From Slides Flashcards

1
Q

TCP/IP Layer Schematic

A
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2
Q

Types of servers

A
  • File Server
  • Print Server
  • Communications Server
  • Telephony Server
  • Fax Server
  • Web Server
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3
Q

SNMP

A

Simple Network Management Protocol

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4
Q

Symbolic Name

A

Names that users are familiar with, like john.doe@brooklyn.edu

www.google.com

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5
Q

Directory Services

A

Used to find the addresses of a named destination user:

convert email or URL to IP address, NPA address, or TCP/UDP port #

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6
Q

Domain Name System (DNS)

A

Total directory system in a TCP/IP suite

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7
Q

Original 6 high-level domains

A

com, edu, gov, mil, net, org

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8
Q

Domain Name Server

A
  • Associated with each institution network is a host that runs an AP known as the Domain Name Server.
  • Associated with the DNS server is a Directory Information Base (DIB) which contains all thedirectory related information for that institution.
  • Each host has a client process known as the Name Resolver which communicates the DNS server
  • Name resolver can cache some symbolic - IP mappings, if it doens’t find then it goes to DNS over TCP/IP
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9
Q

Foreign name server

A

DNS server outside of the autonomous network (?) that is queries if the local name server cannot resolve the current DNS name

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10
Q

DNS Referral

A

If the destination is not listed within the DIB, the local
DNS server creates its own request message (a
referral) which it forwards to another server.

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11
Q

DNS Resolvers: TCP vs. UDP

A

Resolvers use UDP for single queries and TCP for
group queries. (why??)

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12
Q

Recursive vs. Iterave DNS resolution techniques

A
  1. Recursive Technique:
    Query another name server for the desired result
    and then send the result back to A.
  2. Iterative Technique:
    Return to A the address of the next server (C) to
    whom the request should be sent. A then sends
    out a new DNS request to C.

In exchanges between name servers, either the
iterative or recursive technique may be used. For
requests sent by a name resolver , the recursive
technique is used. (Resolver doesn’t go out to the internet, just communicates with DNS server)

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13
Q

Name
Cache

A

Typically, each local name server will maintain a Name
Cache of the most recently referred names.

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14
Q

DNS Message Format

A
  • Identifier:

Assigned by that sender so that it can match queries
and responses.
• Query Response:
Indicates whether this message is a query or
response.
• Opcode:
- standard query,
- an inverse query,
- a server status request.
• Authoritative Answer:
if responding name server is an authority
• Truncated:
if response message was truncated due to length
• Recursion Desired:
If set, directs the server to pursue the query
recursively.
• Recursion Available:
if recursive query support is available
• Response Code:
- no error,
- format error,
- server failure,
- name error,
- not implemented,
- refused
• Qdcount, Ancount, Nscount, ARcount:
number of RRs in the question/ answer/ authority/
additional records section (zero or more).

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15
Q

DNS Question Section Format

A

Query Type: the type of question (e.g.,whether the question refers to a machine name or a mail address).

**QUERY CLASS** specifies the class of the query,
 typically Internet (**IN**)

Query types in image

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16
Q

NVT

A

Nework Virtual Terminal - common paradigm so client and server stations can talk to each other. An NVT is an imaginary device with a well-defined set of characteristics. Using the VTP, aconnection is set up between a terminal user and a remote host. Both sides generate data and control signals in their native language. Each side translates its native data and control signals into those of the NVT and translates incoming NVT traffic into its native data and control signals. Normally, all data is transferred as 7-bit ASCII character strings.

Option requests can be initiated by either side using
WILL, WON’T, DO and DON’T commands.

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17
Q

TELNET

A

allows remote access to a station

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18
Q

Original ARPANET TELNET

A

Dumb terminals needed to gain access to remote servers

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19
Q

VTP Concept

A

Phases of operation (uses TCP)

Connection management:
- Connection request and termination
- Telnet uses TCP
! Negotiation:
- To determine a mutually agreeable set of
characteristics
- NVT has a wide range of capabilities and features
- Real terminal is more limited
- NVT has options, such as line length
! Control:
- Exchange of control information and commands
e.g., end of line, interrupt process
! Data:
- Transfer of data between two correspondents

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20
Q

Principles of TELNET Options Negatiation

A

! Either side can initiate negotiation

! Can ask that an option be enabled or that a currently
enabled option be disabled.

! A request to enable an option may always be rejected.

! A request to disenable an option must always be
accepted.

! Options are not enabled until the negotiation is
complete.

! Never negotiate about something that is already true

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21
Q

TELNET Negotiation messages

A

Examples:

IAC, SB, WILL (DO), ‘0’, SE (send in 8-bit binary)
IAC, SB, DO (WILL), ‘0’ SE (accept)
IAC, SB, DON’T (WON’T), ‘0’ SE (refuse)
(Note: parentheses indicate receiver initiated option
negotiation)

IAC: Begins command sequence

SB: Begins options negotiation string

SE: End option negotiation string

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22
Q

FTP

A

provides access from a client to a remote file
server across a TCP/IP internet connection

Uses TWO TCP/IP connections: Data and Control

23
Q

FTP Options

A

! FTP assumes files are objects in mass storage:
- Files share some properties regardless of machine
- Files are uniquely identified by symbolic names
- Files have owners and protection mechanisms
against unauthorized access
- Files may be created, read from (copied from),
written into, or deleted (within protection rules)

! To support specific computers and operating systems,
FTP can negotiate options in three dimensions:
- Data type,
- File type,
- Transfer mode

! Systems programmer on each system determines:
- How a particular file can be mapped to a standard
file type using one of the standard data types,
and transferred using a standard mode such that
it is useful at the destination.

