BSC-IT 6TH SEMESTER ASSIGNMENTS BSIT-63 (TA & TB)
CommentsBSIT-63 Advanced Computer Networks
Assignment: TA (Compulsory)
1. What is DNS? Why is DNS required? What is the basis to choose the domain to an organization?
ANS:-DNS, the Domain Name System is a distributed hierarchical naming system for computers, services, or any resource connected to the Internet or a private Network. It associates various information’s with domain names assigned to each of the participants.This is required because domain names are alphabetic, as they’re easier to remember. The Internet however,is really based on IP addresses. Every time we use a domain name, therefore, a DNS service must translatethe name into the corresponding IP address. For example, the domain name
www.example.com might translate to 198.105.232.4.
The basics of choosing domain to an organization by attaching random names to IP address and managing them is too nontrivial. So, a structured approach is needed.
• Best way is to employ the postal addressing system.
o Country
o State
o District
o Taluk
o City
o Street
• Internet is divided into 200 Domains at Top level
• Each top-level domain is further divided into sub domain.
• Each sub domain is further divided into one or more levels of sub domains.
• Top level domain can be split into two major classes.
o Generic – generic domain names include
? Om, int, mil, gov, org, net, edu……
? biz, info, name (recent addition 2000 Nov)
? aero, coop, museums (new ones)
• Country – each country has one entry, in, ae, us, jp etc
• Top level domain should be unambiguous and non-contentious.
2.What are the different components of Internet cloud? How does WWW isconnected with Internet cloud? Explain.
ANS:- A cloud client consists of computer hardware and/or computer software that relies on cloud computing for application Delivery, or that is specifically designed for delivery of cloud services and that, in either case, is essentially useless without it. Examples include some computers, phones and other devices, operating systems and browsers Cloud application services or “Software as a Service (SaaS)” deliver software as a service over the Internet,eliminating the need to install and run the application on the customer’s own computers and simplifying maintenance and support. Key characteristics include
(i) Network-based access to, and management of, commercially available (i.e., not custom) software
(ii)Activities that are managed from central locations rather than at each customer’s site, enabling customers to access applications remotely via the Web
(iii)Application delivery that typically is closer to a one-to-many model (single instance, multi-tenant architecture) than to a one-to-one model, including architecture, pricing, partnering, and management characteristics
(iv)Centralized feature updating, which obviates the need for downloadable patches and upgrades.
Cloud platform services or “Platform as a Service (PaaS)” deliver acomputing platform and/or solution stack as a service, often consuming cloud infrastructure and sustaining cloud applications. It facilitates deployment of applications without the cost and complexity of buying and managing the underlying hardware and software layers. Cloud infrastructure services or “Infrastructure as a Service (IaaS)” delivers computer infrastructure, typically a platform virtualization environment as a service.Rather than purchasing servers, software, data center space or network equipment, clients instead buy those resources as a fully outsourced service. The service is typically billed on a utility computing basis and amount of resources consumed (and there fore the cost) will typically reflect the level of activity. It is an evolution of virtual private server offerings. The servers layer consists of computer hardware and/or computer software products that are specifically designed for the delivery of cloud services, including multi-core processors, cloud-specific operating systems and combined offerings.
The Internet is a global system of interconnected computer networks that use the standard Internet Protocol Suite (TCP/IP) to serve billions of users worldwide. It is a network of networks that consists of millions of private, public, academic, business, and government networks of local to global scope that are linked by a broad array of electronic and optical networking technologies. The Internet carries a vast array of information resources and services, most notably the inter-linked hypertext documents of the World Wide Web (WWW) and the infrastructure to support electronic mail. Most traditional communications media, such as telephone and television services, are reshaped or redefined using the technologies of the Internet, giving rise to services such as Voice over Internet Protocol (VoIP) and IPTV. Newspaper publishing has been reshaped into Web sites, blogging, and web feeds. The Internet has enabled or accelerated the creation of new forms of human interactions through instant messaging, Internet forums, and social networking sites.
3.What are the advantages of good routing protocol? Explain one of therouting protocols in detail.
