TCS 221 Transmission Modes & Message Addressing in Computer Networks PDF

TRANSMISSION MODES IN COMPUTER NETWORKS Transmission modes refer to the method through which data is sent from one device to another. Transmission mode is sometimes referred to as communication mode. The different data transmission modes varies in terms of direction of data transfer, the synchroniza...

TRANSMISSION MODES IN COMPUTER NETWORKS Transmission modes refer to the method through which data is sent from one device to another. Transmission mode is sometimes referred to as communication mode. The different data transmission modes varies in terms of direction of data transfer, the synchronization between the sender and the receiver, and the number of bits sent at a time over the network. Types of Transmission Modes (based on direction of data exchange): Simplex Data transmission:  Communication in Simplex mode is unidirectional.  On a connection, only one of the two devices can send, while the other can only receive.  The simplex mode can utilize the whole channel capacity to deliver data in only one direction.  This form of transmission is not widely used since most connections involve the flow of data in both directions. The simplex mode finds its use in commercial applications such as sales that do not require a corresponding response.  The radio station is a simplex channel since it sends the signal but never permits listeners to communicate back.  As an example, consider a keyboard and conventional displays. The keyboard can only provide input, whereas the display can only provide output. Advantages:  During data transfer, it makes complete use of the communication channel’s capacity.  Because the data only goes in one way, it has the fewest or no data traffic concerns. Disadvantages:  Unfortunately, there is no way to return information to its original source (No mechanism for acknowledgement).  As a result, there is no communication between devices. Half-Duplex Transmission:  Each station can broadcast and receive in half-duplex mode, but not at the same time.  When one device sends, the other device can only receive, and vice versa.  The half-duplex mode is used when communication in both directions is not required at the same time. Each direction can use the whole capacity of the channel.  In half-duplex mode, error detection is available, and if an error occurs, the receiver asks the sender to re-transmit the data.  Example: Transmission of messages in a walkie-talkie happens one at a time and in both directions. Advantages:  During data transmission, both devices can send and receive data in the half-duplex mode, which allows them to use the whole bandwidth of the communication channel. Disadvantages:  Due to the fact that one device must wait while the other sends data in half-duplex mode, the data is delayed. Full-Duplex Transmission:  In full-duplex mode, both stations can broadcast and receive data at the same time.  In full-duplex mode, signals travelling in one direction and the signals travelling in the other direction are transmitted on the same link.  This sharing can occur in two ways:  One route is used for sending, and one for receiving. Both are kept separate.  Alternatively, the capacity is shared by signals travelling in both directions.  When communication in both directions is necessary all of the time, full-duplex mode is utilised. The channel’s capacity, on the other hand, must be shared between the two directions.  Example: A telephone network allows two people to communicate over a phone line, which allows both people to talk and listen at the same time. Advantages:  Two-way communication can occur in both directions at the same time.  It is the quickest way of communication between devices. Disadvantages:  The communication channel’s capacity is split into two sections.  It has inefficient channel bandwidth usage since there are two distinct and separate routes for two devices which are communicating. Basis for Simplex mode Half Duplex mode Full Duplex mode Comparison Bidirectional flow of Unidirectional flow of Bidirectional information flow in Direction of information from sender information from the both directions, from the sender communication to receiver but only one at sender to the receiver. to the receiver. a time.  Basis for Simplex mode Half Duplex mode Full Duplex mode Comparison A device can only send Both devices can send and data but cannot receive it, Both devices can send and Transmit/Receive receive data, but only one or it can only receive data receive data simultaneously. can do so at a time. but cannot send it. Relatively faster than Speed Slow Fastest transmission mode. simplex mode. It either uses two simplex The entire bandwidth of It uses the complete bandwidth communication Utilization of the communication bandwidth of the channel or divide the complete bandwidth channel is used in only communicating channel. bandwidth channel into two one direction at a time. parts for data transmission. A telephone network in which Communication between a Communication using a Example two people communicate over a computer and a keyboard. walkie-talkie. phone line. Types of Transmission Modes (based on the synchronization between the transmitter and the receiver): Synchronous Transmission:  The synchronous transmission mode is a type of communication in which bits are delivered one after the other with no start/stop bits or pauses in between.  The transmitter and receiver are both timed by the same system clock.  Bytes are transferred as blocks in a continuous stream of bits. Because the message block lacks start and stop bits, it is the receiver’s job to appropriately arrange the bits.  