Data Link Switching: Switch-to-Switch Protocol (RFC1434)
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2001-Nov-09
Internet Society Requests For Comment (RFCs)
R. Dixon: AUTHOR [+2]
This RFC describes IBM's support of Data Link Switching over TCP/IP. The RFC is being distributed to members of the Internet community in order to solicit their reactions to the proposals contained in it. While the issues discussed may not be directly relevant to the research problems of the Internet, they may be interesting to a number of researchers and implementors.
Network Working Group R. Dixon
Request for Comments: 1434 D. Kushi
Data Link Switching: Switch-to-Switch Protocol
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard. Distribution of this memo is
This RFC describes IBM's support of Data Link Switching over TCP/IP.
The RFC is being distributed to members of the Internet community in
order to solicit their reactions to the proposals contained in it.
While the issues discussed may not be directly relevant to the
research problems of the Internet, they may be interesting to a
number of researchers and implementors.
Any questions or comments relative to the contents of this RFC should
be sent to the following Internet address: firstname.lastname@example.org.
Table of Contents
1. Introduction 2
2. Overview 2
3. Transport Connection 4
3.1. SSP Frame Formats 5
3.2. Address Parameters 8
3.3. Message Types 10
4. Protocol Specification 11
4.1. Protocol Flow Diagrams 11
4.1.1. Connect Protocols 11
4.1.2. Link Restart Protocols 13
4.1.3. Disconnect Protocols 15
4.2. DLS State Machine 16
4.2.1 Data Link Switch States 16
4.2.2 State Transition Tables 21
4.3. NetBIOS Datagrams 30
Security Considerations 32
Authors' Addresses 33
Dixon & Kushi [Page 1]
RFC 1434 DLS: Switch-to-Switch Protocol March 1993
Data Link Switching (DLS) is a forwarding mechanism for the IBM SNA
and IBM NetBIOS protocols. It does not provide full routing, but
instead provides switching at the Data Link layer and encapsulation
in TCP/IP for transport over the Internet. This memo documents the
Switch-to-Switch Protocol (SSP) that is used between IBM 6611 Network
Today, the IBM 6611 supports SNA (PU 2 and PU 4) systems and NetBIOS
systems attached to token-ring networks, as well as SNA (PU 2)
systems attached to SDLC links. For the later case, the SDLC
attached systems are provided with a LAN appearance within the IBM
6611. For the LAN attached systems, the IBM 6611 appears as a
source-routing bridge. Remote systems that are accessed through the
IBM 6611 appear as systems attached to an adjacent ring. This ring
is a virtual ring that is manifested within each IBM 6611.
Data Link Switching was developed to provide support for SNA and
NetBIOS in multi-protocol routers. Since SNA and NetBIOS are
basically connection oriented protocols, the Data Link Control
procedure that they use on the LAN is IEEE 802.2 Logical Link Control
(LLC) Type 2. Data Link Switching also accommodates SNA protocols
over WAN links via the SDLC protocol.
IEEE 802.2 LLC Type 2 was designed with the assumption that the
network transit delay would be small and predictable (i.e., a local
LAN). Therefore the LLC elements of procedure use a fixed timer for
detecting lost frames. When bridging is used over wide area lines
(especially at lower speeds), the network delay is larger and it can
vary greatly based...