CS240 Chapter 5
What are the 3 main functions of the Transport Layer? Describe each
-It links the application software in the application layer with the network - Responsible for delivering the end-to-end delivery of the message - Accepts outgoing messages from the application layer and segments them for transmission for the network layer. - Also responsible for reassembly of messages
The UDP protocol is a connectionless protocol that runs in Transport layer. What is connectionless messaging?
Connectionless Messaging is when there is no connection between sender and receiver. All information packets are treated separately, so they are sequenced and sent on different routes through the network in order to arrive to their destination
Network layer functions - Routing - What type of routing is used when routing decisions are made by each router independently of one another. Routing protocols are programs used to make routing decisions. Also, information needs to be exchanged between routers to prepare routing tables. This is used by the internet.
Decentralized routing
How many bits are in an IPv4 address?
IPV4 uses 32 bits
The most common version of IP used and the one that is running out of space. It uses 32 bits.
IPv4
What is flow control?
Making sure the sender's messages are not being transmitted too quickly so the receiver can keep up with the amount of information that is being received
Network layer functions - Addressing - What is classful addressing?
The concept that an IPv4 address has three parts—network, subnet, and host—as defined by the mask and Class A, B, and C rules. •The number designated in the first 8 bits (octet) determines the Class •A fixed portion of an IP address represents the Network ID and the rest identifies the Host ID •Host ID 0 and Host ID 255 are not assigned to a computer because they are used to designate the network (0) and a broadcast (255)
What are domain name addresses resolved to? How is this done?
The process of converting an application layer domain address like www.Bentley.edu to an IP address that can be read by the network layer. This is done by sending DNS requests to servers until one of them is able to give the IP address to the computer
Network layer functions - Routing - What is routing?
The process of identifying what path to have a packet take through a network from sender to receiver
Three examples of entities that can assign you an address?
System administrators, ICANN and hardware vendors
Network layer functions - Addressing - What is -Dynamic Host Configuration Protocol (DHCP)
The most common protocol for dynamic addressing
When linking the transport layer to the application layer, what are ports used for?
They are used to identify the application
For the network layer functions, what is Addressing used for?
To direct messages from source to destination
Network layer functions - Addressing - What is MAC address resolution ? and how is the resolution done?
To identify MAC address of the next device in the circuit Computer sends broadcast message using Address Resolution Protocol (ARP) to ask for the computer with a given IP address to send its MAC Address
Network layer functions - Addressing - What is domain name resolution ? and who does the translation?
To translate host name to IP address (e.g www.indiana.edu → 129.79.78.193) Translation done by Domain Name Server (DNS)
What are ACKs and NAKs used for? What happens when a NAK is received?
- ACKs: An acknowledgement between a sender and a receiver that signifies that the message was received correctly, this could be used to make sure both parties are synchronized in a session or to make sure the data was not corrupted. - NAKs: Basically, the opposite of an ACK. If a message contains an error, the receiver will indicate that it did not acknowledge the message, so the sender will try to send it again until its an ACK
In the transport layer, what does the function of segmenting do?
- Breaks up large files into smaller segments (and putting them back together) - Segments may be passed individually to application layer or after reassembly
What are the 2 main functions of the Network Layer? Briefly describe each.
- Determines the best route through the network to the final destination (routing). - Identifies the data link layer address of the next computer to which the message should be sent (addressing).
What is the difference between Stop & Wait ARQ and Continuous ARQ?
- Stop-and-wait ARQ: An Automatic Repeat Request in which the sender sends an ACK and waits until it receives an ACK from the receiver for every data packet. - Continuous ARQ: An Automatic Repeat Request that does not wait until the receiver acknowledges the message, it keeps sending more messages to the receiver, if the message fails (NAK), it tries again.
Give two reasons why the Transport Layer performs segmentation on large outgoing messages? (hints: space and speed)
- The data link layer can only transmit at certain lengths, so it is forced to break up messages larger than its capacity. - Allows data to be processed one piece at a time for efficiency, otherwise processing a large chunk of data would take more time to "digest"
Give two examples of when the UDP protocol is used instead of TCP? (hint: message size, nature of transmission)
- When connectionless messaging is being used, UDP is used instead of TCP because the UDP header is much smaller than the TCP header. - When application data is small enough to fit in one single message (for example HTTP requests)
In the transport layer, what is a session and what does the function of session management do?
