Lec05_Protocols_and_Models[1]-modified.pdf

Basic Networking Lecture 4: Protocols and Models The Rules: Communications Fundamentals Computer networks use rules for communications, similar to rules used in human communications. In order for two devices to communicate, they must use the same rules. Networks can vary in size and complexity. It i...

Basic Networking Lecture 4: Protocols and Models The Rules: Communications Fundamentals Computer networks use rules for communications, similar to rules used in human communications. In order for two devices to communicate, they must use the same rules. Networks can vary in size and complexity. It is not enough to have a connection; devices must agree on “how” to communicate. There are three elements to any communication: ▪ Message source (sender): Message sources are people or electronic devices that need to send a message to other individuals or devices. ▪ Message destination (receiver): The destination receives the message and interprets it. ▪ Channel: The channel consists of the media that provide the pathway over which the message travels from source to destination. The Rules: Communications Protocols All communications are governed by protocols. Protocols are the rules that communications will follow. These rules will vary depending on the protocol. The Rules: Rule Establishment ▪ Protocols must account for the following requirements to successfully deliver a message that is understood by the receiver: An identified sender and receiver Common language and grammar Speed and timing of delivery Confirmation or acknowledgment requirements The Rules: Network Protocol Requirements The protocols that are used in network communications share many fundamental traits. In addition to identifying the source and destination, computer and network protocols define the details of how a message is transmitted across a network. Common computer protocols must be in agreement and include the following requirements: Message encoding Message formatting and encapsulation Message size Message timing Message delivery options The Rules: Message Encoding Encoding is the process of converting information into another acceptable form for transmission. Decoding reverses this process to interpret the information. The Rules: Message Formatting and Encapsulation When a message is sent, it must use a specific format or structure. Message formats depend on the type of message and the channel that is used to deliver the message. The process of placing one message format (the letter) inside another message format (the envelope) is called encapsulation. De-encapsulation occurs when the process is reversed by the recipient and the letter is removed from the envelope. IP is responsible for sending a message from the message source to the destination over one or more networks. The Rules: Message Size Another rule of communication governs message size. In a network, the size restrictions on frames requires the source host to break a long message into individual pieces that meet both the minimum and maximum size requirements. A long message is therefore sent in separate frames, with each frame containing a piece of the original message. Each frame has its own addressing information. At the receiving host, the individual pieces of the message are reconstructed into the original message.. The Rules: Message Timing ▪ Message timing is very important in network communications; Message timing includes the following: the process of managing the rate of data transmission. Flow control defines how much information can be sent and the speed at which it can be delivered. ▪ Flow Control – Response Timeout – Manages how long a device waits when it does not hear a reply from the destination..(Hosts on a network use network protocols that specify how long to wait for responses and what action to take if a response timeout occurs.) Access method - Determines when someone can send a message. There may be various rules governing issues like “collisions”. This is when more than one device sends traffic at the same time and the messages become corrupt. Some protocols are proactive and attempt to prevent collisions; other protocols are reactive and establish a recovery method after the collision occurs. The Rules: Message Delivery Options Message delivery may one of the following methods: Unicast – one to one communication Multicast – one to many, typically not all Broadcast – one to all Note: Broadcasts are used in IPv4 networks, but are not an option for IPv6. Later we will also see “Anycast” as an additional delivery option for IPv6. The Rules: Message Delivery Options A Note About the Node Icon Networking documents and topologies often use a node icon—typically a circle—to represent networking and end devices The figure illustrates the use of the node icon for delivery options. Protocols: Network Protocol Overview Network protocols define common formats and sets of rules for exchanging messages between devices Protocol Type Description Can be implemented on Network Communication s enable two or more devices to communicate over one or more networks Network Security secure data to provide authentication, data integrity, and data encryption Routing enable routers to exchange route information, compare path information, and select best path Service Discovery used for the automatic detection of devices or services devices in: Software Hardware Both Protocols have their own: Function Format Rules Protocols: Network Protocol Functions Devices use agreed-upon protocols to