Naming

1
Naming

• Outline
• Terminology
• Domain Naming System
• Distributed File Systems

2
Overview

• What do names do?
• identify objects
• help locate objects
• define membership in a group
• specify a role
• convey knowledge of a secret
• Name space
• defines set of possible names
• consists of a set of name to value bindings

3
Properties

• Names versus addresses
• Location transparent versus location-dependent
• Flat versus hierarchical
• Global versus local
• Absolute versus relative
• By architecture versus by convention
• Unique versus ambiguous

4
Examples

• Hosts
• cheltenham.cs.princeton.edu 192.12.69.17
• 192.12.69.17 8023A8335B9F
• Files
• /usr/llp/tmp/foo (server, fileid)
• Users
• Larry Peterson llp_at_cs.princeton.edu

5
Examples (cont)

• Mailboxes
• Services
• nearby ps printer with short queue and 2MB

6
Domain Naming System

• Hierarchy
• Name
• chinstrap.cs.princeton.edu

7
Name Servers

• Partition hierarchy into zones

edu
com
gov
mil
org
net
uk
fr










princeton
mit
cisco
yahoo
nasa
nsf
arpa
navy
acm
ieee
cs
ee
physics
ux01
ux04

• Each zone implemented by two or more name servers

8
Resource Records

• Each name server maintains a collection of
  resource records
• (Name, Value, Type, Class, TTL)
• Name/Value not necessarily host names to IP
  addresses
• Type
• NS Value gives domain name for host running name
  server that knows how to resolve names within
  specified domain.
• CNAME Value gives canonical name for particle
  host used to define aliases.
• MX Value gives domain name for host running mail
  server that accepts messages for specified
  domain.
• Class allow other entities to define types
• TTL how long the resource record is valid

9
Root Server

• (princeton.edu, cit.princeton.edu, NS, IN)
• (cit.princeton.edu, 128.196.128.233, A, IN)
• (cisco.com, thumper.cisco.com, NS, IN)
• (thumper.ciscoe.com, 128.96.32.20, A, IN)

10
Princeton Server

• (cs.princeton.edu, optima.cs.princeton.edu, NS,
  IN)
• (optima.cs.princeton.edu, 192.12.69.5, A, IN)
• (ee.princeton.edu, helios.ee.princeton.edu, NS,
  IN)
• (helios.ee.princeton.edu, 128.196.28.166, A, IN)
• (jupiter.physics.princeton.edu, 128.196.4.1, A,
  IN)
• (saturn.physics.princeton.edu, 128.196.4.2, A,
  IN)
• (mars.physics.princeton.edu, 128.196.4.3, A, IN)
• (venus.physics.princeton.edu, 128.196.4.4, A, IN)

11
CS Server

• (cs.princeton.edu, optima.cs.princeton.edu, MX,
  IN)
• (cheltenham.cs.princeton.edu, 192.12.69.60, A,
  IN)
• (che.cs.princeton.edu, cheltenham.cs.princeton.edu
  , CNAME, IN)
• (optima.cs.princeton.edu, 192.12.69.5, A, IN)
• (opt.cs.princeton.edu, optima.cs.princeton.edu,
  CNAME, IN)
• (baskerville.cs.princeton.edu, 192.12.69.35, A,
  IN)
• (bas.cs.princeton.edu, baskerville.cs.princeton.ed
  u, CNAME, IN)

12
Name Resolution

• Strategies
• forward
• iterative
• recursive
• Local server
• need to know root at only one place (not each
  host)
• site-wide cache

13
Distributed File Systems

• No Transparency
• Global AFS /cs.princeton.edu/usr/llp/tmp/foo
• Windows f/usr/llp/tmp/foo
• Transparency by Convention
• NFS /usr/llp/tmp/foo
• Or Not /n/fs/fac5/llp/tmp/foo
• Transparency by Architecture
• Sprite /usr/llp/tmp/foo
• Private versus Shared
• ASF /usr/llp/tmp/foo versus /afs/shared

14
Stupid Naming Tricks

• Symbolic links
• Mount points
• Union mounts
• Per-User name spaces
• Logical name spaces
• Computed directories

15
Multimedia

• Outline
• Compression
• RTP
• Scheduling

16
Compression Overview

• Encoding and Compression
• Huffman codes
• Lossless
• data received data sent
• used for executables, text files, numeric data
• Lossy
• data received does not ! data sent
• used for images, video, audio

