CS6250 - Computer Networks

Circuit Switching

In Circuit Switching a dedicated link/path is established across the sender and the receiver which is maintained for the entire duration of conversation. Circuit Switching is generally used in the public networks. It come into existence for handling voice traffic in addition to digital data. How ever digital data handling by the use of circuit switching methods are proved to be inefficient. The network for Circuit Switching is shown in figure.

What are the similarities of the OSI model and five-layered Internet model?

They are both based on layered architecture. The are comparable to each other - see image 1 Both are networking standards

TCP Connection Teardown

Step 1 (FIN From Client) - Suppose that the client application decides it wants to close the connection. (Note that the server could also choose to close the connection). This causes the client send a TCP segment with the FIN bit set to 1 to server and to enter the FIN_WAIT_1 state. While in the FIN_WAIT_1 state, the client waits for a TCP segment from the server with an acknowledgment (ACK). Step 2 (ACK From Server) - When Server received FIN bit segment from Sender (Client), Server Immediately send acknowledgement (ACK) segment to the Sender (Client). Step 3 (Client waiting) - While in the FIN_WAIT_1 state, the client waits for a TCP segment from the server with an acknowledgment. When it receives this segment, the client enters the FIN_WAIT_2 state. While in the FIN_WAIT_2 state, the client waits for another segment from the server with the FIN bit set to 1. Step 4 (FIN from Server) - Server sends FIN bit segment to the Sender(Client) after some time when Server send the ACK segment (because of some closing process in the Server). Step 5 (ACK from Client) - When Client receive FIN bit segment from the Server, the client acknowledges the server's segment and enters the TIME_WAIT state. The TIME_WAIT state lets the client resend the final acknowledgment in case the ACK is lost.The time spent by client in the TIME_WAIT state is depend on their implementation, but their typical values are 30 seconds, 1 minute, and 2 minutes. After the wait, the connection formally closes and all resources on the client side (including port numbers and buffer data) are released.

Explain the TCP Three-way Handshake

Step 1 (SYN) : In the first step, client wants to establish a connection with server, so it sends a segment with SYN(Synchronize Sequence Number) which informs server that client is likely to start communication and with what sequence number it starts segments with Step 2 (SYN + ACK): Server responds to the client request with SYN-ACK signal bits set. Acknowledgement(ACK) signifies the response of segment it received and SYN signifies with what sequence number it is likely to start the segments with Step 3 (ACK) : In the final part client acknowledges the response of server and they both establish a reliable connection with which they will start the actual data transfer

What are the differences between UDP and TCP

TCP - Transmission Control Protocol reliable transport - slower because of the reliability UDP - User Datagram Protocol - like sending a letter in the mail. You know you sent it, but that's it. The receiver isn't aware, you don't know what happened in the end - it was just sent. Quicker but less reliable

Input Port

performs the physical and data-link functions of the packet switch

Code Division Multiplexing (CDM)

signals from multiple senders are transmitted in an assigned frequency band. CDM uses a principle known as spread spectrum, in which transmitted signals are spread out over all frequency channels in the assigned band. In simplest terms, each signal in a CDM system is multiplexed by means of a spreading code assigned to the sender. This spreading code modulation increases the bandwidth required for the signal. The receiver is aware of the spreading code and uses it to demultiplex the signal. Although it increases the bandwidth needed for transmission, CDM has the advantage of being more secure than other types of multiplexing. In CDM transmissions, an individual user's signal is mixed in with the signals of other users in the frequency band. Without the spreading code required for demultiplexing an individual signal, CDM transmissions appear merely to be noise to a receiving device. CDM is used in cellular telephone systems.

Physical Layer

The lowest, or first, layer of the OSI model. Protocols in this layer generate and detect signals so as to transmit and receive data over a network medium. These protocols also set the data transmission rate and monitor data error rates, but do not provide error correction. The lowest layer of the OSI Model is concerned with electrically or optically transmitting raw unstructured data bits across the network from the physical layer of the sending device to the physical layer of the receiving device. It can include specifications such as voltages, pin layout, cabling, and radio frequencies. At the physical layer, one might find "physical" resources such as network hubs, cabling, repeaters, network adapters or modems.

