1. Chapter 3 Application Layer Functionality and Protocols
Paul Morris
CIS151
MHCC

2. Applications: Interface Between the Networks

3. Application Layer: OSI and TCP/IP Models
The Application layer, Layer seven, is the top layer of both the OSI and TCP/IP models.
Provides the interface between the applications we use to communicate and the underlying network.

4.
HTTP
HTTP
HTTP (www)
Application layer protocols are used to exchange data between programs running on the source and destination hosts.
There are many Application layer protocols and new protocols are always being developed.

5. Application Layer: OSI and TCP/IP Models
Functionality of the TCP/IP application layer protocols fit roughly into the framework of the top three layers of the:
OSI model: Application, Presentation and Session layers.
Most early TCP/IP application layer protocols were developed before the emergence of:
personal computers, graphical user interfaces and multimedia objects.
These protocols implement very little of the functionality that is specified in the OSI model Presentation and Session layers.

6. The Presentation Layer
The Presentation layer has three primary functions:
Coding and conversion of Application layer data to ensure that data from the source device can be interpreted by destination device.
Compression of the data in a manner that can be decompressed by the destination device.
Encryption of the data for transmission and the decryption of data upon receipt by the destination.
Compression and Coding formats:
Graphics Interchange Format (GIF)
Joint Photographic Experts Group (JPEG)
Tagged Image File Format (TIFF).

7. The Session Layer
Create and maintain dialogs between source and destination applications.
Handles the exchange of information to:
initiate dialogs
keep them active
restart sessions that are disrupted or idle for a long period of time
Most applications, like web browsers or clients, incorporate functionality of the OSI layers 5, 6 and 7.

8. Application Layer: OSI and TCP/IP Models
Note: Usually a single server will function as a server for multiple applications
Common TCP/IP Protocols
Domain Name Service Protocol (DNS) is used to resolve Internet names to IP addresses.
Hypertext Transfer Protocol (HTTP) is used to transfer files that make up the Web pages of the World Wide Web.
Simple Mail Transfer Protocol (SMTP) is used for the transfer of mail messages and attachments.
Telnet, a terminal emulation protocol, is used to provide remote access to servers and networking devices.
File Transfer Protocol (FTP) is used for interactive file transfer between systems.

9. RFCs: Request For Comments
The protocols in the TCP/IP suite are generally defined by Requests for Comments (RFCs).
Maintained by IETF (Internet Engineering Task Force)
There are a few in there for fun - ftp://ftp.rfc-editor.org/in-notes/rfc1882.txt.

10. Application Layer Software
User applications
Within the Application layer, there are two forms of software programs or processes that provide access to the network:
applications
services
Services
System Operations
Network-Aware Applications
Applications are the software programs used by people to communicate over the network.
They implement the application layer protocols and are able to communicate directly with the lower layers of the protocol stack.
Clients
Web Browsers

11. Application Layer Software
User applications
Services
System Operations
Application layer Services
Other programs may need the assistance of Application layer services to use network resources such as:
File transfer
Network print spooling
These services are the programs that interface with the network and prepare the data for transfer.

12. Application Layer Software
Application layer uses protocols that are implemented within applications and services.
Applications provide people a way to create messages.
Application layer services establish an interface to the network.
Protocols provide the rules and formats that govern how data is treated.
Bottom line:
When discussing an application like "Telnet" we could be referring to the application, the service, or the protocol.

13. Application Layer Protocol Functions
Application layer protocols are used by both the source and destination devices during a communication session.
The application layer protocols implemented on the source and destination host must match.
Protocols: (This will become clearer later! Herding cats.)
Establish consistent rules for exchanging data.
Specify the structure and type of messages that are exchanged.
Types: Request, response, acknowledgement, error message, etc.
Defines the dialogues, ensuring with transmissions met by expected responses, and with the correct service invoked.

14. Application Layer Protocol Functions
Applications and services can use multiple protocols.
Encapsulate the protocol or encapsulated by this protocol
Invoke other protocols
Using a web browser (HTTP):
May invoke:
DNS, ARP, ICMP
May use:
TCP, UDP, Ethernet, PPP
Uses IP

15. Client Server Model Client: the device requesting the information
Server: the device responding to the request is called a server.
The client begins the exchange by requesting data from the server.
Server responds by sending one or more streams of data to the client.
In addition to the actual data transfer, this exchange may also require control information, such as:
user authentication
the identification of a data file to be transferred

16. Servers
A server is usually a computer that contains information to be shared with many client systems.
Web server
server
File or database server
Applications server
Some servers may require authentication of user account information and vary permissions.
Example, if you request to upload data to the FTP server, you may have permission to write to your individual folder but not to read other files on the site.

