Networking Flashcards
List at least two criteria for choosing a network physical media type
Transmission rate and shared or direct access among users
Why layering is needed in networking?
The explicit structure allows identification, and relationship of complex system’s pieces. Modularization eases the maintenance and updating of the system. Structure developers can work in one layer or multiple layer without disturbing the whole networking
List the sources of packet delay.
propagation delay, transmission delay, queuing delay, and processing delay.
How does packet loss occur?
When one or more transmitted data packets fail to arrive at their destination due to network congestion, hardware issues, software bugs, and a number of other factors
What do we mean by a network protocol?
Network protocols are rules that define the format, order of messages sent and received among network entities, and actions taken on msg transmission, receipt communication activity on the Internet governed by protocols
Give some examples of end systems (hosts) and packet switches (networking devices).
end systems=servers, workstations, network-interface print devices, and routers. packet swithces= Ethernet and Frame Relay
What are the key network-layer functions?
The first one is breaking up segments into network packets, and reassembling the packets on the receiving end. The other is routing packets by discovering the best path across a physical network
What Network-layer service model the Internet provides?
The Internet uses a datagram network layer. With a datagram network layer, each time an end system wants to send a packet, it stamps the packet with the address of the destination end system and then pops the packet into the network.
What is a subnet?
Device interfaces that can physically reach each other without passing through an intervening router
How does a host get an IP address?
Hard-coded by sysadmin in the config file. DHCP-Dynamic Host Configuration Protocol: dynamically get address from a server
What is NAT?
Network address translation.
Differences between IPV6 and IPV4
IPv4 is 32-Bit IP address whereas IPv6 is a 128-Bit IP address. IPV4 bits are separated by a dot(.) whereas IPV6 bits are separated by a colon(:). IPv4 is a numeric addressing method whereas IPv6 is an alphanumeric addressing method. IPv4 offers 12 header fields whereas IPv6 offers 8 header fields. IPv4 supports broadcast whereas IPv6 doesn’t support broadcast. IPv4 has checksum fields while IPv6 doesn’t have checksum fields. IPv4 supports VLSM (Variable Length Subnet Mask) whereas IPv6 doesn’t support VLSM. IPv4 uses ARP (Address Resolution Protocol) to map to MAC address whereas IPv6 uses NDP (Neighbour Discovery Protocol) to map to MAC address.
What are the possible Internet transport protocol services that can be provided to applications?
UDP- has a very low overhead for both header size and protocol logic, which means that both the packet transmissions and receptions consume less energy, and each packet has more room for application-layer data
TCP- provides a reliable byte stream and reduces the application complexity at the cost of a larger header size and more complex transport layer protocol logic .
The differences between Non-persistent HTTP and persistent HTTP
After the client receives the object with non-persistent, the connection is immediately closed.
Disadvantages of Non-Persistent HTTP
Requires 2 RTTs per object.
OS overhead for each TCP connection.
Browsers open parallel TCP connections to fetch referenced objects
Advantages of Persistent HTTP
Lower CPU and memory usage because there are less number of connections. Allows HTTP pipelining of requests and responses.
Reduced network congestion (fewer TCP connections).
How DNS application work?
1- Requesting Website Information- If it is present locally, then the website will be displayed. If our computer does not have the information, it will perform a DNS query to retrieve the correct information
2- Contact the Recursive DNS Servers
3- Query the Authoritative DNS Servers
4- Access the DNS Record
5- The Recursive DNS server has the information and returns the A record to your computer.
How do Email applications work?
The email gets sent by the client to an outgoing mail server via Simple Mail Transfer Protocol. The SMTP server is like your local post office, which checks your postage and address and figures out where to send your mail. It doesn’t understand domains, though. They’re a sort of abstract thing, so the SMTP server contacts a Domain Name System server. The DNS server is a sort of phone or address book for the internet; it translates domains like “arrakis.com” to an IP address like “74.238.23.45.” Then, it finds out if that domain has any “MX” or mail exchange servers on it and makes a note of it. This is like your post office consulting maps of where your mail is supposed to go, calling their local post office, and checking to see if your friend has a mailbox or P.O. box to receive mail.
Give examples of applications that use such transport protocols (TCP and UDP)
TCP- browser, email, FTP. UDP- live broadcasts and online games
What is the purpose of the receiver window?
A variable that advertises the amount of data that the destination site can receive.
What is the difference between the sequence number and acknowledgement number in TCP?
The sequence number is the byte number of the first byte of data in the TCP packet sent. The acknowledgement number is the sequence number of the next byte the receiver expects to receive.
Why do we need the checksum bits in the TCP or UDP segments?
In order to determine whether the received data is corrupted along the network
Why do we need the ‘A’, ‘S’ and ‘F’ bits in the TCP segment?
It is the control bits. They are used to establish connections, send data and terminate connections
Benefits of TCP
Performs error checking and attempts error recovery.
Benefits of UDP
Faster because integrity is checked at the arrival time using checksum.
How does TCP work?
First, it orders packets by numbering them. Second, it error-checks by having the recipient send a response back to the sender saying that it has received the message. If the sender doesn’t get a correct response, it can resend the packets to ensure the recipient receives them correctly.
How does UDP work?
When an app uses UDP, packets are just sent to the recipient. The sender doesn’t wait to make sure the recipient received the packet—it just continues sending the next packets. If the recipient misses a few UDP packets here and there, they are just lost—the sender won’t resend them. Losing all this overhead means the devices can communicate more quickly.