As the bits come, the receiver counts them and organises them into eight-bit units.  The information is constantly received by the receiver at the same pace as it was provided by the transmitter. It also listens to messages even if no bits are sent.  Example: Transmission of bits in synchronous mode is shown in the figure below: Advantages:  Because there is no gap between data bits, transmission speed is rapid. Disadvantages:  It is too costly. Asynchronous Transmission:  Asynchronous transmission mode is a type of communication in which a start and stop bit is included in the message during transmission.  The start and stop bits ensure that data is appropriately transferred from the transmitter to the receiver.  In most cases, the start bit is ‘0’ and the end bit is ‘1’.  Data bits can be transferred at any moment in an asynchronous method of communication.  Messages are delivered at random intervals, with only one data byte sent at a time.  This form of data transmission is best suited for short-distance data transfer.  Example: Transmission of bits in asynchronous mode is shown in the figure below: Advantages:  It is a low-cost and efficient means of communication.  Because of the existence of start and stop bits, data transmission accuracy is excellent. Disadvantages:  Because of the gaps between distinct blocks of data, data transmission may be slower. Types of Transmission Modes (based on the number of bits sent simultaneously in the network): Serial Transmission:  Serial data transmission mode is a mode in which data bits are delivered serially, one after the other, via a transmission channel.  It can only communicate over a single transmission line.  The data bits arrive at the receiver side in sync with one another.  The system requires many clock cycles to send the data stream in serial data transmission.  The data integrity is preserved in this mode because transmission of data bits happens in a specified order, one after the other.  This form of transmission is best suited for long-distance data transfer or when the amount of data delivered is minimal.  As an example, consider data transmission between two computers through serial ports. Advantages:  Because it is reliable, it finds its use in long-distance data transmission.  There are fewer cables and the complexity is lower.  It is inexpensive. Disadvantages:  Because there is just one transmission channel, the data transfer rate is slow. Parallel Transmission:  The parallel data transmission mode sends data bits in parallel at the same time.  In such types of transmission, several transmission lines are employed. As a result, many data bytes can be sent in a single system clock.  We use this form of transmission to deliver a significant amount of data in a short period of time.  Its primary application is for short-distance communication.  We need n-transmission lines for n-bits. As a result, the network’s complexity grows, yet its transmission speed remains high.  If two or more transmission lines are excessively close to each other, there is a risk of data interference, which degrades signal quality.  As an example, consider data transmission between a computer and a printer. Advantages:  It is simple to construct and implement  Because of the n-transmission channels, data transmission speed is fast. Disadvantages:  It necessitates additional transmission channels and is hence inefficient in terms of cost.  Interference in data bits, which causes interference in video conferencing too. Parallel transmission always happens in synchronicity with the system clock. Serial transmission, though, can be synchronous or asynchronous. What Factors Need To Be Considered While Choosing Transmission Modes?  Rate of transmission  The distance the data has to travel.  Cost and ease of installation  Resistance/hurdles offered by environmental circumstances. COMMUNICATION MODEL & MESSAGE ADDRESSING IN COMPUTER NETWORKS Whether connection oriented or connectionless communication, synchronous or asynchronous communication, serial or parallel communication, simplex, duplex, or duplex communication, network devices need to know how to identify themselves and locate the recipient of their messages on the network. In human communication, telephone numbers, email addresses, postal addresses, facebook name, instant messaging and social platforms profile or handle, provides the means of identification for both the sender and the receiver of information. The sender must be aware of the receiver’s address before sending a message. Similarly, network devices communicate with the use of addresses. A network’s devices require addresses in order to communicate with one another. Giving a message an address is the first stage, and sending the message to the targeted recipients is the second. These addresses are the layer 2 Media Access Control (MAC) address, the layer 3 Internet Protocol (IP) address and the layer 4 logical port numbers(TCP/UDP) When a ‘message’ such as a file, image or video is transmitted across a network, it is first broken down into small blocks called segments. These are placed into containers called packets, typically by the Internet Protocol (IP). The information added to the data to create the packet is called the IP header. The process of adding the IP header to the data is called ‘encapsulation’. Encapsulation is a complex term used to describe a simple technical process. Think of presents you may be given for your birthday – they are encapsulated in wrapping paper. So, encapsulation is the thin, additional layer of information used to wrap around data when it is sent between computers. However, encapsulation