Co-operative proxy caching algorithms for time-shifted IPTV services
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Co-operative proxy caching algorithms for time-shifted IPTV services
Dept. of Information Technology - Ghent University
3
Introduction • Network requirements for next-generation services - content delivery (IPTV, VoD) • high bandwidth, low jitter
- multiplayer games (server based, P2P) • low delay
- distributed storage • low delay, high availability
- conferencing (IP telephony, video conferencing) • low delay and jitter
- home management (automation, security) • high availability
=> increasing bandwidth and QoS
1/02/2007
Dept. of Information Technology - Ghent University
4
Introduction • High priority: IPTV services - today: broadcast TV (live) or VoD (older content) • highly loaded VoD servers at the network edge • complete files are stored
- solution: time-shifted TV for (very) recent content • distributed servers in the access network, storing fragments
Broadcast TV broadcast server
Time-shifted TV
Video on Demand
Video on Demand
access server
regional server
central server
# requests
Start of live broadcast
1/02/2007
1h
1 day
1 week
Dept. of Information Technology - Ghent University
t
5
Access network IP aware aggregation network
ISP1 Edge router
Internet DSLAM
BAS ISP2 ATM switch
PPP ADSL modem
CPN telephone
IP aware telephone
1/02/2007
• Current architecture - access network per service - broadband Internet (DSL / ATM based) • PPP terminated in single device (BAS) • Single device per subscriber - NAT breaks E2E connectivity
PSTN
• PPP setup hampers autoconfiguration • PPP conflicts with application-based QoS and multicast support Dept. of Information Technology - Ghent University
6
Access network • Next-generation architecture
ISP1 Edge router
aggregation network
- Converged access - IP awareness
Internet DSLAM
BAS
• Multicast support • Local P2P traffic
ISP2 ATM switch
ADSL modem
CPN
- Multi-edge
IP awareness
IP aware
New services
NAP edge router
telephone IP telephone
• Scalability • High availability
- New services (triple play) - Application based QoS
switch
telephone gateway
CPN 1/02/2007
IP DSLAM IP aware
Service enablers (e.g. firewall, caches)
Dept. of Information Technology - Ghent University
Dept. of Information Technology - Ghent University
8
Time-shifted TV • Network view - caching of fragments - p2p techniques at cache level access network regional network
1 2
AR 3
core network AM
CS
ER User 1: real-time
CS: central server ER: edge router AR: access router AM: access multiplexer
1/02/2007
User 2: delayed t1 User 3: delayed t2
Dept. of Information Technology - Ghent University
9
Time-shifted TV • Streaming diagram User 1
User 2
User 3
t_program
t_pause
t0
t1
storage
tw t2
t_viewing
t_storage User 1: real-time User 2: delayed t1 User 3: delayed t2 1/02/2007
Dept. of Information Technology - Ghent University
10
Time-shifted TV • Caching algorithm - storage • small part S (< 1 GB) for learning • large part L for storage of popular / distant segments
- during each interval ∆ (e.g. 5 minutes) • parameter An,p is increased every time a request for program p passes by cache n • increase An,p by 1 (pure popularity) or by the hopcount between cache n and the serving node (popularity & distance)
- after each interval ∆
request for program p
• store all “occupied” segments • store segments with highest An,p
program stored locally? no
yes
is it new? no - stream from other cache - adapt An,p 1/02/2007
window appropriate? yes
- stream from server - cache in S
no - stream from other cache
Dept. of Information Technology - Ghent University
yes - stream locally - set to “occupied” - adapt An,p 11
Time-shifted TV • Input parameters -
5 tsTV channels 6 programs per channel 45 minutes per program 2.5 Mbps streams (≈ 1 GB per hour) - popularity halved after each interval ∆ (= 5 minutes)
ER
AR
AM
• Deployment options - hierarchical caching • caches at AR and AM level
- co-operative caching • co-operating caches at AM level
1/02/2007
Dept. of Information Technology - Ghent University
12
Time-shifted TV ER
AR
AM
• Hierarchical caching
AM caches only
AR and AM caches
80
80 ER -> AR
60
AR -> AM 40
AM -> AR
20
% requests
100
% requests
100
ER -> AR
60
AR -> AM 40
AM -> AR
20
0
0 0
1
2 cache size [GB]
3
4
0
1
2 cache size [GB]
3
4
Server load reduced by 50% to 70% with 0.5GB caches 1/02/2007
Dept. of Information Technology - Ghent University
13
Time-shifted TV ER
AR
AM
• Co-operative caching
100
% requests
80 ER -> AR
60
AM caches only
AR -> AM AM -> AR
40 20 0 0
1
2 cache size [GB]
3
4
Server load reduced by 95% with 6 co-operating 0.5GB caches 1/02/2007
Dept. of Information Technology - Ghent University
Dept. of Information Technology - Ghent University
EPG
16
Proxy implementation • RTSP proxy - measurements • AMD AthlonTM 64 (512MB RAM) • delay between PLAY request and first RTP packet in a server - proxy - client configuration 40
m in delay
35
av delay
delay [ms]
30
m ax delay
25 20 15 10 5 0 content not cached at proxy
1/02/2007
content cached at proxy
server only (proxy disabled)
Dept. of Information Technology - Ghent University
Dept. of Information Technology - Ghent University
18
Conclusions • Access network transformation - from ATM based broadband aggregation to multi-service IP-aware access networks - necessary to meet QoS requirements
• IPTV - identified as highest-priority, bandwidth-intensive residential telecom service - server load and access network load reduced effectively through time-shifted TV using distributed proxy streamers - implementation using RTSP proxy streamers
1/02/2007
Dept. of Information Technology - Ghent University
