Computer Network Protocols and Architecture

Computer Protocol

• Protocols are agreed-upon rules and standard procedures for data transmission between computers.
• Protocols are important because the Internet comprises networks, each containing diverse nodes/hosts, such as Windows, Unix, and Linux.

Protocols

• Protocols are used for communications between entities, like user applications, within a system.
• Systems include computers, terminals, and remote sensors.
• Communication requires speaking the same language.
• A protocol is a set of rules and conventions.
• Key protocol elements involve syntax (data formats, signal levels), semantics (control information, error handling), and timing (speed matching, sequencing).

Protocol Architecture: Layering

• Layering models the services offered by hardware as the physical layer.
• Layers are added sequentially, each providing a higher service level.
• Layering simplifies network building and provides a modular design.

Standards

• Standards are necessary for interoperability.
• Advantages include ensuring a large market for equipment/software and allowing communication between different vendors' products.
• Disadvantages include freezing technology and the potential for competing standards.
• Standards Organizations include Internet Society, ISO, ITU-T (formerly CCITT), and ATM forum.

Protocol Characteristics

• Protocols can be direct (sharing a point-to-point or multi-point link) or indirect (switched networks).
• Protocols can be monolithic/structured: Structured design breaks down complex communications tasks into Layered structure.
• Protocols can be symmetric (communication between peer entities) or asymmetric (client/server).

Establishing the Rules of Communication

• Communication includes an identified sender and receiver.
• An agreed communication method like face-to-face, telephone, letter, or photograph is necessary.
• Common language and grammar use is required.
• Speed and timing of delivery are required.
• Confirmation or acknowledgement requirements

Applying Rules to Message Transfer

• Frames’ size limitations force the source host to segment long messages into smaller pieces.
• Each segment is encapsulated with address information and transmitted.
• The receiving host then reassembles the message for processing and interpretation.

Message Timing

• Access Method restrictions apply
• Flow Control is required
• There is a Response Timeout

Need For Protocol Architecture

• For file transfer, the source must activate communications, inform the network of the destination, and verify the destination is prepared to receive.
• The file transfer application must check that the destination file management system can accept and store the file.
• File format translation may be necessary.
• Tasks are broken into subtasks and implemented separately in layers.
• Functions such as that peer layers should communicate, which are is needed in both systems.

Key Elements of a Protocol

• Syntax defines data formats and signal levels.
• Semantics incorporates control information and error handling.
• Timing includes speed matching and sequencing.

Network Protocols

• Protocols involve message formatting/ structuring.
• They detail how networking devices share information about pathways.
• Protocols specify when and how error/system messages are passed.
• They manage the setup/ termination of data transfer sessions.

Interaction of Protocols

• Application Protocol: Hypertext Transfer Protocol (HTTP)
• Transport Protocol: Transmission Control Protocol (TCP)
• Internet Protocol: Internet Protocol (IP)
• Network Access Protocols: Data Link & Physical layers

IEEE 802 Project Group

• IEEE is an Institution of Electrical and Electronics Engineers, a non-profit organization.
• Project group 802 is responsible for setting standards for the physical link of the network.
• IEEE 802.1: internetworking.
• IEEE 802.2: Logical Link Control (LLC)
• IEEE 802.3: CSMA/CD
• IEEE 802.8: Fiber-Optic Technical Advisory Group.
• IEEE 802.9: Integrated Voice/Data Networks.
• IEEE 802.10: Network Security.
• IEEE 802.11: Wireless Networks.
• IEEE 802.12: Demand Priority Access LANs.
• IEEE 802.4: Token Bus LAN.
• IEEE 802.5: ken Ring LAN.
• IEEE 802.6: Metropolitan Area Network.
• IEEE 802.7: Broadband Technical Advisory Group.

OSI (Open Systems Interconnection)

• OSI was developed by the International Organization for Standardization (ISO).
• OSI has seven layers that are a theoretical system delivered too late.
• TCP/IP is the de facto standard.
• OSI describes how information moves from a software application in one computer through a network medium to another computer’s application.
• It divides network architecture into seven layers: Application, Presentation, Session, Transport, Network, Data Link, and Physical.
• In 1978, the International Standards Organization (ISO) started developing framework architecture for it with an abstract model for networking and specific protocols.
• All aspects of the design evolved from the Advanced Research Projects Agency Network (ARPANET) and the beginning Internet.
• The original concept was provided by Charles Bachman then of Honeywell.

OSI Layers

• Upper layers deal with application issues and is mostly implemented in software such as the application layer where communication begins, and the lower layers handle data transport in hardware and software.