-A session can be thought of as a conversation between two computers or creating a virtual circuit - Sessions provide reliable end-to-end connections, session management can be used with two approaches, connection-oriented messaging (TCP) and connectionless messaging (UDP).
What is the operation for Enhanced Interior Gateway Routing Protocol (EIGRP) Basically: -A dynamic hybrid protocol (developed by Cisco) uses features of both distance vector and link state protocols for interior routing
-Records transmission capacity, delay time, reliability and load for all paths -Stores its routing table as well as the routing tables for its neighbors and uses this information in its routing decisions as well
What is the operation for Routing Information Protocol (RIP) Basically: -Dynamic distance vector protocol used for interior routing -Useful in smaller, less complex networks
1. Network manager builds the routing table 2. Routing tables broadcast periodically (e.g., every minute or so) 3. When new computers are added, router counts "hops" and selects the shortest route
Network layer functions - Routing - _____1________ are used to make routing decisions. They show which path to send packets on to reach a given destination. Also, the are kept by computers making routing decisions _______2_______ are special purpose devices used to handle routing decisions on the Internet They also maintain their own _______1______.
1. Routing tables 2. Routers
Transport layer - Session management function: -Using a session to send data is also called _____1_______. -Sending messages without establishing a session is ___2_____.
1. connection-oriented messaging (TCP, When the sending computer wants to send a message to the receiver, it usually starts by establishing a session with that computer. The sender transmits the segments in sequence until the conversation is done, and then the sender ends the session.) 2. connectionless messaging (UDP, Sometimes, the sender only wants to send one short information message or a request. In this case, the sender may choose not to start a session but just send the one quick message and move on)
Network layer functions - Addressing - In Dynamic Host Configuration Protocol (DHCP), addresses are ___1_____ for a length of time, assigning addresses ______2_______ can be inefficient when devices are not connected to network
1. leased 2. Permanently
A computer connected to a TCP/IP network must be given the following 4 points of information to operate so it can send/receive data. This information can be obtained from a configuration file, but is most commonly obtained from a DHCP server
1.It's IP address 2.It's subnet mask 3.The IP address of its default gateway (router) 4.The IP address of at least one DNS server
Convert the following IP address to binary: 192.168.1.85
11000000.10101000.00000001.01010101
What is Border Gateway Protocol (BGP) Basically: -Dynamic distance vector protocol used for exterior routing -Far more complex than interior routing protocols-Provide routing info only on selected routes (e.g., preferred or best route)
Border routers that communicate with other border routers. Basically, it allows each autonomous network that uses a different protocol internally to communicate with other networks using their own internal protocols.
Network layer functions - Routing - What type of routing is used when the routing decisions are made by one computer, it is also not used anymore.
Centralized routing
The TCP protocol is a connection-oriented protocol that runs in Transport layer. What is connection-oriented messaging?
Connection-Oriented Messaging is a type of session management that uses Transmission Control Protocol (TCP) to set up a session in which the sender and receiver have full access to communicate with each other as long as the receiver sends a SYN (synchronize) request to the sender and receives an ACK (acknowledgement) back.
type of IP that is slowly being adopted due to IPv4 exhaustion. Also it uses 128 bits.
IPv6
Network layer functions - Addressing - Give an Example of Domain name resolution
If a computer wants to know the IP of a website, then it sends a DNS request to a server. Then multiple DNS servers are queried until the one with the entry for the desired IP address is reached.
Network layer functions - Addressing - Give an example of MAC address resolution
If computer A wants to send a message to computer B on the same subnet and doesn't have computer B's MAC address, it sends a broadcast message to all computers on its subnet using the ARP protocol. "Who is xxx.xxx.xxx.xxx?"
What does ICANN stand for and what is their responsibility?
Internet Corporation for Assigned Names and Numbers: An entity responsible for managing web addresses (application layer). They assign unique domain names and IP addresses to users
What is the operation for Open Shortest Path First (OSPF) Basically: -Dynamic link state protocol used for interior routing - The most widely used interior routing protocol on large enterprise networks -Provides more reliable paths -Less burdensome to the network because only updates sent
It uses the number of computers in a route as well as network traffic and error rates to select the best route.
Addresses come in different layers, so what does it mean when addresses are translated from one layer into another.
Resolving
Dynamic routing: Distance vector dynamic routing
Routers count the number of hops along a route. It is based on the number of "hops" between two devices. Routers exchange information with one another regarding #hops and general speed of circuits.
