Introduction Supplementery Slides

Introduction Supplementery Slides
Chapter 1 Introduction Supplementery Slides BLM431 Computer Networks Dr.Refik Samet

A Communications Model
Source generates data to be transmitted Transmitter Converts data into transmittable signals Transmission System Carries data Receiver Converts received signal into data Destination Takes incoming data BLM431 Computer Networks Dr.Refik Samet

BLM431 Computer Networks Dr.Refik Samet
Communications Tasks Transmission system utilization Addressing Interfacing Routing Signal generation Recovery Synchronization Message formatting Exchange management Security Error detection and correction Network management Flow control BLM431 Computer Networks Dr.Refik Samet

Simplified Communications Model - Diagram
BLM431 Computer Networks Dr.Refik Samet

Key Communications Tasks
Transmission System Utilization Interfacing Signal Generation Synchronization Exchange Management Error detection and correction Addressing and routing Recovery Message formatting Security Network Management BLM431 Computer Networks Dr.Refik Samet

Simplified Data Communications Model

Networking Point to point communication not usually practical Devices are too far apart Large set of devices would need impractical number of connections Solution is a communications network BLM431 Computer Networks Dr.Refik Samet

Simplified Network Model

Wide Area Networks Large geographical area Crossing public rights of way Rely in part on common carrier circuits Alternative technologies Circuit switching Packet switching Frame relay Asynchronous Transfer Mode (ATM) BLM431 Computer Networks Dr.Refik Samet

Circuit Switching Dedicated communications path established for the duration of the conversation e.g. telephone network BLM431 Computer Networks Dr.Refik Samet

Packet Switching Data sent out of sequence Small chunks (packets) of data at a time Packets passed from node to node between source and destination Used for terminal to computer and computer to computer communications BLM431 Computer Networks Dr.Refik Samet

Frame Relay Packet switching systems have large overheads to compensate for errors Modern systems are more reliable Errors can be caught in end system Most overhead for error control is stripped out BLM431 Computer Networks Dr.Refik Samet

Asynchronous Transfer Mode
ATM Evolution of frame relay Little overhead for error control Fixed packet (called cell) length Anything from 10Mbps to Gbps Constant data rate using packet switching technique BLM431 Computer Networks Dr.Refik Samet

Integrated Services Digital Network
ISDN Designed to replace public telecom system Wide variety of services Entirely digital domain BLM431 Computer Networks Dr.Refik Samet

Local Area Networks Smaller scope Building or small campus Usually owned by same organization as attached devices Data rates much higher Usually broadcast systems Now some switched systems and ATM are being introduced BLM431 Computer Networks Dr.Refik Samet

Protocols Used for communications between entities in a system Must speak the same language Entities User applications facilities terminals Systems Computer Terminal Remote sensor BLM431 Computer Networks Dr.Refik Samet

Key Elements of a Protocol
Syntax Data formats Signal levels Semantics Control information Error handling Timing Speed matching Sequencing BLM431 Computer Networks Dr.Refik Samet

Protocol Architecture
Task of communication broken up into modules For example file transfer could use three modules File transfer application Communication service module Network access module BLM431 Computer Networks Dr.Refik Samet

Simplified File Transfer Architecture

A Three Layer Model Network Access Layer Transport Layer Application Layer BLM431 Computer Networks Dr.Refik Samet

Network Access Layer Exchange of data between the computer and the network Sending computer provides address of destination May invoke levels of service Dependent on type of network used (LAN, packet switched etc.) BLM431 Computer Networks Dr.Refik Samet

Transport Layer Reliable data exchange Independent of network being used Independent of application BLM431 Computer Networks Dr.Refik Samet

Application Layer Support for different user applications e.g. , file transfer BLM431 Computer Networks Dr.Refik Samet

Addressing Requirements
Two levels of addressing required Each computer needs unique network address Each application on a (multi-tasking) computer needs a unique address within the computer The service access point or SAP BLM431 Computer Networks Dr.Refik Samet