OSI Network Layer

The network layer is responsible for receiving frames from the data link layer, and delivering them to their intended destinations among based on the addresses contained inside the frame. The network layer finds the destination by using logical addresses, such as IP (internet protocol). At this layer, routers are a crucial component used to quite literally route information where it needs to go between networks.

CIDR

..., Classless Inter-Domain Routing -Technique supported by the BGP4 protocol and based on route aggregation. -CIDR enables a router to group routes together to reduce the quantity of routing information carried by the core routers. -With CIDR, a group of IP networks appear to be a single entity to networks outside of the group.

Goals of congestion control

1. User network resources efficiently 2. Avoid congestion collapse

What does the transport layer provide

4th Layer in OSI Model It provides logical communication between application processes running on different hosts within a layered architecture of protocols and other network components In a nutshell, the transport layer collects message segments from applications, and transmits them into the network (Layer 3). Here the segments are reassembled into fully-fledged messages, and passed on to Layer 7 The transport layer is also responsible for the management of error correction, providing quality and reliability to the end user. This layer enables the host to send and receive error corrected data, packets or messages over a network and is the network component that allows multiplexing.

What is a distributed algorithm?

A distributed algorithm is one that is divided in several processors, so that some part of the algorithm is run on one processor, other part in another processor, and so forth. Typically data is partitioned in advance so that each processor doesn't need to wait for the output of another processor, but that is not always feasable, and their is some form of communication between processors. Now something important: If the processors share memory (RAM), it means they run on the same machine and it is called parallel algorithm. If they run on different boxes, it means they need a communication medium like a network cable and they are called distrobuted algorithms. Why make that distinction

What is hot potato routing

A form of routing in which the nodes of a network have no buffer to store packets in before they are moved on to their final predetermined destination. In normal routing situations, when multiple packets contend for a single outgoing channel, packets that are not buffered are dropped to avoid congestion. But in hot potato routing, each packet that is routed is constantly transferred until it reaches its final destination because the individual communication links can not support more than one packet at a time. The packet is bounced around like a "hot potato," sometimes moving further away from its destination because it has to keep moving through the network. This technique allows multiple packets to reach their destinations without being dropped. This is in contrast to "store and forward" routing where the network allows temporary storage at intermediate locations. Hot potato routing has applications in optical networks where messages made from light can not be stored in any medium.

Explain the forwarding (or switching) function of a router

A primary function of a router is to forward packets toward their destination. This is accomplished by using a switching function, which is the process used by a router to accept a packet on one interface and forward it out another interface. A key responsibility of the switching function is to encapsulate packets in the appropriate data link frame type for the outgoing data link.

how do route servers work

A route server is a computer server that was originally developed by the Routing Arbiter project, with funding from the National Science Foundation. This routing process directs information among Border Gateway Protocol (BGP) routers. These servers are placed at Network access points (NAPs), where centralized computers organize and match routing data. Route servers are important because they help manage BGP sessions. BGP sessions have difficulties with overhead when managing sessions where routers with single and multiple domains are connected (also known as full mesh routing connectivity). Route servers reduce overhead by referencing the IP routing table of an autonomous system where the server is located.

What is a socket?

A socket is one endpoint of a two-way communication link between two programs running on the network. A socket is bound to a port number so that the TCP layer can identify the application that data is destined to be sent to.

Stop and Wait ARQ

A stop-and-wait ARQ sender sends one frame at a time; it is a special case of the general sliding window protocol with transmit and receive window sizes equal to one in both cases. After sending each frame, the sender doesn't send any further frames until it receives an acknowledgement (ACK) signal. After receiving a valid frame, the receiver sends an ACK. If the ACK does not reach the sender before a certain time, known as the timeout, the sender sends the same frame again. The timeout countdown is reset after each frame transmission.

