Chapter 2 Network Standards
In what field is the IP packet carried in Ethernet II frames?
Data field.
At what layer will you find standards for switches?
Data link layer and physical layer.
At what layer will you find standards for wireless access points?
Data link layer and physical layer.
At what layer will you find standards for EUI-48 addresses?
Data link layer.
At what layer will you find standards for data links?
Data link layer.
At what layer will you find standards for frames?
Data link layer.
What type of port numbers do clients use when they communicate with server programs?
Ephemeral port numbers.
What is the definition of a trailer?
Everything that comes after the data field.
What is the definition of a header?
Everything that comes before the data field.
What are the four steps in the four-way close?
FIN, ACK, (perhaps additional data segments and ACKS from the other side), FIN, and ACK.
How is the syntax of Ethernet II frames depicted?
Fields are shown one below the other, not 32 bits on a line. They are shown by their field size in octets
What are 1-bit fields called?
Flag fields.
11. datagram
Generic name for a message in a connectionless protocol.
What are the three general parts of messages?
Header, data field, trailer.
9. message syntax
How messages are organized.
What is the syntax of a socket?
IP address, colon, port number.
Is IP a connectionless or connection-oriented protocol?
IP is connectionless. There are no openings, closings, or sequence numbers.
What are the standards agencies for OSI? Just give the abbreviations.
ISO and ITU-T.
Distinguish between ISO and OSI.
ISO is a standards agency. OSI is an architecture.
Under what conditions will a source host TCP process retransmit a segment?
If it does not receive and acknowledgment quickly.
If someone says that a flag field is set, what does this mean?
If it is sent, it has the value 1. If it is not set, it has the value 0
Distinguish between standards and protocols.
In this book, we will use these terms as equivalent.
Describe the three-step opening in TCP.
Initiator sends SYN segment Other side sends SYN/ACK segment. Initiator sends an ACK segment.
What is the standards agency for TCP/IP? (Give both the name and the abbreviation.)
Internet Engineering Task Force (IETF).
At what layer will you find standards for IP addresses?
Internet layer.
At what layer will you find standards for packets?
Internet layer.
At what layer will you find standards for routes?
Internet layer.
What does it do if it does not find an error?
It accepts the packet. No response is sent.
8. TCP segments
A TCP message.
16. octet
A collection of 8 bits; same as a byte.
Is IP reliable or unreliable? Explain.
It is unreliable. It does error checking and discarding if it finds an error. However, it does not do packet retransmission if it finds an error.
At which layers of this architecture are IETF standards dominant?
At the internet and transport layers.
At which layers are ISO and ITU-T standards dominant?
At the physical and data link layers.
What factors in the Internet's informal development process lead to rapid standards development and low-cost products?
Beginning with simple standards. Rough consensus and running code avoid many delays
18. ASCII
Code for representing all American keyboard characters plus some control codes.
17. encoding
Converting messages into bits.
What is encoding?
Converting various types of information—text, numbers, voice, images, etc. into binary.
How does the receiving data link layer process know what is in the data field of an Ethernet II frame?
It looks at the EtherType field.
Describe how the internet process checks an arriving packet for errors.
It simply discards the packet. No response is sent.
What does the receiving internet process do if it finds an error?
It simply discards the packet. No response is sent.
Why aren't all protocols reliable?
It would require extreme total processing power. <Just making TCP reliable catches errors at lower layers.>
What is alphanumeric information?
Limited view: digits (0-9) and letters. Typical: all keyboard characters.
What are the benefits of standards?
Lower cost by permitting competition Innovation beyond the standard to avoid commodity product prices
What is noteworthy about control segments?
TCP control segments only have headers.
What do we call TCP messages?
TCP segments.
What layer or layers govern(s) transmission through the Internet?
TCP/ IP.
If the ACK bit is set, what other field must have a value?
The Acknowledgement Number Field.
What standards architecture do most organizations actually use in practice?
The Hybrid TCP/ IP-OSI Standards Architecture.
What other two standards agencies work together to create network standards?
The International Organization for Standardization (ISO) and the International Telecommunications Union-Telecommunications Standards Sector (ITU-T).
What standards agency creates Internet standards?
The Internet Engineering Task Force (IETF)
Why does this version of the book deal with Ethernet II frames?
The Internet Protocol calls for I P packets to be carried inside Ethernet Ⅱ frames.
What is interoperability?
The ability to work together.
At what layer is the encoding of application messages done?
The application layer. <In OSI, it is done at the presentation layer>
19. binary
The base two counting system where 1s and 0s used in combination can represent whole numbers (integers).
In HTTP, which application program initiates an interaction?
The browser.
How are ephemeral port numbers generated?
The client generates an ephemeral port number randomly for each conversation.
15. socket
The combination of an IP address and a port number, designating a specific connection to a specific application on a specific host. It is written as an IP address, a colon, and a port number, for instance, 128.171.17.13:80.
What higher-layer content does the data field contain?
The content being delivered.
12. port number
The field in TCP and UDP that tells the transport process what application process sent the data in the data field or should receive the data in the data field.
Distinguish between headers and header fields.
The header is everything that comes before the data field. The header is subdivided into header fields, for example source and destination address fields.
To what does a standards layer provide services?
The layer immediately above it.
7. connection-oriented protocol
Type of conversation in which there is a formal opening of the interactions, a formal closing, and maintenance of the conversation in between.
What is the range of port numbers for each type of port?
