Subject: RE: I-D ACTION:draft-zhao-slp-da-interaction-00.txt

From: Mike Day <[email-masked]>
Date: Fri, 19 Nov 1999 08:54:22 -0700

What do you believe to be the upper practical limit on the number of nodes
in a mesh? 

Also, it is possible that different mirrored nodes will have different
connection tables. i.e., for nodes a, b, and c; there could be a situation
where:

	a: b
	b: c
	c: b 

a has b in its table; b has c in its table; and c has a in its table. 

This situation could occur if the connection between a and c goes down due
to a network problem. A servreg to a would get forwarded to b but not to c. 

If you had all mirrored nodes automatically forward all messages to all
their connections, then all nodes would receive messages even when the mesh
is not fully connected, provided a route exists to all nodes.

However, you would need to implement a new message type specifically for
forwarding registrations and deregistrations. This message would need to
have a list of previous receivers or a time-to-live to prevent endless
forwarding. This may be worth considering. Only da's that participate in
mesh would need to support the message. 

Also, such a message would allow connection models other than a fully
connected mesh if scalability is a problem due to network issues. 

comments?

Mike Day,

Legato Systems

-----Original Message-----
From: Weibin Zhao [mailto:[email-masked]]
Sent: Wednesday, November 17, 1999 8:31 AM
To: [email-masked]
Subject: I-D ACTION:draft-zhao-slp-da-interaction-00.txt

Hello,

I submitted an I-D on Interaction of SLP DA. Following is the abstract
and URL. Any comments are much appreciated. Thanks.

Weibin

----------------------------------------------------------------------------
--
A New Internet-Draft is available from the on-line Internet-Drafts
directories.

	Title		: Interaction of SLP Directory Agents for
Reliability 
                          and Scalability
	Author(s)	: W. Zhao, H. Schulzrinne 
	Filename	: draft-zhao-slp-da-interaction-00.txt
	Pages		: 9
	Date		: 16-Nov-99
	
This document proposes a scheme for the interaction of Directory
Agents (DA) in SLPv2 (Service Location Protocol, Version 2). It aims
to provide a reliable and scalable directory service by maintaining a
peer relationship among a fully meshed DA set. Peer DAs exchange SLP
update messages (SrvReg and SrvDeReg), and keep the same consistent
data for each scope. This scheme is entirely backward compatible with
SLPv2. It simplifies Service Agent (SA) registrations and supports
User Agent (UA) query load balancing.

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From: Weibin Zhao <[email-masked]>
Date: Fri, 19 Nov 1999 11:59:07 -0500 (EST)

Hello Mike,

> What do you believe to be the upper practical limit on the number of nodes

Since SLP is used for intranet, the mirrored servers for each scope need
not be too large. As I stated in the draft, 2-3 is the recommended value.
If you have a realy large intranet, and the workload in pretty heavy, 4-5
servers in a mesh maybe the choice. As for 5 servers, 10 TCP connections
are needed for a mesh, this should be OK.

> to a network problem. A servreg to a would get forwarded to b but not to c. 

In your case, the connection between node-a and node-c goes down, so
node-a only forwards SrvReg/SrvDeReg message to node-b, but not to node-c.
If this happens, node-c should be removed from node-a's peer list
according to the draft. Later, when node-a discovers node-c again, it will
forward all the data for the shared scopes to node-c. Therefore, node-c
can get all the data node-a had for the shared scope. 

> is not fully connected, provided a route exists to all nodes.

I adopt a simple forwarding scheme: any SrvReg/SrvDeReg message is ONLY
forwarded for one hop. This is why I use a mesh connection among mirrored
DAs. Otherwise, a multi-hop forwarding scheme is needed which will be
much complicated.

> connected mesh if scalability is a problem due to network issues. 

To be compatible with SLPv2, I am reluctant to define new message
types. To distinguish a forwarded message from a message from an SA,
a flag bit in the message header is enough.

As a reminder, ONLY SrvReg and SrvDeReg messages are forwarded, UA's 
query messages are not in our scheme.

> comments?

Hope above comments could clarify your questions. Thanks.

Weibin