Time Division Multiplexing (TDM)

Almost like round-robin - each input signal (or data stream) is assigned a fixed-length time slot on a communication channel. Each sender transmits a block of data during its assigned time slot. For example, let's say that input streams from three sending devices are being multiplexed into one signal for transmission over a single physical channel. Device 1 transmits a block of data during time slot 1, device 2 transmits a block of data during time slot 2, and device 3 transmits a block of data during time slot 3. After device 3 transmits, the cycle begins again with each device transmitting in turn in its assigned time slot. A drawback to standard TDM is that each sending device has a reserved time slot in each cycle, regardless of whether it is ready to transmit. This can result in empty slots and underutilization of the multiplexed communication channel.

Describe the relationships between ISPs, IXPs, and CDNs

An Internet exchange point (IXP) is a physical location through which Internet infrastructure companies such as Internet Service Providers (ISPs) and CDNs connect with each other. These locations exist on the "edge" of different networks, and allow network providers to share transit outside their own network. By having a presence inside of an IXP location, companies are able to shorten their path to the transit coming from other participating networks, thereby reducing latency, improving round-trip time, and potentially reducing costs.

What is an autonomous system?

An autonomous system (AS) is a collection of connected Internet Protocol (IP) routing prefixes under the control of one or more network operators on behalf of a single administrative entity or domain that presents a common, clearly defined routing policy to the internet

End to End Principle Example

An example of the end-to-end principle is that of an arbitrarily reliable file transfer between two endpoints in a distributed network of a varying, nontrivial size:[3] The only way two endpoints can obtain a completely reliable transfer is by transmitting and acknowledging a checksum for the entire data stream; in such a setting, lesser checksum and acknowledgment (ACK/NACK) protocols are justified only for the purpose of optimizing performance - they are useful to the vast majority of clients, but are not enough to fulfill the reliability requirement of this particular application. A thorough checksum is hence best done at the endpoints, and the network maintains a relatively low level of complexity and reasonable performance for all clients

interconnection network

An interconnection network can forward packets in parallel as long as all the packets are being forwarded to different output ports.

Search Results Featured snippet from the web interior gateway protocol

An interior gateway protocol (IGP) is a type of protocol used for exchanging routing information between gateways (commonly routers) within an autonomous system (for example, a system of corporate local area networks). This routing information can then be used to route network-layer protocols like IP.

Output Port

An output port stores the datagrams that have been forwarded to it through the switching fabric, and then transmits the datagrams on the outgoing link. The output port thus performs the reverse data link and physical layer functionality as the input port.

5 Layer Internet Model - Application Layer

As you might have guessed, the Application layer is where applications requiring network communications live. Examples of these applications include email clients and web browsers. These applications use the Transport Layer to send requests to connect to remote hosts.

OSI Data Link Layer

At the data link layer, directly connected nodes are used to perform node-to-node data transfer where data is packaged into frames. The data link layer also corrects errors that may have occurred at the physical layer. The data link layer encompasses two sub-layers of its own. The first, media access control (MAC), provides flow control and multiplexing for device transmissions over a network. The second, the logical link control (LLC), provides flow and error control over the physical medium as well as identifies line protocols.

OSI Application Layer

At this layer, both the end user and the application layer interact directly with the software application. This layer sees network services provided to end-user applications such as a web browser or Office 365. The application layer identifies communication partners, resource availability, and synchronizes communication.

Original Goals of BGP

BGP was originally designed for scalability, policy (the ability for each AS to implement and enforce various forms of routing policies) and cooperation under competitive circumstances Security was considered later because of the need of the protocol

Two fundamental problems involving routers

Bandwidth and Internet population scaling These scaling issues are caused by: a) An increasing number of devices that connect to the Internet, 2) Increasing volumes of network traffic due to new applications, and 3) New technologies such as optical links that can accommodate higher volumes of traffic. Services at high speeds: New applications require services such as protection against delays in presence of congestion, and protection during attacks or failures. But offering these services at very high speeds is a challenge for routers.

What is the purpose of the router's control plane

Control plane refers to all the functions and processes that determine which path to use. Routing protocols, spanning tree, ldp, etc are examples

Bridge

Data Link Layer - A bridge is a repeater, with add on the functionality of filtering content by reading the MAC addresses of source and destination. It is also used for interconnecting two LANs working on the same protocol. It has a single input and single output port, thus making it a 2 port device.

