Protocols and Switching DDC Pre Finals

Protocols and Switching

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.

Common Network Protocols (White, 2015)

Internet Protocol (IP) provides a connectionless data transfer service over heterogeneous networks by passing and routing IP datagrams.

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.

Create a connection

The TCP header includes a port address that indicates a particular application on a machine.

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.

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.

Internet Control Message Protocol (ICMP)

Performs error reporting for the Internet Protocol and is commonly used by routers.

User Datagram Protocol (UDP)

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.

Address Resolution Protocol (ARP)

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.

Dynamic Host Configuration Protocol

Most popular protocol that handles dynamic assignment.

Network Address Translation (NAT)

Another protocol that is used to assign IP addresses.

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)

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

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.

Packet Switching

In data communications, we need to send messages from one end system to another.

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.

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.

Destination Address

Every packet in a datagram network carries a header that contains, among other information, the destination address of the packet.

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.

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

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.

Addressing

In a virtual-circuit network, two (2) types of addressing are involved:

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.

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.

Space-Division Switch

The paths in the circuit are separated from one another spatially. Example: Crossbar Switch & Multistage Switch

Time-Division Switch

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.

Input Ports

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.

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.

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.

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.

Crossbar Switch

The simplest type of switching fabric is the crossbar switch.

Banyan Switch

A multistage switch with microswitches at each stage that route the packets based on the output port represented as a binary string.

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.