Seamless Access to Services for Mobile Users

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Seamless Access to Services for Mobile Users

• Jennifer RexfordPrinceton University
• http//www.cs.princeton.edu/jrex

Joint work with Matvey Ayre, Mike Freedman, Prem
Gopalan, Steven Ko, Erik Nordstrom, David Shue
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The Internet Does Not Meet the Needs of Online
Services
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Yesterday Host-Centric Network

• ARPAnet was designed for resource sharing
• Naming, addressing, and routing on end hosts

ftp, telnet
UCLA
Stanford
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Today Service-Centric Internet

• Internet is now a platform for accessing services
• Services not tied to a particular host or
  location

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Challenge 1 Multiplicity

• Distributed server replicas
• Early binding of domain nameto an IP address
• Load balancers spreading loadover the server
  replicas
• Multiple interfaces and paths
• A connection can only use one interface on each
  host
• Traffic flows over a single path

3G
WiFi
Separate service, connection, and interface
naming
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Challenge 2 Dynamism

• Client mobility
• Seamless connectivity requires triangle routing
• Connection cannot switch between interfaces
• Virtual machine migration
• Only within a layer-2 domain
• not across subnets or data centers
• Server replica failure/recovery
• Ad hoc updates to load balancers and DNS servers
• IP address caching causes temporary outages

Allow automatic, dynamic updates during a
connection
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Serval Rewiring the End-Host Network Stack for
Online Services
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Solution 1 Service Naming

• Applications should name services explicitly

bind(fd, serviceID) listen(fd)
connect(fd, serviceID)
Network stack must resolve service to instance
for client
Network stack must advertise service for server
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Solution 2 Flow Naming

• Connection consists of multiple flows
• Identified by ltinterface address, flowIDgt pairs
• Delivers data as instructed by the transport
  layer
• Each end demultiplexes on its own identifiers

a1
a3
sC
sS
a2
a4
Host C
Host S
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Resolving and Connecting
First packet from transport carries serviceID and
its response provides remote IP address
connect(fd, X)
SYN serviceID X
SYN-ACK IP address
Local flowID
Local Remote flowID
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Solution 3 Inband Signaling

• Notify remote end-point about changes
• Send RSYN to the remote ltinterface address,
  flowIDgt
• Indicate the new local ltinterface address,
  flowIDgt
• For client mobility, VM migration, and interface
  switching

X
fS1
fC1
a1
a3
sC
sS
fC2
fS2
a2
a4
Host C
Host S
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Putting it All Together
Serval introduces a layer of indirection and
defers mapping to topological identifiers until
communication is established
Application
Transport
Network
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Prototype Implementation

• End-host network stack
• Multi-platform (Linux, Android, BSD)
• Runs in user space and in the kernel
• Decentralized service discovery
• Ported applications
• Iperf, TFTP, PowerDNS, Wget, Elinks, Firefox,
  Mongoose, Memcached, ApacheBench
• Small code changes (70-425 lines of code)
• Experiments
• Competitive throughput with todays TCP
• Fast failover, load shedding, and VM migration

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Incremental Deployment

• No changes to the network layer
• Packet delivery based on IP addresses
• IP addresses correspond to interfaces
• Scalable routing based on hierarchical addresses
• Resolution of service names
• Domain Name System (DNS) and front-end proxies
• Later, routing first packet based on serviceID
• Unmodified hosts and applications
• Proxies in front of clients or servers
• Address translation in the network stack

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Related Work

• Separating identity from location
• By naming hosts LISP, HIP, i3
• By naming services/data SFR, LNA, DONA, CCN
• Migration/Mobility
• Through indirection Mobile-IP
• Through in-band signaling TCP Migrate
• Main differentiators of Serval
• Comprehensive solution for online services
• Solution that focuses on the end-host stack

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Conclusion

• Service-centric networking
• Multiplicity multiple servers, interfaces, and
  paths
• Dynamism mobility, migration, and failover
• Rewiring the end-host stack
• Resolving and registering service names
• Connections consisting of multiple flows
• Inband signaling to migrate flows to new
  addresses
• Without changing the network layer
• Runs on top of IP addressing and packet delivery

http//www.cs.princeton.edu/jrex/papers/serval11.
pdf