Raspberry Pi 5: Challenges and Solutions in Bringing up an OpenGL/Vulkan Driv...
Week 2
1.
2.
3. structured as a hierarchy of layers Network Model
each layer offers certain services to
the higher layers, while hiding from Application
the higher layers the details of how
those services are implemented:
Process-to-Process
hierarchical modularity
channels
a particular layer in one network node
communicates with the corresponding Host-to-Host
layer in another network node by Connectivity
using an agreed protocol for that layer Hop-to-Hop Connectivity
this communication may be actual or
virtual.
Physical Connectivity
Layering reduces the complexity of
building scalable networks through
encapsulation and modularity
4. ISO - OSI Model
In the late 1970’s ISO(International Standard
Organization) formulated a Reference OSI(Open Systems
Interconnection) Model:
◦ To provide a common basis for the coordination of
standards development
◦ To allow existing and evolving standards to be placed
into perspective with one another
◦ has become the stand model for classifying
communications functions
The Model is concerned with the structuring of
Communication to provide a reliable, open
communication service which is independent of any
specific manufacturer’s equipment or conventions
5.
6.
7.
8. As the message travels from A and B, it may pass through many
intermediate nodes.
These intermediate nodes usually involves only the first three
layers of the OSI model.
Within a single machine, each layer calls upon the services of the
layer just below it.
Between machines, layer x on one machine communicates with
layer x on another machine.
Communication between machines is peer-to-peer process using
the protocols appropriate to a given layer.
Interface between each pair of adjacent layers allow passing of
data through layers from A to B and then from B to A
Each interface defines the information and Services a layer must
provide for layer above it.
9.
10. Physical Address
◦ Also known as link address, is the address of a node as defined by its LAN or
WAN.
◦ It is included in the frame used by the data link layer.
◦ It is the lowest level address
◦ Ethernet uses a 6 byte (48-bit) physical address known as MAC address.
Logical Address
◦ Used for universal communications that are independent of underlying
physical networks.
◦ Used to identify each host uniquely, regardless of underlying physical network
also known as IP Address
◦ Logical address in the internet are 32-bit and 64-bit addresses also called
IPv4 and IPv6 address.
Port Numbers
◦ It is 16-bit in length used to identify process on a host. Physical Address will
change from hop-to-hop, but logical and port addresses usually remain same
Specific Address (host name)
◦ Is user friendly address. E.g URL or email
11.
12. Define the characteristics of the interface
between the devices and the transmission
media
Encode bits into signals and decode
signals to get bits
Define transmission rate, which must be
the same for both sender and receiver
Synchronize clocks
13.
14. Framing: divide the data stream into
manageable data units called “frames”
Physical addressing: insert the physical
address of the next node into frame’s
header
Flow control: prevent overflow at receiver
Error control: make sure that frames are
correctly received
Access control: make sure that there is
no link access conflict
15.
16. A node with physical address 10 sends a frame to a node
with physical address 87. The two nodes are connected by
a link. At the data link level this frame contains physical
addresses in the header. These are the only addresses
needed. The rest of the header contains other information
needed at this level. The trailer usually contains extra bits
needed for error detection
17.
18. Logical addressing: e.g., IP addresses
Routing: how to get to the destination?
19.
20. We want to send data from a
node with network address A
and physical address 10,
located on one LAN, to a node
with a network address P and
physical address 95, located
on another LAN. Because the
two devices are located on
different networks, we cannot
use physical addresses only;
the physical addresses only
have local jurisdiction. What
we need here are universal
addresses that can pass
through the LAN boundaries.
The network (logical)
addresses have this
characteristic.
21.
22. Port addressing: A process is associated with a
“port”
Segmentation and reassembly: Application data
are divided into segments and each segment
has sequence no.
Connection control: connection-less or
connection-oriented?
End to end reliability
Flow control ( here its is performed end to end
rather than across single link.)
Service point addressing
Error control (here its is performed end to end
rather than across single link.) error correction
is achieved through re-transmission.
28. Conceptual only and
never seriously
implemented
Session: dialog controller
Presentation: handle
syntax, semantics of the
information exchanged
between the 2 systems,
designed for encryption,
decryption, and
compression
29. Dialog controller. The session layer allows the two
systems to enter into a dialog. It allows the communication
between two processes to take place either in half duplex or
full duplex.
Synchronization. Session layer allows a process to add
checkpoints or synchronization points into a stream of data.
E.g. check file of 2000 pages after every 50 pages and is
acknowledged independently. If system crashes due to some
reason at page# 1000, then retransmission will take place
and page 1000 and onward will be sent.
