05 Handout 1 PDF - Protocols and Switching

IT2006 Protocols and Switching Switching Network protocols are sets of established rules that dictate how to format, transmit, and receive data so computer network devices can communicate regardless of the differences in their underlying infrastructures, designs, or standards. The support for netwo...

IT2006 Protocols and Switching Switching Network protocols are sets of established rules that dictate how to format, transmit, and receive data so computer network devices can communicate regardless of the differences in their underlying infrastructures, designs, or standards. The support for network protocols can be built into software, hardware, or both. Common Network Protocols (White, 2015) Internet Protocol (IP) provides a connectionless data transfer service over heterogeneous networks by passing and routing IP datagrams. o IPv4 Datagram Format ▪ IPv4 addresses are 32 bits in length. Example:1000 0000.1001 1100.0000 1110.0000 0111 ▪ This dotted-decimal notation is created by converting each 8-bit string in the 32-bit IP address into its decimal equivalent. Thus, the IP address above becomes 128.156.14.7. (White, 2015) o IPv6 Datagram Format ▪ IPv6 calls for addresses to be 128 bits long. A 128-bit address gives us virtually unlimited addresses. (White, 2015) ▪ IPv6 addresses are 128 bits in length. For example, they are usually written in hexadecimal form, where each four-bit quantity is replaced by a hexadecimal digit from 0 to F. o Example: 6A3E : BA91 : 7221 : 0000 : OIFC : 922C : 877B : FFEF o If there are four hex 0s in a row, as above, we can save a little typing and incorporate a small abbreviation: 6A3E : BA91 : 7221 : 0 : OlFC : 922C : 877B : FFEF ▪ Longer strings of 0s can be abbreviated further. For example: 6A3E : BA91 : 0 : 0 : 0 : 0 : 877B : FFEF o It can be abbreviated as: 6A3E : BA91 : : 877B : FFEF 05 Handout 1 *Property of STI  [email protected] Page 1 of 6  IT2006 Transmission Control Protocol (TCP) primary function is to turn an unreliable network into a reliable network that is free from lost and duplicate packets. The role of TCP essentially fills in some holes created by IP. o TCP performs the following six functions: Create a connection - The TCP header includes a port address that indicates a particular application on a machine. When TCP creates a connection, it uses a port number to identify the particular application's connection. Release a connection - The TCP software can also dissolve a connection after all the data has been sent and received. Implement flow control - To make sure the sending station does not overwhelm the receiving station with too much data, the TCP header includes a field called the Window value, that allows the receiver to tell the sender to slow down. Establish multiplexing - This multiplexing can be done by creating a different connection that has a port number different from a previous connection. Perform error recovery - TCP numbers each byte for transmission with a sequence number. As the packets of bytes arrive at the destination site, the receiving TCP software checks these sequence numbers for continuity. Establish priority - If the sender has to transmit data of a higher priority, such as an error condition, TCP can set a value in a field (the Urgent Pointer) that indicates that all or a portion of the enclosed data. o TCP Datagram Format - The information in this header is used by the TCP layer at the receiving workstation to perform one or more of the six transport functions. (White, 2015) Internet Control Message Protocol (ICMP) performs error reporting for the Internet Protocol and is commonly used by routers. All ICMP messages contain at least three (3) fields: ▪ A type is simply a number from 0 to n that uniquely identifies the kind of ICMP message, such as invalid port number or invalid IP address. ▪ A code is a value that provides further information about the message type. ▪ The first eight bytes of the IP datagram caused the ICMP message to be generated. User Datagram Protocol (UDP) is a no-frills transport protocol that does not establish connections, does not attempt to keep data packets in sequence, and does not watch for datagrams that have existed for too long. Its header contains only four fields: ▪ Source Port, Destination Port, Length, and Checksum. It is used by a small number of network services, such as DNS, that do not need to establish a connection before sending data. Address Resolution Protocol (ARP) is another small but important protocol that is used to support TCP/IP networks. This takes an IP address in an IP datagram and translates it into the appropriate medium access control layer address for delivery on a local area network. 05 Handout 1 *Property of STI  [email protected] Page 2 of 6  IT2006 Dynamic Host Configuration Protocol is the most popular protocol that handles dynamic assignment. Two basic methods are used to assign an IP address to a workstation: static assignment and dynamic assignment. Functions: ▪ When a workstation running the DHCP client software needs to connect to the Internet, the protocol issues an IP request, which prompts the DHCP server to look in a static table of IP addresses. ▪ DHCP server selects an IP address from an available pool of addresses and assigns it to the workstation. The IP address assignment is temporary, with the default time limit being one hour. DHCP clients may negotiate for a renewal of the assignment if the workstation is still accessing the Internet when the temporary assignment is nearing expiration. Network Address Translation (NAT) is another protocol that is used to assign IP addresses. More precisely, NAT lets a router represent an entire local area network to the Internet as a single IP address. Function: ▪ When a user workstation on a company local area network sends a packet out to the Internet, NAT replaces the IP address of the user workstation with a corporate global IP address. ▪ All packets that leave the corporate network contain this global IP address. ▪ The only IP address that anyone sees outside of the corporate network is the one global IP address. Tunneling Protocols and Virtual Private Networks Whenever a transmission is performed, it is susceptible to interception. Retailers have solved part of the problem by using encryption techniques to secure transactions dealing with private information. ▪ Virtual Private Network (VPN) is a data network connection that makes use of the public telecommunications infrastructure but maintains privacy through the use of a tunneling protocol and security procedures. ▪ Tunneling Protocol is the command set that allows an organization to create secure connections using public resources such as the Internet. Example: Point-to-Point Tunneling