Switch

Data Link Layer - A switch is a multiport bridge with a buffer and a design that can boost its efficiency(a large number of ports imply less traffic) and performance. A switch is a data link layer device. The switch can perform error checking before forwarding data, that makes it very efficient as it does not forward packets that have errors and forward good packets selectively to correct port only. In other words, switch divides collision domain of hosts, but broadcast domain remains same.

What is a bridge, and how does it "learn"

Data Link Layer Device - bridge need to learn which computers are connected to which of its LAN interfaces. More formally, it need to learn the set of source address that are received on each interface. The source address of each received frame is recorded in the address table, together with the port on which the frame was received. This is called learning Used to bridge connections

Distance Vector Routing Algorithm

Distance-vector routing protocol. A distance-vector routing protocol in data networks determines the best route for data packets based on distance. Distance-vector routing protocols measure the distance by the number of routers a packet has to pass, one router counts as one hop

How does a host infer congestion

End-system observers loss or delay

Go Back N ARQ

Go - Back - N ARQ provides for sending multiple frames before receiving the acknowledgment for the first frame. The frames are sequentially numbered and a finite number of frames. The maximum number of frames that can be sent depends upon the size of the sending window. If the acknowledgment of a frame is not received within an agreed upon time period, all frames starting from that frame are retransmitted.

Distance Vector Routing Count to Infinity

If the link between B and C is disconnected, then B will know that it can no longer get to C via that link and will remove it from it's table. Before it can send any updates it's possible that it will receive an update from A which will be advertising that it can get to C at a cost of 2. B can get to A at a cost of 1, so it will update a route to C via A at a cost of 3. A will then receive updates from B later and update its cost to 4. They will then go on feeding each other bad information toward infinity which is called as Count to Infinity problem.

Packet Switching

In Packet Switching, messages are broken up into packets and each of which includes a header with source, destination and intermediate node address information. Individual Packets in packet switching technique take different routes to reach their respective destination. Independent routing of packets is done in this case for following reasons:

Message Switching

In case of Message Switching it is not necessary to established a dedicated path in between any two communication devices. Here each message is treated as an independent unit and includes its own destination source address by its own. Each complete message is then transmitted from one device to another through internetwork

what is flow control

In data communications, flow control is the process of managing the rate of data transmission between two nodes to prevent a fast sender from overwhelming a slow receiver. It provides a mechanism for the receiver to control the transmission speed, so that the receiving node is not overwhelmed with data from transmitting node. Flow control should be distinguished from congestion control, which is used for controlling the flow of data when congestion has actually occurred

What is encapsulation, and how is it used in a layered model?

In networking model, the terms encapsulation and de-encapsulation refer to a process in which protocol information is added to the data and removed from the data when it passes through the layers. Protocol information can be added before and after the data. If information is added before the data, it is known as header. If information is added after the data, it is known as trailer.

What is an IXP

Internet Exchange Point - a physical infrastructure through which Internet service providers (ISPs) & Content Delivery Networks (CDNs) exchange Internet traffic btw their networks (autonomous systems)

How does a router process advertisements?

It updates it's own table and then broadcast to all nodes in it's network the changes

What are the four reasons of IXPs increased popularity

Keeping local traffic local. In other words, the traffic that is exchanged between two networks does not need to travel unnecessarily through other networks if both networks are participants in the same IXP facility. Lower costs. Typically peering at an IXP is offered at lowered cost than eg relying on third-parties to transfer the traffic charging based on volume. Improved network performance due to reduced delay. Incentives. Critical players in today's Internet ecosystem often "incentivize" other networks to connect at IXPs. For example, a big content provider may require another network to be present at a specific IXP(s) in order to peer with them.

