CACHING IN THE WIRELESS ENVIRONMENT

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CACHING IN THE WIRELESS ENVIRONMENT
Sanjay Kulhari Venugopal
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WIRELESS NETWORK ARCHITECTURE

• SOME KEY TERMS
• Domain
• Service Level Agreement (SLA)
• Home Access Server (HAS)
• Domain Access Server (DAS)
• Local Access Server (LAS)
• Network Access Server (NAS)
• Mobile Station (MS)

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• Domain An administrative entity that is capable
• of negotiating SLAs (Service Level Agreements)
  
• with peer entities and is capable of
  generating
• Billing records for a user.
• SLA The means by which domain agree on how
• to bill the roaming users.
• HAS The logical entity with whom the MS needs
• to authenticate with the first time it enters
  the network.
• DAS receives access requests from the user and
• communicate to the HAS.
• LAS Handles the network access requests between
  MS
• and AP.
• NAS Logical point of attachment for the MS.

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HAS
External Network
Home Domain
DAS
HAS-Home Access Server DAS-Domain Access
Server LAS-Local Access Server NAS-Network Access
Server MS-Mobile Station
External Network
Foreign Domain
LAS
Local Cache
NAS
NAS
MS
Architecture of the Wireless Network
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Local Caching

• If a mobile user moves from one access point
• to another it has to get authenticated by the
• Home Access Server (HAS).
• The information necessary to start a new and
• secured connection is cached at the
• Local Access Server (LAS).

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FEATURES OF WIRELESS NETWORKS

• Communication Latency.
• Wireless transmission susceptible to atmospheric
  conditions.
• Low Bandwidth.
• Solutions
• Increasing bandwidth of radio links.
• Using intelligent caching and prefetching
  techniques.

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Other Features

• Lower Bandwidth and Higher Bandwidth
  Variability.
• Location-sensitive Network Resources.
• Need for Mobility Management.

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Access Network
Fixed Network
User
User ID
Network
MSC
BSC
Base Stations
Mobile Terminal
Terminal Mobility
Personal Mobility
MSC Mobile Switching Centre BSC Base Station
Controller
Personal Mobility and Terminal Mobility
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WEB CACHING PROTOCOLS

• INTERNET CACHING PROTOCOL (ICP).
• CACHE ARRAY ROUTING PROTOCOL (CARP).

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INTERNET CACHING PROTOCOL (ICP)

• A client sends an HTTP request to its configured
• cache server.
• If the requested object is not found locally, the
  
• configured cache server then queries all its
  siblings.
• The configured cache server sends an HTTP request
  
• for the object to the sibling, obtains the
  object, caches the object and forwards the object
  to the requestor.
• If the object is not found at the present level,
  request
• is made to the higher level or the original Web
  Server.

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Original Web Server
HTTP
Institutional Sibling Caches
S4
S6
S5
ICP
ICP
HTTP
Departmental Sibling Caches
S1
S3
S2
ICP
ICP
HTTP
Clients
Internet Caching Protocol (ICP)
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DRAWBACKS OF INTERNET CACHING PROTOCOL (ICP)

• Whenever there is a miss each sibling must
  process an ICP request and response message.
• Same objects will get cached at multiple caches
  resulting in wastage of memory and disk
  resources.
• Load on a particular cache server may increase.

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CACHE ARRAY ROUTING PROTOCOL (CARP)

• Before the client sends its request, it first
  hashes
• the URL and determines the set to which the
  hashed
• URL belongs.
• Client then sends the request to the
  corresponding
• sibling.
• If the object is not available a hashing function
  is again
• used to decide which proxy cache at the upper
  level to
• Contact.
• Again if the object is not available it is
  obtained from
• the original web server.

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Original Web Server
HTTP
Institutional Sibling Caches
Set 2 lt3,4gt
Set 1 lt1,2gt
HTTP
Departmental Sibling Caches
lthash(url)3gt
Set 1 lt2,4gt
Set 2 lt1,3gt
HTTP
lthash(url)2gt
Clients
Cache Array Routing Protocol (CARP)
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ADVANTAGES OF CARP OVER ICP

• Each object resides in at most one sibling.
• Efficient use of storage space.
• Client is immediately directed to the correct
  sibling.
• No ICP message explosion.

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Thank You