does not stop at creating packets. Further, down at layer 2, the IP packets are further encapsulated into Frames, by the addition of the MAC header to the IP packet. Below is a diagram that shows how data passes through the protocol stack, being encapsulated and changing form at each layer. The form that a piece of data takes at any layer is called a protocol data unit (PDU) As can be seen from the datagram, the message (file, video, enail etc) when broken into segments also has the transport header added. So encapsulation starts even at the transport layer. The information in the header at each level of the encapsulation stage contains may several details, basically they must contain the addresses at different layers. The diagram below illustrates the address types at each stage of encapsulation. MAC addresses deliver data packets within a local network. IP addresses to help route data packets over large networks like the internet. If there is more than one application ready to accept a packet, then a number called port number distinguishes the targeted application from the other applications. So, proper addressing is required for reliable data transfer To summarise internet addressing types are categorised as logical and physical. While the MAC address is the hardware address that is physically encoded/ programmed into the device by the manufacturer, the IP address and the port numbers are logical addresses. Mac Addresses (Physical Hardware Addresses) A MAC address, which stands for Media Access Control Address, is a physical address that works at the Data Link Layer. MAC Addresses are unique 48-bit hardware numbers of a computer that are embedded into a network card (known as a Network Interface Card) during manufacturing. The MAC Address is also known as the Physical Address of a network device, networking hardware address, or the burned-in address (BIA). MAC Address is worldwide unique since millions of network devices exist and we need to uniquely identify each. Format of MAC Address A MAC Address is a 12-digit hexadecimal number (6-bit binary number), which is mostly represented by Colon-Hexadecimal notation. The First 6 digits (say 00:40:96) of the MAC Address identify the manufacturer, called the OUI (Organizational Unique Identifier). IEEE Registration Authority Committee assigns these MAC prefixes to its registered vendors. Here are some OUI of well-known manufacturers: CC:46:D6 - Cisco 3C:5A:B4 - Google, Inc. 3C:D9:2B - Hewlett Packard 00:9A:CD - HUAWEI TECHNOLOGIES CO.,LTD It is not uncommon for large organisations to have more than one set of OUI, e.g., in some literature for Cisco, you can have 00-40-96 as the OUI The rightmost six digits represent Network Interface Controller, which is assigned by the manufacturer. As discussed above, the MAC address is represented by Colon-Hexadecimal notation. But this is just a conversion, not mandatory. MAC address can be represented using any of the following formats: Types of MAC Address 1. Unicast: A Unicast-addressed frame is only sent out to the interface leading to a specific NIC. If the LSB (least significant bit) of the first octet of an address is set to zero, the frame is meant to reach only one receiving NIC. The MAC Address of the source machine is always Unicast. 2. Multicast: The multicast address allows the source to send a frame to a group of devices. In Layer- 2 (Ethernet) Multicast address, the LSB (least significant bit) of the first octet of an address is set to one. IEEE has allocated the address block 01-80-C2-xx-xx-xx (01-80-C2-00-00-00 to 01-80-C2-FF-FF-FF) for group addresses for use by standard protocols. 3. Broadcast: Similar to Network Layer, Broadcast is also possible on the underlying layer( Data Link Layer). Ethernet frames with ones in all bits of the destination address (FF-FF-FF-FF-FF-FF) are referred to as the broadcast addresses. Frames that are destined with MAC address FF-FF-FF-FF-FF-FF will reach every computer belonging to that LAN segment. IP Addresses (Internet Protocol Addresses) An Internet Protocol (IP) address is the unique identifying number assigned to every device connected to the internet. An IP address definition is a numeric label assigned to devices that use the internet to communicate. Computers that communicate over the internet or via local networks share information to a specific location using IP addresses. IP addresses have two distinct versions or standards. The Internet Protocol version 4 (IPv4) address is the older of the two, which has space for up to 4 billion IP addresses and is assigned to all computers. The more recent Internet Protocol version 6 (IPv6) has space for trillions of IP addresses, which accounts for the new breed of devices in addition to computers. There are also several types of IP addresses, including public, private, static, and dynamic IP addresses. Every device with an internet connection has an IP address, whether it's a computer, laptop, IoT device, or even toys. The IP addresses allow for the efficient transfer of data between two connected devices, allowing machines on different networks to talk to each other.An IP address is not random. The creation of an IP address has the basis of math. The Internet Assigned Numbers Authority (IANA) allocates the IP address and its creation. The full range of IP addresses can go from 0.0.0.0 to 255.255.255.255. Public IP Address Basically, we access the Internet through a public IP address. A public IP address, or external-facing IP address, applies to the main device people use to connect their business or home internet network to their internet service provider (ISP). In most cases, this will