Open Shortest Path First Protocol

Link-state routing protocol that is used to find the best path between the source and the destination router using its own Shortest Path First OSPF uses a shorted path first algorithm in order to build and calculate the shortest path to all known destinations.The shortest path is calculated with the use of the Dijkstra algorithm. The algorithm by itself is quite complicated. This is a very high level, simplified way of looking at the various steps of the algorithm: Upon initialization or due to any change in routing information, a router generates a link-state advertisement. This advertisement represents the collection of all link-states on that router. All routers exchange link-states by means of flooding. Each router that receives a link-state update should store a copy in its link-state database and then propagate the update to other routers. After the database of each router is completed, the router calculates a Shortest Path Tree to all destinations. The router uses the Dijkstra algorithm in order to calculate the shortest path tree. The destinations, the associated cost and the next hop to reach those destinations form the IP routing table. In case no changes in the OSPF network occur, such as cost of a link or a network being added or deleted, OSPF should be very quiet. Any changes that occur are communicated through link-state packets, and the Dijkstra algorithm is recalculated in order to find the shortest path. The algorithm places each router at the root of a tree and calculates the shortest path to each destination based on the cumulative cost required to reach that destination. Each router will have its own view of the topology even though all the routers will build a shortest path tree using the same link-state database. The following sections indicate what is involved in building a shortest path tree.

What are 2 main challenges with BGP

Misconfigurations and faults Unfortunately, the BGP protocol in practice can suffer from two major limitations: misconfigurations and faults. A possible misconfiguration or an error can result in an excessively large number of updates which in turn can result in route instability, router processor and memory overloading, outages, and router failures. One way that ASes can help to reduce the risk that these events will happen is by limiting the routing table size and also by limiting the number of route changes.

What is multiplexing, and why is it necessary

Multiplexing reduces the number of physical communication links needed between two points Think about how TV channels that stream on different frequencies all come in on the same line. Multiplexing basically involves taking multiple signals and combining them into one signal for transmission over a single medium, such as a telephone line. The input signals can be either analog or digital. The purpose of multiplexing is to enable signals to be transmitted more efficiently over a given communication channel, thereby decreasing transmission costs.

Router

Network Layer - A router is a device like a switch that routes data packets based on their IP addresses. Router is mainly a Network Layer device. Routers normally connect LANs and WANs together and have a dynamically updating routing table based on which they make decisions on routing the data packets. Router divide broadcast domains of hosts connected through it.

Computational Complexity of LS Algorithm

O(n^2) What is the computation complexity of this algorithm? That is, given n nodes (not counting the source), how much computation must be done in the worst case to find the least cost paths from the source to all destinations? In the first iteration, we need to search through all n nodes to determine the node, w, not in N that has the minimum cost. In the second iteration, we need to check n−1 nodes to determine the minimum cost; in the third iteration n−2 nodes and so on. Overall, the total number of nodes we need to search through over all the iterations is n*(n+1)/2, and thus we say that the above implementation of the link state algorithm has worst case complexity of order n squared: O(n2). (A more sophisticated implementation of this algorithm, using a data structure known as a heap, can find the minimum in line 9 in logarithmic rather than linear time, thus reducing the complexity).

What are the differences of the OSI model and five-layered Internet model?

OSI is a generic model based on the functions of each layer. TCP is a protocol oriented standard. OSI uses 3 upper layers (application, presentation, and session) while TCP just uses application. Likewise, OSI uses 2 Lower layers (Physical and DataLink) while TCP just uses Link

Hub

Physical Layer - A hub is basically a multiport repeater. A hub connects multiple wires coming from different branches, for example, the connector in star topology which connects different stations. Hubs cannot filter data, so data packets are sent to all connected devices. In other words, collision domain of all hosts connected through Hub remains one. Also, they do not have intelligence to find out best path for data packets which leads to inefficiencies and wastage.

Repeater

Physical Layer - A repeater operates at the physical layer. Its job is to regenerate the signal over the same network before the signal becomes too weak or corrupted so as to extend the length to which the signal can be transmitted over the same network. An important point to be noted about repeaters is that they do not amplify the signal. When the signal becomes weak, they copy the signal bit by bit and regenerate it at the original strength. It is a 2 port device.