ANS:-The main objectives of the network layer are to deliver the packets to the Destination. The delivery of packets is often accomplished using either a connection-oriented or a connectionless network service. In a connection-oriented approach, the network layer protocol first makes a connection with the network layer protocol at the remote site before sending a packet. When the connection is established, a sequence of packets from the same source to the same destination can be sent one after another. In this case, there is a relationship between packets. They are sent on the same path where they follow each other. A packet is logically connected to the packet traveling before it and to packet traveling after it. When all packets of a message have been delivered, the connection is terminated. In a connection oriented approach, the decision about the route of a sequence of packets with the same source and destination addresses can be made only once, when the connection is established. The network device will not compute the route again and again for each arriving packet. In a connectionless situation, the network protocol treats each packet independently, with each packethaving no relationship to any other packet. The packets in a message may not travel the same path to their destination. The internet protocol (IP) is a connectionless protocol. It handles each packet transfer in a separate way. This means each packet travel through different networks before settling to their destination network. Thus the packets move through heterogeneous networks using connection less IP protocol.
DIRECT AND INDIRECT ROUTING
There exits two approaches for the final delivery of the IP packets. In the Direct delivery, the final destination of the packet is a host connected to the same physical network as the deliverer (Figure 1). Direct delivery occurs when the source and destination of the packet are located on the same physical network or if the delivery is between the last router and the destination host.The sender can easily determine if the delivery is direct. It can extract the network address of the destination packet (Mask all the bits of the Host address) and compare this address with the addresses of the networks to which it is connected. If a match is found, then the delivery is direct. In direct delivery, the sender uses the destination IP address to find the destination Physical Address. The IP software then delivers the destination IPaddress with the destination physical address to the data link layer for actual delivery. In practical sense a protocol called address resolution protocol (ARP) dynamically maps an IP address to the corresponding physical address. It is to be noted that the IP address is a FOUR byte code where as the Physical address is aSIX byte code. The Physical address is also called as MAC address, Ethernet address and hardware address.When the network part of the IP address does not match with the network address to which the host is connected, the packet is delivered indirectly. In an indirect delivery, the packet goes from router to router until it reaches the one connected to the same physical network as its final destination. Note that a delivery always involves one direct delivery but zero or more indirect deliveries. Note also that the last delivery is always adirect delivery. In an indirect delivery, the sender uses the destination IP address and a routing table to find theIP address of the next router to which the packet should be delivered. The sender then uses the ARP protocol tofind the physical address of the next router. Note that in direct delivery, the address mapping is between the IPaddress of the final destination and the physical address of the final destination. In an indirect delivery, the address mapping is between the IP address of the next router and the physical address of the next router.Routing tables are used in the routers. The routing table contains the list of IP addresses of neighboring routers.When a router has received a packet to be forwarded, it looks at this table to find the route to the final destination. However, this simple solution is impossible today in an Internet work such as the Internet because the number of entries in the routing table make table look ups inefficient. Several techniques can make the sizeof the routing table manageable and handle such issues as security.
4.What is streaming? Give some examples of streaming. What are the challenges in designing multimedia networking?
ANS:-
Streaming. In a streaming stored audio/video application, a client begins play out of the audio/video of few seconds after it begins receiving the file from the server. This means that the client will be playing out audio/video from one location in the file while it is receiving later parts of the file from the server. This technique, known as streaming, avoids having to download the entire file (and incurring a potentially longdelay) before beginning playout. There are many streaming multimedia products, such as RealPlayer,QuickTime and Media Player.
Examples are :
Streaming stored audio/video,
Streaming live audio/video
Real-time interactive audio/video.
Packet Loss
Consider one of the UDP segments generated by our Internet phone application. The UDP segment is encapsulated in an IP datagram. As the datagram wanders through the network, it passes through buffers (that is, queues) in the routers in order to access outbound links. It is possible that one or more of the buffers in the route from sender to receiver is full and cannot admit the IP data gram. In this case, the IP datagram is discarded, never to arrive at the receiving application.
End-to-End Delay
End-to-end delay is the accumulation of transmission, processing, and queuing delays in routers; propagation delays in the links; and end-system processing delays. For highly interactive audio applications, such as Internet phone.
5.What is the purpose of E-mail? What are the tools provided in the E-mail?Mention different E-mail –service providers and their special features.
ANS:- Electronic mail is the most widely used tool in the present world for fast and reliable communication.It is based on RFC 822.
E-mail system supports five basic functions.
1) Composition: Helps in creating message and answers, supports many functions such as insertion of address after extraction from the original message during replying etc.