be the router. All devices that connect to a router communicate with other IP addresses using the router’s IP address. They are also called routable IP address. Private IP Address A private IP address, or internal-facing IP address, is assigned by an office or home intranet (or local area network) to devices, or by the internet service provider (ISP). The home/office router manages the private IP addresses to the devices that connect to it from within that local network. Network devices are thus mapped from their private IP addresses to public IP addresses by the router. Private IP addresses are reused across multiple networks, thus preserving valuable IPv4 address space and extending addressability beyond the simple limit of IPv4 addressing (4,294,967,296 or 2^32). They are not routable In the IPv6 addressing scheme, every possible device has its own unique identifier assigned by the ISP or primary network organization, which has a unique prefix. Private addressing is possible in IPv6, and when it's used it's called Unique Local Addressing (ULA). Static IP Address All public and private addresses are defined as static or dynamic. An IP address that a person manually configures and fixes to their device’s network is referred to as a static IP address. A static IP address cannot be changed automatically. An internet service provider may assign a static IP address to a user account. The same IP address will be assigned to that user for every session. Dynamic IP Address A dynamic IP address is automatically assigned to a network when a router is set up. The Dynamic Host Configuration Protocol (DHCP) assigns the distribution of this dynamic set of IP addresses. The DHCP can be the router that provides IP addresses to networks across a home or an organization. Each time a user logs into the network, a fresh IP address is assigned from the pool of available (currently unassigned) IP addresses. A user may randomly cycle through several IP addresses across multiple sessions. IP Address Classes Some IP addresses are reserved by the Internet Assigned Numbers Authority (IANA). These are typically reserved for networks that carry a specific purpose on the Transmission Control Protocol/Internet Protocol (TCP/IP), which is used to interconnect devices. Four of these IP address classes include: 0.0.0.0: This IP address in IPv4 is also known as the default network. It is the non-routeable meta address that designates an invalid, non-applicable, or unknown network target. 127.0.0.1: This IP address is known as the loopback address, which a computer uses to identify itself regardless of whether it has been assigned an IP address. 169.254.0.1 to 169.254.254.254: A range of addresses that are automatically assigned if a computer is unsuccessful in an attempt to receive an address from the DHCP. 255.255.255.255: An address dedicated to messages that need to be sent to every computer on a network or broadcasted across a network. Class A: IP address is used for a Large Number of Hosts. 1st octet identifies the network and the remaining 24-bits identify the Host Class B Range of Class B IP addresses: 128 to 191 For local machine loopback testing, the number 127 is set aside. The first 16 bits are known as the “two octets.” The network is identified by two octets, and the host is identified by the remaining 16 bits. Class C Small networks normally make use of Class C IP addresses. Range of Class B IP addresses: 192 to 223. Private IP Ranges Every private IP address belongs to a specific private IP address range reserved for that purpose by the Internet Assigned Numbers Authority (IANA). A private IP address cannot be used to access the Internet and remains only in the local network. Since a private IP address never leaves the LAN, the same private IPs appear on different private networks, and they only have to be unique within that single local network. Each private IP address belongs to one of the following ranges: Class A. Ranging from 10.0.0.0 to 10.255.255.255, it is for large networks and has 8 bits for the network and 24 for hosts. Class B. Ranging from 172.16.0.0 to 172.31.255.255, it is used for medium networks and has 16 bits for the network and 16 for hosts. Class C. Ranging from 192.168.0.0 to 192.168.255.255, it is for smaller networks and has 24 bits for the network and 8 for hosts. Since private IP addresses are reserved for private networks and need to be unique to that network only, the ranges are much smaller than for public IP addresses Difference Between Public and Private IP Address The crucial difference between a public and private IP address is that the public IP can be seen by other devices on the Internet, while the private IP cannot. Therefore, public IPs are used to interact and communicate online, while private IPs operate within a local network. The following table summarizes the key differences between a public and private IP address: IP Address vs. MAC Address When you analyze an IP address vs. a MAC address, you can start with the similarities. For both of these IP address types, you are dealing with a unique identifier with an attachment to that device. The manufacturer of a network card or router is the provider of the MAC address, while the internet service provider (ISP) is the provider of the IP address. The main difference between the two is that the MAC address is the physical address of a device. If you have five laptops on your home Wi-Fi network, you can identify each of those five laptops on your network via their MAC address. The IP address works differently as it is the identifier of the connection of the network with that device. Other differences include:  A MAC address is a 6-byte hexadecimal address while an IP address is a 4 or 16-byte address.  