Network Level Framing in INSTANCE
Pål Halvorsen, Thomas Plagemann, and Vera Goebel
University of Oslo, UniK- Center for Technology at Kjeller
Norway
Overview:
• Application Scenario
• The INSTANCE project:
– Zero-Copy-One-Copy Memory Architecture
– Integrated Error Management
– Network Level Framing
• Conclusions
MIS 2000, Chicago, October 2000
©2000 Pål Halvorsen
Application Scenario
Media-on-Demand server:
Applicable in applications like News- or
Video-on-Demand provided by city-wide
cable or pay-per-view companies
Multimedia Storage Server
Network
Network
Retrieval is the bottleneck:
Project goals:
Some important factors:
• Memory management
• Error management
• Communication protocol processing
Optimize performance within a
single server:
• Reduce resource requirements
• Maximize number of clients
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Zero-Copy-One-Copy I
Zero-Copy
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Delay-Minimized Broadcast
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Zero-Copy-One-Copy II
Zero-Copy
Delay-Minimized Broadcast
Integrated Zero-Copy and Delay-Minimized Broadcasting
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Traditional Error Management
Encoder
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Decoder
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Integrated Error Management
Encoder
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Decoder
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Traditional Storage
TRANSPORT
TRANSPORT TRANSPORT
TRANSPORT
NETWORK
NETWORK
NETWORK
NETWORK
LINK
LINK
LINK
LINK
Upload to server
Frequency: low (1)
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Download from server
Frequency: very high
©2000 Pål Halvorsen
Network Level Framing (NLF)
TRANSPORT TRANSPORT
TRANSPORT
TRANSPORT
NETWORK
NETWORK
NETWORK
NETWORK
LINK
LINK
LINK
LINK
Upload to server
Frequency: low (1)
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Download from server
Frequency: very high
©2000 Pål Halvorsen
NLF:
When to Store Packets
UDP
Transport Layer
TCP
TCP
UDP
UDP
Network Layer
IP
IP
IP
IP
Link Layer
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NLF:
Splitting the UDP Protocol
udp_PreOut()
udp_output()
Temporarily connect
UDP
Prepend UDP and IP headers
udp_output()
Prepend UDP and IP headers
Prepare pseudo header
for checksum
Prepare pseudo header for
checksum, clear unknown fields
UDP
IP
Prealculate checksum
UDP
udp_QuickOut()
Calculate checksum
Update UDP and IP headers
UDP
Fill in some other IP header fields
IP
Update checksum, i.e., only add
checksum of prior unknown fields
Hand over datagram to IP
Fill in other IP header fields
Disconnect connected
socket
Hand over datagram to IP
MIS 2000, Chicago, October 2000
©2000 Pål Halvorsen
NLF:
Checksum Operations I
• The UDP checksum covers three fields:
– A 12 byte pseudo header containg fields from the IP header
– The 8 byte UDP header
– The UDP data
• Checksum calculation function (in_cksum):
u_16int_t *w;
for each mbuf in packet {
w = mbuf->m_data;
while data in mbuf {
checksum += w;
w++;
}
}
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NLF:
Checksum Operations II
• Traditional checksum operation:
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NLF:
Checksum Operations III
• NLF checksum operation:
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Integrated Error Management and NLF
FEC
UDP - PreOut
UDP - QuickOut
Network
UDP - Input
FEC
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Expected Performance Gain
• Traditionally, 60% of the UDP/IP processing is spent
on checksum calculation [Kay et al. 93]
• Performance gain using NLF (packet size
dependent):
– The checksum operation is greatly reduced
• E.g., 4KB packet size  checksum operation on only 0.2% of
data
• Speed-up factor of about 2
– Throughput gain of about 10%
MIS 2000, Chicago, October 2000
©2000 Pål Halvorsen
Conclusion
The INSTANCE project aims at optimizing
the data retrieval in an MoD server:
– Zero-Copy-One-Copy memory architecture
– Integrated Error Management
– Network Level Framing
 Saving time for checksum calculation where expected
performance gain is:
– About 99% reduction of the checksum calculation time
(UDP/IP processing speed-up of 2)
– About 10% increase in throughput
– Future work
MIS 2000, Chicago, October 2000
©2000 Pål Halvorsen