based on allowed “packet” size for a given transmission medium) Reassembles chunks into their original sequence at the receiving end Provides acknowledgements of successful transmissions and requests resends for packets which arrive with errors
5/2/01
CIS 3718 Operating Systems
13
CIS 3718
The OSI Reference Model
Chapter 16
LAYER 3 – The NETWORK Layer Handles addressing messages for delivery, as well as translating logical network addresses and names into their physical counterparts Responsible for deciding how to route transmissions between computers This layer also handles the decisions needed to get data from one point to the next point along a network path This layer also handles packet switching and network congestion control
5/2/01
CIS 3718 Operating Systems
14
CIS 3718
The OSI Reference Model
Chapter 16
LAYER 2 – The DATA LINK Layer Handles special data frames (packets) between the Network layer and the Physical layer At the receiving end, this layer packages raw data from the physical layer into data frames for delivery to the Network layer At the sending end this layer handles conversion of data into raw formats that can be handled by the Physical Layer
5/2/01
CIS 3718 Operating Systems
15
CIS 3718
The OSI Reference Model
Chapter 16
LAYER 1 – The PHYSICAL Layer Converts bits into electronic signals for outgoing messages Converts electronic signals into bits for incoming messages This layer manages the interface between the the computer and the network medium (coax, twisted pair, etc.) This layer tells the driver software for the MAU (media attachment unit, ex. network interface cards (NICs, modems, etc.)) what needs to be sent across the medium The bottom layer of the OSI model
5/2/01
CIS 3718 Operating Systems
16
CIS 3718
The OSI Reference Model
Chapter 16
A convenient aid for remembering the OSI layer names is to use the first letter of each word in the phrase: All People Seem To Need Data Processing
5/2/01
CIS 3718 Operating Systems
17
CIS 3718
The OSI Reference Model Sending Computer
User Application
6 Presentation
6 Presentation
5 Session
5 Session
Transmission Media
7 Application
3 Network
5/2/01
Receiving Computer
7 Application
4 Transport
Chapter 16 User Application
4 Transport 3 Network
2 Data Link
2 Data Link
1 Physical
1 Physical CIS 3718 Operating Systems
18
CIS 3718
TCP/IP
Chapter 16
Transmission Control Protocol/Internet Protocol (TCP/IP) is a DoD developed, widely accepted and used communications protocol. TCP/IP has only four layers, which roughly correspond to groups of the OSI model. The Internet, many internal business networks and some home networks used TCP/IP. The four layers in TCI/IP are: Application Layer Transport Layer Internet Layer Network Interface Layer 5/2/01
CIS 3718 Operating Systems
19
CIS 3718
TCP/IP
Chapter 16
TCP (Transmission Control Protocol) is the portion of TCP/IP that is responsible for reliable delivery of data TCP is a TRANSPORT protocol in the OSI and TCP/IP models
IP (Internet Protocol) is the portion of TCP/IP that provides addressing and routing information IP is a NETWORK protocol in the OSI model and an INTERNET protocol in the TCP/IP model
5/2/01
CIS 3718 Operating Systems
20
CIS 3718
Chapter 16
TCP/IP
Application
vs.
OSI 7 Application 6 Presentation 5 Session
Transport
4 Transport
Internet
3 Network
Network Interface
2 Data Link 1 Physical
5/2/01
CIS 3718 Operating Systems
21
CIS 3718
Operating Systems
Chapter 16
End of Chapter 16
5/2/01
CIS 3718 Operating Systems
22
CIS 3718
Seek Optimization: SSFT
Review
Shortest Seek Time First (SSFT) – the request closest to the request currently being serviced is serviced next Assume: While 12 is being serviced, 11 enters the queue.
Shortest Seek 7 4 2 1 12 11 15 19 -bi-directional queue reordering new - proximity SRQ 15 2 7 12 4 19 1 11
5/2/01
1 2 4
7
11 12
15 19
Arm position at start: CYL 8 CIS 3718 Operating Systems
23
CIS 3718
Review
Seek Optimization: SCAN
SCAN – SSFT with directional preferences – elevator algorithm Assume: While 12 is being serviced, 10, 18 and 4 enter the queue.
SRQ 7 2 12 3 10 18 4
SCAN 12 18 10 7 4 3 2 --
2 3
4
Current Direction of bi-directional sweep queue reordering new – if in direction of current sweep 5/2/01
CIS 3718 Operating Systems
7
10
12
14
18
CYL 8 24
CIS 3718
Seek Optimization: N-Step SCAN
Review
N-Step SCAN – SCAN with newly arriving requests ignored Assume: While 13 is being serviced, 17, 4 and 7 enter the queue.
SRQ 13 11 20 17 4 7
N-Step SCAN 11 13 20 17 7 4 --
2 3 4
Current Direction of sweep 5/2/01
7
CYL 8
CIS 3718 Operating Systems
11
13
17
20
bi-directional queue reordering new – on next direction change 25
CIS 3718
Review
Seek Optimization: C-SCAN
C-SCAN – a unidirectional scan; newly arriving requests ignored Assume: While 11 is being serviced, 16, 3 and 7 enter the queue.
SRQ 13 11 20 16 3 7
C-SCAN 11 13 20 3 7 16 --
2
3
4
uni-directional queue reordering new – wait for next sweep 5/2/01
7
11
13
16
20
CYL 8 Direction of sweep CIS 3718 Operating Systems
26
CIS 3718
Operating Systems
Review
End of Problem Review
5/2/01
CIS 3718 Operating Systems
27
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