A MAC address is in a data link layer, while an IP address is in a network layer.  A third party will have a difficult time finding a MAC address, while it can easily find an IP address.  MAC addresses are static, while IP addresses can change dynamically  MAC addresses and IP addresses are necessary to get a network packet to a destination. However, no one can see your MAC address unless they are on your LAN. Reason to Have Both IP and MAC Addresses. The reason for having both IP and MAC addresses lies in the way the Internet works, specifically in the structure of the OSI Model. This model is a conceptual framework that describes how data is sent and received over a network. It’s divided into seven layers, each performing specific functions.  Layer 2 uses MAC addresses and is responsible for packet delivery from hop to hop.  Layer 3 uses IP addresses and is responsible for packet delivery from end to end. The primary function of MAC addresses is to manage how data is transported from one network node to another on a direct, physical basis – this is also referred to as “hop to hop” delivery. On the other IP addresses are used to identify devices on a network and to route traffic between networks. The IP addresses ensure that the data gets from its original source reaches its final destination and it is also called “end-to-end” delivery of data. When a computer sends data, it first wraps it in an IP header, which includes the source and destination IP addresses. This IP header, along with the data, is then encapsulated in a MAC header, which includes the source and destination MAC addresses for the current “hop” in the path. As the data travels from one router to the next, the MAC address header is stripped off and a new one is generated for the next hop. However, the IP header, which was generated by the original computer, remains intact until it reaches the final destination. This process illustrates how the IP header manages the “end to end” delivery, while the MAC headers handle the “hop to hop” delivery. So, Both IP and MAC addresses are essential for the functioning of the Internet. While MAC addresses facilitate the direct, physical transfer of data between network nodes, IP addresses ensure that the data reaches its final destination. This process from beginning to end is made possioble by what is called Address Resolution Protocol (ARP) Address Resolution Protocol (ARP) Most computer programs/applications use logical addresses (IP Addresses) to send/receive messages. However, the actual communication happens over the Physical Address (MAC Address) that is from layer 2 of the OSI model. So for every communication between end devices on the network, there is a need to get the destination MAC Address. This is where ARP comes into the picture, its functionality is to translate IP addresses to Physical Addresses. Its responsibility is to find the hardware address of a host from a known IP address. How ARP Works? Imagine a device that wants to communicate with others over the network. It needs to determine the MAC address associated with the IP address it wants to send message to. To determine the MAC address associated with a specific IP address, it sends an ARP request message as a broadcast to all the devices on a local network. The request contains the IP address for which the sender needs the MAC address. All devices receive the request, but only the device that matches the requested IP address responds with an ARP reply containing its MAC address. Communication over an IP network is also determined by the association between the sender and the receiver based on the addressing mechanisms. There are three fundamental of such communication mode based on addressing type used on the internet. They are:  Unicast addressing uses a one-to-one association, where each destination address is uniquely identified as a single receiver endpoint. Traditional DNS deployments are configured with unicast addresses.  Multicast addressing uses a one-to-unique many association, where datagrams are routed from a single sender to multiple selected endpoints in a single transmission, using a multicast group address. A common use of multicast is streaming audio, where the audio is published via multicast addressing and clients pick up the routed stream as a channel.   Broadcast addressing uses a one-to-many association, where datagrams are routed from a single sender to all other connected endpoints in a single transmission, using a broadcast address. The network automatically replicates datagrams as needed for all network segments (links) that contain an eligible receiver. Adaptation of the Unicast, Multicast, and Broadcast Communication Model and Addressing Concast Multicast abstraction uses a single network address to represent a group of receivers. When a host sends a packet to a multicast group address, the network makes its best effort to deliver a copy to all receivers in the group. The sender need not know the identities of the receivers, and indeed cannot learn them via the multicast service itself. Internet multicast is a scalable service because it hides the number and identity of receivers behind a single address, and allows a sender to communicate with any number of receivers as a single entity. However, an increasing number of applications now require a communication service in which a receiver collects messages from many senders. With concast, a single network address represents a group of senders. When multiple group members send packets addressed to a single destination, only a single packet is