cmpt 371

© Janice Regan, CMPT 128, Jan 2007

CMPT 371Data Communications and Networking

Summary Switching ,throughput, MultiplexingProtocol 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 )


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)

Source Set 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?


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:


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


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


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


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


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


The OSI Environment

Figure 2.7 Stallings (2003)


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


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


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


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


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


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. 2007-201320Figure 1.11 Stallings (2000)


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).



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.


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


Physical

Data link

network

transport

application

Physical

Data link

network

transport

applicationApplication protocol

Transport protocol

Network

Data link

Physical

Encapsulation PDUs for TCP/IP


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


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 …


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


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)


Physical

Data link

network

transport

application

Network

Data link

PhysicalPhysical

Data link

network

transport

application

Encapsulation at each level


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

Using a relay (switch)


Physical

Data link

network

transport

application

Data link

PhysicalPhysical

Data link

network

transport

application

cmpt 371

Documents

characteristics of protocols

different protocols

set of protocols

nonstandard protocols

protocol stackjanice

single protocol

data communications

single monolithic protocol