2) Transfer: Causes movement of message to the destination. Connection establishments and passage of message is done here.
3) Reporting: Do involve in reporting the origin of email whether it is delivered,lost or abandoned. 4) Disposition: Do involve in invoking certain tools to enable reading email message which come as attachment.
Ex: Abode to read a pdf file attachment.
5) Disposition: Involves, Reading, discarding, savings, replying, forwarding etc.
Additional features of E-mail system
Forwarding: forward email to another email ID
Mail box: storing/retrieving email
Mailing list: Send copies to the entire email list.
Other functions: CC: carbon copy BCC:
Blind copy
High priority
Yahoo, Gmail, Hotmail, AOL etc.
6.How does UBL work? Explain the various steps of server side operation.Give an example.
ANS:- XML is only the foundation on which additional standards can be defined to achieve the goal of true interoperability. The Universal Business Language (UBL) initiative isthe next step in achieving this goal.
The UBL effort addresses this problem by building on the work of the ebXML initiative. EbXML is a joint project of UN/CEFACT, the world body responsible for international Electronic Data Interchange (EDI), and the Organization for the Advancement of Structured Information
Standards (OASIS), a nonprofit consortium dedicated to the open development of XML languages. UBL is organized as an OASIS Technical Committee to guarantee a rigorous, open process for the standardization of the XML business language. The development of UBL within OASIS also helps ensure a fit with other essential ebXML Specifications.
Server Side Operation
Upon clicking a URL, the server side offers the following operations.
(i) Accepts a TCP connection from a client.
(ii)Get the name of the file requested disk.
(iii)Get the file from the disk.
(iv)Return the file to the client.
(v)Release the TCP connection
• Problems with this type is the disk access with every request
• SCSI disk have a disc access time of 5 ms. so it permits 200 disks access per second
• It is still lower if the files are larger.
• To overcome this, the web server maintains a large cache space which holds ‘n’ most recent files.Whenever a request comes, the server first look into caches and respond appropriately.
• To make the server faster, multithreading is adapted.
• There exists different concepts and design in one design. The server has a front end module and k processing modules (threads). The processing modules have access to the cache. The front end module accepts input request and pass it to one of the module. The processing module verifies the cache and responds if the file exists else it invokes disk search and caches the file and also send the file to the client. At any instant of time‘t’ out of k modules, K-X modules may be few to take requests, X modules may be in the queue waiting for disk access and cache search. If the number of disks is enhanced then it is possible to enhance the speed.
1.Each Module does the following.Resolve the name of the Web page requested.
E.g.: http:// www.cisco.com
2.There is no file name here. Default is index .html.
3.Perform access control on the client check to see if there are any restrictions.
4.Perform access control on the web page. Access restrictions on the page itself.
5. Check the cache.
6.Fetch the requested page.
CACHE
Front end
– – – – – – – K Processes
K – Module
Threads
In coming
Request.Out going
Reply
7.Determine MIME type
8.Take care of miscellaneous address ends.
(Building User profile, Satisfaction.)
9.Return the reply to the client.
10.Make an entry in the server log.
If too many requests come in each second, the CPU will not be able to handle the processing load, irrespective of no of disks in parallel. The solution is to add more machine with replicated disks. This is called server form. A front end still accepts the request and sprays them to all CPUsrather than multiple threads to reduce the load on that machine. Individual machines are again Multithreaded with Multiple disks.
It is to be seen that cache is local to each machine. TCP connection should terminate at processing node and not at front end.
7. What are the criteria consider to develop a routing protocol? Explain the OSPF routing protocol in detail?
ANS:- There exits two approaches for the final delivery of the IP packets. In the Direct delivery, the final destination of the packet is a host connected to the same physical network as the deliverer (Figure 1). Direct delivery occurs when the source and destination of the packet are located on the same physical network or if the delivery is between the last router and the destination host.The sender can easily determine if the delivery is direct. It can extract the network address of the destination packet (Mask all the bits of the Host address) and compare this address with the addresses of the networks to which it is connected. If a match is found, then the delivery is direct. Indirect delivery, the sender uses the destination IP address to find the destination physical address. The IP software then delivers the destination IP address with the destination physical address to the data link layer for actual delivery. In practical sense a protocol called address resolution protocol (ARP) dynamically maps an IP address to the corresponding physical address. It is to be noted that the IP address is a FOUR byte codewhere as the Physical address is a SIX byte code. The Physical address is also called as MAC address,Ethernet address and hardware address. When the network part of the IP address does not match with the network address to which the host is connected, the packet is delivered indirectly. In an indirect delivery, the packet goes from router to router until it reaches the one connected to the same physical network as its final destination.
