From owner-freebsd-net Sat Mar 27 20:57:41 1999 Delivered-To: freebsd-net@freebsd.org Received: from mail-out2.apple.com (mail-out2.apple.com [17.254.0.51]) by hub.freebsd.org (Postfix) with ESMTP id D592F14C20 for ; Sat, 27 Mar 1999 20:57:39 -0800 (PST) (envelope-from justin@walker3.apple.com) Received: from mailgate1.apple.com (A17-128-100-225.apple.com [17.128.100.225]) by mail-out2.apple.com (8.8.5/8.8.5) with ESMTP id UAB25030 for ; Sat, 27 Mar 1999 20:54:40 -0800 Received: from scv2.apple.com (scv2.apple.com) by mailgate1.apple.com (mailgate1.apple.com- SMTPRS 2.0.15) with ESMTP id ; Sat, 27 Mar 1999 20:54:38 -0800 Received: from walker3.apple.com (walker3.apple.com [17.219.24.201]) by scv2.apple.com (8.9.3/8.9.3) with ESMTP id UAA19088; Sat, 27 Mar 1999 20:54:36 -0800 Received: by walker3.apple.com (8.9.1/8.9.1) id UAA00698; Sat, 27 Mar 1999 20:54:39 -0800 (PST) Message-Id: <199903280454.UAA00698@walker3.apple.com> To: danny@alpha.net.au Subject: Re: OSI layering Query.. Please Help ME Cc: net@FreeBSD.ORG Date: Sat, 27 Mar 1999 20:54:38 -0800 From: "Justin C. Walker" Reply-To: justin@apple.com X-Mailer: by Apple MailViewer (2.105.dev) Sender: owner-freebsd-net@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org > From: Danny Ho > Date: 1999-03-26 15:47:31 -0800 > To: net@FreeBSD.ORG, Tony Finch > Subject: OSI layering Query.. Please Help ME > X-MSMail-Priority: Normal > X-Priority: 3 > Delivered-to: freebsd-net@freebsd.org > X-Mailer: Microsoft Internet Mail 4.70.1155 > X-Loop: FreeBSD.org > > Hi everyone I am sort of new( 1 year experience in this ISP job) > > Anyway, I have one query about OSI layering. > > What are some of the advantages of OSI layer as seen in the OSI model?? Perhaps the biggest advantage of the OSI model is the language it brings to the design of protocols. Opinions will vary as to the advantages in actual implementation, but generally, some adherence to the layering model makes your code cleaner and more maintainable. You need to weigh that aspect against that of performance, which is where things will get interesting. You can find detailed discussions of the model, and its applicabiliity to IP, in many places. See, e.g., Stallings, "Handbook of Computer Communications Standards, V. 1, The Open Systems Interconnect model ..." (MacMillan/Stallings); Stevens' "TCP/IP Illustrated, V1" (Addison Wesley), discusses layering as it applies specifically to TCP and IP (i.e., up through what OSI calls the transport layer). > And what exactly are PDU? Protocol Data Units - this is OSI-speak for "packets", although it allows you to talk about packets at the various protocol layers (e.g., an IP packet as distinct from a TCP packet or an ethernet packet). > What exactly is SAP?? Service Access Point - it's a protocol addressing term. E.g., in IP terms, an SAP at the network layer would be a port (and is known as an NSAP). You'd need to delve more deeply into the OSI model to appreciate the subtlety of the concept :-}. > I am really confused help me. Hope this helps. Regards, Justin Justin C. Walker, Curmudgeon-At-Large * Institute for General Semantics | Manager, CoreOS Networking | Men are from Earth. Apple Computer, Inc. | Women are from Earth. 2 Infinite Loop | Deal with it. Cupertino, CA 95014 | *-------------------------------------*-------------------------------* To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message