17
Lossless Algorithms

• Run Length Encoding (RLE)
• example AAABBCDDDD encoding as 3A2B1C4D
• good for scanned text (8-to-1 compression ratio)
• can increase size for data with variation (e.g.,
  some images)
• Differential Pulse Code Modulation (DPCM)
• example AAABBCDDDD encoding as A0001123333
• change reference symbol if delta becomes too
  large
• works better than RLE for many digital images
  (1.5-to-1)

18
Dictionary-Based Methods

• Build dictionary of common terms
• variable length strings
• Transmit index into dictionary for each term
• Lempel-Ziv (LZ) is the best-known example
• Commonly achieve 2-to-1 ration on text
• Variation of LZ used to compress GIF images
• first reduce 24-bit color to 8-bit color
• treat common sequence of pixels as terms in
  dictionary
• not uncommon to achieve 10-to-1 compression (x3)

19
Image Compression

• JPEG Joint Photographic Expert Group (ISO/ITU)
• Lossy still-image compression
• Three phase process
• process in 8x8 block chunks (macroblock)
• greyscale each pixel is three values (YUV)
• DCT transforms signal from spatial domain into
  and equivalent signal in the frequency domain
  (loss-less)
• apply a quantization to the results (lossy)
• RLE-like encoding (loss-less)

20
Quantization and Encoding

• Quantization Table
• 3 5 7 9 11 13 15 17
• 5 7 9 11 13 15 17 19
• 7 9 11 13 15 17 19 21
• 9 11 13 15 17 19 21 23
• 11 13 15 17 19 21 23 25
• 13 15 17 19 21 23 25 27
• 15 17 19 21 23 25 27 29
• 17 19 21 23 25 27 29 31
• Encoding Pattern

21
MPEG

• Motion Picture Expert Group
• Lossy compression of video
• First approximation JPEG on each frame
• Also remove inter-frame redundancy

22
MPEG (cont)

• Frame types
• I frames intrapicture
• P frames predicted picture
• B frames bidirectional predicted picture
• Example sequence transmitted as I P B B I B B

23
MPEG (cont)

• B and P frames
• coordinate for the macroblock in the frame
• motion vector relative to previous reference
  frame (B, P)
• motion vector relative to subsequent reference
  frame (B)
• delta for each pixel in the macro block
• Effectiveness
• typically 90-to-1
• as high as 150-to-1
• 30-to-1 for I frames
• P and B frames get another 3 to 5x

24
RTP

• Application-Level Framing
• Data Packets
• sequence number
• timestamp (app defines tick)
• Control Packets (send periodically)
• loss rate (fraction of packets received since
  last report)
• measured jitter

25
Real-Time Scheduling

• Priority
• Earliest Deadline First (EDF)
• Rate Monotonic (RM)
• Proportional Share
• with feedback
• with adjustments for deadlines

26
Elements of a Protocol Implementation

• Outline
• Service Interface
• Process Model
• Common Subroutines
• Example Protocol

27
Socket API

• Creating a socket
• int socket(int domain, int type, int protocol)
• domain PF_INET, PF_UNIX
• type SOCK_STREAM, SOCK_DGRAM
• Passive Open (on server)
• int bind(int socket, struct sockaddr addr, int
  addr_len)
• int listen(int socket, int backlog)
• int accept(int socket, struct sockaddr addr, int
  addr_len)

28
Sockets (cont)

• Active Open (on client)
• int connect(int socket, struct sockaddr addr,
• int addr_len)
• Sending/Receiving Messages
• int send(int socket, char msg, int mlen, int
  flags)
• int recv(int socket, char buf, int blen, int
  flags)

29
Protocol-to-Protocol Interface

• Configure multiple layers
• static versus extensible
• Process Model
• avoid context switches
• Buffer Model
• avoid data copies

30
Configuration

• nametulip
• nameeth protocolstulip
• namearp protocolseth
• nameip protocolseth,arp
• nameicmp protocolsip
• nameudp protocolsip
• nametcp protocolsip