• Note that a delivery always involves one direct delivery but zero or more indirect deliveries.
• Note also that the last delivery is always a direct delivery. In an indirect delivery, the sender uses the destination IP address and a routing table to find the IP address of the next router to which the packet should be delivered.
•The sender then uses the ARP protocol to find the physical address of the next router. Note that in direct delivery, the address mapping is between the IP address of the final destination and the physical address of the final destination.
• In an indirect delivery, the address mapping is between the IP address of the next router and the physical address of the next router.Routing tables are used in the routers. The routing table contains the list of IP addresses of neighboring routers. When a router has received a packet to be forwarded, it looks at this table to find the route to the final destination. However, this simple solution is impossible today in an Internet work such as the Internet because the number of entries in the routing table make table look ups inefficient. Several techniques can make the size of the routing table manageable and handle such issues as security.
* OPEN SHORTEST PATH FIRST(OSPF)
Open Shortest Path First (OSPF) is a routing protocol developed for Internet Protocol (IP) networks by the Interior Gateway Protocol (IGP) working group of the InternetEngineering Task Force (IETF). The working group was formed in 1988 to design an IGP based on the ShortestPath First (SPF) algorithm for use in the Internet. Similar to the Interior Gateway Routing Protocol (IGRP),OSPF was created because in the mid-1980s, the Routing Information Protocol (RIP) was increasingly incapable of serving large, heterogeneous internet works. This chapter examines the OSPF routing environment,underlying routing algorithm, and general protocol components.OSPF was derived from several research efforts, including Bolt,Breakneck, and Newman’s (BBN’s) SPF algorithm developed in 1978 for the ARPANET (a landmark packet-switching network developed in the early 1970s by BBN), Dr. Radia Perlman’s research on fault-tolerant broadcasting of routing information (1988), BBN’s work on area routing (1986), and an early version of OSI’sIntermediate System-to- Intermediate System (IS-IS) routing protocol. OSPF has two primary characteristics.The first is that the protocol is open, which means that it is in the public domain. The OSPF specification is published as Request for Comments (RFC) 1247. The second principal characteristic is that OSPF is based onthe SPF algorithm, which sometimes is referred to as the Dijkstra algorithm, named for the person credited with its creation. OSPF is a link-state routing protocol that calls for the sending of link-state advertisements (LSAs)to all other routers within the same hierarchical area. Information on attached interfaces, metrics used, and other variables is included in OSPF LSAs. As OSPF routers accumulate link-state information, they use the SPFalgorithm to calculate the shortest path to each node. As a link-state routing protocol, OSPF contrasts with RIP and IGRP, which are distance-vector routing protocols. Routers running the distance-vector algorithm send all or a portion of their routing tables in routing-update messages to their neighbors.
8.Why is BGP needed? Explain com 1BGP used in place of the 1GP?