delivered to that destination (Figure). Where a multicast datagram has a unicast source address and a group destination address, a concast datagram contains a group source address and a unicast destination address. Thus concast, too, is scalable: it abstracts away the reality of multiple senders and allows a receiver to avoid implosion--that is, processing a number of incoming packets that grows with the size of the group. Like multicast, a good implementation will conserve bandwidth by reducing or eliminating redundant transmissions. Figure: Multicast and concast services. However, the precise definition of an ``inverse multicast'' service is non-obvious. In particular, two interesting questions arise. First, what packet is delivered to the receiver (as a result of the multiple senders' transmissions)? Second, when is this single packet delivered to the receiver? We refer to the answers to these questions as the merge semantics and the timing semantics, respectively. Various merge and timing semantics are possible, and give rise to different forms of concast service. Concast-style (i.e. many-to-one) communication patterns arise in a wide range of distributed applications. Perhaps the most prominent example is the acknowledgments (positive or negative) sent by the receivers of a message in reliable multicast. Applications that gather data from distributed machines or sensors (e.g., load balancing, distributed monitoring systems) represent another large class that can benefit from some form of concast communication model. Concast service models, like multicast, are best-effort services. The, simple concast, provides generic, application-independent many-to-one communication. It ``fuses'' identical packets from different senders into one copy that is delivered to the receiver. This simple service can be used to implement NACK suppression, which is useful in implementing reliable multicast: the network forwards the first NACK and discards all other NACKS for the same message. The custom concast: is used where different concast service has to be defined for different applications requirements. Custom concast is thus an excellent match for active networks. Anycast Anycast is a network addressing and routing methodology in which a single IP address is shared by devices (generally servers) in multiple locations. Typically, any device or server that connects directly to the Internet will have a unique IP address. Communication between network-connected devices is 1-to-1; each communication goes from one specific device to the targeted device on the other end of the communication. Anycast networks, in contrast, allow multiple servers on the network to use the same IP address, or set of IP addresses. Communication with an Anycast network is 1-to-many. Anycast is not officially supported in IPv4 however, this can be worked around through using BGP. Essentially, multiple hosts are given the same unicast IP and routes are announced through BGP. Therefore, routers interpret this as multiple routes to the same destination whereas in fact, they are routed to different destinations with the same address. Routers direct packets addressed to this destination IP address to the location nearest the sender, using their normal decision-making algorithms, typically the lowest number of BGP network hops. IPv6 on the other hand explicitly supports anycast. IPv6 routers typically won't distinguish an anycast packet from a unicast packet through the network although special handling from the routers near the destination is required. Anycast routing is widely used by content delivery networks (CDNs) such as web and name servers, to bring their content closer to end users. In the context of a CDN, Anycast typically routes incoming traffic to the nearest data center with the capacity to process the request efficiently. Selective routing allows an Anycast network to be resilient in the face of high traffic volume, network congestion, and DDoS attacks. How does Anycast work? Anycast network routing is able to route incoming connection requests across multiple data centers. When requests come into a single IP address associated with the Anycast network, the network distributes the data based on some prioritization methodology. The selection process behind choosing a particular data center will typically be optimized to reduce latency by selecting the data center with the shortest distance from the requester. Anycast is characterized by a 1-to-1 of many association, and is one of the 5 main network protocol methods used in the Internet protocol. Why use an Anycast network? If many requests are made simultaneously to the same origin server, the server may become overwhelmed with traffic and be unable to respond efficiently to additional incoming requests. With an Anycast network, instead of one origin server taking the brunt of the traffic, the load can also be spread across other available data centers, each of which will have servers capable of processing and responding to the incoming request. This routing method can prevent an origin server from extending capacity and avoids service interruptions to clients requesting content from the origin server. What is the difference between Anycast and Unicast? Most of the Internet works via a routing scheme called Unicast. Under Unicast, every node on the network gets a unique IP address. Home and office networks use Unicast; when a computer is connected to a wireless network and gets a message saying the IP address is already in use, an IP address conflict has occurred because another computer on the same Unicast network is already using the same IP. In most cases, that isn't