17. Servers
The server runs a service, or process, sometimes called a server daemon.
Daemons (like other services) typically run in the background and are not under an end user's direct control.
Daemons are described as "listening" for a request from a client.
Programmed to respond whenever the server receives a request for the service provided by the daemon.
When a daemon "hears" a request from a client:
It exchanges appropriate messages with the client, as required by its protocol,
Proceeds to send the requested data to the client in the proper format.

18. Application Layer Services and Protocols
Servers typically have multiple clients requesting information at the same time.
For example, a Telnet server may have many clients requesting connections to it.
These individual client requests must be handled simultaneously and separately for the network to succeed.
The Application layer processes and services rely on support from lower layer functions to successfully manage the multiple conversations.

19. Application Layer Protocols

20. HTTP (WWW)
DHCP
(IP address resolution)
FTP
(file transfer)
DNS
(domain name resolution)
SMTP ( )
SMB
(file sharing)
P2P
Telnet
(file sharing)
(remote login)

21. Reminder of encapsulation/decapsulation
Data Link Header
IP Header
TCP Header
HTTP Header
Data Link Trailer
Data
Data Link Header
Data Link Header
Data Link Trailer
Data Link Trailer
IP Packet
IP Packet
Data Link Header
Data Link Header
Data Link Trailer
Data Link Trailer
IP Packet
IP Packet
Data Link Header
Data Link Header
Data Link Trailer
Data Link Trailer
IP Packet
IP Packet
Data Link Header
IP Header
TCP Header
HTTP Header
Data Link Trailer
Data

22. Focus on Application Header and/or Data
HTTP
HTTP
We will examine how the application (header) and/or data communication with each other between the client and the server.

23. HTTP (HyperText Transfer Protocol)
HTTP Client
HTTP Server
HTTP – The Web’s application layer protocol.
RFC 1945 and RFC 2616
Implemented in:
Client program
Server program
Current version: HTTP/1.1
Encapsulated in TCP

24. HTTP (HyperText Transfer Protocol)
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso " />
<title>Paul Morris, MHCC</title><style type="text/css">
<!--
body {
margin-left: 0px;
margin-top: 0px;
margin-right: 0px;
margin-bottom: 0px;
The base HTML file references other objects in the page.
CIS151
Web page (also called a html document)
Web page consists of objects
Objects (examples):
HTML file
JPEG image
GIF image
JAVA applet
Audio file
CIS152
CIS154

25. Web Browser - Client HTTP Client Browser – The user agent for the Web.
Displays requested Web page and provides navigational and configuration features.
Browser and client may be used interchangeably in this discussion.
HTTP has nothing to do with how a Web page is interpreted (displayed) by the client (browser).

26. Web Server
HTTP Server
Web Server – Stores web objects, each addressable by a URL.
Implement the server side of HTTP.
Examples:
Apache
Microsoft Internet Information Server

27. HTTP Request Message HTTP Server HTTP Client Request Message
GET /content.html / HTTP/1.1
Accept-Language: en-us
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; SLCC1; .NET CLR ; Media Center PC 5.0; .NET CLR ; InfoPath.1)
Host:
Connection: Keep-Alive
Some data omitted for brevity
HTTP Client
HTTP Server
Request Message
Request line
Header lines
ASCII Text
Request line: Method field
GET, POST and HEAD
The great majority of Requests are GETs

28. HTTP Request Message Request Line
GET /content.html/ HTTP/1.1
Accept-Language: en-us
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; SLCC1; .NET CLR ; Media Center PC 5.0; .NET CLR ; InfoPath.1)
Host:
Connection: Keep-Alive
Request Line
GET - Browser/client is requesting an object
/content.html / - Browser is requesting this object in this
directory (default is index.html)
HTTP/ Browser implements the HTTP/1.1 (1.1 is
backwards compatible with 1.0)
Note: HTTP GET is also used by some P2P applications like Gnutella and Bittorrent.