Well-Known: 0-1,023 Ephemeral: 1024-4999
What type of port numbers do servers use for common server programs?
Well-known port numbers.
Can a single TCP segment both send information and provide an acknowledgment?
Yes.
Is 4,307 an integer?
Yes.
Is HTTP a connectionless protocol?
Yes.
Is TCP connection-oriented or connectionless?
Yes.
What layer or layers govern(s) application programs?
Application.
Why are they called ephemeral?
At the end of the conversation, they are discarded.
List the first bit number on each IPv4 header row in 2-12, not including options. (Remember that the first bit in Row 1 is Bit 0.)
0, 32, 64, 96, 128.
How many alternatives can you represent with a 4-bit field? (Answer: 1)
1
If you need to represent 18 alternatives in a field, how many bits long must the field be?
1,024.
Convert 62 to binary.
111110.
ASCII has a 7-bit code. How many keyboard characters can it represent?
128
What is the bit number of the first bit in the Destination IP Address Field in IPv4?
128.
Convert the binary number 1111 to decimal.
15
Convert the binary number 10110 to decimal.
22
How many segments are transmitted to open a connection?
3.
Convert the binary number 100 to decimal.
4
If every host and router connects with a point-to-point connection, how many physical links will there be?
5.
In TCP, port number fields are 16 bits long. How many possible port numbers are there?
64,536.
2. Request For Comments (RFC)
A document produced by the IETF that may become designated as an Official Internet Protocol Standard.
4. Standard Architectures
A family of related standards that collectively allows an application program on one machine on an internet to communicate with another application program on another machine on the internet.
10. flag fields
A one-bit field.
6. connectionless protocol
A protocol in which there is no enduring communication session between two devices. Messages are sent individually with no prior agreement to communicate.
1. Network Standards
A rule of operation that governs the exchange of messages between two hardware or software processes.
What is an integer?
A whole number (as opposed to a decimal number).
What kind of message does the destination host send if it receives an error-free segment?
ACK segment.
3. Standard Agencies
An organization that creates and maintains standards.
What is a network standard?
Network standards are rules of operation that specify how two hardware or software processes work together by exchanging messages.
Is there always a data field in a message?
No, but there is always a header.
If you change a standard at one layer, do standards at other layers need to be changed?
No.
Is 47 an integer?
No.
Is HTTP a reliable protocol?
No.
UDP does error detection and discarding but does not do the retransmission of damaged or lost datagrams. Is UDP reliable? Explain.
No. Both error checking and error correction are needed for reliability.
When the side that initiates the close sends its FIN segment, does it stop transmitting more TCP segments? Explain.
No. It still sends ACKs.
Is every TCP segment acknowledged?
No. Only if it is correctly received. Pure SYNs are not acknowledged.
Are trailers common?
No. They are only found at the data link layer, and not always there.
What kind of message does the destination host send if it does not receive a segment during a TCP connection?
Nothing.
What kind of message does the destination host send if it receives a segment that has an error during a TCP connection?
Nothing.
What layer or layers govern(s) transmission through a single network?
OSI.
What protocols that we saw in this chapter are reliable?
Only TCP.
Do SYN segments have data fields?
Only headers.
What layer or layers govern(s) transmission media?
Physical.
What are IETF standards called? (Spell out the name and give the acronym.)
Requests for Comments (RFCs).
13. well-known port numbers
Standard port number of a major application that is usually (but not always) used. For example, the well-known TCP port number for HTTP is 80. Range from 0 through 1023.
14. ephemeral port number
The temporary number a client selects whenever it connects to an application program on a server. According to IETF rules, these should be between 49153 and 65535.
Why may it be advantageous to change a standard if the standard at the layer below it is upgraded?
The upgrade might provide useful functionality that can only be exploited with an upgrade at the layer receiving services.
Why is Ethernet unreliable despite having a Frame Check Sequence Field that is used to check for errors?
There is error detection and discarding. There is no retransmission, which is needed to fix errors.
Why does it usually not matter what standards agency creates an application layer standard?
They can nearly all run over TCP.
Why are sequence numbers good?
They permit segments to be put in order if they arrive out of order. Unique sequence numbers create unique Acknowledgement Numbers.
What benefits do sequence numbers bring?
They permit segments to be reordered if they arrive out of order. They permit specific segments to be acknowledged.
Why do standards architectures have multiple layers?
This permits division of labor in standards development, with each layer's standards developed by experts at that layer.
What is the purpose of the Acknowledgment Number Field?
To indicate which segments is being acknowledged.
What layer or layers govern(s) application message fragmentation?
Transport.
8a.) If two hosts are connected by five networks, how many packets will there be when one host sends a packet to the other host? (Hint: draw a picture.) 8b.) How many frames? 8c.) How many routers?
a.) 1 b.) 5 c.) 4
a.) What are the four fields in a UDP header? b.) Describe the third. c.) Describe the fourth.
a.) Source port number Destination port number. UDP length UDP checksum b.) It gives the length of the UDP datagram. c.) It checks for errors in the entire UDP datagram. If there is an error, the UDP datagram is discarded.
a.) Which standards agency(ies) is(ar especially important for internet processes? b.) For physical transmission processes? c.) For data link processes? d.) For transport processes? e.) For Internet supervisory processes?
a.) The IETF. b.) ISO and the ITU-T. c.) ISO and the ITU-T. d.) IETF. e.) IETF.