What tasks occur in a router

Providing a router hostname Setting up passwords Disabling DNS lookup Setting up logging Setting timestamps for logging and debugging Defining console, auxiliary, and virtual terminal settings Setting up a Comm Server to access your routers more easily Handling password recovery Downloading a software image from a TFTP server File management tasks

Which services do IXPs provide

Public Peering The most well-known use of IXPs is public peering service - in which two networks use the IXP's network infrastructure to establish a connection to exchange traffic based on their bilateral relations and traffic requirements. The costs required to set up this connection are - one-time cost for establishing the connection, monthly charge for using the chosen IXP port (those with higher speeds are more expensive) and perhaps an annual fee of membership in the entity owning and operating the IXP. However, the IXPs do not usually charge based on the amount of exchanged volume. They also do not usually interfere with bilateral relations between the participants unless there is a violation of the GTC. Even with the set-up costs, IXPs are usually cheaper than other conventional methods of exchanging traffic (such as relying on third parties which charge based on the volume of exchanged traffic). IXP participants also often experience better network performance and QoS because of reduced delays and routing efficiencies. In addition, many companies that are major players in the Internet space (such as Google) incentivize other networks to connect at IXPs by making it a requirement to peering with them. Private Peering: Most operational IXPs also provide a private peering service (Private Interconnects - PIs) that allow direct traffic exchange between two parties of a PI and don't use the IXP's public peering infrastructure. This is commonly used when the participants want a well-provisioned dedicated link capable of handling high-volume, bidirectional and relatively stable traffic. Route Servers and Service Level Agreements: Many IXPs also include service level agreements (SLAs) and free use of the IXP's route servers for participants. This allows participants to arrange instant peering with a large number of co-located participant networks using essentially a single agreement/BGP session. Remote peering through resellers: Another popular service is IXP reseller/partner programs. This allows third parties to resell IXP ports wherever they have infrastructure connected to the IXP. These third parties are allowed to offer the IXP's service remotely, which allows networks that have little traffic to also use the IXP. This also enables remote peering - networks in distant geographic areas can use the IXP. Mobile Peering: Some IXPs also provide support for mobile peering - a scalable solution for interconnection of mobile GPRS/3G networks. DDoS Blackholing: A few IXPs provide support for customer-triggered blackholing, which allows users to alleviate the effects of DDoS attacks against their network. Free value-added services: In the interest of 'good of the Internet', a few IXPs such as Scandinavian IXP Netnod offer free value-added services like Internet Routing Registry (IRR), consumer broadband speed tests9, DNS root name servers, country-code top-level domain (ccTLD) nameservers, as well as distribution of the official local time through NTP.

Frequency Division Multiplexing (FDM)

Radio / Cable TV - Mainly used in Analog Can be used over both wired and wireless each signal is assigned its own frequency range (or channel) within a larger frequency band. Frequency ranges for channels cannot overlap. Frequency bands are often separated by an unused block of the frequency spectrum to reduce interference.

Differences between forwarding and routing

Routing is the decision over which interface a packet is to be sent. This decision has to be made for locally created packets, too. Routing tables contain network addresses and the associated interface or nexthop. This refers to ip route and ip rule (in a Linux context) Forwarding refers to packets which reach a system but are not destined for this system. Forwarding is a decision of the system: "I take the packet and try to get it towards its destination." Instead of just dropping it. "forwarding" is a common term in the context of packet filters. Linux' Netfilter has three chains in its base table: INPUT, OUTPUT, and FORWARD. This chain just makes the decision "Shall this packet be forwarded or dropped?" (if forwarding is generally enabled on the system; Linux again: /proc/sys/net/ipv4/ip_forward)

Selective Acking

SACKs allow a receiver to acknowledge non-consecutive data, so that the sender can retransmit only what is missing at the receiver�s end. This is particularly helpful on paths with a large bandwidth-delay product (BDP)

What is a packet for the transport layer called

Segment. So applications provide byte stream to TCP, and TCP takes care of creating it into discrete pieces of messages. These discrete pieces of messages at Transport Layer(where TCP comes into picture) are called "Segments" https://www.slashroot.in/difference-between-segments-packets-and-frames#:~:text=Frame,numbers%20are%20part%20of%20Segments

What are advantages and disadvantages of a layered architecture?