29. HTTP Request Message Request Line
GET /content.html/ HTTP/1.1
Accept-Language: en-us
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; SLCC1; .NET CLR ; Media Center PC 5.0; .NET CLR ; InfoPath.1)
Host:
Connection: Keep-Alive
Request Line
GET: - Used by browser/client to request an object.
POST: - Used when user has filled out a form and sending
information to the server. (Forms do not have to
use POST.)
- Example: words in a search engine
HEAD: - Similar to a GET, but the server will responds with a
HTTP message but leaves out the requested object.
PUT: - Used with Web publishing tools, upload objects.
DELETE: - Used with Web publishing tools, delete objects.

30. HTTP Request Message Header Lines
GET /content.html/ HTTP/1.1
Accept-Language: en-us
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; SLCC1; .NET CLR ; Media Center PC 5.0; .NET CLR ; InfoPath.1)
Host:
Connection: Keep-Alive
Header Lines
Accept-Language:- User prefers this language of the object
User-Agent: - The browser type making the request
Host: - Host on which the object resides
Connection: - Client/browser is telling the server to keep
this TCP connection Open, known as a
persistent connection.
- We will talk about this later in TCP
(transport layer)

31. HTTP Response Message HTTP Server HTTP Client HTTP/1.1 200 OK
Date: Fri, 22 Feb :34:18 GMT
Server: Apache/ (Red Hat)
Last-Modified: Thu, 15 Nov :33:12 GMT
Content-Length: 15137
Connection: close
Content-Type: text/html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "
<html xmlns="
Some data omitted for brevity
HTTP Client
HTTP Server

32. HTTP Response Message Response message: Status line Header lines
HTTP/ OK
Date: Fri, 22 Feb :34:18 GMT
Server: Apache/ (Red Hat)
Last-Modified: Thu, 15 Nov :33:12 GMT
Content-Length: 15137
Connection: close
Content-Type: text/html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "
<html xmlns="
Response message:
Status line
Header lines
Entity body

33. HTTP Response Message Status Line HTTP/1.1 – Server is using HTTP/1.1
HTTP/ OK
Date: Fri, 22 Feb :34:18 GMT
Server: Apache/ (Red Hat)
Last-Modified: Thu, 15 Nov :33:12 GMT
Content-Length: 15137
Connection: close
Content-Type: text/html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "
<html xmlns="
Status Line
HTTP/1.1 – Server is using HTTP/1.1
200 OK - Status code, request succeeded and information is
returned in response

34. HTTP Response Message Status Codes 200 OK
- Status code, request succeeded and information is returned in response.
301 Moved Permanently
- Requested object has been permanently moved.
400 Bad Request
- Generic error message, request not understood by server.
404 Not Found:
-The requested document does not exist on server.
505 HTTP Version Not Supported
- The requested HTTP protocol version not supported by server.

35. HTTP Response Message Header Lines Date: – Server is using HTTP/1.1
HTTP/ OK
Date: Fri, 22 Feb :34:18 GMT
Server: Apache/ (Red Hat)
Last-Modified: Thu, 15 Nov :33:12 GMT
Content-Length: 15137
Connection: close
Content-Type: text/html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "
<html xmlns="
Header Lines
Date: – Server is using HTTP/1.1
Server: - Status code, request succeeded and
information is returned in response
Last-Modified: – Date/time when object created or modified
Content-Length: – Number of bytes in object being sent
Connection: – Server going to close TCP connection after
sending the requested object.
Content-Type: – Object in entity body is HTML text

36. HTTP Response Message Entity Body
HTTP/ OK
Date: Fri, 22 Feb :34:18 GMT
Server: Apache/ (Red Hat)
Last-Modified: Thu, 15 Nov :33:12 GMT
Content-Length: 15137
Connection: close
Content-Type: text/html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "
<html xmlns="
Entity Body
<!DOCTYPE html PUBLIC etc.:
– HTML text and other objects to be used by the browser/client

