ALTO WG H. Wang
Internet-Draft Tongji University
Intended status: Informational July 8, 2016
Expires: January 9, 2017
Synchronization of Distributed ALTO Servers
draft-wang-alto-dist-sync-00
Abstract
This document imposes the challenges and initial solutions that can
be expected for the composing problem of cross-domain ALTO servers.
The basic idea and problem space for composing is to solve the
problem of synchronization.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Problem Statement . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Challenges . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Challenges about Network Map Synchronization . . . . . . 4
2.2. Challenges about Cost Map Synchronization . . . . . . . . 4
2.3. Challenges about Endpoint Cost Synchronization . . . . . 4
3. Solution Proposal . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Step1: Distributed ALTO Servers Discovery . . . . . . . . 4
3.2. Step2: Real-time incremental update using SSE . . . . . . 4
3.3. Step3: Network trackers between neighbour partitions. . . 5
4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Considerations for Consistency . . . . . . . . . . . . . 5
4.2. Considerations for Update Frequency . . . . . . . . . . . 5
4.3. Considerations for ALTO Topology Extension . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Informative References . . . . . . . . . . . . . . . . . 6
8.2. Normative References . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
In some sceneries that one individual ALTO servers can hardly handle,
such as in large-scale distributed network, or in the network
combined with different ISPs, the conceptions of network partition
and cross-domain ALTO servers should be introduced.
In each network partition, we assume that there is an ALTO server to
provide network information. Hence one possibility is to using small
glimpse of each network partition to compose the information of whole
complete network.
The basic idea and problem space for composing is to solve the
problem of synchronization.
This document imposes the challenges and initial solutions that can
be expected for the composing problem of cross-domain ALTO servers.
In the discussion session, the problems of synchronization of
distributed ALTO servers that we found but haven't given a solution
are listed, such as the consistency and the update frequency.
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1.1. Problem Statement
Before touching the real problem of synchronization, we assume the
network settings as below:
+----------------------------------------------------------+
| .----------. ___ Network |
| | ISP1 | .-----------. / Partition |
| | ALTO +--------+-------| ISP 2 |/ |
| | Server| | | ALTO | |
| `----------' | | Server| |
| .----------. | `-----------' |
| | ISP3 | |---- |
| | ALTO +-------/ \ ... ... |
| | Server| |
| `----------' |
| Complete Network |
+----------------------------------------------------------+
Figure 1: Network Partitions.
In each network partition, there is an individual ALTO server. Each
ALTO server will track and can only track the information of its own
network.
Theoretically, by tracking the information provided by each ALTO
servers, a whole picture of the complete network information will
emerge. However, to synchronize the existing and coming information
from different network partitions can be a big challenge.
1.2. Terminology
o Network Partition: infrastructures in partial network with
connectivity.
o ECS: Endpoint Cost Service
o SSE: Server Sent Event
2. Challenges
Implementing distributed ALTO servers architecture is not easy
because of the synchronization problem. There are several challenges
about distributed ALTO servers synchronization. This document will
focus on discussing about the challenges in three major services of
ALTO: network map service, cost map service and endpoint cost
service.
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2.1. Challenges about Network Map Synchronization
In the previous design, different servers can have identical names.
When it comes to compose the whole network, it will introduce
collisions.
2.2. Challenges about Cost Map Synchronization
How to unify the network map dependency of cost map?
How to compute or indicate the cost between the PIDs in the different
network partitions?
2.3. Challenges about Endpoint Cost Synchronization
How to compute the cost between the endpoints in the different
network partitions?
3. Solution Proposal
This document proposed a basic workflow to make distributed ALTO
servers be able to synchronize with each others.
1. Distributed ALTO servers discovery;
2. Real-time incremental update using SSE between ALTO server;
3. Network trackers between neighbour partitions.
Following will talk more details about these three steps.
3.1. Step1: Distributed ALTO Servers Discovery
The ALTO servers need to find each others before make any information
aggregation. So there need to be some server discovery protocols
deployed in the network.
The draft [ALTO-XDOM-DISC] proposed a cross-domain server discovery
protocol and we can borrow it as well.
3.2. Step2: Real-time incremental update using SSE
Each ALTO server can subscribe the incremental update of the network
map, cost map and endpoint cost service resources in the other ALTO
servers. When the network information update, all of ALTO servers
will receive the update incrementally.
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The draft [ALTO-SSE] gave a solution to implement real-time
incremental update by using SSE.
3.3. Step3: Network trackers between neighbour partitions.
In the current network settings, the network trackers will only
provide the network information inside their own network partitions.
It is impossible to get the network information between network
partitions because there is no components in the architecture
tracking these information.
This document proposed a basic solution to solve this problem. The
solution is to add some new network trackers between neighbour
partitions in the network.
4. Discussion
4.1. Considerations for Consistency
Till now there is no solution to promise the consistency between
different network partitions.
4.2. Considerations for Update Frequency
TBD
4.3. Considerations for ALTO Topology Extension
Suppose ALTO will provide topology information in future, how do we
specially compose the topology information from different network
partition? Most importantly, at which specific frequency should we
update the topology information?
5. IANA Considerations
This document does not define any new media type or introduce any new
IANA consideration.
6. Security Considerations
This document does not introduce any privacy or security issue not
already present in the ALTO protocol.
7. Acknowledgement
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8. References
8.1. Informative References
[DRAFT-DEPLOYMENT]
Stiemerling, M., Kiesel, S., Scharf, M., Seidel, H., and
S. Previdi, "ALTO Deployment Considerations", 2016,
<https://datatracker.ietf.org/doc/draft-ietf-alto-
deployments/>.
[DRAFT-SSE]
Roome, W. and Y. Yang, "ALTO Incremental Updates Using
Server-Sent Events (SSE)", 2015,
<https://datatracker.ietf.org/doc/draft-ietf-alto-incr-
update-sse/>.
[DRAFT-XDOM-DISC]
Kiesel, S. and M. Stiemerling, "Application Layer Traffic
Optimization (ALTO) Cross-Domain Server Discovery", 2016,
<https://datatracker.ietf.org/doc/draft-kiesel-alto-xdom-
disc/>.
8.2. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", March 1997,
<http://xml.resource.org/public/rfc/html/rfc2119.html>.
[RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the
Network Configuration Protocol (NETCONF)", Oct 2010,
<http://xml.resource.org/public/rfc/html/rfc6020.html>.
[RFC7285] Alimi, R., Penno, R., Yang, Y., Kiesel, S., Previdi, S.,
Roome, W., Shalunov, S., and R. Woundy, "Application-Layer
Traffic Optimization (ALTO) Protocol", 2014,
<http://xml.resource.org/public/rfc/html/rfc7285.html>.
Author's Address
Haoran (May) Wang
Tongji University
4800 Cao'an Road
Shanghai 201804
China
Email: whr_hr_r@163.com
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