Protocol Architectures and Networks

Protocols in Simplified Architecture

Protocol Data Units (PDU)
At each layer, protocols are used to communicate Control information is added to user data at each layer Transport layer may fragment user data Each fragment has a transport header added Destination SAP Sequence number Error detection code This gives a transport protocol data unit BLM431 Computer Networks Dr.Refik Samet

Network PDU Adds network header network address for destination computer Facilities requests BLM431 Computer Networks Dr.Refik Samet

Operation of a Protocol Architecture

TCP/IP Protocol Architecture
Developed by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET) Used by the global Internet No official model but a working one. Application layer Host to host or transport layer Internet layer Network access layer Physical layer BLM431 Computer Networks Dr.Refik Samet

Physical Layer Physical interface between data transmission device (e.g. computer) and transmission medium or network Characteristics of transmission medium Signal levels Data rates etc. BLM431 Computer Networks Dr.Refik Samet

Network Access Layer Exchange of data between end system and network Destination address provision Invoking services like priority BLM431 Computer Networks Dr.Refik Samet

Internet Layer (IP) Systems may be attached to different networks Routing functions across multiple networks Implemented in end systems and routers BLM431 Computer Networks Dr.Refik Samet

Transport Layer (TCP) Reliable delivery of data Ordering of delivery BLM431 Computer Networks Dr.Refik Samet

Application Layer Support for user applications e.g. http, SMPT BLM431 Computer Networks Dr.Refik Samet

TCP/IP Protocol Architecture Model

OSI Model Open Systems Interconnection Developed by the International Organization for Standardization (ISO) Seven layers A theoretical system delivered too late! TCP/IP is the de facto standard BLM431 Computer Networks Dr.Refik Samet

OSI Layers Application Presentation Session Transport Network Data Link Physical BLM431 Computer Networks Dr.Refik Samet

OSI v TCP/IP BLM431 Computer Networks Dr.Refik Samet

Standards Required to allow for interoperability between equipment Advantages Ensures a large market for equipment and software Allows products from different vendors to communicate Disadvantages Freeze technology May be multiple standards for the same thing BLM431 Computer Networks Dr.Refik Samet

Standards Organizations
Internet Society ISO ITU-T (formally CCITT) ATM forum BLM431 Computer Networks Dr.Refik Samet

Further Reading Stallings, W. Data and Computer Communications (6th edition), Prentice Hall 1999 chapter 1 Web site for Stallings book Web sites for IETF, IEEE, ITU-T, ISO Internet Requests for Comment (RFCs) Usenet News groups comp.dcom.* comp.protocols.tcp-ip BLM431 Computer Networks Dr.Refik Samet

Networking Configuration

Service Primitives and Parameters
Services between adjacent layers expressed in terms of primitives and parameters Primitives specify function to be performed Parameters pass data and control info BLM431 Computer Networks Dr.Refik Samet

Primitive Types REQUEST A primitive issued by a service user to invoke some service and to pass the parameters needed to specify fully the requested service INDICATION A primitive issued by a service provider either to: indicate that a procedure has been invoked by the peer service user on the connection and to provide the associated parameters, or notify the service user of a provider-initiated action RESPONSE A primitive issued by a service user to acknowledge or complete some procedure previously invoked by an indication to that user CONFIRM A primitive issued by a service provider to acknowledge or complete some procedure previously invoked by a request by the service user BLM431 Computer Networks Dr.Refik Samet

Timing Sequence for Service Primitives

Networking Point to point communication not usually practical Devices are too far apart Large set of devices would need impractical number of connections Solution is a communications network Wide Area Network (WAN) Local Area Network (LAN) BLM431 Computer Networks Dr.Refik Samet

Wide Area Networks Large geographical area Crossing public rights of way Rely in part on common carrier circuits Alternative technologies Circuit switching Packet switching Frame relay Asynchronous Transfer Mode (ATM) BLM431 Computer Networks Dr.Refik Samet

Circuit Switching Dedicated communications path established for the duration of the conversation e.g. telephone network BLM431 Computer Networks Dr.Refik Samet