Osi Model: Layered Tasks

• The tasks of writing a letter, sending and receiving it via carrier and layered according to:
  • Sender
  • Receiver
  • Carrier

OSI Peer-To-Peer Model

• Device A Application Layer talks to Device B application layer, proceeding downwards

OSI Data Encapsulation

• The H refers to the 'Headers', and the numbers indicate which layer is the header for.
• The D refers to data, and the numbers indicate which layer is the data for
• The T refers to Tail

OSI In Action

• A message begins at the application layer and moves down to the bottom physical layer. Then each successive layer will add a header. and when it is read on the device at the receiving end the headers are taken off one layer at a time.

OSI Layer Functions

• Application Layer: Network process to application.
• Presentation Layer: Data representation, encryption, and decryption.
• Session Layer: Interhost communication.
• Transport Layer: End-to-end connections/reliability and flow control.
• Network Layer: Path determination and logical addressing.
• Data Link Layer: Physical addressing.
• Physical Layer: Media, signal, and binary transmission.

OSI Model Layer 1: Physical Layer

• Defines electrical/physical specifications for devices.
• Defines a device’s relationship with a physical medium to establish/terminate a connection to a medium.
• Covers mechanical, electrical, functional, and procedural aspects of communication.
• Defines attributes such as voltage levels, timing, data rates, transmission distances, and connectors.

OSI Model Layer 2: Data Link Layer

• Provides data transfer between network entities.
• It attempts to provide reliable communication over the physical layer interface.
• It breaks outgoing data into frames and reassembles received frames.
• It creates/detects frame boundaries, handles errors, and implements flow control.
• Supports point-to-point and broadcast communication, as well as simplex, half-duplex, and full-duplex.

OSI Model Layer 3: Network Layer

• It provides variable-length data sequence transfer from source to destination across one or more networks, maintaining the Transport Layer's quality of service and implementing routing of packets.
• It defines the optimal path and identifies endpoints with logical addressing.
• It handles congestion and facilitates heterogeneous network interconnection (Internetworking).
• It fragments packets to suit different media.

OSI Model:Layer 4: Transport Layer

• Provides transparent data transfer between end users.
• The purpose is a reliable data exchange mechanism between processes on different computers.
• It controls a data link’s reliability through flow control, segmentation/desegmentation, and error control.
• It ensures error-free and in-sequence data unit delivery.
• There is no loss or duplication of data units.
• Provides connectionless or connection-oriented services, with connection management
• there is Multiplex multiple connection over a single channel.

OSI Model Layer 5: Session Layer

• The Session Layer manages dialogues between computers including initiating, maintaining, and terminating the connections between local and remote applications.
• Provides full/half-duplex and simplex operation.
• Establishes checkpointing, adjournment, termination, and restart procedures.
• It is responsible for terminating connections and graceful session closures and may also handle log-on and passwords

OSI Model Layer 6: Presentation Layer

• Establishes a context between Application Layer entities, allowing higher-layer entities to use different syntax/semantics so long as the presentation service understands both and the mapping between them.
• It provides independence from differences in data representation (e.g., encryption) with translation from application to network format and vice versa
• It defines the format in which data will be exchanged and used to ensure compatibility.
• Sometimes you have to call the syntax layer.

OSI Model Layer 7: Application Layer

• The application layer interacts with application programs to support distributed applications.
• It is the closest layer to the end-user with identifying communication partners, determining resource availability and synchronizing communication.
• Examples include applications for file transfer, electronic mail, and remote login.

Postal Analogy of OSI and Mailing a Letter

• Application Layer: Write a letter containing 20 pages to a foreign country.
• Presentation Layer:Translate the letter so the receiver can read it.
• Session Layer: Insure the intended recipient can receive the letter.
• Transport Layer: Separate and number pages. Includes registered mail, to track delivery and requests another package if one is “lost” or “damaged” in the mail.
• Network Layer: Postal Center sorts letters by postcode to route them closer to destination.
• Data-Link Layer: Local Post Office determines which vehicles to deliver letters.
• Physical Layer: Trucks, Planes, Rail, autos, carry letter between stations.

TCP/IP

• The Internet Protocol Suite (TCP/IP) includes communications protocols used for the Internet/similar networks.
• It is named after the Transmission Control Protocol (TCP) and the Internet Protocol (IP).

Key features include:

• A TCP/IP Layers include transport, network,data link and physical layers
• Application Layer Examples: TELNET, FTP, SMTP, POP3, SNMP, NNTP, DNS, NFS, HTTP,
• Transport Layer Examples: TCP, UDP
• Internet Layer examples include: IP , ICMP, ARP, RARP
• Presentation Layer Example: FDDI, Ethernet, ISDN ,X.25

Encapsulation

• Different headers are required based on the function of each layer, such that at the application layer only Data is present, and as the data passes downstream the encapsulation begins and additional layers are added.

