At 12:33 PM 4/3/02, Scott Nawalaniec wrote: >To the Big Study Group Brain, > >Quick question: > >Which WAN encapsulation protocol has the least amount of overhead? PPP, >HDLC, FR or other?
They are all about the same. A real useful answer, eh? ;-) Seriously they are all based on international standards for frame formatting and are very similar. PPP has two extra bytes to identify the next layer up, but that's not a big deal. Cisco's HDLC has that too actually. PPP also has a little extra overhead for CHAP or PAP during establishment of a circuit. Cisco HDLC has SLARP keepalives which are overhead. But Frame Relay has LMI and PPP has LCP. The gory details of the frame formats are here: Frame Relay: http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/frame.htm#xtocid16 PPP: http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/ppp.htm#xtocid6 SDLC (which is sometimes considered the mother of all WAN protocols): http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/sdlcetc.htm#xtocid4 Cisco's HDLC is actually a unique variety that doesn't match other vendors (except vendors that do Cisco HDLC). I can't find any documents that describe it but it has been addressed on Group Study before. Here's the gist of it: Cisco's HDLC encapsulation starts with a one-byte address field. The second byte is a control byte that is always set to 0x00. The next two bytes are a protocol type field that usually matches Ethernet EtherTypes, with some additions for packet types that don't appear on Ethernet networks. Packets with type 0x8035 carry SLARP data. Anyway, distinguishing these protocols by how much encapsulation overhead they have isn't necessary. You'll want to consider other advantages/disadvantages. Priscilla >Thank you for your opinions. > >Scott ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=40378&t=40343 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