Packet Switching Data sent out of sequence Small chunks (packets) of data at a time Packets passed from node to node between source and destination Used for terminal to computer and computer to computer communications BLM431 Computer Networks Dr.Refik Samet

Frame Relay Packet switching systems have large overheads to compensate for errors Modern systems are more reliable Errors can be caught in end system Most overhead for error control is stripped out BLM431 Computer Networks Dr.Refik Samet

Asynchronous Transfer Mode
ATM Evolution of frame relay Little overhead for error control Fixed packet (called cell) length Anything from 10Mbps to Gbps Constant data rate using packet switching technique BLM431 Computer Networks Dr.Refik Samet

Local Area Networks Smaller scope Building or small campus Usually owned by same organization as attached devices Data rates much higher Usually broadcast systems Now some switched systems and ATM are being introduced BLM431 Computer Networks Dr.Refik Samet

LAN Configurations Switched Switched Ethernet May be single or multiple switches ATM LAN Fibre Channel Wireless Mobility Ease of installation BLM431 Computer Networks Dr.Refik Samet

Metropolitan Area Networks
MAN Middle ground between LAN and WAN Private or public network High speed Large area BLM431 Computer Networks Dr.Refik Samet

Protocols and Architecture Characteristics
Direct or indirect Monolithic or structured Symmetric or asymmetric Standard or nonstandard BLM431 Computer Networks Dr.Refik Samet

Direct or Indirect Direct Systems share a point to point link or Systems share a multi-point link Data can pass without intervening active agent Indirect Switched networks or Internetworks or internets Data transfer depend on other entities BLM431 Computer Networks Dr.Refik Samet

Monolithic or Structured
Communications is a complex task To complex for single unit Structured design breaks down problem into smaller units Layered structure BLM431 Computer Networks Dr.Refik Samet

Symmetric or Asymmetric
Communication between peer entities Asymmetric Client/server BLM431 Computer Networks Dr.Refik Samet

Standard or Nonstandard
Nonstandard protocols built for specific computers and tasks K sources and L receivers leads to K*L protocols and 2*K*L implementations If common protocol used, K + L implementations needed BLM431 Computer Networks Dr.Refik Samet

Use of Standard Protocols

Functions Encapsulation Segmentation and reassmebly Connection control Ordered delivery Flow control Error control Addressing Multiplexing Transmission services BLM431 Computer Networks Dr.Refik Samet

Encapsulation Addition of control information to data Address information Error-detecting code Protocol control BLM431 Computer Networks Dr.Refik Samet

Segmentation (Fragmentation)
Data blocks are of bounded size Application layer messages may be large Network packets may be smaller Splitting larger blocks into smaller ones is segmentation (or fragmentation in TCP/IP) ATM blocks (cells) are 53 octets long Ethernet blocks (frames) are up to 1526 octets long Checkpoints and restart/recovery BLM431 Computer Networks Dr.Refik Samet

Why Fragment? Advantages More efficient error control More equitable access to network facilities Shorter delays Smaller buffers needed Disadvantages Overheads Increased interrupts at receiver More processing time BLM431 Computer Networks Dr.Refik Samet

Connection Control Connection Establishment Data transfer Connection termination May be connection interruption and recovery Sequence numbers used for Ordered delivery Flow control Error control BLM431 Computer Networks Dr.Refik Samet

Connection Oriented Data Transfer

Ordered Delivery PDUs may traverse different paths through network PDUs may arrive out of order Sequentially number PDUs to allow for ordering BLM431 Computer Networks Dr.Refik Samet

Flow Control Done by receiving entity Limit amount or rate of data Stop and wait Credit systems Sliding window Needed at application as well as network layers BLM431 Computer Networks Dr.Refik Samet

Error Control Guard against loss or damage Error detection Sender inserts error detecting bits Receiver checks these bits If OK, acknowledge If error, discard packet Retransmission If no acknowledge in given time, re-transmit Performed at various levels BLM431 Computer Networks Dr.Refik Samet

Addressing Addressing level Addressing scope Connection identifiers Addressing mode BLM431 Computer Networks Dr.Refik Samet

