Xref: utzoo comp.dcom.lans:5669 comp.protocols.tcp-ip:12568 Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!ibmsupt.uucp!bullhead!brunner From: brunner@bullhead.uucp Newsgroups: comp.dcom.lans,comp.protocols.tcp-ip Subject: Re: Token Ring frame sizes? Message-ID: <1990Aug15.213146.2836@ibmpa> Date: 15 Aug 90 21:31:46 GMT References: <38470004@hpindwa.HP.COM> Sender: news@ibmpa (news id) Reply-To: brunner@ibmsupt.UUCP () Organization: IBM AWD Palo Alto Lines: 103 Michael, I guess I should have read all three of your postings before replying to the first one (in the order I received them). I've replied in a seperate posting to the token-ring analyser query. The first half of this posting is in reply to the frame-size query (subject line in this posting), the second half to the source routing query. I use the Ethernet MTU in the drivers I work on (IBM/4.3 for the RT line, and OSF/1 for the PS/2), and since the OS/2 ethernet driver is really an (oldish) IBM4.3 driver, it is possible that their token-ring driver derives from the same token-ring drivers in use on the PS/2 with a ROMP processor. If so, it too uses the Ethernet MTU, 1500. >I believe that most TCP/IP implementations will use Ethernet size frames. >Am I wrong? I don't think so, but bear in mind that _most_ of the token-ringers I've communicated with (in IBM) don't view TCP/IP as their primary suite of protocols to support and tend to say things like "load balancing and (tcp) connection management (forcing a re-arp for a route when tcp reports failure, something Van Jacobson is working on the the current 4.4 post-alpha code) will be done by NETBIOS", etc., etc. RFC1042 is being revised, presently there is a "son of 1042" in draft form. 1042 as is on MTU: - The Maximum Transmission Unit (MTU) differs on the different types of - IEEE 802 networks. In the following there are comments on the MTU - for each type of IEEE 802 network. However, on any particular - network all hosts must use the same MTU. In the following, the terms - "maximum packet size" and "maximum transmission unit" are equivalent. Son-of-1042 as is on MTU: - The Maximum Transmission Unit (MTU) differs on the different types of - IEEE 802 networks. In the following there are comments on the MTU - for each type of IEEE 802 network. However, on any particular - network all hosts must use the same MTU. In addition, if different - types of IEEE 802 networks are connected via transparent link layer - bridges, all hosts on all of these networks should use the same MTU. - In the following, the terms "maximum packet size" and "maximum - transmission unit" are equivalent. I think that there will be problems ahead as non-ip token-ring developers will try to optimize for high-bandwidth applications (video, etc) using larger frame-sizes. Further complications are in order as source-routing bridges (a known evil) are replaced with source-routing-transparent bridges (a recent compromise at the 802 bridge meeting), however, that is seperate from the MTU issue. You can expect to see implementations which hold a token for up to 10ms in the blind pursuit of big frames on what are essentially propriatary networks. >I think Novell actually goes up to 4KB frames. How about Appletalk? I don't know, there is an appletalk working group in the IETF, the mailing list is apple-ip@apple.com, subscribe in the usual fashion. This working group addresses ip/appletalk issues, e.g., ip over appletalk, gateways, appletalk over ip (for the deranged pranksters) and so forth. On source routing, first, some document identifiers: Token-Ring Network Architecture Reference IBM SC30-3374-02, 3rd edition, September 1989 (my abreviation "TRARCH") Local Area Network Technical Reference (IBM SC30-3383-2) 3rd edition, September 1988 (my abreviation "LANTR") Question 1: Is the length of the routing information field 18? or 30? Page 2-6 of TRARCH defines the routing information field as a "2-byte routing control field and up to eight 2-byte route designators". I think that "bytes" here should be understood to be "octets", but it is clear that IBM defines the rif as being a variable sized element of the MAC frame, 2 =< sizeof(RIF) =< 18. What this means in real life is that no more than 8 bridges in a token-ring. When I last spoke with Radia Perlman I learned that the number of bridges (equivalent to the size of the RIF) varies from draft to draft of the IEEE 802.5 working group. I've probably munged her message, but I'll assume 8 hops max until I learn otherwise. Because TRARCH defines the IBM token-ring (802.5 with multi-ring extensions and a presumption of with source route briges, not transparent bridges, from a host's point of view, I assume that the current and near-future IBM bridge implementors will discard frames with a larger routing information field. Question 2: What is the allocation of bits within each of the eight 2-byte routes, how many bits designate the bridge and how many designate the ring. Again, TRARCH, page 2-10. Each ring in a multi-ring network has a unique ring identifier (12 bits), each bridge has a not-necessarily-unique bridge identifier (4 bits). Again, I've cross posted to the tcp-ip list, there are _always_ people who know more than I do, a fact of life I'm happy with. P.S. I have to live with the UB implementation of the 802.5 network adaptor, your milage may vary. Eric Brunner, Consultant, IBM AWD Palo Alto (415) 855-4486 inet: brunner@monet.berkeley.edu uucp: uunet!ibmsupt!brunner trying to understand multiprocessing is like having bees live inside your head.