Protocol (PPTP). Network Switching (Forouzan, 2013) A switched network consists of a series of interlinked nodes, called switches. Switches are devices capable of creating temporary connections between two or more devices linked to the switch. In a switched network, some of these nodes are connected to the end systems (computers or telephones, for example). Packet Switching In data communications, we need to send messages from one end system to another. If the message is going to pass through a packet-switched network, it needs to be divided into packets of fixed or variable size. The size of the packet is determined by the network and the governing protocol. In layman’s term, it serves as a reservation at a restaurant. Without the reservation, it may cause delays. Types of Packet-Switched Networks Datagram Networks - each packet is treated independently of all others. Packets in this approach are referred to as datagrams. Datagram switching is normally done at the network layer. The datagram networks are sometimes referred to as connectionless networks. The term connectionless here means that the switch (packet switch) does not keep information about the connection state. 05 Handout 1 *Property of STI  [email protected] Page 3 of 6  IT2006 (Forouzan, 2013) o Routing Table - In this type of network, each switch (or packet switch) has a routing table that is based on the destination address. The routing tables are dynamic and are updated periodically. The destination addresses and the corresponding forwarding output ports are recorded in the tables. o Destination Address - Every packet in a datagram network carries a header that contains, among other information, the destination address of the packet. When the switch receives the packet, this destination address is examined; the routing table is consulted to find the corresponding port through which the packet should be forwarded. o Efficiency - The efficiency of a datagram network is better than that of a circuit-switched network; resources are allocated only when there are packets to be transferred. o Delay There may be a greater delay in a datagram network than in a virtual-circuit network. Although there are no setup and teardown phases, each packet may experience a wait at a switch before it is forwarded. Virtual-Circuit Networks - is a cross between a circuit-switched network and a datagram network. A virtual- circuit network is normally implemented in the data-link layer, while a circuit-switched network is implemented in the physical layer and a datagram network in the network layer. (Forouzan, 2013) o Addressing - In a virtual-circuit network, two (2) types of addressing are involved: a. Global Addressing - A source or a destination needs to have a global address—an address that can be unique in the scope of the network or internationally if the network is part of an international network. b. Virtual-Circuit Identifier - The identifier that is actually used for data transfer is called the virtual-circuit identifier (VCI) or the label. A VCI, unlike a global address, is a small number that has only switch scope; it is used by a frame between two switches. 05 Handout 1 *Property of STI  [email protected] Page 4 of 6  IT2006 Structure Of A Switch We use switches in circuit-switched and packet-switched networks. Source: https://datacommandnet.blogspot.com/p/structure-of-switch.html Space-Division Switch In space-division switching, the paths in the circuit are separated from one another spatially. Example: Crossbar Switch & Multistage Switch Time-Division Switch Time-division switching uses time-division multiplexing (TDM) inside a switch. The most popular technology is called the time-slot interchange (TSI). Time- and Space-Division Switch Combinations It combines the two (2) results in switches that are optimized both physically (the number of crosspoints) and temporally (the amount of delay). Multistage switches of this sort can be designed as time-space-time (TST) switches. Structure of Packet Switches A switch used in a packet-switched network has a different structure from a switch used in a circuit-switched network. Source: https://datacommandnet.blogspot.com/p/structure-of-switch.html Input Ports An input port performs the physical and data-link functions of the packet switch. The bits are constructed from the received signal. The packet is decapsulated from the frame. Errors are detected and corrected. The packet is now ready to be routed by the network layer. Output Port The output port performs the same functions as the input port but in the reverse order. First, the outgoing packets are queued, then the packet is encapsulated in a frame, and finally, the physical-layer functions are applied to the frame to create the signal to be sent on the line. 05 Handout 1 *Property of STI  [email protected] Page 5 of 6  IT2006 Routing Processor The routing processor performs the functions of the network layer. The destination address is used to find the address of the next hop and, at the same time, the output port number from which the packet is sent out. This activity is sometimes referred to as table lookup because the routing processor searches the routing table. Switching Fabrics The most difficult task in a packet switch is to move the packet from the input queue to the output queue. The speed with which this is done affects the size of the input/output queue and the overall delay in packet delivery. o Crossbar Switch - The simplest type of switching fabric is the crossbar switch. o Banyan Switch (named after the banyan tree) is a multistage switch with microswitches at each stage that route the packets based on the output port represented as a binary string. o Batcher-Banyan Switch: The problem with the banyan switch is the possibility of internal collision even when two packets are not heading for the same output port. The sorting switch uses hardware merging techniques, but we do not discuss the details here. Normally, another hardware module called a trap is added between the Batcher switch and the banyan switch. References: Forouzan, B. (2013). Data communications and network. McGraw-Hill. Ibe, O. (2018). Fundamentals of data communication networks (1st ed.). Wiley & Sons, Inc. Kurose, F., & Ross, K. (2017). Computer networking: A top-down approach (7th ed.). Pearson. TechTarget Network. (n.d.). Network Protocols. Retrieved from https://searchnetworking.techtarget.com/definition/protocol. Sklar, B. (2017). Digital communication: Fundamentals and applications (2nd ed.). Prentice Hall. Speidel, J. (2019). Introduction to digital communications. Springer Nature. White, C. (2015). Data communications and computer networks - A business user's approach. Cengage. 05 Handout 1 *Property of STI  [email protected] Page 6 of 6