Addressing level Level in architecture at which entity is named Unique address for each end system (computer) and router Network level address IP or internet address (TCP/IP) Network service access point or NSAP (OSI) Process within the system Port number (TCP/IP) Service access point or SAP (OSI) BLM431 Computer Networks Dr.Refik Samet

Address Concepts BLM431 Computer Networks Dr.Refik Samet

Addressing Scope Global nonambiguity Global address identifies unique system There is only one system with address X Global applicability It is possible at any system (any address) to identify any other system (address) by the global address of the other system Address X identifies that system from anywhere on the network e.g. MAC address on IEEE 802 networks BLM431 Computer Networks Dr.Refik Samet

Connection Identifiers
Connection oriented data transfer (virtual circuits) Allocate a connection name during the transfer phase Reduced overhead as connection identifiers are shorter than global addresses Routing may be fixed and identified by connection name Entities may want multiple connections - multiplexing State information BLM431 Computer Networks Dr.Refik Samet

Addressing Mode Usually an address refers to a single system Unicast address Sent to one machine or person May address all entities within a domain Broadcast Sent to all machines or users May address a subset of the entities in a domain Multicast Sent to some machines or a group of users BLM431 Computer Networks Dr.Refik Samet

Multiplexing Supporting multiple connections on one machine Mapping of multiple connections at one level to a single connection at another Carrying a number of connections on one fiber optic cable Aggregating or bonding ISDN lines to gain bandwidth BLM431 Computer Networks Dr.Refik Samet

Transmission Services
Priority e.g. control messages Quality of service Minimum acceptable throughput Maximum acceptable delay Security Access restrictions BLM431 Computer Networks Dr.Refik Samet

OSI - The Model A layer model Each layer performs a subset of the required communication functions Each layer relies on the next lower layer to perform more primitive functions Each layer provides services to the next higher layer Changes in one layer should not require changes in other layers BLM431 Computer Networks Dr.Refik Samet

The OSI Environment BLM431 Computer Networks Dr.Refik Samet

OSI as Framework for Standardization

Layer Specific Standards

Elements of Standardization
Protocol specification Operates between the same layer on two systems May involve different operating system Protocol specification must be precise Format of data units Semantics of all fields allowable sequence of PCUs Service definition Functional description of what is provided Addressing Referenced by SAPs BLM431 Computer Networks Dr.Refik Samet

OSI Layers (1) Physical Physical interface between devices Mechanical Electrical Functional Procedural Data Link Means of activating, maintaining and deactivating a reliable link Error detection and control Higher layers may assume error free transmission BLM431 Computer Networks Dr.Refik Samet

OSI Layers (2) Network Transport of information Higher layers do not need to know about underlying technology Not needed on direct links Transport Exchange of data between end systems Error free In sequence No losses No duplicates Quality of service BLM431 Computer Networks Dr.Refik Samet

OSI Layers (3) Session Control of dialogues between applications Dialogue discipline Grouping Recovery Presentation Data formats and coding Data compression Encryption Application Means for applications to access OSI environment BLM431 Computer Networks Dr.Refik Samet

Use of a Relay BLM431 Computer Networks Dr.Refik Samet

TCP/IP Protocol Suite Dominant commercial protocol architecture Specified and extensively used before OSI Developed by research funded US Department of Defense Used by the Internet BLM431 Computer Networks Dr.Refik Samet

TCP/IP Protocol Architecture(1)
Application Layer Communication between processes or applications End to end or transport layer (TCP/UDP/…) End to end transfer of data May include reliability mechanism (TCP) Hides detail of underlying network Internet Layer (IP) Routing of data BLM431 Computer Networks Dr.Refik Samet

TCP/IP Protocol Architecture(2)
Network Layer Logical interface between end system and network Physical Layer Transmission medium Signal rate and encoding BLM431 Computer Networks Dr.Refik Samet

PDUs in TCP/IP BLM431 Computer Networks Dr.Refik Samet

Some Protocols in TCP/IP Suite

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