37. HTTP Request and Response Messages
GET /content.html / HTTP/1.1
Accept-Language: en-us
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; SLCC1; .NET CLR ; Media Center PC 5.0; .NET CLR ; InfoPath.1)
Host:
Connection: Keep-Alive
HTTP
HTTP Server
HTTP
HTTP Client
HTTP/ OK
Date: Fri, 22 Feb :34:18 GMT
Server: Apache/ (Red Hat)
Last-Modified: Thu, 15 Nov :33:12 GMT
Content-Length: 15137
Connection: close
Content-Type: text/html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "
<html xmlns="

38. User-Server Interaction: Cookies
Web servers are considered stateless – they do not maintain state information, keep track of the user.
Higher performance – allowing the server to handle thousands of simultaneous TCP connections (later).
Web servers use cookies to track users.
Cookies defined in RFC 2109

39. User-Server Interaction: Cookies
HTTP Requests: GET (first time)
HTTP: Response Set-cookie: ID
HTTP Server
HTTP Requests (GET) now include ID
HTTP Client
Web server can now track clients activities on the web site.
Web server installs cookies on client when:
Accessed the web site for the first time (Web server does not know client by name.)
and/or
User provides information to the web server. (Web server now knows client by name.)
HTTP on Web server responds with a Set-cookie: header with an ID.
This ID is stored on the client’s computer.
Each time client/browser accesses web site. The GET includes Cookie: or User_ID or similar with the ID.

40. HTTP Request and Response Messages
GET /jpeg/cap81/cam rgb888.enc HTTP/1.1
<information omitted>
Cookie: SLSPOTNAME5=Cowells; SLSPOTNAME4=Waimea%20Bay; SLSPOTNAME3=Pipeline; SLSPOTNAME2=38th%20Ave%2E; SLSPOTNAME1=Cowells; SLSPOTID5=4189; SLSPOTID4=4755; SLSPOTID3=4750; SLSPOTID2=4191; SLSPOTID1=4189; OAX=R8bfwEbcU08ABCBu; USER_ID= <not my actual user-id>; <rest of informaton omitted for brevity>
HTTP: Cookie included
HTTP Server
HTTP data customized for Rick Graziani
HTTP Client
HTTP/ OK
Date: Fri, 22 Feb :00:15 GMT
Server: Apache/ (Unix)
Last-Modified: Fri, 22 Feb :51:47 GMT
ETag: "760a31-18ce-47bf19c3"
Accept-Ranges: bytes
Content-Length: 6350
Keep-Alive: timeout=15, max=257
Connection: Keep-Alive
Content-Type: text/plain <information omitted>

41. Web Caching Web Cache or Proxy Server Client Origin Server
HTTP Request
HTTP Request
Origin Server
HTTP Response
HTTP Response
HTTP Request
HTTP Request
Orgin Server
HTTP Response
Client
HTTP Response
Web cache or proxy server – Web cache satisfies HTTP requests on the behalf of the Origin Web server.
Own disk storage
Keeps copies of recently requested objects
Typically installed at ISP or larger institutions.
Advantages:
Reduces the response time for client requests, especially if there are any bottlenecks in the network.
Reduces traffic on institution’s access link to the ISP (Internet).

42. Web Caching Web Cache or Proxy Server Client Origin Server
HTTP Request
HTTP Request
Origin Server
HTTP Response
HTTP Response
HTTP Request
HTTP Request
Origin Server
HTTP Response
Client
HTTP Response
1. Client/browser sends HTTP Request to Web cache (Proxy server).
2. Web cache checks to see if it has a local copy of the object.
2a. Local copy: Web cache sends object to client’s browser.
2b. No Local copy: Web cache sends HTTP request to origin server.
3. Origin server sends object to Web cache.
4. Web cache stores a local copy of the object.
5. Web cache forwards copy of the object to the client browser.
Note: TCP connections are also created between Client and Web Cache; Web cache and Origin server (later).