30. Translation ( Common Format)
Encryption: To ensure privacy, encryption
is done.
Compression: Reduces the no of bits to be
transmitted. E.g. data, video or audio file
being compressed.
31. Internet (TCP/IP)
Architecture
FTP HTTP DNS TFTP Applications
… …
UDP TCP
TCP UDP
IP
Narrow Waist
Data Link
NET1 NET2 … NETn
Physical
The Hourglass Model
32. FTP HTTP TFTP
TCP UDP
Network IP TCP/UDP
IP
Type Protocol Port No.
Field Field
NET1 NET2 … NETn
Editor's Notes
OSI architecture: ISO was one of the first organizations to formally define a common standard way to connect computers. Their architecture called Open Systems Interconnection architecture partitioned network functionality into seven layers where one or more protocols implement the functionality assigned to a given layer. In this sense, OSI model is not a protocol graph (since it defines layers and not relationships between protocols) but a reference model. ISO, in conjunction with another standardization body called ITU, publishes a series of protocol specifications based on the OSI model. This series is sometimes called the X dot series since the protocols are given names like X.25, X.400 and X.500. Starting at the bottom and moving up, the physical layer handles the transmission of raw bits over a communications link. The data link layer then collects a stream of bits into a large aggregate called a frame . Network adapters, along with device drivers, running in the node's OS typically implement this layer. This means that frames (and not raw bits) are delivered to hosts. The network layer handles routing among nodes within a packet switched network. At this layer, the unit of data exchange is a packet rather than a frame, although they are fundamentally the same thing. The lower three layers are implemented on all nodes nodes in cluding switches within the netwok and hosts connected along the exterior of the network. The transport layer then implements what we have up to this point being called the process to process channel. Here the unit of data is called a message (or segment) rather than a packet or a frame. The transport layer and the higher layers typically run only on the end hosts and not on the intermediata switches or routers. There is less agreement about the definition of the top layers. Skipping ahead to the seventh layer (the top most layer), we find the application layer. Example protocols include HTTP and FTP. Below that presentation layer is concerned with the format of data exchanged between peers; e.g., whether an integer is 16/32/64 bits long and whether the MSB is trasmitted first or last. Finally, the session layer provides a name space that is used to tie together potentially different transport streams that are part of a single application. For example, an audio stream and a video stream may be managed in a teleconferening application.
Transport lay is responsible for source to destination delivery of the entire message. Where as the network layer oversees end to end delivery of individual packets.
Computers runs several prorams at the same time. For this reason source to destination delivery means deliver not only from one computer to next but also from a specific process ( running prog) on one computer to a specific process on another. Therefore transport lay header must include a type of address called SAP or port address. Network lay Get each packet to the correct computer, while the transport lay gets the entire message to the correct process on that computer.
Translation: the process running prog between two sys are usually exchanging information in the form of character, string, numbers and so on. The information should be changed to bit streams before being ransmitted. Because different computers use different encoding sys, presentation lay does interoperability between these different encoding methods. Common format.
Internet Architecture: The internet architecture, also called TCP/ IP architecture based on its two most famous protocols is shown above. The architecture evolved from experience in implementing ARPANET. While the 7 layer OSI model can be applied to the Internet (with some imagination), a four layer model is used instead. At the lowest layer is a variety of network protocols (also called data link layer or subnetwork layer). In practice, these protocols are implemented using a combination of hardware (network adapters) and software (network device driver). For example, you might find Ethernet card or Fiber Distributed Data Interface (FDDI) protocols at this layer. The second layer consists of a single protocol called Internet Protocol (IP). This is the protocol that supports the interconnection of multiple networking technologies into a single logical internetwork. The third layer consists of two main protocols---the Transmission Control Protocol and the User Datagram Protocol (UDP). TCP and UDP provide alternative logical channels to application programs. TCP provides a bye steam channel and UDP provides an unreliable datagram service. TCP and UDP are sometimes called end to end protocol. Running above the transport layer are a range of application protocol such as FTP, TFTP, HTTP, SMTP, Telnet, etc. Difference between application programs and application layer protocol. All the WWW browsers (Safari, Firefox, IE, Opera, Lynx, etc.) There is a similarly large numbers of webservers. The reason all of them can interwork is that they all conform to the HTTP application layer protocol. Internet architecture does not imply strict layering. The application is free to bypass the defined transport layer protocols and to directly use IP or any of the underlying networks. In fact, programmers are free to define new channel abstractions. Hour glass shape: Wide at the top and bottom but narrow at the waist: IP serves as the focal point of the architecture. IP is a common method of exchanging packets among a wide collection of networks. Image source: Jennifer Ruxford
