Question

1. Discuss in detail what is DHCP how it operates and what it does? 2. Discuss in detail what is DNS how it operates and what it does? 3. What are the main components of a Public Switch Telephone Network - PSTN and how they interact with each other? Describe in detail what TCP is, its services, futures is and how a TCP connection is established 4. 5. Describe in detail what is UDP, its services and futures

Answer 1

1dhcp.

DHCP (Dynamic Host Configuration Protocol) is a protocol that is commonly used in networks for dynamic IP addressing configuration. Every user’s device needs at least IP address to join the network and connect to services. When computer first connects to local network with cable or WiFi SSID, first thing is to look for IP address, netmask, default gateway and DNS servers.

How does DHCP work?

1. Host connecting to network (cable or wireless) sends DHCP discover message to all hosts in Layer 2 segment (destination address is FF:FF:FF:FF:FF:FF). Frame with this DISCOVER message hits the DHCP Server.

2. After the DHCP Server receives discover message it suggests the IP addressing offering to the client host by unicast. This OFFER message contains:

• proposed IP address for client (here 192.168.1.10)
• subnet mask to identify the subnet space (here 255.255.255.0)
• IP of default gateway for subnet (here 192.168.1.1)
• IP of DNS server for name translations (here 8.8.8.8)
• Options (read full article)

3. Now after the client receives the offer it requests the information officially sending REQUEST message to server this time by unicast.

4. Server sends ACKNOWLEDGE message confirming the DHCP lease to client. Now client is allowed to use new IP settings.

2.dns

The Domain Name System (DNS) is a distributed directory that resolves human-readable hostnames, such as www.dyn.com, into machine-readable IP addresses like 50.16.85.103. DNS is also a directory of crucial information about domain names, such as email servers (MX records) and sending verification (DKIM, SPF, DMARC), TXT record verification of domain ownership, and even SSH fingerprints (SSHFP).

Intelligent DNS services can manipulate DNS responses, deciding which IP(s) are returned to ensure the best performance and reliability for clients. But why is DNS important? How does it work? What else should you know? Get the answers to these questions and more in this updated article.

How does DNS work?

When you visit a domain such as dyn.com, your computer follows a series of steps to turn the human-readable web address into a machine-readable IP address. This happens every time you use a domain name, whether you are viewing websites, sending email or listening to internet radio stations such as Pandora.

Step 1: Request information

The process begins when you ask your computer to resolve a hostname, such as visiting https://dyn.com. The first place your computer looks for the corresponding IP address is its local DNS cache, which stores information that your computer has recently retrieved.

If your computer doesn’t already know the answer, it needs to perform a DNS query to find out.

Step 2: Ask the recursive DNS servers

If the information is not stored locally, your computer queries (contacts) the recursive DNS servers (resolvers) from your internet service provider (ISP). These specialized computers perform the legwork of a DNS query on your behalf. Resolvers have their own caches, and given that many of the ISP’s customers are using the same resolvers, there is a reasonable chance that popular domains will already be cached. If this is the case for our example, dyn.com, the process usually ends here and the information is returned to the user.

Just about every ISP runs their own resolvers, yet those aren’t necessarily what you could be using. Some companies and perhaps even technically sophisticated home users could run their own resolvers on site. Additionally, there are several very popular open resolvers available, including Google Public DNS, OpenDNS, Dyn Recursive DNS, and Quad9.

Step 3: Ask the root name servers

If the recursive servers don’t have the answer, they query the root name servers. A name server is a computer that answers questions about domain names, such as IP addresses. These 13 servers act as a kind of telephone switchboard for DNS. They don’t know the answer, but they can direct DNS queries to someone that knows where to find it.

Step 4: Ask the TLD name servers

The root name servers will look at the first part of our request, reading from right to left — www.dyn.com — and in our case, direct our query to the top-level domain (TLD) name servers for .com. Each TLD, such as those for .com, .org, and .us, has its own set of name servers, which act like a receptionist for each TLD. These servers don’t have the information we need, but they can refer us directly to the servers that do have the information.

Step 5: Ask the authoritative DNS servers

The TLD name servers review the next part of our request — www.dyn.com — and direct our query to the name servers responsible for this specific domain. These authoritative name servers are responsible for knowing all the information about a specific domain, which is stored in DNS records. There are many types of records, which each contain a different kind of information.

In this example, we want to know the IP address for www.dyn.com, so we ask the authoritative name server for the address record (A record). Some authoritative name servers have intelligence that can analyze an incoming DNS query and return a response that is more performant for the user that originated the query.

Step 6: Retrieve the record

The recursive server retrieves the A record for dyn.com from the authoritative name servers and stores the record in its local cache. If anyone else requests the host record for dyn.com, the recursive server will already have the answer and will not need to go through the lookup process again. All records have a time-to-live value, which is like an expiration date. After a while, the recursive server will need to ask for a new copy of the record to make sure the information doesn’t become out-of-date.