allowed. When a CDN is using a Unicast address, traffic is routed directly to the specific node. This creates a vulnerability when the network experiences extraordinary traffic such as during a DDoS attack. Because the traffic is routed directly to a particular data center, the location or its surrounding infrastructure may become overwhelmed with traffic, potentially resulting in denial-of-service to legitimate requests. Using Anycast means the network can be extremely resilient. Because traffic will find the best path, an entire data center can be taken offline and traffic will automatically flow to a proximal data center. How does an Anycast network mitigate a DDoS attack? After other DDoS mitigation tools filter out some of the attack traffic, Anycast distributes the remaining attack traffic across multiple data centers, preventing any one location from becoming overwhelmed with requests. If the capacity of the Anycast network is greater than the attack traffic, the attack is effectively mitigated. In most DDoS attacks, many compromised "zombie" or “bot” computers are used to form what is known as a botnet. These machines can be scattered around the web and generate so much traffic that they can overwhelm a typical Unicast-connected machine. A properly Anycasted CDN increases the surface area of the receiving network so that the unfiltered denial-of-service traffic from a distributed botnet will be absorbed by each of the CDN’s data centers. As a result, as a network continues to grow in size and capacity it becomes harder and harder to launch an effective DDoS against anyone using the CDN. Geocast Geocast is somewhat similar to multicast in that requests from a sender are routed to multiple endpoints simultaneously, however, the difference is that the network is defined by their geographical location. PORT NUMBERS A port number is a way to identify a specific process to which an internet or other network message is to be forwarded when it arrives at a server. All network-connected devices come equipped with standardized ports that have an assigned number. These numbers are reserved for certain protocols and their associated function. Hypertext Transfer Protocol (HTTP) messages, for example, always go to port 80 -- one of the most commonly used ports. What is the difference between an IP address and a port number? An IP address identifies a machine in an IP network and is used to determine the destination of a data packet. Port numbers identify a particular application or service on a system. Port numbers are part of the addressing information that helps identify senders and receivers of information and a particular application on the devices. Port numbers consist of 16-bit numbers. An application on a system is recognised by a combination of the IP address and the port number. For example, a user request for a file transfer from a client, or local host, to a remote server on the internet uses File Transfer Protocol (FTP) for the transaction. Both devices must be configured to transfer files via FTP. To transfer the file, the Transmission Control Protocol (TCP) software layer in local host identifies the port number of 21, which, by convention, associates with an FTP request -- in the 16-bit port number integer that is appended to the request. A fully qualified address for this request will read something like: 192.168.100.5 : 21. The number after the 4th octet of the IP address is the port number for the requested service. At the server, the TCP layer will read port number 21 and forward the request to the FTP program at the server. What are the different types of port numbers and their uses? There are 65,535 port numbers, but not all are used every day.  Restricted port numbers or well-known port numbers are reserved by prominent companies and range from 0 to 1023. Apple QuickTime, Structured Query Language services and Gopher services use some of these restricted ports. Also known as system port numbers.  Those who want to register a specific port number can choose from 1024 to 49151. Software companies typically register these port numbers. These are called registered port numbers.  Dynamic, ephemeral or private ports ranging from 49152 to 65536 are available for anyone to use. Here are some commonly used ports and their associated networking protocols:  Ports 20 and 21. FTP is used to transfer files between a client and a server.  Port 22. Secure Shell is one of several tunnelling protocols used to build secure network connections.  Port 25. Simple Mail Transfer Protocol (SMTP) is commonly used for email.  Port 53. Domain name system (DNS) is a critical process that matches human-readable domain names to machine-readable IP addresses on the modern internet. It helps users load websites and applications without typing in a long list of IP addresses.  Port 80. HTTP is the protocol that enables the World Wide Web.  Port 123. Network Time Protocol helps computer clocks sync with each other. It's a vital process in encryption  Port 179. Border Gateway Protocol (BGP) helps establish efficient routes between the large networks or autonomous systems that make up the internet. These large networks use BGP to broadcast which IP addresses they control.  Port 443. HTTP Secure (HTTPS) is like HTTP but more secure. All HTTPS web traffic goes straight to port 443. Any network service that uses HTTPS for encryption, such as DNS over HTTPS, also connects directly to this port.  Port 500. Internet Security Association and Key Management Protocol helps set up secure IP Security  Port 3389. Remote Desktop Protocol enables users to connect to their desktop computers from another device remotely.