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draft-ietf-sdr-route-setup-00.txt
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SDR Working Group Deborah Estrin
INTERNET DRAFT Daniel Zappala
USC
Tony Li
cisco Systems
6/22/93
Revision 0
Expiration Date: 12/31/93
Source Demand Routing:
Route Setup
Status of this Memo
This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas,
and its Working Groups. Note that other groups may also distribute
working documents as Internet Drafts.
Internet Drafts are draft documents valid for a maximum of six
months. Internet Drafts may be updated, replaced, or obsoleted by
other documents at any time. It is not appropriate to use Internet
Drafts as reference material or to cite them other than as a "working
draft" or "work in progress".
1 Introduction
This document is a supplement to the internet draft "Source Demand
Routing: Packet Format and Forwarding Specification" [1]. The initial
specification in [1] includes a full SDRP route in every data packet
sent. In some cases, commonly known as "flows", where the duration
of a packet stream is significantly longer than the end-to-end
round-trip delay, and particularly where the amount of payload in the
packet is small, it is worthwhile to "set up" the SDRP route by
saving state information in SDRP routers, instead of carrying the
full SDRP route in every packet. Once this state is established, the
source can use a route identifier to refer to the SDRP route rather
than carrying the full route in each data packet, thereby reducing
the SDRP packet header size and transmission time.
2 Protocol Overview
It is important to our architecture that we not impose setup on SDRP
routers that are short on state space or that otherwise restrict
setup. Therefore, the desire for setup is simply flagged by the
source, and the routers along the SDRP route may choose to accept or
reject the request. If all of the routers along the SDRP route
accept, then the source can begin using a route identifier to refer
to the saved state. If any router refuses setup, the source must
continue including the full source route in each data packet or else
try a different route.
When a router rejects a setup request, it sends an SDRP control
message containing the route identifier to the source. Control
messages are also used in this manner if a router loses or is missing
state for a particular route identifier. When a router accepts a
setup request, it continues forwarding the request along the SDRP
route. Successful route setup is indicated when the final router on
the SDRP route sends an SDRP probe containing the route identifier to
the source.
3 SDRP Packet format
The following diagram is reproduced from [1] and describes the format
of an SDRP packet. Below we describe several new Source Route
Protocol Types and extensions to any other fields necessary to
support these types. All other fields are as described in [1].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ver |D|S|P| | Hop Count |SourceProtoType| Payload Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Route Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Target Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PrefixLength | Notification |SrcRouteLength | NextHopPtr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Route ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload ....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Source Route Protocol Type (1 octet)
The Source Route Protocol Type field indicates the type of information
that appears in the source route. The value 1 in this field indicates
an "Explicit Source Route." The source route is included explicitly
and processed as described in [1]. The value 2 in this field
indicates "Route Setup." The source route is included explicitly and
route setup is performed as described in this document. The value 3
in this field indicates "Use Setup Route." The source route is not
included in the packet and previously established route state should
be used as described in this document.
Notification Code (1 octet)
This field is only meaningful in control packets. In data
packets, this field is transmitted as zero, and should be ignored
on receipt. This document adds the following values for the
Notification Code:
8 - Setup Request Rejected
9 - Setup State Missing
4 Requesting SDRP Setup
A source originating SDRP packets requests SDRP setup by setting the Source
Route Protocol Type to "Route Setup," setting the Probe Indicator bit to 1,
and setting all other fields as described in [1]. The source MAY wait a
full round-trip time for a response to the setup request, in the meantime
sending subsequent packets with the Source Route Protocol type set as
"Explicit Source Route." There is no limit, however, to the number or
frequency of setup requests, thus the source MAY send another "Route
Setup".
A source MAY choose to send packets with a Source Route Protocol Type of
"Use Setup Route" immediately after sending the setup request. This may be
useful if the packets will be useless after waiting a full round-trip time.
In this case, the packets will be delivered if the setup is successful, but
may be dropped otherwise.
The control messages sent by routers to indicate the status of
a setup request are described in section 6.
5 Forwarding SDRP Setup Requests
If the Source Route Protocol Type of a packet is "Explicit Source
Route," it is handled as described in [1].
If the Source Route Protocol Type of a packet is "Use Setup Route," the
router accesses the source route forwarding cache containing the necessary
forwarding information, as described in section 7. The router SHOULD use
this information to modify the destination address of the delivery header
and send the packet to the next hop. If no forwarding information is
found, then the router MAY send a control message with a Notification Code
of "Setup State Missing" to the source of the SDRP packet. Because the
source may be attempting to send many packets before receiving notification
of a successful setup request, the router MAY send notification of a
dropped packet only periodically.
If the Source Route Protocol Type of a packet is "Route Setup" and the
router does not or cannot support setup, the router MAY send the
source a control packet with a Notification Code of "Setup Request
Rejected." It MAY then modify the data packet so that the Source Route
Protocol Type is "Explicit Source Route" and the Probe Indicator bit
is 0, then forwards the packet as described in [1]. The router MAY
send notification of a failed setup request only periodically.
Alternately, a router MAY silently drop the "Route Setup" packet.
If the Source Route Protocol Type of a packet is "Route Setup" and the
router can accept the setup, and there is no matching route in its source
route forwarding cache, then the router SHOULD process the explicit source
route according to [1]. In addition, if the router is not the last hop of
the source route, it creates an entry in the source route forwarding cache
using the source address of the delivery header and the Source Route
Identifier as a key. This entry contains the forwarding information
obtained when processing the source route. The packet is then forwarded to
the next SDRP router. If the router is the last hop of the source route,
it forwards the payload packet and responds to the Probe Indicator bit as
described in [1]. This will return a control message with a Notification
Code of "Probe Completed" and a Source Route Protocol Type of "Route Setup"
to the source of the packet.
6 Processing Control Messages
If the source receives a control message with a Notification Code
of "Probe Completed" and the Source Route Protocol Type set to
"Route Setup," then the SDRP route has been successfully
established. The source MAY send subsequent data packets with
the Source Route Protocol Type set to "Use Setup Route," omitting
the source route and setting all other fields as described in [1].
If the source receives a control message with a Notification Code of "Setup
Request Rejected," the source must send data packets with an explicit
source route or try an alternate route. The source MAY retry the setup.
In general, setup rejections should be weighted more heavily than setup
accepts. In this way, if a path is flopping between two different SDRP
routers in one domain, where one router is full and generates rejects and
the other generates accepts, then the source will tend to use the router
that accepts the setup route.
7 Source Route Forwarding Cache
The setup state maintained by each SDRP router contains any information
necessary to forward packets along a stable route. In addition to the
NEXT_ROUTER or NEXT_DI discovered when processing the explicit source
route, the forwarding information may include the NEXT_HOP, MODE, and
changes to the Loose/Strict Source Route bit, so that the NEXT_HOP
calculation can be periodically refreshed. The delivery source address and
Source Route Identifier serve as a key to this cache.
Each entry in the cache can be timed out at any time, and SHOULD
be timed out after long idle periods. The particular policy used
for timing out cache entries depends on the router.
8 References
[1] Estrin, D., Li, T., Rekhter, Y., Zappala, D., Source Demand Routing:
Packet Format and Forwarding Specification (Version 1), work in progress