Separation of concerns among logical layers promotes flexibility, scalibility, and maintainability. Multiple applications can reuse the components. It enables teams to work on different parts with minimal dependencies on other teams

What are the two main protocols within the transport layer

TCP / UDP TCP: As previously stated, TCP is considered a reliable transport protocol, which means that TCP includes processes to ensure reliable delivery between applications through the use of acknowledged delivery. TCP transport is analogous to sending packages that are tracked from source to destination. If a FedEx order is broken up into several shipments, a customer can check online to see the order of the delivery. TCP breaks up a message into small pieces known as segments. The segments are numbered in sequence and passed to the IP process for assembly into packets. TCP keeps track of the number of segments that have been sent to a specific host from a specific application. If the sender does not receive an acknowledgement within a certain period of time, it assumes that the segments were lost and retransmits them. Only the portion of the message that is lost is resent, not the entire message. On the receiving host, TCP is responsible for reassembling the message segments and passing them to the application. The File Transfer Protocol (FTP) and the Hypertext Transfer Protocol (HTTP) are examples of applications that use TCP to ensure data delivery. UDP: While the TCP reliability functions provide more robust communication between applications, they also incur additional overhead and possible delays in transmission. There is a trade-off between the value of reliability and the burden it places on network resources. Imposing overhead to ensure reliability for some applications could reduce the usefulness of the application and can even be detrimental to the application. In such cases, UDP is a better transport protocol. UDP provides just the basic functions for delivering data segments between the appropriate applications, with very little overhead and data checking. UDP is known as a best-effort delivery protocol. In the context of networking, best-effort delivery is referred to as unreliable, because there is no acknowledgement that the data is received at the destination. With UDP, there are no transport layer processes that inform the sender if successful delivery has occurred. UDP is similar to placing a regular, non-registered, letter in the mail. The sender of the letter is not aware of whether a receiver is available to receive the letter, nor is the post office responsible for tracking the letter or informing the sender if the letter does not arrive at the final destination. UDP: http://teachweb.milin.cc/datacommunicatie/tcp_osi_model/transport_layer.htm#:~:text=Transport%20protocols%20specify%20how%20to,to%20communicate%20and%20transfer%20data.

5 Layer Internet Model - Data Link Layer

The Data Link layer is responsible for creating the frames that move across the network. These frames encapsulate the packets and use MAC addresses to identify the source and destination.

5 Layer Internet Model - Network Layer

The Network layer is responsible for creating the packets that move across the network. It uses IP addresses to identify the packet's source and destination.

5 Layer Internet Model - Physical Layer

The Physical layer encodes and decodes the bits found in a frame and includes the transceiver that drives and receives the signals on the network.

Routing Information Protocol (RIP)

The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols which employ the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from source to destination. The largest number of hops allowed for RIP is 15, which limits the size of networks that RIP can support.

5 Layer Internet Model - Transport Layer

The Transport layer establishes the connection between applications running on different hosts. It uses TCP for reliable connections and UDP for fast connections. It keeps track of the processes running in the applications above it by assigning port numbers to them and uses the Network layer to access the TCP/IP network.

Link state algorithm

The basic idea of link-state routing protocols is that each node sends local topology information to its neighbors. This information then is propagated using sophisticated "flooding" mechanisms through the network

How does an Autonomous System determine what rules to import/export?

The business relationships between different AS's determine the rules etc. The first form is provider-customer transit (aka "transit"), wherein one ISP (the "provider" P in Figure 3) provides access to all (or most) destinations in its routing tables. Transit almost always is meaningful in an inter-AS relationship where financial settlement is involved; the provider charges its customers for Internet access, in return for forwarding packets on behalf of customers to destinations (and in the opposite direction in many cases). Another example of a transit relationship in Figure 3 is between X and its customers (the Cis). The second prevalent form of inter-AS interconnection is called peering. Here, two ASes (typically ISPs) provide mutual access to a subset of each other's routing tables. The subset of interest here is their own transit customers (and the ISPs own internal addresses). Like transit, peering is a business deal, but it may not involve financial settlement. While paid peering is common in some parts of the world, in many cases they are reciprocal agreements. As long as the traffic ratio between the concerned ASs is not highly asymmetric

OSI Presentation Layer

The presentation layer formats or translates data for the application layer based on the syntax or semantics that the application accepts. Because of this, it at times also called the syntax layer. This layer can also handle the encryption and decryption required by the application layer.