Network layer functions - Routing - What is static and dynamic routing?
Static: - Routing tables are fixed, paths are always the same. - Routing is manually configured by network managers - Local adjustments when computers added or removed. Dynamic: -Routing tables are updated periodically -Routers exchange information using protocols to update tables
What is a subnet mask? What would the subnet mask be for an IP address whose first 20 bits are used to specify the subnet? (Give your answer in both binary and decimal).
Subnet masks tell computers what part of an Internet Protocol (IP) address is to be used to determine whether a destination is on the same subnet or on a different subnet. A subnet mask is a 4-byte binary number that has the same format as an IP address and is not routable on the network. A 1 in the subnet mask indicates that that position is used to indicate the subnet. A zero indicates that it is not. Therefore, a mask can only contain a continuous stream of ones
Network layer functions - Addressing - What is classless inner domain routing (CIDR)?
Subnetting allows administrators to divide up a network into subnets for logical grouping, faster transmission, and better security. ( Also : - It is used today •Not bound Class designations like class A address or class C address. •Uses slash notation to designate how many bits will be used for the Network ID (/18) )
At the Transport Layer, messages are formatted using one of two protocols. Which of these protocols formats its messages to support handshaking?
TCP
What is the main difference in use between TCP and UDP? Also which one is the most commonly used?
TCP is used for reliable transmission of data. It is the most common transport layer protocol. UDP is used in time-sensitive situations, for control messages, or when reliability is handled by the application layer.
The network layer is responsible to adding IP address information to an outgoing message. What is a (domain) name server and what service does it provide?
The Domain Name Service provides an address for the application layer, this is the address we can use to look up websites in an easier way instead of managing the IP of the website
What is the internet in terms of routing?
The Internet is a network of connected autonomous systems run by various organizations such as AT&T, Sprint, Verizon, etc.
What are IP addresses resolved to? How is this done?
The process of finding which particular address of a computer in a network. The network layer will request a router or LAN network for the data link layer address (MAC) so it knows which path to take in order to deliver the message to the computer. The IP address is resolved into a data link address like MAC address
What are ports numbers used for?
They are temporary numbers to ports that are assigned to a specific application. These ports can simultaneously send and receive data to and from different servers and different applications on the same server
If a computer A is sending a message to computer B which is on a different network, and computer B's physical address is unknown, where will Computer A send the message first (or what is the first step in message's path to its destination)?
Using its subnet mask, the network layer (IP) will recognize that the DNS server is outside of its subnet. It will attach an IP packet and set the data link layer address to its router's address.
What are the two main pieces of information that can be obtained from an IP address?
We can find what network/subnet the computer belongs to and what particular computer is the host of the address.
Dynamic routing: Link state dynamic routing.
computers or routers track the number of hops in the route, the speed of the circuits in each route, and how busy each route is. In other words, rather than knowing just a route's distance, link state routing tries to determine how fast each possible route is. Each computer or router periodically (usually every 30 seconds or when a major change occurs) exchanges this information with other computers or routers in the network (not just their neighbors) so that each computer or router has the most accurate information possible. Link state protocols are preferred to distance vector protocols in large networks because they spread more reliable routing information throughout the entire network when major changes occur in the network. They are said to converge more quickly.
Network layer functions - Addressing - How are IP addresses assigned to computers?
•Device sends out broadcast message "I need an IP address" •DHCP server responds with IP address chosen from pool of available IP addresses for that network (Less time consuming than manual IP address assignment )
TCP/IP and layers
•Host Computers -Packets move through all layers •Gateways, Routers -Packet moves from Physical layer to Data Link Layer through the network Layer •At each stop along the way -Ethernet frame is removed and a new one is created to target the next node in the path to the destination computer -IP and above packets never change in transit (created by the original sender and destroyed by the final receiver)
Network layer functions - Routing - What is interior routing and exterior routing?
•Interior Routing - Routing within an autonomous network •Exterior Routing - Routing between autonomous networks
Message casting: Define all •Unicast - •Broadcast - •Multicast -
•Unicast - one computer sends message to another computer •Broadcast - one computer sends message to all computers in the subnet •Multicast - one computer sends message to a group of computers (e.g., videoconference) -Want to reach multiple receivers but avoid transmitting it for each individual receiver (reduce network traffic) -Internet Group Management Protocol (IGMP) is used to setup temporary "special" IP addresses to identify the multicast group.
