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Chapter 2 - VINES Data Link Layer Protocols

Introduction

Figure 2-1. Sample VINES Frame

Services Provided

Transfer VINES IP packets
Echo diagnostic packets between neighbors

Data Link Layer Protocol Entities

Architectural Assumptions

Frames can be sent to and received from neighbors.
Frames can be moved as atomic units of data.
Frames can be broadcast. (High-level Data Link Control (HDLC) protocol and Block Asynchronous protocol entities do not support broadcasting.)

The data link layer does not provide guaranteed sequential delivery of error-free packets.
When the network layer sends a packet, the data link layer probably delivers it correctly to the appropriate entity without error. The network layer assumes that the data link layer protocol entity makes its best effort to deliver data.
If a data link layer protocol entity cannot guarantee that received packets are free of data bit errors, the entity notifies the network layer so that it can take appropriate action. For example, the entity includes a checksum in the data packet.

Resolving Differences in Physical Media

ARCNET LANs
IBM PC Network LANs
OmninetTM LANs
HDLC LAPB lines
Block asynchronous lines
X.25 lines

IEEE 802.2 LLC Protocol

Note: As of VINES 5.5, VINES supports the LLC protocol on Token-Ring LANs only. Banyan's AppleTalk Phase 2, IPX/SPX, and Remote Program Load (RPL) implementations support the LLC protocol on both Ethernet LANs and Token-Ring LANs.

IEEE 802.2 LLC Protocol Specification

Figure 2-2. LLC Header in Unnumbered Format

LLC Header Fields

Table 2-1. SAP Values

SNAP Header Fields

A specific, non-zero protocol identifier. For example, 08 00 07 indicates the AppleTalk protocol family.
All 0s (zeroes), indicating the field should be ignored.

Table 2-2. PIFs and Packet Types

IEEE 802.2 LLC Protocol Implementation Notes

CSMA/CD Ethernet Access Method

CSMA/CD Ethernet Protocol Specification

Figure 2-3. VINES Ethernet Frame

Table 2-3. Packet Type Field Value for Ethernet Frames

CSMA/CD Ethernet Protocol Implementation Notes

IEEE 802.5 Token-Ring Access Method

IEEE 802.5 Token-Ring Protocol Specification

Figure 2-4. VINES Token-Ring Frame

Table 2-4. VINES Packet Type Field Value for Token-Ring Frames

IEEE 802.5 Protocol Implementation Notes

ARCNET Protocol

ARCNET Protocol Specification

Figure 2-5. VINES ARCNET Frame

ARCNET Protocol Implementation Notes

Omninet Protocol

Omninet Protocol Specification

Figure 2-6. VINES Omninet Frame

Omninet Protocol Implementation Notes

IBM PC Network Protocol

IBM PC Network Protocol Specification

Figure 2-7. VINES IBM PC Network Frame

IBM PC Network Protocol Implementation Notes

ProNET-10 Protocol

ProNET-10 Protocol Specification

Figure 2-8. VINES ProNET-10 Frame

ProNET-10 Protocol Implementation Notes

Link Access Procedure Balanced Protocol

LAPB Protocol Specification

Figure 2-9. VINES LAPB Frame for HDLC Point-to-Point Communications

LAPB Protocol Implementation Notes

X.25 Protocol

X.25 Protocol Specification

Figure 2-10. VINES X.25 Packet in an LAPB Frame

X.25 Protocol Implementation Notes

X.3/X.28/X.29 Protocols

PC dial-in over X.25 public and private networks (also known as X.29 dial-in)
Asynchronous terminal emulation

X.3/X.28/X.29 Protocol Specification

Figure 2-11. X.25 Packet Encapsulating Block Asynchronous Headers

X.3/X.28/X.29 Protocol Implementation Notes

VINES Block Asynchronous Protocol

VINES Block Asynchronous Protocol Specification

Figure 2-12. VINES Block Asynchronous Frame

Table 2-5. Frame Type Header Values

VINES Block Asynchronous Protocol Implementation Notes

Sequence Numbers

The number of the fragment that is out of sequence can be more than one greater than the number of the last fragment that arrived in sequence.
The number of the fragment that is out of sequence can be less than the number of the last fragment that arrived in sequence. This typically occurs following transmission of an acknowledgment frame.
The number of the fragment that is out of sequence is equal to the number of the last fragment that arrived in sequence.

Example Sequence Number Greater than It Should Be

The fragment that was supposed to follow the last correctly sequenced fragment (for example, fragment with sequence number 5)
All the fragments after 5

Figure 2-13. Sequence Number Greater than It Should Be

Example Sequence Number Less than It Should Be

The next properly sequenced fragment (for example, fragment with sequence number 6)
All the fragments after 6

Figure 2-14. Sequence Number Less than It Should Be

Example Current Sequence Number Equals Previous Sequence Number

The next properly sequenced fragment (for example, fragment with sequence number 6)
All the fragments after 6

Figure 2-15. Equal Sequence Numbers

Connection Timeouts

Checksum Method

T1 Protocols

Fractional T1 communications using the ICAplus card. For a single FT1 connection to another server, this card supports up to six 64 Kbps DS0 circuits using the LAPB protocol.
Full and fractional T1 communications using the Link Access Procedure on the D-Channel (LAPD) protocol and SNAP. Currently, the Promptus T-1 Access ModuleTM provides this support.

LAPD Protocol Specification

Figure 2-16. VINES LAPD Frame

LAPD Protocol Implementation Notes

ISDN Protocol

ISDN Protocol Specification

Figure 2-17. VINES ISDN Server-to-Server Frame

ISDN Protocol Implementation Notes

VINES FRP

VINES FRP Specification

Figure 2-18. VINES FRP Header

Figure 2-19. Control Field of First Packet Fragment

VINES FRP Implementation Notes

The next sequence number to send to the neighbor
The last sequence number received from the neighbor

Processing the First Packet Fragment

Figure 2-21. Processing the First Packet Fragment

Processing Fragments that Follow the First Packet Fragment

Checking the Sequence Number - The FRP entity checks the sequence number in the frame against the last sequence number received from the neighbor. The entity concatenates the fragment to the rest of the VINES IP packet if the sequence number in the frame is equal to the last sequence number plus 1 (modulo 256). If this condition is met, the entity updates the value of the last sequence number received in the state table. Otherwise, the entity discards both the fragment and the current, partially assembled VINES IP packet.

Checking the Control Field - If the FRP entity accepts the received fragment, the entity checks the control field in the FRP header to determine if the fragment is the end of a VINES IP packet. If it is at the end of the packet, the FRP entity passes the assembled VINES IP packet to the target network layer protocol entity on the local node. Otherwise, the FRP entity waits for the next fragment to arrive.

VINES Echo Protocol

VINES Echo Protocol Specification

Figure 2-22. Sample Echo Frame

VINES Echo Protocol Implementation Notes

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