INFO (revision 305)

Line	Revision	Contents
1	27	Interested parties about FSP please email
2		to Radim Kolar
3	161	hsn at sendmail.cz
4	27	visit our homepage on
5		http://fsp.sourceforge.net/
6		and join us!
7
8		For more than 7 years benefits of FSP protocol were unnoticed
9		and FSP software was not maintained...
10
11		FSP today
12	105
13	27	Written by Radim Kolar
14
15	105	Protocol related
16
17		FSP uses UDP datagrams and it is reliable even when there is
18		high number of packet loss. It is usable on WiFi network with
19	276	60%-80% packet loss.
20	277
21	105	FSP can very quickly addapt to changing line condition. This
22	277	is excelent for wireless packet networks where network condition
23		changes wildly based on receiver location and disturbance.
24		Unlike TCP based protocols, FSP has a fast restart when
25		line condition improves - It do not needs any RTT for retuning
26		self. FSP goes immediatly back to maximum possible speed.
27	105
28		Maximum FSP speed is by design lower than maximum speed of TCP
29		based protocols because it has only 1 packet in the network.
30		TCP protocol has about 3 packets. Design of FSP protocol
31		makes impossible to send more than 1 packet into network.
32	279	This is nice method for bandwidth protection, better handling
33		traffic spikes and for sever protection against denial of
34		service attacks on server.
35	105
36		FSP server do not sends any data out unless is asked for. This
37		solves problem with transfering duplicate data when using TCP
38		protocol on overloaded lines. About 30% are dupes, thrown out
39		by client. Note: TCP stacks from BSD family has this dupe
40		ratio much lower.
41
42		Embedded devices
43
44		FSP protocol is very easy to implement; client core has about
45		one page of C code. It is ideal for embedded devices for
46		file-transfer tasks, like firmware downloading. Because of its
47		simplicity, there is a little chance to writing buggy
48		implementation.
49
50	278	FSP is also good for remote booting. It is simplier, faster
51		and more reliable than TFTP and supports directory listings.
52	105
53		FSP protocol can be used as wire-protocol even without using
54		any layer 2 stuff. It operates in degraded mode with extra
55		features disabled.
56
57	280	Stealth operation
58	105
59		UDP ports are not often port scanned today, only one exception
60		is scanning for Windows/Samba file sharing service. Nobody
61		will notice that you are running a fsp server.
62
63		FSP uses UDP which is unnoticed by many firewalls. FSP server
64		runs on 21 port by default, if you move it to port 53 (dns)
65		even strictly configured firewall can be worked around.
66
67		You want to run anonymous archive and want to keep lamers out.
68
69	280	Busy sites
70
71	105	You want to share something without ruining your valueable
72	280	bandwidth or latency. FSP protocol is slower than TCP based
73		protocol it means that more bandwith will be left for your own use.
74		Important point is that starting data sharing via FSP do not
75		considerably raises your network latency because FSP can
76		have just 1 packet floating in network. In ideal condition you will
77		not notice increased latency at all.
78	105
79	280	You have overloaded archive site. It is historicaly proven fact
80		that FSP handles overloaded lines or sites better than anything else.
81		FSP is very suitable for distributing updates to very large number
82		of subscribers because it can easily handle traffic spikes without
83		breaking connections and it can be very easily distributed between
84		multiple servers because it is more or less connectionless.
85	105
86		You do want to share large data files (movies, ISO images) on
87		slow (or you do not want to waste valuable bandwidth) lines.
88		Ideal for sharing files on modem lines.
89	27
90		FSP daemon is a very light server.
91	105
92	27	What is the purpose of FSP (V2.8.1):
93	105
94	27	Written by A.J.Doherty@reading.ac.uk
95
96		FSP is a set of programs that implements a public-access archive
97		similar to an anonymous-FTP archive. It is not meant to be a
98		replacement for FTP; it is only meant to do what anonymous-FTP
99		does, but in a manner more acceptable to the provider of the
100		service and more friendly to the clients.