ANS:- The Border Gateway Protocol (BGP) is the protocol backing the core routingdecisions on the Internet. It maintains a table of IP networks or ‘prefixes’ which designatenetwork reach ability among autonomous systems (AS). It is described as a path vector protocol. BGP does not use traditional Interior Gateway Protocol (IGP) metrics, but makes routing decisions based on path, network policies and/or rule sets. For this reason, it is more appropriately termed a reach ability protocol rather than routing protocol. BGP wascreated to replace the Exterior Gateway Protocol (EGP) routing protocol to allow fullydecentralized routing in order to allow the removal of the NSFNet Internet backbonenetwork. This allowed the Internet to become a truly decentralized system. Since 1994,version four of the BGP has been in use on the Internet. All previous versions are . The major enhancement in version 4 was support of Classless Inter-Domain Routing and use of route aggregation to decrease the size of routing tables. Since January 2006, version 4 is codified in RFC 4271, which went through more than 20 draftsbased on the earlier RFC 1771 version 4. RFC 4271 version corrected a number of errors,clarified ambiguities and brought the RFC much closer to industry practices. Most Internet users do not use BGP directly. Since most Internet service providers must use BGP to establish routing between one another (especially if they are multihued), it is one of the most important protocols of the Internet. Compare this with Signaling System 7(SS7), which is the inter-provider core call setup protocol on the PSTN. Very large private IP networks use BGP internally. An example would be the joining of a number of large Open Shortest Path First (OSPF) networks where OSPF by itself would not scale to size.Another reason to use BGP is multihoming a network for better redundancy either tomultiple access points of a single ISP (RFC 1998) or to multiple ISPs.BGP neighbors, or peers, are established by manual configuration between routers to create a TCP session on port 179. A BGP speaker will periodically send 19-byte keep-alive messages to maintain the connection (every 60seconds by default). Among routing protocols, BGP is unique in using TCP as its transport protocol. When BGP is running inside an autonomous system (AS), it is referred to as Internal BGP (IBGP or Interior Border Gateway Protocol). When it runs between autonomous systems, it is called External BGP (EBGP or Exterior Border GatewayProtocol). Routers on the boundary of one AS exchanging information with another AS are called border or edge routers. In the Cisco operating system, IBGP routes have an administrative distance of 200, which is less preferred than either external BGP or any interior routing protocol. Other router implementations also prefer EBGP to IGPs, andIGPs to IBGP.
Assignment : TB (Compulsory)
PART – A
1. Explain Domain Name System (DNS).
Ans- DNS stand for Domain Name System. It translates the domain name into IP address and also maps the domain name into Common Generic Name.Working of DNS:- Whenever an application program calls a library procedure called‘Resolver’ with its domain name as parameter. The Resolver sends an UDP packet to the local DNS server. The DNS server searches its table and returns the IP address which matches the domain name. Now, the program can establish a connection or send UDP packets.
2. Explain Post Office Protocol (POP).
Ans- POP3 stands for Post Office Protocol version 3. It begins when a user starts the mailreader. The mail reader calls up the ISP and establishes a TCP connection with themessage transfer agent at port 110.Once the connection has been established, the POP3 protocol goes through three stages in sequence:
Authorization:- This state deals with the user log inTransactions:- This state deals with the user collecting e-mail messages and markingthem for deletion from the mailbox.
Update:- The update state causes the e-mail messages to be deleted. During the authorization state, at times, when the server is set for three passwords trials, if you givethe wrong password thrice, your mail box will get locked.
3. List out the advantages and disadvantages of WLAN.Ans-
Advantages :-
i) WLANs are more flexible. With in radio coverage, nodes cancommunicate without further restriction.
ii) Wireless network allow communication without previous planning.
iii) Wireless networks can survive in disasters.
Disadvantages:-
i) WLANs offer lower quality due to less bandwidth than wired
networks.
ii) WLAN adapter are very costly. Ex- PC-Card is available in the range from 100 pounds.
iii) WLANs are limited to low power senders and certain license-free frequency bands.
iv) Using radio waves for data transmission might interfere with other high-techequipment.
4. Explain conventional encryption model.
Ans- CONVENTIONAL ENCRYPTION MODELBefore the development of public key encryption, the conventional encryption (single-key encryption) was available to secure the networks. There are two types of encryption, classical encryption and modern encryption techniques. These are key based algorithms known as symmetric and public key algorithms.In conventional algorithms, the encryption key can be calculated from the decryption key. Alternatively, the decryption key can be calculated from the encryption key. In these algorithms, the encryption key and the decryption key are same.
5. Compare direct and indirect forms of routing.
Ans:-
Direct Routing: – It occurs when the source and destination of the packet are on same physical network. In direct routing the final destination of the packet is a host connected to the same physical network.In direct routing, the sender extracts the network address of the destination packet and compares this address with the addresses of the network to which it is connected. If match is found, then packet is delivered directly. The sender uses the destination IP address to find the destination physical address. ARP maps the address of final destination to its corresponding physical address.
Indirect Routing: – In an indirect delivery, the data packet goes from router to router until it reaches to its final destination connected to the same physical network.In an indirect routing, the sender uses the destination IP address and a routing table to find the IP address of the next router to which the packet should be delivered. ARP protocol is also used to find the physical address of next router. ARP maps the address of the next router and the physical address of the next router
(i) Substitution cipher,
(ii) Mono alphabetic cipher,
(iii) Play fair cipher,
(iv) Hill cipher, &
(v) Transposition cipher.
