Roadmap  Introduction to Basics  Computer Network – Components | Classification  Internet  Clients and Servers  Network Models  Protocol Layers - Architecture and Services  OSI – ISO Model  TCP/IP Model  Network Edge: Connection Oriented and Connectionless Services  Network Core: Switching Techniques

OSI Layer 4- Transport Layer  Transport Layer  Exchange of data between end systems  Error control (end-to-end)  Flow control (end-to-end)  In sequence (segment)  No losses  No duplicates  Quality of service( Throughput, transit delay, error rate)

OSI Layers (5,6,7)  Session  Control of dialogues between applications/Dialogue discipline  Grouping  Synchronization/check points  Recovery  Presentation  Data formats  Architecture specific (Big-endian or Little-endian)  Provide conversion from one encoding schema to another encoding schema  Data compression  Encryption  Application  Means for applications to access OSI environment  E mail, web browsers.

Layered Architecture – Protocols Diagram

Application Layer Protocol PortTransport Layer Protocol HTTP80TCP FTP20 & 21TCP DNS53UDP & TCP Telnet23TCP SMTP25TCP POP3110TCP HTTPS443TCP

Error Control and Flow Control DLL  Interruption of the physical media may lead to loss of one or more frames  A valid frame may be discarded at the receiver due to buffer overflow  A valid frame may be discarded at the receiver as determined by protocol procedures (e.g., error or flow control) Transport Layer  The Network layer may loose packets or even misroute packets  Segment loss

Roadmap  Introduction to Basics  Computer Network – Components | Classification  Internet  Clients and Servers  Network Models  Protocol Layers - Architecture and Services  OSI – ISO Model  TCP/IP Model  Network Edge: Connection Oriented and Connectionless Services  Network Core: Switching Techniques

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  Network Layer  Data Link Layer (Network access layer)  Physical layer

Physical Layer  Similar to OSI model physical layer  Physical interface between data transmission device (e.g. computer) and transmission medium or network  Characteristics of transmission medium  Signal levels  Data rates

Network Access/Data Link layer(1)  Data Link Control(Logical Link Control) Sub Layer  Means of activating, maintaining and deactivating a reliable link  Framing (Header)  Error detection and control

Data Link layer(2)  Media Access Control (MAC) sub layer  Allocation of channel  Physical addressing (MAC address)  Higher layers do not need to know about underlying technology  Virtual point-point links between pair of stations

Network Layer  Exchange of data between end system and network  Destination address provision (IP Address)  Systems may be attached to different networks  PDU is called as “Datagram”  Routing functions across multiple networks  Implemented in end systems and routers  Invoking services like priority  Connection less service  Fragmentation  Routing and IP addresses  ARP and RARP

Transport Layer (TCP/UDP)  Connection-less and connection oriented service  Reliable delivery of data  Segments  Congestion control  Ordering of delivery(Reassembling)  Addressing (Port no. or SAP)  UDP (TFTP, NFS, DNS)  TCP (SMTP, HTTP, FTP)  Error Control  Flow Control

Application Layer  Support for user applications  File transfer  User applications  Reliable data transfer for UDP users  Network management  E.g. HTTP, SMTP, FTP, etc.

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)

Role of Header and trailer  The seven OSI layers use various forms of control information to communicate with their peer layers in other computer systems. This control information consists of specific requests and instructions that are exchanged between peer OSI layers.  Control information typically takes one of two forms: headers and trailers. Headers are prepended to data that has been passed down from upper layers. Trailers are appended to data that has been passed down from upper layers.

Contd.  Headers, trailers, and data are relative concepts, depending on the layer that analyzes the information unit. At the network layer, for example, an information unit consists of a Layer 3 header and data. At the data link layer, however, all the information passed down by the network layer (the Layer 3 header and the data) is treated as data.  In other words, the data portion of an information unit at a given OSI layer potentially can contain headers, trailers, and data from all the higher layers. This is known as encapsulation.

Example Header Information  Destination port  Sequence number  Checksum

PDUs in TCP/IP

Protocol Stack  A list of protocols used by a certain system, one protocol per layer, is called a protocol stack.

Internet protocol stack  application: supporting network applications  FTP, SMTP, STTP  transport: host-host data transfer  TCP, UDP  network: routing of datagrams from source to destination  IP, routing protocols  link: data transfer between neighboring network elements  PPP, Ethernet  physical: bits “on the wire” application transport network link physical

Roadmap  Introduction to Basics  Computer Network – Components | Classification  Internet  Clients and Servers  Network Models  Protocol Layers - Architecture and Services  OSI – ISO Model  TCP/IP Model  Network Edge: Connection Oriented and Connectionless Services  Network Core: Switching Techniques

Connection Oriented and Connectionless services  Connection oriented reliable services guarantees that data transmitted from sender to receiver will eventually be delivered to the receiver in order and in its entirety.  Connectionless unreliable services does not make any guarantees about eventual delivery.

Roadmap  Introduction to Basics  Computer Network – Components | Classification  Internet  Clients and Servers  Network Models  Protocol Layers - Architecture and Services  OSI – ISO Model  TCP/IP Model  Network Edge: Connection Oriented and Connectionless Services  Network Core: Switching Techniques

Switching techniques  Packet switching  Circuit switching  Virtual circuit switching