communicate. Protocols may have one or functions. Function Description Addressing Identifies sender and receiver Reliability Provides guaranteed delivery Flow Control Ensures data flows at an efficient rate Sequencing Uniquely labels each transmitted segment of data Error Detection Determines if data became corrupted during transmission Application Interface Process-to-process communications between network applications Protocols: Protocol Interaction Networks require the use of several protocols. Each protocol has its own function and format. Protocol Function Hypertext Transfer Protocol (HTTP) ▪ ▪ Governs the way a web server and a web client interact Defines content and format Transmission Control Protocol (TCP) ▪ ▪ ▪ Manages the individual conversations Provides guaranteed delivery Manages flow control Internet Protocol (IP) Delivers messages globally from the sender to the receiver Ethernet Delivers messages from one NIC to another NIC on the same Ethernet Local Area Network (LAN) Protocol Suites: Network Protocol Suites Protocols must be able to work with other protocols. Protocol suite: A group of inter-related protocols necessary to perform a communication function Sets of rules that work together to help solve a problem The protocols are viewed in terms of layers: Higher Layers Lower Layers- concerned with moving data and provide services to upper layers Protocol Suites: Evolution of Protocol Suites There are several protocol suites. Internet Protocol Suite or TCP/IP- The most common protocol suite and maintained by the Internet Engineering Task Force (IETF) Open Systems Interconnection (OSI) protocols- Developed by the International Organization for Standardization (ISO) and the International Telecommunications Union (ITU) AppleTalk- Proprietary suite release by Apple Inc. Novell NetWare- Proprietary suite developed by Novell Inc. Protocol Suites: TCP/IP Protocol Example TCP/IP protocols operate at the application, transport, and internet layers. The most common network access layer LAN protocols are Ethernet and WLAN (wireless LAN). Protocol Suites: TCP/IP Protocol Suite TCP/IP is the protocol suite used by the internet and includes many protocols. TCP/IP is: An open standard protocol suite that is freely available to the public and can be used by any vendor A standards-based protocol suite that is endorsed by the networking industry and approved by a standards organization to ensure interoperability Protocol Suites: TCP/IP Communication Process A web server encapsulating and sending a web page to a client. A client de-encapsulating the web page for the web browser Standards Organizations: Open Standards Standard organizations create the standards that allow devices to communicate independently of any specific vendor. The software or hardware only needs to apply the standard, regardless of vendor. Open standards encourage: interoperability competition innovation Standards organizations are: vendor-neutral non-profit organizations established to develop and promote the concept of open standards. Standards Organizations: Internet Standards Internet Society (ISOC) - Promotes the open development and evolution of internet Internet Architecture Board (IAB) - Responsible for management and development of internet standards Internet Engineering Task Force (IETF) - Develops, updates, and maintains internet and TCP/IP technologies Internet Research Task Force (IRTF) - Focused on long-term research related to internet and TCP/IP protocols Standards Organizations: Internet Standards (Cont.) Standards organizations involved with the development and support of TCP/IP Internet Corporation for Assigned Names and Numbers (ICANN) Coordinates IP address allocation, the management of domain names, and assignment of other information Internet Assigned Numbers Authority (IANA) - Oversees and manages IP address allocation, domain name management, and protocol identifiers for ICANN Standards Organizations: Electronic and Communications Standards Institute of Electrical and Electronics Engineers (IEEE, pronounced “I-triple-E”) - dedicated to creating standards in power and energy, healthcare, telecommunications, and networking Electronic Industries Alliance (EIA) - develops standards relating to electrical wiring, connectors, and the 19-inch racks used to mount networking equipment Telecommunications Industry Association (TIA) - develops communication standards in radio equipment, cellular towers, Voice over IP (VoIP) devices, satellite communications, and more International Telecommunications Union-Telecommunication Standardization Sector (ITU-T) - defines standards for video compression, Internet Protocol Television (IPTV), and broadband communications, such as a digital subscriber line (DSL) Data Encapsulation: Segmenting Messages Segmenting is the process of breaking up messages into smaller units. Multiplexing is the processes of taking multiple streams of segmented data and interleaving them together. Segmenting messages has two primary benefits: Increases speed - Large amounts of data can be sent over the network without tying up a communications link. Increases efficiency - Only segments which fail to reach the destination need to be retransmitted, not the entire data stream. Data Encapsulation: Sequencing Sequencing messages is the process of numbering the segments so that the message may be reassembled at the destination. TCP is responsible for sequencing the individual segments. Data Encapsulation: Protocol Data Units Encapsulation is the process where protocols