43. HTTPS
HTTPS (Hypertext Transfer Protocol over Secure Socket Layer) is a URL scheme used to indicate a secure HTTP connection.
HTTPS is not a separate protocol
combination of a normal HTTP interaction over an encrypted:
Secure Sockets Layer (SSL) or
Transport Layer Security (TLS) connection

44. FTP (File Transfer Protocol)
FTP Client
FTP Server
FTP was developed to allow for file transfers between a client and a server.
Used to push and pull files from a server running the FTP daemon (FTPd).
Uses get and put commands.
RFC 959

45. FTP (File Transfer Protocol)
TCP control connection port 21
Username and password
Change directory on Server
TCP data connection port 20
Copy file from client to server – Connection Closed
TCP data connection port 20
Copy file from server to client – Connection Closed
TCP control connection port 21
Quit FTP Application – Connection Closed
Client initiates a TCP control connection with FTP server using port 21.
This connection remains open until the user quits the FTP application.
TCP port 21 connection includes:
Username and password is sent over TCP port 21.
Remote directory changes
This state information significantly reduces total number of sessions on server.
For each file transferred, TCP opens and closes a TCP data connection on port 20.
More later on TCP ports and connections.

46. SMTP – Simple Mail Transfer Protocol
– One of the killer applications of the Internet.

47. SMTP – Simple Mail Transfer Protocol
User agent
Mail server
Mail server
User agent
SMTP
SMTP
POP3 IMAP
Internet mail involves:
User agents
Allows users to read, reply, compose, forward, save, etc., mail messages
GUI user agents: Outlook, Eudora, Messenger
Text user agents: mail, pine, elm
Mail servers
Stores user mail boxes, communicates with local user agents and other mail servers.
SMTP
Principle application layer protocol for Internet mail
Sent over TCP
Mail access protocols: POP3, IMAP, HTTP

48. SMTP – Simple Mail Transfer Protocol
User agent
Mail server
Mail server
User agent
SMTP
SMTP
POP3 IMAP
SMTP
RFC 2821
Transfers messages from sender’s mail server to recipient’s mail server
Push protocol, not a pull protocol
Push (from client to server or server to server)
Pull (from server to client)
Retrieving
Historically, users would log into local mail server to read mail.
Since early 1990’s, clients use mail access protocols:
POP3
IMAP
HTTP

49. SMTP – Simple Mail Transfer Protocol
POP3 (Post Office Protocol)
RFC 1939
Limited functionality
Uses TCP port 110
Download-and-delete mode
Retrieves messages on server and store the locally
Delete messages on server
Download-and-keep mode
Does not delete messages on server when retrieved.
Problem
Difficult to access from multiple computers – work and home.
Some may have already been downloaded on another computer (work) – download-and-delete
To read from another computer, must leave on server – download-and-keep
Does not provide means for user to create remote folders on mail server

50. SMTP – Simple Mail Transfer Protocol
User agent
Mail server
Mail server
User agent
SMTP
SMTP
IMAP HTTP
IMAP (Internet Message Access Protocol)
RFC 2060
Mail not downloaded, but kept on server
Received is associated with user’s INBOX
Users can create and manage remote folders
Users can retrieve portions of the
Message header: Subject line and Sender
Web-based
Introduced with Hotmail in mid-1990’s
Communicates with remote mailbox using HTTP
HTTP is used to push (client to server) and pull the (server to client)

51. SMTP Mail software, processes used: MTA and MDA
receives from the client's MUA
passes to the MDA for final delivery
uses SMTP to route between servers
Mail software, processes used: MTA and MDA
MUA (Mail User Agent) – client software.
MTA (Mail Transfer Agent) – Software that governs transfer of between mail servers.
Includes UNIX sendmail, Microsoft Exchange Server, Postfix, and Exim
MDA (Mail Delivery Agent) – Software that governs transfer of from mail servers to clients.
On Unix systems, procmail and maildrop are the most popular MDAs.

52. Telnet Telnet Telnet Server
Telnet provides a standard method of emulating text-based terminal devices over the data network.

53. Telnet Telnet Telnet Server
Allows a user to remotely access another device (host, router, switch).
A connection using Telnet is called a Virtual Terminal (VTY) session, or connection.
Telnet uses software to create a virtual device that provides the same features of a terminal session with access to the server command line interface (CLI).
Telnet clients:
Putty
Teraterm
Hyperterm

54. Telnet Telnet supports user authentication, but does not encrypt data.
All data exchanged during a Telnet sessions is transported as plain text.
Secure Shell (SSH) protocol offers an alternate and secure method for server access.
Stronger authentication
Encrypts data

55. DHCP – Dynamic Host Configuration Protocol
IP addresses and other information can be obtained:
Statically
Dynamically (DHCP)

56. DHCP DHCP Information can include: IP address Subnet mask
Default gateway
Domain name
DNS Server
DHCP servers can be:
Server on LAN
Router
Server at ISP