PART – B
1. a) Explain Open Shortest Path First (OSPF) routing protocol.
Ans:- Open Shortest Path First (OSPF) is a routing protocol developed for Internet Protocol (IP) networks by the Interior Gateway Protocol (IGP) working group of the Internet Engineering Task Force (IETF). The working group was formed in 1988 to design an IGP based on the Shortest Path First (SPF) algorithm for use in the Internet.
OSPF was derived from several research efforts, including Bolt, Beranek, and Newman’s (BBN’s) SPF algorithm developed in 1978 for the ARPANET (a landmark packet-switching network developed in the early 1970s by BBN), Dr. Radia Perlman’s research on fault-tolerant broadcasting of routing information (1988), BBN’s work on area routing (1986), and an early version of OSI’s Intermediate System-to- Intermediate System (IS-IS) routing protocol.
OSPF has two primary characteristics. The first is that the protocol is open, which means that its specification is in the public domain. The OSPF specification is published as Request For Comments (RFC) 1247. The second principal characteristic is that OSPF is based on the SPF algorithm, which sometimes is referred to as the Dijkstra algorithm, named for the person credited with its creation.
6. a) Explain internet security model.
Ans:- When two parties exchanging their information through internet. They need securityso that no one could access their information or messages. To accomplish it, a securitymodel will designed to protect the information transmission form an opponent who may present a threat to confidentiality. This technique has two components:–
i) A security-related transformation on the information to be sent.
ii) Some secret information shared by the two principals and it is hoped, unknown to the opponent.A third party is needed to achieve secure transmission Or a third party is needed to arbitrate dispute the two principals concerning the authenticity of a message transmission.Designing of Internet Security Model include following:-
i) Design an algorithm for performing the security-related transformation.
ii) Generate secrete information to be used with the algorithm.
iii) Develop methods for the distribution and sharing of the secret information.
iv) Specify a protocol to be used by the two principals that makes use of the security algorithm and the secret information to achieve a particular security service.
b) What is steganography ? Explain.
Ans:-Steganography :-
This is technique that hides the message in other messages. Thesender writes an innocuous message and then conceals on the same piece of paper. Somemethods of stenography are: -Character marking:- Selected letters of printed written text are over written in pencil.These marks are ordinarily not visible unless the paper is held at an angle to bright light.
Invisible inks :- A number of substances can be used for writing but leave no visible trace until heat or some chemical is applied to the paper.
Pin punctures:-Small pin punctures on selected letters are ordinarily not visible unless the paper is held up in front of a light.
Typewriter correction ribbon:- It is used between lines typed with a black ribbon, theresults of typing with the correction tape are visible only under a strong light.
The advantage of steganography is that the parties can employ the stenographer toreveal the secrecy of the message. It main disadvantage is that it requires a lot of overhead to hide few bits of information and once the system is discovered, it becomes useless without maintaining the secrecy.
7. Compare IEEE 802.11a, 802.11b, 802.11g WLAN architectures and blue tooth.
8. Write short note on :
a) Time out timer Ans- Time out timer is used to help purge invalid routes from a RIP node. Routes that arenot refreshed for a given period of time are likely to be invalid because of some change inthe network. Thus, RIP maintains a timeout timer for each known route. When a route’stimeout timer expires, the route is marked invalid but is retained in the table until theroute-flush timer expires.
b) CSMA/CA mechanism
Ans:- CSMA/CA is a network contention protocol that listens to a network in order toavoid collisions, unlike CSMA/CD that deals with network transmissions once collisionshave been detected. The basic mechanism is shown in following figure:
If the mechanism is sensed idle for at least the duration of DIFS, a node can access themedium at once. This allows for short access delay under light load.If the medium is busy, nodes have to wait for the duration of DIFS, entering a contention phase afterwards. Each node now chooses a random back off time with a contentionwindow and additionally delays medium access for this random amount of time.The additionally waiting time is measured in multiples of slots. Slots time is derived from the medium propagation delay, transmitter delay and other PHY dependent parameters.
c) Best effort service.
Ans:-
best effort service by which we can make several design decisions and employ afew tricks to improve the user-perceived quality of a multimedia networking application.Limitations of the best effort service are:
? Packet loss,
? Excessive end-to-end delay
? Packet jitter
