The copperbelt university
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BBF221 FINAL CA - FT
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- [2 marks] Consider the TCP connection mechanism. i. What mechanism is used to set up a TCP connection [1 mark]
| QUESTION THREE
Briefly explain how the Domain Name Service (DNS) is implemented and how DNS queries are resolved in the DNS system. [3 marks] Why is datagram fragmentation not an issue in IPv6? How is this achieved? [2 marks] What is the role of the transport layer in the 5 layer TCP/IP protocol stack? [3 marks] Describe the functionality provided by the Transmission Control Protocol (TCP) [2 marks] Consider the TCP connection mechanism. i. What mechanism is used to set up a TCP connection? [1 mark] ii. Why is the mechanism needed? [2 marks] iii. Outline how the mechanism works. [3 marks] Compare and contrast the application protocols SMTP and HTTP. [5 marks] ANSWER The Domain Name System maps names to IP addresses. It is a distributed database implemented in hierarchy of many name servers has an application-layer protocol for host, routers, and name servers to communicate to resolve names. There are 13 root servers; it is broken into zones containing primary and secondary name servers. In a recursive query, a DNS resolver queries a single DNS server, which may in turn query other DNS servers on behalf of the requester. For example, a simple stub resolver running on a home router typically makes a recursive query to the DNS server run by the user's ISP. A recursive query is one for which the DNS server answers the query completely by querying other name servers as needed. In typical operation, a client issues a recursive query to a caching recursive DNS server, which subsequently issues non-recursive queries to determine the answer and send a single answer back to the client. The resolver, or another DNS server acting recursively on behalf of the resolver, negotiates use of recursive service using bits in the query headers. DNS servers are not required to support recursive queries. The iterative query procedure is a process in which a DNS resolver queries a chain of one or more DNS servers. Each server refers the client to the next server in the chain, until the current server can fully resolve the request. For example, a possible resolution of www.example.com would query a global root server, then a "com" server, and finally an "example.com" server. IPv6 cannot allow fragmentation at routers, the transmitter creates datagrams of the maximum transmission unit. ICMP v6 tells the source what the max transport unit (mtu) of the path is. Transports data units from application layer, using network layer services. Provide logical communication between application processes running on different hosts. Transport protocols run in end systems sender side: breaks application messages into segments, passes to network layer receiver side: reassembles segments into messages, passes to application layer. Point-to-point, connection oriented, full duplex, reliable, in-order byte steam, with pipelining and flow control features. i. 3 way handshake ii. overcomes issue of duplicate connection requests and spurious data packet delivery can be rejected iii. Diagram: HTTP = pull SMTP = push Both use ASCII based command/response interactions and status codes Both typically have a header plus a body for content. Both use TCP connections. HTTP = each object encapsulated in its own response message, identifying the encoded object SMTP = multiple objects sent in a multi-part message, uses MIME (multimedia extensions) for message encoding SMTP – pushes message from client to SMTP server, email message contains list of recipients: user@destination, server delivers mail to remote (destination) server, client polls server to receive email. HTTP – user selects content identified by URL, which identifies the server on which it is located. Server responds with requested content. Server may tailor content to browser/user. Download 290.5 Kb. Share with your friends:
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