101
102		Providing anonymous-FTP service can be costly --- each active
103		session consumes one process slot in the OS and one stream socket
104		entry in the network sub-system. The servers can also run
105		concurrently, adding to the system load. A popular archive site
106		can easily be overwhelmed as a result. Some were forced to
107		shutdown and some impose inconvenient access restrictions.
108
109		Unlike FTP, FSP is connection-less and virtually state-less. One
110		server handles requests from all clients machines. Each active
111		client machine takes up 16-bytes in a dynamically extensible
112		table. Since only one server exists on a server machine at any
113		time, the load added to the server machine is no more than one.
114
115		In exchange for allowing site operators to keep their sites open
116		and do away with cumbersome access restrictions, this is what the
117		clients accept with FSP:
118
119		1) Lower transfer rate. The maximum rate is 1 kbyte per UDP
120		message round-trip time between the client and the server.
121
122		In addition to the potential for more abundant sites and more
123		accessible sites, this is what the clients gain with FSP:
124
125		1) Robustness. Since FSP is connectionless, fluctuations in
126		the network will not abort a FSP transaction. Furthermore,
127		the 16-bytes of data for each client can be regenerated at
128		any point during any transaction. Thus, if the server goes
129		down at any point during a transaction, the transaction will
130		resume when the server is restarted. (like NFS)
131
132		2) Friendlier user interface. FSP does not have its own command
133		interpretor like FTP. Since it is connectionless, there is
134		no reason to carry much information from one command to the
135		next, and the commands can all be made into individual Unix
136		programs. For instance, there is one program you run to list
137		the directory and another you run to download a file.
138
139		3) Client protection. FSP oversees a directory structure similar
140		to that of an anonymous-FTP. However, a directory created
141		via FSP transaction is owned by the client machine that issued
142		the creation request. The client can create and delete files
143		and subdirectories in that directory. In addition, the client
144		can enable any of the four attributes for that directory:
145
146		A) Give all other clients the permission to create files.
147
148		B) Give all other clients the permission to delete files
149		or subdirectories.
150
151		C) Give all other clients the permission to read files.
152		(this is true by default)
153
154		D) Give all other clients the permission to create sub-
155		directories.
156
157		Note: A subdirectory can be deleted if it is empty and the
158		client owns the subdirectory.
159
160		4) Server protection. FSP server does not spawn sub-programs.
161		It will accept only paths that are downward relative to its
162		designated working directory. On systems with symbolic links,
163		the server will follow symbolic links, but it does not follow
164		uplinks (".."). Clients cannot create symbolic links and
165		care should be taken so that other users on the server machine
166		cannot create symbolic links in the server's work space.
167
168		It is also fairly difficult to formulate an attack to force a
169		shutdown of a FSP site by actions of a rogue site. About the
170		only way to disrupt a FSP service is to flood the FSP site
171		with network packets. FSP server prevents itself from
172		'counter-flooding' by filtering for legitimate requests using
173		the following method:
174
175		A) Each request message contains a key. For each client,
176		server database contains the keys to be used for the
177		next client request and for the previous client request.
178
179		B) If the next request does not contain a key that matches
180		either of the two keys, it is accepted only if at least
181		one minute has elapsed since the last time a request
182		is accepted. If the key does match the old key
183		(retransmit by client) it is accepted if the elapse time
184		is greater than 3 seconds.
185
186		C) Every request message accepted is acknowledged with
187		one reply message. The reply message contains a new
188		key to used for the next request. The new key is
189		computed by the server with a pseudo-random number
190		generator.
191
192		Flooding is a blatant violation of network etiquette because
193		a site can be subjected to flooding attack whether it has FSP
194		running or not, and flooding congests every link and gateway
195		between the rogue client and the server. As a further measure
196		of protection, the server loads a table of rogue clients on
197		startup. The server will not respond to requests from any of
198		those clients.
199
200		***********************************************************************
201
202		This is a free software. Be creative; make your own macros and tools
203		and let me know of any bugs and suggestions.
204
205		***********************************************************************
206
207		Source code uses several BSD-like licenses; Whole FSP is distributed
208		under 2-point BSD license, also known as MIT X11 License.

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