add their information to the data. The form that a piece of data takes at any layer is called a Protocol Data Unit (PDU) At each stage of the process, a PDU has a different name to reflect its new functions. There is no universal naming convention for PDUs, in this course, the PDUs are named according to the protocols of the TCP/IP suite. PDUs passing down the stack are as follows: 1. Data (Data Stream) 2. Segment 3. Packet 4. Frame 5. Bits (Bit Stream) Encapsulation Example Encapsulation is a top down process (top to bottom). The level above does its process and then passes it down to the next level of the model. This process is repeated by each layer until it is sent out as a bit stream. Data Encapsulation: De-encapsulation Example Data is de-encapsulated as it moves up the stack. When a layer completes its process, that layer strips off its header and passes it up to the next level to be processed. This is repeated at each layer until it is a data stream that the application can process. 1. Received as Bits (Bit Stream) 2. Frame 3. Packet 4. Segment 5. Data (Data Stream) Data Access: Addresses Both the data link and network layers use addressing to deliver data from source to destination. Network layer source and destination addresses - Responsible for delivering the IP packet from original source to the final destination, which may be on the same network or on a remote network. Data link layer source and destination addresses – Responsible for delivering the data link frame from one network interface card (NIC) to another NIC on the same network. Data Access: Layer 3 Logical Address The IP packet contains two IP addresses: Source IP address - The IP address of the sending device, original source of the packet. Destination IP address - The IP address of the receiving device, final destination of the packet. These addresses may be on the same link or remote. Data Access: Layer 3 Logical Address (Cont.) An IP address contains two parts: Network portion (IPv4) or Prefix (IPv6) The left-most part of the address indicates the network group which the IP address is a member. Each LAN or WAN will have the same network portion. Host portion (IPv4) or Interface ID (IPv6) The remaining part of the address identifies a specific device within the group. This portion is unique for each device on the network. Data Access: Devices on the Same Network When devices are on the same network the source and destination will have the same number in network portion of the address. PC1 – 192.168.1.110 FTP Server – 192.168.1.9 Data Access: Role of the Data Link Layer Addresses: Same IP Network When devices are on the same Ethernet network the data link frame will use the actual MAC address of the destination NIC. MAC addresses are physically embedded into the Ethernet NIC and are local addressing. The Source MAC address will be that of the originator on the link. The Destination MAC address will always be on the same link as the source, even if the ultimate destination is remote. Data Access: Devices on a Remote Network What happens when the actual (ultimate) destination is not on the same LAN and is remote? What happens when PC1 tries to reach the Web Server? Does this impact the network and data link layers? Data Access: Role of the Network Layer Addresses When the source and destination have a different network portion, this means they are on different networks. PC1 – 192.168.1 Web Server – 172.16.1 Data Access: Role of the Data Link Layer Addresses: Different IP Networks When the final destination is remote, Layer 3 will provide Layer 2 with the local default gateway IP address, also known as the router address. The default gateway (DGW) is the router interface IP address that is part of this LAN and will be the “door” or “gateway” to all other remote locations. All devices on the LAN must be told about this address or their traffic will be confined to the LAN only. Once Layer 2 on PC1 forwards to the default gateway (Router), the router then can start the routing process of getting the information to actual destination. Data Access: Role of the Data Link Layer Addresses: Different IP Networks (Cont.) The data link addressing is local addressing so it will have a source and destination for each link. The MAC addressing for the first segment is : Source – AA-AA-AA-AA-AA-AA (PC1) Sends the frame. Destination – 11-11-11-11-11-11 (R1Default Gateway MAC) Receives the frame. Note: While the L2 local addressing will change from link to link or hop to hop, the L3 addressing remains the same. Data Access: Data Link Addresses Since data link addressing is local addressing, it will have a source and destination for each segment or hop of the journey to the destination. The MAC addressing for the first segment is: Source – (PC1 NIC) sends frame Destination – (First Router- DGW interface) receives frame Data Access: Data Link Addresses (Cont.) The MAC addressing for the second hop is: Source – (First Router- exit interface) sends frame Destination – (Second Router) receives frame Data Access: Data Link Addresses (Cont.) The MAC addressing for the last segment is: Source – (Second Router- exit interface) sends frame Destination – (Web Server NIC) receives frame Data Access: Data Link Addresses (Cont.) Notice that the packet is not modified, but the frame is changed, therefore the L3 IP addressing does not change from segment to segment like the L2 MAC addressing. The L3 addressing remains the same since it is global and the ultimate destination is still the Web Server. THANKS! Best Regards!