Step 7: Receive the answer

Armed with the answer, recursive server returns the A record back to your computer. Your computer stores the record in its cache, reads the IP address from the record, then passes this information to your browser. The browser then opens a connection to the webserver and receives the website.

This entire process, from start to finish, takes only milliseconds to complete.

3.pstn

1 – CPE (customer premises equipment)

Customer premises equipment refers to devices such as telephones, routers, switches, residential gateways, set-top boxes, fixed mobile convergence products, home networking adapters and Internet access gateways that enable consumers to access communications service providers’ services and distribute them around their house via a local area network (LAN).

A CPE can be an active equipment, as the ones mentioned above or a passive equipment such as analogue-telephone-adapters or xDSL-splitters.

2 – Transmission/Transport

The transmission (or ‘transport’ as it is sometimes known) node consists of the equipment and media that carry information between nodes of a network. This can include things like amplifiers, repeaters, multiplexers, digital cross-connect systems, and digital loop carriers.

3 – Access

The access node is responsible for connecting a user to the core network. Access equipment is typically installed within the telephone exchange or a roadside serving area interface cabinet.

4 – Core/Switching

In telecommunications, the core network is the central element of a network that provides services to customers who are connected by the access network. There are a number of services that the core network provides, but one of the main functions is to route telephone calls across the PSTN (public switched telephone network). This includes deciding when to setup, hold, charge, and release connections, and getting that information to the correct outlets that maintain and bill for each section of the network.

Typically, the core networks provide aggregation, authentication, call control/switching, charging, service invocation and gateways.

The induvial parts of the PSTN are constantly evolving and updating to fulfil the needs of an ever-increasing user base, however the fundamental structure of the networks have endured and become fundamental to global connectivity.

As the importance of global telecommunications increases and more bandwidth is required, this importance will only increase.

4.tcp services

TCP Services:

The services offered by TCP to the processes at the application layer are as follows:

Process-to-Process Communication:

TCP provides process-to-process communication using port numbers. The following table lists some well-known port numbers used by TCP.

Stream Delivery Service:

TCP, unlike UDP, is a stream-oriented protocol. TCP, on the other hand, allows the sending process to deliver data as a stream of bytes and allows the receiving process to obtain data as a stream of bytes. TCP creates an environment in which the two processes seem to be connected by an imaginary "tube" that carries their data across the Internet. This imaginary environment is depicted in the following figure. The sending process produces (writes to) the stream of bytes, and the receiving process consumes (reads from) them.

Sending and Receiving Buffers:

Because the sending and the receiving processes may not write or read data at the same speed, TCP needs buffers for storage. There are two buffers, the sending buffer and the receiving buffer, one for each direction and these buffers are also necessary for flow and error control mechanisms used by TCP.) One way to implement a buffer is to use a circular array of 1-byte locations

Full-Duplex Communication:

TCP offers full-duplex service, in which data can flow in both directions at the same time. Each TCP then has a sending and receiving buffer, and segments move in both directions. Connection-Oriented Service:
TCP, unlike UDP, is a connection-oriented protocol. When a process at site A wants to send and receive data from another process at site B, the following occurs:

1. The two TCPs establish a connection between them.

2. Data are exchanged in both directions.

3. The connection is terminated.

The TCP segment is encapsulated in an IP datagram and can be sent out of order, or lost, or corrupted, and then resent. Each may use a different path to reach the destination. There is no physical connection. TCP creates a stream-oriented environment in which it accepts the responsibility of delivering the bytes in order to the other site.

Reliable Service

TCP is a reliable transport protocol. It uses an acknowledgment mechanism to check the safe and sound arrival of data. We will discuss this feature further in the section on error control.

5.udp services and features

Features of UDP:

• Provides connectionless, unreliable service.
• So UDP faster than TCP.
• Adds only checksum and process-to-process addressing to IP.
• Used for DNS and NFS.
• Used when socket is opened in datagram mode.
• It sends bulk quantity of packets.
• No acknowledgment.
• Good for video streaming it is an unreliable protocol.
• It does not care about the delivery of the packets or the sequence of delivery.
• No flow control /congestion control, sender can overrun receiver's buffer.
• Real time application like video conferencing needs (Because it is faster).
• An UDP datagram is used in Network File System (NFS), DNS, SNMP, TFTP etc.
• It has no handshaking or flow control.
• It not even has windowing capability.
• It is a fire and forget type protocol.
• An application can use a UDP port number and another application can use the same port number for a TCP session from the same IP address.
• UDP and IP are on different levels of the OSI stack and corresponds to other protocols like TCP and ICMP.
• No connection establishment tear down; data is just sent right away.
• For data transfer with UDP a lock-step protocol is required (to be implemented by the application).
• No error control; corrupted data is not retransmitted (even though UDP header has a checksum to detect errors and report these to the application).