Layers are present in the TCP/IP model

• Layer 4: Application
• Layer 3: Transport
• Layer 2: Internet
• Layer 1: Network access
• There are layers in the TCP/IP model, but the layers can have the same name. DO NOT CONFUES!

TCP/IP Protocol Architecture

• Application layer: Supports applications for user applications, like e.g. HTTP, SMTP.
• Transport layer: is in charge of the Reliable delivery and ordering of data.
• Internet layer: Systems may be attached to different networks, but are in charge of Routing functions across multiple networks and are implemented in end systems and routers.
• Network access layer: exchange of data between end system and network, including Destination address provision and Invoking services like priority.
• Physical layer has a Physical interface between data transmission device (e.g. computer) and transmission medium or network and the Characteristics of transmission medium, signal levels and Data rates.

TCP/IP Protocols and Suite

• The different protocols included in the TCP/IP Suite include HTTP, ICMP, TCP and UDP.

UDP: Datagram Protocol

• UDP is an Alternative to TCP in the TCP/IP Suite.
• It sends messages with minimal protocol overhead
• It does not guarantee delivery, preservation of sequence, or protection against duplication
• UDP Adds port addressing capability to IP and is commonly used with Simple Network Management Protocol also known as an SNMP
• Because there is finer control.There is now delay and there is also no connection overhead.

UDP Use Cases

• UDP packets are small like an eight byte header. It is also an Alternative to TCP in the TCP/IP Suite.
• It is very beneficial because it is also sent with minimum protocol.

Applications That Use UDP

• Applications that Use UDP includes multimedia streaming. If there is a
• Retransmission of lost/corrupted packets, it is not worthwhile. Also, the time taken for he packet to retransmit will not be worth it. In Example, s telephone calls, video conferencing, gaming. Simple query protocols like Domain Name System
• It is also beneficial because the connection can be Easier to have application and if that overhead of connection also needed, that is also a benefit.

TCP (Transmission Control Protocol)

• TCP: transport layer protocol for most applications
• TCP provides a reliable connection for transfer of data between applications
• TCP segment: the basic protocol unit
• TCP tracks segments between entities for duration of each connection
• Temporary association between entities in different systems for identify respective users (applications)

TCP Operation

• Is a connection-oriented protocol as it Provides of data Management. TCP is used across the networks and is known for Transferring reliably over streams. It also requires the user to have all data that is accurately received, is in sequence so the hosts needs to establish a synchronization process the "3-way handshake”. The Syn bit is inside the TCP header to achieve this.

TCP Operation: Virtual Connection

• Prior to data transmission, hosts establish a virtual connection via a synchronization process. The synch process is a 3-way is “3-way Handshake”, which ensures both sides are ready to transfer data and determines the initial sequence numbers. The syn bit is stored in the TCP header.

TCP vs UDP

• TCP provides a connection-oriented, reliable byte stream service (lots of overhead).
• UDP offers minimal datagram delivery service (as little overhead as possible).
• It depends which is better on the application.

TCP Handshake

• Is a connection oriented protocol. Communicating hosts go through a synchronization process to establish a virtual connection that insures that both sides are ready for data transmission. Also, it allows the devices to determine the initial sequence numbers. The reference sequence numbers are stored here for each device to go to SYN, thus the receiver will know the connection request

DoS Attacks

• SYN Flooding is a DoS attack that spoofs the syn.

Transmission Control Protocol TCP Windows and Flow Control (Handshaking)

• It is often too large to be to be sent in a single segment, Thus, TCP splits the data into segments. There is control in this area because “windowing” sets the how often it goes through which is measured by “byes per window" and that determines the Windows between ACKs.

Flow and Windowing Size

• the Window size determines the amount of data to transmit before receiving the acknowledgment. The SlidIng Window: It is necessary to make ensure the size is Dynamic during a session. If a code is not working and it is showing timeout, Then it is important to retransmit at a much slower rate.

Sequencing and Positive Acknowledgement

• TCP utilizes PAR to control data flow and confirm data so that each TCP segment is numbered and the ACK's also identifies identified missing data pieces to re-transmit so that when the Source sends packet, it all starts the timer awaiting the ACK. If the Timer expires before the source receives ACK, then the source must re-transmit the packet and restarts the timer.

TCP/IP Address Requirement

• It must have a unique level of Addressing on both the host and a sub-network.