OSI Session Layer

The session layer controls the conversations between different computers. A session or connection between machines is set up, managed, and termined at layer 5. Session layer services also include authentication and reconnections.

OSI Transport Layer

The transport layer manages the delivery and error checking of data packets. It regulates the size, sequencing, and ultimately the transfer of data between systems and hosts. One of the most common examples of the transport layer is TCP or the Transmission Control Protocol.

When would an application layer protocol choose UDP over TCP

UDP is used when speed is preferred over integrity and error correction. Some common applications include streaming video and music, live broadcasts, voice and video calling (VoIP), and online gaming. In these scenarios, it doesn't really matter if you lose the occasional video frame or button press, which favors UDP. DNS traffic is usually exchanged over the UDP protocol.

BGP messages

UPDATE Announcements: These messages advertise new routes and updates to existing routes. They include several standardized attributes. Withdrawals: These messages are sent when a previously announced route is removed. This could be due to some failure or due to a change in the routing policy. 2. KEEPALIVE: These messages are exchanged to keep a current session going

Automatic Repeat Request

Waits for a time period to receive an ack - if it doesn't the packet is re-transmitted. The main function of these protocols is, the sender receives an acknowledgment from the receiver end implying that the frame or packet is received correctly before a timeout occurs, timeout is a specific time period within which the acknowledgment has to be sent by the receiver to the sender. If a timeout occurs: the sender does not receive the acknowledgment before the specified time, it is implied that the frame or packet has been corrupt or lost during the transmission. Accordingly, the sender retransmits the packet and these protocols ensure that this process is repeated until the correct packet is transmitted. ARQ is an error-control strategy used in a two-way communication system. It is a group of error-control protocols to achieve reliable data transmission over an unreliable source or service. These protocols reside in Transport Layer and Data Link Layer of the OSI(Open System Interconnection) model . These protocols are responsible for automatic retransmission of packets that are found to be corrupted or lost during the transmission process.

Congestion Control

What you do to prevent networks from congesting. Leaky bucket algorithm

What is the end-to-end (e2e) principle?

When a function has to be supported in a networked system, the designer often asks if it should be implemented at the end systems; or should it be implemented within the communication subsystem that interconnects all the end systems. The end-to-end argument or principle states that it's proper to implement the function in the end systems. The communication system itself may provide a partial implementation but only as a performance enhancement. The architecture and growth of the Internet was shaped by the end-to-end principle. It allowed us to keep the Internet simple and add features quickly to end systems. The principle enabled innovation.

Solution to Count to Infinity DV Issue (Route Poisoning - Poison Reverse

When a route fails, distance vector protocols spread the bad news about a route failure by poisoning the route. Route poisoning refers to the practice of advertising a route, but with a special metric value called Infinity. Routers consider routes advertised with an infinite metric to have failed. Each distance vector routing protocol uses the concept of an actual metric value that represents infinity. RIP defines infinity as 16. The main disadvantage of poison reverse is that it can significantly increase the size of routing announcements in certain fairly common network topologies.

Flap Damping

an AS will track the number of updates to a specific prefix over a certain amount of time. If the tracked value reaches a configurable value, the AS can suppress that route until a later time.

What is the EvoArch model?

an hourglass model that consists of six protocol and application layers that originate from a single bubble - IPv4

Two types of BGP sessions

eBGP - sessions betweeon BGP-speaking routers in different autonomous systems iBGP = sessions between BGP speaking routers in the same autonomous systems eBGP is the "STANDARD" mode in which BGP is used - the original reason it was designed was to exchange routing information between different ASes in the internet.

Fast Retransmit

if a receiver receives a data segment that is out of order, it immediately sends a duplicate acknowledgement to the sender. If the sender receives three duplicate acknowledgements, it assumes that the data segment indicated by the acknowledgements is lost and immediately re-transmits the lost segment. With FRR, time is not lost waiting for a timeout in order for re-transmission to begin.

What are the basic components of a router

interface processor internetwork operating system (IOS) RAM NVRAM ROM Flash Memory Configuration Register Buses

Network Assisted Congestion Control

routers provide feedback to end systems