Upload
dwayne-evans
View
221
Download
2
Tags:
Embed Size (px)
Citation preview
© Janice Regan, CMPT 128, Jan 2007
CMPT 371Data Communications and Networking
Summary Switching ,throughput, Multiplexing
Protocol layers
1
Janice Regan © Sept. 2007-20132
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 )
Janice Regan © Sept. 2007-20133
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)
SourceSet SwitchFixed connection Destinatio
n
SourceNetworkActive Intermediate nodes
Destination
4Janice Regan © Sept. 2007-2013
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?
Janice Regan © Sept. 2007-20135
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:
Janice Regan © Sept. 2007-20136
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
7Janice Regan © Sept. 2007-2013
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)
Janice Regan © Sept. 2007-2013 8
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
Janice Regan © Sept. 2007-20139
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
Janice Regan © Sept. 2007-201310
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
Janice Regan © Sept. 2007-201311
The OSI model A classic model that is not generally implemented Layered 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
Janice Regan © Sept. 2007-201312
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
Janice Regan © Sept. 2007-201314
The OSI layers: Application
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
Janice Regan © Sept. 2007-201315
The OSI layers: Session Layer
Initiation, management, termination of sessions between local and remote devices
Presentation Layer: Defines the format of the data to be exchanged between applications
Data compression, encryption as Implemented in the internet as part of applications/protocols like SSL, Mime
Janice Regan © Sept. 2007-201316
The OSI layers: Transport 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
Janice Regan © Sept. 2007-201317
The OSI layers: Network
Network Layer: managing 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
Janice Regan © Sept. 2007-201318
The OSI layers: Data Link
Data Link Layer: making the physical link reliable 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
Janice Regan © Sept. 2007-201319
The OSI layers: Physical 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
Janice Regan © Sept. 2007-201321
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
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).
Janice Regan © Sept. 2007-2013 22
Janice Regan © Sept. 2007-201323
TCP/IP Protocol Architecture Application layer: Provides interface to
communications between processes or applications on separate hosts
Transport Layer: (TCP, UDP) Provides end to end data transfer service, including reliability control and sequencing.
Encapsulates the network, hiding networking details from applications. Includes the protocols the applications use to exchange data.
Janice Regan © Sept. 2007-201324
TCP/IP Protocol Architecture Internet Layer: (IP) procedures for
routing across multiple heterogeneous networks and through routers
Network Access Layer: Interface between end system and network, routing within a single network, access to a particular network, Depends on type of network
Physical Layer: Defines characteristics of the transmission medium, signaling rate, and encoding
TCP-IP Protocol Architecture
Janice Regan © Sept. 2007-2013 25
Physical
Data link
network
transport
application
Physical
Data link
network
transport
applicationApplication protocol
Transport protocol
Network
Data link
Physical
Encapsulation PDUs for TCP/IP
Janice Regan © Sept. 2007-2013 26
Physical
Data link
network
transport
application Application data
Application data
Application data
Application data
TCP segment
IP datagram
Ethernetframe
TCP/UDP
TCP/UDP
TCP/UDP
IP
IPEthernet
Janice Regan © Sept. 2007-201327
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 …
Janice Regan © Sept. 2007-201328
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
Janice Regan © Sept. 2007-201329
Encapsulation: PDU Headers Ethernet Frame: IP Datagram + Ethernet
header Next hop and/or source Ethernet address May be hardware specific (works for
hardwares other than Ethernet) Flow and sharing for the physical media Error detection information
Using a relay (router)
Janice Regan © Sept. 2007-2013 30
Physical
Data link
network
transport
application
Network
Data link
PhysicalPhysical
Data link
network
transport
application
Encapsulation at each level
Janice Regan © Sept. 2007-2013 31
Physical
Data link
network
transport
application Application data
Application data
Application data
Application data
TCP segment
IP datagram
Ethernetframe
TCP/UDP
TCP/UDP
TCP/UDP
IP
IPEthernet