57. DHCP
We will discuss DHCP more when we discuss IPv4.

58. DNS – Domain Name System
DNS allows users (software) to use domain names instead of IP addresses

59. Name Resolution Need the IP address Resolver
DNS client programs used to look up DNS name information.
Name Resolution
The two types of queries that a DNS resolver (either a DNS client or another DNS server) can make to a DNS server are the following:
Recursive queries
Queries performed by Host to Local DNS Server
Iterative queries
Queries performed Local DNS server to other servers

60. DNS Name Resolution User types http://www.example.com Step 1.
The DNS resolver on the DNS client sends a recursive query to its configured Local DNS server.
Requests IP address for "
The DNS server for that client is responsible for resolving the name
Cannot refer the DNS client to another DNS server.

61. DNS Name Resolution Step 2.3
DNS Name Resolution 1
Step 2.
Local DNS Server forwards the query to a Root DNS server.
Step 3.
Root DNS server
Makes note of .com suffix
Returns a list of IP addresses for TLD (Top Level Domain Servers) responsible for .com.

62. DNS Name Resolution Root DNS Servers
There are 13 Root DNS servers (labeled A through M)
TLD Servers
Responsible for domains such as .com, edu, org, .net, .uk, jp, fr
Network Solutions maintains TLD servers for .com
Educause maintains TLD servers for .edu
There are redundant servers throughout the world.

63. DNS Name Resolution Step 4.5
Step 4.
The local DNS server sends query for to one of the TLD servers.
Step 5.
TLD Server
Makes note of example.com
Returns IP address for authoritative server example.com (such as dns.example.com server)

64. DNS Name Resolution Step 6.7
Step 6.
Local DNS server sends query for directly to DNS server for example.com
Step 7.
example.com DNS server responds with its IP address for

65. DNS Name Resolution Step 8.7
Step 8.
Local DNS server sends the IP address of to the DNS client.
DNS Caching
When a DNS server receives a DNS reply (mapping hostname to an IP address) it can cache the information in its local memory.
DNS servers discard cached information after a period of time (usually 2 days)
A local DNS server can cache TLD server addresses, bypassing the root DNS servers in the query chain.

66. DNS Name Resolution
In the worst cases, you'll get a dialog box that says the domain name doesn't exist - even though you know it does.
This happens because the authoritative server is slow replying to the first, and your computer gets tired of waiting so it times-out (drops the connection) or the domain name does not exist.
But if you try again, there's a good chance it will work, because the authoritative server has had enough time to reply, and your name server has stored the information in its cache.

67. nslookup nslookup Displays default DNS server for your host
Can be used to query a domain name and get the IP address

68. DNS Name Resolution ipconfig /displaydns
After a certain amount of time, specified in the Time to Live (TTL) associated with the DNS resource record, the resolver discards the record from the cache.
ipconfig /flushdns – Manually deletes entries
The default TTL for positive responses is 86,400 seconds (1 day).
The default TTL for negative responses is 300 seconds.

69. (Missing Info) DNS:

73. SMB – Server Message Block Protocol
The Server Message Block (SMB) is a client/server file sharing protocol. IBM developed Server Message Block (SMB) in the late 1980s to describe the structure of shared network resources, such as directories, files, printers, and serial ports.

74. SMB Request-response protocol .
Unlike FTP, clients establish a long term connection to servers.
Client can access the resources on the server as if the resource is local to the client host.
SMB is sent over TCP
Prior to Windows 2000 windows used a proprietary protocol (NETBIOS) to send SMB.
Linux/UNIX have similar protocol: SAMBA

75. SMB SMB messages can: Start, authenticate, and terminate sessions
Control file and printer access
Allow an application to send or receive messages to or from another device

76. Peer-to-Peer (P2P) Networking and Applications
In addition to the client/server model for networking, there is also a peer-to-peer model.
Two or more computers are connected via a network and can share resources (such as printers and files) without having a dedicated server.
End devices (peers) can function as either a server or client.

77. P2P File Sharing
P2P (Peer-to-Peer) file sharing accounts for more traffic on the Internet than any other application (2004).
Peers (hosts) act as both clients and servers.
No centralized file server.
HTTP GET and responses are commonly used.

