0. CMPT 371 Data Communications and Networking
Summary Switching ,throughput, Multiplexing
Protocol layers

1. What is a Protocol
A set of definitions and rules defining the method by which data is transferred between two or more entities or systems.
The key elements of a protocol are:
Syntax: definitions of data format, size and content of messages or packets (headers and data)
Semantics: control, responses to messages or packets, coordination, error handling
Timing/Synchronization: maintaining synchronization between the communicating entities (speed matching, sequencing, recovery from timing related errors )
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2. Characteristics of Protocols: 1
Direct: data passes from source to destination without active intervention (point to point or multipoint link)
Indirect: data from source must pass through intermediate active entities to reach the destination (switched networks)
Set Switch
Fixed connection
Source
Destination
Network
Active Intermediate nodes
Source
Destination
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3. Characteristics of Protocols: 2
Monolithic: Single protocol for all aspects of data transfer
Structured: uses a set of protocols interacting based on a chosen architecture. (Layered, client server …)
Consider computer networks, A lot of complexity
Hosts , routers, switches, applications, varied hardware and software, varied communication needs
Any chance a single monolithic protocol is the best way to organize and manage the Internet?
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4. Characteristics of Protocols: 3
Symmetric: communications between peers that is the same regardless of which entity is source and which is destination (peer to peer)
Asymmetric: unequal source and receiver (client – server)
Internet needs to support both
Source/Destination
Destination/Source
Source: Controls Transfer
Destination:
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5. Characteristics of Protocols: 4
Standard: independent of hardware and application
Used by all members of network, no need for translation
Operates in a given layer regardless of operating system or system hardware (may require multiple implementations)
Nonstandard: designed for specific hardware or application
Must translate between nonstandard protocols increasing load on system rapidly as number of nonstandard systems increases
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6. Internet Protocol Choices
Structured (layered): uses a set of protocols, several different protocols per layer
Standardized: uses same protocols, may use different implementation on different hardware
Figure 2.3 Stallings (2003)
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7. Layered Protocol Architecture
Flexible protocols can become very complicated very quickly.
Reduce complexity, separate communication functions into modules.
Layer these modules using clean interfaces
Each module becomes a separate protocol layer
Each layer provides services to the layer above through an interface that hides the complexities of how the service is implemented.
With one or more protocols per layer the complete network architecture is known as a protocol stack
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8. Standardization
Clearly defined functions for each layer allow for independent and simultaneous development of multiple layers (Lower layers = more detail)
Protocol specification for each layer and for interfaces between layers must be exact
Format of data units
allowed sequence of PDUs
Semantics (meanings) of all fields
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9. Standardization
Particular operations are localized in a given layer regardless of operating system or system hardware (may require multiple implementations)
Service Definition: standards for services provided by a layer, using a given set of protocols, to the layer above it
Addressing: Provide the defined services to entities with particular addresses
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10. Layered models
Each layer performs a different set of communications functions.
Each layer encapsulates and hides complexity from the layer above it
Each layer uses the layer below it the perform more primitive and detailed functions
Clear interfaces between layers make independent changes in one layer independent of the other layers
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11. Encapsulation
The addition of control information to data before passing the resulting frame to the next protocol level
A PDU (protocol data unit) may or may not contain data but will contain control information such as
Addresses
Error detection checksums or redundancy checks
Sequence numbers
Other control information
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12. The OSI Environment Figure 2.7 Stallings (2003)
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13. TCP/IP Protocol Suite
TCP/IP is the most commonly used protocol stack on the internet
TCP/IP uses a layered structure, with fewer layers than the OSI model
TCP/IP protocols for a given layer use the services available from lower levels to complete the tasks they are responsible for
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14. Janice Regan © Sept
Figure 1.11 Stallings (2000)

15. Application Layer
Application Layer: Working environment / support for applications
Provides services used directly by applications
Hides the complexities of services provided by the other layers from the user
Provides an interface to communications between processes or applications on separate hosts
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16. Transport Layer
Manages exchange of application data between end systems
Connection oriented reliable delivery (TCP)
Manages connections and error free, In sequence, loss and duplication free data transfer
Best effort delivery (UDP)
Packet oriented, connectionless
Process level addressing, Segmentation, Multiplexing / De-multiplexing
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17. Network Layer
manages how data moves from one host to another in a network
Hides specifics of network technology from higher levels
Addressing, forwarding and routing in the network. How to get your packet from A to B
Fragmentation / Reassembly
Error detection and handling
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18. Link Layer
Data Link Layer: making the physical link reliable and usable
Operates on frames containing messages sent between directly connected devices.
Bit level error detection and handling (finds corruption that happens during transmission)
Link control and management, Link level addressing
Media access control, sharing the physical media between multiple devices
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19. Physical Layer
Physical Layer: raw bit stream service. Operates on bits
Mechanical: properties of connection to network (connector)
Electrical: representation of bits as voltages (encoding and signaling)
Functional: Defines functions performed by particular circuits at the interface between the system and the transmission media
Procedural: Defines how bit streams are exchanged through the physical media
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20. Some Application layer Protocols
Users most commonly directly use application layer protocols like Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP); Telnet,
Other common application layer protocols help facilitate the use and management of TCP/IP networks: These include Domain Name System (DNS), the Routing Information Protocol (RIP), the Simple Network Management Protocol (SNMP).
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21. TCP-IP Protocol Architecture
Physical
Data link
network
transport
application
Application protocol
Physical
Data link
network
transport
application
Transport protocol
Network
Data link
Physical
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22. Encapsulation PDUs for TCP/IP
Physical
Data link
network
transport
application
Application data
TCP segment
TCP/UDP
Application data
IP datagram IP
TCP/UDP
Application data
Ethernet
frame
Ethernet IP
TCP/UDP
Application data
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23. Encapsulation: PDU Headers
TCP segment: User data +Transport Header
Destination and source process address of each occurrence of an application, called a port
Sequence Number used to manage packet flow, deliver packets in the correct order
Checksum preserves reliability of data transfer and assure delivery to correct destination
Lengths, flags …
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24. Encapsulation: PDU Headers
IP Datagram: TCP segment + IP Header
Destination and/or source network address (IP address)
Protocol Identification
Indicate transport protocol used
Flow and error control information (including fragmentation)
Error detection (header only) information
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25. Encapsulation: PDU Headers
Ethernet Frame: IP Datagram + Ethernet header
Next hop and source Ethernet address
May be hardware specific (works for hardwares other than Ethernet)
Flow and sharing for the physical media
Error detection information
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26. Using a relay (router) application application transport transport
Physical
Data link
network
transport
application
Physical
Data link
network
transport
application
Network
Data link
Physical
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27. Encapsulation at each level
Physical
Data link
network
transport
application
Application data
TCP segment
TCP/UDP
Application data
IP datagram IP
TCP/UDP
Application data
Ethernet
frame
Ethernet IP
TCP/UDP
Application data
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28. Using a relay (switch) application application transport transport
Physical
Data link
network
transport
application
Physical
Data link
network
transport
application
Data link
Physical
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29. History Please be sure to read the excellent summary in your text book
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