24
Q

4 Data Types supported in FTP

A
  • ASCII (most common, for text files)
  • EBCDIC (only appropriate if both machines are IBM hosts)
  • Image (bit by bit replication, useful for arbitrary files between similar machines with same operating systems)
  • Logical byte size (specifies byte size other than 8 bits, useful for executable files that have to be interpreted on the new machine)
25
3 File Types used in FTP
File Structure (most common, assumes that file is a string of bytes, terminating with EOF marker) Record Structure (useful for checkpointing and error detection -- file is treated as a stream of records, separated by standards End of Record market) Page Structure (used for files not stored contiguously on disk, wher page structure needs to be maintained)
26
3 FTP transmission modes
Modes used to optimize the use of the network 1. Stream mode (default): least burdensome, no restriction on file type 2. Block mode: allows restarting of failed or interrupted transfer. Has a descriptor that can indicate: last block in a record, last block in file, suspect data, restart marker 3. Compressed Mode: allows source to squeeze sequences of same character into a shorter coded sequence
27
TFTP
Uses UDP Uses Stop-and-Wait protocol for file transfer (as opposed to sliding window, every message has to be acknowledged) Data blocks are all 512 octets, except last byte Only 5 Message types
28
SMTP Spooling Area
intermediary between email applications and SMTP message sending
29
Mail handler/email gateway/forwarder/exploder
Server creates mailboxes for incoming mail, users access this
30
Post Office Protocol (POP)
POP allows a user's mailbox to reside on a computer that runs a mail server. A mail server accepts a messages from an arbitrary sender, while the POP server only allows a user access to their mailbox only after the user enters authentication information.
31
SMTP Limitations
* SMTP cannot transmit binary files. * SMTP is limited to 7-bit ASCII textual data * SMTP servers reject mail messages over a certain size * SMTP gateways that translate between ASCII and EBCDIC do not use a consistent set of mappings
32
MIME content types
* text * multipart (generally used for executables) * ...
33
URL
Uniform resource locator
34
HTTP
* Protocol for transmitting info with the efficiency necessary for making hypertext jumps * Transaction-oriented, client-server * Uses TCP * Stateless: each transaction is treated independently (since each connection accesses a different server, more efficient to stop old connection)
35
URI
Uniform resource identifier - generic WWW identifier. More general than URL, which designates access protocol and specific internet address
36
HTTP Proxy
Security intermediary on client side of firewall Determines whether the origin server is safe, if so, delivers requests via authenticated connection Acts as both a server (to the orginal requesting user) and a client (to the internet)
37
HTTP Gateway
Security intermediary on the server side of a firewall Receives HTTP requests, determines whether they should be sent out to the internet Non-HTTP server
38
HTTP Tunnel
Relay point between two TCP connections External server can establish and maintain an authenticated connection for HTTP transactions Once tunnel is established, the tunnel is not actively filtering requests (Servers cannot use cache when they are acting as a tunnel)
39
HTTP Message Fields
Request Line: Identifies the message type and the requested resource. Request-Line= Method SP Request-URL SP HTTP-Version CRLF Status Line: Provides status information about this response. Status-Line= HTTP-Version SP Status-Code SP Reason-Phrase CRLF General-Header: Contains fields that are applicable to both request and response messages, but which do not apply to the entity being transferred. Request-Header: Contains information about the request and the client. Response-Header: Contains information about the response. Entity-Header: Contains information about the resource identified by the request and information about the entity body. Entity-Body: The body of the message.
40
HTTP General Header Fields
Cache-Control Connection Date Forwarded Keep-Alive MIME-Version Pragma Upgrade
41
HTTP Request Methods
Options Get Head Post Put Patch Copy/Move Delete
42
HTTP Request Header Fields
Function as request modifiers Accept Accept-Charset Accept-Encoding Accept-Language Authorization From Host
43
HTTP Entity Header Fields
Provides optional information about the entity body or if no body is present, about the resource identified by the request.
44
Jitter
Inter-arrival delay between packets
45
Time delay buffer
Compensates for jitter, ensures that VOIP packets arrive at the right pace
46
Continuous data source
Fixed-size packets are generated at fixed intervals. This characterizes applications that are constantly generating data, have few redundancies, and that are too important to compress in a lossy way. Examples are air traffic control radar and real-time simulations
47
On/off source:
The source alternates between periods when fixedsize packets are generated at fixed intervals and periods of inactivity. A voice source, such as in telephony or audio conferencing, fits this profile.
48
Variable packet size
The source generates variable-length packets at uniform intervals. An example is digitized video in which different frames may experience different compression ratios for the same output quality level.
49
Soft real-time applications
- can tolerate the loss of some portion of the communicated data. - impose fewer requirements on the network - focus on maximizing network utilization, even at the cost of some lost or misordered packets.
50
Hard real-time applications
- have zero loss tolerance. - a deterministic upper bound on jitter and high reliability take precedence over network utilization considerations.
51
SIP
Application-level protocol, for setting up, modifying, and terminating real-time sessions between participants over an IP data network Generally runs over UDP Connection-oriented supports single-media and multimedia sessions including teleconferencing
52
5 facets of SIP communications
User location User availability User capabilities (media and media parameters) Session setup Session managememt
53