31
Protocol Objects

• Active Open
• Sessn xOpen(Protl hlp, Protl llp,
• Part participants)
• Passive Open
• XkReturn xOpenEnable(Protl hlp,Protl llp,
• Part participant)
• XkReturn xOpenDone(Protl hlp,
• Protl llp,Sessn session,
• Part participants)
• Demultiplexing
• XkReturn xDemux(Protl hlp, Sessn lls,
• Msg message)

32
Session Objects

• Local end-point of a channel
• Interpret messages and maintain channel state
• Export operations for sending and receiving
  messages
• Operations
• send a message
• XkReturn xPush(Sessn lls,Msg message)
• deliver a message
• XkReturn xPop(Sessn hls, Sessn lls,
• Msg message,void hdr)

33
Process Model
Process-per-Protocol
Process-per-Message
34
Message Library

• Add header

• Strip header

35
Message Library (cont)

• Fragment message

• Reassemble messages

m
m1
m2
abcd
efg
msgFragment
(
m
,
new
, 3)
msgReassemble(new, m1, m2)
new
m
new
defg
abc

36
Event Library

• Scheduling Timeouts Book-keeping activity
• Operations
• Event evSchedule(EvFunc function,
• void argument,
• int time)
• EvCancelReturn evCancel(Event event)

37
Map Library

• Demultiplex Packets
• Operations
• Map mapCreate(int number,int size)
• Binding mapBind(Map map,
• void key,
• void id)
• XkReturn mapResolve(Map map,
• void key,void id)

38
Example

• static Sessn
• aspOpen(Protl self, Protl hlp, Part p)
• Sessn asp_s
• Sessn lls
• ActiveId key
• ProtlState pstate (ProtlState
  )self-gtstate
• bzero((char )key, sizeof(key))
• / High level protocol must specify both /
• / local and remote ASP port /
• key.localport ((AspPort ) partPop(p0))
• key.remoteport ((AspPort ) partPop(p1))
• / Assume failure until proven otherwise /
• asp_s XK_FAILURE

39

• / Open session on low-level protocol /
• lls xOpen(self, xGetDown(self, 0), p)
• if ( lls ! XK_FAILURE )
• key.lls lls
• / Check for session in active map /
• if (mapResolve(pstate-gtactivemap, key,
• (void )asp_s) XK_FAILURE)
• / Session not in map initialize it /
• asp_s asp_init_sessn(self, hlp, key)
• if ( asp_s ! XK_FAILURE )
• / A successful open /
• return asp_s
• / Error has occurred /

40

• static XkReturn aspPush(Sessn s, Msg msg)
• SessnState sstate
• AspHdr hdr
• void buf
• / create a header /
• sstate (SessnState ) s-gtstate
• hdr sstate-gthdr
• hdr.ulen msgLen(msg) HLEN
• / attach header and send /
• buf msgAddrHdr(msg, HLEN)
• aspHdrStore(hdr, buf, HLEN, msg)
• return xPush(xGetDown(s, 0), msg)

41

• static XkReturn aspDemux(Protl self, Sessn lls,
  Msg msg)
• AspHdr h
• Sessn s
• ActiveId activeid
• PassiveId passiveid
• ProtlState pstate
• Enable e
• void buf
• pstate (ProtlState )self-gtstate
• / extract the header from the message /
• buf msgStripHdr(msg, HLEN)
• aspHdrLoad(h, buf, HLEN, msg)
• / construct a demux key from the header /
• bzero((char )activeid, sizeof(activeid))
• activeid.localport h.dport

42

• / see if demux key is in the active map /
• if (mapResolve(pstate-gtactivemap, activeid,
• (void )s) XK_FAILURE)
• / didn't find an active session, /
• / so check passive map /
• passiveid h.dport
• if (mapResolve(pstate-gtpassivemap,
  passiveid,
• (void )e) XK_FAILURE)
• / drop the message /
• return XK_SUCCESS
• / port was enabled, so create a new /
• / session and inform hlp /
• s asp_init_sessn(self, e-gthlp,
  activeid)
• xOpenDone(e-gthlp, s, self)

43

• static XkReturn
• aspPop(Sessn s, Sessn ds, Msg msg, void inHdr)
• AspHdr h (AspHdr ) inHdr
• / truncate message to length shown in header
  /
• if ((h-gtulen - HLEN) lt msgLen(msg))
• msgTruncate(msg, (int) h-gtulen)
• / pass message up the protocol stack /
• return xDemux(xGetUp(s), s, msg)