78. By Peter Svensson
The Associated Press
Oct. 19, 2007
“Peer-to-peer applications account for between 50 percent and 90 percent of overall Internet traffic, according to a survey this year by ipoque GmbH, a German vendor of traffic-management equipment.”

79. P2P – Centralized Directory
Peer
1 – Inform and Update
Peer
Centralized Directory Server
1 – Inform and Update
Peer
1 – Inform and Update
3 – File Transfer
1 – Inform and Update
Peer
2 – Query for content
Napster
Challenge with P2P – locating content across thousands or millions of peers.
One solution – centralized directory
Approach done by Napster
Problems (non-legal problems)
Single point of failure
Performance bottlenecks

80. P2P – Centralized Directory
Peer B
1 – Inform and Update
Peer
Centralized Directory Server
1 – Inform and Update
Peer
1 – Inform and Update
3 – File Transfer
1 – Inform and Update
Peer A
2 – Query for content
1. Peer A starts P2P application
2. Informs centralized directory server of its:
IP address
Names of objects making available for sharing (MP3, videos, etc.)
3. Directory server collects information from each peer that becomes active.
Dynamic database
Maps IP addresses with object names
4. Peer A queries directory server for IP addresses of other peers for specific content
Directory Server returns IP addresses for those peers (Peer B)
5. Peer A establishes TCP connection and downloads file (i.e. HTTP GET) from other peer, Peer B.
6. Directory server removes Peer from database when Peer closes application or disconnects from Internet (periodic messages – pings – from server).

81. P2P – Query Flooding Gnutella
Query hit
Peer B
Peer C
Query hit
File transfer
Query
Query
Peer A
Peer D
Peer E
Query
Query hit
Peer F
Gnutella
Gnutella – public domain file sharing application
Fully distributed approach
No centralized server
Gnutella peer maintains peering relationship (TCP connection – later) which a number of other peers (usually fewer than 10).

82. P2P – Query Flooding Peer A searches for a file
Query hit
Peer B
Peer C
Query hit
File transfer
Query
Query
Peer A
Peer D
Peer E
Query
Query hit
Peer A searches for a file
1. Peer A sends query to all neighboring peers.
2. If neighboring peer does not have file, forwards query to all its neighboring peers
3. If any peer has the file it returns a query hit message.
4. Peer A selects a peer, Peer C, to retrieve file (HTTP GET)
5. A direct TCP connection is made with selected peer, Peer C.
6. HTTP response is used to send file.
Query Flooding
Non-scalable and causes a significant amount of traffic on Internet.
Gnutella modified it to limited-scope flooding which limits how many peers away the query is sent to, usually 7 to 10. (similar to TTL – later).
Peer F

83. P2P – Query Flooding How a peer joins and departs Gnutella network
Query hit
Peer B
Peer C
Query hit
File transfer
Query
Query
Peer A
Peer D
Peer E
Query
Query hit
How a peer joins and departs Gnutella network
1. Finding peers:
Bootstrap program: Client maintains a list of peer IP addresses who are usually up
Contact Gnutella site that maintains a list
2. Client attempts to make contact with peers (TCP connection – later)
3. Client sends Gnutella ping message to peer.
Forwards Gnutella ping to other peers, who continue to forward ping until limited-scope is reached.
4. Each peer returns a Gnutella pong message including:
Its IP address
Number of files it is sharing
Total size of the files
Peer F

84. P2P - Combination Kazaa Kazaa combines ideas from Napster and Gnutella
2004 – Contributed to more traffic on Internet than any other application
2007 – Bittorrent became the leading application
Proprietary technology

85. P2P - Combination Kazaa does not use a centralized server
Group Leader
Group Leader
Query
Group Leader
Query
Query
Query Reply
File Transfer
Kazaa does not use a centralized server
Group leader peers (parent)
Higher bandwidth and Internet connectivity
Greater Gnutella responsibilites
Peers (child) – non-group leaders
Child peer establishes TCP connection with a group leader
Group leader:
maintains database directory of child peers including their IP addresses
maintain TCP connections with other group leaders
Child peers query group leaders who forward the query to other group leaders
Child peer selects peer for TCP connection and file transfer

86. Chapter 3 Application Layer Functionality and Protocols
Paul Morris
CIS151
MHCC