Semester Copyright USM EEE442 Computer Networks Introduction: Protocols En. Mohd Nazri Mahmud MPhil (Cambridge, UK) BEng (Essex, UK) Room 2.14

Semester Copyright USM Protocols and Architecture Simple Network Architecture The Three Layer Model TCP/IP OSI Model

Semester Copyright USM Protocol Architecture When computers, terminals, and/or other data processing devices exchange data, the procedures involved can be quite complex Examples? The peer layers communicate using a set of rules or conventions known as a protocol. Instead of implementing the complex logic for this as a single module, the task is broken up into modules. In a protocol architecture, the modules are arranged in a vertical stack, each layer in the stack performs a related subset of the functions. It relies on the next lower layer to perform more primitive functions.

Semester Copyright USM Simplified Network Architecture Source: Stallings

Semester Copyright USM The Three Layer Model

Semester Copyright USM The Three Layer Model Network Access Layer, Transport layer, Application Layer. Network Access Layer – concerns with the exchange of data between a computer and the network to which it is attached Transport Layer – Ensure reliable exchange of data Application Layer – contains logic needed to support the various user applications

Semester Copyright USM The Three Layer Model

Semester Copyright USM Protocol Data Units

Semester Copyright USM TCP/IP Protocol Architecture Most widely used developed by US Defense Advanced Research Project Agency (DARPA) for ARPANET packet switched network used by the global Internet protocol suite comprises a large collection of standardized protocols

Semester Copyright USM TCP/IP Layers no official model but tasks can be separated into 5 relatively independent layers –Application layer –Host-to-host, or transport layer –Internet layer –Network access layer –Physical layer

Semester Copyright USM TCP/IP Model

Semester Copyright USM Physical Layer concerned with physical interface between computer and network concerned with issues like: –characteristics of transmission medium –signal levels –data rates –other related matters

Semester Copyright USM Network Access Layer exchange of data between an end system and attached network concerned with issues like : –destination address provision –invoking specific services like priority –access to & routing data across a network link between two attached systems allows layers above to ignore link specifics

Semester Copyright USM Internet Layer (IP) routing functions across multiple networks for systems attached to different networks using IP protocol implemented in end systems and routers routers connect two networks and relays data between them

Semester Copyright USM Transport Layer (TCP) common layer shared by all applications provides reliable delivery of data in same order as sent commonly uses TCP

Semester Copyright USM Application Layer provide support for user applications need a separate module for each type of application

Semester Copyright USM Protocol Functions Encapsulation Segmentation and reassembly Connection control Ordered delivery Flow control Error Control Addressing Multiplexing Transmission services

Semester Copyright USM Protocol Functions Encapsulation –The addition of control information to data –Data are accepted or generated by an entity and encapsulated into a PDU containing that data plus control information –Control information falls into 3 general categories Address Error-detecting code Protocol control

Semester Copyright USM Protocol Functions Segmentation and reassembly –Segmentation is the breaking up of data into blocks of some smaller bounded size –Needed because some communication network only accept block of certain size (eg ATM 53 octets, Ethernet – 1526 octets) for more efficient error control for more equitable access to shared transmission medium Can allocate smaller buffers in the receiver For intermediate checking and restart/recovery operations

Semester Copyright USM Protocol Functions Connection control –For controlling connection establishment, data transfer and termination –Can be in connectionless or connection-oriented mode –Involves connection request, accepts or rejects, acknowledgments and termination requests –Some complex set up include negotiation concerning some optional features of the protocol

Semester Copyright USM Protocol Functions Ordered delivery –PDUs may go through different paths in the network and may arrive at the destination not in order –Protocol ensures that data received in the original order it was sent

Semester Copyright USM Protocol Functions Flow control –A function performed by the receiving entity to limit the amount or rate of data that is sent by a transmitting entity.

Semester Copyright USM Protocol Functions Error Control –Too guard against loss or damage data and control information –Typically implemented as two separate functions for error detection and retransmission –The sender inserts and error detecting code in the transmitted PDU –The receiver checks the value of the code and if an error is detected discards the PDU. –The sender retransmits after timeout for acknowledgement

Semester Copyright USM Protocol Functions Addressing –Typically, a unique address is associated with each end system and each intermediate system (eg router). This refers to a network-level address –The network-level address is used to route a PDU through a network or networks to a system indicated by a network level address in the PDU. –Once data arrive at a destination system, they must be routed to some process or application in the system. –Typically a system supports multiple applications and each application may support multiple users –Each application and each concurrent user is assigned a unique identifier referred to as port in TCP/IP architecture

Semester Copyright USM Protocol Functions Multiplexing –One form or multiplexing is supported by means of multiple connections into a single system for example a number of circuits are multiplexed over a single physical interface between the end system and the network –Another form permits simultaneous connections for example multiple TCP connections terminating in a given system, each connection supporting a different pair of ports.

Semester Copyright USM Protocol Functions Transmission services –Priority –Quality of service –Security

Semester Copyright USM Standardized Protocol Architecture Standards are needed to promote interoperability among vendor equipment and to encourage economies of scale Functions are broken into more manageable parts and organised as a communications architecture Functions are partitioned into a hierarchical set of layers Each layer performs a related subset of the functions It relies on the next lower layer to perform more primitive functions It provides services to the next higher layer Ideally, the layers should be defined so that changes in one layer do not require changes in the other layers

Semester Copyright USM Operation of TCP and IP

Semester Copyright USM Addressing Requirements two levels of addressing required each host on a subnet needs a unique global network address –its IP address each application on a (multi-tasking) host needs a unique address within the host –known as a port

Semester Copyright USM Operation of TCP/IP

Semester Copyright USM Transmission Control Protocol ( TCP) usual transport layer is (TCP) provides a reliable connection for transfer of data between applications a TCP segment is the basic protocol unit TCP tracks segments between entities for duration of each connection

Semester Copyright USM TCP Header

Semester Copyright USM User Datagram Protocol (UDP) an alternative to TCP no guaranteed delivery no preservation of sequence no protection against duplication minimum overhead adds port addressing to IP

Semester Copyright USM UDP Header

Semester Copyright USM IP Header

Semester Copyright USM IPv6 Header

Semester Copyright USM TCP/IP Applications have a number of standard TCP/IP applications such as –Simple Mail Transfer Protocol (SMTP) –File Transfer Protocol (FTP) –Telnet

Semester Copyright USM OSI Open Systems Interconnection developed by the International Organization for Standardization (ISO) has seven layers

Semester Copyright USM OSI Layers

Semester Copyright USM OSI v TCP/IP